Correlation between the expression of the HNK-1 epitope and cellular invasiveness in prestreak epiblast cells of chick embryos

During avian gastrulation, certain cells present in the epiblast layer ingr ess through the basement membrane sealing the basal surface of themselves. Previously we reported that chick prestreak epiblast cells show two differe nt behavioral phenotypes upon reconstituted basement membrane and laminin g el in vitro. Half of the dissociated epiblast cells invade the gel substrat um after one-day of culture, whereas the others attach to the gel but do no t invade. It is expected that such heterogeneity in the behavior of the epi blast cells reflects some mechanism that sorts the cells into those that wi ll ingress into the blastocoelic cavity and those that will remain in the e piblast layer. To test this hypothesis, we dissociated chick prestreak epib last cells into single cells, cultured them on the laminin gel, and then st ained them with anti-HNK-1 antibody. This antibody binds to an epitope pres ent on half of the prestreak epiblast cells which are thought to differenti ate into presumptive mesoendodermal cells. We found that 80% of the invasiv e epiblast cells were HNK-1-positive whereas 77% of the non-invasive cells were HNK-1 negative. In the case of invasive cells, the edges of the proteo lytic holes made by the invasive cells were often stained. These results su ggest that the cells expressing the HNK-1 carbohydrate chain are preferenti ally invasive, and this induces selective ingression of the carrier cells f or mesoendodermal differentiation in vivo.