<i>Neurog1</i> expression causes disorganization of both hair cells and supporting cells in the heterozygous KI mice.

<p>Immunochemistry of Myo7a shows normal rows of hair cells with loss of some outer hair cells in P7 heterozygous KI mice (white arrows in a, a’, a””). Co-labeling of Myo7a with the supporting cell-specific markers, Prox1 and Tubulin shows the loss of few outer hair cells in areas of misaligned and/or ectopic pillar cell formation as well as disorganization of Deiters' cells (white arrows in a’-a””; b,b’). Some ectopic hair cells are found in the position of inner hair cells more apparently at P9 and also in between the rows of outer hair cells which are associated with the disorganization of supporting cells (yellow arrows in a- a””, c-c”) followed by loss of some inner hair cells and pillar cells by P26 (arrows in d-d”). Anti-Prox1 specifically labels outer pillar cells and third rows of Deiters’ cells at P7 whereas anti-Tubulin strongly labels outer pillar and all three rows of Deiters' cells. Anti-Tubulin more weakly labels inner pillar cells in heterozygous (a’-a””, c’,c”,d’,d”) and wild-type cochlea (b, b’). Prox1 is shown in cyan in a’ and lilac in a” and b for better contrast. Scanning electron microscopy P1 control (<i>Pax2-cre; Atoh1^+/f</i>) mice reveal four parallel rows of hair cells in the organ of Corti with a staircase-pattern of stereocilia (e). SEM in E18.5 to P26 heterozygous KI mice reveals defects in hair cell stereocilia development and patterning (f-l). Hair cells show kinocilia that are not centered in relation to the symmetry of the stereocilia bundle (shown with yellow arrows and red asterisks in f,f’,g). At P1, some abnormal patches of stereocilia form in the inner hair cells (red arrow in g) as well as some ectopic hair cells adjacent to inner hair cells (red arrows in h and h’). At P9, occasionally extra rows of outer hair cells form with unequal length of the ‘W’ end of the stereocilia (i, red asterisk in j). In addition, the stereocilia of inner hair cells are sporadically disrupted or fused abnormally (k, k’) and some inner hair cells at P26 are missing (arrow in l) consistent with gaps seen with the Myo7a immunochemistry. Bar indicates 10 µm except 2 µm in e’, f’, g’, j’.