Distinct Steps of Neural Induction Revealed by Asterix, Obelix and TrkC, Genes Induced by Different Signals from the Organizer

The amniote organizer (Hensen's node) can induce a complete nervous system when grafted into a peripheral region of a host embryo. Although BMP inhibition has been implicated in neural induction, non-neural cells cannot respond to BMP antagonists unless previously exposed to a node graft for at least 5 hours before BMP inhibitors. To define signals and responses during the first 5 hours of node signals, a differential screen was conducted. Here we describe three early response genes: two of them, Asterix and Obelix, encode previously undescribed proteins of unknown function but Obelix appears to be a nuclear RNA-binding protein. The third is TrkC, a neurotrophin receptor. All three genes are induced by a node graft within 4–5 hours but they differ in the extent to which they are inducible by FGF: FGF is both necessary and sufficient to induce Asterix, sufficient but not necessary to induce Obelix and neither sufficient nor necessary for induction of TrkC. These genes are also not induced by retinoic acid, Noggin, Chordin, Dkk1, Cerberus, HGF/SF, Somatostatin or ionomycin-mediated Calcium entry. Comparison of the expression and regulation of these genes with other early neural markers reveals three distinct “epochs”, or temporal waves, of gene expression accompanying neural induction by a grafted organizer, which are mirrored by specific stages of normal neural plate development. The results are consistent with neural induction being a cascade of responses elicited by different signals, culminating in the formation of a patterned nervous system

Calfacilitin is a calcium channel modulator essential for initiation of neural plate development.

Calcium fluxes have been implicated in the specification of the vertebrate embryonic nervous system for some time, but how these fluxes are regulated and how they relate to the rest of the neural induction cascade is unknown. Here we describe Calfacilitin, a transmembrane calcium channel facilitator that increases calcium flux by generating a larger window current and slowing inactivation of the L-type CaV1.2 channel. Calfacilitin binds to this channel and is co-expressed with it in the embryo. Regulation of intracellular calcium by Calfacilitin is required for expression of the neural plate specifiers Geminin and Sox2 and for neural plate formation. Loss-of-function of Calfacilitin can be rescued by ionomycin, which increases intracellular calcium. Our results elucidate the role of calcium fluxes in early neural development and uncover a new factor in the modulation of calcium signalling

Induction neurale chez les Oiseaux. Rapport temporel entre la neurulation du blastoderme-h\uf4te et l\u27apparition de l\u27\ue9bauche neural induite par un fragment de la ligne primitive

Volume: 75Start Page: 227End Page: 23

Culture in vitro des blastodermes de Poulet. Rapports entre les feuillets embryonnaires et le milieu nutritif contenant de la g\ue9lose

Volume: 70Start Page: 587End Page: 59

L\u27expansion p\ue9riph\ue9rique du blastoderme et la formation de l\u27aire vasculaire chez l\u27embryon du poulet

Volume: 84Start Page: 301End Page: 30

Dissociation exp\ue9rimentale entre la morphogen\ue8se et la diff\ue9renciation de l\u27\ue9bauche neurale chez les Amphibiens

Volume: 68Start Page: 311End Page: 33

Recherches compar\ue9es sur le d\ue9veloppement du neurectoblaste pr\ue9chordal transplant\ue9 sur l\u27embryon ou enrob\ue9 dans l\u27ectoblaste "in vitro" (Triton alpestris)

Volume: 55Start Page: 295End Page: 30

Mise en \ue9vidence du r\uf4le de l\u27ectoblaste dans la diff\ue9renciation des somites chez les Oiseaux

Volume: 73Start Page: 492End Page: 50