Sequence of expression of MyoD1 and various cell surface and cytoskeletal proteins in regenerating mouse muscle fibers following treatment with sodium dihydrogen phosphate

An immunohistochemical study was performed in order to evaluate the sequence of expression of various cell surface proteins [neural cell adhesion molecule (NCAM) and its polysialylated isoform, PSA NCAM, and utrophin], cytoskeletal proteins (myosin heavy chain isoforms, desmin) and the transcription factor MyoD1 in regenerating mouse muscle fibers following treatment with sodium dihydrogen phosphate. The sequence of the regeneration process with this new myotoxic agent is similar to that which can be observed with other myotoxic substances (local anaesthetics such as bupivacaine or snake venoms). The results show that NCAM, PSA NCAM and desmin were already present on the first day after injury in the presumptive myoblasts. The highest level of all of these proteins was observed on the third day. At this stage, regenerating muscle fibers also strongly and diffusely expressed myosin heavy chain isoforms and utrophin throughout their sarcolemma, whereas NyoD1 expression was observed in the regenerating myonuclei. PSA NCAM and MyoD1 had gradually disappeared from the muscle fibers by the seventh day, by which time, the expression of the other developmentally regulated proteins had also decreased. On the 21st day after injury, a few fibers still expressed NCAM but not the other proteins. This study first shows that sodium dihydrogen phosphate is a new myotoxic agent that is cheap, widely available and easy to handle. It also establishes the schedule of expression of various developmentally regulated proteins in regenerating mouse muscle fibers. (C) 1999 Elsevier Science B.V. All rights reserved.