Zeta Actin Muscle Specific (MSA) Antibody. Zeta’s mouse monoclonal antibody recognizes Actin, Muscle Specific (MSA). This monoclonal antibody to Actin (MSA) reacts with Actin (MSA) from tissue extracts of uterus, ileum, aorta, diaphragm, heart, and smooth muscle cells. This monoclonal antibody to Actin (MSA) recognizes the alpha actin from skeletal, cardiac, and smooth muscle and the gamma actin from smooth muscle sources. Finally, the monoclonal antibody to Actin (MSA) stains tumors of smooth muscle (leiomyomas and leiomyosarcomas) as well as skeletal muscle (rhabdomyomas and rhabdomyosarcomas).