Molecular cloning, characterization and expression profiles of a SoxB2 gene related to gonadal development in mud crab (Scylla paramamosain)

ABSTRACT The molecular mechanisms underlying sex differentiation and gonad development remain elusive in crustaceans. Here, we report the cloning and characterization of a Sry-related high-mobility group family B2 gene (SpSoxB2) from an economic crustacean species, the mud crab Scylla paramamosain. The SpSoxB2 encodes a putative HMG-box protein (317 amino acids) clustered with invertebrate Sox14 homologues in the SoxB2 subgroup, but shared low similarity with SpSox14. SpSoxB2 was expressed in the hepatopancreas, thoracic ganglion, and gonads (relatively higher expression in testis than ovary). In hepatopancreas, SpSoxB2 expression was not significantly affected by sex or gonadal development stages. In testis, it was demonstrated that the SpSoxB2 expression level increased from Stage I to Stage III and then decreased afterwards. During ovarian development, the SpSoxB2 expression level continually increased from Stage I to Stage V. Furthermore, fluorescence in-situ hybridization showed that SpSoxB2 transcripts were present in both somatic and developing germ cells in the gonads. In testis, SpSoxB2 transcripts were strongly localized in spermatocytes and spermatids. In ovary, SpSoxB2 transcripts were detected in follicle cells, oogonia and oocytes, with the strongest signal in follicle cells. Our results demonstrated that the SpSoxB2 gene may play an important role during gonadal development in mud crab.