Data from: Contributions of mirror-image hair cell orientation to mouse otolith organ and zebrafish neuromast function: Part 1/2, Zebrafish data

Otolith organs in the inner ear and neuromasts in the fish lateral-line
harbor two populations of hair cells oriented to detect stimuli in
opposing directions. The underlying mechanism is highly conserved: the
transcription factor EMX2 is regionally expressed in just one hair cell
population and acts through the receptor GPR156 to reverse cell
orientation relative to the other population. In mouse and zebrafish, loss
of Emx2 results in sensory organs that harbor only one hair cell
orientation and are not innervated properly. In zebrafish, Emx2 also
confers hair cells with reduced mechanosensory properties. Here, we
leverage mouse and zebrafish models lacking GPR156 to determine how
detecting stimuli of opposing directions serves vestibular function, and
whether GPR156 has other roles besides orienting hair cells. We find that
otolith organs in Gpr156 mouse mutants have normal zonal
organization and normal type I-II hair cell distribution and
mechano-electrical transduction properties. In
contrast, gpr156 zebrafish mutants lack the smaller
mechanically-evoked signals that characterize Emx2-positive hair cells.
Loss of GPR156 does not affect orientation-selectivity of afferents in
mouse utricle or zebrafish neuromasts. Consistent with normal otolith
organ anatomy and afferent selectivity, Gpr156 mutant mice do not
show overt vestibular dysfunction. Instead, performance on two tests that
engage otolith organs is significantly altered – swimming and
off-vertical-axis rotation. We conclude that GPR156 relays hair cell
orientation and transduction information downstream of EMX2, but not
selectivity for direction-specific afferents. These results clarify how
molecular mechanisms that confer bi-directionality to sensory organs
contribute to function, from single hair cell physiology to animal
behavior.