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
✍ Scribed by Kent D. Taylor; Dr. Lajos Pikó
- Publisher
- John Wiley and Sons
- Year
- 1995
- Tongue
- English
- Weight
- 738 KB
- Volume
- 40
- Category
- Article
- ISSN
- 1040-452X
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✦ Synopsis
Abstract
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. This rapid buildup of the mitochondrial oxidative phosphorylation system appears to be mostly preparatory for postimplantation development. © 1995 Wiley‐Liss, Inc.