Molecular characterization and expression of a heat-shock cognate 70 (Hsc70) and a heat-shock protein 70 (Hsp70) cDNAs in Rana (Pelophylax) lessonae embryos.

Heat-Shock Protein 70 (HSP70) is a class of highly conserved proteins which is involved in essential functions as molecular chaperones and in the acquired tolerance processes. In this work, two cDNAs encoding a constitutive Hsc70 and an inducible Hsp70 from the water frog Rana (Pelophylax) lessonae, belonging to the Rana (P.) esculenta complex of central Italy, have been isolated and characterized. The two cDNA clones, named Rl-Hsc70 and Rl-Hsp70, encode 646 and 640 amino acid proteins respectively, which present extremely conserved functional domains characteristic of cytosolic members of the HSP70 family. Comparative studies of the amino acid sequences showed that Rl-Hsc70 and Rl-Hsp70 had the highest homology with constitutive and inducible HSP70 members of other amphibian species. The phylogenetic analysis also demonstrated a separate clustering of the Rl-Hsc70 and Rl-Hsp70 with constitutive and inducible members from other vertebrate species. Heat-inducibility assays performed during embryogenesis showed that the two isolated mRNAs displayed different expression profiles. Rl-Hsp70 was induced only in heat shock-treated embryos, whereas Rl-Hsc70 transcript levels, which were constitutively modulated in non-stressed embryos, did not increase following the heat treatment. In situ hybridization experiments demonstrated that both transcripts showed a tissue-specific enrichment in the central nervous system and in the somites.