Wtip is required for AV boundary formation, but does not affect chamber patterning. Hearts of transgenic Tg(myl7:EGFP) embryos were visualized in 48 hpf (A) control or (B) wtip morphant embryos (1.035 pmol/embryo) to assess the extent of cardiac looping. (C) Diagram depicting the cardiac LA, defined as the degree of difference in the anterior/posterior body axis and the plane of the AV junction. (D) Wtip depletion decreases the mean LA by 48 hpf. The mean ± standard error is shown. *P<0.000359. n=10 embryos/treatment. 48 hpf whole-mount in situ hybridization in (E,F,I,J,M,N,Q) control and (G,H,K,L,O,P,L) wtip morphant embryos (1.035 pmol/embryo) of (E-H) myl7, (I-L) amhc, (M-P) vmhc and (Q,R) nppa. (E,G,I,K,M,O,Q,R) Ventral view and (F,H,J,L,N,P) lateral view. Wtip does not regulate chamber patterning, but regulates nppa expression to maintain chamber myocardium expression and exclusion from the myocardium of the AV boundary. Wtip, Wilm′s tumor 1 interacting protein; AV, atrioventricular; myl7, myosin light chain 7; EGFP, enhanced green fluorescent protein; hpf, hours post fertilization; LA, looping angle; amhc, α myosin heavy chain; vmhc, ventricular myosin heavy chain; nppa, natriuretic peptide A; conMO, control morpholino oligonucleotide; A, anterior; P, posterios; avj, AV junction.
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