Recent years have witnessed striking advances in research on axons at a
cellular level that substantially impact our current understanding of
axonal biology. Newer findings and their ramifications are critically
reviewed in the 16 chapters of this volume by authors highly qualified
by virtue of their scientific contributions to research areas they know
and write about.
Five basic areas (I to V) germane to axonal biology are highlighted,
beginning with (I) signaling interactions mediating myelination, and
differentiation of axonal membrane domains; (IIa) issues surrounding
organization and transport dynamics of neurofilaments in axons, (IIb)
mechanisms regulating microtubule organization and dynamics,
misregulation of which causes axonal degeneration, and (IIc) the roles
actin binding proteins play in regulating organization and functions of
the actin filament system in mature and growing axons; (IIIa) myosin
motor proteins and cargoes intrinsic to the axon compartment, (IIIb)
mitochondrial transport motors, and imperatives governing transport
dynamics and directional delivery, (IIIc) mechanisms mediating
retrograde signaling associated with NGF's role in trophic-dependent
neuronal survival, and (IIId) potential for impaired subcellular
targeting of a -synuclein as a mechanism for accumulation of Lewy body
inclusions in synucleinopathies; (IVa) occurrence and organization of
discrete ribosome-containing domains in axons, (IVb) endogenous mRNAs,
classes of proteins translated locally, and RNP trafficking in axons,
(IVc) importance of locally synthesized nuclear encoded mitochondrial
proteins for maintenance, function and survival of axons, (IVd)
occurrence of RNA trafficking from glial cells to axons, and
significance glial RNA transcripts may play in expression in axons and
axon terminals, (IVe) RNA trafficking and localization of RNA
transcripts in axonal growth cones, and signaling pathways that modulate
local protein synthesis for directional elongation, and (IVf) genetic
and molecular defects underlying spinal muscular atrophy, and roles that
SMN gene product plays as a molecular chaperone in mRNA transport and
translation; (Va) injury-induced local synthesis of a protein forming a
retrograde signaling complex in axons to stimulate regeneration, and
(Vb) endogenous and exogenous factors that condition axonal regenerative
capacity in PNS and CNS, including injury-induced activation of specific
genes governing regeneration.
Emergent complexities revealed in this volume compel a major revision in
the traditional conceptual model of the axon's intrinsic makeup and
capacities.
