The dynamics of human mitochondrial nucleoids within the mitochondrial network
Kuupäev
2021-12-15
Autorid
Ajakirja pealkiri
Ajakirja ISSN
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Kirjastaja
Abstrakt
Mitokondrid on endosmbiontset päritolu päristuumse raku organellid, millede enimtuntud funktsiooniks on makroergilise ühendi ATP tootmine oksüdatiivse fosforüülimise teel. Lisaks on mitokondritel oluline roll ka näiteks kaltsiumi homöostaasis, programeeritud rakusurmas ja rasvhapete β-oksüdatsioonis. Mitokondritel on väike ja kompaktne genoom, mtDNA, millelt kodeeritakse mitokondriaalse hingamisahela komponente ning mitokondriaalseid tRNA-sid ja rRNA-sid. Inimese mtDNA on pakitud peaasjalikult TFAM valgu abil üksustesse, mida nimetatakse nukleoidideks. Nukleoidid on seotud mitokondri sisemembraaniga ning vastavalt nende funktsioonile ja kooslusele esineb vähemalt kaks nukleoidide populatsiooni. Aktiivselt replitseeruvad nukleoidid, mida iseloomustab helikaasi Twinkle esinemine, on muuhulgas seotud kolesteroolirikka membraanistruktuuriga (replikatsiooni mikrodomään). Antud struktuur on omakorda assotsieerunud ER-mitokonder ühendustega, mida nimetatakse mitokondritega assotsieerunud ER membraanideks (MAM). MAM kontaktid on mtDNA segregatsiooni seisukohast väga olulised, kuna mitokondrite jagunemine ning nukleoidide jaotumine leiab aset MAM kontaktide vahetus läheduses. Samas pole teada täpne regulatsioon, kuidas mitokondriaalsed nukleoidid mõjutavad MAM kontaktpunktide moodustumist kohas, kus toimub mtDNA süntees. Antud töö tulemused aitavad mõista nukleoidide ja organellidevaheliste kontaktide omavahelist koosmõju. Töö käigus leiti, et nukleoidi pakkimisvalgu TFAM allareguleerimisel leiab aset nukleoidide agregeerumine, oluline mtDNA koopiaarvu langus, replikatiivsete nukleoidide populatsiooni suurenemine ning MAM kontaktide ümberorganiseerimine. Antud tulemused näitavad, et nukleoidide terviklikkus on üheks oluliseks eelduseks ER-i ja mitokondri vaheliste interaktsioonide moodustmiseks. Muuhulgas heidavad käesoleva töö tulemused valgust mtDNA ning mtRNA metabolismiga seotud valkude funktsioonidele, aidates kaasa mtDNA säilitamisega seotud häirete tekkepõhjuste mõistmisele.
In eukaryotic cells, mitochondria are organelles of endosymbiotic origin with a well-known function in the synthesis of ATP via oxidative phosphorylation. Mitochondria also play an important role in calcium homeostasis, programmed cell death and β-oxidation of free fatty acids. Mitochondria possess a small and compact genome, which encoded in the mtDNA, which encodes for essential subunits of the electron transport chain, mitochondrial tRNAs and rRNAs. Human mtDNA is packaged exclusively by the TFAM protein into units called nucleoids. Nucleoids are associated with the inner mitochondrial membrane and based on their composition and function at least two pools of nucleoids exist. Nucleoids actively engaged in replication and characterized by the presence of helicase Twinkle are associated with a cholesterol rich membrane structure (replication microdomain). This structure is in turn associated with ER-mitochondria junctions termed mitochondria associated ER membranes (MAM). MAM contacts are essential for mtDNA segregation, as mitochondrial division and nucleoid allocation occur in the vicinity of a subset of MAM. However, it remains to be elucidated how nucleoids impact the formation of MAM at sites of mtDNA synthesis. The results in this thesis provide further knowledge on the interplay between nucleoids and organelle tethers. It was found that a downregulation of nucleoid packaging protein TFAM results in nucleoid aggregation, significant decrease in mtDNA copy number, increased proportion of replicating nucleoids and reorganization of MAM contacts. These results show that the nucleoid integrity is prerequisite for the formation of ER-mitochondria connections. Additionally, this study helps to shed light onto the functions of the proteins involved in mtDNA and mtRNA metabolism, thereby contributing to the understanding of defects associated with mtDNA maintenance.
In eukaryotic cells, mitochondria are organelles of endosymbiotic origin with a well-known function in the synthesis of ATP via oxidative phosphorylation. Mitochondria also play an important role in calcium homeostasis, programmed cell death and β-oxidation of free fatty acids. Mitochondria possess a small and compact genome, which encoded in the mtDNA, which encodes for essential subunits of the electron transport chain, mitochondrial tRNAs and rRNAs. Human mtDNA is packaged exclusively by the TFAM protein into units called nucleoids. Nucleoids are associated with the inner mitochondrial membrane and based on their composition and function at least two pools of nucleoids exist. Nucleoids actively engaged in replication and characterized by the presence of helicase Twinkle are associated with a cholesterol rich membrane structure (replication microdomain). This structure is in turn associated with ER-mitochondria junctions termed mitochondria associated ER membranes (MAM). MAM contacts are essential for mtDNA segregation, as mitochondrial division and nucleoid allocation occur in the vicinity of a subset of MAM. However, it remains to be elucidated how nucleoids impact the formation of MAM at sites of mtDNA synthesis. The results in this thesis provide further knowledge on the interplay between nucleoids and organelle tethers. It was found that a downregulation of nucleoid packaging protein TFAM results in nucleoid aggregation, significant decrease in mtDNA copy number, increased proportion of replicating nucleoids and reorganization of MAM contacts. These results show that the nucleoid integrity is prerequisite for the formation of ER-mitochondria connections. Additionally, this study helps to shed light onto the functions of the proteins involved in mtDNA and mtRNA metabolism, thereby contributing to the understanding of defects associated with mtDNA maintenance.
Kirjeldus
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Märksõnad
mitochondrial DNA, replication, transcription factors