Fig. 10

emx2 regulates hair bundle polarity in neuromasts.

(A) Surface view of an A-P and D-V oriented neuromast and a sagittal view of the cellular architecture of a neuromast in the lateral line of zebrafish. (B) HCs with opposite orientation are in a 1:1 ratio. (C–C'') An example and (C''') quantification showing only HCs (parvalbumin-positive, blue) with hair bundles (phalloidin, red) oriented toward the posterior (C, asterisks) or ventral direction are positive for anti-Emx2 staining (green) in A-P and D-V neuromasts, respectively (55 neuromasts from 26 larvae, ***p<0.001; Figure 10—source data 1). (D–D'') An example and (D”') quantification of HCs in emx2 knockouts showing all HCs are emx2-negative (D') and pointing towards the same direction (36 neuromasts, 18 larvae, ***p<0.001; Figure 10—source data 1). (E–E''') All hair bundles (visualized using m6b:βactin-GFP, red) are Emx2-positive (E',E'', green) and pointing toward the posterior in the A-P oriented neuromasts of gof mutants. (E''') Quantification of hair bundle polarity in 43 A-P and D-V neuromasts from 23 larvae (Figure 10—source data 1). ***p<0.001. (F–J) In response to an anterior-to-posterior stimulus (F') or posterior-to-anterior stimulus (G') a similar percentage of wildtype HCs show mechanically-evoked increase in calcium levels (J; Figure 10—source data 2). Emx2 gof HCs only respond to an anterior-to-posterior stimulus (H') and are inhibited by a posterior-to-anterior stimulus (I'). The heatmap indicates the change in calcium levels during the first half of the 2s-step stimulus (2 larvae and 4 neuromasts in control, 2 larvae and 7 neuromasts in emx2 gof). Error bar represents SEM.