Transcriptome analysis of different life-history stages and screening of male-biased genes in Daphnia sinensis.

Background: In the life history of Daphnia, the reproductive mode of parthenogenesis and sexual reproduction alternate in aquatic ecosystem, which are often affected by environmental and genetic factors. Recently, the sex-biased genes are of great significance for clarifying the origin and evolution of reproductive transformation and the molecular regulation mechanism of sex determination in Daphnia. Although some genes on reproductive transition of Daphnia had been researched, molecular mechanism on the maintenance of sexually dimorphic phenotypes of Daphnia are still not well known, including differentially expressed genes in different life-history stages. Results: In this study, four life-history stages of Daphnia sinensis, juvenile female (JF), parthenogenetic female (PF), sexual female (SF) and male (M), were performed for transcriptome, and male-biased genes were screened. A total of 110437 transcripts were obtained and assembled into 22996 unigenes. In the four life-history stages (JF, PF, SF and M), the number of unique unigenes is respectively 2863, 445, 437 and 586, and the number of common unigenes is 9708. The differentially expressed genes (DEGs) between male and other three female stages (M vs JF, M vs PF and M vs SF) were 4570, 4358 and 2855, respectively. GO gene enrichment analysis showed that the up-regulated genes in male were mainly enriched in hydrolase activity and peptidase activity. Thirty-six genes in male were significantly higher expression than in the three female stages, including one Doublesex (Dsx) gene, one laminin gene, five trypsin genes and one serine protease genes, and one chitin synthase gene and two chitinase genes. Conclusions: Our results showed that thirty-six candidate genes may be as the male-biased genes involving in the maintenance of sexually dimorphic phenotypes. This work will provide a reference for further exploring the functional genes related to sex differentiation in Daphnia species. Moreover, according to previous investigations, we thought that the expression level of functional genes may be related to the life-history stages of organisms, and may be also affected by different Daphnia species. [ABSTRACT FROM AUTHOR]