Mammals express three class V myosins. Myosin Va is widely expressed,
but enriched in the brain, testes and melanocytes, myosin Vb is
expressed ubiquitously, and myosin Vc is believed to be
epithelium-specific. Myosin Va is the best characterized of the three
and plays a key role in the transport of cargo to the plasma membrane.
Its cargo includes cell-surface receptors, pigment and organelles such
as the endoplasmic reticulum. It is also emerging that RNA and RNA-BPs
(RNA-binding proteins) make up another class of myosin Va cargo. It has
long been established that the yeast class V myosin, Myo4p, transports
mRNAs along actin cables into the growing bud, and now several groups
have reported a similar role for class V myosins in higher eukaryotes.
Myosin Va has also been implicated in the assembly and maintenance of
P-bodies (processing bodies), cytoplasmic foci that are involved in mRNA
storage and degradation. The present review examines the evidence that
myosin Va plays a role in the transport and turnover of mRNA.