Progressive induction of caudal neural character by graded Wnt signaling

Abstract

Early in differentiation, all neural cells have a rostral character. Only later do posteriorly positioned neural cells acquire characteristics of caudal forebrain, midbrain and hindbrain cells. Caudalization of neural tissue in the chick embryo apparently involves the convergent actions of (i) fibroblast growth factor (FGF) signaling and (ii) signaling from the caudal paraxial mesoderm, or 'PMC activity', which has not yet been defined molecularly. Here we report evidence that Wnt signaling underlies PMC activity, and show that Wnt signals act directly and in a graded manner on anterior neural cells to induce their progressive differentiation into caudal forebrain, midbrain and hindbrain cells.

Choice of either β-catenin or Groucho/TLE as a co-factor for Xtcf-3 determines dorsal-ventral cell fate of diencephalon during Xenopus development

“…However, it remains unknown how the dorsal-specific activation of Wnt/β-catenin signaling is established in this territory. The gradient of Wnt/β-catenin signaling along the A-P axis in the neuroectoderm occurs in a direct and long-range fashion from the mesoderm and posterior ectoderm (McGrew et al 1997;Kiecker and Niehrs 2001;Dorsky et al 2003;Nordstrom et al 2002). Although several type-1 Wnts, including Xwnt-1, Xwnt-3A and Xwnt-8, are expressed in the anterior neuroectoderm, no dorsal-specific expression is detected in the prospective diencephalon territory.…”

Models for the generation of the embryonic body axes: ontogenetic and evolutionary aspects

“…in the marginal zone in Xenopus or germ ring in fish). As in hydra, the signalling molecule belongs to the Wnt family [18,19]. It causes a posterior transformation of an anterior default state (for modelling, see Figure 3c and Chitnis, this issue).…”

“…the marginal zone in Xenopus or the germ ring in the fish) is a large ring. Nevertheless, in vertebrates the ancestral part of the AP axis (brain and heart) is organized from the (large) ring-shaped blastoporus, presumably involving Wnt [18,19], in complete analogy to the situation in hydra. This does not require a Spemann-type dorsal organizer [24].…”

The canonical Wnt pathway in early mammalian embryogenesis and stem cell maintenance/differentiation

“…Studies of brain patterning in the chick led to a model that increasing levels of Wnt along the anterior-posterior axis specifies neural cells with initial rostral character into gradually more caudal character [40]. Consistent with this model, continued inhibition of Wnt signaling in the mouse is necessary for forebrain specification following initial head induction.…”