Dynein and the actin cytoskeleton control kinesin-driven cytoplasmic streaming in Drosophila oocytes.
Mass movements of cytoplasm, known as cytoplasmic streaming, occur in some large eukaryotic cells. In Drosophila oocytes there are two forms of microtubule-based streaming. Slow, poorly ordered streaming occurs during stages 8-10A, while pattern formation determinants such as oskar mRNA are being localized and anchored at specific sites on the cortex. Then fast well-ordered streaming begins during stage 10B, just before nurse cell cytoplasm is dumped into the oocyte. We report that the plus-end-directed microtubule motor kinesin-1 is required for all streaming and is constitutively capable of driving fast streaming. Khc mutations that reduce the velocity of kinesin-1 transport in vitro blocked streaming yet still supported posterior localization of oskar mRNA, suggesting that streaming is not essential for the oskar localization mechanism. Inhibitory antibodies indicated that the minus-end-directed motor dynein is required to prevent premature fast streaming, suggesting that slow streaming is the product of a novel dynein-kinesin competition. As F-actin and some associated proteins are also required to prevent premature fast streaming, our observations support a model in which the actin cytoskeleton triggers the shift from slow to fast streaming by inhibiting dynein. This allows a cooperative self-amplifying loop of plus-end-directed organelle motion and parallel microtubule orientation that drives vigorous streaming currents and thorough mixing of oocyte and nurse-cell cytoplasm.
Serbus
Laura R
LR
Department of Biology, Indiana University, Bloomington, 1001 East 3rd Street, IN 47405, USA.
Cha
Byeong-Jik
BJ
Theurkauf
William E
WE
Saxton
William M
WM
D000199:Actins / Q000378:metabolism*; D000818:Animals; D003595:Cytoplasmic Streaming / Q000502:physiology*; D003599:Cytoskeleton / Q000378:metabolism*; D004330:Drosophila / Q000502:physiology*; D029721:Drosophila Proteins / Q000235:genetics / Q000378:metabolism; D004398:Dyneins / Q000378:metabolism*; D017403:In Situ Hybridization; D016547:Kinesins / Q000378:metabolism*; D018613:Microscopy, Confocal / Q000379:methods; D008870:Microtubules / Q000378:metabolism; D009865:Oocytes / Q000166:cytology / Q000502:physiology; D020033:Protein Isoforms / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism; D013997:Time Factors
D000199:Actins; D029721:Drosophila Proteins; D020033:Protein Isoforms; D012333:RNA, Messenger; C091675:osk protein, Drosophila; D004398:Dyneins; D016547:Kinesins