Loss of the putative catalytic domain of HDAC4 leads to reduced thermal nociception and seizures while allowing normal bone development.

Histone deacetylase 4 (HDAC4) has been associated with muscle & bone development [1]-[6]. N-terminal MEF2 and RUNX2 binding domains of HDAC4 have been shown to mediate these effects in vitro. A complete gene knockout has been reported to result in premature ossification and associated defects resulting in postnatal lethality [6]. We report a viral insertion mutation that deletes the putative deacetylase domain, while preserving the N-terminal portion of the protein. Western blot and immuno-precipitation analysis confirm expression of truncated HDAC4 containing N-terminal amino acids 1-747. These mutant mice are viable, living to at least one year of age with no gross defects in muscle or bone. At 2-4 months of age no behavioral or physiological abnormalities were detected except for an increased latency to respond to a thermal nociceptive stimulus. As the mutant mice aged past 5 months, convulsions appeared, often elicited by handling. Our findings confirm the sufficiency of the N-terminal domain for muscle and bone development, while revealing other roles of HDAC4.

Wnk1 kinase deficiency lowers blood pressure in mice: a gene-trap screen to identify potential targets for therapeutic intervention.

The availability of both the mouse and human genome sequences allows for the systematic discovery of human gene function through the use of the mouse as a model system. To accelerate the genetic determination of gene function, we have developed a sequence-tagged gene-trap library of >270,000 mouse embryonic stem cell clones representing mutations in approximately 60% of mammalian genes. Through the generation and phenotypic analysis of knockout mice from this resource, we are undertaking a functional screen to identify genes regulating physiological parameters such as blood pressure. As part of this screen, mice deficient for the Wnk1 kinase gene were generated and analyzed. Genetic studies in humans have shown that large intronic deletions in WNK1 lead to its overexpression and are responsible for pseudohypoaldosteronism type II, an autosomal dominant disorder characterized by hypertension, increased renal salt reabsorption, and impaired K+ and H+ excretion. Consistent with the human genetic studies, Wnk1 heterozygous mice displayed a significant decrease in blood pressure. Mice homozygous for the Wnk1 mutation died during embryonic development before day 13 of gestation. These results demonstrate that Wnk1 is a regulator of blood pressure critical for development and illustrate the utility of a functional screen driven by a sequence-based mutagenesis approach.

Blindness and auditory impairment caused by loss of the sodium bicarbonate cotransporter NBC3.

Normal sensory transduction requires the efficient disposal of acid (H+) generated by neuronal and sensory receptor activity. Multiple highly sensitive transport mechanisms have evolved in prokaryotic and eukaryotic organisms to maintain acidity within strict limits. It is currently assumed that the multiplicity of these processes provides a biological robustness. Here we report that the visual and auditory systems have a specific requirement for H+ disposal mediated by the sodium bicarbonate cotransporter NBC3 (refs. 7,8). Mice lacking NBC3 develop blindness and auditory impairment because of degeneration of sensory receptors in the eye and inner ear as in Usher syndrome. Our results indicate that in certain sensory organs, in which the requirement to transduce specific environmental signals with speed, sensitivity and reliability is paramount, the choice of the H+ disposal mechanism used is limited.