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Mitochondrial DNA level, but not active replicase, is essential for Caenorhabditis elegans development.

Bratic I, Hench J, Henriksson J, Antebi A, Bürglin TR, Trifunovic A - Nucleic Acids Res. (2009)

Bottom Line: Our results indicate that the gonad is the primary site of mtDNA replication, whilst the mtDNA of adult somatic tissues mainly stems from the developing embryo.Furthermore, we show that the mtDNA copy number shows great plasticity as it can be almost tripled as a response to the environmental stimuli.Finally, we show that the mtDNA copy number is an essential limiting factor for the worm development and therefore, a number of mechanisms set to maintain mtDNA levels exist, ensuring a normal development of C. elegans even in the absence of the mitochondrial replicase.

View Article: PubMed Central - PubMed

Affiliation: Department of Laboratory Medicine, Division of Metabolic Diseases, Novum, Karolinska Institutet, Stockholm SE-141 86, Sweden.

ABSTRACT
A number of studies showed that the development and the lifespan of Caenorhabditis elegans is dependent on mitochondrial function. In this study, we addressed the role of mitochondrial DNA levels and mtDNA maintenance in development of C. elegans by analyzing deletion mutants for mitochondrial polymerase gamma (polg-1(ok1548)). Surprisingly, even though previous studies in other model organisms showed necessity of polymerase gamma for embryonic development, homozygous polg-1(ok1548) mutants had normal development and reached adulthood without any morphological defects. However, polg-1 deficient animals have a seriously compromised gonadal function as a result of severe mitochondrial depletion, leading to sterility and shortened lifespan. Our results indicate that the gonad is the primary site of mtDNA replication, whilst the mtDNA of adult somatic tissues mainly stems from the developing embryo. Furthermore, we show that the mtDNA copy number shows great plasticity as it can be almost tripled as a response to the environmental stimuli. Finally, we show that the mtDNA copy number is an essential limiting factor for the worm development and therefore, a number of mechanisms set to maintain mtDNA levels exist, ensuring a normal development of C. elegans even in the absence of the mitochondrial replicase.

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Gonad morphology of wild-type (N2) and polg-1(ok1548) animals. Electron micrographs of gonads isolated from worms at first (A) and sixth (B) day of adulthood; m: mitochondria, n: nuclei. (C) 3D representation of the gonad morphology in wild-type (N2) and polg-1(ok1548) mutant adult hermaphrodites. 3D reconstruction of microscopic images was performed after Hoechst staining of isolated gonads with the software Endrov (ver. 2.11.0).
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Figure 3: Gonad morphology of wild-type (N2) and polg-1(ok1548) animals. Electron micrographs of gonads isolated from worms at first (A) and sixth (B) day of adulthood; m: mitochondria, n: nuclei. (C) 3D representation of the gonad morphology in wild-type (N2) and polg-1(ok1548) mutant adult hermaphrodites. 3D reconstruction of microscopic images was performed after Hoechst staining of isolated gonads with the software Endrov (ver. 2.11.0).

Mentions: Next we analyzed mitochondria in the gonad, the only proliferating tissue in adult worms. Gonadal development in polg-1(ok1548) animals appears to be normal until the first embryos are produced. However, the number of mitochondria is drastically reduced in polg-1 deficient gonads and the remaining mitochondria appear to be enlarged and display a number of morphological abnormalities in young adults (Figure 3A). Later in adulthood the gonad seems to be seriously depleted of mitochondria, probably due to the production of a certain number of embryos and inability to replicate mtDNA (Figure 3B). These results are in agreement with our previous observation that the majority of the mtDNA replication appears to take place in proliferating gonads. In addition, adult polg-1(ok1548) hermaphrodites did not develop a rachis, the central core of cytoplasm that connects the developing oocytes in the syncytial gonad, which in wild-type worms contains a large number of mitochondria (Figure 3B). No obvious difference in the number of nuclei was observed in isolated polg-1(ok1548) gonads stained with Hoechst 33258 (data not shown).Figure 3.


Mitochondrial DNA level, but not active replicase, is essential for Caenorhabditis elegans development.

Bratic I, Hench J, Henriksson J, Antebi A, Bürglin TR, Trifunovic A - Nucleic Acids Res. (2009)

Gonad morphology of wild-type (N2) and polg-1(ok1548) animals. Electron micrographs of gonads isolated from worms at first (A) and sixth (B) day of adulthood; m: mitochondria, n: nuclei. (C) 3D representation of the gonad morphology in wild-type (N2) and polg-1(ok1548) mutant adult hermaphrodites. 3D reconstruction of microscopic images was performed after Hoechst staining of isolated gonads with the software Endrov (ver. 2.11.0).
© Copyright Policy - creative-commons
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2665216&req=5

Figure 3: Gonad morphology of wild-type (N2) and polg-1(ok1548) animals. Electron micrographs of gonads isolated from worms at first (A) and sixth (B) day of adulthood; m: mitochondria, n: nuclei. (C) 3D representation of the gonad morphology in wild-type (N2) and polg-1(ok1548) mutant adult hermaphrodites. 3D reconstruction of microscopic images was performed after Hoechst staining of isolated gonads with the software Endrov (ver. 2.11.0).
Mentions: Next we analyzed mitochondria in the gonad, the only proliferating tissue in adult worms. Gonadal development in polg-1(ok1548) animals appears to be normal until the first embryos are produced. However, the number of mitochondria is drastically reduced in polg-1 deficient gonads and the remaining mitochondria appear to be enlarged and display a number of morphological abnormalities in young adults (Figure 3A). Later in adulthood the gonad seems to be seriously depleted of mitochondria, probably due to the production of a certain number of embryos and inability to replicate mtDNA (Figure 3B). These results are in agreement with our previous observation that the majority of the mtDNA replication appears to take place in proliferating gonads. In addition, adult polg-1(ok1548) hermaphrodites did not develop a rachis, the central core of cytoplasm that connects the developing oocytes in the syncytial gonad, which in wild-type worms contains a large number of mitochondria (Figure 3B). No obvious difference in the number of nuclei was observed in isolated polg-1(ok1548) gonads stained with Hoechst 33258 (data not shown).Figure 3.

Bottom Line: Our results indicate that the gonad is the primary site of mtDNA replication, whilst the mtDNA of adult somatic tissues mainly stems from the developing embryo.Furthermore, we show that the mtDNA copy number shows great plasticity as it can be almost tripled as a response to the environmental stimuli.Finally, we show that the mtDNA copy number is an essential limiting factor for the worm development and therefore, a number of mechanisms set to maintain mtDNA levels exist, ensuring a normal development of C. elegans even in the absence of the mitochondrial replicase.

View Article: PubMed Central - PubMed

Affiliation: Department of Laboratory Medicine, Division of Metabolic Diseases, Novum, Karolinska Institutet, Stockholm SE-141 86, Sweden.

ABSTRACT
A number of studies showed that the development and the lifespan of Caenorhabditis elegans is dependent on mitochondrial function. In this study, we addressed the role of mitochondrial DNA levels and mtDNA maintenance in development of C. elegans by analyzing deletion mutants for mitochondrial polymerase gamma (polg-1(ok1548)). Surprisingly, even though previous studies in other model organisms showed necessity of polymerase gamma for embryonic development, homozygous polg-1(ok1548) mutants had normal development and reached adulthood without any morphological defects. However, polg-1 deficient animals have a seriously compromised gonadal function as a result of severe mitochondrial depletion, leading to sterility and shortened lifespan. Our results indicate that the gonad is the primary site of mtDNA replication, whilst the mtDNA of adult somatic tissues mainly stems from the developing embryo. Furthermore, we show that the mtDNA copy number shows great plasticity as it can be almost tripled as a response to the environmental stimuli. Finally, we show that the mtDNA copy number is an essential limiting factor for the worm development and therefore, a number of mechanisms set to maintain mtDNA levels exist, ensuring a normal development of C. elegans even in the absence of the mitochondrial replicase.

Show MeSH
Related in: MedlinePlus