![]() Amphioxus FGF signaling predicts the acquisition of vertebrate morphological traits. Essential role of Bmp signaling and its positive feedback loop in the early cell fate evolution of chordates. Kozmikova, I., Candiani, S., Fabian, P., Gurska, D. Insights from the amphioxus genome on the origin of vertebrate neural crest. Opposing Nodal/Vg1 and BMP signals mediate axial patterning in embryos of the basal chordate amphioxus. Axial patterning in cephalochordates and the evolution of the organizer. Experimental studies on the neural induction in amphioxus. Neural tissue in ascidian embryos is induced by FGF9/16/20, acting via a combination of maternal GATA and Ets transcription factors. The BMP/CHORDIN antagonism controls sensory pigment cell specification and differentiation in the ascidian embryo. BMP inhibition initiates neural induction via FGF signaling and Zic genes. Neural induction in Xenopus requires early FGF signalling in addition to BMP inhibition. Neural induction requires BMP inhibition only as a late step, and involves signals other than FGF and Wnt antagonists. A truncated FGF receptor blocks neural induction by endogenous Xenopus inducers. An early requirement for FGF signalling in the acquisition of neural cell fate in the chick embryo. I., Graziano, E., Harland, R., Jessell, T. Initiation of neural induction by FGF signalling before gastrulation. Neural induction and early patterning in vertebrates. Dorsal–ventral patterning and neural induction in Xenopus embryos. Neural induction: 10 years on since the ‘default model’. Vertebrate embryonic cells will become nerve cells unless told otherwise. in Foundation of Experimental Embryology (eds Willer, B. This study further reveals the diversity of neural inducers used during chordate evolution and provides support against a universally conserved molecular explanation for this process. Together, our results allow us to propose that Nodal–Activin was a major factor for neural induction in the ancestor of chordates. In addition, we demonstrate that Nodal–Activin is the main signal eliciting neural induction in amphioxus, and that it also functions as a bona fide neural inducer in the classical vertebrate model Xenopus. Here we show, by using graft and micromanipulation experiments, that the dorsal blastopore lip of the cephalochordate amphioxus is homologous to the vertebrate organizer and is able to trigger the formation of neural tissues in a host embryo. Moreover, how this process evolved in the chordate lineage remains unresolved. Studies in classical vertebrate models have produced contrasting views about the molecular nature of neural inducers and no unifying scheme could be drawn. This first step of central nervous system formation is triggered by the ‘Spemann organizer’ in amphibians and by homologous embryonic regions in other vertebrates. a = anterior an = animal bc = blastocoel bp = blastopore d = dorsal dl = dorsal lip dm = deep mesoderm fg = foregut fp = floor plate hg = hindgut l = left no = notochord ov = otic vesicle p = posterior r = right s = somite v = ventral veg = vegetal.Neural induction is the process through which pluripotent cells are committed to a neural fate. (E’,E”) Histological sections (levels indicated in (E)) highlighting expression in the otic vesicle (E’) and nephrostomes ((E”), arrowheads). (E) Staining in the otic vesicle and nephrostomes (arrowheads). Enlargements show multiciliated skin cells ( (D”) cilia indicated by arrowheads) and GRP cells after intercalation into the notochord ( (D”’) arrowheads). (D) Expression at stage 23 in ciliated cells of the epidermis and the floor plate (sagittal section shown in (D’)). (C’) Histological section (plane marked in (C)). (C) Expression in the gastrocoel roof plate (GRP) at stage 17 (dorsal explant shown in ventral view). Note that the superficial mesoderm (SM) was free of PACRG mRNA (inset in (B’)). (B’) Sagittal hemisection (plane indicated in (B)) revealing mRNA localization in deep mesoderm. Persistent differences in staining intensities between dorsal and ventral side. Enlargements (boxes) indicate higher expression levels on the dorsal side. (A’) Sagittal hemisection of embryo shown in (A). (A) Expression at the four-cell stage (top view). PACRG expression during early Xenopus development.
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