Mitochondrial dynamics resulting from competing fusion and fission reactions are required for normal cellular function in eukaryotes. Mgm1, a dynamin related protein, is a key component in yeast mitochondrial fusion and is evolutionarily conserved. Previous in vivo studies suggest that the GTPase domain and oligomerization are required for Mgm1 mediated mitochondrial inner membrane fusion. This work demonstrates that purified Mgm1 forms dynamic low order oligomers, and has GTPase activity and kinetic properties consistent with a mechanoenzyme and with a role in inner membrane mitochondrial fusion. Mutations of key residues in the GTPase domain show diminished GTPase activity, while a mutation in the GTPase effector domain implicated in self-assembly results in a lower propensity to form oligomers. Together these data indicate that Mgm1 mediates fusion through oligomerization and GTP binding/hydrolysis in a manner similar to other dynamin mechanoenzymes.

Mitochondrial dynamics resulting from competing fusion and fission reactions are required for normal cellular function in eukaryotes. Mgm1, a dynamin related protein, is a key component in yeast mitochondrial fusion and is evolutionarily conserved. Previous in vivo studies suggest that the GTPase domain and oligomerization are required for Mgm1 mediated mitochondrial inner membrane fusion. This work demonstrates that purified Mgm1 forms dynamic low order oligomers, and has GTPase activity and kinetic properties consistent with a mechanoenzyme and with a role in inner membrane mitochondrial fusion. Mutations of key residues in the GTPase domain show diminished GTPase activity, while a mutation in the GTPase effector domain implicated in self-assembly results in a lower propensity to form oligomers. Together these data indicate that Mgm1 mediates fusion through oligomerization and GTP binding/hydrolysis in a manner similar to other dynamin mechanoenzymes.

Mitochondria exist in a dynamic network regulated by the opposing processes of mitochondrial fusion and fission. Regulation of mitochondrial morphology is critical for metabolism, quality control and cell survival, among other cellular processes. Large GTPases are responsible for shaping the mitochondrial network. Mitofusins 1 and 2 and Opa1 regulate outer and inner mitochondrial membrane fusion, respectively. Conversely, Drp1 is recruited to mitochondria to carry out fission. Although many proteins have been implicated in these processes, there are still many unknowns. We sought to identify novel regulators of mitochondrial morphology and conducted a genome-wide RNAi screen to identify candidate genes. We identified Reactive Oxygen species Modulator 1 (ROMO1) as a novel regulator of mitochondrial fusion and cristae integrity. In the absence of ROMO1, the mitochondrial network fragments and cristae are lost. These defects lead to impaired mitochondrial respiration and sensitization to cytochrome c release and downstream apoptosis. ROMO1 is regulated by mitochondrial REDOX at 4 cysteine residues that couple REDOX signaling to mitochondrial morphology. We have characterized ROMO1 as an interactor with the MINOS complex, required for cristae junction maintenance, and the inner mitochondrial membrane fusion GTPase OPA1. Through these interactions ROMO1 couples cristae junction security to mitochondrial fusion.

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<p>Leydig-ove&nbsp; ćelije&nbsp; testisa&nbsp; su&nbsp; primarno&nbsp; mesto&nbsp; sinteze mu&scaron;kih polnih hormona. Ovi hormoni su neophodani za reproduktivno,&nbsp; ali&nbsp; i&nbsp; za&nbsp; op&scaron;te&nbsp; zdravlje&nbsp; budući&nbsp; da&nbsp; su<br />ozbiljni zdravstveni problemi često povezani sa njihovom smanjenom produkcijom.&nbsp; Insulin i insulinu sličan faktor rasta&nbsp; 1,&nbsp; IGF1&nbsp; <em>(engl.</em>&nbsp; insulin&nbsp; like&nbsp; growth&nbsp; factor&nbsp; 1),&nbsp; i<br />signalizacija koju pokreću preko svojih receptora&nbsp; (INSR i IGF1R),&nbsp; su&nbsp; jedan&nbsp; od&nbsp; ključnih&nbsp; faktora&nbsp; koji&nbsp; reguli&scaron;u specifični razvoj tkiva, pa i samih gonada. Ipak,&nbsp; uloga&nbsp; i<br />mehanizmi&nbsp; delovanja&nbsp; ovih&nbsp; receptora&nbsp; u&nbsp; steroidogenim tkivima nisu&nbsp; u potpunosti&nbsp; poznati.&nbsp; Stoga je&nbsp; istraživanje&nbsp; uokviru ove&nbsp; doktorske&nbsp; disertacije&nbsp; koncipirano sa ciljem da se,&nbsp; na&nbsp; modelu&nbsp; prepubertalnih&nbsp; (P21)&nbsp; i&nbsp; adultnih&nbsp; (P80) mužjaka mi&scaron;eva sa kondicionalnom delecijom<em> Insr </em>i <em>Igf1</em>r gena&nbsp; u&nbsp; steroidogenim&nbsp; ćelijama&nbsp; (Insr/Igf1r-DKO), defini&scaron;e uloga INSR i IGF1R u regulisanju diferencijacije i&nbsp; steroidogene&nbsp; funkcije&nbsp; Leydig-ovih&nbsp; ćelija.&nbsp; Pored&nbsp; toga, mužjaci&nbsp; i&nbsp; ženke&nbsp; P21&nbsp; mi&scaron;eva&nbsp; sa&nbsp; istom&nbsp; delecijom&nbsp; su kori&scaron;ćeni&nbsp; za&nbsp; praćenje&nbsp; ekspresije&nbsp; glavnih&nbsp; markera mitohondrijalne&nbsp; biogeneze&nbsp; i&nbsp; fuzije/arhitekture&nbsp; u&nbsp; Leydigovim&nbsp; ćelijama,&nbsp; ovarijumima&nbsp; i&nbsp;&nbsp; nadbubrežnim&nbsp; žlezdama. Rezultati&nbsp; su&nbsp; potvrdili&nbsp; da&nbsp; delecija&nbsp; Insr&nbsp; i&nbsp; Igf1r&nbsp; u<br />steroidogenim&nbsp; tkivima&nbsp; utiče&nbsp; na&nbsp; diferencijaciju&nbsp; i funkcionalne karakteristike Leydig-ovih ćelija P21 i P80 mi&scaron;eva,&nbsp; upućujući&nbsp; na&nbsp; pojavu&nbsp; tzv.&nbsp; &bdquo;feminizacije&ldquo;.&nbsp; Broj<br />Leydig-ovih&nbsp; ćelija&nbsp; izolovanih&nbsp; iz&nbsp; P21&nbsp; i&nbsp; P80&nbsp; Insr/Igf1rDKO&nbsp; mi&scaron;eva&nbsp; bio&nbsp; je&nbsp; smanjen,&nbsp; a&nbsp; morfologija&nbsp; i ultrastruktura&nbsp; ovih&nbsp; ćelija&nbsp; izmenjene&nbsp; kod&nbsp; P21&nbsp; Insr/Igf1rDKO&nbsp; mi&scaron;eva.&nbsp; Steroidogeni&nbsp; kapacitet&nbsp; i&nbsp; aktivnost,&nbsp; kao&nbsp; i ekspresija&nbsp; glavnih&nbsp; elemenata&nbsp; steroidogene&nbsp; ma&scaron;inerije <em>(Lhcgr, Star, Cyp11a1, Cyp17a1, Hsd3b1&nbsp; i&nbsp; 6, Hsd17b3,</em><br /><em>Sf</em>1)&nbsp; bili su&nbsp; smanjeni&nbsp; u Leydig-ovim ćelijama P21 i P80 <em>Insr/Igf1</em>r-DKO mi&scaron;eva,&nbsp; dok je ekspresija transkripcionih represora&nbsp; steroidogeneze&nbsp; (Arr19&nbsp; i&nbsp; Dax1)&nbsp; bila&nbsp; povećana specifično&nbsp; u&nbsp; istim&nbsp; ćelijama,&nbsp; ali&nbsp; ne&nbsp; i&nbsp; u&nbsp; ostatku&nbsp; testisa.<br />Transkripcioni&nbsp; profil&nbsp; markera&nbsp; mu&scaron;kog&nbsp; pola&nbsp; (<em>Sry,&nbsp; Sox9, Amh</em>)&nbsp; bio&nbsp; je&nbsp; izmenjen&nbsp; u Leydig-ovim ćelijama P21 i P80 <em>Insr/Igf1r</em>-DKO&nbsp; mi&scaron;eva.&nbsp; Transkripcija&nbsp; markera&nbsp; ženskog pola (<em>Rspo1, Wnt4</em>) u testisima,&nbsp; kao i ekspresija&nbsp; Cyp19a1 i&nbsp; produkcija estradiola (E2) u Leydig-ovim ćelijama,&nbsp; P21 i&nbsp; P80&nbsp;<em> Insr/Igf1r</em>-DKO&nbsp; mi&scaron;eva&nbsp; bile&nbsp; su&nbsp; povećane. Transkripcija&nbsp; markera&nbsp; mitohondrijalne&nbsp; biogenze (<em>Ppargc1a,&nbsp; Tfam</em>,&nbsp; <em>Mtnd1</em>)&nbsp; bila&nbsp; je&nbsp; smanjena&nbsp; u&nbsp; Leydigovim&nbsp; ćelijama&nbsp; P21&nbsp; <em>Insr/Igf1r</em>-DKO&nbsp; mi&scaron;eva,&nbsp; dok&nbsp; supromene&nbsp; ekspresije&nbsp; izostale&nbsp; u&nbsp; ovarijumima&nbsp; ženki&nbsp; istog&nbsp; genotipa.&nbsp; Isti&nbsp; markeri&nbsp; su&nbsp; bili&nbsp; povećani&nbsp; u&nbsp; nabdubrežnim&nbsp; žlezdama&nbsp; oba&nbsp; pola.&nbsp; Markeri&nbsp; mitohondrijalne fuzije/arhitekture&nbsp; (<em>Mfn1&nbsp; i&nbsp; Mfn2)</em>&nbsp; bili&nbsp; su&nbsp; povećani&nbsp; u Leydig-ovim ćelijama P21 <em>Insr/Igf1r</em>-DKO mi&scaron;eva, &scaron;to je&nbsp; praćeno&nbsp; i&nbsp; naru&scaron;enom&nbsp; mitohondrijalnom&nbsp; fazom steroidogeneze (produkcija progesterona), kao i brojem i&nbsp; morfologijom ovim organela.&nbsp; Ekspresija istih markera u ovarijumima&nbsp; bila&nbsp; je&nbsp; nepromenjena.&nbsp; Sumirano,&nbsp; rezultati ovog istraživanja&nbsp; su&nbsp; pokazali&nbsp; da su&nbsp; INSR i IGF1R&nbsp; važni za&nbsp; diferencijaciju&nbsp; i&nbsp; steroidogenu&nbsp; funkciju&nbsp; Leydig-ovih&nbsp; ćelija&nbsp; P21&nbsp; i&nbsp; P80&nbsp; mi&scaron;eva.&nbsp; Takođe,&nbsp; ovi&nbsp; receptori&nbsp; su&nbsp; važni regulatori&nbsp; markera&nbsp; mitohondrijalne&nbsp; biogeneze&nbsp; i fuzije/arhiteture u steroidogenim ćelijama mu&scaron;kih gonada&nbsp; P21 mi&scaron;eva, ali ne i u steroidogenim ćelijama ovarijuma.&nbsp;</p> / <p>Leydig cells of testes are the primary site of the male sex hormones&nbsp; synthesis.&nbsp; These&nbsp; hormones&nbsp; are&nbsp; indispensable for&nbsp; both&nbsp; reproductive&nbsp; and&nbsp; general&nbsp; health&nbsp; since&nbsp; serious health&nbsp; problems&nbsp; are&nbsp; often&nbsp; associated&nbsp; with&nbsp; their&nbsp; reduced production.&nbsp; Insulin&nbsp; and&nbsp; insulin-like&nbsp; growth&nbsp; factor&nbsp; 1, IGF1&nbsp; (insulin&nbsp; like&nbsp; growth&nbsp; factor&nbsp; 1),&nbsp; and&nbsp; signaling triggered through&nbsp; their receptors (INSR and IGF1R), are&nbsp; one of the key&nbsp; factors&nbsp; that regulate specific development of&nbsp; tissue&nbsp; including&nbsp; gonads.&nbsp; However,&nbsp; the&nbsp; role&nbsp; and mechanisms&nbsp; of&nbsp; these&nbsp; receptors&nbsp; action&nbsp; in&nbsp; steroidogenic tissues are not known enough. This study was designed to&nbsp; observe &nbsp; the role of INSR and IGF1R in regulating the differentiation and steroidogenic function of Leydig cells by using the model of prepubertal (P21) and adult (P80) male mice with the conditional deletion of the&nbsp; Insr&nbsp; and Igf1r&nbsp; genes&nbsp; in&nbsp; steroidogenic&nbsp; cells&nbsp; (<em>Insr/Igf1r-</em>DKO).&nbsp; In addition,&nbsp; male&nbsp; and&nbsp; female&nbsp; P21&nbsp; mice&nbsp; with&nbsp; the&nbsp; samedeletion were used to monitor the expression of the main markers&nbsp; of&nbsp; mitochondrial&nbsp; biogenesis&nbsp; and fusion/architecture&nbsp; in&nbsp; Leydig&nbsp; cells,&nbsp; ovaries&nbsp; and&nbsp; adrenal glands.&nbsp; The&nbsp; results&nbsp; confirmed&nbsp; that&nbsp; deletion&nbsp; of&nbsp;<em> Insr</em>&nbsp; and<em> Igf1r&nbsp;</em> in&nbsp; steroidogenic&nbsp; tissues&nbsp; influences&nbsp; differentiation and&nbsp; functional&nbsp; characteristics&nbsp; of&nbsp; Leydig&nbsp; cells&nbsp; isolated from&nbsp; P21&nbsp; and&nbsp; P80&nbsp; mice,&nbsp; suggesting&nbsp; an&nbsp; appearance&nbsp; of &quot;feminization&quot;.&nbsp; The&nbsp; number&nbsp; of&nbsp; Leydig&nbsp; cells&nbsp; isolated from&nbsp; both&nbsp; P21&nbsp; and&nbsp; P80&nbsp; <em>Insr/Igf1</em>r-DKO&nbsp; mice&nbsp; was reduced.&nbsp; Morphology&nbsp; and&nbsp; ultrastructure&nbsp; of&nbsp; Leydig&nbsp; cells were&nbsp; disturbed&nbsp; in&nbsp; P21&nbsp; <em>Insr/Igf1r-</em>DKO&nbsp; mice. Steroidogenic capacity and activity, as well as expression of the main elements of&nbsp; steroidogenic machinery (<em>Lhcgr, Star, Cyp11a1, Cyp17a1, Hsd3b1&nbsp; and&nbsp; 6, Hsd17b3, Sf1) </em>were&nbsp; decreased&nbsp; in&nbsp; Leydig&nbsp; cells&nbsp; from&nbsp; P21&nbsp; and&nbsp; P80 I<em>nsr/Igf1</em>r-DKO&nbsp; mice,&nbsp; while&nbsp; the&nbsp; expression&nbsp; of transcriptional&nbsp; repressors&nbsp; of&nbsp; steroidogenesis&nbsp; (<em>Arr19</em>&nbsp; and <em>Dax1) </em>was increased&nbsp; in the same cells, but not in the rest of&nbsp; the&nbsp; testes.&nbsp; Transcription&nbsp; profile&nbsp; of&nbsp; the&nbsp; male&nbsp; sex markers&nbsp; (<em>Sry,&nbsp; Sox9</em>,&nbsp; <em>Amh</em>)&nbsp; was&nbsp; altered&nbsp; in&nbsp; Leydig&nbsp; cells from&nbsp; P21&nbsp; and&nbsp; P80&nbsp; <em>Insr/Igf1</em>r-DKO&nbsp; mice.&nbsp; Transcription of the female sex markers (<em>Rspo1, Wnt4</em>) in the testes, as well&nbsp; as&nbsp; <em>Cyp19a1&nbsp; </em>expression&nbsp; and&nbsp; estradiol&nbsp; (E2) production in Leydig cells,&nbsp; from P21 and P80&nbsp; I<em>nsr/Igf1</em>rDKO&nbsp; mice&nbsp; were&nbsp; increased.&nbsp; Transcription&nbsp; of mitochondrial&nbsp; biogenesis&nbsp; markers&nbsp; (<em>Ppargc1a,&nbsp; Tfam, Mtnd1</em>)&nbsp; was&nbsp; declined&nbsp; in&nbsp; Leydig&nbsp; cells&nbsp; from&nbsp; P21<em> Insr/Igf1r-</em>DKO mice, while changes were absent in&nbsp; the ovaries of the same genotype.&nbsp; Transcription of the&nbsp; same markers&nbsp; was&nbsp; increased&nbsp; in&nbsp; the&nbsp; adrenal&nbsp; glands&nbsp; of&nbsp; both sexes.&nbsp; The&nbsp; mitochondrial&nbsp; fusion/architecture&nbsp; markers (<em>Mfn1</em>&nbsp; and&nbsp; <em>Mfn2</em>)&nbsp; were&nbsp; increased&nbsp; in&nbsp; Leydig&nbsp; cells&nbsp; from<em> Insr/Igf1r</em>-DKO&nbsp; mice&nbsp; and&nbsp; followed&nbsp; by&nbsp; disturbedmitochondrial&nbsp; phase&nbsp; of&nbsp; steroidogenesis&nbsp; (progesterone production), as well as&nbsp; decreased&nbsp; number and&nbsp; disturbed morphology&nbsp; of&nbsp; mitochondria.&nbsp;&nbsp; Expression&nbsp; of&nbsp; the&nbsp; same markers&nbsp; in&nbsp; the&nbsp; ovaries&nbsp; was&nbsp; unchanged.&nbsp; In&nbsp; summary, results&nbsp; of&nbsp; this&nbsp; study&nbsp; showed&nbsp; that&nbsp; INSR&nbsp; and&nbsp; IGF1R&nbsp; are important in differentiation and steroidogenic function of Leydig&nbsp; cells&nbsp; from&nbsp; P21&nbsp; and&nbsp; P80&nbsp; mice.&nbsp; Also,&nbsp; these receptors&nbsp; are&nbsp; important&nbsp; regulators&nbsp; of&nbsp; mitochondrial biogenesis&nbsp; and&nbsp;&nbsp; fusion/architecture&nbsp; markers&nbsp; in steroidogenic&nbsp; cells&nbsp; of&nbsp; P21&nbsp; male&nbsp; mice,&nbsp; but&nbsp; not&nbsp; in steroidogenic cells of ovaries.</p>