Neurite retraction and regrowth regulated by membrane retrieval, membrane supply, and actin dynamics.

Structural remodeling of neurons occurs during development, regeneration, and in relation to learning and memory acquisition processes. These processes are associated with reconfiguration of the cytoskeleton, and are accompanied by adjustments of the plasma membrane surface area. Using cultured Aplysia neurons, we examined the role of membrane budgeting and the submembrane actin skeleton in determining the dimensions and shape of neurons. We found that the dimensions and cytoarchitecture of cultured neurons reach a steady state by maintaining a balance between constitutive plasma membrane retrieval and insertion. Constitutive membrane retrieval and the addition of Golgi-derived membranes are not coupled. Therefore, inhibition of Golgi-derived membrane supply by brefeldin A (BFA) leads to total retraction of the neurites. The process of BFA-induced neurite retraction is reversible upon washout. BFA-induced neurite retraction is associated with orderly retrograde shortening of the microtubule (MT) skeleton. The actin-perturbing drugs cytochalasin B, latrunculin A, or jasplakinolide block constitutive membrane retrieval. In the presence of the actin-perturbing drugs, depletion of Golgi-derived membrane supply by BFA does not lead to neurite retraction. Taken together, the present study reveals that the ratio of constitutive plasma membrane retrieval/exocytosis plays a pivotal role in defining the neuron's dimensions and cytoarchitecture. Submembrane actin dynamics plays a key role in regulating the rates of constitutive membrane retrieval. We propose that the coordination between MT polymerization and the surface area of the plasma membrane is coordinated by a linking mechanism in which the submembrane actin plays a major role.