Sex biased expression of Fem-1 in larval stages suggests its function in early sex differentiation of Litopeneaus vannamei

The Pacific white shrimp Litopenaeus vannamei (L. vannamei) is an economically important species worldwide. As females exhibit a faster growth rate than males, it is crucial to understand the mechanism of sex determination and differentiation for the purpose of mono-sex breeding in shrimp. The feminization-1 gene (Fem-1) serves as a sex-determining gene in Caenorhabditis elegans, and the Fem-1 family is implicated in sex development in several crustaceans. In this study, three Fem-1 family members, namely LvFem-1a, LvFem-1b, and LvFem-1c, were identified and characterized in L. vannamei. Based on genetic sex marker, individuals were separated by sex during the early developmental stages. The expression profiles of these genes were analyzed in female or male larvae. Significant differences between females and males were observed during the early stages of development. In Zoea III or earlier stages, the expressions levels in males were significantly higher than those in females. Intriguingly, there was a shift towards higher expression in females during the mysis and post-larval stages. These findings indicate that the Zoea III stage may be crucial for sex differentiation in shrimp. In addition, the analysis of gene expression across various ovarian stages and tissues was conducted. Results showed that all three genes were highly expressed in the ovary, with particularly elevated levels in ovarian development stage II. These findings suggest that the Fem-1 genes play a critical role in early ovary development. This study is the first research focusing on the sex-specific expression of sex differentiation genes in shrimp. The obtained results provide new insights into to the role of the Fem-1 gene family in sex differentiation and gonadal development.