Figure 3.

Lamellipodia segregate and condense during MAP2c-induced neurite initiation. Neuro-2a cells were transfected with GFP-MAP2c and imaged using confocal microscopy as described in Materials and Methods. The extent of the plasma membrane of the cell (white line) was manually traced from images in which low-level signals were maximized. At the beginning of the time sequence, the cell exhibited a broad lamellipodium (00:00, 00:12) surrounding a large portion of the cell body. MAP2c-decorated microtubules were readily visualized during the time course. During the first minutes, single microtubules or small microtubule bundles emerged from the soma and penetrated into the lamellipodium without inducing neurites (00:12). At a later stage (00:55), the lamellipodium became segmented, and shortly thereafter, a thick microtubule bundle rapidly formed (00:55, 01:28, 01:34). This neurite remained stable for at least 2 hr (also see Fig 3.mov; time points represent hours:minutes). Fluorescent images represent either confocal planes or three-dimensional reconstructions (3d Recon).