Meiotic induction by Xenopus cyclin B is accelerated by coexpression with mos^Xe

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.