Pivot homozygotes have a moderate circling phenotype, difficulty orienting in water, and complete deafness by 4 weeks of age. Mid-modiolar cross sections of whole cochlea from P3 homozygotes on the C57BL/6J congenic background showed a poorly developed stria vascularis. By 1 month of age the stria vascularis had degenerated, the endolymph volume was reduced in the scala media and Reissner’s membrane had collapsed. Inner ear scanning electron microscopy at P3 additionally revealed regions of hair cell crowding from the mid-turn toward the apex in the basal region of the cochlea, which result in disorganization and an occasional fourth row of hair cells. Whole mounts of adult inner ears from homozygous mutants showed gross malformations of the semicircular canals. The pivot mutation has not been cloned, but segregates within a congenic interval bounded by rs13479533 and rs13479550. The pivot phenotype is similar to that caused the 648 bp head bobber (<i>hb</i>) deletion, which is within the pivot map interval. 

This spontaneous mutation causes defects of the inner ears that result in a moderate circling phenotype, difficulty orienting in water, and complete deafness by 4 weeks of age.

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