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. Author manuscript; available in PMC: 2015 Oct 24.
Published in final edited form as: Circ Res. 2014 Sep 16;115(10):845–856. doi: 10.1161/CIRCRESAHA.115.304356

Figure 3. Clonal analysis of myofibril organization in individual myocardial subtypes at 4.5 dpf.

Figure 3

The larval zebrafish heart contains three clearly distinguishable myocardial subtypes. (A) Clone of three atrial cardiomyocytes. (B) Abluminal surface scan of a single cardiomyocyte in the ventricular compact wall. (C) Cross-section through the ventricular lumen showing trabecular myofibers. (D) Cardiomyocytes of the ventricular wall during the process of trabeculation. While the apical (abluminal) side of ventricular wall cardiomyocytes is filled with a dense network of myofibrils (B, D′), the basal side contains thicker, cortically localized myofibrils which are clearly observable in a maximum intensity projection of the whole cell (D, white arrowhead) but not in a scan along the apical surface (D′, red arrowhead). (D″) Optical cross-sectioning through the cortical region of cardiomyocytes of the compact wall also show this polarized localization (dashed lines indicate cell-cell boundaries). Cellular protrusions (pseudocolored in red) which extend into the ventricular lumen appear entirely free of thin myofibrils (D). (E) Trabecular cardiomyocytes are tubular cells of variable length with cortically localized cell-spanning myofibrils and a central nucleus (red). At their respective ends, the myofibrils branch and connect to intercellular membranes of compact layer (CL) cardiomyocytes or adjacent trabecular cells. (F) Clonal analysis of ventricular wall cardiomyocytes, one of which (boxed) is in the process of leaving the ventricular wall. (F′) Closeup of the cardiomyocyte from (F); luminal protrusions (pseudocolored in red), the nucleus containing cell body residing in the wall (green). See Online Movie II for 3D reconstruction. (G–H) Schematic representation of individual myocardial subtypes and their typical myofibril organization and localization (nucleus in blue). (G) Atrial cardiomyocyte. (H) Ventricular wall cardiomyocyte. (I) Trabecular cardiomyocyte. These architectural features can also be observed in Online Movies IIIa and IIIb in beating hearts.