Mutations in the hepatocyte nuclear factor-1alpha gene in maturity-onset diabetes of the young (MODY3)

The cut-homeodomain transcriptional activator HNF-6 is coexpressed with its target gene HNF-3 beta in the developing murine liver and pancreas

Murine hepatocyte nuclear factor-3 beta (HNF-3 beta) protein is a member of a large family of developmentally regulated transcription factors that share homology in the winged helix/fork head DNA binding domain and that participate in embryonic pattern formation. HNF-3 beta also mediates cell-specific transcription of genes important for the function of hepatocytes, intestinal and bronchiolar epithelial, and pancreatic acinar cells. We have previously identified a liver-enriched transcription factor, HNF-6, which is required for HNF-3 beta promoter activity and also recognizes the regulatory region of numerous hepatocyte-specific genes. In this study we used the yeast one-hybrid system to isolate the HNF-6 cDNA, which encodes a cut-homeodomain-containing transcription factor that binds with the same specificity as the liver HNF-6 protein. Cotransfection assays demonstrate that HNF-6 activates expression of a reporter gene driven by the HNF-6 binding site from either the HNF-3 beta or transthyretin (TTR) promoter regions. We used interspecific backcross analysis to determine that murine Hnf6 gene is located in the middle of mouse chromosome 9. In situ hybridization studies of staged specific embryos demonstrate that HNF-6 and its potential target gene, HNF-3 beta, are coexpressed in the pancreatic and hepatic diverticulum. More detailed analysis of HNF-6 and HNF-3 beta's developmental expression patterns provides evidence of colocalization in hepatocytes, intestinal epithelial, and in the pancreatic ductal epithelial and exocrine acinar cells. The expression patterns of these two transcription factors do not overlap in other endoderm-derived tissues or the neurotube. We also found that HNF-6 is also abundantly expressed in the dorsal root ganglia, the marginal layer, and the midbrain. At day 18 of gestation and in the adult pancreas, HNF-6 and HNF-3 beta transcripts colocalize in the exocrine acinar cells, but their expression patterns diverge in other pancreatic epithelium. HNF-6, but not HNF-3 beta, expression continues in the pancreatic ductal epithelium, whereas only HNF-3 beta becomes restricted to the endocrine cells of the islets of Langerhans. We discuss these expression patterns with respect to specification of hepatocytes and differentiation of the endocrine and exocrine pancreas.

Studies on the enzymatic and transcriptional activity of the dimerization cofactor for hepatocyte nuclear factor 1

The relationship between the enzymatic and the transcriptional activity of the bifunctional protein pterin-4a-carbinolamine dehydratase/dimerization cofactor for hepatocyte nuclear factor 1 (DCoH) has been elucidated by site-directed mutagenesis. DCoH dimers harbor a binding site for hepatocyte nuclear factor 1 (HNF1), two active centers that bind pterins, and a saddle-shaped surface that resembles nucleic acid binding domains. Two domains of the protein have been selectively targeted to determine if a change in one activity affects the other. No strong correlation has been found, supporting the idea that carbinolamine dehydratase activity is not required for HNF1 binding in vitro or transcriptional coactivation in vivo. Double mutations in the active center, however, influence the in vivo transcriptional activity but not HNF1 binding. This finding suggests that some active center residues also are used during transcription, possibly for binding of another (macro)molecule. Several mutations in the saddle led to a surprising increase in transcription, therefore linking this domain to transcriptional regulation as well. The transcriptional function of DCoH therefore is composed of two parts, HNF1 binding and another contributing effect that involves the active site and, indirectly, the saddle.

A set of polyclonal and monoclonal antibodies reveals major differences in post-translational modification of the rat HNF1 and vHNF1 homeoproteins

The related homeodomain-containing transcription factors HNF1 (HNF1 alpha) and vHNF1 (HNF1 beta) recognise common target DNA sequences in the regulatory regions of many genes and are expressed in several parenchymal cell types, predominantly in liver, kidney, intestine and pancreas. HNF1-null mutant mice, with a wild-type vHNF1 gene, develop normally, but die within a few weeks of birth with severe liver and kidney failure. Humans with a mutation in the HNF1 alpha gene develop non-insulin dependent diabetes on maturity (MODY 3). To determine distinctive roles for each of these proteins we produced a set of polyclonal sera and monoclonal antibodies, directed against different parts of the rat HNF1 and vHNF1 proteins. These antibodies reveal that HNF1 is present in vivo as a heterogeneous mixture of 92-98 kDa molecular mass polypeptides, a mass higher than that expected from its amino acid sequence. vHNF1 is present in the form of two isoforms of roughly the expected molecular masses, 65 and 68 kDa. In addition, some antibodies prepared against bacterially-produced HNF1 recognise vHNF1 but not HNF1, in liver and kidney extracts. Hence, we present the first evidence for differential post-translational modification of HNF1 and vHNF1 proteins.

Fatty acids decrease IDX-1 expression in rat pancreatic islets and reduce GLUT2, glucokinase, insulin, and somatostatin levels

IDX-1 (islet/duodenum homeobox-1) is a transcription factor expressed in the duodenum and pancreatic beta and delta cells. It is required for embryonic development of the pancreas and transactivates the Glut2, glucokinase, insulin, and somatostatin genes. Here we show that exposure of isolated rat pancreatic islets to palmitic acid induced a approximately 70% decrease in IDX-1 mRNA and protein expression as well as 40 and 65% decreases in the binding activity of IDX-1 for its cognate cis-regulatory elements of the Glut2 and insulin promoters, respectively. The inhibitory effect of palmitic acid required its mitochondrial oxidation since it was prevented by the carnitine palmitoyltransferase I inhibitor bromopalmitic acid. The palmitic acid effect on IDX-1 was correlated with decreases in GLUT2 and glucokinase expression of 40 and 25%, respectively, at both the mRNA and protein levels. Insulin and somatostatin mRNA expression was also decreased by 40 and 60%, whereas glucagon mRNA expression was not modified. After 48 h of exposure to fatty acids, total islet insulin, somatostatin, and glucagon contents were decreased by 85, 55, and 65%, respectively. At the same time, total hormone release was strongly stimulated (13-fold) for glucagon, whereas its was only marginally increased for insulin and somatostatin (1.5- and 1.7-fold, respectively). These results indicate that elevated fatty acid levels 1) negatively regulate Idx-1 expression; 2) decrease the expression of genes transactivated by IDX-1 such as those for GLUT2, glucokinase, insulin, and somatostatin; and 3) lead to an important increase in glucagon synthesis and secretion. Fatty acids thus have pleiotropic effects on pancreatic islet gene expression, and the negative control of Idx-1 expression may be an initial event in the development of these multiple defects.

The maturity-onset diabetes of the young (MODY1) transcription factor HNF4alpha regulates expression of genes required for glucose transport and metabolism

Hepatocyte nuclear factor 4alpha (HNF4alpha) plays a critical role in regulating the expression of many genes essential for normal functioning of liver, gut, kidney, and pancreatic islets. A nonsense mutation (Q268X) in exon 7 of the HNF4alpha gene is responsible for an autosomal dominant, early-onset form of non-insulin-dependent diabetes mellitus (maturity-onset diabetes of the young; gene named MODY1). Although this mutation is predicted to delete 187 C-terminal amino acids of the HNF4alpha protein the molecular mechanism by which it causes diabetes is unknown. To address this, we first studied the functional properties of the MODY1 mutant protein. We show that it has lost its transcriptional transactivation activity, fails to dimerize and bind DNA, implying that the MODY1 phenotype is because of a loss of HNF4alpha function. The effect of loss of function on HNF4alpha target gene expression was investigated further in embryonic stem cells, which are amenable to genetic manipulation and can be induced to form visceral endoderm. Because the visceral endoderm shares many properties with the liver and pancreatic beta-cells, including expression of genes for glucose transport and metabolism, it offers an ideal system to investigate HNF4-dependent gene regulation in glucose homeostasis. By exploiting this system we have identified several genes encoding components of the glucose-dependent insulin secretion pathway whose expression is dependent upon HNF4alpha. These include glucose transporter 2, and the glycolytic enzymes aldolase B and glyceraldehyde-3-phosphate dehydrogenase, and liver pyruvate kinase. In addition we have found that expression of the fatty acid binding proteins and cellular retinol binding protein also are down-regulated in the absence of HNF4alpha. These data provide direct evidence that HNF4alpha is critical for regulating glucose transport and glycolysis and in doing so is crucial for maintaining glucose homeostasis.

Analysis of the glucokinase gene in Mexican families displaying early-onset non-insulin-dependent diabetes mellitus including MODY families

Non-insulin-dependent diabetes mellitus (NIDDM) is the most common form of diabetes, affecting 5% of the general population. Genetic factors play an important role in the development of the disease. While in other populations NIDDM is usually diagnosed after the fifth decade of life, in Mexico a large proportion of patients develop the disease at an early age (between the third and the fourth decade). In Caucasian population, mutations in the glucokinase gene, the TCF1, and TCF14 genes, have been identified in a subgroup of early-onset NIDDM patients denominated MODY (maturity-onset diabetes of the young), which show an autosomal dominant pattern of inheritance. As a first step in the molecular characterization of Mexican families displaying early-onset NIDDM we searched for mutations in the glucokinase gene through SSCP analysis and/or direct sequencing in 26 individuals from 22 independent families, where at least four can be classified as MODY. No mutations were detected in the exons or the intron-exon boundaries of the gene in any of the screened individuals. The phenotype and clinical profile of some of the studied patients is compatible with that of patients carrying mutations in the TCF1 or TCF14 genes, while others may carry mutations in different loci. Through computer simulation analysis we identified at least four informative families which will be used for further linkage studies.

Genetics of complex disease: approaches, problems, and solutions

Complex or multifactorial diseases are defined as diseases that are ultimately determined by a number of genetic and environmental factors. Although there are many technologies and strategies that can be used to detect genetic factors influencing complex diseases, these technologies and strategies have inherent limitations. In fact, the very name "complex disease" suggests that the results from relevant studies will not be simple to decipher. Ultimately, both the detection and precise characterization of a factor's contribution to a complex disease are difficult undertakings, because the effect of any one factor may be obscured or confounded by other factors. However, the genetic dissection of complex diseases can be greatly facilitated by paying heed to two very basic distinctions. The first distinction is between complexity at the level of individuals and complexity at the level of populations. The second distinction is between the two sequentially pursued components of gene discovery paradigms: gene identification and gene effect characterization. Although genetic epidemiology, as a research field, is oriented to both components of gene discovery for complex diseases, it is suited to gene effect characterization at the population level more than anything else. This paper reviews the origins of the genetic basis of complex traits, as well as the problems plaguing genetic epidemiologic analysis strategies, with the hope of showing how greater attention to these distinctions, as well as a greater integration of relevant knowledge, can alleviate confusion and shape future investigations. In addition, a new discipline, "phenomics" or "phenometrics," could be initiated that would complement genomic research as presently performed.

Hepatocyte nuclear factor 3beta is involved in pancreatic beta-cell-specific transcription of the pdx-1 gene

The mammalian homeobox gene pdx-1 is expressed in pluripotent precursor cells in the dorsal and ventral pancreatic bud and duodenal endoderm, which will produce the pancreas and the rostral duodenum. In the adult, pdr-1 is expressed principally within insulin-secreting pancreatic islet beta cells and cells of the duodenal epithelium. Our objective in this study was to localize sequences within the mouse pdx-1 gene mediating selective expression within the islet. Studies of transgenic mice in which a genomic fragment of the mouse pdx-1 gene from kb -4.5 to +8.2 was used to drive a beta-galactosidase reporter showed that the control sequences sufficient for appropriate developmental and adult specific expression were contained within this region. Three nuclease-hypersensitive sites, located between bp -2560 and -1880 (site 1), bp -1330 and -800 (site 2), and bp -260 and +180 (site 3), were identified within the 5'-flanking region of the endogenous pdx-1 gene. Pancreatic beta-cell-specific expression was shown to be controlled by sequences within site 1 from an analysis of the expression pattern of various pdr-1-herpes simplex virus thymidine kinase promoter expression constructs in transfected beta-cell and non-beta-cell lines. Furthermore, we also established that this region was important in vivo by demonstrating that expression from a site 1-driven beta-galactosidase reporter construct was directed to islet beta-cells in transgenic mice. The activity of the site 1-driven constructs was reduced substantially in beta-cell lines by mutating a hepatocyte nuclear factor 3 (HNF3)-like site located between nucleotides -2007 and -1996. Gel shift analysis indicated that HNF3beta present in islet beta cells binds to this element. Immunohistochemical studies revealed that HNF3beta was present within the nuclei of almost all islet beta cells and subsets of pancreatic acinar cells. Together, these results suggest that HNF3beta, a key regulator of endodermal cell lineage development, plays an essential role in the cell-type-specific transcription of the pdx-1 gene in the pancreas.

Gluconeogenesis, glucose handling, and structural changes in livers of the adult offspring of rats partially deprived of protein during pregnancy and lactation

Maternal protein restriction is a model of fetal programming of adult glucose intolerance. Perfused livers of 48-h- starved adult offspring of rat dams fed 8% protein diets during pregnancy and lactation produced more glucose from 6 mM lactate than did control livers from rats whose dams were fed 20% protein. In control livers, a mean of 24% of the glucose formed from lactate in the periportal region of the lobule was taken up by the most distal perivenous cells; this distal perivenous uptake was greatly diminished in maternal low protein (MLP) livers, accounting for a major fraction of the increased glucose output of MLP livers. In control livers, the distal perivenous cells contained 40% of the total glucokinase of the liver; this perivenous concentration of glucokinase was greatly reduced in MLP livers. Intralobular distribution of phosphenolpyruvate carboxykinase was unaltered, though overall increased activity could have contributed to the elevated glucose output. Hepatic lobular volume in MLP livers was twice that in control livers, indicating that MLP livers had half the normal number of lobules. Fetal programming of adult glucose metabolism may operate partly through structural alterations and changes in glucokinase expression in the immediate perivenous region.

Hepatic function in a family with a nonsense mutation (R154X) in the hepatocyte nuclear factor-4alpha/MODY1 gene

Maturity-onset diabetes of the young (MODY) is a genetically heterogeneous monogenic disorder characterized by autosomal dominant inheritance, onset usually before 25 yr of age, and abnormal pancreatic beta-cell function. Mutations in the hepatocyte nuclear factor(HNF)-4alpha/MODY1, glucokinase/MODY2, and HNF-1alpha/MODY3 genes can cause this form of diabetes. In contrast to the glucokinase and HNF-1alpha genes, mutations in the HNF-4alpha gene are a relatively uncommon cause of MODY, and our understanding of the MODY1 form of diabetes is based on studies of only a single family, the R-W pedigree. Here we report the identification of a second family with MODY1 and the first in which there has been a detailed characterization of hepatic function. The affected members of this family, Dresden-11, have inherited a nonsense mutation, R154X, in the HNF-4alpha gene, and are predicted to have reduced levels of this transcription factor in the tissues in which it is expressed, including pancreatic islets, liver, kidney, and intestine. Subjects with the R154X mutation exhibited a diminished insulin secretory response to oral glucose. HNF-4alpha plays a central role in tissue-specific regulation of gene expression in the liver, including the control of synthesis of proteins involved in cholesterol and lipoprotein metabolism and the coagulation cascade. Subjects with the R154X mutation, however, showed no abnormalities in lipid metabolism or coagulation except for a paradoxical 3.3-fold increase in serum lipoprotein(a) levels, nor was there any evidence of renal dysfunction in these subjects. The results suggest that MODY1 is primarily a disorder of beta-cell function.

The genetics of human noninsulin-dependent (type 2) diabetes mellitus

Familial aggregation and concordance in monozygotic and dizygotic twins argue strongly for a genetic etiology to noninsulin-dependent diabetes (NIDDM). Nonetheless, studies of pathways implicated by the known physiology have failed to identify gene defects that can explain the genetic susceptibility. In contrast, studies of early onset dominant diabetes have revealed three major loci resulting in diminished insulin secretion. Recently, studies have taken a new approach to map the genes causing typical NIDDM using large numbers of families or sibling pairs. The first reports of these studies have suggested possible loci on chromosomes 1, 2 and 12, but no report has been confirmed. Other studies have examined the quantitative defects that may be precursors of clinical NIDDM such as hyperinsulinemia, hyperglycemia, insulin response to glucose and obesity. These studies have suggested additional loci that may contribute to NIDDM susceptibility, but the genes responsible for most of these loci remain unknown. Studies of NIDDM susceptibility and the role of obesity genes in that susceptibility have entered an exciting new phase, but the challenges of complex disease genetics in humans will have to be conquered to translate this research into preventive or therapeutic benefits.

Transcriptional synergy between LIM-homeodomain proteins and basic helix-loop-helix proteins: the LIM2 domain determines specificity

LIM-homeodomain proteins direct cellular differentiation by activating transcription of cell-type-specific genes, but this activation requires cooperation with other nuclear factors. The LIM-homeodomain protein Lmx1 cooperates with the basic helix-loop-helix (bHLH) protein E47/Pan-1 to activate the insulin promoter in transfected fibroblasts. In this study, we show that two proteins originally called Lmx1 are the closely related products of two distinct vertebrate genes, Lmx1.1 and Lmx1.2. We have used yeast genetic systems to delineate the functional domains of the Lmx1 proteins and to characterize the physical interactions between Lmx1 proteins and E47/Pan-1 that produce synergistic transcriptional activation. The LIM domains of the Lmx1 proteins, and particularly the second LIM domain, mediate both specific physical interactions and transcriptional synergy with E47/Pan-1. The LIM domains of the LIM-homeodomain protein Isl-1, which cannot mediate transcriptional synergy with E47/Pan-1, do not interact with E47/Pan-1. In vitro studies demonstrate that the Lmx1.1 LIM2 domain interacts specifically with the bHLH domain of E47/Pan-1. These studies provide the basis for a model of the assembly of LIM-homeodomain-containing complexes on DNA elements that direct cell-type-restricted transcription in differentiated tissues.

Genetic analysis reveals that PAX6 is required for normal transcription of pancreatic hormone genes and islet development

We present genetic and biochemical evidence that PAX6 is a key regulator of pancreatic islet hormone gene transcription and is required for normal islet development. In embryos homozygous for a mutant allele of the Pax6 gene, Small eye (Sey(Neu)), the numbers of all four types of endocrine cells in the pancreas are decreased significantly, and islet morphology is abnormal. In the remaining islet cells, hormone production, particularly glucagon production, is markedly reduced because of decreased gene transcription. These effects appear to result from a lack of PAX6 protein in the mutant embryos. Biochemical studies identify wild-type PAX6 protein as the transcription factor that binds to a common element in the glucagon, insulin, and somatostatin promoters, and show that PAX6 transactivates the glucagon and insulin promoters.

Patterning the expression of a tissue-specific transcription factor in embryogenesis: HNF1 alpha gene activation during Xenopus development

Tissue-specific transcription factors play an essential role in establishing cell identity during development. We review our knowledge of the molecular events involved in the activation of the gene encoding the tissue-specific transcription factor HNF1 alpha (LFB1). The available data suggest that the maternal factors OZ-1, HNF4 alpha and HNF4 beta act as initial activators of the HNF1 alpha promoter. We present evidence suggesting that the mesoderm-inducing factor activin A plays a critical role by acting through the HNF4 binding site of the HNF1 alpha promoter. The activity of this embryonic morphogen seems to form a gradient opposing the distribution of the maternal HNF4 proteins that are concentrated at the animal pole of the egg. After zygotic gene transcription the HNF1 alpha-related transcription factor HNF1 beta accumulates faster than HNF1 alpha itself and thus is likely to contribute to the activation of the HNF1 alpha transcription via the HNF1 binding site. The cofactor of the HNF1 proteins (DCoH) is present throughout development and thus cannot limit the activation potential of HNF1 alpha in early development. Our results provide a detailed description of setting up the expression pattern of a tissue-specific transcription factor during embryogenesis.

A multicomponent insulin response sequence mediates a strong repression of mouse glucose-6-phosphatase gene transcription by insulin

Glucose-6-phosphatase (G6Pase) catalyzes the final step in the gluconeogenic and glycogenolytic pathways. The transcription of the gene encoding the catalytic subunit of G6Pase is stimulated by glucocorticoids, whereas insulin strongly inhibits both basal G6Pase gene transcription and the stimulatory effect of glucocorticoids. To identify the insulin response sequence (IRS) in the G6Pase promoter through which insulin mediates its action, we have analyzed the effect of insulin on the basal expression of mouse G6Pase-chloramphenicol acetyltransferase (CAT) fusion genes transiently expressed in hepatoma cells. Deletion of the G6Pase promoter sequence between -271 and -199 partially reduces the inhibitory effect of insulin, whereas deletion of additional sequence between -198 and -159 completely abolishes the insulin response. The presence of this multicomponent IRS may explain why insulin potently inhibits basal G6Pase-CAT expression. The G6Pase promoter region between -198 and -159 contains an IRS, since it can confer an inhibitory effect of insulin on the expression of a heterologous fusion gene. This region contains three copies of the T(G/A)TTTTG sequence, which is the core motif of the phosphoenolpyruvate carboxykinase (PEPCK) gene IRS. This suggests that a coordinate increase in both G6Pase and PEPCK gene transcription is likely to contribute to the increased hepatic glucose production characteristic of patients with non-insulin-dependent diabetes mellitus.

Homeodomain protein IDX-1: a master regulator of pancreas development and insulin gene expression

The homeodomain protein IDX-1 appears to be a "master regulator" of pancreas development and beta-cell differentiation and function. In murine gene inactivation models and in a human subject with a homozygous mutation of the IDX-1 gene, the pancreas fails to develop. In the adult endocrine pancreas, IDX-1 is primarily expressed in beta cells, where it is a key factor in the upregulation of insulin gene transcription and appears to have a role in the regulation of the somatostatin, glucokinase, glucose transporter-2, and islet amyloid polypeptide genes. Recent studies also suggest a role for IDX-1 in the neogenesis and proliferation of beta cells. The observed functions of IDX-1 and its downregulation in parallel with insulin in glucose-toxicity models implicate IDX-1 as a potential factor contributing to the pathogenesis of diabetes mellitus. Future directions include the use of conditional gene inactivation to determine more precisely the role of IDX-1 throughout endocrine pancreas differentiation and the exploration of IDX-1 as a potential target for gene therapy of diabetes mellitus.

Genetic modifiers of Leprfa associated with variability in insulin production and susceptibility to NIDDM

In an attempt to identify the genetic basis for susceptibility to non-insulin-dependent diabetes mellitus within the context of obesity, we generated 401 genetically obese Leprfa/Leprfa F2 WKY13M intercross rats that demonstrated wide variation in multiple phenotypic measures related to diabetes, including plasma glucose concentration, percentage of glycosylated hemoglobin, plasma insulin concentration, and pancreatic islet morphology. Using selective genotyping genome scanning approaches, we have identified three quantitative trait loci (QTLs) on Chr. 1 (LOD 7.1 for pancreatic morpholology), Chr. 12 (LOD 5.1 for body mass index and LOD 3.4 for plasma glucose concentration), and Chr. 16 (P < 0.001 for genotype effect on plasma glucose concentration). The obese F2 progeny demonstrated sexual dimorphism for these traits, with increased diabetes susceptibility in the males appearing at approximately 6 weeks of age, as sexual maturation occurred. For each of the QTLs, the linked phenotypes demonstrated sexual dimorphism (more severe affection in males). The QTL on Chr. 1 maps to a region vicinal to that previously linked to adiposity in studies of diabetes susceptibility in the nonobese Goto-Kakizaki rat, which is genetically closely related to the Wistar counterstrain we employed. Several candidate genes, including tubby (tub), multigenic obesity 1 (Mob1), adult obesity and diabetes (Ad), and insulin-like growth factor-2 (Igf2), map to murine regions homologous to the QTL region identified on rat Chr. 1.

Extrahepatic expression of NAD(P)H:menadione oxidoreductase, UDP glucuronosyltransferase-1A6, microsomal aldehyde dehydrogenase, and hepatic nuclear factor-1 alpha mRNAs in ch/ch and 14CoS/14CoS mice

Oxidative stress-induced gene expression in liver of the untreated newborn c14CoS/c14CoS mouse, as compared with that in the cch/cch wild-type mouse, appears to be caused by homozygous loss of the fumarylacetoacetate hydrolase (Fah) gene on Chr 7 and absence of the FAH enzyme, which leads to increased levels of endogenous reactive oxygenated metabolites (ROMs) formed in the tyrosine degradative pathway. In these mice almost all studies to date have been carried out in liver. We have examined the extrahepatic expression of four genes. Two genes are members of the [Ah] battery and induced by ROM-mediated oxidative stress: NAD(P)H:menadione oxidoreductase (Nmo1) and UDP glucuronosyltransferase-1A6 (Ugt1a6). The other two genes are decreased in the livers of 14CoS/ 14CoS mice as compared with that in ch/ch mice: microsomal aldehyde dehydrogenase (Ahd3) and hepatocyte-specific nuclear factor-1 alpha HNF-1 alpha (Hnf1 alpha). In liver plus nine extrahepatic tissues of untreated newborn 14CoS/14CoS mutant and ch/ch wild-type mice, we compared NMO1, UGT1A6, AHD3 and HNF-1 alpha mRNA levels. Our results show a wide variation in extrahepatic tissue-specific expression of all four transcripts and indicate that numerous differences exist in the extrahepatic expression of these genes between 14CoS/14CoS and ch/ch mice.

Characterization of the MODY3 phenotype. Early-onset diabetes caused by an insulin secretion defect

Maturity-onset diabetes of the young (MODY) type 3 is a dominantly inherited form of diabetes, which is often misdiagnosed as non-insulin-dependent diabetes mellitus (NIDDM) or insulin-dependent diabetes mellitus (IDDM). Phenotypic analysis of members from four large Finnish MODY3 kindreds (linked to chromosome 12q with a maximum lod score of 15) revealed a severe impairment in insulin secretion, which was present also in those normoglycemic family members who had inherited the MODY3 gene. In contrast to patients with NIDDM, MODY3 patients did not show any features of the insulin resistance syndrome. They could be discriminated from patients with IDDM by lack of glutamic acid decarboxylase antibodies (GAD-Ab). Taken together with our recent findings of linkage between this region on chromosome 12 and an insulin-deficient form of NIDDM (NIDDM2), the data suggest that mutations at the MODY3/NIDDM2 gene(s) result in a reduced insulin secretory response, that subsequently progresses to diabetes and underlines the importance of subphenotypic classification in studies of diabetes.

Mutations in the hepatocyte nuclear factor-4alpha gene in maturity-onset diabetes of the young (MODY1)

The disease maturity-onset diabetes of the young (MODY) is a genetically heterogeneous monogenic form of non-insulin-dependent (type 2) diabetes mellitus (NIDDM), characterized by early onset, usually before 25 years of age and often in adolescence or childhood, and by autosomal dominant inheritance. It has been estimated that 2-5% of patients with NIDDM may have this form of diabetes mellitus. Clinical studies have shown that prediabetic MODY subjects have normal insulin sensitivity but suffer from a defect in glucose-stimulated insulin secretion, suggesting that pancreatic beta-cell dysfunction rather than insulin resistance is the primary defect in this disorder. Linkage studies have localized the genes that are mutated in MODY on human chromosomes 20 (MODY1), 7 (MODY2) and 12 (MODY3), with MODY2 and MODY3 being allelic with the genes encoding glucokinase, a key regulator of insulin secretion, and hepatocyte nuclear factor-1alpha (HNF-1alpha), a transcription factor involved in tissue-specific regulation of liver genes but also expressed in pancreatic islets, insulinoma cells and other tissues. Here we show that MODY1 is the gene encoding HNF-4alpha (gene symbol, TCF14), a member of the steroid/thyroid hormone receptor superfamily and an upstream regulator of HNF-1alpha expression.