Actin cytoskeleton of extraembryonic endoderm and teratocarcinoma-derived endoderm cells

Distinct F-actin- and myosin-containing stress fibers were observed in situ in many endoderm cells of parietal yolk sacs from 11-day mouse embryos. In visceral endoderm (VE) such fibers were not seen, and F-actin was concentrated in the cell periphery. Correspondingly, in electron microscopy ventral cell membrane-associated bundles of microfilaments were revealed in the periphery of parietal endoderm (PE) cells but not in VE cells. Both PE and VE cells formed stress fibers in primary cultures. Undifferentiated F9 embryonal carcinoma cells formed only short actin spikes and fibrils irrespective of growth substratum. In PE-like derivatives of F9 cells, on the other hand, distribution of F-actin was markedly affected by the growth substratum: They formed distinct stress fibers when plated on fibronectin but did not when plated on gelatin. Similarly, in teratocarcinoma-derived PE cells (PYS-2) adhesion to fibronectin induced the formation of distinct bundles of F-actin and plaques of vinculin. The results suggest that the susceptibility of teratocarcinoma cell actin cytoskeleton to the influence of molecular composition of surrounding matrix is developmentally regulated. On the other hand, the reason for the presence of stress fibers in PE cells and for their absence in VE cells is unclear.