MOLECULAR CHARACTERIZATION OF A HEAT-SHOCK COGNATE CDNA OF ZEBRAFISH,HSC70, AND DEVELOPMENTAL EXPRESSION OF THE CORRESPONDING TRANSCRIPTS

To elucidate the potential role of the hsp70 gene family in developmen tal processes in vertebrates, we chose io study the expression of one of these genes in zebrafish. A zebrafish gastrula cDNA library was scr eened with a Pleurodeles waltl hsp70 cDNA probe. A 2.3-kb cDNA was thu s isolated and sequenced. The predicted amino acid sequence contained an open reading frame encoding for a 649-amino acid polypeptide. Seque nce analysis showed strong homology with hsp70 related gene sequences in other species; in particular, the strongest homology was found with the cognate members of this family. Tests of heat inducibility reveal ed that transcripts were expressed al normal temperature, but the leve l of transcript expression increased after heal shock. Moreover, exper iments of the neosynthesis of total proteins in heal shock conditions and corresponding immunoblotting assays showed thai 24-h-stage embryos are able to respond to heal shock. The quantity of 70 kDa proteins, r ecognized by a specific antibody of the HSP/C70 protein family, is exp ressed in control condition and increased significantly after heal sho ck. Furthermore, Northern blot analysis of transcript expression showe d that the corresponding mRNAs were detected throughout embryonic deve lopment in the absence of any heal shock. Our clone, named hsc70, thus corresponded io a cognate member of the hsp70 gene family, expressed under normal conditions during development, but also heal inducible. T he spatio-temporal pattern of transcripts during development was deter mined by in situ hybridization on wholemount embryos at different stag es. As a maternal RNA, hsc70 mRNA was uniformly present in the embryo, up to the end of gastrulation. later, a tissue-specific enrichment of hsc70 transcripts was detected in the central nervous system (CNS) an d in a fraction of the somites. These results suggest that the hsc70 g ene may be involved in developmental differentiation events. (C) 1997 Wiley-Liss, Inc.