Nascent muscle fiber appearance in overloaded XXXX slow-tonic muscle.

@entity71033 @entity1184 @entity1347 @entity73 @entity1573 @entity71034
The application of a weight overload to the humerus of @entity1573 induces a @entity1184 of @entity1347 ( @entity1347 ) muscle fibers. This growth is accompanied by a rapid and almost complete replacement of one slow-tonic @entity71033 isoform, @entity71034 , by another slow-tonic isoform, @entity71033 . In addition, a population of small fibers appears mainly in extrafascicular spaces and, concurrently, three additional @entity71033 bands are detected by gel electrophoresis. Five antibodies against @entity71033 ( @entity71033 ) isoforms were selected as immunocytochemical probes to determine the cellular location and nature of these myosins. The antibodies react with ventricular, fast skeletal muscle and either @entity71034 or @entity71033 , or both the @entity73 . The antifast and antiventricular antibodies react with @entity71033 present in the 10-day embryonic @entity1347 muscle but do not react with @entity71033 in posthatch @entity1347 muscle. The small fibers in overloaded muscle contain a @entity71033 isoform characteristically expressed during the embryonic stage of @entity1347 muscle development and therefore are named nascent myofibers. Some of the nascent myofibers do not react with the antibody to both @entity73 , indicating the lack of the normal adult slow-tonic myosins which are expressed in 10-day embryos. In order to explore the origin of the nascent fibers, an electron microscopic study was performed. Stereological analysis of the existing fibers shows a stimulation of numbers and sizes of satellite cells. In addition, the volume occupied by nonmuscle and undifferentiated cells increases dramatically. Myotube formation with incipient myofibrils is seen in extrafascicular spaces. These data suggest that new muscle fiber formation accompanies @entity1184 in overloaded @entity1573 @entity1347 muscle and the process may involve satellite cell migration.
