tag:blogger.com,1999:blog-29738036978649792112024-03-12T19:08:54.778-07:00Imperial MitochondriacsDiscussion of work in mitochondrial physiology and bioenergetics by <a href="http://systems-signals.blogspot.co.uk/">the Systems and Signals Group</a>Unknownnoreply@blogger.comBlogger246125tag:blogger.com,1999:blog-2973803697864979211.post-25311208445828937592020-10-16T01:33:00.000-07:002020-10-16T01:33:04.499-07:00Updating the Free Radical Theory of Aging<p><a href="https://www.frontiersin.org/articles/10.3389/fcell.2020.575645/full">https://www.frontiersin.org/articles/10.3389/fcell.2020.575645/full </a></p><p>Adam S. Ziada, Marie-Soleil R. Smith and Hélène C. F. Côté.</p><p><br /></p><p>INTRODUCTION - TRANSITION AND TRASNVERSION MUTATIONS</p><p><b>Transversions</b> are point mutations in which a purine (A or G) is changed for a pyrimidine (T or C) or vice-versa. <b>Transitions</b> are point mutations that change a purine for another purine or a pyrimidine for another pyrimidine.</p><p>Although there are twice as many possible transversions as transitions, the latter are more common (approximately 2/3 of point mutations are transitions).</p><p><br /></p><p>A POLYMERASE <span style="font-size: large;">γ</span> - CENTRIC THEORY OF MITOCHONDRIAL AGEING</p><p>The free radical theory of aging hypothesizes that
oxidative damage to the mtDNA induces random de novo mtDNA mutations which gradually accumulate over time, potentially reaching pathological levels. The authors summarise recent
studies have showing that transition mtDNA mutations rather than transversion mutations gradually build up overtime and are
amplified, via clonal expansion, to pathological levels. </p><p>Given that transition mutations are generally associated with replication errors made by the mitochondrial
polymerase γ, the age associated accumulation of mtDNA mutations could result from free radicals interacting with polymerase γ, potentially reducing its fidelity
and/or inhibiting mtDNA replication. This would in turn lead to random de novo transition mutations and their subsequent clonal amplification. Conditions
hypothesized to induce accelerated aging via oxidative damage/stress could include chronic infections such as HIV, chronic inflammatory conditions, or tobacco
smoking</p><p>The authors conclude suggesting the possibility that free radicals, rather than directly contributing to
mtDNA mutations via oxidative lesions, affect
the mitochondrial polymerase and decrease its fidelity, indirectly
increasing somatic transition mutations. </p>Ferdinando Insalatahttp://www.blogger.com/profile/15316468429318156803noreply@blogger.com0tag:blogger.com,1999:blog-2973803697864979211.post-4387969646462296112019-11-14T10:15:00.004-08:002019-11-14T10:15:53.593-08:00Metformin Improves Mitochondrial Respiratory Activity through Activation of AMPK<a href="https://www.sciencedirect.com/science/article/pii/S2211124719312677?via%3Dihub">https://www.sciencedirect.com/science/article/pii/S2211124719312677?via%3Dihub</a><br />
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Wang Y., An H., Liu T., Qin C., Sesaki H., Guo S., Radovick S., Hussain M., Maheshwari A., Wondisford F. E. , O'Rourke B., He L.<br />
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<br />
<ul>
<li>Metformin is the first-line medication for the treatment of type 2 diabetes (T2D), particularly in people who are overweight. It is estimated that around 150 million people around the world. </li>
<li>Metformin works mainly by improving patients' hyperglycemia (suppressing liver's glucose production) and alleviating insulin resistance. However, its mechanisms of actions are currently not understood.</li>
<li>It is known that mitochondrial dysfunctions are involved in the development of T2D and that patients with T2D have decreased mitochondrial copy number and respiration.</li>
<li>The author show that therapeutic doses of metformin increase mito respiration, ATP level and membrane potential and promote mitochondrial fission in liver cells. Through knock-out studies, they determine that the enzyme AMPK is required for metformin to be effective.</li>
<li>The author also report that very high concentration of the drug can lead to a stop of respiration, by depleting cellular ADP levels. Respiration was restored through the addition of exogenous ADP.</li>
</ul>
Ferdinando Insalatahttp://www.blogger.com/profile/15316468429318156803noreply@blogger.com0tag:blogger.com,1999:blog-2973803697864979211.post-78573933744060191172019-10-24T05:14:00.003-07:002019-10-24T05:16:41.623-07:00Mitochondria as multifaceted regulators of cell death<a href="https://www.nature.com/articles/s41580-019-0173-8">https://www.nature.com/articles/s41580-019-0173-8</a><br />
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Florian J. Bock, Stephen W. G. Tait</div>
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INTRODUCTION</div>
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It might look paradoxical that mitochondria are central to life as well as to cell death. However, programmed cell death is essential for health. The authors discuss the roles of mitochondria in cell death and their implications for health and disease. Here, I summarise the information about the involvement of mitochondria in apoptosis and other, recently described, forms of cell death.</div>
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<ol>
<li style="text-align: justify;">The role of mitochondria is well established in <b>apoptosis</b>, where mitochondrial outer membrane permeabilization (MOMP) initiates a signalling cascade that leads to cell death. Recently, it has been appreciated that there are non-lethal functions of MOMP, triggering inflammation and immune response. See <a href="http://imperialmitochondriacs.blogspot.com/2019/04/a-nondeath-function-of-mitochondrial.html">this</a> blog post for more detail and a reference.</li>
<li style="text-align: justify;"><b>Necroptosis</b> is a programmed form of cell death that shares morphological and inflammatory characteristics with necrosis, an unregulated and passive form of cell death due to disease, injury, or failure of the blood supply. Mitochondria are involved at least in some cell types: levels of ROS may be an important determinant as to whether a cell initiates necroptosis. Therefore, progressive mitochondrial dysfunction, like that observed during ageing, may increase the propensity of cells to undergo necroptosis. It has been observed, however, that necroptosis can proceed independently of mitochondria.</li>
<li style="text-align: justify;"><b>Pyroptosis</b> is a highly inflammatory form of programmed cell death. It occurs most frequently upon infection with intracellular pathogens and is probably part of the antimicrobial response. There is little evidence that mitochondria play an important role in pyroptosis, but there is extensive crosstalk exists between pyroptosis and mitochondrial apoptosis.</li>
<li style="text-align: justify;"><b>Ferroptosis</b> is a type of regulated cell death triggered by lipid peroxides that kill the cell by attacking lipid membranes. It is dependent on iron (hence the name) and ROS (hence the mitochondrial involvement) in that lipid peroxides are produced through the Fenton reaction, requiring iron and peroxides. Ferroptosis is characterized morphologically by morphological aberration of mitochondria.</li>
</ol>
<span style="text-align: justify;">Even though the role of mitochondria in 2-4 appears less crucial, or at least context dependent, these different cell death modalities crosstalk with one another and this crosstalk involves mitochondria.</span><br />
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Ferdinando Insalatahttp://www.blogger.com/profile/15316468429318156803noreply@blogger.com0tag:blogger.com,1999:blog-2973803697864979211.post-25758307916916589342019-10-16T01:01:00.000-07:002019-10-17T05:58:34.299-07:00Individual cristae within the same mitochondrion display different membrane potentials and are functionally independent<a href="https://www.embopress.org/doi/10.15252/embj.2018101056">https://www.embopress.org/doi/10.15252/embj.2018101056</a><br />
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Dane M Wolf, Mayuko Segawa, Arun Kumar Kondadi, Ruchika Anand, Sean T Bailey, Andreas S Reichert, Alexander M van der Bliek, David B Shackelford, Marc Liesa, Orian S Shirihai<br />
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<ul>
<li style="text-align: justify;">It is often supposed that the inner mitochondrial membrane is at a uniform membrane potential (<span style="background-color: white; color: #333333; font-family: "montserrat" , sans-serif; font-size: 16px;">ΔΨ</span><span style="background-color: white; bottom: -0.25em; box-sizing: border-box; color: #333333; font-family: "montserrat" , sans-serif; font-size: 12px; line-height: 0; position: relative; vertical-align: baseline;">m</span>). </li>
<li style="text-align: justify;">The authors develop an approach to evaluate <span style="background-color: white; color: #333333; font-family: "montserrat" , sans-serif; font-size: 16px;">ΔΨ</span><span style="background-color: white; bottom: -0.25em; box-sizing: border-box; color: #333333; font-family: "montserrat" , sans-serif; font-size: 12px; line-height: 0; position: relative; vertical-align: baseline;">m</span> at the level of individual cristae.</li>
<li style="text-align: justify;">The authors find the existence of heterogeneity in <span style="background-color: white; color: #333333; font-family: "montserrat" , sans-serif; font-size: 16px;">ΔΨ</span><span style="background-color: white; bottom: -0.25em; box-sizing: border-box; color: #333333; font-family: "montserrat" , sans-serif; font-size: 12px; line-height: 0; position: relative; vertical-align: baseline;">m</span> throughout the inner mitochondrial membrane, with individual cristae possessing different membrane potentials.</li>
<li style="text-align: justify;">Interventions causing acute depolarization to a particular crista may leave other cristae unchanged in their membrane potential.</li>
<li style="text-align: justify;">In other words, individual cristae seen to act as independent bioenergetic units, so that the failure of a specific one does not spread to the entire mitochondrion. Therefore, mitochondria should be thought of not as electric wires, but as sets of batteries.</li>
<li style="text-align: justify;">The loss of this cristae compartmentalization, causing the spread of damage among regions of a mitochondrion, may be implied in pathological states. Several diseases are associated with structural perturbations in cristae. Restoring the heterogeneity of <span style="background-color: white; color: #333333; font-family: "montserrat" , sans-serif; font-size: 16px;">ΔΨ</span><span style="background-color: white; bottom: -0.25em; box-sizing: border-box; color: #333333; font-family: "montserrat" , sans-serif; font-size: 12px; line-height: 0; position: relative; vertical-align: baseline;">m </span><span style="font-family: inherit;">could represent a therapeutic avenue. </span></li>
<li style="text-align: justify;">A fascinating area of future investigation would be to link cristae membrane heterogeneity to mitochondrial genetics.</li>
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<br />Juvid Aryamanhttp://www.blogger.com/profile/05751288336964830816noreply@blogger.com0tag:blogger.com,1999:blog-2973803697864979211.post-18518717874017506102019-09-02T01:32:00.001-07:002019-09-02T01:32:20.072-07:00Chemoptogenetic damage to mitochondria causes rapid telomere dysfunction<a href="https://www.pnas.org/content/early/2019/08/22/1910574116.long">https://www.pnas.org/content/early/2019/08/22/1910574116.long</a><br />
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Wei Qian, Namrata Kumar, Vera Roginskaya, Elise Fouquerel, Patricia L. Opresko, Sruti Shiva, Simon C. Watkins, Dmytro Kolodieznyi, Marcel P. Bruchez, and Bennett Van Houten<br />
<br />
<br />
<ul>
<li>The authors develop a chemoptogenetic technology to specifically induce mitochondrial reactive oxygen species with precise spatio-temporal control by using light stimulation.</li>
<li>The authors show that induction of mitochondrial reactive oxygen species can result in increased hydrogen peroxide levels inside the nucleus, resulting in telomere loss.</li>
</ul>
Juvid Aryamanhttp://www.blogger.com/profile/05751288336964830816noreply@blogger.com0tag:blogger.com,1999:blog-2973803697864979211.post-45121373172717091462019-08-08T05:00:00.001-07:002019-08-08T05:00:49.546-07:00Mitochondrially-targeted APOBEC1 is a potent mtDNA mutator affecting mitochondrial function and organismal fitness in Drosophila<a href="https://www.nature.com/articles/s41467-019-10857-y">https://www.nature.com/articles/s41467-019-10857-y</a><br />
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Simonetta Andreazza, Colby L. Samstag, Alvaro Sanchez-Martinez, Erika Fernandez-Vizarra, Aurora Gomez-Duran, Juliette J. Lee, Roberta Tufi, Michael J. Hipp, Elizabeth K. Schmidt, Thomas J. Nicholls, Payam A. Gammage, Patrick F. Chinnery, Michal Minczuk, Leo J. Pallanck, Scott R. Kennedy & Alexander J. Whitworth<br />
<br />
<br />
<ul>
<li>The authors describe a new mtDNA mutator model, whereby a cytidine deaminase is targetted to mitochondria to induce mutations (mito-APOBEC1), in fruit flies.</li>
<li>The most established system for understanding the physiological consequences of mtDNA mutation is to knock-in a proofreading deficient version of the mtDNA polymerase (POLG). Doing so introduces high levels of point mutations, and also small indels, but has surprisingly limited impact on organismal longevity or fitness in flies, given the level of mutation which this mutation induces (see <a href="http://imperialmitochondriacs.blogspot.com/2018/09/mutations-of-mitochondrial-dna-are-not.html">here</a>). In contrast, mito-APOBEC1 exclusively introduces C:G>T:A transitions (which is the most predominant mutation profile in human ageing), with no indels or mtDNA depletion. The authors argue that mutations of this type (rather than those induced by the POLG mutation) cause dramatic reduction in organismal fitness, even at modest heteroplasmy.</li>
</ul>
Juvid Aryamanhttp://www.blogger.com/profile/05751288336964830816noreply@blogger.com0tag:blogger.com,1999:blog-2973803697864979211.post-7763400200171942302019-07-23T03:20:00.001-07:002019-07-23T03:20:48.361-07:00A nanoscale, multi-parametric flow cytometry based platform to study mitochondrial heterogeneity and mitochondrial DNA dynamics<a href="https://www.nature.com/articles/s42003-019-0513-4">https://www.nature.com/articles/s42003-019-0513-4</a><br />
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Julie A. MacDonald, Alisha M. Bothun, Sofia N. Annis, Hannah Sheehan, Somak Ray, Yuanwei Gao, Alexander R. Ivanov, Konstantin Khrapko, Jonathan L. Tilly, and Dori C. Woods<br />
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<ul>
<li>The authors describe a new technology for isolation and analysis of single mitochondria using flow cytometry, called "fluorescence-activated mitochondria sorting" (FAMS).</li>
<li>Mitochondria isolated from liver tissue exhibited intact outer and inner membranes, and cristae structure, when evaluated by electron microscopy.</li>
<li>Staining samples with the DNA stain DAPI, the authors found correlation between side-scatter of organelles and DNA content, suggesting that larger organelles, containing larger amounts of DNA, have larger side-scatter. </li>
<li>The authors used the membrane potential sensor dye JC-1 to categorise mitochondria into high/low membrane potential populations. They found that whilst both low and high-membrane potential populations generated ATP when provided with ADP, high-membrane potential mitochondria produced approximately x6 more ATP, and approximately x3 more Mt-ND1 and Mt-Nd4, than low-membrane potential mitochondria. The low-membrane potential mitochondria had ~2.5x lower FSC-PMT, potentially indicating their smaller size [Question: do differences in mitochondrial size confound the inference of differential membrane potential using the JC-1 dye, due to the surface area to volume ratio affecting the aggregation rate? If smaller mitochondria have a higher surface area to volume ratio then perhaps the true difference in mitochondrial membrane potential is even larger.]</li>
<li>The authors generated mixed samples for two mouse strains, with two different mtDNA haplotypes, and performed single-molecule PCR. Of 54 organelles measured, 2 showed mixtures of mtDNA sequences, suggesting a relatively low rate of artificial fusion of mitochondrial in mixed samples.</li>
<li>The authors measured the median number of mtDNAs per mitochondrion was 3, ranging from 1 to 22 molecules per sorted organelle.</li>
<li>The authors used beads to calibrate FSC-PMT and SSC to define two gates: ~0.22-0.5 um, and 0.5-1um, and found that the small gate had approximately 1-2 mtDNAs per organelle, whereas the large gate had 6.5-7.5 mtDNAs per organelle. </li>
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Juvid Aryamanhttp://www.blogger.com/profile/05751288336964830816noreply@blogger.com0tag:blogger.com,1999:blog-2973803697864979211.post-9742345812126793862019-07-14T04:41:00.003-07:002019-07-14T04:43:49.706-07:00Energetic costs of cellular and therapeutic control of stochastic mitochondrial DNA populations<a href="https://journals.plos.org/ploscompbiol/article?id=10.1371/journal.pcbi.1007023">https://journals.plos.org/ploscompbiol/article?id=10.1371/journal.pcbi.1007023</a><br />
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<span style="font-size: small;">Hanne Hoitzing,</span><span style="font-size: small;"> Payam A. Gammage, Lindsey Van Haute, Michal Minczuk, Iain G. Johnston,</span><span style="font-size: small;"> and Nick S. Jones </span><span class="email"> </span><br />
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<u>Background on mitochondrial DNA dynamics and control</u><br />
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Mitochondria have their own genomes (mtDNAs). These genomes can mutate upon division and at any one given time, mixture of normal (wildtype, <i>w</i>) and mutated (<i>m) </i>mtDNA can exist within a cell. Heteroplasmy is defined as the fraction of mutant mtDNA molecules.<br />
<u> </u><br />
The birth and death of mtDNAs is a stochastic process, their numbers fluctuating over time. Some kind of feedback control must be present, as mtDNA numbers in normal healthy cells tend to remain within certain bounds.<br />
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Treatments exist to reduce the load of mutant mtDNAs inside cells. For example, nucleases which are targeted to the specific sequence of a mutant mtDNA can be introduced in cells. They will bind to these mutant sequences and cut the (though off-target cutting of the wildtype genomes is a problem). <br />
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Thinking about controlling levels of mtDNA gives rise to various questions:<br />
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<ul>
<li> What exactly is this feedback control? What is the quantity that is being controlled (e.g. is it total mtDNA copy number, or is it the overall energy level)? </li>
<li>How does the type of control influence heteroplasmy levels? Does one type of control lead to faster mutant accumulation than another?</li>
<li>How does the cell choose a particular feedback control? Does it do this randomly or does it minimize some 'cost function'? </li>
<li>Can we somehow interfere with the cellular feedback control to reduce mutant loads?</li>
</ul>
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<u>Paper results</u><br />
<br />
This paper investigates these questions a bit more closely. Some of the main findings are:<br />
<ul>
<li>Many different forms of feedback control (e.g. linear, quadratic, etc..) can give rise to similar mtDNA dynamics and heteroplasmy dynamics.</li>
<li>What makes all the difference, however, is <b><i>which</i></b> quantity is being controlled (rather than <i>how</i> it is controlled). Is it total copy number (<i>w + m</i>)? Is it only the number of wildtypes (<i>w</i>)? Is it some more general linear combination (<i>w + </i>𝛿 <i>m)?</i></li>
<li>The more strongly one species is controlled, the more control is lost over the other</li>
<li>A mitochondrial cost function is introduced, and it is shown that it can actually be more expensive for a cell to contain a mixture of mutant and wildtype molecules, rather than only mutants!</li>
<li>A control based on energy levels seems to make more sense than blindly controlling total mtDNA copy number. This means that if mutants produce less energy, the quantity being controlled is (<i>w + </i>𝛿 <i>m)</i> with 𝛿 < 1.</li>
<li>Variance of mtDNA dynamics is important! An increase in variance in
mutant and/or wildtype copy numbers (which will always occur over time)
can lead to an increase in cost of maintaining a tissue </li>
<li>Gene therapies specifically targeting mutant mtDNAs can successfully lower heteroplasmy levels, but this becomes hard when high tissue heteroplasmy levels are caused by only a small fraction of cells (i.e. a few cells have very high heteroplasmy levels and most cells are ok). Again, it's the mtDNA variance that's important!</li>
<li>Long and weak gene therapies seem to reach lower overall heteroplasmy levels compared to short and strong therapies. </li>
</ul>
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Unknownnoreply@blogger.com0tag:blogger.com,1999:blog-2973803697864979211.post-55571182508040555102019-07-14T04:33:00.004-07:002019-07-14T05:03:30.565-07:00Mitochondrial Network State Scales mtDNA Genetic Dynamics<a href="https://doi.org/10.1534/genetics.119.302423">https://doi.org/10.1534/genetics.119.302423</a><br />
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Juvid Aryaman, Charlotte Bowles, Nick S. Jones and Iain G. Johnston<br />
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(Mirrored from <a href="http://mitomaths.blogspot.com/2019/07/article-coupling-mitochondrial-physics.html" target="_blank">Evolution, Energetics & Noise</a>)<br />
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Mitochondrial DNA (mtDNA) populations within our cells encode vital energetic machinery. MtDNA is housed within mitochondria, cellular compartments lined by two membranes, that lead a very dynamic life. Individual mitochondria can fuse when they meet, and fused mitochondria can fragment to become individual smaller mitochondria, all the while moving throughout the cell. The reasons for this dynamic activity remain unclear (we’ve compared hypotheses about them before <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4672710/" target="_blank">here</a> and <a href="https://www.cell.com/molecular-plant/fulltext/S1674-2052(18)30337-X" target="_blank">here</a>, with blog articles <a href="http://systems-signals.blogspot.com/2015/04/the-function-of-mitochondrial-networks.html" target="_blank">here</a>). But what influence do these physical mitochondrial dynamics have on the genetic composition of mtDNA populations?<br />
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MtDNA populations can, naturally or as a result of gene therapies, consist of a mixture of different mtDNA types. Typically, different cells will have different proportions of, say, type A and type B. For example, one cell may be 20% type A, another cell may be 40% type A, and a third may be 70% type A. This variability matters because when a certain threshold (often around 60%) is crossed for some mtDNA types, we get devastating diseases.<br />
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We previously showed <a href="https://www.cell.com/ajhg/fulltext/S0002-9297(16)30397-4" target="_blank">mathematically</a> (<a href="http://mitomaths.blogspot.com/2016/10/article-maths-of-mitochondrial-dna.html" target="_blank">blog</a>) and <a href="https://www.nature.com/articles/s41467-018-04797-2" target="_blank">experimentally</a> (<a href="http://systems-signals.blogspot.com/2018/09/aging-in-variance-increasing-variation.html" target="_blank">blog</a>) that this cell-to-cell variability in mtDNA proportions (often called “heteroplasmy variance” and sometimes referred to via the “mtDNA bottleneck”) is expected to increase linearly over time. However, this analysis pictured mtDNAs as individual molecules, outside of their mitochondrial compartments. When mitochondria fuse to form larger compartments, their mtDNA is more protected: smaller mitochondria (and their internal mtDNA) are subject to greater degradation. More degradation means more replication, and more opportunities for the fraction of a particular type of mtDNA to change per unit time. In a new paper <a href="https://www.genetics.org/content/early/2019/07/11/genetics.119.302423" target="_blank">here</a> in Genetics, we show that this protection can dramatically influence cell-to-cell mtDNA variability. Specifically, the rate of heteroplasmy variance increase is scaled by the proportion of mitochondria that exist in a fragmented state. (It turns out that it's the proportion of mitochondria that are fragmented that's important -- not whether the rate of fission-fusion is fast or slow).<br />
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<br />
This has knock-on effects for how the cell can best get rid of low-quality mutant mtDNA. In particular, if mitochondria are allowed to fuse based on their quality (“selective fusion”), we show that intermediate rates of fusion are best for removing mutants. Too much fusion, and all mtDNA is protected; too little, and good mtDNA cannot be sorted from bad mtDNA using the mitochondrial network. This mechanism could help explain why we see different levels of mitochondrial fusion in different conditions. More broadly, this link between mitochondrial physics and genetics (which we’ve also speculated about <a href="https://www.frontiersin.org/articles/10.3389/fgene.2018.00718/full" target="_blank">here</a> (<a href="http://systems-signals.blogspot.com/2019/02/how-mitochondria-can-vary-and.html" target="_blank">blog</a>) and <a href="https://www.cell.com/molecular-plant/fulltext/S1674-2052(18)30337-X" target="_blank">here</a>) suggests one way that selective pressures and tradeoffs could influence mitochondrial dynamics, giving rise to the wide variety of behaviours that remain unexplained. Juvid, Nick, and IainJuvid Aryamanhttp://www.blogger.com/profile/05751288336964830816noreply@blogger.com0tag:blogger.com,1999:blog-2973803697864979211.post-34305008645934661692019-07-11T02:53:00.001-07:002019-07-11T02:53:07.950-07:00Respiratory Syncytial Virus co-opts host mitochondrial function to favour infectious virus production<a href="https://elifesciences.org/articles/42448">https://elifesciences.org/articles/42448</a><br />
<br />
MengJie Hu, Keith E Schulze, Reena Ghildyal, Darren C Henstridge, Jacek L Kolanowski, Elizabeth J New, Yuning Hong, Alan C Hsu, Philip M Hansbro, Peter AB Wark, Marie A Bogoyevitch, David A Jans<br />
<br />
<br />
<ul>
<li>Respiratory syncytial virus (RSV) is responsible for more deaths each year than influenza. Here, the authors investigate how RSV hijacks mitochondria for viral production.</li>
<li>The authors suggest that RSV induces perinuclear clustering of mitochondria, reduction in mitochondrial respiration, impaired mitochondrial membrane potential, and increased reactive oxygen species production. </li>
<li>The authors find that inhibiting the dynein motor protein, or inhibiting mitochondrial ROS production, suppresses RSV production in vivo.</li>
</ul>
Juvid Aryamanhttp://www.blogger.com/profile/05751288336964830816noreply@blogger.com0tag:blogger.com,1999:blog-2973803697864979211.post-11671919507106099332019-07-11T02:28:00.000-07:002019-07-11T02:28:48.208-07:00RNA sequence analysis reveals macroscopic somatic clonal expansion across normal tissues<a href="https://science.sciencemag.org/content/364/6444/eaaw0726?ijkey=747d2d8299edcfd1fdfe566522ccbcf3ba841b1f&keytype2=tf_ipsecsha">https://science.sciencemag.org/content/364/6444/eaaw0726?ijkey=747d2d8299edcfd1fdfe566522ccbcf3ba841b1f&keytype2=tf_ipsecsha</a><br />
<br />
Keren Yizhak, François Aguet, Jaegil Kim, Paz Polak, Kristin G. Ardlie, Gad Getz and others<br />
<br />
<br />
<ul>
<li>The authors study the RNA sequence of >6000 samples across 29 normal tissues (using a method they call RNA-MuTect), and find multiple macroscopic somatic mutations in normal tissues.</li>
<li>Genes which are highly expressed may be investigated for evidence of somatic mosaicism</li>
<li>Sun-exposed skin, esophagus, and lung have a higher mutation load than other tested tissues, suggesting an evironmental role</li>
<li>Mutation burden was associated with age and tissue-specific proliferation rate</li>
<li>Normal tissues were found to harbour mutations in known cancer genes</li>
<li>See also Cristian Tomasetti's summary <a href="https://science.sciencemag.org/content/364/6444/938" target="_blank">here</a></li>
</ul>
<br />
<br />
<br />Juvid Aryamanhttp://www.blogger.com/profile/05751288336964830816noreply@blogger.com0tag:blogger.com,1999:blog-2973803697864979211.post-24683333373631137162019-07-08T09:36:00.004-07:002019-07-09T08:22:34.784-07:00Mitochondrial Stress Response in Neural Stem Cells Exposed to Electronic Cigarettes<a href="https://www.sciencedirect.com/science/article/pii/S2589004219301713">https://www.sciencedirect.com/science/article/pii/S2589004219301713</a><br />
<br />
Atena Zahedi, Rattapol Phandthong, Angela Chaili, Sara Leung, Esther Omaiye, Prue Talbot<br />
<br />
A WORD ON MITOCHONDRIAL DYNAMICS (from <a href="https://www.embopress.org/cgi/doi/10.1038/emboj.2009.130">this publication</a>)<br />
<ul>
<li>Mitochondria of healthy cells continually divide and fuse with each other, forming an ever-changing mitochondrial network. This is referred to as mitochondrial dynamics.</li>
<li>Fusion promotes exchange of mtDNA and other vital components, thus reinvigorating the mitochondrial network.</li>
<li>Fission allows for disposal of faulty mitochondrial fragments through mitophagy. Moreover, when cells become committed to apoptosis, they shatter their mitochondrial networks.</li>
<li>Modest levels of stress (well below the threshold to induce apoptosis) lead mitochondria to fuse extensively. This response was called <i>stress‐induced mitochondrial hyperfusion </i>(SIMH)<i>,</i> and might counter stress by optimizing mitochondrial ATP production.</li>
</ul>
<div>
<br /></div>
FINDINGS OF THE PAPER<br />
<ul>
<li style="text-align: justify;">Stem cells are critical to our wellbeing (controlling organ development and tissue renewal/repair) and the damage they accumulate over life can lead to disease.</li>
<li style="text-align: justify;">During development, neural stem cells are highly sensitive to toxicants and more vulnerable to stress than differentiated cells. Mitochondria are good indicators of stress in stem cells.</li>
<li style="text-align: justify;">Electronic cigarettes are marketed as a healthy substitute to cigarettes, and are targeted at youth and pregnant women.</li>
<li style="text-align: justify;">The authors exposed stem cells to EC fluid in a set of in vitro experiments. They argue that the nicotine present in EC fluid causes SIMH of stem cells. SIMH is a survival response in stem cells and is accompanied by increased oxidative stress and alterations in mitochondrial morphology and dynamics.</li>
<li style="text-align: justify;">Further, an interruption of autophagy was observed when stem cells were exposed to nicotine. Since autophagy is a defense mechanism of the cell, clearing damaged mitochondria, its inhibition is deleterious the the stem cell population.</li>
<li style="text-align: justify;">The main message of the study is that EC are not as harmless as they are claimed to be, and that similar findings could apply to any product containing nicotine.</li>
</ul>
Ferdinando Insalatahttp://www.blogger.com/profile/15316468429318156803noreply@blogger.com0tag:blogger.com,1999:blog-2973803697864979211.post-83168687193433236442019-07-03T05:47:00.001-07:002019-07-03T05:47:12.953-07:00DNA Microscopy: Optics-free Spatio-genetic Imaging by a Stand-Alone Chemical Reaction<a href="https://www.sciencedirect.com/science/article/pii/S0092867419305471">https://www.sciencedirect.com/science/article/pii/S0092867419305471</a><br />
<br />
Joshua A. Weinstein, Aviv Regev, and Feng Zhang<br />
<br />
<br />
<ul>
<li>The authors develop a novel method of determining spatial localisation of transcripts within the cell through "DNA Microscopy". </li>
<li>The method consists, firstly, of randomly tagging individual transcripts or DNA molecules with DNA unique molecular identifiers (UMIs), which are random nucleotide sequences of a particular length. </li>
<li>The UMI-concatenated molecules are then amplified through PCR, and diffuse in the cell. UMI tags are designed to contain overhanging complementary regions, such that tagged molecules are subsequently able to bind to another complementary molecule which is in close spatial proximity (called "beacon" and "target" amplicons). Through this process, "unique event identifiers" (UEIs) are generated. The cell can then be lysed, and sequenced through next-generation sequencing.</li>
<li>The rate at which UMIs bound to a particular molecule concatenate indicates the distance between their points of origin.</li>
<li>A computational algorithm then decodes molecular proximities from these UEIs to infer the spatial distribution of transcripts at cellular resolution. </li>
</ul>
Juvid Aryamanhttp://www.blogger.com/profile/05751288336964830816noreply@blogger.com0tag:blogger.com,1999:blog-2973803697864979211.post-49067665961524797252019-06-27T02:28:00.001-07:002019-06-27T02:28:39.212-07:00Atlas of Subcellular RNA Localization Revealed by APEX-Seq<a href="https://www.cell.com/cell/fulltext/S0092-8674(19)30555-0">https://www.cell.com/cell/fulltext/S0092-8674(19)30555-0</a><br />
<br />
Fazal FM, Han S, Parker KR, Kaewsapsak P, Xu J, Boettiger AN, Chang HY, Ting AY<br />
<br />
<ul>
<li>The authors introduce the method APEX-seq, which is a method for whole-transcriptome spatial profiling in living cells. It is based on direct proximity labelling of RNA using the peroxidase enzyme APEX2. </li>
<li>The APEX protein may be localised to different cellular subcomponents, such as the nucleolus, nuclear pore, endoplasmic reticulum, nuclear lamina, outer mitochondrial membrane, and mitochondrial matrix. Once there, APEX biotinylates mRNAs and proteins, allowing mRNAs from the targeted region to be purified and sequenced through RNA-seq.</li>
</ul>
<br />
<br />
<br />Juvid Aryamanhttp://www.blogger.com/profile/05751288336964830816noreply@blogger.com0tag:blogger.com,1999:blog-2973803697864979211.post-16388474466315271172019-06-27T01:32:00.002-07:002019-06-27T01:32:25.613-07:00Cell population heterogeneity driven by stochastic partition and growth optimality<a href="https://arxiv.org/pdf/1805.07768.pdf">https://arxiv.org/pdf/1805.07768.pdf</a><br />
<br />
Jorge Fernandez-de-Cossio-Diaz, Roberto Mulet, Alexei Vazquez<br />
<br />
<ul>
<li>The authors suggest that a cellular quantity which i) has an optimal value for growth rate; ii) is stochastically partitioned at cell division; may display a bimodal distribution in the population. </li>
<li>Whether the distribution is unimodal or bimodal depends on the sharpness of (i) and the extent of noise in (ii). The authors suggest mitochondria as a potential cellular component for which their theory is applicable.</li>
</ul>
<br />
<div>
<br /></div>
Juvid Aryamanhttp://www.blogger.com/profile/05751288336964830816noreply@blogger.com0tag:blogger.com,1999:blog-2973803697864979211.post-73243537151571789082019-06-27T01:20:00.002-07:002019-06-27T01:20:55.593-07:00Quasi-Mendelian Paternal Inheritance of mitochondrial DNA: A notorious artifact, or anticipated mtDNA behavior?<a href="https://www.biorxiv.org/content/10.1101/660670v1?ct=">https://www.biorxiv.org/content/10.1101/660670v1?ct=</a><br />
<br />
Sofia Annis, Zoe Fleischmann, Mark Khrapko, Melissa Franco, Kevin Wasko, Dori Woods, Wolfram S. Kunz, Peter Ellis, Konstantin Khrapko<br />
<br />
<br />
<ul>
<li><a href="https://www.pnas.org/content/115/51/13039" target="_blank">A recent publication</a> suggested that biparental inheritance of mtDNA may sometimes occur in humans</li>
<li>It has since been suggested that these observations may be explained by the presence of mtDNA nuclear pseudogenes (NUMTs) in the father's nuclear genome, rather than biparental inheritance</li>
<li>The authors of this article suggest another interpretation: that the original authors did in fact observe biparental inheritance of mtDNA, and that the paternal mtDNA was inherited by nascent cells with low copy number, and that the paternal mtDNA had a selective advantage. </li>
<li>Using computational modelling (based on <a href="https://www.nature.com/articles/ng0601_147" target="_blank">this publication</a>), the authors predict a somatic mosaic distribution of paternal mtDNA in the resulting progeny, including in the germline.</li>
</ul>
Juvid Aryamanhttp://www.blogger.com/profile/05751288336964830816noreply@blogger.com0tag:blogger.com,1999:blog-2973803697864979211.post-16069964083503861232019-06-26T02:51:00.002-07:002019-06-26T02:51:22.447-07:00Mitochondrial behaviors prime the selective inheritance against harmful mitochondrial DNA mutations<a href="https://www.biorxiv.org/content/biorxiv/early/2019/05/24/646638.full.pdf">https://www.biorxiv.org/content/biorxiv/early/2019/05/24/646638.full.pdf</a><br />
<br />
Zhe Chen, Zong-Heng Wang, Guofeng Zhang and Hong Xu<br />
<br />
<br />
<ul>
<li>The authors investigate the mechanism of selective inheritance of a deleterious temperature-sensitive mitochondrial DNA mutation in the germline of Drosophila. At 29C, this allele is selected against.</li>
<li>They show that mitochondria become fragmented such that >90% of organelles contain a single mitochondrial nucleoid in the germarium 2A region of developing Drosophila ovaries. Nucleoids were found to contain 1.3 mtDNAs on average, suggesting that intra-nucleoid complementation is limited.</li>
<li>Inhibition of fission caused the inter-generational selection against the mutation to essentially be eliminated. </li>
<li>They show that in region 2B, mitochondrial transcripts are expressed (shown via fluoresence in-situ hybridization), and the TMRM:MitoTracker ratio is increased by ~x3 fold.</li>
<li>Knock-down of cox5A resulted in diminished selection, suggesting that activation of mitochondrial respiration is necessary for selection. Similarly, expression of AOX, which by-passes the electron transport chain, resulted in diminished selection. Also, inhibition of mtDNA replication diminished selection (although mean heteroplasmy was also lower in the control setting, at the permissive temperature of 18C, in this case).</li>
<li>To summarise, the authors demonstrate that mitochondrial fission, combined with a suppression of mtDNA replication, in proliferating germ cells segregates mtDNA into individual organelles. The expression of mtDNA induces a genotype-phenotype correspondence for individual organelles, whereby defective organelles are removed and consequently an elimination of mutated molecules of mtDNA.</li>
</ul>
Juvid Aryamanhttp://www.blogger.com/profile/05751288336964830816noreply@blogger.com0tag:blogger.com,1999:blog-2973803697864979211.post-61611572509596466852019-06-12T02:34:00.001-07:002019-06-12T02:34:59.744-07:00Mitochondrial fusion supports increased oxidative phosphorylation during cell proliferation<a href="https://elifesciences.org/articles/41351">https://elifesciences.org/articles/41351</a><br />
<br />
Cong-Hui Yao, Rencheng Wang, Yahui Wang, Che-Pei Kung, Jason D Weber, Gary J Patti<br />
<br />
<br />
<ul>
<li>The authors show that mouse fibroblasts increase oxidative phosphorylation by nearly x2, and mitochondrial coupling efficiency by ~30%, during proliferation. Both of these changes are supported by mitochondrial fusion.</li>
<li>Modulating mitochondrial fusion through Mfn2 levels caused modulation in proliferation rate. Decreases in fusion decreased OXPHOS but not ATP levels.</li>
<li>The authors suggest that cell proliferation requires increased OXPHOS supported by mitochondrial fusion.</li>
</ul>
Juvid Aryamanhttp://www.blogger.com/profile/05751288336964830816noreply@blogger.com0tag:blogger.com,1999:blog-2973803697864979211.post-62242220983285086692019-06-12T02:14:00.000-07:002019-06-12T02:14:18.736-07:00Mammalian cell growth dynamics in mitosis<a href="https://elifesciences.org/articles/44700">https://elifesciences.org/articles/44700</a><br />
<br />
Teemu P Miettinen, Joon Ho Kang, Lucy F Yang, Scott R Manalis<br />
<br />
<br />
<ul>
<li>The authors use a suspended microchannel resonator and protein synthesis assays to measure the accumulation of cell mass through the cell cycle, for single mammalian cells.</li>
<li>For various animal cell types, the growth rate in prophase (the first stage of the cell cycle) is comparable to or larger than interphase (the phase where DNA is copied) growth rates. Growth is only stopped in the metaphase-to-anaphase transition. </li>
<li>The authors find that a range of mitotic arrest mechanisms inhibit cell growth. Their results counter the traditional idea that cell growth is negligible during mitosis.</li>
</ul>
<br />
<br />
<br />Juvid Aryamanhttp://www.blogger.com/profile/05751288336964830816noreply@blogger.com0tag:blogger.com,1999:blog-2973803697864979211.post-75254564080846215222019-06-05T09:30:00.001-07:002019-06-05T09:30:10.734-07:00Germline selection shapes human mitochondrial DNA diversity<a href="https://science.sciencemag.org/content/364/6442/eaau6520.abstract">https://science.sciencemag.org/content/364/6442/eaau6520.abstract</a><br />
<br />
Wei Wei, Salih Tuna, Michael J. Keogh, Katherine R. Smith, Timothy J. Aitman, F. Lucy Raymond, Mark Caulfield, Ernest Turro, Patrick F. Chinnery and others<br />
<br />
<br />
<ul>
<li>The authors analyse 1526 mother-offspring pairs from rare-disease patients in the 100,000 genomes project, to show that 45% of individuals display heteroplasmy at >1% variant allele frequency (VAF).</li>
<li>The authors define 3 kinds of variant: transmitted/inherited (present in both mother and offspring and heteroplasmic in at least one; transmitted = mother, inherited = offspring), lost (present in mother, absent in offspring) and de novo (present in offspring, absent in mother). Absence is defined as VAF < 1%.</li>
<li>Transmitted variants had a much larger heteroplasmic fraction than lost and de novo variants. </li>
<li>Transmitted VAF correlates with inherited VAF (in logit-transformed space).</li>
<li>Heteroplasmy transmission/inheritance did not display a significantly skewed distribution in the inter-generational VAF shift, which is compatible with this set of mutations undergoing neutral drift.</li>
<li>The D-loop had an approximately 4 times higher inter-generational mutation rate per base pair than the rest of the mitochondrial genome, suggesting the existence of stronger selective pressures against mutation on the reset of the genome, or potentially an intrinsically lower de novo mutation rate.</li>
<li>tRNA, rRNA, and non-synonymous mutations tended to have a lower VAF than D-loop and synonymous mutations, suggesting the existence of selection.</li>
<li>The authors identified haplogroup-matched (92%) and haplogroup-mismatched (2.3%) groups within their dataset (6% could not be identified). Haplogroup mismatching arises from mixed-race ancestry. The heteroplasmic variants in the mismatched group were significantly more likely to match the ancestry of the nuclear genetic background than the mtDNA background on which the heteroplasmy occurred.</li>
</ul>
Juvid Aryamanhttp://www.blogger.com/profile/05751288336964830816noreply@blogger.com2tag:blogger.com,1999:blog-2973803697864979211.post-6073939883622970952019-06-03T07:39:00.003-07:002019-06-04T04:26:25.045-07:00Epigenetic Control of Mitochondrial Fission Enables Self-Renewal of Stem-likeTumor Cells in Human Prostate Cancer.<a href="https://www.ncbi.nlm.nih.gov/pubmed/31130467">https://www.ncbi.nlm.nih.gov/pubmed/31130467</a><br />
<br />
Gianluca Civenni, Roberto Bosotti, Andrea Timpanaro, Ramiro Vàzquez, Jessica Merulla, Shusil Pandit, Simona Rossi, Domenico Albino, Sara Allegrini, Abhishek Mitra, Sarah N. Mapelli, Luca Vierling, Martina Giurdanella, Martina Marchetti, Alyssa Paganoni, Andrea Rinaldi, Marco Losa, Enrica Mira-Catò, Rocco D’Antuono, Diego Morone, Keyvan Rezai, Gioacchino D’Ambrosio, L’Houcine Ouafik, Sarah Mackenzie, Maria E. Riveiro, Esteban Cvitkovic, Giuseppina M. Carbone and Carlo V. Catapano<br />
<br />
INTRODUCTION<br />
<ul>
<li style="text-align: justify;">Prostate cancer (PC) is the most common neoplasy in men and one of the main causes of cancer death in developed countries.</li>
</ul>
<ul>
<li style="text-align: justify;">Cancer stem cells (CSCs) are a small subset of cancer cells with stem-cell like properties. They contribute to treatment failure and relapse. Understanding the mechanisms which regulate their self-renewal, differentiation and senescence could lead to new therapeutic strategies.</li>
</ul>
<ul>
<li style="text-align: justify;">Mitochondrial reprogramming has important functions in CSCs. Mitochondrial dynamics control asymmetric cell division, self-renewal, and the fate of stem cells. Fission and clearance of dysfunctional mitochondria avoid senescence and prevent stem cell exhaustion.</li>
</ul>
<div style="text-align: justify;">
MAIN FINDINGS OF THE PAPER</div>
<ul>
<li style="text-align: justify;">The authors uncover a novel link between the protein BRD4, mitochondrial dynamics and self-renewal of CSCs.</li>
</ul>
<ul>
<li style="text-align: justify;">Genetic knockdown of BRD4 or chemical inhibitors blocked mitochondrial fission and caused CSC exhaustion and loss of tumorigenic properties. This is mediated through the inhibition of mitochondrial fission factor (Mff) caused by BRD4 knockdown.</li>
</ul>
<ul>
<li style="text-align: justify;">Evidence for this is that suppression of Mff transcription reproduced the effects of BRD4 knockdown, whereas ectopic expression of Mff rescued CSCs from exhaustion. Therefore the authors conclude that targeting mitochondrial plasticity in CSCs is a promising avenue for new and more effective therapies. </li>
</ul>
Ferdinando Insalatahttp://www.blogger.com/profile/15316468429318156803noreply@blogger.com0tag:blogger.com,1999:blog-2973803697864979211.post-21383229393617809852019-05-22T10:12:00.000-07:002019-05-22T10:12:31.302-07:00Mutational signatures of redox stress in yeast single-strand DNA and of aging in human mitochondrial DNA share a common feature<a href="https://journals.plos.org/plosbiology/article?id=10.1371/journal.pbio.3000263">https://journals.plos.org/plosbiology/article?id=10.1371/journal.pbio.3000263</a><br />
<br />
Natalya P. Degtyareva, Natalie Saini, Joan F. Sterling, Victoria C. Placentra, Leszek J. Klimczak, Dmitry A. Gordenin, Paul W. Doetsch<br />
<br />
<br />
<ul>
<li>The authors report on the mutational spectra of redox stress in single-stranded DNA of budding yeast and in human mitochondrial DNA in the context of healthy aging, finding that the predominance of C>T transitions is a predominant feature in both.</li>
<li>The authors find that the frequencies of hydrogen peroxide-induced mutations in proof-reading deficient yeast mutants supports the conclusion that this form of mutagenesis is the result of direct damage to DNA, rather than misincorporation errors.</li>
<li>They propose that mutations may occur to the heavy strand of mtDNA when DNA replication starts at the light chain, temporarily making the displaced, heavy strand more vulnerable to damage.</li>
</ul>
Juvid Aryamanhttp://www.blogger.com/profile/05751288336964830816noreply@blogger.com0tag:blogger.com,1999:blog-2973803697864979211.post-39975079647894991872019-05-22T08:28:00.000-07:002019-05-22T08:28:05.418-07:00An aerobic eukaryotic parasite with functional mitochondria that likely lacks a mitochondrial genome<span style="background-color: white; color: #333333; font-family: "merriweather" , sans-serif; font-size: 16px;"><a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6482013/pdf/aav1110.pdf">https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6482013/pdf/aav1110.pdf</a></span><br />
<span style="background-color: white; color: #333333; font-family: "merriweather" , sans-serif; font-size: 16px;"><br /></span>
<span style="background-color: white; color: #333333; font-family: "merriweather" , sans-serif; font-size: 16px;">John U, Lu Y, Wohlrab S, Groth M, Janouškovec J, Kohli GS, Mark FC, Bickmeyer U, Farhat S, Felder M, Frickenhaus S, Guillou L, Keeling PJ, Moustafa A, Porcel BM, Valentin K, Glöckner G</span><br />
<span style="background-color: white; color: #333333; font-family: "merriweather" , sans-serif; font-size: 16px;"><br /></span>
<br />
<ul>
<li><span style="color: #333333; font-family: merriweather, sans-serif;"><span style="background-color: white;">A long-standing debate in the field of mitochondrial physiology is the purpose of mitochondrial DNA. The "co-location for redox regulation" (CoRR) hypothesis states that mitochondrial genomes are necessary to provide local control of the electron transport chain.</span></span></li>
<li><span style="background-color: white; color: #333333; font-family: "merriweather" , sans-serif; font-size: 16px;">The authors describe an aerobic eukaryotic parasite (<i>Amoebophyra ceratii</i>) with functional mitochondria, but have completely lost their mitochondrial genome, finding that all mitochondrial proteins appear to be lost or encoded in the nucleus. </span></li>
<li><span style="background-color: white; color: #333333; font-family: "merriweather" , sans-serif; font-size: 16px;">This finding challenges the CoRR hypothesis, and potentially suggests the possibility of complete transfer of the mitochondrial genome into the nuclear genome for more complex organisms.</span></li>
</ul>
<br />
<br />Juvid Aryamanhttp://www.blogger.com/profile/05751288336964830816noreply@blogger.com0tag:blogger.com,1999:blog-2973803697864979211.post-42836519838984460472019-05-22T01:25:00.000-07:002019-05-22T01:25:21.202-07:00Mitochondrial fragmentation drives selective removal of deleterious mtDNA in the germline<a href="https://www.nature.com/articles/s41586-019-1213-4">https://www.nature.com/articles/s41586-019-1213-4</a><br />
<br />
Toby Lieber, Swathi P. Jeedigunta, Jonathan M. Palozzi, Ruth Lehmann & Thomas R. Hurd<br />
<br />
<br />
<ul>
<li>The authors generate mutated fruit flies by transfering mitochondria from a wild-type strain of Drosophila yakuba into a strain of Drosophila melanogaster in which the mtDNA contain a temperature-sensitive mutation in Complex IV of the electron transport chain.</li>
<li>The authors designed fluorescent probes to specifically bind to the D-loop of either D. yakuba or D. melanogaster, allowing them to visualise heteroplasmy.</li>
<li>At 18C, the point mutation does not affect Complex IV activity, whereas at the inhibitory temperature of 29C, Complex IV activity is greatly reduced and is selected against </li>
<li><span style="background-color: white; color: #222222; font-family: Lora, Palatino, Times, "Times New Roman", serif; font-size: 17px; letter-spacing: 0.17px;">Selection first manifests during oogenesis, where a reduction in mitofusins causes fragmentation of the mitochondrial network</span></li>
<li><span style="background-color: white; color: #222222; font-family: Lora, Palatino, Times, "Times New Roman", serif; font-size: 17px; letter-spacing: 0.17px;">The authors identify the proteins Atg1 and BNIP3 as necessary for the selective removal of mitochondria with mutated mtDNAs</span></li>
<li><span style="background-color: white; color: #222222; font-family: Lora, Palatino, Times, "Times New Roman", serif; font-size: 17px; letter-spacing: 0.17px;">A reduction in Atg1 or BNIP3 decreases the amount of wild-type mtDNA, suggesting a link between mitochondrial degradation and replication</span></li>
<li><span style="background-color: white; color: #222222; font-family: Lora, Palatino, Times, "Times New Roman", serif; font-size: 17px; letter-spacing: 0.17px;">At the restrictive temperature, selection occured in the germline but not in the somatic cells which surround the germline in the ovariole, and was largely absent in the male germ line (possibly because only female mtDNA is inherited)</span></li>
<li><span style="background-color: white; color: #222222; font-family: Lora, Palatino, Times, "Times New Roman", serif; font-size: 17px; letter-spacing: 0.17px;">Inhibiting cell death through over-expression of the cell-death inhibitor p35 did not block selection</span></li>
<li><span style="background-color: white; color: #222222; font-family: Lora, Palatino, Times, "Times New Roman", serif; font-size: 17px; letter-spacing: 0.17px;">Expression of the alternative oxidase protein (AOX) bypasses the function of complex IV and partially blocked selection, suggesting that the selection process senses defects in oxidative phosphorylation</span></li>
<li><span style="background-color: white; color: #222222; font-family: Lora, Palatino, Times, "Times New Roman", serif; font-size: 17px; letter-spacing: 0.17px;">The authors observed greater fragmentation in the germline mitochondria relative to the soma. Using photoactivatable GFP, the authors show that mitochondrial contents rarely pass from one mitochondrion to another, suggesting that the purpose of fragmentation is to reduce complementation so that the genotype of individual mitochondria may be sensed through their phenotype.</span></li>
<li><span style="background-color: white; color: #222222; font-family: Lora, Palatino, Times, "Times New Roman", serif; font-size: 17px; letter-spacing: 0.17px;">Reducing Mitofusin expression in somatic cells also induced selection</span></li>
<li><span style="background-color: white; color: #222222; font-family: Lora, Palatino, Times, "Times New Roman", serif; font-size: 17px; letter-spacing: 0.17px;">The authors inhibited the protein IF1, to allow ATP synthase to run in reverse and maintain mitochondrial membrane potential by burning ATP. In doing so, the authors did not observe statistically significant selection, which may suggest that membrane potential sensing is the mechanism by which mitochondria are selected.</span></li>
<li><span style="background-color: white; color: #222222; font-family: Lora, Palatino, Times, "Times New Roman", serif; font-size: 17px; letter-spacing: 0.17px;">Expression of a dominant-negative form of ATP synthase caused a reduction in mtDNA copy number of both mutants and wild-types</span></li>
</ul>
Juvid Aryamanhttp://www.blogger.com/profile/05751288336964830816noreply@blogger.com0tag:blogger.com,1999:blog-2973803697864979211.post-34784228614770734212019-05-10T01:15:00.000-07:002019-05-10T01:15:52.892-07:00Quantitative mitochondrial DNA copy number determination using droplet digital PCR with single cell resolution: a focus on aging and cancer <a href="https://www.biorxiv.org/content/biorxiv/early/2019/03/16/579789.full.pdf">https://www.biorxiv.org/content/biorxiv/early/2019/03/16/579789.full.pdf</a><br />
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Ryan O’Hara, Enzo Tedone,, Andrew Ludlow, Ejun Huang, Beatrice Arosio, Daniela Mari, Jerry W. Shay<br />
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<li>The authors develop a protocol to measure single-cell mtDNA copy number using digital droplet PCR</li>
<li>The authors find ~10-fold inter-cellular variability in mtDNA copy number (in an immortalised human cell line, H1299), which could not be fully explained by cell cycle variations.</li>
<li>The authors investigated how mtDNA copy number changes after stimulation of peripheral blood mononuclear cells (PBMCs, a heterogeneous cellular population largely consisting of T cells). Previous studies have shown a decline in mtDNA copy number with ageing in this cell population. The authors studied stimulated PBMCs in young, old, and healthy/frail centenarians. Healthy centenarians tended to have higher mtDNA copy number than frail, or ~70 year old, individuals. </li>
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Juvid Aryamanhttp://www.blogger.com/profile/05751288336964830816noreply@blogger.com0