Primordial germ cells in the dorsal mesentery of the chicken embryo demonstrate left–right asymmetry and polarized distribution of the EMA 1 epitope

Despite the importance of the chicken as a model system, our understanding of the development of chicken primordial germ cells ( PGC s) is far from complete. Here we characterized the morphology of PGC s at different developmental stages, their migration pattern in the dorsal mesentery of the chicken embryo, and the distribution of the EMA 1 epitope on PGC s. The spatial distribution of PGC s during their migration was characterized by immunofluorescence on whole‐mounted chicken embryos and on paraffin sections, using EMA 1 and chicken vasa homolog antibodies. While in the germinal crescent PGC s were rounded and only 25% of them were labeled by EMA 1, often seen as a concentrated cluster on the cell surface, following extravasation and migration in the dorsal mesentery PGC s acquired an elongated morphology, and 90% exhibited EMA 1 epitope, which was concentrated at the tip of the pseudopodia, at the contact sites between neighboring PGC s. Examination of PGC migration in the dorsal mesentery of Hamburger and Hamilton stage 20–22 embryos demonstrated a left–right asymmetry, as migration of cells toward the genital ridges was usually restricted to the right, rather than the left, side of the mesentery. Moreover, an examination of another group of cells that migrate through the dorsal mesentery, the enteric neural crest cells, revealed a similar preference for the right side of the mesentery, suggesting that the migratory pathway of PGC s is dictated by the mesentery itself. Our findings provide new insights into the migration pathway of PGC s in the dorsal mesentery, and suggest a link between EMA 1, PGC migration and cell–cell interactions. These findings may contribute to a better understanding of the mechanism underlying migration of PGC s in avians.