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sema7a-/- mutants exhibit aberrant sensory-axon arborization throughout development. (A) Micrographs depict the overall morphologies and sema7a genomic profiles of 2 dpf control (top) and sema7a-/- larvae (bottom). The schematic diagram on the right depicts the mutation site and the resulting early truncation of the encoded protein. (B) The plot quantitates the number of hair cells from 33, 29, and 35 neuromasts from 2 dpf, 3 dpf, and 4 dpf control larvae, respectively and 17, 53, and 27 neuromasts from 2 dpf, 3 dpf, and 4 dpf sema7a-/- mutant larvae, respectively. No significant change in hair cell number was observed between the control and the sema7a-/- neuromasts across developmental stages. (C) Micrographs depict maximum intensity projections of 4 dpf neuromasts from control and sema7a-/- larvae where the hair cells (green) are stained with FM 4–64 (magenta). The sensory arbors (arrowheads, magenta) tightly enwrap the clustered hair cells in the control neuromast but show aberrant arborization in the sema7a-/- larvae. (D) The plot quantitates the average FM 4–64 intensities from the hair cells of the control and the sema7a-/- neuromasts. (E, F) Micrographs depict combined 4 dpf hair cell clusters, each of whose centers arise located at (0,0). The X- and Y-coordinates represent the anteroposterior (AP) and dorsoventral (DV) axes of the larva, respectively. Positive values of the X- and Y-coordinates represent posterior and ventral directions, respectively. Combined hair cell clusters from 27 control and 27 sema7a-/- mutant neuromasts are represented. (G, H) Micrographs depict the skeletonized networks of the combined 2 dpf hair cell clusters from 17 control and 17 sema7a-/- mutant neuromasts. (I, J) Micrographs depict the skeletonized networks of the combined 3 dpf hair cell clusters from 29 control and 29 sema7a-/- mutant neuromasts. (K) A plot quantitates the densities of the sensory arbors around the center of the combined hair cell clusters for 33 control (magenta) and 17 sema7a-/- (red) neuromasts at 2 dpf. The shaded area marks the region proximal to the boundary of the combined hair cell cluster. (L) A plot quantitates the densities of the sensory arbors around the center of the combined hair cell clusters for 29 control (magenta) and 53 sema7a-/- (red) neuromasts at 3 dpf. The shaded area marks the region proximal to the boundary of the combined hair cell cluster. Scale bars, 5 µm; au, arbitrary units; ns, not significant.
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