MEIOTIC INDUCTION BY XENOPUS CYCLIN B IS ACCELERATED BY COEXPRESSION WITH MOSXE

We have investigated the relationship between Xenopus laevis c-mos (mos(Xe)) and the cyclin B component of maturation-promoting factor. Microinjection of Xenopus oocytes with in vitro-synthesized RNAs encoding Xenopus cyclin B1 or cyclin B2 induces the progression of meiosis, characterized by germinal vesicle breakdown (GVBD). By preinjecting oocytes with a mos(Xe)-specific antisense oligonucleotide, we show that GVBD induced by cyclin B does not require expression of the mos(Xe) protein. GVBD induced by cyclin B proceeds significantly faster than GVBD induced by progesterone or Mos(Xe). However, coinjection of RNAs encoding cyclin B1 or cyclin B2 with mos(Xe) RNA results in a 2.5- to 3-fold acceleration in GVBD relative to that induced by cyclin B alone. This acceleration of GVBD does not correlate with changes in the level of cyclin B1 and cyclin B2 phosphorylation.