Onset of zygotic transcription and maternal transcript legacy in the rabbit embryo

Onset of zygotic transcription is progressive from the one-cell stage onwar d in the rabbit embryo. Maternal transcripts remain fairly stable until the 8-16 cell stage when major transcriptional activation of the zygotic genom e takes place. To understand the mechanisms of the maternal-to-zygotic tran sition in the genetic information governing development, we asked whether a progressive synthesis of zygotic transcripts takes over the maternal molec ules, or whether the synthesis of zygotic transcripts is very abrupt and in dependent of the persistence of the maternal counterparts. To answer this q uestion, we set up mRNA differential display experiments comparing the mRNA content of rabbit embryos at different stages during the preimplantation p eriod. We isolated eight zygotic transcripts whose synthesis is abruptly tu rned on at the 8-16 cell stage. These transcripts are involved in general c ellular metabolism and their maternal counterparts are still present up to the four-cell and even the 8-16 cell stage. This identification of early zy gotic transcripts suggests that global long range modifications of chromati n structure result in a rapid increase in transcription rates during the ma jor transcriptional activation of the zygotic genome. (C) 2001 Wiley-Liss, Inc.