Growth control in miniclones of human glial cells

An improved method for the production of haptotactic palladium islands is described. Tissue culture dishes were coated with a thin layer of agarose, which was air-dried. Palladium was evaporated, using electron-microscope grids for masking. When seeded on such dishes, glial cell attachment and spreading was entirely confined to the palladium-coated areas. The method allowed the analysis of the clonal growth of several hundreds of glial cells seeded on 7 200 and 12 500 μm² squares. It was found that the mass population consisted of cells with widely differing potentials for clonal growth. A fraction of non-dividing cells increased with increasing passage level. Eventually, after more than a week of incubation, proliferation ceased on the squares although a considerable part of the periphery of the marginal cells was free of contacts with other cells. The finding is compatible with the idea that restriction of cell spreading, and not cell contact, may cause density-dependent inhibition of proliferation.