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Published on: July 30, 2020
Analyses of mitogen-activated protein kinase function in the maturation of porcine oocytes
Satoshi Ohashi1, Kunihiko Naito, Koji Sugiura
1Department of Animal Resource Sciences, Graduate School of Agricultural and Life Sciences, University of Tokyo, Bunkyo-ku, Tokyo 113-8657, Japan.
Abstract:
The function of mitogen-activated protein kinase (MAPK) during porcine oocyte maturation was examined by injecting oocytes with either mRNA or antisense RNA of porcine c-mos protein, an upstream kinase of MAPK. The RNAs were injected into the cytoplasm of porcine immature oocytes immediately after collection from ovaries, then the oocytes were cultured for maturation up to 48 h. The phosphorylation and activation of MAPK were observed at 6 h after injection of the c-mos mRNA injected-oocytes, whereas in control oocytes, MAPK activation was detected at 24 h of culture. The germinal vesicle breakdown (GVBD) rate at 24 h of culture was significantly higher in c-mos mRNA-injected oocytes than in control oocytes. In contrast, although injection of c-mos antisense RNA completely inhibited phosphorylation and activation of MAPK throughout the maturation period, the GVBD rate and its time course were the same in noninjected oocytes. The degree of maturation-promoting factor (MPF) activation was, however, very low in oocytes in the absence of MAPK activation. Most of those oocytes had both abnormal morphology and decondensed chromosomes at 48 h of culture. These results suggest that MAPK activation is not required for GVBD induction in porcine oocytes and that the major roles of MAPK during porcine oocyte maturation are to promote GVBD by increasing MPF activity and to arrest oocytes at the second metaphase.
Insights
Mitogen-activated protein kinase (MAPK) is not essential for germinal vesicle breakdown in pig oocytes but is crucial for maturation. MAPK promotes maturation by enhancing maturation-promoting factor (MPF) activity and arresting oocytes at metaphase II.
Area of Science:
- Reproductive Biology
- Cell Signaling
- Molecular Endocrinology
Background:
- Porcine oocyte maturation is a complex process regulated by intracellular signaling pathways.
- Mitogen-activated protein kinase (MAPK) and maturation-promoting factor (MPF) are key regulators of meiosis.
- The precise role of MAPK in porcine oocyte maturation, particularly its relationship with MPF, requires further elucidation.
Purpose of the Study:
- To investigate the role of MAPK in porcine oocyte maturation.
- To determine if MAPK activation is required for germinal vesicle breakdown (GVBD).
- To examine the influence of MAPK on MPF activation and meiotic arrest.
Main Methods:
- Porcine immature oocytes were microinjected with c-mos mRNA or antisense RNA.
- Oocytes were cultured for maturation up to 48 hours.
- MAPK phosphorylation and activation, GVBD, MPF activation, and chromosomal morphology were assessed.
Main Results:
- c-mos mRNA injection accelerated MAPK activation and increased GVBD rates.
- Inhibition of MAPK activation by antisense RNA did not prevent GVBD but led to low MPF activation.
- Oocytes lacking MAPK activation exhibited abnormal morphology and decondensed chromosomes at 48 hours.
Conclusions:
- MAPK activation is not essential for the induction of GVBD in porcine oocytes.
- MAPK plays a significant role in promoting oocyte maturation by enhancing MPF activity.
- MAPK is involved in arresting porcine oocytes at the second metaphase stage of meiosis.
