Figure 5. mef2cb function buffers against mef2ca loss.

(A) Schematic of mef2cb exonic structure, mutant allele used in this study, and regions encoding proposed functional domains are annotated. (B) Zebrafish heterozygous for both mef2ca^b1086 and mef2cb were pairwise intercrossed. 6 days post fertilization (dpf) larvae were stained with Alcian blue and Alizarin red to label cartilage and bone. Stained larvae were genotyped, flat mounted, and imaged. The following craniofacial skeletal elements are indicated in a wild-type individual: opercle bone (op), branchiostegal ray (br), Meckel’s (mc), ceratohyal (ch), symplectic (sy) cartilages, interhyal (ih), and jaw (jj) joints. Indicated phenotypes associated with mef2ca mutants include: ectopic bone (arrowheads), interhyal and jaw-joint fusions (^), dysmorphic ch (arrows), reduced mc (double arrowhead), and a shortened sy (red arrows). Dashed outline indicates symplectic cartilage. Scale bar: 50 μm (C and D) The penetrance of mef2ca mutant-associated phenotypes observed in 6 dpf larvae is indicated. Asterisk indicates significant difference in penetrance between the indicated genotypes by Fishers exact test. (E) Symplectic cartilage length was measured from 6 dpf larvae from the indicated genotypes. Asterisks indicate significant differences in symplectic length. The p-values from a Dunnet’s T3 test are indicated (*≤0.05, ***≤0.001, and ****≤0.0001) (F) Table listing F-test values for significant differences in variation between genotypes. For box and whisker plots, the box extends from the 25th to 75th percentiles. The line in the middle of the box is plotted at the median, and the bars are minimum and maximum values. N’s for all analyses are indicated in C and D.

Figure 5—figure supplement 1. Zebrafish mef2ca;mef2cb double homozygous mutants develop nonspecific developmental defects.

Zebrafish double heterozygous for mef2ca^b1086 and mef2cb were intercrossed. Offspring were stained with Alcian blue and Alizarin red then genotyped for both genes. In whole-mount images of double homozygous mutants, severe edema (arrows) and craniofacial cartilage malformations (asterisks) are observed with 100% penetrance.

Figure 5—figure supplement 2. Increased severity is not associated with increased within-individual.

(A, C, E, and G) Symplectic cartilage length on left and right sides of 6 days post fertilization (dpf) zebrafish stained with Alcian blue and Alizarin red was measured to determine fluctuating asymmetry or the absolute difference between left and right for fish with the indicated genotypes. (B, D, F, and H) Table listing the Dunnett’s test values for significant differences in fluctuating asymmetry between fish with the indicated genotypes. For box and whisker plots, the box extends from the 25th to 75th percentiles. The line in the middle of the box is plotted at the median, and the bars are minimum and maximum values.