Actin-associated hnRNP proteins as transacting factors in the control of mRNA transport and localization.

Upon nuclear export, RNP particles are either localized to polysomes or further assembled into larger RNA granules which are transported to the cellular periphery for localized translation. These mechanisms are important for asymmetric mRNA and protein distribution and have profound impact on cellular physiology. mRNA transport and localization requires cis-acting elements and cellular transacting factors. hnRNP A2 functions as transacting factor for MBP mRNA transport in myelin-producing oligodendrocytes processes through a mechanism of direct RTS recognition. Here we examine the molecular mechanisms which regulate MBP mRNA transport in mouse oligodendrocytes in view of the recent discovery of CBF-A as novel transacting factor. CBF-A is highly conserved and in humans it is referred to as hnRNP A/B. Since actin has a key role in mRNA biogenesis and it is associated with both CBF-A and hnRNP A2 in pre-mRNP/mRNP complexes, we discuss integrative models underscoring the importance of actin-associated hnRNPs in mRNA biogenesis control at the post-transcriptional level.