Movie S2.

Tail-suspension test of WT and heterozygous SoxC CKO mice. When held by its tail, a 4-wk-old WT mouse reaches downward for the substrate. Under identical conditions a heterozygous SoxC CKO (Het) littermate displays ataxic curling, which suggests that the animal relies on proprioception for the detection of its position. The mouse also demonstrates propelling behavior. These phenotypes of the mutant indicate the abnormal functioning of the organs that detect static position, the utricle and saccule.