High Resolution Mapping of tlt, a mouse mutant lacking otoconia:"The ability to sense gravity is enhanced by an extracellular structure that overlies the macular sensory epithelium. This complex consists of high density particles, otoconia, embedded within a gelatinous membrane. The tilted mouse specifically lacks otoconia, yet has no other detectable anatomic lesions...". Click the image at right to view the genetic map of tlt on mouse chromosome 5.

Overexpression of EGFP-Otop1 in COS7 cells alters the purinergic response. Left) WT COS7 cells (n=23) show a biphasic response to 200µM ATP characterized by a sharp peak in [Ca2+]i and a rapid reduction in [Ca2+]i to an elevated plateau (bracket). After removal of purinergic stimulus (wash), [Ca2+]i returns to the pre-stimulation baseline. Cells transfected with EGFP-Otop1 (n=17) respond to ATP with an increase in [Ca2+]i to an elevated plateau and a delay in the return of the [Ca2+]i to baseline after removal of ATP (arrow). Right) WT COS7 cells (n=16) respond to 200µM UTP with a sharp increase in [Ca2+]i. Cells transfected with EGFP-Otop1 (n=11) did not respond to UTP.

QT Movie: Mouse Swim Test (Possible slow download! Approximately 1.5 MB). The swimming test is a sensitive measure of vestibular function. The phenotype of homozygous tilted mice can be scored by observing their ability to swim when dropped from a height of 20 cm into a deep tank of water. When dropped into water, control mice promptly resurface and swim with nose and tail maintained above the water line (this is normal swimming behavior). In contrast, when tlt/tlt mice are dropped into water, they spiral underwater and require immediate rescuing (this is non-swimming behavior).

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