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Somatic cells and the G2 to M-phase transition in sheep oocytes
Abstract:
New protein synthesis is essential in sheep oocytes for the progression of the meiotic cycle to metaphase. Inhibition of transcription by alpha-amanitin, a specific inhibitor of RNA polymerase II, arrests meiosis in the G2 phase in cumulus enclosed oocytes but denuded oocytes progress to M-phase. Denuded oocytes injected with alpha-amanitin also undergo maturation. Cumulus-enclosed and denuded oocytes were also cultured on transcriptionally inactive follicle shells to examine the influence of transcription in the granulosa cell compartment on the progression of meiosis. No effect of alpha-amanitin was detected on the maturation rate of both cumulus enclosed and denuded oocytes. We conclude that transcription is required in the cumulus cells to allow translation of stored messages within the oocytes coding for cell-cycle proteins.
Insights
New protein synthesis is crucial for sheep oocyte maturation. Transcription in surrounding cumulus cells, not the oocyte itself, drives this process by enabling the translation of essential cell-cycle proteins.
Area of Science:
- Reproductive biology
- Molecular biology
- Cell biology
Background:
- Oocyte maturation is a complex process requiring new protein synthesis.
- The role of transcription within the oocyte versus surrounding somatic cells during meiosis is not fully understood.
Purpose of the Study:
- To investigate the necessity of new protein synthesis for meiotic progression in sheep oocytes.
- To determine whether transcription within the oocyte or the surrounding cumulus cells is essential for maturation.
Main Methods:
- Sheep oocytes (cumulus-enclosed and denuded) were treated with alpha-amanitin, a specific RNA polymerase II inhibitor.
- Oocytes were cultured on transcriptionally inactive follicle shells to isolate the effects of oocyte transcription.
- Meiotic progression was assessed by observing the transition to M-phase.
Main Results:
- Inhibition of transcription in cumulus-enclosed oocytes arrested meiosis at the G2 phase.
- Denuded oocytes, whether exposed to alpha-amanitin or injected with it, progressed to M-phase.
- Culturing oocytes on inactive follicle shells did not alter maturation rates, indicating transcription in somatic cells is not the sole factor.
Conclusions:
- Transcription is required in the cumulus cells for sheep oocyte maturation.
- This transcription facilitates the translation of stored messenger RNAs within the oocyte that code for critical cell-cycle proteins.
- The findings highlight the importance of the oocyte-somatic cell communication in reproductive processes.