New evidence confirms that the mitochondrial bottleneck is generated without reduction of mitochondrial DNA content in early primordial germ cells of mice

• Published in: PLoS genetics 2009-12, Vol.5 (12), p.e1000756-e1000756
• Main Authors: Cao, Liqin, Shitara, Hiroshi, Sugimoto, Michihiko, Hayashi, Jun-Ichi, Abe, Kuniya, Yonekawa, Hiromichi
• Format: Article
• Language: English
• Subjects: Alkaline Phosphatase - metabolism; Animals; Biomarkers - metabolism; Cell Separation; Chromosomal Proteins, Non-Histone; copy number; Deoxyribonucleic acid; Disease transmission; DNA; DNA, Mitochondrial - metabolism; Embryo, Mammalian - cytology; Embryo, Mammalian - metabolism; Embryonic development; Embryos; Gene Dosage; Gene Expression Regulation, Developmental; Genetic research; Genetics and Genomics/Animal Genetics; Genomes; Germ cells; Germ Cells - cytology; Germ Cells - enzymology; Germ Cells - metabolism; Luminescent Proteins - metabolism; Mice; Mice, Transgenic; Mitochondria; Mitochondria - genetics; Mitochondrial DNA; Mutation; Myopathy; Neurological diseases; Neurotransmission; Nucleoids; Oocytes; Oogenesis; Positive Regulatory Domain I-Binding Factor 1; Progeny; Red Fluorescent Protein; Replication; Repressor Proteins - genetics; Repressor Proteins - metabolism; Reproducibility of Results; Staining and Labeling; Studies; Transcription Factors - metabolism; Transgenic mice
• ISSN: 1553-7404; 1553-7390; 1553-7404
• DOI: 10.1371/journal.pgen.1000756

In mammals, observations of rapid shifts in mitochondrial DNA (mtDNA) variants between generations have led to the creation of the bottleneck theory for the transmission of mtDNA. The bottleneck could be attributed to a marked decline of mtDNA content in germ cells giving rise to the next generation, to a small effective number of mtDNA segregation units resulting from homoplasmic nucleoids rather than the single mtDNA molecule serving as the units of segregation, or to the selective transmission of a subgroup of the mtDNA population to the progeny. We have previously determined mtDNA copy number in single germ cells and shown that the bottleneck occurs without the reduction in germline mtDNA content. Recently one study suggested that the bottleneck is driven by a remarkable decline of mtDNA copies in early primordial germ cells (PGCs), while another study reported that the mtDNA genetic bottleneck results from replication of a subpopulation of the mtDNA genome during postnatal oocyte maturation and not during embryonic oogenesis, despite a detected a reduction in mtDNA content in early PGCs. To clarify these contradictory results, we examined the mtDNA copy number in PGCs isolated from transgenic mice expressing fluorescent proteins specifically in PGCs as in the aforementioned two other studies. We provide clear evidence to confirm that no remarkable reduction in mtDNA content occurs in PGCs and reinforce that the bottleneck is generated without reduction of mtDNA content in germ cells.