Cardiac morphological analysis of adult MCU mutants. (A) Genotypic distribution of F1 generation from MCU heterozygous parents matches closely with Mendelian ratio and show no signs of embryonic lethality. (B) Comparable exterior phenotypic traits between wildtype and MCU mutant zebrafish. (C) Defects in cardiac structure observed in dissected adult MCU mutant hearts. Mutant hearts were characterized by enlarged atrial volume and limited ventricular blood flow. (D) Reduction in tissue density and disorganization of myocardium observed in histological sections (Hematoxylin and Eosin stains) of MCU mutant hearts. Nuclei rich regions stained blue and cytoplasmic regions and ECM stained pink. (E) Selected image frames during systolic and diastolic phases were analyzed to compare ventricular-to-atrial surface area ratio. Ventricular:atrial SA ratio were significantly reduced in MCU mutant hearts (n = 14 for each group, p < 0.0001). (F) α-actinin staining marks the Z-lines of intact sarcomeres in ventricular cardiomyocytes of wild type adult fish (yellow bracket). Adult MCU ventricles contain regions with intact myofibrils/sarcomeres (yellow bracket), but also exhibit areas of patchy α-actinin staining indicative of damaged myofibrils and broken-down sarcomeres (magenta asterisks). Scale bars indicate 10 μm.
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