Smooth muscle myosin light chain kinase is transiently expressed in skeletal muscle during embryogenesis and muscle regeneration both in vivo and in vitro

Byusing a polyclonal antibody raised against smooth muscle MyosinLight Chain Kinase of adult chicken we show that the 135 kDasmooth muscle Myosin Light Chain Kinase isoform is present inneonatal and regenerating rat skeletal muscle, as well as inadult atrial myocardium. No reaction was evident in adultskeletal muscle fibres. In neonatal and in early regeneratingmuscle smooth muscle Myosin Light Chain Kinase is associated withembryonic myosin as revealed by their co-presence in musclefibres. Experiments in vitro show the same results in myotubes.In atrial myocardium there is a patchy positivity in certaingroup of myocytes. Immunoblotting experiments show in muscle cellcultures, in neonatal and in regenerating skeletal muscle aprotein band with electrophoretic mobility corresponding to thatof smooth muscle Myosin Light Chain Kinase. These results suggestthat the expression of smooth muscle Myosin Light Chain Kinase isnot fully tissue-specific and that regulation of the contractilemachinery could be different during myogenesis and in adulthood,in relation to the peculiar dynamic characteristics of developingmuscles