Fig. 2. Analysis of TF gene expression in the developing GI tract according to protein families. (A) TF gene families show divergent patterns of expression and temporal modulation during intestine development, with proportionally higher representation of basic-leucine zipper (bZip) and zinc-binding (ZnB) factors. Nuclear receptor (NR), homeodomain (HD) and high-mobility group (HMG) factors have the highest degree of temporal modulation. Except for HD and NR, most families are distributed similarly in intestine (In, shown here) and stomach (St, data are shown only for NR and HD). (B) Comparative gene expression for a single TF subfamily, Hox-cluster genes, commonly proposed as candidates for anteroposterior gut patterning. Expression in the developing gut is limited to genes at the 3' ends of collinear clusters and, with the few exceptions marked in red type, is very similar in extent and modulation in fetal stomach and small intestine. (C) As a group, NRs showed the greatest increase during intestine development, mostly from E11 to E13. One factor expressed with these dynamics is Nr2e3, previously regarded as a photoreceptor-specific product. (D) Nr2e3 mRNA, expressed in the developing gut, is abrogated in adult mice. (E) Fetal expression of Nr2e3 is restricted to the proximal small bowel. (F) In situ hybridization (E15 intestine) reveals Nr2e3 expression in the epithelial compartment (arrows).