Expression pattern of heat shock protein 90AB (HSP90AB) and stress-inducible protein 1 (Stip1) during spermatogenesis of mudskipper Boleophthalmus pectinirostris

Heat shock protein 90 (HSP90), which functions as a molecular chaperone, plays an important role in reproduction and cellular defense. Among the HSP90 family, HSP90AB is an important isoform. Stress-inducible protein 1 (Stip1) acts as a co-chaperone that mediates interactions with HSP90 and appears to be a player in spermatogenesis and stress response. However, the functions of both HSP90 and Stip1 during spermatogenesis and heat stress response in Boleophthalmus pectinirostris remain unknown. We investigated mRNA expression patterns of HSP90AB and Stip1 under heat stress conditions. The results showed that mRNA levels of HSP90AB and Stip1 were significantly upregulated in the gill and liver tissues, indicating that HSP90AB and Stip1 appear to play roles in protection against heat stress. Then we cloned the complete cDNA of HSP90AB and Stip1, which have product lengths of 2546 and 2652 bp, respectively. The predicted secondary and tertiary structures of B. pectinirostris. HSP90AB and Stip1 contain conserved domains. We investigated the expression patterns of HSP90AB and Stip1 in different tissues by quantitative real-time polymerase chain reaction, HSP90AB and Stip1 were found to be ubiquitously expressed in all major tissues and exhibited varying expression levels, indicating that HSP90AB and Stip1 have conserved biological functions. HSP90AB and Stip1 were found to be strongly expressed in the testis, indicating their special roles in this organ. We also tracked the dynamic locations of germinal cells using in situ hybridization. Results from in situ hybridization and immunofluorescence localization showed that both mRNA transcripts and proteins of HSP90AB and Stip1 were ubiquitously expressed in spermatocytes, spermatids, and spermatozoa, indicating that HSP90AB and Stip1 are both involved in spermatogenesis.