Intracellular trafficking of messenger RNA in oligodendrocytes

Date of Completion

January 2000


Biology, Cell




In eucaryotic cells, RNAs are assembled into granules, which follow characteristic trafficking pathways determined by cis-acting elements in the RNA and trans-acting factors in the cell. RNAs with different trafficking pathways are segregated into different granules. RNAs with similar trafficking pathways are coassembled into the same granules. RNA sorting is mediated by cis/trans trafficking determinants. RNA granules contain both kinesin and dynein motors. Perikaryal retention of RNA requires dynein activity, and peripheral translocation of RNA requires kinesin activity. RNA granules exhibit three types of microtubule-dependent motion: vibration, oscillation and translocation. Vibration is a rapid back and forth motion thought to reflect stochastic fluctuation of opposing motor activities in the granule. Oscillation is a slower back and forth movement thought to reflect cycles of binding and release of opposing motors at microtubule termini. Translocation is sustained biased directional movement during transit of RNA towards its destination. The direction and velocity of translocation reflect differential regulation of opposing motor activities by cis /trans trafficking determinants. Connexin32 (Cx32) RNA granules are localized to the endoplasmic reticulum (ER) at sites of Cx32 protein synthesis. Mislocalization of Cx32 RNA by insertion of heterologous RNA trafficking sequences or disruption of microtubules represses translation, indicating that translation of Cx32 RNA in oligodendrocytes is localization-dependent. Cx32 protein oligomerizes at sites of synthesis in the ER. Cx32 clusters exhibit two types of microtubule-dependent motion: short-range intra-ER oscillations and long-range retrograde or anterograde vectorial translocations. Some Cx32 clusters are located on the plasma membrane, indicating that Cx32 can traverse the secretory pathway and be inserted into the plasma membrane. This work provides new insights into the mechanisms of RNA sorting and granule assembly, microtubule-dependent transport and translation regulation. ^