molecularly specialized, with transcriptomes and proteomes that are distinct from those of their parent cell bodies. There are many cytoskeletal-associated proteins, which perform a variety of duties within the growth cone, such as anchoring actin and microtubules to each other, to the membrane, and to other cytoskeletal components. Some of these components include molecular motors that generate force within the growth cone and membrane-bound vesicles which are transported in and out of the growth cone via microtubules. Some examples of cytoskeletal-associated proteins are fascin and filamins (actin bundling), talin (actin anchoring), myosin (vesicle transport), and mDia (microtubule-actin linking). Axon branching and outgrowth The highly dynamic nature of growth cones allows them to respond to the surrounding environment by rapidly changing direction and branching in response to various stimuli. There are three stages of axon outgrowth, which are termed: protrusion, engorgement, and consolidation. During protrusion, there is a rapid extension of filopodia and lamellar extensions along the leading edge of the growth cone. Engorgement follows when the filopodia move to the lateral edges of the growth cone, and microtubules invade further into the growth cone, bringing vesicles and organelles such as mitochondria and endoplasmic reticulum. Finally, consolidation occurs when the F-actin at the neck of the growth cone depolymerizes and the filopodia retract. The membrane then shrinks to form a cylindrical axon shaft around the bundle of microtubules. One form of axon branching also occurs via the same process, except that the growth cone “splits” during the engorgement phase. This results in the bifurcation of the main axon. An additional form of axon branching is termed collateral (or interstitial) branching;. Collateral branching, unlike axon bifurcations, involves the formation of a new branch from the established axon shaft and is independent of the growth cone at the tip of the growing axon. In this mechanism, the axon initially generates a filopodium or lamellipodium which following invasion by axonal microtubules can then develop further into a branch extending perpendicular from the axon shaft. Established collateral branches, like the main axon, exhibit a growth cone and develop independently of the main axon tip. Overall, axon elongation is the product of a process known as tip growth. In this process, new material is added at the growth cone while the remainder of the axonal cytoskeleton remains stationary. This occurs via two processes: cytoskeletal-based dynamics and mechanical tension. With cytoskeletal dynamics, microtubules polymerize into the growth