The scanning electron micrograph shown here illustrates the difference in behavior of the leading edge of the involuting mesodermal material in the Xenopus gastrula. Note that these leading edge cells have lamellipodia, which they use to migrate along the blastocoel roof as gastrulation proceeds. Given that the leading edge cells are migratory, this raises questions about what sort of substratum they use for migration. Recent studies, both embryological and those using specific antibodies as perturbing reagents, indicate that the blastocoel roof supports migration of leading edge cells in specific ways. The next section discusses the possible ways in which the blastocoel roof mediates guidance of leading edge cells.
Scanning electron micrograph of leading edge cells in Xenopus