Functional differentiation of small heat shock proteins in diapause‐destined A rtemia embryos

Encysted embryos of A rtemia franciscana cease development and enter diapause, a state of metabolic suppression and enhanced stress tolerance. The development of diapause‐destined A rtemia embryos is characterized by the coordinated synthesis of the small heat shock proteins (s H sps) p26, A r H sp21 and A r H sp22, with the latter being stress inducible in adults. The amounts of s H sp m RNA and protein varied in A rtemia cysts, suggesting transcriptional and translational regulation. By contrast to p26, knockdown of A rHsp21 by RNA interference had no effect on embryo development. A r H sp21 provided limited protection against stressors such as desiccation and freezing but not heat. A r H sp21 may have a non‐essential or unidentified role in cysts. Injection of A rtemia adults with amounts of A r H sp22 double‐stranded RNA less than those used for other s H sps killed females and males, curtailing the analysis of A r H sp22 function in developing embryos and cysts. The results indicate that diapause‐destined A rtemia embryos synthesize varying amounts of s H sps as a result of differential gene expression and m RNA translation and also suggest that these s H sps have distinctive functions.