RNA helicases of the DEAD-box and related families are involved in various cellular processes including DNA replication,DNA repair,and RNA processing.However,the function of DEAD-box proteins in aquaculture species is poorly understood at molecular level.We obtained the full-length cDNA sequences of two genes encoding helicase-related proteins,Fc-vasa and Fc-PL10a,from the testes of Chinese shrimp,Fenneropenaeus chinensis.The two predicted amino acid sequences contain all the conserved motifs characterized by the DEAD-box family and several RGG repeats in the N-terminal regions.Homology and phylogenetic analyses indicate that they belong to the vasa and PL10 subfamilies.The three-dimensional structures of the two proteins were predicted with a homology modeling approach.Both core proteins consist of two tandem RecA-like domains similar to those of the DEAD-box RNA helicase.Using reverse transcription-polymerase chain reaction (RT-PCR) and real-time PCR we found that Fc-vasa was expressed specifically in the adult gonads.Transcription decreased in the ovary but increased in the testis during gonadal development.Fc-PL10a expression was widely distributed in the tissues we examined.Using in situ hybridization,we demonstrated that the Fc-vasa transcript is localized to the cytoplasm of the spermatogonia and oocytes.Thus,our results suggest that Fc-vasa plays an important role in germ-line development,and has utility as a germ cell lineage marker which will help to generate new insight into the origin and differentiation of germ cells as well as the regulation of reproduction in F.chinensis. RNA helicases of the DEAD-box and related families are involved in various cellular processes including DNA replication, DNA repair, and RNA processing. However, the function of DEAD-box proteins in aquaculture species is poorly understood at molecular level. We obtained the full -length cDNA sequences of two genes encoding helicase-related proteins, Fc-vasa and Fc-PL10a, from the testes of Chinese shrimp, Fenneropenaeus chinensis. The two predicted amino acid sequences contain all the conserved motifs characterized by the DEAD-box family and Several RGG repeats in the N-terminal regions. Homology and phylogenetic analysis indicate that they belong to the vasa and PL10 subfamilies. The three-dimensional structures of the two proteins were predicted with a homology modeling approach. B. core proteins consist of two tandem RecA -like domains similar to those of the DEAD-box RNA helicase. Using Reverse transcription-polymerase chain reaction (RT-PCR) and real-time PCR we found that Fc-vasa was express Expression of the in situ hybridization, we demonstrated that the Fc-vasa transcript is localized to the cytoplasm of the spermatogonia and oocytes.Thus, our results suggest that Fc-vasa plays an important role in germ-line development, and has utility as a germ cell lineage marker which will help to generate new insight into the origin and differentiation of germ cells as well as the regulation of reproduction in F. chinensis.