Analysis of the complex expression of claudin genes and transcription factors during intestinal epithelial cell differentiation across the crypt-to-surface colonic axis. Characterization of the complex expression gradients of transcription factors Hopx, Hnf4a, Klf4 and Tcfl2 and 12 claudin genes. In vitro confirmatory methods identified two pathways that stimulate claudin expression; Hopx/Klf4 activation of Cldn4, 7 and 15, and Tcf7l2/Hnf4a upregulation of Cldn23. Chromatin Immunoprecipitation confirmed a Tcf7l2/Hnf4a/Claudin23 cascade. Hnf4a conditional knockout mice fail to induce Cldn23 during colonocyte differentiation. Overall design: The distal colon tissue was obtained from 4 male, 10-12 week old, C57BL/6 (WT) mice. The Arcturus Laser Capture Microdissection (LCM) system (Applied Biosystems/Life Technologies) was used to isolate crypt-base and surface cell populations providing two samples per mouse (crypt-base and surface). This resulted in 8 total samples for microarray analysis.