Premature microtubule-dependent cytoplasmic streaming in cappuccino and spire mutant oocytes.

Embryonic axis specification in Drosophila melanogaster is achieved through the asymmetric subcellular localization of morphogenetic molecules within the oocyte. The cappuccino and spire loci are required for both posterior and dorsoventral patterning. Time-lapse confocal microscopic analyses of living egg chambers demonstrated that these mutations induce microtubule reorganization and the premature initiation of microtubule-dependent ooplasmic streaming. As a result, microtubule organization is altered and bulk ooplasm rapidly streams during the developmental stages in which morphogens are normally localized. These changes in oocyte cytoarchitecture and dynamics appear to disrupt axial patterning of the embryo.