Biological properties of crude growth inhibiting factor produced by embryonic spinal cord cells in culture

Abstract

Cultured chick spinal cord cells produced a soluble factor or factors which inhibited growth and development of muscle cells in culture. The activity of cord inhibitory factor depended on the number of cord cells inoculated into culture, and the duration of their incubation in culture. Nonreplicating frozen and thawed cells produced little or no inhibitory factor. Cord inhibitory factor was produced by chick cord cells from embryos tested at 11 to 21 days of age. While “stale” media from thigh, heart, and skin cell cultures also were slightly inhibitory, their activity was several-fold less potent than that of cord cells. Media collected from liver cell cultures stimulated growth and protein synthesis. Crude cord inhibitory factor had little or no effect on target muscle cells (plated at 1 × 10 6 cells per dish) after the first 2 days of culture. Cells began in culture at lower density, however (1 × 10 5 cells per dish), retained their susceptibility for at least 4 days in culture while continuing active DNA synthesis. This suggests that cord inhibitory factor acted on cells while they were replicating. Although inhibited cells did not incorporate [ 14C]lysine into protein normally, they retained the ability to take up the amino acid into their cytoplasm. Inhibitory activity of crude cord factor was also demonstrable against cultures of heart and skin cells. Cord cell cultures, however, were relatively resistant. It is at present not known whether the inhibitory factor is produced by neuronal or glial cells.