Salogiannis et al. identify a linker protein that helps peroxisomes hitchhike through the cell on early endosomes.
In most eukaryotic cells, organelles and other cargoes move through the cytoplasm along microtubules, using specific adaptor molecules to recruit microtubule-based motor proteins such as cytoplasmic dynein or plus end–directed kinesins. Following up on a genetic screen for genes involved in the transport of various organelles through the multinucleate cells of the filamentous fungus A. nidulans, Salogiannis et al. studied the function of PxdA, a protein specifically required for the bidirectional movement of peroxisomes.
In the absence of PxdA, peroxisomes clustered at hyphal tips instead of dispersing throughout the cell, whereas the motility and distribution of other organelles, including early endosomes, was unaffected. Surprisingly, however, PxdA mainly localized to early endosomes. Salogiannis et al. found that the protein links these highly motile organelles to peroxisomes, potentially allowing peroxisomes to move through the cell without recruiting their own set of motor proteins. PxdA’s central coiled-coil domain was necessary and sufficient for the protein’s localization and organelle linker function. Senior author Sam Reck-Peterson now wants to investigate how PxdA interacts with both early endosomes and peroxisomes.
In a recent JCB paper, Guimaraes et al. revealed that not only peroxisomes, but also lipid droplets and ER membranes, hitchhike on early endosomes in the pathogenic fungus U. maydis. Reck-Peterson says it will be important to determine if PxdA links these other organelles to early endosomes, and whether this phenomenon occurs in animal cells as well.
Text by Ben Short