Mutation of RPE65 can cause severe blindness from birth or early childhood, and RPE65 protein is associated with retinal pigment epithelium (RPE) vitamin A metabolism. Here, we show that Rpe65-deficient mice exhibit changes in retinal physiology and biochemistry. Outer segment discs of rod photoreceptors in Rpe65-/- mice are disorganized compared with those of Rpe65+/+ and Rpe65+/- mice. Rod function, as measured by electroretinography, is abolished in Rpe65-/- mice, although cone function remains. Rpe65-/- mice lack rhodopsin, but not opsin apoprotein. Furthermore, all-trans-retinyl esters over-accumulate in the RPE of Rpe65-/- mice, whereas 11-cis-retinyl esters are absent. Disruption of the RPE-based metabolism of all-trans-retinyl esters to 11-cis-retinal thus appears to underlie the Rpe65-/- phenotype, although cone pigment regeneration may be dependent on a separate pathway.

Cardiac calsequestrin (Casq2) is thought to be the key sarcoplasmic reticulum (SR) Ca 2+ storage protein essential for SR Ca 2+ release in mammalian heart. Human CASQ2 mutations are associated with catecholaminergic ventricular tachycardia. However, homozygous mutation carriers presumably lacking functional Casq2 display surprisingly normal cardiac contractility. Here we show that Casq2-null mice are viable and display normal SR Ca 2+ release and contractile function under basal conditions. The mice exhibited striking increases in SR volume and near absence of the Casq2-binding proteins triadin-1 and junctin; upregulation of other Ca 2+ -binding proteins was not apparent. Exposure to catecholamines in Casq2-null myocytes caused increased diastolic SR Ca 2+ leak, resulting in premature spontaneous SR Ca 2+ releases and triggered beats. In vivo, Casq2-null mice phenocopied the human arrhythmias. Thus, while the unique molecular and anatomic adaptive response to Casq2 deletion maintains functional SR Ca 2+ storage, lack of Casq2 also causes increased diastolic SR Ca 2+ leak, rendering Casq2-null mice susceptible to catecholaminergic ventricular arrhythmias.

Maternal effect genes produce mRNA or proteins that accumulate in the egg during oogenesis. We show here that Mater, a mouse oocyte protein dependent on the maternal genome, is essential for embryonic development beyond the two-cell stage. Females lacking the maternal effect gene Mater are sterile. Null males are fertile.

Regulated expression of the H19 long noncoding RNA gene has been well characterized as a paradigm for genomic imprinting, but the H19 RNA's biological function remains largely unclear. H19 is abundantly expressed maternally in embryonic tissues but is strongly repressed after birth, and significant transcription persists only in skeletal muscle. Thus, we examined the role of the H19 RNA in skeletal muscle differentiation and regeneration. Knockdown of H19 RNA in myoblast cells and H19 knockout mouse satellite cells decreases differentiation. H19 exon1 encodes two conserved microRNAs, miR-675-3p and miR-675-5p, both of which are induced during skeletal muscle differentiation. The inhibition of myogenesis by H19 depletion during myoblast differentiation is rescued by exogenous expression of miR-675-3p and miR-675-5p. H19-deficient mice display abnormal skeletal muscle regeneration after injury, which is rectified by reintroduction of miR-675-3p and miR-675-5p. miR-675-3p and miR-675-5p function by directly targeting and down-regulating the anti-differentiation Smad transcription factors critical for the bone morphogenetic protein (BMP) pathway and the DNA replication initiation factor Cdc6. Therefore, the H19 long noncoding RNA has a critical trans-regulatory function in skeletal muscle differentiation and regeneration that is mediated by the microRNAs encoded within H19.

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Mutations in the gene encoding for the K ؉ channel ␣-subunit KCNQ1 have been associated with long QT syndrome and deafness. Besides heart and inner ear epithelial cells, KCNQ1 is expressed in a variety of epithelial cells including renal proximal tubule and gastrointestinal tract epithelial cells. At these sites, cellular K ؉ ions exit through KCNQ1 channel complexes, which may serve to recycle K ؉ or to maintain cell membrane potential and thus the driving force for electrogenic transepithelial transport, e.g., Na ؉ ͞glucose cotransport. Employing pharmacologic inhibition and gene knockout, the present study demonstrates the importance of KCNQ1 K ؉ channel complexes for the maintenance of the driving force for proximal tubular and intestinal Na ؉ absorption, gastric acid secretion, and cAMP-induced jejunal Cl ؊ secretion. In the kidney, KCNQ1 appears dispensable under basal conditions because of limited substrate delivery for electrogenic Na ؉ reabsorption to KCNQ1-expressing mid to late proximal tubule. During conditions of increased substrate load, however, luminal KCNQ1 serves to repolarize the proximal tubule and stabilize the driving force for Na ؉ reabsorption. In mice lacking functional KCNQ1, impaired intestinal absorption is associated with reduced serum vitamin B12 concentrations, mild macrocytic anemia, and fecal loss of Na ؉ and K ؉ , the latter affecting K ؉ homeostasis.