The pancreatic ␤ cell can respond in the long term to hyperglycemia both with an increased capacity for insulin production and, in susceptible individuals, with apoptosis. When glucose-induced apoptosis offsets the increasing ␤ cell capacity, type 2 diabetes results. Here, we tested the idea that the pathway of glucose metabolism that leads to the modification of intracellular proteins with the O-linked monosaccharide N-acetylglucosamine (O-GlcNAc) is involved in the glucose-induced apoptosis. This idea is based on two recent observations. First, the ␤ cell expresses much more O-GlcNAc transferase than any other known cell, and second, that the ␤ cell-specific toxin, streptozotocin (STZ), itself a GlcNAc analog, specifically blocks the enzyme that cleaves O-GlcNAc from intracellular proteins. As a consequence, we now show that hyperglycemia leads to the rapid and reversible accumulation of O-GlcNAc specifically in ␤ cells in vivo. Animals pretreated with STZ also accumulate O-GlcNAc in their ␤ cells when hyperglycemic, but this change is sustained upon re-establishment of euglycemia. In concert with the idea that STZ toxicity results from the sustained accumulation of O-GlcNAc after a hyperglycemic episode, we established a low-dose STZ protocol in which the ␤ cells' toxicity of STZ was manifest only after glucose or glucosamine administration. Transgenic mice with impaired ␤ cell glucosamine synthesis treated with this protocol are resistant to the diabetogenic effect of STZ plus glucose yet succumb to STZ plus glucosamine. This study provides a causal link between apoptosis in ␤ cells and glucose metabolism through glucosamine to O-GlcNAc, implicating this pathway of glucose metabolism with ␤ cell glucose toxicity.T he pancreatic ␤ cell is the primary regulator of glucose flux into stored energy in vertebrates. To accomplish this function, ␤ cells must sense the plasma glucose concentration and secrete the appropriate amount of insulin to direct glucose uptake and storage of its chemical energy in the fat, muscle, and liver. Considerable progress has been made in the understanding of glucose sensing by the ␤ cell. Glucose enters the ␤ cell through the GLUT2 glucose transporter (1), and it is phosphorylated by glucokinase, which has a K m for glucose that allows substantial glucose phosphorylation to proceed only when plasma glucose concentrations exceed 5 mM (2). Once glucose is phosphorylated, it can enter a variety of metabolic pathways, including glycolysis. An increased ATP͞ADP from glucose metabolism generally is believed to regulate the immediate release of insulin (3, 4). The normal ␤ cell is also capable of adapting its capacity for insulin release depending on long-term nutritional status. For example, exposure to a higher than normal carbohydrate load can condition the ␤ cell to secrete even more insulin after exposure to the same load several hours later (5). Finally, the ␤ cell is capable of even more long-term adaptation by increasing the ␤ cell number through hyperplasia (6, 7). However, this hyp...

The ErbB2 receptor tyrosine kinase (RTK) is expressed in basal cells of squamous epithelia and the outer root sheath of hair follicles. We previously showed that constitutive expression of activated ErbB2 directed to these sites in the skin by the keratin 14 (K14) promoter produces prominent hair follicle abnormalities and striking skin hyperplasia in transgenic mice. However, perinatal lethality precluded the establishment of a transgenic line for analysis of ErbB2 function in adult animals. To investigate the signi®cance of ErbB2 signaling in epithelial tissues during and post development, we developed a K14-rtTA/TetRE-ErbB2`Tet-On' bitransgenic mouse system. These mice were normal until the ErbB2 transgene was induced by exposure to doxycycline (Dox). Prenatal induction resulted in perinatal death. Postnatally, ErbB2 transgene expression was observed at 4 h after the initiation of Dox, and reached a plateau at 24 h. Skin hyperplasia followed after 2 days and these changes reverted to normal upon Dox withdrawal. In adults, as in the neonates, prolonged ErbB2 induction caused prominent skin and hair follicle hyperplasias. Severe hyperplasias in the cornea, eye lids, tongue and esophagus were also observed. ErbB2 transgene induction was accompanied by increased expression of TGFa, a ligand of epidermal growth factor receptor (EGFR), and to a lesser extent, EGFR, further enhancing RTK signal transduction. We conclude that ErbB2 plays important roles in both development and maintenance of hair follicles and diverse squamous epithelia and that this ligand-inducible and tissue-speci®c Tet-On' transgenic mouse system provides a means to study transgenes with perinatal toxicity.

Type III cGMP-inhibited phosphodiesterases (PDE3s) play important roles in hormonal regulation of lipolysis, platelet aggregation, myocardial contractility, and smooth muscle relaxation. We have recently characterized two PDE3 subtypes (PDE3A and PDE3B) as products of distinct but related genes. To elucidate their biological roles, in this study we compare cellular patterns of gene expression for these two enzymes during rat embryonic and postnatal development using in situ hybridization. PDE3A mRNA is abundant in adipose tissue and is also expressed in hepatocytes throughout development. This mRNA is also highly abundant in embryonic neuroepithelium including the neural retina, but expression is greatly reduced in the mature nervous system. Finally, PDE3A mRNA is localized in spermatocytes and renal collecting duct epithelium in adult rats.PDE3B mRNA is highly expressed in the cardiovascular system, including myocardium and arterial and venous smooth muscle, throughout development. It is also abundant in bronchial, genitourinary and gastrointestinal smooth muscle and epithelium, megakaryocytes, and oocytes. PDE3B mRNA demonstrates a complex, developmentally regulated pattern of gene expression in the central nervous system. In summary, the two different PDE3s show distinctive tissue-specific patterns of gene expression suggesting that PDE3A is involved in hormonal regulation of lipolysis and glycogenolysis, while regulation of myocardial and smooth muscle contractility appears to be a function of PDE3B. In addition, the present findings suggest previously unsuspected roles for these enzymes in gametogenesis and neural development. (J. Clin. Invest. 1995Invest. . 95:1528Invest. -1538

The CHIP28 water channel is a maijor component of red cell and renal tubule membranes; however, its ontogeny and tissue distribution remain undefined. Three patterns of expression were identified when CHIP28 mRNA was surveyed by in situ hybridization histochemistry in rats between embryonic day 14 and maturity. (i) CHIP28 mRNA and protein were very abundant in hematopoietic tissue and kidneys of mature rats, but strong expression did not occur until after birth, when it appeared in renal proximal tubules and descending thin limbs, red pulp of the spleen, and membranes of circulating red cells. (ii) CHIP28 mRNA was abundant in choroid plexus epithelium throughout fetal development and maturity. (iii) CHIP28 mRNA was transiently observed in periosteum, heart, vascular endothelium, and cornea during fetal development. The ontogeny of kidney and red cell CHIP28 expression coincides with the ability of kidneys to concentrate urine, suggesting that CHIP28 promotes water reabsorption in the proximal nephron and provides red cell osmoregulation needed for passage through the hypertonic medulla. Its presence in the choroid plexus suggests that CHIP28-mediated water transport contributes to secretion of cerebrospinal fluid. The functional role of CHIP28 in developing bone, heart, and eye is unclear. These findings further establish the general physiologic role of CHIP28 as a water channel involved in reabsorption, osmoregulation, and secretion. The studies also suggest other possible functions during fetal development and predict that complex mechanisms will be needed for regulation of CHIP28 gene expression in diverse tissues at distinct points in development.