Abstract 940: C-kit Positive Cardiac Progenitor Cells Contribute to the Embryonic Development of the Heart
Recently, a compartment of c-kit positive cardiac progenitor cells (CPCs) has been identified in the adult mouse heart. Whether CPCs are restricted to the adult myocardium or are present throughout ontogenesis and contribute to heart development is unknown. For this purpose, a transgenic mouse in which EGFP was driven by the c-kit promoter was employed. C-kit-EGFP positive cells were present in the heart at all stages of embryonic and fetal development, and their number increased with time reaching 400 cells at E17. Symmetric and asymmetric division of c-kit-positive cells was identified respectively by the uniform and non-uniform localization of the endocytic proteins, Numb and α-adaptin. The presence of symmetric and asymmetric division was consistent with the rapid expansion of the pool of c-kit positive cells and the simultaneous generation of a committed progeny. A fraction of c-kit-EGFP positive cells expressed the myocyte transcription factors Nkx2.5 and MEF2C or specific sarcomeric proteins, α-sarcomeric actin, β-cardiac actinin, β-myosin heavy chain and troponin T. These findings demonstrated a linear relationship between CPCs and myocyte formation. Importantly, observations by two-photon microscopy showed that c-kit-EGFP positive cells in the forming heart exhibited morphogenic movements. Conversely, c-kit-EGFP positive cells from extracardiac regions or from the yolk sac did not translocate to the developing heart. Importantly, cardiac c-kit positive cells were negative for markers of hematopoietic stem cells CD34 and CD45. When c-kit-EGFP-positive cells were isolated from the embryonic heart and plated in vitro at limiting dilution, they formed single-cell derived clones. Almost all cells in the clones continued to express c-kit and EGFP. However, few cells located at the periphery of the clones were no longer positive for c-kit and EGFP and began to express sarcoplasmic proteins. In conclusion, c-kit positive cells in the developing myocardium exhibit the properties of stem cells; they are clonogenic and self-renewing and participate in the growth of the embryonic and fetal heart.