Region-specific heat-shock protein synthesis correlates with a biphasic acquisition of thermotolerance in Xenopus laevis embryos

Abstract

Embryos of Xenopus laevis, heat shocked before the midcell blastula stage, do not survive heat shock. Heat-shocked midcell blastulae only partially survive heat shock, exhibiting normal development of animal hemisphere derivatives (ectoderm and mesoderm) but exogastrulation of the vegetally derived endoderm. Fine-cell blastulae and early gastrulae are completely thermotolerant. We examined the synthesis of heat-shock proteins (hsps) in whole embryos and in their animal and vegetal hemispheres during heat shock. Hsp synthesis was first observed in embryos that are partially thermotolerant (midcell blastulae). Cells from both the animal and vegetal hemispheres synthesize 87- and 68- to 70-kDa hsps at this time. Completely thermotolerant fine-cell blastulae and early gastrulae synthesize additional hsps upon heat shock. Animal hemisphere cells synthesize 87- and 68- to 70-kDa hsps and small amounts of 57- and 43-kDa hsps. The vegetal cells also synthesize the 57- and 43-kDa hsps, but in large amounts. In addition, they synthesize a 35-kDa hsp not observed in the animal cells. The latter is the earliest observed example of region-specific protein synthesis in amphibians and may account for the delayed acquisition of thermotolerance of the vegetal hemisphere cells.