Celsr3, dync1h1, cyfip2, and phr are required for the extent of caudally directed Mauthner axonal regrowth. a–h Mauthner axons were labeled in double transgenic zebrafish larvae: Tg(hspGFF62a), expressing Gal4 in the Mauthner combined with Tg(UAS:gap431–20-citrine), driving expression of membrane-attached citrine. Extent of caudally directed Mauthner axonal regrowth at 48 hpt is shown. A stitched low magnification image of the entire length of a regrown wild-type axon is shown in (a). b is the zoomed-in image of the boxed area in (a), showing the regrown wild-type axon around and caudal to the transection site. At the same magnification as the regrown wild-type axon in (b), images of celsr3, dync1h1, and cyfip2-mutant axons at 48 hpt are shown (c–e), quantified in (h), demonstrating that celsr3, dync1h1, and cyfip2 are required for the extent of Mauthner axonal regrowth. At the same magnification as the regrown wild-type axon in (a), an image of a regrown phr mutant axon around and caudal to the transection site is shown in (f) and a zoomed-in image of the boxed area in (f) is shown in (g), quantified in (h), demonstrating that PHR is also required for the full extent of caudally directed Mauthner axonal regrowth. An extraspinally regrown axon branch is marked by a white asterisk (f). In addition to the caudally regrown axon, several branches have regrown rostrally (white arrows), towards the neuronal cell body in the brain stem. Transection sites are marked by a yellow arrowhead. All scale bars are 30 µm. P-values in (h) were determined using two-tailed Student’s t-test (celsr3, phr) or Mann–Whitney test (dync1h1, cyfip2). N = 21 nonmutant celsr3 siblings, n = 16 celsr3 mutants, n = 6 nonmutant dync1h1 siblings, n = 5 dync1h1 mutants, n = 8 nonmutant cyfip2 siblings, n = 8 cyfip2 mutants, n = 48 nonmutant phr siblings, n = 36 phr mutants were analyzed
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