Actin Reorganisation in Nerve Morphogenesis

Abstract

Anatomists over centuries have described nerve cells which are notable for their diversity of architectures ranging from rather simple cells to highly complex and beautiful shapes. The soma of most neurons has two types of projections – dendrites, which receive inputs from the environment or other nerve cells, and axons, which specialise in information transfer. The correct shape of a neuron and its connectivity which forms the basis of a functional circuit is crucial for the normal physiology of an animal. Defects in neuronal morphogenesis have been shown to be the cause of several neurological diseases. In this article, we focus on a key molecule – actin, a component of the cytoskeleton – that forms the basis of cell shape and growth. We discuss how signals from within the cells and from its developmental milieu influence the organisation of actin which in turn impacts on the shape and function of a nerve cell.

Key Concepts

• Actin is enriched in areas of neurons which undergo rapid changes in shape.
• Actin dynamics is regulated by multiple upstream signals and intracellular effectors.
• Local destabilisation of the actin cytoskeleton is a key downstream event during selection of an axon.
• Actin dynamics in the growth cone regulates filopodial extension/retraction.
• Actin cytoskeleton is highly dynamic in dendritic spines.
• Neuronal activity-dependent spine enlargement is correlated with a shift in F-/G-actin equilibrium towards F-actin.
• Rho GTPases are major intracellular regulators of actin dynamics.