The molecular analysis of the dorsal organizer formation in zebrafish early development.

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In zebrafish, wnt3a and wnt8 are expressed in overlapping domains in the blastoderm margin and later in the tailbud. The combined inhibition of Wnt3a and Wnt8 by antisense morpholino oligonucleotides led to anteriorization of the neuroectoderm, expansion of the dorsal organizer, and loss of the tail structure. The ventrally expressed homeobox genes vox, vent, and ved mediated Wnt3a/8 signaling to restrict the dorsal organizer domain. The expression of the caudal-related cdx1a and cdx4 was strongly reduced in the wnt3a/8 morphant embryos. Like the wnt3a/8 morphant embryos, cdx1a/4 morphant embryos displayed complete loss of the tail structure, suggesting that Cdx1a and Cdx4 mediate Wnt-dependent tail formation. We also found that cdx1a/4 expression is dependent on Fgf signaling. hoxa9a expression was down-regulated in the wnt3a/8 and cdx1a/4 morphant embryos. Fgf signaling was required for Cdx-mediated hoxa9a expression. These data indicate that the cdx genes mediate Wnt signaling and p … More lay essential roles in the morphogenesis of the tail. We isolated a zebra fish mutant (cdh1^<rk3>) that has a mutation in the e-cadherin/cdh1 gene. The most severely affected embryos displayed epiboly delay, decreased convergent extension movements, and the dissociation of cells from the embryos. The less severely affected embryos showed flattened anterior neural tissue, abnormal positioning and morphology of the hatching gland, scattered trigeminal ganglia. Maternal-zygotic cdh1^<rk3> embryos displayed epiboly arrest during gastrulation, in which the enveloping layer(EVL) and the yolk syncytial layer but not the deep cells(DC) completed epiboly. Immunohistochemistry with an anti-beta-catenin antibody and electron microscopy revealed that adhesion between the DCs and the EVL was mostly disrupted but that the adhesion between DCs was relatively unaffected in the MZcdh1^<rk3> mutant. These data suggest that E-cadherin-mediated cell adhesion between the DC and EVL plays a role in the epiboly movement in zebrafish. Less