CONTROL OF GENE-EXPRESSION IN XENOPUS EARLY DEVELOPMENT

We examine the control of gene expression before and through the MBT i n Xenopus laevis. The generalized repression of transcription that occ urs before the midblastula transition (MBT) is regulated by a dynamic competition between chromatin and transcription complex assembly. Cond itions favoring the access of basal factors (TBP) or transactivators c an overcome this transcriptional repression. Changes in DNase I hypers ensitivity patterns of the chromatin during early development show tha t it is more accessible to DNase I before the MBT (and by extension to other DNA interacting proteins) than after the MET. We also show that at the level of genomic domains, organization of the chromatin matrix attachment sites is random before MET. We propose that these three co mponents, chromatin domain structure, DNA accessibility, and the trans cription complex-chromatin dynamic competition, combine to regulate tr anscription in the embryo before and through the MBT. (C) 1998 Wiley-L iss, Inc.