Spatial expression of Myocardin protein
Vascular smooth muscle cell (VSMC) dedifferentiation, a phenomenon found in virtually all vascular diseases, is characterized by a transcriptional switch from a contractile to a phenotypically modulated state. Myocardin (MYOCD) is a smooth muscle-restricted co-activator that is necessary and sufficient for the differentiation of VSMC through the transcriptional activation of a battery of SMC-restricted cytoskeletal and contractile genes.  Despite 25 years of research on MYOCD, the reliable expression of this protein continues to be poorly represented and understood. Accordingly, we generated a novel HA-tagged rat model to extend previous work in a similarly constructed mouse model. Western blotting studies document the highest MYOCD protein expression in aorta, bladder and uterus with low or undetectable expression in all other tissues of the rat, including heart. Predictive modeling supports the C-terminus of MYOCD to be most immunoreactive where the HA tag and one other commercial immunogen reside. Of note, the latter immunogen was used to generate what appears to be the most trustworthy commercial antibody against MYOCD. In vitro transcription/translation and phosphatase treatment of ectopic and endogenous MYOCD protein reveal an intrinsically high molecular weight of MYOCD that has eluded virtually all prior reports. Importantly, we show the very first spatial expression profile of MYOCD protein across mouse and rat tissues under baseline and vascular injury conditions.  These results offer the SMC community new resources and insight into the reliable detection of MYOCD protein.