New insights into mRNA trafficking in axons

In recent years, it has been demonstrated
that mRNAs localize to axons of young and
mature central and peripheral nervous system neurons
in culture and in vivo. Increasing evidence is supporting a
fundamental role for the local translation of these
mRNAs in neuronal function by regulating axon growth,
maintenance and regeneration after injury. Although
most mRNAs found in axons are abundant transcripts
and not restricted to the axonal compartment, they are
sequestered into transport ribonucleoprotein particles
and their axonal localization is likely the result of specific
targeting rather than passive diffusion. It has been
reported that long-distance mRNA transport requires
microtubule-dependent motors, but the molecular mechanisms
underlying the sorting and trafficking of mRNAs
into axons have remained elusive. This review places particular
emphasis on motor-dependent transport of
mRNAs and presents a mathematical model that
describes how microtubule-dependent motors can
achieve targeted trafficking in axons. A future challenge
will be to systematically explore how the numerous axonal
mRNAs and RNA-binding proteins regulate different
aspects of specific axonal mRNA trafficking during development
and after regeneration.