Molecular characterization of the Sex-lethal gene in mud crab Scylla paramamosain and its potential role in sexual development

Sex-lethal (Sxl) gene operates as a master switch of sexual differentiation in Drosophila melanogaster. In this study, we cloned and characterized the full-length cDNA of Sxl in mud crab (Scylla paramamosain) (SpSxl). The deduced amino acid sequence of SpSxl contained two RNA-binding motifs (RRM), namely RRM1 and RRM2. The SpSxl mRNA levels were abundant in the androgenic glands of the male crab, implying its potential role in male sexual development. This hypothesis was supported by the RNAi experiment, revealing that the injection of SpSxl dsRNA in vivo caused an increase in the expression of SpIAG, which is a key gene of male sexual differentiation in crustaceans. The interference result of SpTra-2 suggested that SpSxl and SpTra-2 may be involved in sex-differentiation by direct or indirect regulation of SpIAG gene. The eye stalk ablation (ESA) experiments further confirmed that SpSxl could not regulate SpIAG through eyestalk neuropeptide, implying other regulation pathways. In addition, treatment with SpSxl dsRNA had no effects on SpDmrt expression, suggesting that sex determination in S. paramamosain is different from that in D. melanogaster.