Expression of the otoferlin gene is not detected in these mutant mice, indicating that this missense mutation has a severe effect on the stability of the protein and potentially its localization. Auditory brainstem response analysis demonstrated that mice homozygous for the missense mutation are profoundly deaf, consistent with an essential role for otoferlin in inner hair cell neurotransmission. Vestibular-evoked potentials of mutant mice, however, is equivalent to those of wildtype mice, indicating that otoferlin is unnecessary for vestibular function even though it is highly expressed in both vestibular and cochlear hair cells.
Wright et al. found multiple reasons for failed neurotransmission from hair cells, despite normal tonotopic organization. The volume of the ventral cochlear nuclei is smaller than normal by nearly half, the auditory nerve is approximately half the normal thickness, the end bulbs of Held are fewer in number, wispier, and less branched than normal, and some of the axons leading to them are thinner. The bushy cells are contacted by slightly more nerve fibers in mutants (average 2.6) then in hearing controls (average 2.0) and the spontaneous miniature excitatory postsynaptic currents are 24% larger in mutants, despite occurring with similar frequencies and with similar shapes to those of hearing controls.
The deaf5Jcs mutation was generated by ENU mutagenesis of C57BL/6J males, which were then bred with C3HeB/FeJ-Rw/+ females to permit tracking of the mutated male-derived Chromosome 5. The male G1 offspring of this cross were then bred with Rw +/+ Hm females and the non-Hm-bearing Rw/+ offspring, which would carry the Chromosome 5 that was potentially mutagenized in the Rw deletion region, were selected and intercrossed to reveal any recessive mutations. Clickbox screening revealed the deaf5Jcs mutation. A homozygous deaf5Jcs male, on this mixed background of predominantly C57BL/6J and C3HeB/FeJ, was bred to a BALB/cJ female and the resulting offspring were intercrossed. A homozygous male from this STOCK background was sent from Dr. John Schimenti at Cornell University to Dr. Kenneth Johnson at The Jackson Laboratory, and in vitro fertilization was carried out with C3HeB/FeJ females. The line was then sibling inbred and reached generation F5 in 2007.
|Allele Name||deaf 5, John C Schimenti|
|Allele Type||Chemically induced (ENU)|
|Gene Symbol and Name||Otof, otoferlin|
|Strain of Origin||C57BL/6J|
|Molecular Note||A T to A base substitution in exon 10 yields an isoleucine to asparagine change in a highly conserved residue of the C2B protein domain and immunohistochemistry of the cochlea fails to detect this protein.|