Nrg2a Signaling Is Required for Notch Reporter Activity in Zebrafish CMs
(A–D'') Confocal images (mid-sagittal sections) of 96-hpf Tg(TP1:VenusPEST) zebrafish larvae from a nrg2a+/− incross (A–B''). Images show a number of Notch-reporter-positive CMs in the compact layer in the presence of Nrg2a function (A–A'', arrows), while the number of TP1:VenusPEST-positive CMs is dramatically reduced in the absence of Nrg2a function (B–B'', Ø). (C) Graph showing the number of TP1:VenusPEST-positive CMs per 96-hpf heart in nrg2a+/− (n = 11) versus nrg2a−/− (n = 8) larvae. Each dot represents one heart. Data are shown as mean ± SEM. ∗∗∗p < 0.001 by Student’s t test.
(D–F) Confocal images (mid-sagittal section) of 96-hpf Tg(TP1:VenusPEST) larval heart. Non-injected larvae show TP1:VenusPEST-positive CMs in the compact layer (D, arrows). tnnt2a morphants show absence of Tg(TP1:VenusPEST) expression in CMs (E, Ø). In tnnt2a morphants, mosaic expression of nrg2a in CMs activates Tg(TP1:VenusPEST) expression in neighboring CMs (F, arrows).
(G) Graph shows the percentage of hearts showing TP1:VenusPEST positive CMs at 96 hpf in non-injected larvae (n = 18), tnnt2a morphants (n = 31) and tnnt2a morphants overexpressing nrg2a in the myocardium (n = 23).
Yellow dashed line outlines the tnnt2a morphant heart (E). At, atrium; V, ventricle; AVC, atrioventricular canal. Scale bars, 50 μm.