Figure 2

(A) Fluorescent stereoscopic images of 3 dpf WT and gnptab morphants (MO) in the myl7:EGFP (labels cardiomyocytes) background show reduced looping and inferior edema (red arrow) in MLII hearts. Red arrowheads highlight edema. Similar phenotypes are noted in gnptab mutants (ga2.5 shown) stained immunohistochemically for myosin. Scale bar: 50μm. V, ventricle; A, atrium. Percent values equal the number of embryos exhibiting phenotypes similar to the picture. n = 30 embryos from 4–5 independent matings. (B) Schematic of AV valve formation. (C) Live confocal imaging of tie2:EGFP⁺ hearts reveal abnormal uncondensed valves in gnptab morphants that do not open and close as the heart beats. n = 35–40 total embryos from 3 independent matings. Scale bar: 10 μm. Red arrowheads highlight the canal between the left and right sides of the valve. (D) Live confocal imaging of tie2:EGFP⁺gnptab mutant (ga2.5 shown) valves show similar disruption in architecture and behavior. Images 1–4 show WT valves opening and closing at regular intervals, while the gnptab/MLII mutant valves remain open in images 1,2, and 4. Scale bar: 20μm. n = 25 embryos from 3 matings. Red arrowheads highlight left and right sides of the valve, which fully “close” in WT but not mutant embryos. (E) In situ analyses of notch1b transcripts show that differentiation of endocardial and AV valve cells is disrupted in both gnptab morphants and mutants, with expression present throughout the endocardium (yellow lines) instead of restricted to valvular regions (yellow arrow heads). Scale bar: 50μm. Percent values equal the number of animals with pictured phenotype. n = 75 embryos from 3 experiments. (F) Schematic illustrates key aspects of early heart and valve development and summarizes the events disrupted in MLII embryos.