Calcium signalling during neural induction in Xenopus laevis embryos.
In Xenopus, experiments performed with isolated ectoderm suggest that neural determination is a 'by default' mechanism, which occurs when bone morphogenetic proteins (BMPs) are antagonized by extracellular antagonists, BMP being responsible for the determination of epidermis. However, Ca(2+) imaging of intact Xenopus embryos reveals patterns of Ca(2+) transients which are generated via the activation of dihydropyridine-sensitive Ca(2+) channels in the dorsal ectoderm but not in the ventral ectoderm. These increases in the concentration of intracellular Ca(2+)([Ca(2+)]i) appear to be necessary and sufficient to orient the ectodermal cells towards a neural fate as increasing the [Ca(2+)]i artificially results in neuralization of the ectoderm. We constructed a subtractive cDNA library between untreated and caffeine-treated ectoderms (to increase [Ca(2+)]i) and then identified early Ca(2+)-sensitive target genes expressed in the neural territories. One of these genes, an arginine methyltransferase, controls the expression of the early proneural gene, Zic3. Here, we discuss the evidence for the existence of an alternative model to the 'by default' mechanism, where Ca(2+) plays a central regulatory role in the expression of Zic3, an early proneural gene, and in epidermal determination which only occurs when the Ca(2+)-dependent signalling pathways are inactive.
Moreau
Marc
M
Centre de Biologie du Développement, UMR 5547 and GDR 2688, Université Paul Sabatier, 118 route de Narbonne, 31062 Toulouse, France. moreau@cict.fr
Néant
Isabelle
I
Webb
Sarah E
SE
Miller
Andrew L
AL
Leclerc
Catherine
C
D000818:Animals; D019485:Bone Morphogenetic Proteins / Q000378:metabolism; D002118:Calcium / Q000378:metabolism*; D004627:Embryonic Induction / Q000502:physiology*; D008954:Models, Biological; D009420:Nervous System / Q000196:embryology* / Q000378:metabolism; D015398:Signal Transduction / Q000502:physiology*; D014982:Xenopus laevis / Q000196:embryology* / Q000378:metabolism
D019485:Bone Morphogenetic Proteins; D002118:Calcium