Growth cone movement

Role of the growth cone in neuronal differentiation

Nerve growth cones are motile, exploring organelles at the tip of a growing neurite. The growth cone is a highly specialized structure, equipped with a complex machinery for reversible membrane expansion and rapid cytoskeletal reorganization, a machinery required for growth cone motility and neurite elongation. It also contains perception systems that enable the growth cone to respond to external signals, thereby steering the trailing neurite to the correct target. Soluble and substrate bound guidance molecules in the environment modulate growth cone behavior either through direct interaction or classical receptor activation coupled to second messengers. A prominent phosphoprotein of the growth cone is B-50. We propose a role for this growth-associated protein kinase C substrate in signal transduction processes in the growth cone.

The distribution and movement of organelles in maturing growth cones: correlated video-enhanced and electron microscopic studies

The morphology of growth cones from identified neurons of Aplysia californica was analysed both with video-enhanced contrast differential-interference contrast (VEC-DIC) microscopy, and through serial electron microscopic reconstructions of the same growth cones. The largest structures seen in the living growth cones, the large irregular refractile bodies (LIRBs), were shown in electron micrographs to be unique structures, composed predominantly of dense-core vesicles but including mitochondria and smooth membrane profiles. The LIRBs were stratified in the growth cones, occurring predominantly in sections distant from the substrate and relatively devoid of microtubules. VEC-DIC observations showed that LIRBs formed in the peripheral regions of the organelle-rich central growth cone, and grew in size through fusion with other LIRBs, accumulating into a large central mass in more proximal regions. The distribution of microtubules and LIRBs and the movements of LIRB suggest that there is an overall circulatory pattern in the growth cones, with the delivery of new vesicles occurring at distal areas close to the substrate, and the accumulation and retrograde processing of organelles occurring in more proximal areas away from adhesive contacts.