Anti-human Crb3 antibody recognizes all zebrafish Crb family proteins ( Hsu et al., 2006). Whereas the localization of the Crb family proteins and Moe detected by the antibodies against these proteins were accumulated at the apical surface in the WT, these accumulations were not observed in the moerw306 mutant ( Figures 2Ae–2Ah). To investigate whether the Crb⋅Moe complex is required for the correct formation of the
vagus motor nuclei, we repressed the expression of another component of the Crb⋅Moe complex, Nagie oko (membrane protein, palmitoylated 5a according to the Zebrafish Nomenclature Committee; Icotinib known as Pals1 in mammals and hereafter referred to as Nok), which is required for the establishment and maintenance of neuroepithelial polarity in the developing retina and brain of zebrafish (Wei and Malicki, 2002). The nok morphants also showed fusion of the bilateral vagus motor nuclei (36/40, 90%; Figures 2Ai and 2Aj). Recent genetic studies in Drosophila have demonstrated that a fly ortholog of Moe, Yurt, negatively regulates Crb ( Laprise et al., 2006, Laprise NVP-BGJ398 mouse et al., 2009 and Laprise
et al., 2010). Overexpression of Crb2 partially impaired the formation of the bilaterally segregated vagus motor nuclei (5/30, 17%; Figure 2Ak, arrow). These results suggest that the Crb⋅Moe complex is required for the correct formation of the vagus motor nuclei. To determine which cells require the moe activity for the correct formation of the vagus motor nuclei, we performed a mosaic analysis by transplanting rhodamine-dextran-labeled WT cells at the blastoderm stage into the moe morphant host embryos at the shield stage. The WT vagus motor neuron precursors in the hindbrains of the moe morphant embryos were positioned ectopically, close to the midline, as observed for the moerw306 mutants ( Figures 2Ba and 2Ba′; n = 6). This result suggests that expression
of Moe in the vagus motor neuron precursors is not sufficient to ensure that they migrate in the appropriate directions. Neuroepithelial cells are likely to be regulators of vagus motor neuron precursor migration, as they support the tangential migrations of the facial and vagus motor neuron precursors ( Ohata et al., 2009a and Wada et al., 2006). In fact, when GBA3 the WT neuroepithelial cells were placed in the dorsomedial region of the hindbrain of the moe morphant, the morphant vagus motor precursors were found to migrate to their normal positions ( Figures 2Bb, 2Bb′, and 2Bb″; n = 4, dotted-lines). In contrast, the morphant vagus motor neuron precursors entered the dorsomedial region when not surrounded by WT cells ( Figures 2Bb and 2Bb′, arrow). These results suggest that neuroepithelial cells require moe to guide the migration of the vagus motor neuron precursors. The Crb⋅Moe complex is a key regulator of epithelial polarity (Hsu et al., 2006 and Laprise et al.