Induction of axon-like and dendrite-like processes in neuroblastoma cells

Neuroblastoma cells are widely utilized models for the study of the neuritic outgrowth phase of neuronal differentiation, but relatively few such studies have attempted to identify the nature of the process outgrowths. This identification will be necessary in developing strategies for utilizing these models to distinguish the underlying mechanisms involved in axonogenesis vs dendritogenesis. In an effort to identify procedures for inducing specific types of neurite outgrowth, and for distinguishing axon- from dendrite-like processes, we have subjected two neuroblastoma cell lines to a variety of stimuli previously shown to induce neurite outgrowth in these cells. These include neuraminidase, ionomycin, KCl+dibutyryl cAMP, cholera toxin B subunit, retinoic acid, dibutyryl cAMP (alone), GM1 ganglioside, and low serum. The first four of these (group 1) gave rise to neurites with axon-like characteristics, including immunostaining that was positive for phosphorylated high molecular weight neurofilament protein (NF-H) and synaptic vesicle protein-2 (SV2), but negative for microtubule-associated protein-2 (MAP2). The next three treatments (group 2) resulted in dendrite-like processes, as evidenced in immunostaining that was positive for MAP2 and negative for NF-H and SV2. Neurites produced by low serum had mixed properties. These cytoskeletal differences were supported by immunoblot analysis with antisera to the above cytoskeletal proteins. Striking morphological differences were also noted, group 2-induced neurites being significantly shorter with more branch points than those generated by group 1 stimulants. Time of exposure to stimulatory agent was crucial in determining expression of the neuritic phenotype. Correlation with previous studies suggests that axon-like neurites result from stimulants which elevate intracellular Ca2+, a dependence not previously reported to our knowledge. Dendrite-like process outgrowth, on the other hand, does not appear to depend on altered intracellular Ca2+.