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celsr2 compensates for loss of celsr3 during Mauthner development. A-F) j1229a:GFP transgene expression (A,B,D,E) labels Mauthner (A,B) and spiral fiber (asterisks; A,B,D,E) neurons in celsr2-/- (A-C) and celsr3-/-;celsr2-/- (D-F) larvae. α-3A10 (A,C,D,F) labels spiral fiber axons at midline crossing (white arrowheads) and Mauthner axons (A,C). White dashed brackets (D-F) indicate positions where Mauthner neurons are absent. All images and quantifications in figure are of 5 dpf larvae. Scale bar = 20μM, Z-projection. G) Mauthner cell number in celsr3 sib;celsr2-/- (100% 2 M-Cells; n = 44), celsr3-/-;celsr2+/+ (5% 1 M-cell, 95% 2 M-cells; n = 20), celsr3-/-;celsr2+/- (20% 0 M-cell, 39% 1 M-cell, 41% 2 M-cells; n = 41), and celsr3-/-;celsr2-/- (91% 0 M-cell, 9% 1 M-cell; n = 22). p-values calculated with Chi-square tests. H) Percentage of twenty acoustic stimuli that elicited any response for celsr3 sib;celsr2-/- (n = 28) and celsr3-/-;celsr2-/- (n = 17) larvae. I) For larvae from (H), percentage of twenty acoustic stimuli that elicited a fast escape (latency <17 ms). Points outlined in black indicate celsr3-/-;celsr2-/- larvae with one Mauthner (5/17), while the remaining celsr3-/-;celsr2-/- larvae had zero Mauthners. J) For celsr3 sib;celsr2-/- larvae from (I) that performed at least six escapes (100% of larvae), escape C1-bend ratio, normalized so all fish turning only one direction, left or right, appear at the same y position. K) Latency (time to first head movement) for individual fast escapes in celsr3-/-;celsr2-/- larvae with one (1M) or zero (0M) Mauthners. n = 19 responses 1M, 12 responses 0M.
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