Extracellular signals, cell interactions and transcription factors involved in the induction of the neural crest cells

The neural crest is induced at the border between the neural plate and the epidermis. A complex set of signals is required for the specification of the crest cells between the epidermis and the neural plate. Here we discuss evidence supporting a model for neural crest induction in which different signals contribute in a sequential order. First, a gradient of bone morphogenic proteins (BMPs) is established in the ectoderm that results in segregation into neural plate, neural folds and epidermis at increasing levels of BMP activity. Thus, the neural folds are induced at a precise threshold concentration of BMP, but this neural fold has an anterior character. In a second step, these anterior neural folds are transformed into prospective neural crest by posteriorizing signals due to fibroblast growth factor, Wnts and retinoic acid. Finally, the induced cells interact to complete neural crest induction by a process that requires Notch/Delta signaling. Once neural crest formation has been induced by this combination of extracellular and intracellular signals, a cascade of transcription factors is activated in these cells that culminates in the ultimate steps of neural crest differentiation (AU)#SP#

Alteration of morphogenetic cell interactions by 1-beta-D-arabinofuranosylcytosine in Bufo arenarum embryo

Amphibian gastrulation was used as a model system to study the action of the nucleoside 1-beta-D-arabinofuranosylcytosine (Ara-C) on the early events of amphibian morphogenesis. Ara-C inhibits both glycoprotein and glycolipid synthesis and interferes with DNA synthesis. Thus, it is useful to investigate the importance of the cell surface and the nucleous during Bufo arenarum morphogenesis. Living embryos were incubated with Ara-C at blastula and gastrula stages. Treated-embryos undergo abnormal gastrulation, most of the embryos exogastrulate, although some do not gastrulate at all. This antimetabolite did not interfere with neural induction, as partial exogastrulae developed a small neural tube. We have proven that Area-C disturbs the typical intercellular organization and inhibits the radial intercalation of the blastocoelic roof. The mesodermal migration is the most affected morphogenetic process. The results described in this paper demonstrate that the timing of gastrulation movements strongly involves the participation of surface and extracellular molecules in cell recognition and cell interaction but does not involve a significant increase in cell division rate and can also occur in the absence of the cell division.