Expression and localization of Hsp83 RNA in the early Drosophila embryo

Citation

Halsell, Susan Richardson (1995) Expression and localization of Hsp83 RNA in the early Drosophila embryo. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/cx4q-tz48. https://resolver.caltech.edu/CaltechETD:etd-10092007-075248

Abstract

The Hsp83 gene encodes the sole Drosophila homolog of the mammalian Hsp90 family of regulatory molecular chaperones. Hsp90 has been implicated in regulating the activity of several signal transduction molecules, including receptor tyrosine kinases, steroid hormone receptors, src family tyrosine kinases, raf kinase, Weel cell cycle kinase, eIF-2[alpha], protein kinase C and casein kinases. We show that Hsp83 is dynamically expressed during Drosophila oogenesis and embryogenesis. Maternally transcribed mRNA is uniformly distributed in the early embryo, but becomes localized to the posterior pole by a unique mechanism of generalized degradation and localized protection. Hsp83 mRNA is a component of the posterior polar plasm, and the polar plasm is necessary and sufficient for the protection of the maternal RNA from degradation. In vivo analysis reveals that the protection is mediated by sequence elements within the 3'UTR of the Hsp83 mRNA. Maternal Hsp83 mRNA is taken up into the germline progenitor cells (the pole cells) as they form, and RNA is detected in the pole cells throughout embryogenesis. Hsp83 is first expressed zygotically throughout stage 3 embryos but this RNA disappears after only 20 minutes and is undetectable in stage 4 embryos. Hsp83 is then expressed in the anterior third of stage 5 embryos under the control of the anterior morphogen, BICOID. Cis-regulatory sequences necessary for transcriptional activation by BICOID map 1124 bp within the single intron of the Hsp83 gene. In vitro gel shift analysis shows that BICOID binds to a site within this sequence, suggesting that Hsp83 is a direct target of BICOID. In addition, we show that there is a later, independent phase of transcription within the anterior of the early embryo. These analyses form the basis for detailed molecular analysis of Hsp83 functions during early embryogenesis.

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