This project involves the investigation of the mechanisms regulating expression of the Plasma Membrane Calcium ATPase type 2 (PMCA2). It has previously been shown that naturally occurring mutations in the Atp2b2 gene, which encodes PMCA2, result in deafness (and varying degrees of vestibular/balance deficits) in mice. Several mutations in this gene have been identified by previous research in the Tempel laboratory, as well as in other labs. These range from point mutations such as deafwaddler (dfw) and the wriggle mouse sagamiwri (wri), to frame-shifting deletions such as the deafwaddler alleles dfw2J, dfw3J, and dfw4J.
Additionally, a targeted deletion of the Atp2b2 gene in mouse displayed a similar phenotype to the more severe alleles of dfw, suggesting that this gene is indeed critical for normal hearing.
An interesting phenomenon, which suggests that the regulation of this gene may be important, is that animals which are heterozygous for mutations in PMCA2 display moderate hearing loss, particularly at high frequencies. This implies that this gene is subject to haploinsufficiency.
These previous findings led to the hypothesis that subtle changes in PMCA2 expression level may be a factor in age-related or noise-induced hearing loss. My work on this subject involves the characterization of the 5'-end of the Atp2b2 gene, identification of putative promoter elements, and evaluation of mRNA expression within the cochlea.
Identification of Genetic Factors Contributing to Noise-Induced Hearing Loss
It has been known for a long time that noise exposure, either occupational or otherwise, can cause temporary and/or permanent hearing loss. It has also been well described that within groups of individuals who have exposed to similar noise levels, there is a wide range of effect. This can range from minimal effect to profound loss of hearing. A reasonable assertion is that there are some people who could be categorized as "resistant", and others who are "susceptible". It is also likely that multiple genetic factors contribute to these phenotypes.
Conveniently, but probably not surprisingly, this phenomenon of "resistance" and "susceptibility" can also be observed between strains of inbred mice. It is possible, therefore, to use the mouse as a model for identifying potential genetic factors that contribute to noise resistance and/or susceptibility. There are several ways of approaching this problem. One such way is via genetic mapping of the loci that cosegregate with the desired phenotype. Another approach is to analyze differences in gene expression between strains of mice using DNA microarray technology. Microarrays allow for the analysis of 10,000 or more genes simultaneously. In this project, I plan to compare gene expression in the cochleas of normal (susceptible) strain mice, with a strain which is remarkably resistant to noise damage. The comparison will be performed under baseline (pre-exposure) and noise-exposed conditions. This will enable several different questions to be addressed. First, it will be possible to identify potential genetic differences between the strains that account for their different resistances to noise. Second, it will be possible to identify genes whose expression is affected by noise exposure. Third, it will allow the potential identification of differences in the genetic response to noise in the two strains. Additionally, by performing expression studies at various timepoints following noise exposure, it may be possible to separate out the changes in expression that relate to such phenomena as excitotoxicity and/or oxidative stress and apoptosis. Perhaps it will be possible to identify changes in expression that correspond to an active protective mechanism in the noise-resistant animals.