The endoplasmic reticulum (ER) slides along acetylated microtubules, possibly helping it to meet up with other organelles such as mitochondria, Friedman et al. report.
The ER constantly reorganizes, extending new tubules or retracting old ones. In some cases, tubule ends attach to the tips of dynamic microtubules as they grow or shrink but, more commonly, ER membranes slide along a stable, preexisting tubulin filament. Friedman et al. found that this second type of ER movement occurs on acetylated microtubules.
The researchers determined that acetylated microtubules are highly curved compared to unmodified filaments, and that dynamic ER tubules followed these winding tracks in living cells. The amount of ER sliding was increased by boosting microtubule acetylation. Why the ER makes these movements is still mysterious, however. One possibility is that it helps the ER contact other organelles to facilitate calcium signaling and lipid synthesis and exchange. Friedman et al. therefore looked to see if other organelles met up with the ER on acetylated microtubules.
Mitochondria were tightly associated with ER tubules sliding along stable, acetylated microtubules whereas endosomes, despite making numerous contacts with the ER, weren't preferentially localized to this modified subpopulation of the cytoskeleton. Thus, the ER might slide along acetylated microtubules to search out particular organelles. Senior author Gia Voeltz now wants to identify ER proteins specifically involved in these sliding movements so that she can disrupt the process and investigate its function.