SMOOTH-MUSCLE MYOSIN LIGHT-CHAIN KINASE IS TRANSIENTLY EXPRESSED IN SKELETAL-MUSCLE DURING EMBRYOGENESIS AND MUSCLE REGENERATION BOTH IN-VIVO AND IN-VITRO

By using a polyclonal antibody raised against smooth muscle Myosin Lig ht Chain Kinase of adult chicken we show that the 135 kDa smooth muscl e Myosin Light Chain Kinase isoform is present in neonatal and regener ating rat skeletal muscle, as well as in adult atrial myocardium. No r eaction was evident in adult skeletal muscle fibres. In neonatal and i n early regenerating muscle smooth muscle Myosin Light Chain Kinase is associated with embryonic myosin as revealed by their co-presence in muscle fibres. Experiments in vitro show the same results in myotubes. In atrial myocardium there is a patchy positivity in certain group of myocytes. Immunoblotting experiments show in muscle cell cultures, in neonatal and in regenerating skeletal muscle a protein band with elec trophoretic mobility corresponding to that of smooth muscle Myosin Lig ht Chain Kinase. These results suggest that the expression of smooth m uscle Myosin Light Chain Kinase is not fully tissue-specific and that regulation of the contractile machinery could be different during myog enesis and in adulthood, in relation to the peculiar dynamic character istics ol: developing muscles.