Fig. 1. Deletion of the Fgf3-coding region in mice. (A) The genomic locus with the exons and coding regions of the Fgf3 gene indicated. The coding region was replaced by a FGF3 cDNA and a neo^r gene flanked by loxP sites by homologous recombination. The introduced sequences were removed by Cre-mediated excision between the external loxP sites. (B) Southern blot analysis was carried out using the probes indicated in A to detect the correct targeting event in ES cells and subsequent deletion of the introduced sequences. (C) PCR analysis using primer pairs indicated by pink arrows in A demonstrating the presence and absence of specific products amplified from the targeted locus and after generation of the knock out allele. (D) Whole-mount RNA hybridisation analysis of Fgf3 expression in the hindbrain of an E8.5 Fgf3^–/– mutant embryo and a wild-type littermate. Scale bar: 100 µm.