Masterblind insights into CNS patterning

The Wnt signalling pathway controls anteroposterior (AP) patterning in the dorsal CNS of many species. Now Kapsimali and colleagues report that, in zebrafish, Wnt signalling also influences the AP identity of ventral CNS midline tissue (see p. 5923). Ventral midline cells form floorplate throughout the CNS, except in the anterior forebrain where they form the hypothalamus. The researchers show that masterblind zebrafish embryos, which lack functional Axin1 (an intracellular inhibitor of Wnt pathway activation), have more prospective floorplate and less prospective hypothalamic tissue than normal embryos. They also show that axin1 overexpression in normal prospective floorplate induces hypothalamic gene expression. The researchers suggest that Axin1 might modulate the response of ventral CNS cells to signals, such as Nodal, that induce ventral CNS identity and thus help to integrate dorsoventral and AP patterning information in the developing CNS.