Isolation of chicken <i>vasa</i> homolog gene and tracing the origin of primordial germ cells

TLDR

The study isolated a chicken vasa homolog (Cvh) to serve as a molecular probe for tracing germ cell lineage origins in birds. Immunohistochemistry with a specific anti‑CVH antibody revealed CVH protein localized in germ cells from primordial stages to adult gametes, including cytoplasmic distribution in PGCs, spermatids, and oocytes. CVH protein is expressed exclusively in germ cells throughout development, localizing to the basal furrow during early cleavages, to specific germinal zones at successive stages, and to granulofibrillar structures in oocytes, indicating that the chicken germline is determined by maternally inherited germ plasm.

Abstract

ABSTRACT To obtain a reliable molecular probe to trace the origin of germ cell lineages in birds, we isolated a chicken homolog (Cvh) to vasa gene (vas), which plays an essential role in germline formation in Drosophila. We demonstrate the germline-specific expression of CVH protein throughout all stages of development. Immunohistochemical analyses using specific antibody raised against 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 central zone of the area pellucida at stage X, later 45-60 cells were found in the hypoblast layer and subsequently 200-250 positive cells were found anteriorly in the germinal crescent due to morphogenetic movement. Furthermore, in the oocytes, CVH protein was predominantly localized in granulofibrillar structures surrounding the mitochondrial cloud and spectrin protein- enriched structure, indicating that the CVH-containing cytoplasmic structure is 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.