Showing papers by "Mary Ann Cheatham published in 2009"
TL;DR: Data indicate that EHD4 is a novel CDH23-interacting protein that could regulateCDH23 trafficking/localization in a calcium-sensitive manner.
30 citations
TL;DR: A group of de novo genes closely associated with known deafness loci identified, and the data indicate that the hair cell tip link interacts directly with calcium binding proteins, shed light on some protein networks in cochlear hair cells.
Abstract: Although outer hair cells (OHCs) play a key role in cochlear amplification, it is not fully understood how they amplify sound signals by more than 100 fold. Two competing or possibly complementary mechanisms, stereocilia-based and somatic electromotility-based amplification, have been considered. Lacking knowledge about the exceptionally rich protein networks in the OHC plasma membrane, as well as related protein-protein interactions, limits our understanding of cochlear function. Therefore, we focused on finding protein partners for two important membrane proteins: Cadherin 23 (cdh23) and prestin. Cdh23 is one of the tip-link proteins involved in transducer function, a key component of mechanoelectrical transduction and stereocilia-based amplification. Prestin is a basolateral membrane protein responsible for OHC somatic electromotility. Using the membrane-based yeast two-hybrid system to screen a newly built cDNA library made predominantly from OHCs, we identified two completely different groups of potential protein partners using prestin and cdh23 as bait. These include both membrane bound and cytoplasmic proteins with 12 being de novo gene products with unknown function(s). In addition, some of these genes are closely associated with deafness loci, implying a potentially important role in hearing. The most abundant prey for prestin (38%) is composed of a group of proteins involved in electron transport, which may play a role in OHC survival. The most abundant group of cdh23 prey (55%) contains calcium-binding domains. Since calcium performs an important role in hair cell mechanoelectrical transduction and amplification, understanding the interactions between cdh23 and calcium-binding proteins should increase our knowledge of hair cell function at the molecular level. The results of this study shed light on some protein networks in cochlear hair cells. Not only was a group of de novo genes closely associated with known deafness loci identified, but the data also indicate that the hair cell tip link interacts directly with calcium binding proteins. The OHC motor protein, prestin, also appears to be associated with electron transport proteins. These unanticipated results open potentially fruitful lines of investigation into the molecular basis of cochlear amplification.
17 citations
TL;DR: A proportional reduction in sensitivity and in the tip length of CAP tuning curves as the number of OHCs derived from the KO genome increases is demonstrated; i.e., genotype ratio and phenotype are closely related.
Abstract: A chimera is a genetic composite containing a unique mix of cells derived from more than one zygote. This mouse model allows one to learn how cells of contrasting genotype functionally interact in vivo. Here, we investigate the effect that different proportions of prestin-containing outer hair cells (OHC) have on cochlear amplification. To address this issue, we developed a prestin chimeric mouse in which both ROSA26 wild-type (WT) and prestin knock-out (KO) genotypes are present in a single cochlea. The WT ROSA26 mice express a cell marker, allowing one to identify cells originating from the WT genome. Examination of cochlear tissue indicated that prestin chimeric mice demonstrate a mosaic in which mutant and normal OHCs interleave along the cochlear partition, similar to all other chimeric mouse models. The anatomical distribution of prestin-containing OHCs was compared with physiological data including thresholds and tuning curves for the compound action potential (CAP) recorded in anesthetized mice. Analysis of these measures did not reveal mixed phenotypes in which the distribution of prestin-containing OHCs impacted sensitivity and frequency selectivity to different degrees. However, by reducing the number of prestin-containing OHCs, phenotypes intermediate between WT and KO response patterns were obtained. Accordingly, we demonstrate a proportional reduction in sensitivity and in the tip length of CAP tuning curves as the number of OHCs derived from the KO genome increases; i.e., genotype ratio and phenotype are closely related.
15 citations
01 Feb 2009
TL;DR: In this paper, a model simulating the cochlear microphonic (CM) measured at the round window in mice was constructed, similar to what others have done [1, 2] for guinea pig.
Abstract: Based on the assumption that individual hair-cell current contributions are proportional to local basilar-membrane amplitude and phase, a model simulating the cochlear microphonic (CM) measured at the round window in mice was constructed, similar to what others have done [1, 2] for guinea pig. Hair-cell contributions were vectorially summed along the length of the cochlear partition. Due to rapidly changing phase in the amplified tip region of the traveling wave, this segment contributes negligibly to the summed response, except at very high frequencies. As a result, the CM is usually dominated by hair-cell outputs on the mechanically linear tails of the traveling wave, i.e., the CM reflects passive cochlear responses. The CM recorded at the round window from mice lacking prestin is consistent with model predictions. Hence, the CM is not a good metric to assay integrity of the cochlear amplifier.