Hsp90 in Artemia franciscana During Development and Diapause
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Females of the extremophile crustacean, Artemia franciscana, either release motile nauplii via the ovoviviparous pathway of development or encysted embryos (cysts) via the oviparous pathway. Cysts contain an abundant amount of the ATP-independent small heat shock protein termed p26 that contributes to stress tolerance and embryo development, however, little is known of the role of ATP-dependent molecular chaperones such as Hsp90 in stress tolerance. In other organisms Hsp90 is required for the maturation of substrate proteins, often termed clients, and is involved via a dynamic ATP-dependent cycle in ensuring protein folding, degradation and tolerance to stress. In this study, Hsp90 mRNA and protein were respectively detected in cell free extracts of A. franciscana nauplii and cysts by qRT-PCR and immunoprobing of western blots. RNA interference (RNAi) was then used to characterize Hsp90 in A. franciscana nauplii and cysts, with the latter one of the few times Hsp90 has been examined in vivo during diapause. The partial knock down of Hsp90 slowed the development of nauplius-destined, but not cyst-destined embryos. Hsp90 knockdown also reduced the survival and stress tolerance of nauplii newly released from A. franciscana females. Although reduction of Hsp90 had no effect on the development of diapause-destined embryos, the resulting cysts displayed reduced tolerance to desiccation and low temperature, two stresses normally encountered by A. franciscana in its natural environment. The results reveal that Hsp90 contributes to development, growth and stress tolerance of A. franciscana, an organism of practical importance as a feed source in aquaculture.