ABSTRACT
Neuromesodermal (NM) stem cells reside in the primitive streak (PS) of gastrulating vertebrate embryos and generate precursors of the spinal cord and musculoskeletal system. Although Wnt3a/ß-catenin signaling is crucial for NM stem cell maintenance and differentiation, few key transcriptional effectors have been identified. Through a concerted transcriptional profiling and genetic approach we have determined that two Zn(2+)-finger transcription factors, Sp5 and Sp8, are regulated by Wnt3a in the PS, and are essential for neural and musculoskeletal patterning. These results identify Sp5 and Sp8 as pivotal downstream effectors of Wnt3a, and suggest that they are essential for the self-renewal and differentiation of NM stem cells.
Subject(s)
DNA-Binding Proteins/genetics , Mesoderm/metabolism , Neural Stem Cells/metabolism , Primitive Streak/metabolism , Transcription Factors/genetics , Wnt3A Protein/genetics , beta Catenin/genetics , Animals , DNA-Binding Proteins/metabolism , Embryo, Mammalian , Gastrulation/genetics , Gene Expression Profiling , Gene Expression Regulation, Developmental , Mesoderm/cytology , Mice , Mice, Transgenic , Mutation , Neural Stem Cells/cytology , Primitive Streak/cytology , Transcription Factors/metabolism , Transcription, Genetic , Wnt3A Protein/metabolism , beta Catenin/metabolismABSTRACT
In Xenopus laevis embryonic development, activation of the Wnt/ß-catenin pathway promotes mesoderm cell fate determination via Xnr (Xenopus nodal-related) expression. We have demonstrated previously that Rel/NF-κB (nuclear factor κB) proteins expressed in presumptive ectoderm limit the activity of Xnrs to the marginal zone of embryos during mesoderm induction, which assists to distinguish mesoderm from ectoderm. The mechanism of this regulation, however, is unknown. In the present study, we investigated whether Rel/NF-κB proteins are able to modulate mesoderm formation by mediating Wnt/ß-catenin signalling. We determined that ectopic expression of XrelA or Xrel3 in the dorsal marginal zone perturbed dorsal mesoderm formation by down-regulating multiple Wnt/ß-catenin target genes including Xnr3, Xnr5 and Xnr6. Ventral co-expression of XrelA or Xrel3 with either wild-type ß-catenin or constitutively active ß-cateninS37A abrogated ß-catenin-induced axis duplication and attenuated ß-catenin-stimulated reporter transcription. Lastly, we provide evidence that Xrel3, but not XrelA, can interact with ß-catenin without affecting the association of ß-catenin with other transcriptional co-activators in vitro. Both Xrel3 and XrelA, however, prevented the accumulation, in nuclei, of exogenously expressed and endogenous ß-catenin in vivo. These results suggest that Rel proteins are able to bind ß-catenin and attenuate ß-catenin-mediated transcription by nuclear exclusion.
