Proteomics reveals the gender differences in humoral immunity and physiological characteristics associated with reproduction in the sea cucumber Apostichopus japonicus.

Due to the importance of characteristics associated with the immunity and physiology of organisms, gender is always taken into account when improving the breeding efficiency of economically important animals. Protein variations in the cell-free ceolomic fluid (CCF) of male and female Apostichopus japonicus before and after spawning were investigated using a comparative proteomic approach, for the purpose of understanding the influence of gender and gender associated reproductive processes on humoral immunity and physiological characteristics of the sea cucumber, A. japonicus. A total of 6839 peptides were obtained and a set of 1466 proteins were identified in the CCF of male and female A. japonicus before and after spawning. Partial least squares discrimination analysis indicated that protein expression profiles in the CCF of A. japonicus were significantly affected by both gender and reproductive processes. In addition, the differentially expressed proteins (DEPs) in the CCF of different genders and reproductive stages of A. japonicus were determined and immune-related proteins in these DEPs were screened. Findings revealed that the alternative pathway of complement activation in both male and female A. japonicus before spawning might take precedence over that after spawning. Further KEGG enrichment analyses of DEPs suggested that the capacity of muscle contraction in A. japonicus females, and food digestion, nutrition absorption, epithelial differentiation as well as growth in A. japonicus males might be enhanced after spawning. Further, compared with A. japonicus females, males may have an advantage in growth in the stages following spawning. Besides, according to KEGG annotation related to metabolism, arginine biosynthesis and purine metabolism were dominant in the CCF of male and female A. japonicus, respectively, suggesting notable metabolic differences in female and male A. japonicus. Overall, our study provides new insight into the understanding of molecular mechanisms underlying gender-determined immune and physiological differences in A. japonicus. SIGNIFICANCE: The current study aimed to reveal the gender differences in humoral immunity and physiological characteristics associated with reproduction in the sea cucumber Apostichopus japonicus. To the best of our knowledge, this is the first proteomic study analyzing the differences in protein profile between male and female A. japonicus. By analyzing the expression differences of the proteome via label-free proteomic technology, we revealed that both gender and reproduction could alter the protein composition and abundance in the cell-free colemic fluid (CCF) of A. japonicus. Based on the recognition of differentially expressed proteins (DEPs) related to immune function among the CCFs, shifts in humoral immunity of male and female A. japonicus that underwent reproduction were obtained. Moreover, according to the enrichment analyses of DEPs based on Kyoto Encyclopedia of Genes and Genomes, a draft view of how the male and female A. japonicus affected by reproduction physiologically was drawn. The results suggested that the alternative pathway of complement activation in both male and female A. japonicus were weakened after spawning. In addition, after reproduction, the capacity of muscle contraction might be enhanced in female A. japonicus, and the nutrients consumption, epithelial differentiation and growth might be strengthened in males. Further, ipath analysis indicated that A. japonicus with different genders also had notable differences in metabolism that related to arginine biosynthesis and purine metabolism. The findings presented here will improve the cognition of researchers in the molecular mechanism underlying the gender-determined immune and phyisological differences of A. japonicus and contribute for the meticulous breeding of A. japonicus.