International Mammalian Genome Society

The 15th International Mouse Genome Conference (2001)


Charlotte Rhodes
MRC Institute of Hearing Research
University Park
Nottingham NG7 2RD

Co-Authors: 1)Rhodes CR, 2)Parkinson N, 2)Tsai H, 3)Brook D, 3)Robinson T, 2)Brown SDM, 1)Steel KP
Institutions: 1)MRC Institute of Hearing Research, 2)MRC Mammalian Genetics Unit and UK Mouse Genome Centre, 3)Institute of Genetics, Queens Medical Centre

A phenotypic approach has been adopted in the mouse to identify molecules involved in ear development and function.  Mutant mice were obtained using N-ethyl-N-nitrosourea mutagenesis and were screened for new dominant mutations that affect hearing and/or balance.  The genetic and phenotypic analysis of one of these mutants, Pardon, is described.

Pardon mice (Pdo/+) are identified by their lack of a Preyer reflex (ear flick) following the delivery of a 20kHz 90dB SPL tone burst.  Dissection of the middle ear has revealed morphological defects of the ossicles which disrupt the ossicular chain resulting in a conductive hearing loss.  Physiological recordings of cochlear responses of Pardon mutants show very raised thresholds which could not be accounted for by a conductive hearing loss alone.  Analysis of the surface of the organ of Corti by scanning electron microscopy has revealed an increase in numbers of outer hair cells.  Pdo/+ mutants appear to be healthy and fertile but Pdo/Pdo mutants die shortly after birth.   The reason for their demise requires further investigation.

Pdo was mapped to mouse chromosome 19 between markers D19Mit137 and D19Mit6.  The homeobox gene, Emx2 was located in this region and was considered a strong candidate for Pdo due to its expression in the branchial arches and the otic vesicle. Sequence analysis of the Emx2 gene in Pdo mutants revealed a missense mutation causing a non-conservative amino acid change in the homeodomain. This work is supported by the MRC, Defeating Deafness and a grant from the EC (contract number QLG2-CT-1999-00988).

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