REGULATION OF MITOTIC-ACTIVITY AND THE CELL-CYCLE IN PRIMARY CHICK MUSCLE-CELLS BY NEUROTRANSFERRIN

Neurotransferrin (NTF), a transferrin extracted from adult chicken peripheral nerves, promotes growth of primary chick muscle cells in the absence of embryo extract. NTF stimulates DNA synthesis and cell proliferation. NTF was demonstrated a mitogen using 2 counts of orcein-stained mitotic figures and analysis of cell cycle kinetics with a fluorescence-activated cell sorter. In low-density cultures mitotic activity increases with increasing doses of NTF followed by a plateau at concentrations > 6 .mu.g/ml. Residual, embryonic mitotic activity progressively declines with time after plating muscle cells in the absence of NTF. Absence of NTF for 2 days causes cells to lose irreversibly their myogenic potential. In the presence of NTF, mitotic activity increases for 2 days followed by a decline concurrent with myoblast fusion and formation of myotubes. Cell cycle analysis showed that NTF addition causes cell populations to shift from G1 to S and G2 + M within 18.5 h. Muscle cells, plated at high densities in the absence of NTF, show mitotic activities similar to those plated at low densities in the presence of NTF. Addition of NTF to high-density cultures is ineffective in stimulating mitosis. A typical cell plating densities, NTF is a required mitogen for primary chick muscle cell cultures.