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Figure 4
(A–F) Confocal projection images of the heart of Tg(cdh5:Gal4ff); Tg(UAS:LIFEACT-GFP) zebrafish at 24 hours post-fertilization (hpf) (A–B) and of the heart of Tg(myl7:mCherry-CAAX); Tg (cdh5:Gal4ff); Tg(UAS:LIFEACT-GFP) (C–F) zebrafish at 48 (C–D) and 72 (E–F) hpf. Maximum intensity projections (A–B) and mid-sagittal sections (C–F). (A) Endocardial protrusions (arrows) in apln+/+ embryos at 24 hpf. (B) The number of endocardial protrusions (arrows) is reduced in apln-/- siblings at 24 hpf. (C–D) The numbers of endocardial protrusions (arrows) and touchdowns (white asterisks) are reduced in apln-/- embryos (D) at 48 hpf compared with apln+/+ siblings (C). (E–F) apln-/- larvae (F) exhibit reduced trabeculation (arrowheads) and thicker cardiac jelly (CJ) (yellow asterisks) at 72 hpf compared with apln+/+ siblings (E). (G–H) Quantification of the number of endocardial protrusions in the ventricle of apln+/+ and apln-/- siblings at 24 (G) and 48 (H) hpf. (I) Distribution and average number of endocardial protrusions in different regions of mid-sagittal sections of the ventricle from 48 hpf apln+/+ and apln-/- siblings. (J) Quantification of the percentage of trabecular cardiomyocytes (CMs) in the outer curvature of apln+/+ and apln-/- siblings at 72 hpf. (K–K’) Maximum intensity projections. apln-/- larvae (K’) exhibit a thicker CJ at 72 hpf compared with apln+/+ siblings (K). (L) Quantification of the CJ volume in the outer curvature of apln+/+ and apln-/- siblings at 72 hpf. All images are ventral views, anterior to the top. V, ventricle; A, atrium; +/+, apln+/+; -/-, apln-/-. Data in graphs expressed as mean ± SEM.
Loss of Apelin signaling leads to reduced endocardial protrusion and reduced myocardial trabeculation.