Developmental Regulation of Xenopus 5S RNA Genes

The problem of how differentiated cells stably main-tain specific patterns of gene expression is a central theme in developmental biology. Moreover, mechan-isms of establishing this control must exist whereby genes required for differentiated phenotypes are selected for transcription and others are stably inac-tivated. We are utilizing the 5S RNA gene system in Xenopus as a model for understanding developmental control at the transcriptional level of gene expression. This regulation e compasses the activation of oocyte 5S RNA genes throughout oogenesis, their subsequent in-activation during embryogenesis, and the maintenance of this repressed state in somatic ells when somatic 5S RNA genes continue to be expressed. Recently, we proposed that the formation of stable,