THE HEAT-SHOCK RESPONSE IN XENOPUS OOCYTES, EMBRYOS, AND SOMATIC-CELLS - A REGULATORY ROLE FOR CHROMATIN

The heat shook response in Xenopus laevis has been reported to be deve lopmentally regulated at the transcriptional level. We find that the h eat shock response of an exogenous Xenopus hsp70 gene introduced into Xenopus oocytes, embryos, and somatic cells is dependent on the transc riptional assay conditions employed. Under conditions of efficient chr omatin assembly, transcription from the Xenopus hsp70 gene promoter is repressed in oocytes and embryos, yet the promoter responds to heat s hock by activating transcription. Under conditions of inefficient chro matin assembly, the Xenopus hsp70 gene is constitutively active in ooc ytes and somatic cells. Our results resolve previous controversy conce rning the existence of a heat shock response for the hsp70 promoter in oocytes and illustrate the importance of considering chromatin assemb ly as a contributory factor in reconstructing the developmental contro l of gene expression. (C) 1995 Academic Press, Inc.