The markers Xslug, Xsnail, and Xtwist all are expressed in the presumptive neural folds and are thought to delineate the presumptive neural crest. However, their interrelationship and relative spatiotemporal distributions are not well understood. Here, we present a detailed in situ hybridization analysis of the relative patterns of expression of these transcription factors from gastrulation through neurulation and post-neural crest migration. The three genes mark the prospective neural crest and roof plate, coming on sequentially, with Xsnail preceding Xslug preceding Xtwist. By combining gene expression analysis with a fate map of the same region using DiI labeling, we determined the correspondence between early and late domains of gene expression. At the beginning of gastrulation, Xsnail is present in a unique domain of expression in a lateral region of the embryo in both superficial and deep layers of the ectoderm, as are Xslug and Xtwist. During gastrulation and neurulation, the superficial layer moves faster toward the dorsal midline than the deep layer, producing a relative shift in these cell populations. By early neurula stage, the Xsnail domain is split into a medial domain in the superficial ectoderm (fated to become the roof plate) and a lateral domain in the deep layer of the ectoderm (fated to become neural crest). Xsnail is down-regulated in the most anterior neural plate and up-regulated in the posterior neural plate. Our results show that changes in the expression of Xsnail, Xslug, and Xtwist are a consequence of active cell movement in some regions coupled with dynamic changes in gene expression in other regions.
Copyright 2000 Academic Press.