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Fgf3 displays a dynamic and complex expression pattern during mouse embryogenesis. To address the molecular mechanisms underlying Fgf3 expression, we used a transgenic approach to assay genomic regions from the mouse Fgf3 gene for regulatory activity. We identified an enhancer that mediates major components of embryonic expression, governing expression in the midbrain, hindbrain, surface ectoderm, dorsal roots and dorsal root ganglia (DRG), proximal sensory ganglia, and the developing central nervous system (CNS). Deletional analysis of the enhancer further delimited this regulatory activity to a 5.7-kb fragment. We have also revealed sonic hedgehog (Shh) -dependent and Shh-independent aspects of Fgf3 expression through breeding the Fgf3 reporter transgene into Shh mutants. In the absence of Shh signalling, Fgf3 reporter expression is lost in the ventral CNS, DRG, and superior cervical nerves, whereas activation of reporter expression in cranial ganglion cells is Shh independent. Moreover, detailed re-examination of the Shh phenotype revealed that Shh signalling is required for the correct development/maturation of the DRG., (Copyright 2004 Wiley-Liss, Inc.)

Deregulation of beta-catenin activity is an important step in the development of colorectal cancers. One consequence of this is transcriptional activation of cyclin D1, an oncogene known to be overexpressed in colorectal cancers. We tested the hypothesis that cyclin D1 gene activation is important for intestinal tumorigenesis. Multiple intestinal neoplasia mice (a model for human familial adenomatous polyposis) were crossed with cyclin D1 knockout (Ccnd1(-/-)) mice. Despite the absence of cyclin D1, intestinal tumors still developed. However, Ccnd1(-/-) multiple intestinal neoplasia mice developed significantly fewer tumors than Ccnd1(+/-) or Ccnd1(+/+) mice (P = 0.003). We conclude that cyclin D1 is not essential for intestinal tumorigenesis, but it may act as a modifier gene.