For fission yeast nuclei, it takes two to tango

Two minus end–directed microtubule motors work in parallel to bring haploid nuclei together during fission yeast mating, Scheffler et al. reveal.

Mating yeast cells must move their nuclei toward each other so that they can fuse and undergo meiosis. In budding yeast, nuclear congression is driven by Kar3, a member of the kinesin-14 family of minus end–directed motor proteins. To investigate whether the kinesin-14 Klp2 performs a similar function in fission yeast, Scheffler et al. trapped cells in microfluidic chambers so they could follow the mating process by live imaging.

Nuclear congression was delayed in the absence of Klp2 but, unlike in budding yeast lacking Kar3, haploid nuclei eventually converged and fused together. The process was also delayed in fission yeast lacking the minus end–directed motor dynein, the researchers found, and almost completely blocked in cells lacking both motor proteins.

Klp2 localized to microtubules emanating from the spindle pole bodies associated with each haploid nucleus, and could potentially bring the nuclei together by sliding antiparallel microtubules past each other. Dynein, in contrast, localized to the spindle pole bodies themselves, where it might pull on microtubules emanating from the other nucleus once Klp2 has brought them into close proximity. Dynein’s localization and its ability to promote nuclear congression depended on its light intermediate chain, the researchers discovered.

In higher eukaryotes, nuclear congression is driven by dynein but not kinesin-14. Fission yeast are thus unique in their reliance on two minus end–directed motors operating in parallel, a mechanism that may improve the efficiency of nuclear congression if the rod-shaped cells mate and fuse at odd angles.