The choice between epidermal and neural fate: a matter of calcium.

Abstract

The development of the vertebrate embryo, which includes the induction and the patterning of the three germ layers, requires signaling among cells. In vertebrates, cells of the embryonic ectoderm have a choice during gastrulation between two fates; they give rise to epidermal progenitors on the ventral side and neural progenitors on the dorsal side. It was first shown by Spemann and Mangold in 1924 that the dorsal mesoderm (also called the SpemannMangold Organizer) has a potent biological capacity to induce nervous system from the adjacent ectoderm. A similar observation was reported in amniotes, indicating that neural induction by the Organizer is a conserved process controlling the initial steps in vertebrates neurogenesis. Molecular studies of the last decade have led to the identification of signaling molecules which participate in these embryonic decisions. Epidermis induction occurs through a signaling cascade involving Bone Morphogenetic Proteins (BMP 2, 4, 7) and receptor-regulated Smad proteins which translocate into the nucleus to form active transcriptional complexes. These molecules mediate BMPs effect to activate epidermal-specific gene expression and to repress neural-specific gene transcription. Neural fate is revealed by factors secreted by the dorsal mesoderm (Noggin, Chordin, Follistatin, …) which act by blocking BMP signaling. Consequently, epidermal fate is an induced fate while neural fate is interpreted as a default state of the ectoderm. In this review, we describe the signaling pathways which act to determine the fate of the ectoderm and discuss an alternative model in which neural fate is not a default state. This new model integrates the activation of a calcium-dependent signaling pathway due to an influx of calcium through L-type calcium channels. In this model, calcium plays a central regulatory role. While calcium is required for neural determination, epidermal determination occurs when calcium-dependent signaling pathways are inactive.

Plasticity of neuropeptide Y in the dentate gyrus after seizures, and its relevance to seizure-induced neurogenesis

“…It also suggests a potential "division of labor" among NPY receptors: Y2 and Y5 may primarily influence synaptic transmission, whereas Y1 may be dedicated to other types of functions, such as neurogenesis. The actions of Y1 receptors on the regulation of calcium entry may actually work in part to modulate neurogenesis and proliferation indirectly, since it is likely that intracellular calcium will influence the cell cycle and associated events [37,38].…”

Recent advances in understanding trans-epithelial acid-base regulation and excretion mechanisms in cephalopods

“…The process of epidermal development, including the differentiation of ionocytes relies on balanced signaling gradients secreted from non-neural (BMPs) and the neural ectoderm (including the chordin and noggin), and is evolutionarily conserved among vertebrates. 63,64 Under stimulation by BMPs, downstream targets of the transcription factor, DNp63, are activated in epidermal stem cells, which thereafter undergo the subsequent process of terminal differentiation. 58,65 So far, in many model teleosts, such as zebrafish and Japanese medaka, these regulatory pathways are controlling the formation of specific epithelial ionocytes during development.…”

L’induction neurale chez les amphibiens

“…Cette augmentation est provoquée par une sortie du Ca 2+ intracellulaire due à la modification du gradient calcique entre les milieux intra-et extracellulaires [7]. Ces résultats ainsi que ceux obtenus par l'équipe de De Robertis [8] montrent que l'effet observé n'est pas dû à une simple dilution des inducteurs épidermiques (BMP) ou une variation d'affinité de ces molécules vis-à-vis de leurs récepteurs qui entraîneraient une neuralisation de l'ectoderme par défaut comme il a été proposé par certains auteurs [9].…”