Abstract 173: Clonal Analysis Reveals Limited Proliferative Capacity of Mature Cardiomyocytes during Embryonic Development.
There is growing evidence that supports the ability of the heart to generate new cardiomyocytes during development and in response to injury albeit at a very low rate. It still remains unclear whether the newly generated cells originate from cardiac progenitor/stem cells or from pre-existing cardiomyocytes that re-enter the cell cycle. Understanding the cellular mechanisms regulating new cardiomyocyte formation is imperative towards the development of novel clinical strategies. We assessed the hypothesis that the cardiomyocytes generated during cardiac development are derived from cardiac progenitor cells and to a lesser extent form proliferating cardiomyocytes. We performed clonal analysis of cardiomyocyte formation by utilizing a stochastic multicolor reporter system (Rainbow) that allows random labeling of cells with three fluorescent proteins upon Cre-mediated recombination. Rainbow mice were crossed to αMHC-CreER mice for selective marking of cardiomyocytes or to Actin-CreER mice where all types of cells can be labeled. We induced rare recombination events at embryonic day E12.5 and clonal expansion of labeled cells was retrospectively analyzed at different time-points from E15.5 to postnatal day P30. To determine at which developmental stage cardiac cells lose their ability to proliferate, recombination was induced at different time-points from early embryonic to postnatal life and analysis was performed at P30. For each time-point, data was collected from ten mice. In αMHC-CreER;Rainbow mice, we observed mainly single cell labeling, a few doublets and some rare four-cell clones. At the same time-points, Actin-CreER;Rainbow hearts exhibited a large number of clones ranging from doublets to clones of more than twenty cells. Interestingly, clone formation and expansion was reduced with age. In conclusion, our results indicate that αMHC-positive cardiomyocyte proliferation is limited during development. On the other hand, non-αMHC expressing cells exhibited clonal expansion suggesting the possible contribution of cardiac progenitors even during late cardiovascular development.
- © 2013 by American Heart Association, Inc.