| The cultured cells of the human neuroblastoma clone SY5Y extend long, narrow, neurite-like processes. These processes appear under all of the culture conditions tested, but their length and number can be changed by nerve growth factor {NGF}, dibutyryl cyclic adenosine monophosphate {dbcAMP}, and fetal calf serum.;SY5Y cells and processes have an ultrastructure similar to that of developing sympathetic ganglion cells. The cell bodies exhibit eccentric nuclei, and dispersed, sparse, rough endoplasmic reticulum and golgi complexes. The neurites are dominated by microtubules with few intermediate filaments and they end in structures typical of neuronal growth cones. The fine structure is not appreciably altered by agents which alter neurite outgrowth.;NGF causes SY5Y cells in serum-containing medium to double the percentage of cells with processes greater than 100 (mu)m. However, the population doubling time, the length, width and the area of the substrate covered by the cell, the distribution of cell shapes in the population, the number of processes longer that 25 (mu)m and the average number of processes of any size per cell remain the same as in non-NGF treated controls. This indicates that NGF acts not by inducing new processes, but by lengthening the processes that are normally on the cell.;When SY5Y cells are grown in a serum-free medium which supports population growth, there are some differences from serum fed cells, but the percentage of cells with long processes remains the same as in serum. Added NGF does not increase this number, but does reduce population growth and causes a pronounced clumping of the cells. The cells under this condition also show a pronounced aversion to areas bordering scratches made on the culture substrate, a property not seen under other conditions. An hypothesis is presented that NGF alters the adhesive properties of the cells and that serum modulates the expression of the adhesive change.;The effects of dbcAMP in serum and serum-free medium are the opposite of NGF. Long process extension is not influenced by dbcAMP in serum but is greatly stimulated in serum-free medium. Although both dbcAMP and NGF can stimulate process formation they probably act through different mechanisms. |
