Fig. 9

Kif20b mutant axons are more likely to retract and retract farther than controls. A Example brightfield images of live 2 DIV cortical neuron imaged at time 0 h and 6 h. This neuron grew its axon 48 μm. Arrowheads point to growth cone. Scale bar, 10um. B Change in axon length after 6 h for each individual neuron was plotted as a scatter plot, and the distribution as a box plot. The dot representing the axon imaged in A is marked by an arrow. n = 38 control (+/-, black dots) and 38 Kif20b mutant (-/-, white dots) neurons, imaged over 7 different experiments from 6 +/- embryos and 7 -/- embryos. Axons of similar starting lengths were chosen for imaging (averages 52 and 48 μm for +/- and -/-, respectively, p-value n.s.). C Mutant axons (-/-) were more likely to retract and less likely to pause than control axons (+/-) in 6 h. The change in category distribution is significantly different by Fisher’s exact test, p = 0.03. “Grew” signifies at least +3 μm length change; “Retracted”, at least -3 μm; “Paused”, within ±2.9 μm of starting length. D The average length retracted in 6 h among axons that shrank was significantly increased in the Kif20b-/- neurons. The average length increase in 6 h among axons that grew was not significantly different. Here, all above-zero changes were averaged for “positive” and all below-zero changes were averaged for “negative”. E The absolute values of length changes were binned and plotted as a histogram to show greater length changes in Kif20b mutant axons (white bars) compared to heterozygous controls (black bars). The median was higher in the mutants (6.9 μm versus 4.4 μm, Mann-Whitney U-test p = 0.04). *, p <0.05; n.s., not significant, t-test