Mitosis without wind

From nuclear pore to kinetochore uclear proteins are turning up in some odd places lately. First, the nuclear-transport factor Ran was implicated in spindle formation. Then, the mitotic checkpoint proteins Mad1 and Mad2 turned up at the nuclear pore, in a switch with the mRNA export factor hRae1, which appeared with the mitotic checkpoint protein mBUB1 at the kinetochore. Now, Belgareh et al. report that two structural nuclear pore complex constituents also localize to the kinetochore (page 1147). Belgareh et al. were interested in characterizing the human version of a budding yeast nuclear pore subcomplex that is involved in mRNA export. They identified hNup133 by homology, and identified three other members of the subcomplex through immunoprecipitation experiments. The surprise came in the localization studies, when both antibody staining and GFP fluorescence indicated that at least two of these nucleoporins are found at kinetochores from prophase through to late anaphase. This simple observation has many possible interpretations, none of which (as yet) comes with any significant supporting evidence. First, nucleoporins at the kinetochore could act to seed the formation of a specific subset of nuclear pores at the end of mitosis, while the nuclear envelope reforms around chromosomes. Second, the nucleoporins could have some unspecified function at the kinetochore, although a role in spindle formation is not obvious as none of the nucleoporins under discussion has the FG N Nuclear pore proteins (green) on the kinetochores of metaphase chromosomes (red). he relatively minor effects of interfering with a kinesin that mediates polar ejection forces suggests that kinetochores may be smarter than once thought. This conclusion comes from a report on page 1135 from Levesque and Compton. Their antibody experiments target a human T Some chromosomes get stuck at the pole when Kid is inhibited. kinesin motor called Kid that sticks to chromosome arms and is thought to mediate chromosome movement out along spindle microtubules. This polar ejection force has been proposed as a mechanism for pushing chromosomes away from spindle poles and thus aligning chromosomes on the metaphase plate. The importance of Kid and the polar ejection force has been shown in fly germ cells mutant for the Nod kinesin, and in frog extracts, where depletion of Kid resulted in widespread wandering of chromosomes away from in vitro assembled metaphase plates. Levesque and Compton set out to see if Kid was equally important in a mitotic rather than meiotic system. After …