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p34 cdc2 expression and meiotic competence in growing goat oocytes
Author(s) -
Dedieu T.,
Gall L.,
Hue I.,
Ledan E.,
Crozet N.,
Ruffini S.,
Sevellec C.
Publication year - 1998
Publication title -
molecular reproduction and development
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.745
H-Index - 105
eISSN - 1098-2795
pISSN - 1040-452X
DOI - 10.1002/(sici)1098-2795(199807)50:3<251::aid-mrd1>3.0.co;2-i
Subject(s) - germinal vesicle , maturation promoting factor , biology , oocyte , meiosis , okadaic acid , andrology , cyclin dependent kinase 1 , microbiology and biotechnology , phosphatase , genetics , gene , phosphorylation , cell cycle , embryo , medicine
The expression of the catalytic subunit of the maturation promoting factor (MPF), p34 cdc2 , was analyzed during meiosis and final growth of goat oocytes. Western blot analysis revealed the presence of p34 cdc2 in fully grown oocytes (follicles >3 mm in diameter) prior to and during meiotic maturation. p34 cdc2 was present in partially competent oocytes at the germinal vesicle stage (follicles 0.5 to 0.8 mm and 1 to 1.8 mm in diameter). In contrast, p34 cdc2 was not expressed in meiotically incompetent oocytes from small antral follicles (follicles <0.5 mm in diameter). The amount of p34 cdc2 increased with oocyte growth and acquisition of meiotic competence. Moreover, p34 cdc2 accumulated in partially competent and incompetent oocytes within 27 hr of culture, but the level of p34 cdc2 in incompetent oocytes remained very low and was not sufficient to allow spontaneous resumption of meiosis. The expression of the cdc2 gene was analyzed by polymerase‐chain‐reaction (PCR) on reverse transcribed mRNA. The presence of the cdc2 transcript was evidenced in both competent and incompetent oocytes at the germinal vesicle stage. These data indicate that a deficiency in the expression of p34 cdc2 that could be regulated at the translational level, may be a limiting factor for meiotic competence acquisition in goat oocytes. We further investigated the mechanisms of MPF activation in competent and incompetent oocytes by using okadaic acid, a protein phosphatase inhibitor. Okadaic acid induced the premature resumption of meiosis associated with MPF activation in competent oocytes. In partially competent oocytes, okadaic acid induced premature meiosis reinitiation and MPF activation, but only after pre‐culture for 10 hr. Acquisition of sensitivity to okadaic acid treatment was dependent on protein synthesis since it failed to occur when cycloheximide was added during the pre‐culture period. Incompetent oocytes responded to okadaic acid treatment only after 27 hr of culture, when they had accumulated small amounts of p34 cdc2 . These data suggest that okadaic acid may bypass the subthreshold level of p34 cdc2 , provided the oocytes have synthesized some additional factors that remain to be identified. Mol. Reprod. Dev. 50:251–262, 1998. © 1998 Wiley‐Liss, Inc.