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These mutants show body tremor, head tossing behavior, bi-directional circling, and intermittently move backwards; occasional ataxia, i.e. lifting of both hind limbs simultaneously and slight leaning to the side can also be observed. Results of an auditory brainstem recording (n=1) suggest they are also deaf, since no response was obtained at every frequency tested (click, 8, 16, 32kHz). The on-set of the overt phenotype is at 3.7 weeks (+/- 0.6; n=53) of age; mutants breed well and a colony can be maintained through regular breeding. Because of the general map position and this characteristic phenotype, complementation analysis with a vertigo mutant, Kcnq1vtg-2J(Jax#4407), was performed. A homozygous (Kcnq1vtg-2J) by heterozygous (nmf455) mating resulted in 11 mutants in a total of 26 progeny, confirming that nmf455 represents an allele of Kcnq1. Standard pathology work-up on two mutants (123 days of age) showed no abnormalities. However, serial sections of the ears revealed severe malformations in the cochlea and vestibular area, characterized by collapse of both the cochlear ducts and the endolymphatic part of the vestibular system (scala media; to view a section of control tissue, see Zheng et al., 2005). In addition, whole ear exam revealed abnormal otoconia.
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