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The basic helix-loop-helix transcription factor NeuroD1 regulates cell fate in the nervous system but previously has not been considered to function similarly in the endocrine pancreas due to its reported expression in all islet cell types in the newborn mouse. Because we found that NeuroD1 potently represses somatostatin expression in vitro, its pattern of expression was examined in both strains of mice in which lacZ has been introduced into the NeuroD1 locus by homologous recombination. Analysis of adult transgenic mice revealed that NeuroD1 is predominantly expressed in ␤-cells and either absent or

Peptide YY is a 36-amino-acid hormone (45) synthesized primarily in L-type enteroendocrine cells in the colon and ileum and in cells along the periphery of pancreatic islets. Like that of other gastrointestinal hormones, release of peptide YY appears to be stimulated by the presence of enteral secretagogues, especially dietary fat, present in the distal intestine. The mechanisms that control this release are not completely understood (14). Peptide YY functions as a ligand for a number of receptors of the closely related neuropeptide Y. Peptide YY appears to have widespread inhibitory effects on gastrointestinal function, including inhibition of gastric emptying, gastric motility, and pancreatic exocrine secretion (25, 31). The putative actions of peptide YY do not appear to result from direct effects on neuropeptide Y receptors in the gastrointestinal tract but instead by binding to receptors in the dorsal vagal complex of the brain stem and inhibiting vagal tone (16,32).Recent work has suggested that peptide YY might function as a major regulator of food intake, consistent with observations that peptide YY is released in proportion to caloric intake (33). Peptide YY 3-36 , which is generated by enzymatic cleavage of the full-length peptide by dipeptidyl peptidase IV (26), inhibited food intake for up to 12 h when administered to either rodents and humans (3). Following a meal, approximately 63% of circulating peptide YY in humans was shown to be peptide YY 3-36 (13). Unlike the full-length peptide, peptide YY 3-36, functions as a ligand for the Y2 receptor (22) and appeared to regulate food intake in mice via Y2 receptors on neurons in the hypothalamus that inhibit the orixegenic neuropeptide Y system in the arcuate nucleus (3).We previously showed that peptide YY was expressed in murine pancreatic and colonic endocrine cells when they first appeared during embryonic development. This observation raised the possibility that cells expressing peptide YY were endocrine precursor cells (49,50). Several studies suggested that pancreatic polypeptide or possibly neuropeptide Y were expressed in immature islets in the developing murine pancreas (17, 46). Subsequently, peptide YY was identified as the pancreatic polypeptide (PP) family member expressed during the earliest stage of endocrine differentiation at embryonic day 9.5 (E9.5), when the pancreas is budding from the foregut (21, 49). These peptide YY-positive cells were also immunopositive for glucagon and, in many cases, insulin immunoreactivity. Peptide YY was coexpressed in somatostatin and pancreatic polypeptide cells when they first appeared, later in development. This early coexpression was not maintained in adult mice, where peptide YY was expressed in only a fraction of glucagon-producing alpha cells and was not expressed in insulin-producing ␤ cells. These observations led to the suggestion that peptide YY was expressed in a common islet progenitor cell and that its expression was extinguished during the maturation of alpha and ␤ cells (49).Peptide YY is ...

Menin, the product of the tumor suppressor gene MEN1, is widely expressed in mammalian endocrine and non-endocrine tissues, including intestine. Its known abundant expression in several types of cells with high proliferative capacity led us to investigate the physiological function of the protein menin in intestinal epithelium, one of the most rapidly growing epithelia. Here we showed that the Men1 gene is mainly expressed in the crypt compartment of the proximal small intestine and that its expression was increased during fasting in vivo, both suggesting a role of menin in the control of cell growth. Indeed, specific reduction of menin expression by transfected antisense cDNA in the rat duodenal crypt-like cell line, IEC-17, increased cell proliferation. Menin is a 610 amino acid protein encoded by the tumor suppressor gene MEN1 (1). Germline mutations are responsible for multiple endocrine neoplasia type 1 (MEN1), 1 an autosomal-dominant cancer syndrome featuring parathyroid cell hyperplasia and tumors of the pituitary and duodeno-pancreatic endocrine tissues. Biallelic inactivation of the Men1 gene in mice results in embryonic lethality at mid-gestation (2, 3). Heterozygote Men1 mutant mice develop the similar range of endocrine tumors as seen in the human MEN1 syndrome (4).Menin is highly conserved in humans and rodents (5, 6). The protein sequence does not include consensus motives from which its putative function could be deduced. Menin has been shown to interact directly with an ever increasing list of molecular partners such as JunD, Smad3, nm23, NF-B (for a review, see Ref. 7). It is predominantly located in the nucleus, with two independent nuclear localization signals (1).Despite the endocrine specificity of the MEN1 syndrome tumors, menin RNA and protein are widely expressed in endocrine and non-endocrine rodent and human tissues (6, 8 -10), suggesting a large panel of physiological functions for the protein. In the intestinal tract of mouse and rat, menin RNA was detected by Northern blotting in small and large intestine (6,8). Interestingly, in adult human tissues, the expression of the MEN1 gene detected by in situ hybridization was predominant in actively proliferating cells such as the proliferative phase of endometrium and parabasal cells of the esophageal mucosa, but faint in the secretory phase of the endometrium (10).The aim of the present study was to investigate the physiological function of menin in the intestinal epithelium, which is among the most rapidly renewing tissues of the mammalian organism. First, we provide direct evidence that the Men1 gene is mainly expressed in the crypt compartment of the small intestine. We then demonstrate that menin inactivation increases cell proliferation and promotes tumorigenesis both in vitro and in vivo in intestinal epithelial cells. EXPERIMENTAL PROCEDURESIn Situ Hybridization-Deparaffinized mouse proximal small intestine sections were treated for 10 min with pepsin (0.4%) in 0.2 N HCl, followed by ethanol treatment and air drying. Hybridization ...