MYOCYTE DIFFERENTIATION AND BODY-WALL MUSCLE REGENERATION IN THE PLANARIAN GIRARDIA-TIGRINA

Freshwater planarians (Platyhelminthes, Turbellaria) show a great degr ee of morphological plasticity, making them a useful model for studyin g cell differentiation and pattern restoration processes during regene ration. Using confocal microscopy and a monoclonal antibody specific f or muscle cells (TMUS-13), we have monitored the restoration of the bo dy wall musculature during head regeneration in whole-mount organisms. Our results show that until the 4th day of regeneration the blastema is occupied by very disorganized muscle fibers, that from this moment become progressively organized restoring the original muscle pattern. In addition to recognizing mature muscle cells, TMUS-13 also recognize s differentiating myocytes, allowing us to trace the origin of newly f ormed muscle cells. We report that myocytes are detected in the postbl astema region as early as day 1 of regeneration. This is the first dem onstration that, in addition to serving as a proliferative zone as pre viously described, overt differentiation begins in the postblastema, a t least for muscle cells. We also show that the TMUS13 antigen is the myosin heavy-chain gene from planarians.