It has been suggested that the heat shock response of Xenopus oocytes might provide a good model system to study the regulation of translation in early development: oocytes were thought to contain a store of hsp70 mRNA, which was unmasked reversibly on heat shock. However, more recently it has been reported that the hsp70 apparently synthesized in oocytes is in fact made entirely in the attached follicle cells. A method was developed to reliably remove follicle cells. Two-dimensional gel analysis of radioactively labelled oocytes revealed that, although hsp70 was the major protein synthesized during heat shock if follicle cells were present, it could not be detected if these cells were removed. Oocytes do contain up to 15pg of hsp70 mRNA; it is not clear if this is translated. In some experiments synthesis of a group of proteins was induced in oocytes during heat shock, but none was hsp70. To test whether oocytes can synthesize hsp70, plasmids encoding Xenopus hsp70 genes were injected. These were transcribed efficiently, yielding RNA that was indistinguishable in length and polyadenylation status from heat-induced transcripts in follicle cells. Synthesis of hsp70 was detected in defol1iculated, injected oocytes: it was translated well even during heat shock (when translation of other mRNAs was greatly reduced), suggesting that oocytes regulate translation of exogenous transcripts appropriately. Surprisingly, flu nucleoprotein RNA transcribed in oocytes was also preferentially translated during heat shock in some experiments. The 5' leaders of hsp70 and NP RNAs contain a region of homology. As injection of RNA provides a more direct way of controlling transcript levels in oocytes, polyadenylated RNA encoding hsp70 was transcribed in vitro (from a variety of templates) and injected into oocytes. Products of a hsp70/globin fusion and a truncated hsp70 gene were never detected. Native hsp70 was synthesized, but it was not made preferentially during heat shock. Similarly, when influenza NP mRNA was injected, preferential translation was never observed. It appears therefore that exogenous RNA is regulated appropriately during heat shock when it is introduced by the route of DNA injection, but not when RNA itself is injected.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:234541 |
| Date | January 1988 |
| Creators | Horrell, Judith Ann |
| Publisher | University of Warwick |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://wrap.warwick.ac.uk/99025/ |
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