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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.

Salmonids are teleost fish of profound research and economic interest. Embryonic development is a key aspect of salmonid biology that can be critically affected by environmental parameters. Still, their proteome during embryogenesis remains largely unexplored. This study investigates the proteome of the eyed-egg and hatching stages of embryonic development of a salmonid species, European grayling (Thymallus thymallus), using a shotgun proteomic approach. To deal with limited grayling protein resources, the generated spectra were compared against an all-salmonid database using search and multiple protein grouping algorithms to infer identifications. Functional enrichment analysis was carried out at different levels (gene ontologies, pathways, networks) using zebrafish as a reference genome. A total of 213 and 239 proteins were confidently detected in eyed and hatching stages, respectively. Cell cycle, energy, and protein metabolism were the major processes common to both stages. Nuclear activity and brain and eye development were the predominant functions in the eyed-stage proteome, while central nervous system, skeletal muscle, and heart development prevailed in the hatching stage. Overall, this research constitutes the first effort to describe the proteome during embryogenesis in grayling or any salmonid species. It also presents a systematic approach by which existing resources can enable proteome research in salmonids.