Neonatal mouse gonocyte proliferation assayed by an in vitro clonogenic method.

Survival and proliferation of mouse gonocytes was studied using a single cell clonogenic assay in vitro. The effect of growth factors and extracellular matrix on clonogenic development was quantitated. Fundamental requirements for growth of neonatal gonocytes included addition of fetal calf serum and coating culture wells with collagen IV alone or with added fibronectin. After 4-5 days, colonies ranged in size from four to > 128 cells, and some contained very elongated cells indicating migratory behaviour. Soluble stem cell factor did not have any effect on clonogenicity, although STO (subline of SIM mouse fibroblasts) cells, which produce membrane-bound stem cell factor, reduced colony formation from 79 +/- 5.9% to 20 +/- 3.3% without added growth factor. The majority of gonocytes and type A spermatogonia express the c-kit receptor according to in situ hybridization studies. However, the results indicate that the receptor may not be functional in neonatal gonocytes and their immediate progeny. The current assay for gonocytes can be extended to test new growth factors or proliferation-inducing agents directly, as well as to study cell-cell interactions. This assay and long-term propagation of neonatal germ cells will provide the much needed resources to enable greater understanding of the early development of germ cells.