Researchers are exploring whether these ubiquitous fluorinated molecules might worsen infections or hamper vaccine effectiveness.
Image credit: Shutterstock/Dmitry Naumov.
Edited by Gary G. Borisy, The Forsyth Institute, Cambridge, MA, and approved August 2, 2016 (received for review May 23, 2016)
Significance
Cell division occurs by the assembly and constriction of a ring of actin and myosin; however, the organization of proteins within cytokinetic apparatus is still unknown. Without better information about the organization of contractile rings, we cannot understand how they assemble or constrict. In fission yeast, cytokinetic proteins are first recruited around the equator as cortical spots, called nodes, that coalesce into a ring. Here we used high-speed quantitative fluorescence photoactivation localization microscopy to obtain a molecular model of this basic cytokinetic unit. Nodes are discrete structures with distinct distributions of six different proteins. Nodes persist in contractile rings and move around the circumference as the ring constricts.
Abstract
Cytokinesis in animals, fungi, and amoebas depends on the constriction of a contractile ring built from a common set of conserved proteins. Many fundamental questions remain about how these proteins organize to generate the necessary tension for cytokinesis. Using quantitative high-speed fluorescence photoactivation localization microscopy (FPALM), we probed this question in live fission yeast cells at unprecedented resolution. We show that nodes, protein assembly precursors to the contractile ring, are discrete structural units with stoichiometric ratios and distinct distributions of constituent proteins. Anillin Mid1p, Fes/CIP4 homology-Bin/amphiphysin/Rvs (F-BAR) Cdc15p, IQ motif containing GTPase-activating protein (IQGAP) Rng2p, and formin Cdc12p form the base of the node that anchors the ends of myosin II tails to the plasma membrane, with myosin II heads extending into the cytoplasm. This general node organization persists in the contractile ring where nodes move bidirectionally during constriction. We observed the dynamics of the actin network during cytokinesis, starting with the extension of short actin strands from nodes, which sometimes connected neighboring nodes. Later in cytokinesis, a broad network of thick bundles coalesced into a tight ring around the equator of the cell. The actin ring was ∼125 nm wide and ∼125 nm thick. These observations establish the organization of the proteins in the functional units of a cytokinetic contractile ring.
Footnotes
↵1Present address: Weldon School of Biomedical Engineering, Purdue University, West Lafayette, IN 47907.
- ↵2To whom correspondence should be addressed. Email: thomas.pollard{at}yale.edu.
Author contributions: C.L. and T.D.P. designed the experiments; C.L. and I.R.T. generated yeast strains; C.L. collected and analyzed the data using MatLab codes written by F.H.; C.L. and T.D.P. prepared the manuscript and figures with input from F.H., I.R.T., and J.B.; and J.B. provided the microscope.
Conflict of interest statement: J.B. has a significant financial interest in Bruker Corporation, and J.B. and F.H. have a significant financial interest in Hamamatsu Photonics.
This article is a PNAS Direct Submission.
This article contains supporting information online at www.pnas.org/lookup/suppl/doi:10.1073/pnas.1608252113/-/DCSupplemental.
“Molecular model of the cytokinetic node.”
Article Classifications
- Biological Sciences
- Cell Biology
Sign up for Article Alerts
Jump to section
You May Also be Interested in
Recent experiments and simulations are starting to answer some fundamental questions about how life came to be.
Image credit: Shutterstock/Radoslaw Lecyk.
Archaeologists have long tried to define the transition between the two time periods.
Image credit: Ceri Shipton.
Jonathon Yuly, David Beratan, and Peng Zhang investigate how electron bifurcation reactions work.
A study finds that giant pandas roll in horse manure to increase their cold tolerance.
Image credit: Fuwen Wei.