Expression of c-myc proto-oncogene during the early development of Xenopus laevis.

c-myc proto-oncogene expression in Xenopus laevis oocytes and developing embryos has been investigated. Stage VI oocytes as well as unfertilized eggs contain a high level of Xenopus c-myc mRNA (1-2.5 x 10(7) copies). However, this high level of maternal c-myc mRNA declines gradually during the time of rapid and synchronous cell cleavage and becomes almost undetectable after the mid-blastula transition. The zygotic genes then become activated for the first time, whereupon the amount of newly synthesized c-myc mRNA starts to increase again. The level of c-myc mRNA in the 1 day old embryo (stage 22) is comparable to that of oocyte or unfertilized egg. The finding suggest that c-myc gene products may play an important role during early embryogenesis, especially during the rapid synchronous cell cleavage period and onset of the mid-blastula transition.