Regulation of Gene Expression During Embryonic Development

Abstract

The South African clawed toad, Xenopus laevis, is a suitable experimental system to investigate gene expression during the early development of vertebrates. Embryogenesis takes place outside the maternal body and enormous amounts of fertilized eggs can be easily obtained after hormone induced breeding. Embryonic development is characterized by rapid morphogenetic changes which might be induced by different cellular interactions or by the action of morphogenetic factors but is finally based upon differential gene expression. Its regulation can occur at the levels of transcription, processing and translation. In Xenopus, translational control mechanisms may play a decisive role during oocyte maturation [1] and also in the first post-fertilization stages. The hormone induced conversion of the stage six oocyte to the egg is accompanied by a 20-fold increase of histone synthesis [2] without detectable changes in the concentration of total translatable histone mRNA [3]. On the other hand it has been shown, that at least in the case of two-cell-stage mouse embryos, the paternal genome is already actively transcribed and expressed into proteins [4], The present investigation has been started to isolate those genes which are stage-specifically expressed during embryogenesis and to elucidate mechanisms which control their expression.