ORIGINAL ARTICLE Hiroyuki Mutoh . Hirotsugu Sakamoto . Hiroko Hayakawa . Yukitomo Arao . Kiichi Satoh . Mitsuhiro Nokubi . Kentaro Sugano The intestine-specific homeobox gene Cdx2 induces expression of the basic helix–loop–helix transcription factor Math1 Received November 13, 2005; accepted in revised form February 26, 2006 Abstract The basic helix–loop–helix transcription factor Math1, which is transiently expressed in prolif- erating neural precursors in multiple domains of the developing nervous system, is also related to the cell fate decision of enteroendocrine, goblet, and Paneth cells in the intestine. On the other hand, the transcription factor Cdx2, which is normally confined to intestinal epithelial cells, is related to the differentiation of these cells. Therefore, we investigated the relationship between Math1 and Cdx2 in intestinal epithelial cells. The Math1 and Cdx2 expressions in normal intestinal mu- cosa and intestinal metaplastic mucosa from mouse and human stomachs, as well as an intestinal crypt-derived cell line, were analyzed by immunohistochemistry, reverse transcription-polymerase chain reaction and Northern blotting, and Math1 enhancer element was analyzed by luciferase reporter assays. Math1-positive epithelial cells co-expressing Cdx2 were found in normal intestinal mucosa from humans and mice. Furthermore, Math1-producing epithelial cells that showed positive immunostaining for Cdx2 were also observed in intes- tinal metaplastic mucosa from human and Cdx2 transgenic mouse stomachs, although they were not de- tected in normal gastric mucosa of humans and mice. Expression of Cdx2 stimulated endogenous Math1 mRNA expression in the intestinal crypt-derived cell line IEC-6, corroborating observations in Cdx2-ex- pressing intestinal metaplastic mucosa. Furthermore, expression of Cdx2 in IEC-6 cells conferred the ability to express a Math1 reporter gene containing a Math1 enhancer. Based on these results, we hypothesize that Cdx2 is involved in activating Math1 expression in intestinal epithelial cells. Key words Cdx2  Math1  intestine Introduction Cdx2, a caudal-related homeobox transcription factor, is selectively localized in the nuclei of fetal and adult mucosal epithelial cells in the small and large intestines in both humans and mice (Meyer and Gruss, 1993). Cdx2 haploinsufficiency results in abnormal differenti- ation of the midgut endoderm (Chawengsaksophak et al., 1997). Inactivation of Cdx2 by homologous re- combination results in the development of multiple intestinal polyp-like lesions in pericecal areas of the midgut of heterozygous mice (Beck et al., 1999; Tamai et al., 1999; Beck et al., 2003). These polyps do not express Cdx2 and consist of hamartoma-containing ar- eas that resemble the keratinizing stratified squamous epithelium found in the mouse forestomach, columnar mucous-secreting cells found in the gastric cardia and parietal cells found in the gastric corpus (Beck et al., 1999; Tamai et al., 1999; Beck et al., 2003). Thus, under Hiroyuki Mutoh ( . *)  Hirotsugu Sakamoto  Hiroko Hayakawa  Kiichi Satoh  Kentaro Sugano Department of Gastroenterology Jichi Medical School Yakushiji 3311-1, Minamikawachimachi, Kawachigun, Tochigi 329-0498 Japan Tel: 181 285 58 7348 Fax: 181 285 44 8297 E-mail: muto@jichi.ac.jp Yukitomo Arao Department of Environmental Medicine Center for Community Medicine Tochigi, Japan Mitsuhiro Nokubi Department of Pathology Jichi Medical School Tochigi, Japan U.S. Copyright Clearance Center Code Statement: 0301–4681/2006/7406–313 $ 15.00/0 Differentiation (2006) 74:313–321 DOI: 10.1111/j.1432-0436.2006.00074.x r 2006, Copyright the Authors Journal compilation r 2006, International Society of Differentiation