Sex-biased protein expression in threespine stickleback, Gasterosteus aculeatus

In the threespine stickleback, males and females are sexually dimorphic, having slight differences in body morphology but pronounced differences in reproductive behaviors and phenotype during the mating season. Recent interest in sex chromosome evolution and sex-specific gene expression has surged toward understanding the molecular basis of sexual dimorphism in this species. Sex-biased gene expression at the transcriptome level in liver tissue of nonreproductively active fish was reported recently, yet proteome level investigations in the species are scarce. Thus, proteome level investigations will supplement ongoing genomic studies in threespine stickleback. In this study, protein expression in liver was compared between the sexes using label-free quantitation. Over 300 proteins with a 95% confidence level were identified from fish that were not reproductively active. Common functions included metabolism related to amino acids and lipids and energy metabolism characteristic of normal liver function. Of the identified proteins, 5.8% were differentially expressed between the sexes. Male-biased genes had functions related to amino acid metabolism and signaling whereas female-biased genes were related to protein synthesis.