Characterization of a new allele of Ames waltzer generated by ENU mutagenesis

Mutation in the protocadherin 15 (Pcdh15) gene causes hair cell dysfunction and is associated with abnormal stereocilia development. We have characterized the first allele (Pcdh15(av-nmf19)) of Ames waltzer (av) obtained by N-ethyl-N-nitrosourea (ENU) mutagenesis. Pcdh15(av-nmf19) was generated in the Neuroscience Mutagenesis Facility (NMF) at The Jackson Lab (Bar Habor, USA). Pcdh15(av-nmf19) mutants display circling and abnormal swimming behavior along with lack of auditory-evoked brainstem response at the highest intensities tested. Mutation analysis shows base substitution (A--> G) in the consensus splice donor sequence linked to exon 14 resulting in the skipping of exon 14 and the splicing of exon 13-15. This results in the introduction of a stop codon in the coding sequence of exon 15 due to shift in the reading frame. The effect of nmf19 mutation is expected to be severe since the expressed Pcdh15 protein is predicted to truncate in the 5th cadherin domain. Abnormalities of cochlear hair cell stereocilia are apparent in Pcdh15(av-nmf19) mutants near the time of birth and by about P15 (15 days after birth) there is evidence of sensory cell degeneration. Disorganization of outer hair cell stereocilia is observed as early as P2. Inner hair cell stereocilia are also affected, but less severely than those of the outer hair cells. These results are consistent with characteristics of the mutation in the Pcdh15(av-nmf19) allele and they support our previous finding that Protocadherin 15 plays an important role in hair-bundle morphogenesis.