To find out whether and how actin might play a role in the position of the meiotic spindle, postdoctoral researcher and first author Kexi Yi, Ph.D., incubated mouse oocytes with several known inhibitors of the actin cytoskeleton. "Within minutes of applying CK-666, a brand new and very specific inhibitor, the spindle drifted away from the cortical cap towards the center of the oocyte."
CK-666 inhibits the Arp2/3 complex, a major regulator of the actin cytoskeleton that is known to play a role in cell locomotion and membrane trafficking. It binds to existing actin filaments and initiates the growth of new "branch" filaments. Further experiments revealed that myosin-II contractility, better known for producing muscle contractions, pushes the spindle away from the cortical cap when the Arp2/3 complex is inhibited.
Previous work by Li and her team had shown that meiotic chromosomes, when positioned close to the cortex of an oocyte in meiosis II, induces the formation of a cortical actin cap by propagating the regulatory signal from the Ran protein. When Yi tested the effect of intercepting the Ran signal, they found that Ran also regulates Arp2/3 localization and by extension, spindle position.
Yi then turned to high-resolution time-lapse confocal microscopy and spatiotemporal correlation spectroscopy (STICS), in collaboration with Stowers imaging experts, Jay Unruh, Ph.D., and Brian Slaughter, Ph.D., both co-authors on the paper, to track the dynamics of the cytoplasmic actin network in oocytes labeled with a live F-actin probe.
"STICS analysis showed that the actin flow originates at the cortical cap and continues down along both sides of the lateral cortex before it converges near the center of the oocyte and reverses direction to
|Contact: Gina Kirchweger|
Stowers Institute for Medical Research