As part of a search for chemical agents able to promote the fusion of mouse A 9 fibroblasts, oleylamine, a positively charged compound, has been investigated for its fusogenic properties. In the pH range 5.5-7.5 and in the presence of dextran, fibroblast polykaryons were produced on treatment of monolayers of cultured cells with oleylamine dispersed directly in a modified Eagle's medium at concentrations of not less than 0.111 mg/ml. Electron microscopy demonstrated the absence of a dividing plasma membrane between the constituent nuclei of the polykaryons, and showed clustering of other subcellular organelles around their original parent nuclei.

Fusion, which was preceded by rounding and swelling of the cells, occurred between cells in contact after 10-15 min. Oleylamine in lipid droplets containing glyceryl mono- and dioleate also caused swelling and fusion but to a lesser extent. Phosphatidylcholine appeared to have an inhibitory effect on oleylamine-induced fusion: lecithin liposomes containing oleylamine were only weakly fusogenic. The fusion process, but not the preceding swelling, was calcium-dependent; fusion was inhibited by low concentrations of lanthanum ions.

While oleylamine inhibited cell division in monolayer cultures and prevented adhesion of fibroblasts in suspension to glass coverslips, oleylamine in lipid droplets was less toxic and is thus potentially more useful in this form for interspecific hybridization experiments.

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