Clonal variation in colony morphology and growth of CHO cells cultured on agar.

Single Chinese hamster ovary (CHO) cells plated on agar form macroscopic colonies with high efficiency. Colonies produced by cells from the uncloned cell line increase in diameter continuously for 10-12 days after plating to form mounds of cells about 1 mm in diameter. With further incubation, some of these colonies do not increase in diameter (arrested dome), some form an expanding annular monolayer of cells around the central mount (fried egg), and some grow by enlarging the central mound into a low multilayered disc (saucer). These colony types on agar appear to be clonal characteristics of the CHO cell line. Cloning the line gives two kinds of isolates: one forms a mixture of arrested dome and fried egg colonies in an inheritable ratio, and the other forms saucer colonies. Cells from saucer colonies form saucer colonies when replated on agar. Cells from all colony types replate with similar efficiency on plastic or agar, and exhibit the same growth rate and cell size in liquid suspension culture. On plastic substrate, all these CHO cells form colonies which increase continuously in diameter for as long as 21 days, and little clonal difference in the morphology of colonies or of single cells is observed. These observations reveal a previously unsuspected heterogeneity in an established line of cultured mammalian cells and provide a method for studying new classes of in vitro growth control phenomena. These control phenomena may help in the building an in vitro model for tumor growth.