Isolation of chicken vasa homolog gene and tracing the origin of primordial germ cells

To obtain a reliable molecular probe to trace the origin of germ cell linea ges in birds, we isolated a chicken homolog (Cvh) to vasa gene (vas), which plays an essential role in germline formation in Drosophila. We demonstrat e the germline-specific expression of CVH protein throughout all stages of development. Immunohistochemical analyses using specific antibody raised ag ainst CVH protein indicated that CVH protein was localized in cytoplasm of germ cells ranging from presumptive primordial germ cells (PGCs) in uterine -stage embryos to spermatids and oocytes in adult gonads. During the early cleavages, CVH protein was restrictively localized in the basal portion of the cleavage furrow, About 30 CVH-expressing cells were scattered in the ce ntral zone of the area pellucida at stage X, later 45-60 cells were found i n the hypoblast layer and subsequently 200-250 positive cells were found an teriorly in the germinal crescent due to morphogenetic movement, Furthermor e, in the oocytes, CVH protein was predominantly localized in granulofibril lar structures surrounding the mitochondrial cloud and spectrin protein-enr iched structure, indicating that the CVH-containing cytoplasmic structure i s the precursory germ plasm in the chicken, These results strongly suggest that the chicken germline is determined by maternally inherited factors in the germ plasm.