Opening closed pores

JCB • VOLUME 167 • NUMBER 6 • 2004 994 Opening closed pores closed mitosis may be less closed than was thought, based on results from Colin De Souza, Stephen Osmani, and colleagues (The Ohio State University, Columbus, OH). The authors find that a fungus opens nuclear pores during mitosis to permit diffusion into and out of the nucleus. Simple organisms may thus be viable model systems for the study of nuclear changes during mammalian mitosis. As the nuclear envelope is not broken down during a closed mitosis, the cell must regulate the nuclear entry of mitotic kinases and tubulin. This was assumed to occur through cell cycle regulated alterations of specific transport pathways. “I, and probably most everyone,” says Osmani, “almost took for granted that subtle changes in the transport properties of the pore alter import pathways slightly. Probably in [budding yeast] this is the case. But no one thought it could A Dynamin in fission and fusion he same GTPase that tears membranes apart is needed to put them back together, based on results from Christopher Peters, Andreas Mayer, and colleagues (Université de Lausanne, Switzerland). The dual regulation may ensure that only one of the two competing processes goes on at any one time. The Swiss group finds that yeast cells lacking the dynamin homologue Vps1p resemble both fission and fusion mutants. The effects were seen in the morphology of the vacuoles, where Vps1p was localized. Some cells had a single enlarged vacuole, whereas others had many small vacuolar fragments. The two phenotypes were seen because Vps1p functions in both pathways. As expected given dynamin’s known fission activity, vacuole T