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Thus far, only one gene from the heat shock protein 70 ( HSP70 ) family has been identified in Artemia franciscana . Here, we used the draft Artemia transcriptome database to search for other genes in the HSP70 family. Four novel HSP70 genes were identified and designated heat shock cognate 70 ( HSC70 ), heat shock 70 kDa cognate 5 ( HSC70-5 ), Immunoglobulin heavy-chain binding protein (BIP) , and hypoxia up-regulated protein 1 ( HYOU1 ). For each of these genes, we obtained nucleotide and deduced amino acid sequences, and reconstructed a phylogenetic tree. Expression analysis revealed that in the juvenile state, the transcription of HSP70 and HSC70 was significantly ( P < 0.05) higher in a population of A . franciscana selectively bred for increased induced thermotolerance (TF12) relative to a control population (CF12). Following non-lethal heat shock treatment at the nauplius stage, transcription of HSP70 , HSC70 , and HSC70-5 were significantly ( P < 0.05) up-regulated in TF12. In contrast, transcription of the other HSP70 family members in A . franciscana ( BIP , HYOU1 , and HSPA4 ) showed no significant ( P > 0.05) induction. Gene expression analysis demonstrated that not all members of the HSP70 family are involved in the response to heat stress and selection and that especially altered expression of HSC70 plays a role in a population selected for increased thermotolerance.

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