The jitterbug mutation is a 97 bp intragenic deletion that causes skipping of exon 5, which creates a translational frame shift and premature stop codon that is a null allele for both transcripts. CLIC5 protein is absent in tissues of homozygous mutant mice. Homozygotes are viable and fertile, but display head bobbing and circling behavior and the inability to right themselves in water. Histological analysis of mutant inner ears revealed dysmorphic stereocilia and progressive hair cell degeneration although stereocilia appear to develop normally. ABR thresholds are elevated to 40-50 dB above normal at 1-5 months of age and deafness is indicated by 7 months of age. Scanning electron micrographs from 3-day-old homozygotes showed normal cochlear hair bundle orientation and morphology and nearly normal stereocilia, but subsequently stereocilia degeneration begins in the outer hair cells then progresses to inner hair cells. Radixin immunostaining appears reduced in hair bundles of jitterbug mutant mice.(Gagnon et al., 2006)
CLIC5 expression is enriched podocytes and localizes to the apical and basal membranes and areas proximal to slit diaphragms. It associates with ezrin/radixin/moesin complex and podocalyxin and is essential for proper podocyte foot process integrity. Clic5jbg homozygotes were found to develop proteinuria (Pierchala et al., 2010) and microalbuminuria (Wegner et al., 2010).
Assessing Clic5jbg homozygotes on a mixed C3H/HeJ x C57BL/6J background, Bradford et al. found a minor reduction in gastric acid secretion but a high proportion responded to fasting with gastric hemorrhaging and accompanying rapid loss of body weight, and decrease in body temperature and heart rate. They reported that homozygotes are hyperactive, smaller and leaner than normal, and males were found to be highly aggressive. Homozygotes consume more food than controls but have reduced body fat, especially in males, despite normal fat absorption across the intestine. Females were found to be resistant to the usual weight gain when on a high fat diet. Non-fasting plasma leptin, insulin, and glucose levels were found to be dramatically reduced and leptin levels remained low even on a high fat diet. Consistent with this, homozygotes were found to have an increased peripheral metabolism particularly during the dark cycle. White blood cell counts also found a reduction in neutrophils, eosinophils and monocytes.
