Neurite elongation from Drosophila neural BG2-c6 cells stimulated by 20-hydroxyecdysone

Neurite elongation is a critical process in the formation of nerve systems from neural cells. During metamorphosis, the holometabolous insect Drosophila melanogaster reorganizes its central nervous system (CNS) under the influence of the steroid molting hormone 20-hydroxyecdysone (20E). A neural cell line that responds to 20E treatment is therefore desired in order to analyze its signal transduction process. Here, we show that cells of the Drosophila neural cell line BG2-c6 extended long projections of over 30 microm in length after being stimulated with 20E. Most of these projections contained both actin filaments and microtubules. Since microtubules are structural markers of neurites, the projections were considered to be neurites. Live imaging of cells expressing GFP tagged alpha-tubulin showed that the neurites did not have a lamellipodial structure at their tips. Under an electron microscope, microtubules were found to run alongside the actin filaments in the neurite shaft but did not reach the tip, where the actin filaments were loosely bundled rather than being arranged into a meshwork as in lamellipodia. These results indicate that BG2-c6 cells project neurites without the typical growth-corn structure at their tips after 20E stimulation.