Characterization of gonad differentially expressed SoxB2 genes in mud crab Scylla paramamosain

Members of sox gene family play critical roles in development, and some of them have crucial functions in sexual dimorphism. To understand the role of two SoxB2 genes, Sox14b and Sox21 of mud crab Scylla paramamosain, the full-length 1939 bp SpSox14b cDNA sequence and 861 bp SpSox21 cDNA sequence were obtained from the crab's transcriptome database, which encode 397 and 259 amino acids respectively. The results of sq-PCR showed that SpSox14b was expressed in all tissues, while SpSox21 was only expressed in the testis and brain. qRT-PCR showed that the expression level of SpSox14b in ovary was significantly higher than that of testis, and during the gonad development its expression was the highest in O2 (previtellogenesis) stage. The expression level of SpSox21 in testis was much higher than in brain, and was significantly higher in T3 (the mature sperm stage) than in other stages of testis development. Meanwhile, in different stages of larval development, SpSox21 was low expressed in zoea, then increased significantly in megalopa. Therefore we speculated that SpSox14b and SpSox21 may play different roles in the gonad development of mud crab, especially SpSox21 may be involved in the development and maintenance of testis. The expression level of SpSox14b and SpSox21 during the eye-pigment formation was significantly higher than that in other embryonic development stages, the results of whole-mount in situ hybridization showed that SpSox14b and SpSox21 were mainly located near the head and the compound eyes in eye-pigment formation stage and hatching. It suggested that they may be involved in the formation of brain nerves and are related to the regulation of body segments, and play different roles in sexual dimorphism.