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beta-Catenin Regulates Intercellular Signalling Networks and Cell-Type Specific Transcription in the Developing Mouse Midbrain-Rhombomere 1 RegionChilov, Dmitri; Sinjushina, Natalia; Saarimaki-Vire, Jonna; Taketo, Makoto M.; Partanen, Juha; Mei, Lin; Department of Neurology (2010-06-3)b-catenin is a multifunctional protein involved in both signalling by secreted factors of Wnt family and regulation of the cellular architecture. We show that b-catenin stabilization in mouse midbrain-rhombomere1 region leads to robust upregulation of several Wnt signalling target genes, including Fgf8. Suggestive of direct transcriptional regulation of the Fgf8 gene, b-catenin stabilization resulted in Fgf8 up-regulation also in other tissues, specifically in the ventral limb ectoderm. Interestingly, stabilization of b-catenin rapidly caused down-regulation of the expression of Wnt1 itself, suggesting a negative feedback loop. The changes in signal molecule expression were concomitant with deregulation of anteriorposterior and dorso-ventral patterning. The transcriptional regulatory functions of b-catenin were confirmed by b-catenin loss-of-function experiments. Temporally controlled inactivation of b-catenin revealed a cell-autonomous role for b-catenin in the maintenance of cell-type specific gene expression in the progenitors of midbrain dopaminergic neurons. These results highlight the role of b-catenin in establishment of neuroectodermal signalling centers, promoting region-specific gene expression and regulation of cell fate determination.