Guidance of neural crest migration. Latex beads as probes of surface-substratum interactions.

The experiments reviewed in this chapter examine the translocation of various cell types and latex beads on a neural crest pathway. The cells and beads are implanted into the embryo via an injection technique that can be used to characterize the embryonic pathways or the injected cells themselves. The results demonstrate that postmigratory neural crest cells, undifferentiated neural crest cells, and retinal pigment epithelial cells will translocate to ventral sites after implantation. By contrast, somitic and fibroblastic cells fail to translocate. No correlation was found between the inherent motile ability of a cell and the ability to move along the ventral route. Therefore, the role of cell surface molecules in movement along the neural crest pathway was examined. Latex beads, which lack inherent motility, were used as probes of the neural crest pathway. Uncoated beads as well as latex beads coated with a variety of ECM molecules and polyamino acids were injected into embryos in order to explore interactions between the cell surface and the embryonic substrata that might be involved in neural crest localization. The distribution pattern of the latex beads was altered by the nature of the surface properties of the beads. Two distinct patterns of localization were observed. Those beads coated with FN, cell-binding fragment of FN, laminin, or PL remained primarily associated with the dermamyotomal cells of the implantation site. By contrast, uncoated beads or beads coated with BSA, collagen, or PT translocated to ventral sites, usually around the sympathetic ganglia or dorsal aorta. In order to analyze mechanisms that may be involved in translocation of latex beads along neural crest pathways, we examined the possible effects of (1) bead surface charge; and (2) the removal of endogenous neural crest cells. To examine the effects of electrostatic interactions in bead translocation or restriction, the initial surface charge of beads coated with various macromolecules was measured and compared with their subsequent ability to translocate along the ventral pathway. No correlation was observed between the sign of the surface charge and subsequent distribution of beads, suggesting that initial surface charge properties alone cannot account for the restriction or translocation. To dissect the role of endogenous neural crest cells in bead movement, the host neural crest was ablated using a laser microbeam. After injection of latex beads into ablated embryos, the latex beads translocated ventrally even in the absence of the neural crest. Thus, latex beads are not merely carried ventrally by adhering to migrating neural crest cells.(ABSTRACT TRUNCATED AT 400 WORDS)