The dynamic development of germ cells during chicken embryogenesis

Appropriate regulation of cell proliferation during embryogenesis is crucial for the maintenance of germness. An in-depth understanding of germ cell developmental processes may yield valuable information on germ cell biology and applied sciences. However, direct evidences about germ cell proliferation and cell cycling during avian embryonic development has not been well-studied. Thus, we explored chicken germ cell dynamics during embryonic development via flow cytometry employing a germ cell-specific anti-cVASA antibody (the chicken VASA homolog is termed CVH) and propidium iodide staining. The numbers of male germ cells increased significantly during early embryonic development, but proliferation was decreased significantly with accumulation at the G0/G1 phase after embryonic d 14 (E. 14), indicating initiation of mitotic arrest in the testis. On the other hand, the number of female germ cells increased significantly throughout embryogenesis, and proliferating cells were continuously evident in the ovary to the time of hatching, although gradual accumulation of cells at the G2/M phase was also evident. 5-ethynyl-2'-deoxyuridine (EdU) incorporation analysis revealed that populations of mitotically active germ cells existed in both sexes during late embryogenesis, indicating either the maintenance of stem cell populations, or asynchronous meiosis. Collectively, these results indicate that chicken germ cells exhibited conserved developmental processes that were clearly sexually dimorphic.