ASSEMBLY AND DYNAMICS OF AN ANASTRAL, ASTRAL SPINDLE - THE MEIOSIS-IISPINDLE OF DROSOPHILA OOCYTES

The meiosis II spindle of Drosophila oocytes is distinctive in structu re, consisting of two tandem spindles with anastral distal poles and a n aster-associated spindle pole body between the central poles, Assemb ly of the anastral:astral meiosis II spindle occurs by reorganization of the meiosis I spindle, without breakdown of the meiosis I spindle, The unusual disk- or ring-shaped central spindle pole body forms de no vo in the center of the elongated meiosis I spindle, followed by forma tion of the central spindle poles. gamma-Tubulin transiently localizes to the central spindle pole body, implying that the body acts as a mi crotubule nucleating center for assembly of the central poles. Localiz ation of gamma-tubulin to the meiosis II spindle is dependent on the m icrotubule motor protein, Nonclaret disjunctional (Ncd). Absence of Nc d results in loss of gamma-tubulin localization to the spindle and des tabilization of microtubules in the central region of the spindle. Ass embly of the anastral:astral meiosis II spindle probably involves rapi d reassortment of microtubule plus and minus ends in the center of the meiosis I spindle - this can be accounted for by a model that also ac counts for the loss of gamma-tubulin localization to the spindle and d estabilization of microtubules in the absence of Ncd.