Cyclin B1 expression in meiotically competent and incompetent goat oocytes.

To start determining the nature of meiotic incompetence in goat oocytes, we have examined the expression of one of the potential pre-MPF subunits: the cyclin B1. We have been isolating a small DNA probe encoding the goat cyclin B1 box to analyze the expression of the cyclin B1 gene in competent and incompetent goat oocytes. This probe was easily obtained by polymerase-chain-reaction (PCR) on reverse-transcribed mRNA from granulosa cells, using cyclin B specific primers derived from a bovine cDNA. The transcript corresponding to cyclin B1 in goat granulosa cells is 1.8 kb. In situ hybridization analysis indicated that competent and incompetent oocytes contained cyclin B1 mRNA, but also that active cyclin B1 mRNA synthesis occurred at the end of the growth phase, e.g., when oocytes progressed in the acquisition of meoitic competence. Western blot analysis, performed with a monoclonal anticyclin B1 antibody, revealed in competent and incompetent oocytes a polypeptide of 65 kDa corresponding to the goat cyclin B1 protein. This pattern of cyclin B1 expression further suggested that meiotic incompetence in goat oocytes could not be primarily correlated with a lack of cyclin B1 protein as potential pre-MPF subunit, but to a limiting amount of this protein.