Abstract 1066: Serum Response Factor Orchestrates Cardiac Myogenesis: Advanced from Embryonic Models to ES Cell Rescue in a Cofactor Specific Fashion
We asked what the essence of SRF is during early path of cardiac commitment. To approach so, we engineered a chromosome carrying SrflacZ (null) and Nkx2.5Cre to generate SRF early cardiac knockout using Cre/LoxP system. This Srfcko mutant suffered with an immotile tubular heart at ~8.0 – 8.5 dpc, which is the earliest non-beating heart defect due to ablation of cardiac transcription factor. Expression of both cardiac and smooth muscle α-actins was blocked in mutant shown by in situ, which was further demonstrated at protein level. Ultrastructural analysis indicated that neither aligned filament nor Z disk was formed in multiple Srfcko mutants. The phenotype of Srfcko with the blockage in contractile actin expression, blockage in sarcomere formation and blockage of heart beating was strikingly in contrast to the Nkx2.5(null):Srf(hetero) compound mutant, which did have heart beating and actin expression. These embryonic studies suggested that SRF functions as the core factor orchestrating cardiac myogenesis in vivo. Next, we try to catch the function of specific transcription factor interaction during myogenesis in ES cell differentiation. We applied lentivirus delivery system to achieve uniformed expression of wild type and mutated forms of human SRF in mouse Srf-/- ES cell. Our pilot experiment demonstrated that both hSRF (wild type) and hSRF162A (similar to wild type) can successfully rescue myocyte differentiation and beating in embryoid body. However, hSRF162D (mimicking phosphorylation, blocking major cofactors interaction) failed to do so. Rescue potentials of mutated SRFs, which affect particular cofactor interaction, such as Nkx2.5, Gata4 and myocardin, were currently under investigation. In conclusion, SRF plays a central role in cardiac myogenic hierarchy and importance of specific association between SRF and its cofactors will be discussed.
*This project was supported by Grants P01 HL49953 and R01HL79628 – 01 from the National Institutes of Health.