Do Xenopus oocytes have a heat shock response?
Xenopus oocytes have been reported to respond to heat shock in a unique fashion by inducing the translation of performed mRNA encoding the 70,000-Da heat shock protein (hsp70). We have reexamined Xenopus oocytes for this response by analyzing [35S]methionine-labeled oocyte proteins synthesized at ambient (22 degrees C) and at heat shock (35 degrees C) temperatures. Our objective was to use this response in studies directed at understanding how inactive messages are selected for translation. We found no evidence for the induction of hsp70 in completely defolliculated heat-shocked stage 6 oocytes, although they do appear to synthesize constitutively a 70-kDa protein which is a member of the hsp70 complex of proteins. Defolliculated oocytes were also found to be thermotolerant in vitro. Unfertilized eggs, naturally defolliculated at ovulation, also failed to induce detectable hsp70 synthesis after heat shock. In contrast, fibroblasts and the approximately 1000 follicle cells comprising the theca and follicular layers surrounding each oocyte have a classic heat shock response regulated at the transcriptional level. The hsp70 synthesized by stressed follicle cells was not transported into oocytes. We suggest that oocytes in general may represent an exception to the apparent universality of the heat shock response.
D000818:Animals; D002450:Cell Communication; D002478:Cells, Cultured; D005260:Female; D006360:Heat-Shock Proteins / Q000096:biosynthesis*; D006358:Hot Temperature; D008970:Molecular Weight; D009865:Oocytes / Q000166:cytology / Q000378:metabolism*; D006080:Ovarian Follicle / Q000166:cytology / Q000502:physiology; D014982:Xenopus laevis / Q000378:metabolism*
D006360:Heat-Shock Proteins