151 - Cardiomyocyte Ploidy, Proliferation, and Cell Size in the Leopard Gecko (Eublepharis Macularius): Utilizing Cellular Attributes as Predictive Tools for Heart Regeneration Across Vertebrates

Poster Board Number: 151
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Abstract Body : While the overall function of the heart is conserved across vertebrates, cellular attributes of individual muscle cells (cardiomyocytes) vary across species. Emerging evidence indicates that these attributes are associated with the ability of the heart to regenerate. For example, among non-regenerating species like humans and mice, cardiomyocytes typically have more than two sets of chromosomes (=polyploid), rarely proliferate, and are comparatively large. In contrast, in regeneration-competent zebrafish, cardiomyocytes are diploid, spontaneously proliferate, and are relatively small. Accordingly, cardiomyocyte ploidy, proliferative capacity, and relative size may serve as predictive tools for screening the potential for heart regeneration in other species. Here, we investigate these cardiomyocyte attributes in the reptile Eublepharis macularius, the leopard gecko. Using dissociated ventricles and the nuclear counterstain DAPI to measure fluorescence intensity as a proxy for DNA content, we found that ~90% of gecko cardiomyocytes are diploid. Using serial histology and immunostaining for the DNA synthesis phase of the cell cycle, we determined that gecko cardiomyocytes spontaneously proliferate in both subadults and adults (~11% vs. ~0.1%, p=0.0001). Using the lectin wheat germ agglutinin to immunostain the plasma membrane of cardiomyocytes, we measured cross-sectional area as a proxy for cell size. We found that gecko cardiomyocytes are comparatively small, even in adulthood (~6 um^2 vs. ~9 um^2). The size of gecko cardiomyocytes were more than 10X smaller than those of mice (~129 um^2, p< 0.0001), and comparable to sizes observed in zebrafish. Taken together, our data predicts that geckos are capable of regenerating cardiomyocytes and point towards the use of these cellular attributes as predictive tools in other vertebrate taxa.