The ATP-sensitive K
(K
) channel controls blood glucose levels by coupling glucose metabolism to insulin secretion in pancreatic β-cells. E23K, a common polymorphism in the pore-forming K
channel ...subunit (
) gene, has been linked to increased risk of type 2 diabetes. Understanding the risk-allele-specific pathogenesis has the potential to improve personalized diabetes treatment, but the underlying mechanism has remained elusive. Using a genetically engineered mouse model, we now show that the K23 variant impairs glucose-induced insulin secretion and increases diabetes risk when combined with a high-fat diet (HFD) and obesity. K
-channels in β-cells with two K23 risk alleles (KK) showed decreased ATP inhibition, and the threshold for glucose-stimulated insulin secretion from KK islets was increased. Consequently, the insulin response to glucose and glycemic control was impaired in KK mice fed a standard diet. On an HFD, the effects of the KK genotype were exacerbated, accelerating diet-induced diabetes progression and causing β-cell failure. We conclude that the K23 variant increases diabetes risk by impairing insulin secretion at threshold glucose levels, thus accelerating loss of β-cell function in the early stages of diabetes progression.
Mutations in transcription factors often exhibit pleiotropic effects related to their complex expression patterns and multiple regulatory targets. One such mutation in the zinc finger homeobox 3 ...(ZFHX3) transcription factor, short circuit (Sci, Zfhx3Sci/+), is associated with significant circadian deficits in mice. However, given evidence of its retinal expression, we set out to establish the effects of the mutation on retinal function using molecular, cellular, behavioral and electrophysiological measures. Immunohistochemistry confirms the expression of ZFHX3 in multiple retinal cell types, including GABAergic amacrine cells and retinal ganglion cells including intrinsically photosensitive retinal ganglion cells (ipRGCs). Zfhx3Sci/+mutants display reduced light responsiveness in locomotor activity and circadian entrainment, relatively normal electroretinogram and optomotor responses but exhibit an unexpected pupillary reflex phenotype with markedly increased sensitivity. Furthermore, multiple electrode array recordings of Zfhx3Sci/+retina show an increased sensitivity of ipRGC light responses.
Two bottlenecks impeding the genetic analysis of complex traits in rodents are access to mapping populations able to deliver gene-level mapping resolution and the need for population-specific ...genotyping arrays and haplotype reference panels. Here we combine low-coverage (0.15×) sequencing with a new method to impute the ancestral haplotype space in 1,887 commercially available outbred mice. We mapped 156 unique quantitative trait loci for 92 phenotypes at a 5% false discovery rate. Gene-level mapping resolution was achieved at about one-fifth of the loci, implicating Unc13c and Pgc1a at loci for the quality of sleep, Adarb2 for home cage activity, Rtkn2 for intensity of reaction to startle, Bmp2 for wound healing, Il15 and Id2 for several T cell measures and Prkca for bone mineral content. These findings have implications for diverse areas of mammalian biology and demonstrate how genome-wide association studies can be extended via low-coverage sequencing to species with highly recombinant outbred populations.
A mouse mutant identified during a recessive N-ethyl-N-nitrosourea (ENU) mutagenesis screen exhibited ocular hemorrhaging resulting in a blood-filled orbit, and hence was named "redeye." We aimed to ...identify the causal mutation in redeye, and evaluate it as a model for diabetic retinopathy (DR).
The causative gene mutation in redeye was identified by haplotype mapping followed by exome sequencing. Glucose tolerance tests, detailed histologic and immunofluorescence analyses, and vascular permeability assays were performed to determine the affect of redeye on glucose metabolism, pericyte recruitment, and the development of the retinal vasculature and blood-retinal barrier (BRB).
A mutation was identified in the Pdgfrb gene at position +2 of intron 6. We show that this change causes partial loss of normal splicing resulting in a frameshift and premature termination, and, therefore, a substantial reduction in normal Pdgfrb transcript. The animals exhibit defective pericyte recruitment restricted to the central nervous system (CNS) causing basement membrane and vascular patterning defects, impaired vascular permeability, and aberrant BRB development, resulting in vascular leakage and retinal ganglion cell apoptosis. Despite exhibiting classic features of diabetic retinopathy, redeye glucose tolerance is normal.
The Pdgfrb(redeye/redeye) mice exhibit all of the features of nonproliferative DR, including retinal neurodegeneration. In addition, the perinatal onset of the CNS-specific vascular phenotype negates the need to age animals or manage diabetic complications in other organs. Therefore, they are a more useful model for diseases involving pericyte deficiencies, such as DR, than those currently being used.
We identified a dominant missense mutation in the SCN transcription factor Zfhx3, termed short circuit (Zfhx3Sci), which accelerates circadian locomotor rhythms in mice. ZFHX3 regulates transcription ...via direct interaction with predicted AT motifs in target genes. The mutant protein has a decreased ability to activate consensus AT motifs in vitro. Using RNA sequencing, we found minimal effects on core clock genes in Zfhx3Sci/+ SCN, whereas the expression of neuropeptides critical for SCN intercellular signaling was significantly disturbed. Moreover, mutant ZFHX3 had a decreased ability to activate AT motifs in the promoters of these neuropeptide genes. Lentiviral transduction of SCN slices showed that the ZFHX3-mediated activation of AT motifs is circadian, with decreased amplitude and robustness of these oscillations in Zfhx3Sci/+ SCN slices. In conclusion, by cloning Zfhx3Sci, we have uncovered a circadian transcriptional axis that determines the period and robustness of behavioral and SCN molecular rhythms.
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•Zfhx3 missense mutation underlies the short circuit (Zfhx3Sci) circadian phenotype•Zfhx3Sci reduces the ability of ZFHX3 to activate transcription via AT motifs•Zfhx3Sci phenotype is associated with decreased activation of AT motif in neuropeptide promoters•Circadian activation in SCN reveals AT motif as a new clock-regulated transcriptional axis
A transcription factor expressed in discrete adult hypothalamic nuclei, including the suprachiasmatic nucleus, regulates circadian locomotor rhythms in vivo through the expression of distinct neuropeptidergic genes to ensure robust synchronous oscillations and circadian rhythms.
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