The POU domain, class 4, transcription factor 3, encoded by the Pou4f3 gene, is expressed in auditory and in vestibular hair cells, retina, striatum and brain stem.
Mutations in this gene are associated with progressive hearing loss and deafness. These Pou4f3DTR knock-in mice express the human diptheria toxin receptor (HBEGF) from the endogenous Pou4f3 locus. Heterozygous Pou4f3DTR/+ mice have a normal complement of inner ear hair cells and normal hearing and balance.
Diphtheria toxin treatment on cochlear explants from neonatal heterozygous mice ablates inner hair cells completely and outer hair cells almost completely. In mature heterozygous mice, by 3 days postinjection of diphtheria toxin (25ng/g dose), auditory brainstem responses (ABRs) indicate profound hearing loss and by 5 days post-injection the mice are totally deaf. No hearing recovery is observed, at least out to 4 months post-injection. A smaller diphtheria toxin dose of 10 ng/g delays the hearing loss by one or 2 days. At 6 days postinjection (25 ng/g), almost all hair cells are ablated, with loss starting in the basal turn proceeding to the apex. Inner hair cells are ablated more slowly than outer hair cells. In mature mice, treatment does not result in neuronal loss.
In young heterozygous mice, postnatal day 5, a dose of 5 ng/g diphtheria toxin results in loss of hair cells before hearing onset. In neonates, most hair cells (<1% remaining) are ablated by 8 days post-injection with transneuronal loss of neurons in the ventral cochlear nucleus and spiral ganglion neuron. Supporting cells are not altered by diphtheria toxin exposure.
Mice that are heterozygous for the targeted mutation are viable and fertile. Homozygotes (untreated) exhibit severe ataxia, vestibular defects and have not been tested for fertility.
