Scanning electron microscopy of aggregating embryonic neural retina cells.

Scanning electron microscopy of in vitro reaggregation of trypsin-dissociated neural retina cells from 10-day chick embryos revealed that filopodial projections participate in the assembly of the dispersed cells into clusters. Freshly dissociated cells displayed numerous elongated, randomly projecting filopodia. With the onset of cell reaggregation these filopodia bridged and connected distant cells becoming shorter as the cells came together and formed aggregates. In 24-h cell aggregates only short microvilli were seen, mostly on cell surfaces facing the periphery of the aggregate. Cells dissociated from retina tissue pre-treated with inhibitors of protein synthesis, or cells exposed to these inhibitors immediately after dissociation were mostly devoid of filopodial projections; such cells failed to re-aggregate histotypically. Thus, metabolic and biosynthetic processes are required for the changes in the cell periphery which result in formation or maintenance of filopodia, and which enable trypsin-dissociated cells to reform histotypic associations. Possible relationships between the formation of filopodia and histotypic reaggregation of cells is discussed.