Background-The development of improved strategies for efficient and reproducible in vivo gene transfer into the murine heart will ultimately allow the intersection of somatic and germline gene transfer strategies to study complex features of cardiac biology and diseases. Methods and Results-For embryonic gene transfer, an adenovirus vector expressing ␤-galactosidase was injected in utero into the ventricular cavity of living embryos via microsurgical approaches. The injected embryos were

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... ed to term, and efficient expression of the transgene was detected in all cell types in the heart. For postnatal cardiac gene transfer, adenovirus was injected into the cardiac ventricle of neonatal mice, resulting in efficient expression of the transgene in the outer layer of the myocardium as well as cardiomyocytes in the middle and inner layers of the cardiac wall. Mice examined after 3 weeks displayed a pattern of expression that completely mimicked the pattern seen after 3 days, and gene expression was also found after 6 months. The infected myocytes can be identified by coinfection of an adenovirus expressing green fluorescent protein without affecting their normal physiological function. Conclusions-We have developed a new strategy to achieve efficient and long-term foreign gene expression in both embryonic and postnatal mouse myocardium via direct intracardiac injection of recombinant adenovirus. The strategy should allow the functional assessment of the expression of dominantly acting exogenous genes, overexpression of wild-type genes, and Cre recombinase-mediated gene ablations at the single-cell level in the context of the intact adult mouse myocardium. (Circulation. 2000;101:178-184.)