Neurotrophic and hepatotrophic stimulation of proliferation of embryonic chick muscle cells in vitro: Assay and partial characterization of mitogenic activity in chick embryonic organ and tissue extracts

Abstract

Whole embryo extract is routinely employed as a growth-promoting supplement in chick embryonic muscle cell cultures. In assessing the effect of the extract on muscle cell cultures, extracts of various embryonic tissues and organs were substituted for whole embryo extract and the effects on proliferation of dissociated 12-day chick embryonic leg muscle cells were observed. The effects were measured according to [ 3H]thymidine incorporation into deoxyribonucleic acid (DNA) and were confirmed with total cell counts. Brain and liver extracts were found to be especially effective in stimulating muscle cell proliferation. The extracts were found to be heat and trypsin labile. Further analysis of activity in the extracts by dialysis and Sephadex G-25 fractionation revealed the presence of at least two classes of activity—one of high molecular weight (>5000) and one of low molecular weight (<5000)—which must be present together to yield the full activity of crude extracts from embryonic liver and brain. The results are discussed against the background of our interest in the neurotrophic phenomenon.