Although acetylation appears to peak at four days post-fusion, there is no statistically significant difference between any time point past day one, suggesting that histone H3K9/K14 acetylation of the human MyoD promoter reaches stable levels rapidly following fusion. Finally, to evaluate the potential utility of targeted cell fusion for regenerative medicine, we investigated the ability of Ha7 to increase the efficiency of fusion between non-myogenic cells and skeletal muscle fibers in vivo. In order to accomplish this, mouse embryonic fibroblasts were infected with the lentiviral vectors, LV-HIG and LV-FIY, which encode Ha7-IRES-GFP and F-IRES-YFP respectively, and cells were subsequently purified by flow cytometry . Doubly infected MEFHa7/F as well as singly infected MEFHa7 control cells were then transplanted into the tibialis anterior muscle of C57BL/6 recipient mice. One week after transplantation, mice were sacrificed and hind limbs were examined for the presence of GFP-positive muscle fibers. As seen in Figure 5C,D, a large number of GFP-positive fibers exhibiting normal morphology and surrounded by basal lamina were PI3K inhibitor observed in all recipients of MEFHa7/F cells. Considering the fact that various forms of muscle damage are known to augment the contribution of transplanted cells to myofiber regeneration, we also transplanted MEFHa7/F and control MEFHa7 cells via intramuscular co-injection with the myotoxic phospholipase, notexin . As seen in Figure 5C, the number of GFP-positive fibers observed following coadministration of notexin was roughly 3.5-fold greater than the number observed in undamaged recipients. Although the GFPpositive fibers observed in notexin treated recipients were smaller than those observed in undamaged recipients this phenomenon is a Evofosfamide CYP17 inhibitor common hallmark of regenerating muscle . We have created a cell fusion reagent, Ha7, which overcomes the low efficiency, high toxicity and lack of specificity exhibited by existing chemical and physical fusogens. As opposed to PEG and electrofusion, our system is based on a specific ligand-receptor interaction, which simultaneously promotes the proper pairing and efficient fusion of cells. This feature maximizes the generation of heterokaryons and virtually eliminates the non-productive formation of homokaryons. In vitro, cells expressing Ha7 routinely fused with over 90% of cultured myotubes and consistently yielded 12 to 17-fold more heterokaryons than a standard PEG-mediated protocol.