Microtubules remodel actomyosin networks in Xenopus egg extracts via two mechanisms of F-actin transport.
Interactions between microtubules and filamentous actin (F-actin) are crucial for many cellular processes, including cell locomotion and cytokinesis, but are poorly understood. To define the basic principles governing microtubule/F-actin interactions, we used dual-wavelength digital fluorescence and fluorescent speckle microscopy to analyze microtubules and F-actin labeled with spectrally distinct fluorophores in interphase Xenopus egg extracts. In the absence of microtubules, networks of F-actin bundles zippered together or exhibited serpentine gliding along the coverslip. When microtubules were nucleated from Xenopus sperm centrosomes, they were released and translocated away from the aster center. In the presence of microtubules, F-actin exhibited two distinct, microtubule-dependent motilities: rapid ( approximately 250-300 nm/s) jerking and slow ( approximately 50 nm/s), straight gliding. Microtubules remodeled the F-actin network, as F-actin jerking caused centrifugal clearing of F-actin from around aster centers. F-actin jerking occurred when F-actin bound to motile microtubules powered by cytoplasmic dynein. F-actin straight gliding occurred when F-actin bundles translocated along the microtubule lattice. These interactions required Xenopus cytosolic factors. Localization of myosin-II to F-actin suggested it may power F-actin zippering, while localization of myosin-V on microtubules suggested it could mediate interactions between microtubules and F-actin. We examine current models for cytokinesis and cell motility in light of these findings.
Waterman-Storer
C
C
Department of Cell Biology and Institute for Childhood and Neglected Diseases, The Scripps Research Institute, La Jolla, California 92037, USA.
Duey
D Y
DY
Weber
K L
KL
Keech
J
J
Cheney
R E
RE
Salmon
E D
ED
Bement
W M
WM
D000199:Actins / Q000378:metabolism*; D000205:Actomyosin / Q000378:metabolism*; D000818:Animals; D002148:Calmodulin-Binding Proteins / Q000378:metabolism; D002455:Cell Division / Q000502:physiology*; D002465:Cell Movement / Q000502:physiology*; D003593:Cytoplasm / Q000378:metabolism; D003599:Cytoskeleton / Q000378:metabolism*; D003600:Cytosol / Q000378:metabolism; D004398:Dyneins / Q000378:metabolism; D005260:Female; D008870:Microtubules / Q000378:metabolism*; D024701:Myosin Type V; D009419:Nerve Tissue Proteins / Q000378:metabolism; D009865:Oocytes / Q000166:cytology / Q000378:metabolism*; D014981:Xenopus
D000199:Actins; D002148:Calmodulin-Binding Proteins; D009419:Nerve Tissue Proteins; C078829:chicken brain myosin-V p190; D000205:Actomyosin; D024701:Myosin Type V; D004398:Dyneins