Myosin expression in semitendinosus muscle during fetal development of cattle: immunocytochemical and electrophoretic analyses

― The pattern of expression of different types of myosin and the development of different muscle cell populations were studied in the semitendinosus muscle of cattle from 39 d of gestation to 30 d of post-natal life. Monoclonal antibodies specific to different myosin heavy chains were used. Two cell generations were identified during myogenesis. They appeared successively and were characterized by different patterns of expression of myosins. The first population, which was present from the first stage studied (39 d of gestation), gave rise to type I fibers, which, in the mature animal, express only slow myosin. A second generation became differentiated at about 120 d of fetal life and then developed into type II fibers (Ila, lib or llc). The beginning of differentiation was characterized in all the cell populations by the expression of specific types of embryonic or fetal myosins. A comparison of these results with findings from previous works shows a marked similarity between species in the pattern of myogenesis but great differences in the length of the different stages of de- velopment. In this respect, myogenesis in cattle closely resembles that in man. bovine I fetus I muscle fiber I differentiation I myosin Rsum ― Expression de diffrentes formes de myosine dans le muscle semitendinosus au cours du dveloppement foetal chez le bovin : tude immunocytochimique et lectrophortique. Le profil d'expression des diffrents types de myosines, et le dveloppement de diffrentes gnrations de cellules musculaires ont t tudis au cours de la vie fcstale chez le bovin, l'aide d'anticorps monoclonaux dirigs contre les chanes lourdes de myosines. On a identifi 2 popula- tions cellulaires apparaissant successivement au cours du dveloppement, et caractrises par des profils d'expression des myosines diffrents. La premire population, dj psente lors du premier stade fcetal tgudi (39 j de gestation), est l'origine des fibres de type 1 qui expriment chez l'adulte une myosine de type lent. Une seconde population est reconnaissable ds l'ge fcetal de 120 j, et conduit ultrieurement aux fibres de type Il (Ila, Ilb et Ilc). Enfin, le dbut de la diffrenciation des fibres musculaires est caractris dans les 2 gnrations de cellules par l'expression de myosines spcifiques de type fcetal ou embryonnaire que l'on ne retrouve pas chez l'adulte. La comparaison de ces rsultats avec ceux obtenus chez d'autres mammifres fait apparatre une grande similarit entre espces dans le profil gnral de la myogense, mais aussi des diffrences importantes dans la dure des diffrentes tapes du dveloppement musculaire. cet gard, la myogense chez le bovin ressemble beaucoup ce que l'on observe chez l'homme. bovin / fcetus / fibre musculaire / differenciation / myosine