Developmental expression pattern of the Fc-vasa-like gene, gonadogenesis and development of germ cell in Chinese shrimp, Fenneropenaeus chinensis

The vasa gene, a member of the DEAD-box gene family, has been reported to be restricted exclusively to the germ cell lineage in most animals, and thus is the most reliable molecular marker for studies on germ cell development. In this study, the developmental expression pattern of the vasa-like gene in Fenneropenaeus chinensis (Fc-vasa-like) is presented. The origin and migration of the germ cell are revealed by whole mount in situ hybridization (ISH). Furthermore, gonadogenesis is observed by histological techniques and ISH. Fc-vasa-like mRNA is located in the cytoplasm of oocytes before and after spawning, and equally distributed in the cytoplasm of early embryos, from the 2-cell embryo to the blastula, indicating that Fc-vasa-like mRNA is maternally supplied. Later on, the expression of the Fc-vasa-like gene centralizes gradually, and is restricted to five cell clusters as precursor cells of primordial germ cells (PGCs) at the limb bud stage. The five cell clusters are located at the base of the antennules and antenna, as well as the cephalic lobe, implying an epigenetic mechanism of germ cell specification in this species. These cells migrate to a dorsolateral position in naupliar and zoeal stages, and gradually enter the genital ridge at the mysis 1 stage. The gonad is first detected histologically at the post-larval 1 stage (PL1, 1st day postlarva), and germ stem cells (GSCs) are distinguished in cluster in juveniles with the body length of 30 mm. Our findings show that the developmental expression pattern of Fc-vasa-like is different from that of other Crustaceans, and suggest an epigenetic mechanism of germ cell development in Chinese shrimp.