CASE STUDY Using Zebrafish as a Heart Disease Model rrhythmogenic cardiomyopathy (ACM) is a highly arrhythmic form of human heart disease and a significant cause of sudden death in the young. Degeneration of cardiac myocytes (muscle cells) and replacement by fibro-fatty scar tissue develop with dis- ease progression, but arrhythmias are often the earliest feature of ACM, and typically precede structural remod- eling of the myocardium (heart muscle). ACM is caused by mutations in genes that encode proteins in the des- mosome (cell adhesion sites) of cardiomyocytes. Abnor- mal localization of the desmosomal protein plakoglobin has been observed in patients with ACM. It has been proposed that ACM develops as a consequence of altered electrical signaling mediated by the mutant des- mosomal proteins. To efficiently explore ACM pathophysiology, research- ers developed a stable inducible transgenic zebrafish model. They used the GAL4/UAS transactivation sys- tem to drive cardiac myocyte-specific expression of the human 2057del2 (2-base pair deletion) mutation in the gene encoding the desmosomal protein plakoglobin. This mutation is found in certain human cardiomyopathic defects. Transgenic fish expressing this mutation develop abnormal cardiac physiology within 48 hours of fertiliza- tion, with subsequent progression within 4 to 6 weeks. Answer the questions based on the following figure. AS Original Research Data from authors. (a and bị Representative images of a 5-week-old control sibling (a) and 2057del2 plakoglobin (PG) zebrafish (b) (laft panelsi: dissected hearts (center panela) Icontrol sibling (a") and 2057del2 plakoglobin (b'): OFT, outflow tract; a, atrium: v, ventricle); and stained sections (right panels) [control sibling (a") and 2057del2 plakoglobin mutant fish (b"), show ing cardiomegaly, wall thinning, and chamber dila- tation in narly adulthood). (e) Survival curves for control and 2057del2 plakoglobin mutant fish. Data were pooled from three independent experiments and presented as a total percentage of fish survival as a function of time (n- 125; P<0.0001). WT, wild type. Source: Asimaki A. Kapoor S, Plovie E, at al. Identification of a new modulator of the inter- calated disc in a zebrafish model of arrhyth- mogenic cardilomyopathy. Sci Transl Med. 2014 Jun 11:6(240):240ra74. doi:10.1126/ mind scitransimed.3008008. Parcentmunival sibling (a) and 2057del2 plakoglobin (PG) zebrafish (b) (left panels); dissected hearts (center panels) Icontrol sibling (a') and 2057del2 plakoglobin (b'): OFT, outflow tract; a, atrium; v, ventricle); and stained sections (right panels) [control sibling (a") and 2057del2 plakoglobin mutant fish (b"), show- ing cardiomegaly, wall thinning, and chamber dila- tation in early adulthood). (c) Survival curves for control and 2057del2 plakoglobin mutant fish. Data were pooled from three independent experiments and presented as a total percentage of fish survival as a function of time (n= 125; P<0.0001). WT, wild type. WT contral Cum ORS Cul G Source: Asimaki A. Kapoor S, Plovie E, et al. Identification of a new modulator of the inter- calated disc in a zebrafish model of arrhyth- mogenic cardiomyopathy. Sci Transt Med. 2014 Jun 11:6(240):240ra74. doi:10.1126/ scitransimed.3008008. Commu ladS 3. How does this zebrafish model improve the ability to study potential remedies for this type of mutation in humans with arrhythmogenic cardiomyopathy? Questions Answers can be found at www.pearsonglobaleditions.com 1. Why do zebrafish make good animal models for human arrhythmogenic cardiomyopathy? 4. What are the likely next steps in this type of research. 2. Why were sibling fish chosen to measure the sur- vival rates for the heart mutation?