Hapln1a promotes atrial growth. (A?C) mRNA in situ hybridization analysis of hapln1a expression at 26hpf in embryos from an incross of hapln1a?241 heterozygous carriers. Wild-type and heterozygous siblings express hapln1a in the heart (bracket A, B, respectively), whereas hapln1a is absent in homozygous mutants (arrow C). (D?I) mRNA in situ hybridization expression analysis at 50hpf of myl7 (D?F) and myh6 (G?I) in wild-type siblings (D and G), hapln1a?241 heterozygous siblings (E and H) or hapln1a?241 homozygous mutant embryos (F and I). Scale bar = 50 ?m. (J and K) Quantification of atrial area (J), and atrial outer curvature (K) in ISH-processed sibling embryos (wt/het) and hapln1a?241 or hapln1a?187 mutants (mut) at 50hpf. Atrial area is significantly reduced in hapln1a?241 mutants compared to wild-type siblings (P = 0.013), and atrial outer curvature is significantly reduced in both hapln1a?187 and hapln1a?241 mutants (P = 0.033 and P = 0.032). In both J and K, n = 54 hapln1a?187 wt; 104 hapln1a?187 het; 60 hapln1a?187 mut, 66 hapln1a?241 wt; 116 hapln1a?241 het; 53 hapln1a?241 mut. (L?O) Maximum intensity projections of light-sheet z-stacks of live 50hpf (L and M) and 72hpf (N and O) Tg(myl7:lifeActGFP); Tg(fli1a:AC-TagRFP) transgenic wild-type (L and N), and hapln1a?241 mutant embryos (M and O). Scale bar = 50?m. (P and Q) Quantification of atrial area (P), and atrial outer curvature (Q) in live light-sheet z-projections from wild-type sibling embryos and hapln1a?241 or hapln1a?187 mutants at 50hpf and 72hpf. Atrial area and atrial outer curvature are significantly reduced in hapln1a?241 mutants (mut) compared to wild-type siblings (wt/het) at 50hpf (P = 0.0002, and P = 0.014). In both (P) and (Q), n = 4 hapln1a?187 50hpf wt; 5 hapln1a?187 50hpf mut, 7 hapln1a?241 50hpf wt; 10 hapln1a?241 50hpf mut; 4 hapln1a?187 72hpf wt; 7 hapln1a?187 72hpf mut, 9 hapln1a?241 72hpf wt; 10 hapln1a?241 72hpf mut. Comparative statistics carried out using a Kruskal?Wallis test with multiple comparisons.
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