Inductive interactions underlie neural crest formation

Abstract

The neural crest is a transient population of cells defined in terms of their ectodermal origin, their migratory behavior, and their derivatives. Neural crest cells classically have been thought to be a segregated population within the neural plate, bordered laterally by presumptive epidermis and medially by prospective central nervous system (CNS). Cell lineage analyses in vitro and in vivo have demonstrated that individual neural crest cells are multipotent. In fact, they have the properties of stem cells with at least a limited ability to self-renew. The experiments summarized in this chapter demonstrate that interactions between the presumptive neural plate and the nonneural ectoderm lead to induction of the avian neural crest at the interface between these tissues. This supports the idea that an inductive signal travels through the epidermis to generate neural crest cells in the gastrulating embryo. On the other hand, the competence of the neural plate to form different types of neural crest derivatives appears to change with time. BMP4 and BMP7 (bone morphogenetic proteins) have been shown to be sufficient to substitute for the nonneural ectoderm in inducing neural crest cells. The neural tube has a characteristic polarity along the rostrocaudal and the dorsoventral axes. Rostrocaudal regionalization is manifested by the formation of subdivisions in the neural tube, such as the forebrain, midbrain, hindbrain, and spinal cord. Neural crest cells arising from different axial levels contribute to derivatives characteristic of the axial level of origin. It has been demonstrated that dorsalizing signals influence development of not only the neural crest, but also the dorsal neural tube. Various genes are selectively expressed in the dorsal, but not in the ventral, portion of the neural tube.