Distribution of extracellular matrix in the migratory pathway of avian primordial germ cells

The appearance and distribution of extracellular matrix (ECM) was documented along the migratory route of chicken primordial germ cells (PGCs). The antimouse embryonal carcinoma cell antibody, EMA-1, was used to label PGCs (Urven et al.: Development 103:299-304, 1988). Antibodies against laminin, fibronectin, chondroitin sulfate proteoglycan and collagen type IV were used to label extracellular matrix components. When the PGCs emerged from the epiblast, all four ECM molecules were restricted principally to the basement membrane of the epiblast. Chondroitin sulfate was also located between hypoblast cells during this period. In late germinal crescent stages, when the PGCs entered the lumina of blood vessels, the same ECM molecules were more widespread in the mesoderm and in extracellular spaces. In addition, laminin and collagen type IV were identified on lateral surfaces of ectodermal cells at this stage. When the germ cells moved through the mesenchyme into the germinal ridge, the ECM molecules were found around mesenchymal cells, and, in the cases of laminin, fibronectin and collagen type IV, in the basement membranes of the germinal ridge epithelia. Because the appearance of these ECM components is temporally and spatially correlated with the movement of PGCs, we suggest that early PGC migration may depend on their timely appearance.