PC12 cell aggregation and neurite growth in gels of collagen, laminin and fibronectin.

PC12 cells form aggregates when suspended within three-dimensional, self-assembled, type I collagen gels; these aggregates increase in size over time. In addition, when the cells are cultured in the presence of nerve growth factor, they express neurites, which extend through the three-dimensional matrix. In this report, the roles of fibronectin, laminin and nerve growth factor in PC12 cell aggregation and neurite growth following suspension in collagen matrices were evaluated. Single cells and small clusters of cells were suspended in collagen gels; the kinetics of aggregation were determined by measurement of the projected area of each aggregate, and neurite lengths were determined by measurement of end-to-end distance. Fibronectin and laminin inhibited the aggregation of PC12 cells at 50 micrograms/ml, and fibronectin, but not laminin, inhibited the growth of neurites at 100 micrograms/ml. In the absence of serum, the aggregation of cells cultured with nerve growth factor was almost completely inhibited, but the average neurite length was unaffected. In the presence of nerve growth factor, the extent of cell aggregation could not be explained simply by an increase in cell number, suggesting the presence of two separate mechanisms for aggregate growth: one dependent on cell motility and another dependent on cell proliferation.