Sexual dimorphism in Grp78 and Hsp90A heat shock protein expression in the estuarine copepod Eurytemora affinis

Abstract

Aquatic organisms are constantly exposed to both natural and anthropogenic stressors. Under stress conditions, they elicit a cellular stress response, involving heat shock proteins (HSPs). HSPs are essential to protect proteins against aggregation and to help in the folding of native proteins or refolding of damaged ones. Because of their conservation among taxons and their inducibility after environmental/chemical stress, HSPs are commonly used as ecological and ecotoxicological biomarkers. However, the appropriate use of such molecular tools requires the investigation of the influence of biotic factors on their basal levels. As a first step in biomarker characterization, the present study aims to evaluate the impact of the reproductive cycle on the expression of the two major HSPs, Grp78 and Hsp90A in the estuarine copepod Eurytemora affinis. The constitutive expression of both genes in males was weak when compared to female levels suggesting gender-specific stress tolerance. Transcript levels gradually increased during oogenesis and maximal levels were recorded in ovigerous females. The present data support the view that the reproductive condition of individuals has to be considered as a confounding factor in stress evaluation by HSP quantification.

Fig. 1

Reproductive stages of E. affinis. a Male (ventral view; ga geniculate antenna). b Female stage 1, immature (dorsal view). Any oocyte can be observed in the oviducts (sp spermatophore). c Female stage 2A, initiating maturation (dorsal view). The female presents small early vitellogenic oocytes in thin oviducts. d Female stage 2B, advanced maturation (dorsal view). The female presents enlarged oviducts full of late-vitellogenic ovocytes. e Female stage 3, ovigerous (dorsal view). The female—without any oocyte in the oviducts—carries a cluster of eggs

Fig. 2

Grp78 and Hsp90A expression during the reproductive cycle of E. affinis. Grp78 (a) and Hsp90A (b) expression was studied by quantitative PCR according to sexual differentiation (♂, male; ♀, female) and oogenesis stage (stages 1 to 3). Each bar represents the mean of cDNA copy number ± standard deviation of independent biological samples. Significant differences are indicated by different letters (p < 0.005)