Proteome analysis of silkworm, Bombyx mori, larval gonads: characterization of proteins involved in sexual dimorphism and gametogenesis.

Sexual dimorphism is initialed by the components of the sex determination pathway and is most evident in gonads and germ cells. Although striking dimorphic expressions have been detected at the transcriptional level between the silkworm larval testis and the ovary, the sex-dimorphic expressions at the protein level have not yet been well characterized. The proteome of silkworm larval gonads was investigated using a shotgun-based identification. A total of 286 and 205 nonredundant proteins were identified from the silkworm testis and ovary, respectively, with a false discovery rate (FDR) lower than 1%. Only 40 and 16 proteins were previously identified, and 246 and 189 proteins were newly identified in the silkworm testis and the ovary, respectively. The gametogenesis mechanism of silkworm was demonstrated using the protein expression profile and bioinformatics analysis. Cellular retinoic acid binding protein (CRABP) showed to be highly abundant in testis, while tubulins were abundant in ovary. Several homologies of Drosophila essential proteins for gametogenesis were identified in silkworm, such as male meiotic arrest gene product ALY and VISMAY in testis, and maternal mRNA localization protein exuperantia and SQUID in ovary. The gene ontology (GO) annotation and pathway analysis provide system-level insights into the sexual dimorphism and gametogenesis.