Induction of neural cell adhesion molecule (NCAM) in Xenopus embryos

Using a classical neural induction protocol (H. Spemann and H. Mangold (1924). Roux' Arch. Entwicklungsmech. Org. 123, 389-517), it has been demonstrated that the sustained presence of NCAM in Xenopus embryos, as detected by immunohistochemistry, was confined to the experimentally induced nervous system and the primary host nervous system. Furthermore, in vitro NCAM expression by dorsal blastopore lip and animal pole tissue was detected only when the two tissues were cultured in contact. These and other results show that readily detected and sustained levels of NCAM expression in Xenopus can be used as a marker for neural tissue and an early positive indicator that neural induction has occurred. They suggest that the observed levels of NCAM are a consequence of and not a prerequisite for induction. Using NCAM expression in vitro to determine the minimum time necessary for this induction to occur in vivo, it was found that NCAM was first detected in cultured animal pole that had been removed at stage 10.75 or later. Thus, an inductive step necessary and sufficient for stimulation of NCAM expression in animal pole tissues had not occurred or was reversible prior to the first 2 to 2.5 hr of gastrulation.