The characterization and potential roles of bone morphogenetic protein 7 during spermatogenesis in Chinese mitten crab Eriocheir sinensis.

Bone morphogenetic proteins (BMPs), which belong to the transforming growth factor-β superfamily, have been implicated in various biological and physiological processes, especially in the gonad development. However, scarce studies were focused on the roles of BMPs in the reproductive system of crustaceans. In this study, the whole gene encoding BMP7 protein was cloned and characterized firstly in Chinese mitten crab Eriocheir sinensis. The bioinformatics analysis of the deduced amino acid sequence showed that Es-BMP7 was composed of prodomain/latency-associated peptide and the TGF-β characteristic domain. The sequence conservation and phylogenetic analysis were also conducted. Quantitative real-time PCR was conducted indifferent tissues. The highest expression in testis indicated the potential role of BMP7 to male gonad development. Western blot results showed the different translational levels of BMP7 in different tissues. In-situ hybridization revealed that the expression of es-bmp7 signals presented in a bimodal manner: highest in spermatogonia, decreased in spermatocytes and stage I spermatids, disappeared in stage II spermatids, and showed up again in stage III spermatids and mature sperm. To further verify the potential roles during spermatogenesis, immunofluorescence was conducted and results showed the similar expression tendency with in situ hybridization. The protein signal was highest in the cytoplasm of spermatogonia, continued to decline in the cytoplasm of spermatocytes and the following stages, and weak signal was found in the mature sperm. Taken together, our results revealed that Es-BMP7 might play a part in testis development in Eriocheir sinensis, presumably by maintaining the self-renewal of spermatogonia and promoting the germ cell differentiation/meiotic mitosis, or facilitating the successful fertilization.