Yoshida et al. identify a new job for microtubule-organizing centers (MTOCs)—helping telomeres huddle during meiosis.
The most famous MTOC is the centrosome, a permanent structure that serves as a hub for the cell’s microtubules and anchors the spindle during mitosis. But cells also deploy ephemeral MTOCs to perform other tasks. In fission yeast, for instance, part-time MTOCs help position the nucleus during mitosis.
Yoshida et al. uncovered a new MTOC function in fission yeast while studying the clustering of telomeres, the caps that protect chromosome ends. During meiosis, telomeres crowd together near the nuclear membrane, a maneuver that enables homologous chromosomes to pair. Previous studies suggested that dynein helps bring telomeres together, and the researchers found that kinesin motors also provide a push.
Because these molecular motors stick to microtubules, the team investigated how these filaments affect telomere movements. They discovered that a γ-tubulin–containing MTOC, which they dubbed the telocentrosome, formed near the telomeres and that its microtubules helped draw the chromosome caps together near the spindle pole body, the yeast equivalent of the centrosome. In cells lacking one protein necessary for telocentrosome formation, telomeres remained aloof, and homologous chromosomes didn’t pair properly.
The researchers think that dynein and kinesin interconnect the microtubules linked to the spindle pole body and the telocentrosome, sliding along these fibers to help reel in the telomeres. Still unknown is what spurs the telocentrosome to form at a specific point in meiosis and what causes it to disassemble.
Text by Mitch Leslie