Fig. 3. Cdx1 expression in LRE and LRE+RARE mutants. Whole-mount in situ hybridization analysis of Cdx1 expression in wild-type mouse embryos (A-C), and in LRE (D-F) and LRE+RARE (G-I) homozygous mutant embryos. All embryos were processed in parallel, although mutant specimens were stained four times longer than the wild type to reveal residual expression. Approximate chronological stage is shown above. (A,D,G). The onset of Cdx1 expression at late primitive streak in wild-type controls (A) was delayed to early head-fold stage in the mutants (D,G), and subsequently transcript levels were reduced (compare wild-type controls in B with mutants in E,H). Cdx1 transcripts became undetectable after the 4- to 5-somite stage in both mutant lines (E,F,H,I), whereas expression was readily detected in wild-type controls (B,C). Arrows in C indicate Cdx1 expression in mesoderm in the tailbud region at E9.5.