Fig. 3: Divergent fin shape is accompanied by disruptions in skeletal growth and presaged by differences in regional cell proliferation.

Development of the caudal skeleton in (A) control and (B) shh pulsed larvae. sp7 reporter-expressing osteoblasts shown in yellow; sox10 reporter-expressing chondrocytes shown in magenta. Arrow indicates the location of the hypural diastema separating the dorsal from ventral lobes in A; asterisk indicates the absence of the diastema in B in both the ossified rays and the cartilaginous hypural complex (*). Bar, 500 uM. A’ and B’ show higher magnification images of boxed areas. (C) In these early stages of fin development (~6.0 SL), the length of the longest rays is less in shh-pulsed larvae than in control siblings. Significance determined using Welch’s two-sample T-tests. (D) control (E) and shh pulsed sibling caudal fin growth from 14 to 36 dpf. Dashed lines indicate the distal edge and overall shape of the fins. Scale bars, 500 µm. (F) The emergence of WT forked fin shape (gray lines) is the result of a lower growth rate in central rays (solid lines) relative to peripheral rays (dashed lines). Following embryonic shh pulse (green lines), central rays exhibit increased growth rates throughout development while peripheral rays retain a WT growth trajectory. (G-H) Dual Fucci reporter showing non-proliferating cells in red and cells in G2, S or M phase in cyan in the dorsal lobe of caudal fin folds of (G) control siblings and (H) larvae that experienced shh pulse. Bar, 200µm. (I) In control developing forked fins, proliferation is relatively lower in central regions, while shh pulse causes increased proliferation in central regions of the developing truncate fin Significance is determined by ANOVA followed by Tukey’s post hoc test. (J) Across the entire organ, proliferation becomes more uniform following shh pulse (closer to 1.0) compared to WT. Significance determined by Welch two-sample T-test. Difference between central / peripheral proliferation comparing WT to shh pulse is still significant when outlier in shh pulse group is removed.