Diabetes Insipidus in Mice with a Mutation in Aquaporin-2

Congenital nephrogenic diabetes insipidus (NDI) is a disease characterized by failure of the kidney to concentrate urine in response to vasopressin. Human kindreds with nephrogenic diabetes insipidus have been found to harbor mutations in the vasopressin receptor 2 (Avpr2) gene or the vasopressin-sensitive water channel aquaporin-2 (Aqp2) gene. Development of a treatment is rendered difficult due to the lack of a viable animal model. Through forward genetic screening of ethylnitrosourea-mutagenized mice, we report the identification and characterization of a mouse model of NDI, with an F204V mutation in the Aqp2 gene. Unlike previously attempted murine models of NDI, our mice survive to adulthood and more exactly recapitulate the human disorder. Previous in vitro experiments using renal cell lines suggest recessive Aqp2 mutations result in improper trafficking of the mutant water pore. Using these animals, we have directly proven this hypothesis of improper AQP2 translocation as the molecular defect in nephrogenic diabetes insipidus in the intact organism. Additionally, using a renal cell line we show that the mutated protein, AQP2-F204V, is retained in the endoplasmic reticulum and that this abnormal localization can be rescued by wild-type protein. This novel mouse model allows for further mechanistic studies as well as testing of pharmacological and gene therapies for NDI

Temperature Regulates Transcription in the Zebrafish Circadian Clock

It has been well-documented that temperature influences key aspects of the circadian clock. Temperature cycles entrain the clock, while the period length of the circadian cycle is adjusted so that it remains relatively constant over a wide range of temperatures (temperature compensation). In vertebrates, the molecular basis of these properties is poorly understood. Here, using the zebrafish as an ectothermic model, we demonstrate first that in the absence of light, exposure of embryos and primary cell lines to temperature cycles entrains circadian rhythms of clock gene expression. Temperature steps drive changes in the basal expression of certain clock genes in a gene-specific manner, a mechanism potentially contributing to entrainment. In the case of the per4 gene, while E-box promoter elements mediate circadian clock regulation, they do not direct the temperature-driven changes in transcription. Second, by studying E-box-regulated transcription as a reporter of the core clock mechanism, we reveal that the zebrafish clock is temperature-compensated. In addition, temperature strongly influences the amplitude of circadian transcriptional rhythms during and following entrainment by light–dark cycles, a property that could confer temperature compensation. Finally, we show temperature-dependent changes in the expression levels, phosphorylation, and function of the clock protein, CLK. This suggests a mechanism that could account for changes in the amplitude of the E-box-directed rhythm. Together, our results imply that several key transcriptional regulatory elements at the core of the zebrafish clock respond to temperature

Negative Regulators of Insulin Signaling Revealed in a Genome-Wide Functional Screen

Type 2 diabetes develops due to a combination of insulin resistance and β-cell failure and current therapeutics aim at both of these underlying causes. Several negative regulators of insulin signaling are known and are the subject of drug discovery efforts. We sought to identify novel contributors to insulin resistance and hence potentially novel targets for therapeutic intervention.An arrayed cDNA library encoding 18,441 human transcripts was screened for inhibitors of insulin signaling and revealed known inhibitors and numerous potential novel regulators. The novel hits included proteins of various functional classes such as kinases, phosphatases, transcription factors, and GTPase associated proteins. A series of secondary assays confirmed the relevance of the primary screen hits to insulin signaling and provided further insight into their modes of action.Among the novel hits was PALD (KIAA1274, paladin), a previously uncharacterized protein that when overexpressed led to inhibition of insulin's ability to down regulate a FOXO1A-driven reporter gene, reduced upstream insulin-stimulated AKT phosphorylation, and decreased insulin receptor (IR) abundance. Conversely, knockdown of PALD gene expression resulted in increased IR abundance, enhanced insulin-stimulated AKT phosphorylation, and an improvement in insulin's ability to suppress FOXO1A-driven reporter gene activity. The present data demonstrate that the application of arrayed genome-wide screening technologies to insulin signaling is fruitful and is likely to reveal novel drug targets for insulin resistance and the metabolic syndrome

A Role for Alström Syndrome Protein, Alms1, in Kidney Ciliogenesis and Cellular Quiescence

Premature truncation alleles in the ALMS1 gene are a frequent cause of human Alström syndrome. Alström syndrome is a rare disorder characterized by early obesity and sensory impairment, symptoms shared with other genetic diseases affecting proteins of the primary cilium. ALMS1 localizes to centrosomes and ciliary basal bodies, but truncation mutations in Alms1/ALMS1 do not preclude formation of cilia. Here, we show that in vitro knockdown of Alms1 in mice causes stunted cilia on kidney epithelial cells and prevents these cells from increasing calcium influx in response to mechanical stimuli. The stunted-cilium phenotype can be rescued with a 5′ fragment of the Alms1 cDNA, which resembles disease-associated alleles. In a mouse model of Alström syndrome, Alms1 protein can be stably expressed from the mutant allele and is required for cilia formation in primary cells. Aged mice developed specific loss of cilia from the kidney proximal tubules, which is associated with foci of apoptosis or proliferation. As renal failure is a common cause of mortality in Alström syndrome patients, we conclude that this disease should be considered as a further example of the class of renal ciliopathies: wild-type or mutant alleles of the Alström syndrome gene can support normal kidney ciliogenesis in vitro and in vivo, but mutant alleles are associated with age-dependent loss of kidney primary cilia

Obesity, hyperphagia and increased metabolic efficiency in Pc1 mutant mice.

Prohormone convertase 1 (PC1) mutations lead to obesity in humans. However, Pc1 knockout mice do not become obese; in fact, they are runted due to a defect in growth-hormone releasing hormone processing, leading to the speculation that PC1 subserves different functions between mouse and human. Here, we report a novel allele of mouse Pc1 (N222D) that leads to obesity, abnormal proinsulin processing and multiple endocrinological defects. Increased energy intake and a more efficient metabolism contribute to the obesity in Pc1(N222D/N222D) mice. Defective proinsulin processing leads to glucose intolerance, but neither insulin resistance nor diabetes develop despite obesity. The obesity is associated with impaired autocatalytic activation of mature PC1 and reduced hypothalamic alpha-MSH. This is the first characterization of Pc1 mutation in a model organism that mimics human PC1 deficiency

AQP2 Subcellular Localization and Translocation in Mouse Kidney Collecting Ducts and MDCK Cell Lines

<div><p>(A) Immunohistochemistry on collecting ducts in kidney sections from an AQP2-F204V mutant (Mut) mouse and an age-sex matched wild-type (WT) littermate. Mice were injected intraperitoneally with PBS (NT) or dDAVP before sacrificing and fixation of the kidneys. Kidneys sections were immunostained for AQP2 (red) and the basolateral marker AQP3 (green). The images were merged and an area of the cytoplasm was magnified (zoom). Note that mutant AQP2 is not properly localized to the subapical compartment, nor does it respond to dDAVP.</p><p>(B) MDCK cell lines, stably transfected with constructs encoding mouse WT or AQP2-F204V, were treated with and without 150 μM forskolin for 90 min, after which cells were fixed, permeabilized, and subjected to immunocytochemistry. AQP2 is shown in green, and the basolateral marker Na⁺/K⁺-ATPase is shown in red, alongside the nuclear stain DAPI. The z-profile images were reconstructed from multiple z-sections, along the dotted line. Mutant AQP2 fails to localize to the cell surface upon forskolin stimulation. Rather, the perinuclear staining is consistent with an ER localization of mutant AQP2.</p><p>(C) The MDCK cell line expressing AQP2-F204V was grown on fibronectin-coated coverslips until tight junctions formed, at which point the cells were treated with 150 μM forskolin for 90 min. Cells were fixed, permeabilized, and sequentially immunoblotted for AQP2 (green) and calnexin (red), an ER marker. The merged image shows that AQP2-F204V colocalizes with the endoplasmic reticulum marker. Scale bar refers to 10 μm.</p></div

Anatomy and Histology of Mouse Kidneys

<div><p>(A) Gross anatomy of an affected mouse (8-mo-old male). This shows the enlargement and cystic dilatation of the renal pelvis. There is thinning of the overlying renal parenchyma imparting a translucent appearance to portions of the kidney and collecting system. The bladder is also dilated.</p><p>(B) Left kidney from mutant mouse (right) shown in (A) compared to a kidney from an age-sex matched unaffected littermate (left).</p><p>(C) Hematoxylin and eosin stained section of ureter from a mutant mouse, showing normal histology despite bloating of the kidney.</p><p>(D) Hematoxylin and eosin stained histologic section of a kidney from a 4-wk-old female mutant mouse. The mutant kidney shows marked dilatation of the renal pelvis with blunting of the papilla. There is preservation of the cortex and medulla.</p></div