Identification and expression profiles of Fox transcription factors in the Yesso scallop (Patinopecten yessoensis)

The forkhead box (Fox) gene family is a family of transcription factors that play important roles in a variety of biological processes in vertebrates, including early development and cell proliferation and differentiation. However, at present, studies on the mollusk Fox family are relatively lacking. In the present study, the Fox gene family of the Yesso scallop (Patinopecten yessoensis) was systematically identified. In addition, the expression profiles of the Fox gene family in early development and adult tissues were analyzed. The results showed that there were 26 Fox genes in P. yessoensis. Of the 26 genes, 24 belonged to 20 subfamilies. The Fox genes belonging to the I, Q1, R and S subfamilies were absent in P. yessoensis. The other 2 genes formed 2 independent clades with the Fox genes of other mollusks and protostomes. They might be new members of the Fox family and were named FoxY and FoxZ. P. yessoensis contained a FoxC-FoxL1 gene cluster similar in structure to that of Branchiostoma floridae, suggesting that the cluster might already exist in the ancestors of bilaterally symmetrical animals. The gene expression analysis of Fox showed that most of the genes were continuously expressed in multiple stages of early development, suggesting that Fox genes might be widely involved in the regulation of embryo and larval development of P. yessoensis. Nine Fox genes were specifically expressed in certain tissues, such as the nerve ganglia, foot, ovary, testis, and gills. For the 9 genes that were differentially expressed between the testis and ovary, their expression levels were analyzed during the 4 developmental stages of gonads. The results showed that FoxL2, FoxE and FoxY were highly expressed in the ovary during all developmental stages, while FoxZ was highly expressed in the testis during all developmental stages. The results suggested that these genes might play an important role in sex maintenance or gametogenesis. The present study could provide a reference for evolutionary and functional studies of the Fox family in metazoans.