Wnt1 regulates neurogenesis and mediates lateral inhibition of boundary cell specification in the zebrafish hindbrain

Abstract

The formation of localised signalling centres is essential for patterning of a number of tissues during development. Previous work has revealed that a distinct population of boundary cells forms at the interface of segments in the vertebrate hindbrain, but the role of these cells is not known. We have investigated the function of the Wnt1 signalling molecule that is expressed by boundary and roof plate cells in the zebrafish hindbrain. Knockdown of wnt1 or of tcf3b, a mediator of Wnt signalling, leads to ectopic expression of boundary cell markers, rfng and foxb1.2, in non-boundary regions of the hindbrain. Ectopic boundary marker expression also occurs following knockdown of rfng, a modulator of Notch signalling required for wnt1 expression at hindbrain boundaries. We show that the boundary and roof plate expression of wnt1 each contribute to upregulation of proneural and deltagene expression and neurogenesis in non-boundary regions, which in turn blocks ectopic boundary marker expression. Boundary cells therefore play a key role in the regulation of cell differentiation in the zebrafish hindbrain. The network of genes underlying the regulation of neurogenesis and lateral inhibition of boundary cell formation by Wnt1 has a striking similarity to mechanisms at the dorsoventral boundary in the Drosophila wing imaginal disc.

Migratory routes and fates of cells transcribing the Wnt‐1 gene in the murine hindbrain

“…Wnt-1 is often more extensively expressed at rhombomere boundaries (Fig. 1G), suggesting a role for Wnt-1 in metameric segmentation as identified in the hindbrain of zebrafish (Amoyel et al, 2005). The rhombomere by rhombomere control of the size of and migrations from the WL emphasizes that, while Wnt-1 expression contributes to dorsal-ventral patterning, it reflects rostrocaudal patterning as well.…”

Signalling from hindbrain boundaries regulates neuronal clustering that patterns neurogenesis

“…The in situ hybridisation probes for neurog1, rfng (Amoyel et al, 2005), fgf20a and etv5b (Gonzalez-Quevedo et al, 2010) are as previously described. Based on published sequence information, PCR products were cloned as probe templates into pGemT-Easy (Promega, A1360) using the primers described above for sema3gb (AY766121), sema3fb (AY766119.1), nrp2a (NM_212965.1) and nrp2b (NM_212966.1).…”

“…2004; Amoyel et al, 2005), are not essential for neuronal differentiation and might regulate other aspects of hindbrain development.…”

“…The absence of neurogenesis at hindbrain boundaries might be due to Notch activation promoted by Rfng, which is expressed by boundary cells (Cheng et al, 2004;Qiu et al, 2009). Apparent support for the role of a boundary signal in organising neurogenesis came from the effects of knockdown of Wnt genes expressed in hindbrain boundaries (Riley et al, 2004;Amoyel et al, 2005); however, later work revealed that the altered neurogenesis was due to non-specific activation of the Bcl-caspase pathway, which has a non-apoptotic role in hindbrain boundary cell formation (Gerety and Wilkinson, 2011).…”

A New Role of Hindbrain Boundaries as Pools of Neural Stem/Progenitor Cells Regulated by Sox2

“…Similar to the MHB, HB cells (HBCs) express a variety of signaling molecules, including FGFs (in mice and chicks) or Wnts (in zebrafish) [20,[34][35][36][37][38][39]. Additionally, repressors of neural differentiations, such as Hes1, Id1 and Radical Fringe, were reported to be expressed in HBCs of chick, mice or fish [40][41][42].…”