Figure 6

tbx1 mutants have a dysmorphic OFT and hypocellular arterial valve primordia. (A–B′) Representative brightfield image of WT sibling (A, n = 6) and tbx1^tm208 homozygous mutant (B, n = 12) at 70 hpf, dashed boxes in (A) and (B) highlights heart shown in (A′) and (B′). In tbx1^tm208 mutants (B′), the pharyngeal arches are absent (asterisk), and the angle of the OFT angle is steeper than in WT (white). (C–D″) Representative images of mRNA in situ hybridization for elnb in WT sibling (C) and tbx1^tm208 homozygous mutants (D–D″) at 70 hpf. tbx1 mutants display variability in size of elnb domain. (E and F) Representative midline sections of immunohistochemistry on WT sibling (E) and tbx1^tm208 homozygous mutants (F) carrying Tg(fli1a:AC-TagRFP) to mark the endocardium (green), cardiac troponin (cyan), and MLCK (magenta). The tbx1^tm208 OFT is smaller and dysmorphic with diffuse MLCK expression. (G and G′) Quantification of number of cells in arterial valve primordia (yellow, E and F) at 70 hpf in WT sibling and tbx1^tm208 homozygous mutants at 70 hpf. Loss of tbx1 results in a significant reduction in number of VICs and impacts the dextral (D) and sinistral (S) primordia equally (WT sibling, n = 13; tbx1^tm208, n = 12). (G) and (G′): Mean ± S.E.M, Welch’s unpaired t-tests. ****, P < 0.0001; ns, not significant. V, ventricle; BA, bulbus arteriosus; D, dextral; S, sinistral. Scale bars: (A) and (B): 500 μm; (A′) and (B′): 50 μm; (C)–(D′): 20 μm; (E) and (F): 10 μm.