Hsp70 and small Hsps are the major heat shock protein members involved in midgut metamorphosis in the common cutworm, Spodoptera litura

Heat shock proteins (Hsps) are important chaperones, which are involved in various signal pathways and regulate lots of physiological processes. Early research suggested that some Hsps are involved in insect development. However, few studies have been carried out to explore the roles of Hsps, especially in larval-pupal metamorphosis. In the present study, 49 Hsp unigenes were identified in the Spodoptera litura transcriptome and their mRNA expression profiles during midgut metamorphosis were examined using a tag-based digital gene expression system. The genes with the most different levels of expression were then cloned and their expression patterns in midguts from sixth instar larvae to pupae were analysed using real time quantitative PCR. The responses of these genes to juvenile hormone (JH) and 20-hydroxyecdysone (20E) were also studied. The results showed that the mRNA levels of 22 Hsp unigenes changed significantly during midgut metamorphosis. Amongst these 22 unigenes, hsp70, hsp20.4 and hsp20.8 were the most up-regulated members, and hsp15.9, hsp19.3 and hsp22.0 were the most down-regulated ones. Further studies showed that hsp70, hsp20.4 and hsp20.8 were remarkably up-regulated by JH. In addition, 20E slightly increased the mRNA levels of both hsp20.4 and hsp20.8. However, hsp15.9, hsp19.3 and hsp22.0 did not respond to either JH or 20E. These results indicate that Hsp70 and small Hsps (sHsps) are probably the major players in midgut metamorphosis in S. litura. The current findings provide valuable insights into the roles of the Hsp superfamily in insect metamorphosis.