Fig. 1. Deletion of FCE1 from the endogenous locus alters Lfng expression in the posterior PSM. (A) The Lfng endogenous locus (boxes signify coding exons and FCE1), the targeting vector replacing the 110 bp FCE1 sequence with an EcoRV site and the structure of the targeted locus are shown. The floxed Neo/Testis-CRE cassette is excised upon passage through the male germline (Bunting et al., 1999). Locations of probes (solid lines) and primers (numbered arrows) used for genotyping are indicated. (B) After electroporation into TC1 cells (Deng et al., 1996), G418 resistant colonies were screened by Southern blot. A representative colony containing the Lfng^FCE1 allele and a mouse genotyping PCR are shown. Arrows, endogenous band; arrowheads, targeted bands. (C) RNA in situ analysis demonstrates cyclic Lfng expression in wild-type embryos at 10.5 dpc (c-e, n=4/14 Phase 1, 5/14 Phase 2, 5/14 Phase 3). In homozygous mutant embryos, expression is seen only in the anterior PSM (g, n=11). PSM expression patterns are summarized (f,h). Lfng RNA expression at other sites is unaffected (a,b).