In higher plants, the preprophase band （PPB） of microtubules （MTs） forecasts the cell division site prior to mitosis and specifies the organization of MTs into a bipolar prophase spindle surrounding the nucleus. H...In higher plants, the preprophase band （PPB） of microtubules （MTs） forecasts the cell division site prior to mitosis and specifies the organization of MTs into a bipolar prophase spindle surrounding the nucleus. However, the mechanisms governing this PPB-dependent establishment of bipolarity are unclear. Here, we present evidence from live cell imaging studies that suggest a role for the MTs bridging the PPB and the prophase nucleus in mediating this function. Results from drug treatments, along with genetic evidence from null kinesin plants, suggest that these MTs contribute to the bipolarity, orientation, and position of the prophase spindle. Specifically, the absence of these bridge MTs is associated with lack of bipolarity, while non-uniform distributions of bridge MTs correlate with prophase spindle migration, deformation, and enhanced bipolarity toward the region of highest bridge MT density. This behavior does not require actomyosin-based forces, and is enhanced by suppressing MT dynamics with taxol. These observations occur during late prophase, and are coincident with the gradual closing of annular spindle poles. Based on these data, we describe a hypothetical mechanism for bridge MT-dependent organization of prophase spindles.展开更多
基金This work was funded by grants from the National Science Foundation, the United States Department of Agriculture and Department of Energy. J.C.A. was supported by a National Science Foundation training grant.We thank D. Fisher for critical reading ofthe manuscript, T. Hashimoto for the generous gift of GFP：TUB6, and the Salk Institute Genomic Analysis Laboratory for providing the sequence-indexed Arabidopsis T-DNA insertion mutants. No conflict of interest declared.
文摘In higher plants, the preprophase band （PPB） of microtubules （MTs） forecasts the cell division site prior to mitosis and specifies the organization of MTs into a bipolar prophase spindle surrounding the nucleus. However, the mechanisms governing this PPB-dependent establishment of bipolarity are unclear. Here, we present evidence from live cell imaging studies that suggest a role for the MTs bridging the PPB and the prophase nucleus in mediating this function. Results from drug treatments, along with genetic evidence from null kinesin plants, suggest that these MTs contribute to the bipolarity, orientation, and position of the prophase spindle. Specifically, the absence of these bridge MTs is associated with lack of bipolarity, while non-uniform distributions of bridge MTs correlate with prophase spindle migration, deformation, and enhanced bipolarity toward the region of highest bridge MT density. This behavior does not require actomyosin-based forces, and is enhanced by suppressing MT dynamics with taxol. These observations occur during late prophase, and are coincident with the gradual closing of annular spindle poles. Based on these data, we describe a hypothetical mechanism for bridge MT-dependent organization of prophase spindles.
