Mitochondrial biogenesis in early mouse embryos: expression of the mRNAs for subunits IV, Vb, and VIIc of cytochrome c oxidase and subunit 9 (P1) of H(+)-ATP synthase.
The mouse egg contains about 90,000 mitochondria which undergo a buildup of mitochondrial cristae and increase in respiratory activity during cleavage. The mitochondrial DNA does not replicate during preimplantation development but is transcribed actively from the two-cell stage onward (Pikó and Taylor, 1987: Dev Biol 123:364-374). To gain further insight into mitochondrial biogenesis, we have now determined the steady state amounts of the mRNAs for the cytochrome c oxidase (COX) subunits IV, Vb and VIIc and the H(+)-ATPase subunit 9 (P1) (all encoded by nuclear genes) in slot hybridization experiments of total RNA from oocytes and early embryos. All four mRNAs showed a similar developmental pattern of prevalence, characterized by a steady decline in mRNA copy numbers from the late growth-phase oocyte through the two-cell embryo, and an about 30-fold rise during cleavage through the blastocyst stage. However, the ATPase subunit 9 (P1) mRNA was about three times more prevalent in cleavage-stage embryos than the COX mRNAs. A similar pattern was obtained previously for the mitochondrial-encoded COX I and II mRNAs, but the latter accumulate at a 30-50-fold excess over the nuclear-encoded COX subunit mRNAs during the cleavage stages. The results suggest a coordinated activation and transcription of the mitochondrial and nuclear genes for the components of the respiratory apparatus beginning with the two-cell stage. It is estimated that new respiratory chains are produced at a rate of 50-100 chains hr-1/mitochondrion in the early blastocyst, accounting for 3.5-7% of the total protein synthetic activity at this stage.(ABSTRACT TRUNCATED AT 250 WORDS)
Taylor
K D
KD
Developmental Biology Laboratory, Veterans Administration Medical Center, Sepulveda, CA 91343.
Pikó
L
L
D000818:Animals; D001755:Blastocyst / Q000378:metabolism; D018076:DNA, Complementary / Q000235:genetics; D003576:Electron Transport Complex IV / Q000737:chemistry / Q000235:genetics*; D004622:Embryo, Mammalian / Q000378:metabolism*; D005314:Embryonic and Fetal Development / Q000235:genetics; D005260:Female; D018507:Gene Expression Regulation, Developmental; D051379:Mice; D008807:Mice, Inbred BALB C; D008811:Mice, Inbred DBA; D008928:Mitochondria / Q000378:metabolism*; D009865:Oocytes / Q000378:metabolism; D011247:Pregnancy; D011487:Protein Conformation; D006180:Proton-Translocating ATPases / Q000737:chemistry / Q000235:genetics*; D012313:RNA / Q000235:genetics / Q000378:metabolism; D015347:RNA Probes; D012333:RNA, Messenger / Q000235:genetics* / Q000378:metabolism; D000077278:RNA, Mitochondrial
D018076:DNA, Complementary; D015347:RNA Probes; D012333:RNA, Messenger; D000077278:RNA, Mitochondrial; D012313:RNA; D003576:Electron Transport Complex IV; D006180:Proton-Translocating ATPases