Wnt/β-catenin regulation of the Sp1-related transcription factor sp5l promotes tail development in zebrafish

Abstract

Tail formation in vertebrates involves the specification of a population of multipotent precursors, the tailbud, which will give rise to all of the posterior structures of the embryo. Wnts are signaling proteins that are candidates for promoting tail outgrowth in zebrafish, although which Wnts are involved, what genes they regulate, and whether Wnts are required for initiation or maintenance steps in tail formation has not been resolved. We show here that both wnt3a and wnt8 are expressed in the zebrafish tailbud and that simultaneous inhibition of both wnt3a and wnt8 using morpholino oligonucleotides can completely block tail formation. In embryos injected with wnt3a and wnt8morpholinos, expression of genes in undifferentiated presomitic mesoderm is initiated, but not maintained. To identify genes that might function downstream of Wnts in tail formation, a DNA microarray screen was conducted,revealing that sp5l, a member of the Sp1 family of zinc-finger transcription factors, is activated by Wnt signaling. Moreover, we show that sp5l expression in the developing tail is dependent on both wnt3a and wnt8 function. Supporting a role for sp5lin tail formation, we find that inhibition of sp5l strongly enhances the effects of wnt3a inhibition, and overexpression of sp5l RNA is able to completely restore normal tail development in wnt3a morphants. These data place sp5l downstream of wnt3a and wnt8 in a Wnt/β-catenin signaling pathway that controls tail development in zebrafish.

PR130 is a modulator of the Wnt-signaling cascade that counters repression of the antagonist Naked cuticle

“…Because development of the tail requires Wnt signaling (23), the phenotype of Xpr130 knockdown might be explained by inhibition of Wnt signaling during development. Similarly, development of the tail was found to be impaired when Wnt signaling was inhibited in zebrafish (24). However, we cannot exclude any Wnt-independent effects on growth in general.…”

The Evolution of the Wnt Pathway

“…Similarly to the posterior growth zone in amphioxus tail buds (Schubert et al 2001), nuclear b-catenin also forms a posterior-to-anterior gradient in vertebrates. Wnt signaling is involved in tail development in zebrafish (Agathon et al 2003;Shimizu et al 2005;Thorpe et al 2005), where Wnt3a determines the anterior-posterior position of the somite determination front (Aulehla et al 2003;Dunty et al 2008;De Robertis 2010;Niehrs 2010). …”

A direct role for Wnt8 in ventrolateral mesoderm patterning

“…Other studies have suggested that Wnt signaling prevents posterior mesoderm progenitor differentiation, thereby maintaining a posterior mesoderm progenitor pool (Shimizu et al, 2005;Thorpe et al, 2005;Martin and Kimelman, 2008;Row and Kimelman, 2009). This suggests an additional role for wnt8 wherein BMPs are necessary for the maintenance of the tailbud, but the release of progenitors into presomitic mesoderm is a Wntregulated process.…”

“…The mesodermal phenotype of wnt8 mutants could be explained by two alternative hypotheses: on the one hand, mesoderm dorsalization may result in specification of fewer ventrolateral/posterior mesoderm progenitors, thereby restricting the progenitor pool that contributes to ventral and posterior fates. On the other hand, Wnt signaling may have a role in promoting the maintenance or expansion of posterior mesoderm progenitors, for example through cdx or no tail/brachyury gene regulation (Shimizu et al, 2005;Thorpe et al, 2005;Martin and Kimelman, 2008).…”