Nr2e3-directed transcriptional regulation of genes involved in photoreceptor development and cell-type specific phototransduction

The retinal transcription factor Nr2e3 plays a key role in photoreceptor development and function. In this study we examine gene expression in the retina of Nr2e3(rd7/rd7) mutants with respect to wild-type control mice, to identify genes that are misregulated and hence potentially function in the Nr2e3 transcriptional network. Quantitative candidate gene real time PCR and subtractive hybridization approaches were used to identify transcripts that were misregulated in Nr2e3(rd7/rd7) mice. Chromatin immunoprecipitation assays were then used to determine which of the misregulated transcripts were direct targets of NR2E3. We identified 24 potential targets of NR2E3. In the developing retina, NR2E3 targets transcription factors such as Ror1, Rorg, and the nuclear hormone receptors Nr1d1 and Nr2c1. In the mature retina NR2E3 targets several genes including the rod specific gene Gnb1 and cone specific genes blue opsin, and two of the cone transducin subunits, Gnat2 and Gnb3. In addition, we identified 5 novel transcripts that are targeted by NR2E3. While mislocalization of proteins between rods and cones was not observed, we did observe diminished concentration of GNB1 protein in adult Nr2e3(rd7/rd7) retinas. These studies identified novel transcriptional pathways that are potentially targeted by Nr2e3 in the retina and specifically demonstrate a novel role for NR2E3 in regulating genes involved in phototransduction.

A mouse model for Meckel syndrome type 3

Meckel-Gruber syndrome type 3 (MKS3; OMIM 607361) is a severe autosomal recessive disorder characterized by bilateral polycystic kidney disease. Other malformations associated with MKS3 include cystic changes in the liver, polydactyly, and brain abnormalities (occipital encephalocele, hydrocephalus, and Dandy Walker-type cerebellar anomalies). The disorder is hypothesized to be caused by defects in primary cilia. In humans, the underlying mutated gene, TMEM67, encodes transmembrane protein 67, also called meckelin (OMIM 609884), which is an integral protein of the renal epithelial cell and membrane of the primary cilium. Here, we describe a spontaneous deletion of the mouse ortholog, Tmem67, which results in polycystic kidney disease and death by 3 wk after birth. Hydrocephalus also occurs in some mutants. We verified the mutated gene by transgenic rescue and characterized the phenotype with microcomputed tomography, histology, scanning electron microscopy, and immunohistochemistry. This mutant provides a mouse model for MKS3 and adds to the growing set of mammalian models essential for studying the role of the primary cilium in kidney function.

New mouse models for recessive retinitis pigmentosa caused by mutations in the Pde6a gene

The heterotetrameric phosphodiesterase (PDE) 6 complex, made up of alpha, beta and two gamma subunits, regulates intracellular cGMP levels by hydrolyzing cGMP in response to light activation of G protein coupled receptors in cones and rods, making it an essential component of the visual phototransduction cascade [Zhang, X. and Cote, R.H. (2005) cGMP signaling in vertebrate retinal photoreceptor cells. Front. Biosci., 10, 1191-1204.]. Using a genetic positional candidate cloning strategy, we have identified missense mutations within the catalytic domain of the Pde6a gene in two mouse models from an ethyl nitrosourea chemical mutagenesis screen. In these first small rodent models of PDE6A, significantly different biochemical outcomes and rates of degeneration of murine photoreceptor cells were observed, indicating allelic variation and previously unrecognized structure-function relationships. In addition, these new models reveal that the mutations not only affect the function of the PDE6A protein itself, but also the level of PDE6B within the retina. Finally, we show that the variation of the disease phenotype by background modifier genes may be dependent upon the particular disease allele present.

Allelic variance between GRM6 mutants, Grm6nob3 and Grm6nob4 results in differences in retinal ganglion cell visual responses

An electroretinogram (ERG) screen identified a mouse with a normal a-wave but lacking a b-wave, and as such it was designated no b-wave3 (nob3). The nob3 phenotype mapped to chromosome 11 in a region containing the metabotropic glutamate receptor 6 gene (Grm6). Sequence analyses of cDNA identified a splicing error in Grm6, introducing an insertion and an early stop codon into the mRNA of affected mice (designated Grm6(nob3)). Immunohistochemistry of the Grm6(nob3) retina showed that GRM6 was absent. The ERG and visual behaviour abnormalities of Grm6(nob3) mice are similar to Grm6(nob4) animals, and similar deficits were seen in compound heterozygotes (Grm6(nob4/nob3)), indicating that Grm6(nob3) is allelic to Grm6(nob4). Visual responses of Grm6(nob3) retinal ganglion cells (RGCs) to light onset were abnormal. Grm6(nob3) ON RGCs were rarely recorded, but when they were, had ill-defined receptive field (RF) centres and delayed onset latencies. When Grm6(nob3) OFF-centre RGC responses were evoked by full-field stimulation, significantly fewer converted that response to OFF/ON compared to Grm6(nob4) RGCs. Grm6(nob4/nob3) RGC responses verified the conclusion that the two mutants are allelic. We propose that Grm6(nob3) is a new model of human autosomal recessive congenital stationary night blindness. However, an allelic difference between Grm6(nob3) and Grm6(nob4) creates a disparity in inner retinal processing. Because the localization of GRM6 is limited to bipolar cells in the On pathway, the observed difference between RGCs in these mutants is likely to arise from differences in their inputs.

Regulation of Alström syndrome gene expression during adipogenesis and its relationship with fat cell insulin sensitivity

Alström syndrome (ALMS) is an autosomal recessive genetic disease with characteristic phenotypical features including multi-organ fibrosis, insulin resistance, obesity and type 2 diabetes. ALMS1, a ubiquitously expressed gene mutated in ALMS patients, gives rise to a protein of unknown function localized to basal bodies of ciliated cells and centrosomes. Together with Bardet-Biedl syndrome, ALMS is a member of genetic ciliopathies, but the link between cilia/centrosome deficits and metabolic abnormalities remains to be determined. In this study for the first time we quantified Alms1 expression in a cellular model of adipogenesis during the differentiation of 3T3-L1 cells. An early decrease in Alms1 mRNA was observed during preadipocyte to adipocyte conversion. However, acute treatment of preadipocytes with the adipogenic factors did not result in significant change of Alms1 expression. In addition, to study the possible relationship between Alms1 and the degree of fat cell insulin sensitivity, as assessed with an insulin-dependent 2-[1-3H]-deoxyglucose uptake assay, we induced either a reduction or an increase in 3T3-L1 adipocytes insulin sensitivity by a chronic treatment with insulin or rosiglitazone respectively. In all these conditions Alms1 expression remained unchanged. In conclusion, our results show that Alms1 is expressed at higher level in preadipocytes suggesting a role of the gene in the early phase of adipogenesis. Moreover, changes in fat cell insulin sensitivity do not imply any effect on Alms1 expression.

A novel dwarfism with gonadal dysfunction due to loss-of-function allele of the collagen receptor gene, Ddr2, in the mouse

Smallie (slie), a spontaneous, autosomal-recessive mutation causes dwarfing and infertility in mice. The purpose of this study was to determine and characterize the underlying molecular genetic basis for its phenotype. The slie locus was mapped to chromosome 1, and fine-structure mapping narrowed the slie allele within 2 Mb between genetic markers D1Mit36 and Mpz. To pinpoint the underlying mutation quantitative real-time PCR was used to measure the relative expression levels for the genes residing within this region. Expression of one gene, Ddr2, which encodes discoidin domain receptor 2 (DDR2), was absent in slie homozygote mice. Genomic sequencing analysis detected a 150-kb deletion that extended into the Ddr2 gene transcript. Detailed phenotype analysis revealed that gonadal dysregulation underlies infertility in slie mice because all females were anovulatory and most adult males lacked spermatogenesis. The pituitary gland of prepubertal slie mice was smaller than in wild-type mice. The basal levels and gene expression for pituitary and hypothalamic hormones, and gene expression for hypothalamic-releasing hormones, were not significantly different between slie and wild-type mice. Circulating levels of IGF-1 did not differ in slie mice despite lower Igf-1 mRNA expression in the liver. After exogenous gonadotropin administration, the levels of secreted steroid hormones in both male and female adult slie mice were blunted compared to adult wild-type, but was similar to prepubertal wild-type mice. Taken together, our results indicate that the absence of DDR2 leads to growth retardation and gonadal dysfunction due to peripheral defects in hormonal-responsive pathways in slie mice.

Full-field electroretinography and marked variability in clinical phenotype of Alström syndrome

OBJECTIVES

To characterize the clinical phenotype and to study the course of disease in patients with Alström syndrome, with an emphasis on retinal function assessed with full-field electroretinography (ERG).

METHODS

Three age- and sex-matched patients with Alström syndrome were selected from our retinitis pigmentosa register for repeated ophthalmologic examinations that included tests for color vision and visual fields using Goldmann perimetry and for repeated assessment of full-field ERGs.

RESULTS

Electroretinography demonstrated cone-rod degeneration in all 3 patients. A concomitant impairment of color vision and visual fields was also observed as well as marked variation in retinal function and in disease severity.

CONCLUSIONS

Full-field ERGs confirmed that Alström syndrome is associated with a cone-rod type of retinal degeneration. In this study, we have shown a striking variability in retinal function and disease onset and severity, which has, to our knowledge, not been described previously in Alström syndrome.

Spectrum of ALMS1 variants and evaluation of genotype-phenotype correlations in Alström syndrome

Alström syndrome is a monogenic recessive disorder featuring an array of clinical manifestations, with systemic fibrosis and multiple organ involvement, including retinal degeneration, hearing loss, childhood obesity, diabetes mellitus, dilated cardiomyopathy (DCM), urological dysfunction, and pulmonary, hepatic, and renal failure. We evaluated a large cohort of patients with Alström syndrome for mutations in the ALMS1 gene. In total, 79 disease-causing variants were identified, of which 55 are novel mutations. The variants are primarily clustered in exons 8, 10, and 16, although we also identified novel mutations in exons 12 and 18. Most alleles were identified only once (45/79), but several were found recurrently. Founder effects are likely in families of English and Turkish descent. We also identified 66 SNPs and assessed the functional significance of these variants based on the conserved identity of the protein and the severity of the resulting amino acid substitution. A genotype-phenotype association study examining 18 phenotypic parameters in a subset of 58 patients found suggestive associations between disease-causing variants in exon 16 and the onset of retinal degeneration before the age of 1 year (P = 0.02), the occurrence of urological dysfunction (P = 0.02), of DCM (P = 0.03), and of diabetes (P = 0.03). A significant association was found between alterations in exon 8 and absent, mild, or delayed renal disease (P = 0.0007). This data may have implications for the understanding of the molecular mechanisms of ALMS1 and provides the basis for further investigation of how alternative splicing of ALMS1 contributes to the severity of the disease.

Molecular analysis and long-term clinical evaluation of three siblings with Alström syndrome

Alström syndrome is a rare, autosomal recessive disorder characterized by a wide spectrum of clinical features including early-onset retinal degeneration leading to blindness, sensorineural hearing loss, short stature, obesity, type 2 diabetes, hyperlipidemia and dilated cardiomyopathy. Renal, hepatic and pulmonary dysfunction may occur in the later phases of the disease. The three affected sisters, from a consanguineous Turkish family, with the characteristic features of Alström syndrome, were clinically diagnosed in 1987 and followed for 20 years. DNA sequence analysis of ALMS1, the causative gene in Alström syndrome, identified a novel homozygous disease-causing mutation, c.8164C>T, resulting in a premature termination codon in exon 10 in each of the three affected sisters. Furthermore, we describe the longitudinal disease progression in this family and report new clinical findings likely associated with Alström syndrome, such as pes planus and hyperthyroidism.

Alström syndrome

Alström Syndrome is an autosomal recessive, single gene disorder caused by mutations in ALMS1 (Chr 2p13), a novel gene of currently unknown molecular function. Alström Syndrome is multisystemic, with cone-rod retinal dystrophy leading to juvenile blindness, sensorineural hearing loss, obesity, insulin resistance with hyperinsulinemia, and type 2 diabetes mellitus. Very high incidences of additional disease phenotypes that may severely affect prognosis and survival include endocrine abnormalities, dilated cardiomyopathy, pulmonary fibrosis and restrictive lung disease, and progressive hepatic and renal failure. Other clinical features in some patients are hypertension, hypothyroidism, hyperlipidemia, hypogonadism, urological abnormalities, adult short stature, and bone-skeletal disturbances. Most patients demonstrate normal intelligence, although some reports indicate delayed psychomotor and intellectual development. The life span of patients with Alström Syndrome rarely exceeds 40 years. There is no specific therapy for Alström Syndrome, but early diagnosis and intervention can moderate the progression of the disease phenotypes and improve the longevity and quality of life for patients.

Effect of metformin and rosiglitazone in a prepubertal boy with Alström syndrome

Alström syndrome (AS) is an autosomal recessive disorder characterized by progressive pigmentary retinopathy, sensorineural hearing loss, fatty liver infiltration, obesity, insulin resistance and early-onset type 2 diabetes mellitus (DM2). Early onset of insulin resistance and DM2 are key components of this syndrome.

AIM

To study the effect of early initiation of the insulin sensitizer metformin combined with rosiglitazone in a patient with AS with impaired glucose tolerance.

PATIENT

An 8 year-old boy with AS presented with acanthosis nigricans and insulin resistance at the age of 6 years. He had progressive excessive weight gain from 9 months of age. By the age of 1 year he developed photosensitivity, blindness and nystagmus. At the age of 5.5 years, his body mass index (BMI) was above the 95th percentile. He developed impaired glucose tolerance at 6 years of age and treatment with metformin was initiated. After 8 months of treatment with metformin he developed DM2. The dose of metformin was increased, and rosiglitazone added.

METHODS

A 2-hour oral glucose tolerance test (OGTT) and a rapid intravenous glucose tolerance test (IVGTT) were performed before treatment was initiated, after treatment with metformin and at the end of 1 year of combination therapy with metformin and rosiglitazone to calculate quantitative insulin sensitivity check index (QUICKI) and acute insulin response (AIR). For mutation analysis, all exons and splice site sequences of the ALMS1 gene were amplified and sequenced.

RESULTS

Metformin treatment alone at the stage of impaired glucose tolerance did not prevent progression to DM2. However, metformin at a higher dose and in combination with rosiglitazone resulted in improvement of pancreatic beta-cell function, shown by markedly improved first-phase insulin response to glucose measured by AIR. The patient was found to have two heterozygous nonsense mutations in ALMS1, 8008 C-->T Ter, R2670X, and 11449 C-->T Ter, Q3817X. These alterations cause premature stops and result in a truncated ALMS1 protein.

CONCLUSION

We suggest that early initiation of combined therapy comprising a high dose of metformin plus rosiglitazone may be valuable in managing insulin resistance and DM2 in children with AS.

The transcription factor Nr2e3 functions in retinal progenitors to suppress cone cell generation

The transcription factor Nr2e3 is an essential component for development and specification of rod and cone photoreceptors; however, the mechanism through which it acts is not well understood. In this study, we use Nr2e3(rd7/rd7) mice that harbor a mutation in Nr2e3, to serve as a model for the human retinal disease Enhanced S Cone Syndrome. Our studies reveal that NR2E3 is expressed in late retinal progenitors and differentiating photoreceptors of the developing retina and localized to the cell bodies of mature rods and cones. In particular, we demonstrate that the abnormal increase in cone photoreceptors observed in Nr2e3(rd7/rd7) mice arise from ectopic mitotic progenitor cells that are present in the outer nuclear layer of the mature Nr2e3(rd7/rd7) retina. A prolonged phase of proliferation is observed followed by abnormal retinal lamination with fragmented and disorganized photoreceptor synapses that result in a progressive loss of rod and cone function. An extended and pronounced wave of apoptosis is also detected at P30 and temporally correlates with the phase of prolonged proliferation. Approximately twice as many apoptotic cells were detected compared to proliferating cells. This wave of apoptosis appears to affect both rod and cone cells and thus may account for the concurrent loss of rod and cone function. We further show that Nr2e3(rd7/rd7) cones do not express rod specific genes and Nr2e3(rd7/rd7) rods do not express cone specific genes. Our studies suggest that, based on its temporal and spatial expression, NR2E3 acts simultaneously in different cell types: in late mitotic progenitors, newly differentiating post mitotic cells, and mature rods and cones. In particular, this study reveals the function of NR2E3 in mitotic progenitors is to repress the cone generation program. NR2E3 is thus one of the few genes known to influence the competency of retinal progenitors while simultaneously directing the rod and cone differentiation.

Carbonic anhydrase related protein 8 mutation results in aberrant synaptic morphology and excitatory synaptic function in the cerebellum

Carbonic anhydrase related protein 8 (Car8) is known to be abundantly expressed in Purkinje cells (PCs), and its genetic mutation causes a motor coordination defect. To determine the underlying mechanism, we analyzed the mouse cerebellum carrying a Car8 mutation. Electrophysiological analysis showed that spontaneous excitatory transmission was largely diminished while paired pulse ratio at parallel fiber-PC synapses was comparable to wild-type, suggesting functional synapses have normal release probability but the number of functional synapses may be lower in mutants. Light microscopic study revealed an abnormal extension of climbing fibers to the distal PC dendrites. At the ultrastructural level, we found numerous PC spines not forming synapses primarily in distal dendrites and occasionally multiple spines contacting a single varicosity. These abnormalities of parallel fiber-PC synapses may underlie the functional defect in excitatory transmission. Thus, Car8 plays a critical role in synaptogenesis and/or maintenance of proper synaptic morphology and function in the cerebellum.

Multiple trait measurements in 43 inbred mouse strains capture the phenotypic diversity characteristic of human populations

The breadth of genetic and phenotypic variation among inbred strains is often underappreciated because assessments include only a limited number of strains. Evaluation of a larger collection of inbred strains provides not only a greater understanding of this variation but collectively mimics much of the variation observed in human populations. We used a high-throughput phenotyping protocol to measure females and males of 43 inbred strains for body composition (weight, fat, lean tissue mass, and bone mineral density), plasma triglycerides, high-density lipoprotein and total cholesterol, glucose, insulin, and leptin levels while mice consumed a high-fat, high-cholesterol diet. Mice were fed a chow diet until they were 6-8 wk old and then fed the high-fat diet for an additional 18 wk. As expected, broad phenotypic diversity was observed among these strains. Significant variation between the sexes was also observed for most traits measured. Additionally, the response to the high-fat diet differed considerably among many strains. By the testing of such a large set of inbred strains for many traits, multiple phenotypes can be considered simultaneously and thereby aid in the selection of certain inbred strains as models for complex human diseases. These data are publicly available in the web-accessible Mouse Phenome Database (http://www.jax.org/phenome), an effort established to promote systematic characterization of biochemical and behavioral phenotypes of commonly used and genetically diverse inbred mouse strains. Data generated by this effort builds on the value of inbred mouse strains as a powerful tool for biomedical research.

Characterization of the IGF system in 15 patients with Alström syndrome

BACKGROUND

Alström syndrome (ALMS) is a rare recessively inherited progressive disease (OMIM 203800). Among its diverse spectrum of clinical features are phenotypes associated with deficiencies of the GH/IGF-I axis, including short stature, obesity, insulin resistance, hypertriglyceridaemia and heart failure.

PATIENTS AND MEASUREMENTS

To characterize the IGF system in ALMS, we evaluated a subset of 15 young adults with ALMS for hepatic, renal and thyroid function. Glycaemic and hormone measurements such as insulin, GH, FSH, LH, testosterone and 17-beta-oestradiol were clinically assessed. In addition, we measured IGF-I, IGF-II, IGF binding-protein-3 (IGFBP-3) and acid labile subunit (ALS - the subunits that constitute the main somatomedin complex in the circulation), and IGFBP-1 and IGFBP-2 (known to influence the bioavailability of the IGFs).

RESULTS

A significantly lower height was observed in ALMS patients compared to age-matched controls. ALMS patients were clinically obese (by weight and body mass index (BMI) standards) and leptin levels correlated with BMI. Renal and hepatic dysfunction was implicated in some patients by increased values of blood urea nitrogen (BUN) and creatinine, and transaminases, respectively. One-third of the patients presented with fasting hyperglycaemia and 80% were hyperinsulinaemic. TSH was slightly increased in 20% of patients. Baseline FSH and LH in females were within the normal range, while half of the males had abnormally low testosterone values. Male patients with hypogonadism showed significantly lower testosterone, oestrogen and ALS levels. Baseline GH values were not found to be increased. ALS and IGFBP-1 were significantly reduced and IGFBP-2 was markedly increased in ALMS patients compared to age-matched controls. The IGFs and IGFBPs were not significantly different between males and females affected with ALMS. No significant association was observed between IGFs or IGFBPs levels and weight, height, BMI, glycaemia, hyperinsulinaemia and testosterone levels. However, we found a significant association of gamma-glutamyltransferase (GGT) with IGFBP-2. IGF-I levels were significantly associated with LH in female patients.

CONCLUSIONS

In summary, the reduction of ALS and the increase of IGFBP-2 points to a growth hormone deficiency (GHD) condition in ALMS. However, further tests, including GH dynamics, are needed to determine whether, or to what degree disturbances in the GH/IGF axis contribute to the relatively short stature.

Phenotypic characterization of polygenic type 2 diabetes in TALLYHO/JngJ mice

The TALLYHO/JngJ (TH) strain is a newly established, polygenic mouse model for type 2 diabetes (T2D) and obesity, and we have previously reported some key physiological features of this model after the overt onset of diabetes. In the present work, we conducted a comprehensive phenotypic characterization of TH in order to completely characterize this new and relevant model for human T2D and obesity. We monitored the development of obesity and diabetes starting at 4 weeks of age by measuring body weight, glucose tolerance, and plasma levels of insulin, glucose, and triglyceride. Additionally, histological alterations in the pancreas and glucose uptake and glucose transporter 4 (GLUT4) content in soleus muscle were also examined. Compared with age- and sex-matched C57BL/6J (B6) mice, both male and female TH mice were significantly heavier, hyperleptinemic, and hyperinsulinemic at 4 weeks of age, without glucose intolerance or hyperglycemia. TH mice maintained higher body weights throughout the study period of 16 weeks. The hyperinsulinemia in TH mice worsened with age, but to a lesser degree in females than in males. Both the male and the female TH mice had enlarged pancreatic islets. Male TH mice showed impaired glucose tolerance at 8 weeks that became more prominent at 16 weeks. Plasma glucose levels continuously increased with age in male TH mice resulting in frank diabetes, while female TH mice remained normoglycemic throughout the study. Impaired glucose tolerance and hyperglycemia in male TH mice were accompanied by impaired 2-deoxyglucose uptake in the soleus muscle at basal and insulin-stimulated states, but without any reduction in GLUT4 content. Interestingly, male TH mice exhibited a drastic elevation in plasma triglyceride levels in the pre-diabetic stage that was maintained throughout the study. These findings suggest that obesity and insulin resistance are an inherent part of the TH phenotype and glucose intolerance is evident preceding progression to overt diabetes in male TH mice.

Defective carbohydrate metabolism in mice homozygous for the tubby mutation

Tub is a member of a small gene family, the tubby-like proteins (TULPs), with predominant expression in neurons. Mice carrying a mutation in Tub develop retinal and cochlear degeneration as well as late-onset obesity with insulin resistance. During behavioral and metabolic testing, we found that homozygous C57BL/6J-Tub(tub) mice have a lower respiratory quotient than C57BL/6J controls before the onset of obesity, indicating that tubby homozygotes fail to activate carbohydrate metabolism and instead rely on fat metabolism for energy needs. In concordance with this, tubby mice show higher excretion of ketone bodies and accumulation of glycogen in the liver. Quantitation of liver mRNA levels shows that, during the transition from light to dark period, tubby mice fail to induce glucose-6-phosphate dehydrogenase (G6pdh), the rate-limiting enzyme in the pentose phosphate pathway that normally supplies NADPH for de novo fatty acid synthesis and glutathione reduction. Reduced G6PDH protein levels and enzymatic activity in tubby mice lead accordingly to lower levels of NADPH and reduced glutathione (GSH), respectively. mRNA levels for the lipolytic enzymes acetyl-CoA synthetase and carnitine palmitoyltransferase are increased during the dark cycle and decreased during the light period, and several citric acid cycle genes are dysregulated in tubby mice. Examination of hypothalamic gene expression showed high levels of preproorexin mRNA leading to accumulation of orexin peptide in the lateral hypothalamus. We hypothesize that abnormal hypothalamic orexin expression leads to changes in liver carbohydrate metabolism and may contribute to the moderate obesity observed in tubby mice.

Ocular abnormalities in Largemyd and Largevls mice, spontaneous models for muscle, eye, and brain diseases

Here we demonstrate previously unreported ocular defects in mice homozygous for a new allele of the Large gene, veils, and for Large(myd) mice. Clinically, vitreal fibroplasia and retinal vessel tortuosity and fluorescein leakage are observed. These vascular defects may be due to the extreme disorganization of the astrocytic template on which endothelial cells migrate in the retina. Abnormal electroretinograms recorded from Large(vls) or Large(myd) mice are accompanied by disorganization of the outer plexiform layer (OPL) with a dramatic reduction in the number of synaptic complexes. In both mutants, the internal limiting membrane (ILM) is disrupted with ectopic cells in the vitreous. Interestingly, while all components of the dystrophin glycoprotein complex are present at reduced levels in the OPL, they were absent in the ILM of affected mice. Finally, hypoglycosylation of alpha-dystroglycan previously implicated in muscle and brain defects is also observed in the retina and may contribute to the ocular abnormalities.

Novel leptin receptor mutation in NOD/LtJ mice suppresses type 1 diabetes progression: I. Pathophysiological analysis

A spontaneous single-base mutation in the leptin receptor of type 1 diabetes-prone NOD/LtJ mice (designated as Lepr(db-5J)) produced a glycine640valine transversion in the extracellular domain. All mutant mice became obese and hyperinsulinemic at weaning, with 70-80% developing early-onset hyperglycemia. However, these obese diabetic mice continued to gain weight without insulin therapy. Spontaneous diabetes remission was observed in all obese females and a subset of obese males. Insulitis was largely limited to islet perimeters, with intraislet insulitis infrequently observed. In 17 obese males (age 39 weeks), we observed phenotypic heterogeneity, including full remission from hyperglycemia (24%), intermediate hyperglycemia with elevated body weight (41%), and severe hyperglycemia and weight loss (35%). The remitting normoglycemic and intermediate hyperglycemic phenotypes were associated with extensive beta-cell hyperplasia. Unlike the extensive intraislet insulitis present in diabetic lean NOD/Lt mice, the severe obese diabetic phenotype was associated with islet atrophy without extensive intraislet insulitis. These results indicated that the manipulation of the leptin/leptin receptor axis may provide a novel means of downregulating autoimmunity in type 1 diabetes and confirmed a role for leptin as a mediator in the development of this disease in NOD mice.

Genetic modifiers interact with Cpe(fat) to affect body weight, adiposity, and hyperglycemia

Obesity and Type II diabetes are complex diseases in the human population. The existence of a large number of contributing loci and gene-gene as well as gene-environment interactions make it difficult to identify the disease genes underlying these complex traits. In mouse models of obesity and Type II diabetes such as the murine fat mutation, genetic crosses can be used to dissect the genetic complexity influencing the observed phenotypes. The underlying defect in the fat mutant is a Ser202Pro change in carboxypeptidase E (CPE), an enzyme responsible for the final proteolytic processing step of prohormone intermediates. On the HRS/J (HRS) inbred strain background, mice homozygous for the fat mutation exhibit early onset hyperinsulinemia followed by postpubertal moderate obesity without hyperglycemia. In contrast, on the C57BLKS/J (BKS) genetic background, fat/fat mice become severely obese, hyperinsulinemic, and hyperglycemic. Therefore, in the Cpe(fat) genetic model, the fat mutation is necessary but not sufficient for the development of obesity, Type II diabetes, and related metabolic disorders. To dissect the susceptibility loci responsible for modifying obesity- and diabetes-associated traits, we characterized, both genetically and phenotypically, fat/fat male progeny from a large intercross between BKS. HRS-fat/fat and HRS-+/+ mice. Four major loci were mapped, including a locus for body weight (body weight 1) on chromosome 14; a locus for hyperglycemia (fat-induced diabetes 1) on chromosome 19; a locus for hyperglycemia, hyperinsulinemia, and hypercholesterolemia (fat-induced diabetes 2) on chromosome 5; and a locus for adiposity and body weight (fat-induced adiposity 1) on chromosome 11. The identification of these interacting genetic determinants for obesity and Type II diabetes may allow better definition of the obesity/diabetes-related hormone signaling pathways and ultimately may provide new insights into the pathogenesis of these complex diseases.

Type 2 diabetes mouse model TallyHo carries an obesity gene on chromosome 6 that exaggerates dietary obesity

The TallyHo (TH) mouse strain is a polygenic model for Type 2 diabetes with obesity. Genetic analysis in backcross progeny from a cross between F1 [C57BL/6J (B6) x TH] and TH mice mapped a quantitative trait locus (QTL) named TH-associated body weight 2 (tabw2) to chromosome 6. The TH-derived allele is associated with increased body weight. As a first step to identify the molecular basis of this obesity QTL, we constructed a congenic line of mice on the B6 genetic background that carries a genomic region from TH mice containing tabw2. Congenic mice homozygous for tabw2 (B6.TH-tabw2/tabw2) fed a chow diet exhibited slightly, but significantly, higher body weight and body fat and plasma leptin levels compared with controls (B6.TH-+/+). This difference was exacerbated when the animals were maintained on a high-fat and high-sucrose (HFS) diet. The diet-induced obesity in tabw2 congenic mice is accompanied by hyperleptinemia, mild hyperinsulinemia, impaired glucose tolerance, and reduced glucose uptake in adipose tissue in response to insulin administration. Using F2 progeny fed a HFS diet from an intercross of B6.TH-tabw2/+ mice, we were able to refine the map position of the tabw2 obesity susceptibility locus to a 15-cM region (95% confidence interval) extending distally from the marker D6Mit102. In summary, tabw2 congenic mice are a new animal model for diet-induced obesity that will be valuable for the study of gene-diet interactions.

New Alström syndrome phenotypes based on the evaluation of 182 cases

BACKGROUND

Alström syndrome is a recessively inherited genetic disorder characterized by congenital retinal dystrophy that leads to blindness, hearing impairment, childhood obesity, insulin resistance, and type 2 diabetes mellitus. We provide new details on cardiologic, hepatic, gastrointestinal, urologic, pulmonary, and neurobehavioral phenotypes in Alström syndrome and describe the histopathologic findings in 5 individuals.

METHODS

We obtained data on 182 patients from clinical examinations, medical record reviews, standardized questionnaires, and personal interviews with physicians and parents.

RESULTS

Dilated cardiomyopathy occurred in 60% of patients. Age at onset was either during infancy, often before vision disturbances were noted, or in adolescence or adulthood. There is a risk of recurrence of infantile cardiomyopathy. Hyperinsulinemia (92%) developed in early childhood and progressed to type 2 diabetes mellitus in 82% of those older than 16 years. Hypertriglyceridemia (54%) precipitated pancreatitis in 8 patients. Urologic dysfunction and gastrointestinal disturbances occurred in 48% and 35% of patients, respectively. Fifty-three percent of patients had persistent pulmonary symptoms. Neurologic symptoms in 20% of patients included clonic tic and absence seizures. Developmental motor or language delays were observed in 46% of patients. Fibrotic infiltrations of multiple organs, that is, kidney, heart, liver, lung, urinary bladder, gonads, and pancreas, were observed.

CONCLUSIONS

The wide-ranging and complex spectrum of phenotypes reported herein broadens those previously described for Alström syndrome. These findings will aid physicians in making an early and accurate diagnosis and will help effect appropriate monitoring and treatment.

Searching QTL by gene expression: analysis of diabesity

Background

Recent developments in sequence databases provide the opportunity to relate the expression pattern of genes to their genomic position, thus creating a transcriptome map. Quantitative trait loci (QTL) are phenotypically-defined chromosomal regions that contribute to allelically variant biological traits, and by overlaying QTL on the transcriptome, the search for candidate genes becomes extremely focused.

Results

We used our novel data mining tool, ExQuest, to select genes within known diabesity QTL showing enriched expression in primary diabesity affected tissues. We then quantified transcripts in adipose, pancreas, and liver tissue from Tally Ho mice, a multigenic model for Type II diabetes (T2D), and from diabesity-resistant C57BL/6J controls. Analysis of the resulting quantitative PCR data using the Global Pattern Recognition analytical algorithm identified a number of genes whose expression is altered, and thus are novel candidates for diabesity QTL and/or pathways associated with diabesity.

Conclusion

Transcription-based data mining of genes in QTL-limited intervals followed by efficient quantitative PCR methods is an effective strategy for identifying genes that may contribute to complex pathophysiological processes.

Mouse genetic approaches to access pathways important in retinal function

The laboratory mouse is a premier research tool for understanding human biology and disease. With the availability of the first complete draft sequences of the mouse genome and ongoing large scale screens for new mouse mutations to serve as novel models, the usefulness of the mouse will only increase. The vision research field, in particular, which has identified many human diseases for which no models are yet available, will benefit from the newly developed tools in mouse molecular genetics.