The effect of the BMP signaling pathway on the development of secondary sexual characteristics of swimming crab Portunus trituberculatus

The influence of the bone morphogenetic protein (BMP) signaling pathway on the development of secondary sexual characteristics of Portunus trituberculatus was investigated in this study by treating early-stage juvenile crabs with a BMP signaling pathway inhibitor (LDN-193189 2HCl) and an activator (SB4). A set of morphological traits was measured, and key genes involved in BMP signaling and sex differentiation were analyzed. The results showed that, compared to the blank group, the ratio of fourth abdominal width to abdominal length (AW4/AL) in female juvenile crabs treated with the inhibitor was significantly decreased in the first crab (C I) stage, but significantly increased in the third crab (C III) stage. For male crabs, the first abdominal width to abdominal length (AW1/AL) and third abdominal width to abdominal length (AW3/AL) ratios at the second crab (C II) stage, as well as the AW4/AL ratio at the C III stage, were significantly increased in the inhibitor group. However, after activator treatment, there were no significant differences in the standardized indicators during the C I–C III stages for either female or male juvenile crabs. Secondary sexual characteristics appearing during the C I–C III stages were observed by scanning electron microscopy. The results indicated that gender could be identified by the presence or absence of the gonopore at the C I stage and by the morphology and number of the pleopods at the C II stage. In addition, treatment with the inhibitor induced deformities in female gonopores at the C III stage, while the activator had no significant effect on the gonopores or pleopods of juvenile crabs during the C I–C III stages. Following inhibitor treatment, the relative expression levels of BMP signaling pathway genes, including BMPR1B , BMPR2 , Smad5 , and Smad4 , were significantly increased in female juvenile crabs at the C III stage. Concurrently, the relative expression levels of insulin-like androgenic gland hormone ( IAG ) and crustacean female sex hormone ( CFSH ) were also significantly increased. Although the expression levels of several genes were altered in the activator group, the above changes were not observed. In conclusion, the BMP signaling pathway may influence the development of abdominal morphology and gonopores of P. trituberculatus by regulating the expression levels of the critical genes IAG and CFSH during sex differentiation. • Gender can be identified by the presence or absence of the gonopore at the C Ⅰ stage. • Gender can be distinguished by pleopods' morphology and number at the C Ⅱ stage. • BMP signaling inhibition caused deformation of the female crab gonopore. • BMP signaling inhibition affects the abdominal morphology of Portunus trituberculatus . • BMP signaling may affect IAG and CFSH gene expression during sex differentiation.