removal-an-internal-translational-start-site-from-mrna-while

Removal of an Internal Translational Start Site from mRNA While Retaining Expression of the Full-Length Protein

The CRISPR-Cas9 gene-editing system, based on genome repair mechanisms, enables the generation of gene-modified mouse models more quickly and easily ...

University of Utah

Proximal tubule (PT) angiotensinogen (AGT) is part of a tubular renin-angiotensin system (RAS) that participates in the regulation of sodium reabsorption along the entire nephron. Physiologic maneuvers affecting AGT expression in PT also affect systemic RAS. Here, we tested the hypothesis that PT AGT is regulated by increased glomerular filtration rate (GFR).

Expression of angiotensinogen in proximal tubule as a function of glomerular filtration rate.

Genetic variation in the human angiotensinogen gene (AGT) influences plasma AGT concentration and susceptibility to essential hypertension by a mechanism that remains to be clarified. When one or two additional copies of the gene were inserted by gene titration (by homologous recombination with gap-repair at the AGT locus), both plasma AGT and arterial pressure were elevated in the physiological range in the mouse. The causal dependency between plasma AGT and blood pressure and the relative contribution of the various tissues that express AGT to these two phenotypic parameters remained to be determined. To address these issues, we generated a transgenic mouse with overexpression of the mouse AGT gene restricted to the liver. The transgene was examined in two contrasted genetic backgrounds, the sodium-sensitive C57BL/6J and the sodium-resistant A/J. Transgenic and control male animals underwent continuous cardiovascular monitoring by telemetry for 14 days while under a standard sodium diet (0.2%). Moderate but significant increases in plasma AGT (40%, p = 0.01) and systolic blood pressure (4-6 mmHg, p ranging from 0.01 to <0.001) were observed in the sodium-sensitive background, but not in the sodium-resistant animals. Statistical analysis of a large number of consecutive, repeated measurements of blood pressure afforded power to detect small effects in the physiological range by use of advanced mixed models of analysis of variances and covariances. Although plasma renin activity was increased in the sodium-sensitive background, it did not reach statistical significance. These observations underline a potential contribution of systemic AGT to the mechanism of AGT-mediated hypertension, but the significance of sodium sensitivity in the genetic background suggests participation of the kidney in expression of the elevated blood pressure phenotype, a matter that will warrant further studies. They also highlight the challenge of identifying the contribution of individual genes in complex inheritance, as their effects are modulated by other genetic and environmental determinants.

Response to genetic manipulations of liver angiotensinogen in the physiological range.

Total anomalous pulmonary venous return (TAPVR) is a congenital heart defect inherited via complex genetic and/or environmental factors. We report detailed mapping in extended TAPVR kindreds and mutation analysis in TAPVR patients that implicate the PDGFRA gene in the development of TAPVR. Gene expression studies in mouse and chick embryos for both the Pdgfra receptor and its ligand Pdgf-a show temporal and spatial patterns consistent with a role in pulmonary vein (PV) development. We used an in ovo function blocking assay in chick and a conditional knockout approach in mouse to knock down Pdgfra expression in the developing venous pole during the period of PV formation. We observed that loss of PDGFRA function in both organisms causes TAPVR with low penetrance (approximately 7%) reminiscent of that observed in our human TAPVR kindreds. Intermediate inflow tract anomalies occurred in a higher percentage of embryos (approximately 30%), suggesting that TAPVR occurs at one end of a spectrum of defects. We show that the anomalous pulmonary venous connection seen in chick and mouse is highly similar to TAPVR discovered in an abnormal early stage embryo from the Kyoto human embryo collection. Whereas the embryology of the normal venous pole and PV is becoming understood, little is known about the embryogenesis or molecular pathogenesis of TAPVR. These models of TAPVR provide important insight into the pathogenesis of PV defects. Taken together, these data from human genetics and animal models support a role for PDGF-signaling in normal PV development, and in the pathogenesis of TAPVR.

Dysregulation of the PDGFRA gene causes inflow tract anomalies including TAPVR: integrating evidence from human genetics and model organisms.

Platelet-derived growth factor receptor alpha (Pdgfralpha) identifies cardiac progenitor cells in the posterior part of the second heart field. We aim to elucidate the role of Pdgfralpha in this region. Hearts of Pdgfralpha-deficient mouse embryos (E9.5-E14.5) showed cardiac malformations consisting of atrial and sinus venosus myocardium hypoplasia, including venous valves and sinoatrial node. In vivo staining for Nkx2.5 showed increased myocardial expression in Pdgfralpha mutants, confirmed by Western blot analysis. Due to hypoplasia of the primary atrial septum, mesenchymal cap, and dorsal mesenchymal protrusion, the atrioventricular septal complex failed to fuse. Impaired epicardial development and severe blebbing coincided with diminished migration of epicardium-derived cells and myocardial thinning, which could be linked to increased WT1 and altered alpha4-integrin expression. Our data provide novel insight for a possible role for Pdgfralpha in transduction pathways that lead to repression of Nkx2.5 and WT1 during development of posterior heart field-derived cardiac structures.

Cardiac malformations in Pdgfralpha mutant embryos are associated with increased expression of WT1 and Nkx2.5 in the second heart field.

Synaptic target specificity, whereby neurons make distinct types of synapses with different target cells, is critical for brain function, yet the mechanisms driving it are poorly understood. In this study, we demonstrate Kirrel3 regulates target-specific synapse formation at hippocampal mossy fiber (MF) synapses, which connect dentate granule (DG) neurons to both CA3 and GABAergic neurons. Here, we show Kirrel3 is required for formation of MF filopodia; the structures that give rise to DG-GABA synapses and that regulate feed-forward inhibition of CA3 neurons. Consequently, loss of Kirrel3 robustly increases CA3 neuron activity in developing mice. Alterations in the Kirrel3 gene are repeatedly associated with intellectual disabilities, but the role of Kirrel3 at synapses remained largely unknown. Our findings demonstrate that subtle synaptic changes during development impact circuit function and provide the first insight toward understanding the cellular basis of Kirrel3-dependent neurodevelopmental disorders. 

The intellectual disability gene Kirrel3 regulates target-specific mossy fiber synapse development in the hippocampus.

A panel of clinician scientists with expertise in neuromuscular blockade (NMB) monitoring was convened with a charge to prepare a consensus statement on indications for and proper use of such monitors. The aims of this article are to: (a) provide the rationale and scientific basis for the use of quantitative NMB monitoring; (b) offer a set of recommendations for quantitative NMB monitoring standards; (c) specify educational goals; and (d) propose training recommendations to ensure proper neuromuscular monitoring and management. The panel believes that whenever a neuromuscular blocker is administered, neuromuscular function must be monitored by observing the evoked muscular response to peripheral nerve stimulation. Ideally, this should be done at the hand muscles (not the facial muscles) with a quantitative (objective) monitor. Objective monitoring (documentation of train-of-four ratio ≥0.90) is the only method of assuring that satisfactory recovery of neuromuscular function has taken place. The panel also recommends that subjective evaluation of the responses to train-of-four stimulation (when using a peripheral nerve stimulator) or clinical tests of recovery from NMB (such as the 5-second head lift) should be abandoned in favor of objective monitoring. During an interim period for establishing these recommendations, if only a peripheral nerve stimulator is available, its use should be mandatory in any patient receiving a neuromuscular blocking drug. The panel acknowledges that publishing this statement per se will not result in its spontaneous acceptance, adherence to its recommendations, or change in routine practice. Implementation of objective monitoring will likely require professional societies and anesthesia department leadership to champion its use to change anesthesia practitioner behavior.

Consensus Statement on Perioperative Use of Neuromuscular Monitoring.

In patients who receive a nondepolarizing neuromuscular blocking drug (NMBD) during anesthesia, undetected postoperative residual neuromuscular block is a common occurrence that carries a risk of potentially serious adverse events, particularly postoperative pulmonary complications. There is abundant evidence that residual block can be prevented when real-time (quantitative) neuromuscular monitoring with measurement of the train-of-four ratio is used to guide NMBD administration and reversal. Nevertheless, a significant percentage of anesthesiologists fail to use quantitative devices or even conventional peripheral nerve stimulators routinely. Our hypothesis was that a contributing factor to the nonutilization of neuromuscular monitoring was anesthesiologists' overconfidence in their knowledge and ability to manage the use of NMBDs without such guidance.

Anesthesiologists' Overconfidence in Their Perceived Knowledge of Neuromuscular Monitoring and Its Relevance to All Aspects of Medical Practice: An International Survey.

Article	Year
Expression of angiotensinogen in proximal tubule as a function of glomerular filtration rate. Kidney international\| PubMed ID: 15149328	2004
Response to genetic manipulations of liver angiotensinogen in the physiological range. Journal of human genetics\| PubMed ID: 18600297	2008
Dysregulation of the PDGFRA gene causes inflow tract anomalies including TAPVR: integrating evidence from human genetics and model organisms. Human molecular genetics\| PubMed ID: 20071345	2010
Cardiac malformations in Pdgfralpha mutant embryos are associated with increased expression of WT1 and Nkx2.5 in the second heart field. Developmental dynamics : an official publication of the American Association of Anatomists\| PubMed ID: 20658695	2010
The intellectual disability gene Kirrel3 regulates target-specific mossy fiber synapse development in the hippocampus. eLife\| PubMed ID: 26575286	2015
Consensus Statement on Perioperative Use of Neuromuscular Monitoring. Anesthesia and analgesia\| PubMed ID: 29200077	2018
Anesthesiologists' Overconfidence in Their Perceived Knowledge of Neuromuscular Monitoring and Its Relevance to All Aspects of Medical Practice: An International Survey. Anesthesia and analgesia\| PubMed ID: 31094776	2019
Heuristics, Overconfidence, and Experience With Management of Neuromuscular Block: Self-Correction Is Unlikely. Anesthesia and analgesia\| PubMed ID: 31478929	2019

Jennifer Hunter

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