CYTOLOGICAL APPROACH TO MORPHOGENESIS IN THE PLANARIAN BLASTEMA .1. CELL BEHAVIOR DURING BLASTEMA FORMATION

Electron microscopy of the planarian blastema has been carried out in an attempt to understand the mechanism of morphogenetic cell differentiation. There was considerable variability regarding the cell profiles which reflect the stage of cell differentiation in the one-day blastema. Moreover, the blastema noticeably displayed a regionally distinct pattern in cell orientation. Migrating cells became aligned perpendicularly to the wound surface and showed membrane ruffling at their leading edge. The distinct pattern of cell distribution was lost in the colchicine-treated regenerates, Immunocytochemical staining for beta-tubulin revealed reactive products in blastema-forming cells. These results suggest that directed cell locomotion correlates with normal development of the blastema and that microtubules are a morphological expression of a cytoskeleton which operates on the directed migration.