The nodal network In addition to specialized actin structures such as lamellipodia and stress fibers, cells are thought to contain a contractile actomyosin matrix that maintains cell shape. Luo et al. describe the organization and dynamics of an actomyosin network that may fulfill this function. This network is formed by actin nodes that contain the formin DAAM1 and the crosslinker filamin A, and that are connected to each other by myosin II. This biosights episode presents the paper by Luo et a...
Sep 30, 2013•10 min
Shrinking microtubules pull the centrosome into place When a T cell encounters a target antigen-presenting cell, it moves its centrosome to the immunological synapse that connects the two cells. Yi et al. reveal that centrosome repositioning is a biphasic process driven by the dynein-dependent capture and depolymerization of microtubules. This biosights episode presents the paper by Yi et al. from the September 2, 2013, issue of The Journal of Cell Biology and includes an interview with senior a...
Sep 02, 2013•8 min
Epithelia restored by healing waves Epithelial cells around the edge of a wound assemble an actomyosin cable that constricts to draw the wound closed, but the events that precede cable formation are largely unknown. Antunes et al. reveal that wounding induces a wave of actomyosin assembly and cell constriction that flows toward the wound edge to promote cable assembly and tissue repair. This biosights episode presents the paper by Antunes et al. from the July 22, 2013, issue of The Journal of Ce...
Aug 05, 2013•7 min
Vinculin delivers a clutch performance At the leading edge of migrating cells, actin assembly and membrane protrusion are closely coupled with the formation of integrin-based focal adhesions that attach to the extracellular matrix. Thievessen et al. reveal that the focal adhesion protein vinculin acts as part of a molecular clutch that engages actin flow to coordinate actin and focal adhesion dynamics. This biosights episode presents the paper by Thievessen et al. from the July 8, 2013, issue of...
Jul 08, 2013•9 min
Netrin Throws Anchor Cells into the Breach Cell invasion through basement membranes is crucial for both normal development and cancer metastasis but relatively little is known about the process because it is difficult to observe in vivo. By imaging the invasion of anchor cells during C. elegans development, Hagedorn et al. reveal that, after invadopodia-like structures form an initial breach in the basement membrane, localized netrin signaling helps generate a stable invasive protrusion that wid...
Jun 10, 2013•8 min
Ventral lamellipodia plug the gaps When leukocytes enter or exit the blood stream, they leave small wounds both in and between the vascular endothelial cells, which must be quickly repaired so that the endothelium can maintain its barrier function. Martinelli et al. reveal that wounding causes a loss of tension in endothelial cells, inducing the formation of ventral lamellipodia that close the holes left by transmigrating leukocytes. This biosights episode presents the paper by Martinelli et al....
May 13, 2013•10 min
Frog oocytes evade the checkpoint Most dividing cells possess a spindle assembly checkpoint that prevents them from entering anaphase until all their chromosomes are correctly attached to the metaphase spindle. Shao et al. reveal that Xenopus eggs lack this checkpoint, allowing them to undergo meiosis in the absence of microtubules or in the presence of monopolar spindles. This biosights episode presents the paper by Shao et al. from the April 15, 2013 issue of The Journal of Cell Biology and in...
Apr 15, 2013•7 min
Breaking egg symmetry During the first meiotic division of mammalian oocytes, the meiotic spindle and chromosomes move from the interior to the periphery of the cell. Yi et al. reveal that chromosome migration occurs in two sequential phases driven by the actin nucleators Fmn2 and the Arp2/3 complex. This biosights episode presents the paper by Yi et al. from the March 4, 2013, issue of The Journal of Cell Biology and includes an interview with senior author Rong Li (Stowers Institute for Medica...
Mar 18, 2013•8 min
Erecting a myosin scaffold for cytokinesis Cell division requires the coordinated action of proteins that promote actomyosin contraction, membrane trafficking, and extracellular matrix remodeling. Wloka et al. reveal that, in budding yeast, the type II myosin Myo1 acts as an immobile scaffold at the bud neck to organize proteins involved in forming the primary septum during cytokinesis. This biosights episode presents the paper by Wloka et al. from the February 4, 2013, issue of The Journal of C...
Feb 18, 2013•7 min
How cell shape changes unfold Under certain conditions, cells form protrusions that oscillate rapidly around the cell periphery. Kapustina et al. reveal that these oscillatory protrusions, which may be related to processes involved in amoeboid cell migration, are driven by the cyclic folding and unfolding of the plasma membrane and its underlying actin cortex. This biosights episode presents the paper by Kapustina et al. from the January 7, 2013, issue of The Journal of Cell Biology and includes...
Jan 21, 2013•8 min
At the end of cytokinesis, the microtubule-rich midbody connecting the daughter cells is either shed into the extracellular space or retained by one of the daughters. Chai et al. find that the midbodies released from C. elegans Q neuroblasts are cleared via a pathway that closely mimics the removal of apoptotic cell corpses. This biosights episode presents the paper by Chai et al. from the December 24, 2012 issue of the Journal of Cell Biology and includes an interview with senior author Guangsh...
Dec 24, 2012•7 min
Fission yeast are thought to assemble their cytokinetic actomyosin rings from actin filaments nucleated at myosin-containing nodes around the cell equator. Using an improved actin-binding probe, Huang et al. find that actin cables are nucleated all over the cortex of mitotic fission yeast and are transported to the division site for incorporation into the contractile ring. This biosights episode presents the paper by Huang et al. from the November 26, 2012, issue of The Journal of Cell Biology a...
Nov 26, 2012•6 min
A stiff test for collectively migrating cells The mechanical properties of the extracellular matrix are known to regulate the migration of single cells, but whether substrate stiffness also affects collective cell migration is unclear. Ng et al. reveal that epithelial sheets move faster on stiffer matrices due to increased myosin contractility and mechanical coupling through cell-cell adhesions. This biosights episode presents the paper by Ng et al. from the October 29, 2012, issue of The Journa...
Oct 29, 2012•9 min
The position of the mitotic spindle is controlled by the microtubule-based motor dynein and a ternary complex of the proteins NuMA, LGN, and Ga. Kotak et al. demonstrate that the ternary complex's primary function is to localize dynein to the cell cortex and that cortical dynein is sufficient to position the mitotic spindle in HeLa cells. This biosights episode presents the paper by Kotak et al. from the October 1, 2012, issue of The Journal of Cell Biology and includes an interview with author ...
Oct 01, 2012•7 min
C. elegans embryos are protected by a trilaminar eggshell that is thought to make the embryos impermeable to small molecules. Olson et al. describe the hierarchical assembly of the different eggshell layers but reveal that the permeability barrier is a distinct structure that lies in between the shell and the embryo surface. This biosights episode presents the paper by Olson et al. from the August 20, 2012, issue of The Journal of Cell Biology and includes an interview with authors Sara Olson (P...
Sep 03, 2012•9 min
In animal cells, the nuclear lamina keeps nuclear pore complexes evenly distributed throughout the nuclear envelope. Steinberg et al. reveal that fungi, which lack nuclear laminae, prevent their nuclear pores from clustering by moving them around on cytoskeletal tracks, a process that also helps to organize fungal chromosomes and optimize nucleocytoplasmic transport. This biosights episode presents the paper by Steinberg et al. from the August 6, 2012, issue of the Journal of Cell Biology and in...
Aug 06, 2012•8 min
In early Drosophila embryos, nuclei undergo rapid, synchronous divisions without being separated into individual cells by cytokinesis. Telley et al. develop a cell-free assay to reveal that microtubule asters help disperse the nuclei throughout the embryonic cytoplasm, moving them to the right position for development to continue. This biosights episode presents the paper by Telley et al. from the June 25, 2012, issue of The Journal of Cell Biology and includes an interview with lead author Ivo ...
Jul 09, 2012•8 min
Activated T cell receptors stimulate actin polymerization at the periphery of the immunological synapses that form between lymphocytes and antigen-presenting cells. Babich et al. reveal that the retrograde flow of actin, largely driven by continuous polymerization, is required to sustain downstream signaling events and T cell activation. This biosights episode presents the paper by Babich et al. from the June 11, 2012 issue of The Journal of Cell Biology and includes an interview with senior aut...
Jun 11, 2012•8 min
Fibroblasts moving across two-dimensional surfaces form lamellipodial protrusions at their leading edge, but how cells move through three-dimensional environments is less well understood. Petrie et al. reveal that, depending on the strength of intracellular RhoA signaling and on the elastic properties of the extracellular matrix, fibroblasts can migrate through 3D environments using either lamellipodia or blunt, cylindrical protrusions called lobopodia. This biosights episode presents the paper ...
May 14, 2012•10 min
Phosphoinositide 3-kinase (PI3K) and its phospholipid products are polarized toward the front of migrating fibroblasts, but their exact function in persistent motility remains unclear. Welf et al. reveal that PI3K signaling helps reorient migrating fibroblasts by stabilizing branched protrusions at the leading edge, allowing the cell to pivot and move in a different direction. This biosights episode presents the paper by Welf et al. from the April 2, 2012, issue of The Journal of Cell Biology an...
Apr 16, 2012•8 min
The adhesions between endothelial cells transiently remodel in response to angiogenic growth factors and inflammatory cytokines. Huveneers et al. reveal that remodeling takes place at a subset of adhesions called focal adherens junctions, which recruit the mechanosensory protein Vinculin to resist tension from the actomyosin cytoskeleton and avoid excessive disruption during the remodeling process. This biosights episode presents the paper by Huveneers et al. from the March 5, 2012, issue of The...
Mar 19, 2012•7 min
Autophagy is a cellular degradation pathway essential for neuronal survival, but little is known about the dynamics of autophagic organelles in neurons. Maday et al. reveal that autophagosomes form and engulf cargo at the distal tips of neurites and then mature into degradative autolysosomes as they move toward the cell body. This biosights episode presents the paper by Maday et al. from the February 20, 2012, issue of the Journal of Cell Biology and includes an interview with authors Sandra Mad...
Feb 20, 2012•8 min
T cells require the septin family of GTP-binding proteins to maintain the integrity of their plasma membranes as they invade through tissues. Gilden et al. reveal that septins function by assembling on membrane blebs to retract them back into shape. This biosights episode presents the paper by Gilden et al. from the January 9, 2012, issue of the Journal of Cell Biology and includes an interview with senior author Max Krummel (University of California, San Francisco). Produced by Caitlin Sedwick ...
Jan 23, 2012•7 min
Desmosomes are intercellular adhesions whose adhesive core is formed by two distinct classes of cadherin molecules – desmogleins and desmocollins. Nekrasova et al. reveal that these two cadherins are independently transported to the cell surface by two different kinesin motors. This biosights episode presents the paper by Nekrasova et al. from the December 26, 2011, issue of the Journal of Cell Biology and includes an interview with senior author Kathleen Green (Northwestern University Feinberg ...
Dec 26, 2011•8 min
When a T cell encounters a target antigen-presenting cell, the lymphocyte's centrosome relocalizes to a specialized contact between the two cells called the immunological synapse. Zyss et al. reveal that casein kinase Iδ helps to reposition the centrosome in activated T cells, perhaps by working with the microtubule plus-end binding protein EB1 to regulate microtubule growth. This biosights episode presents the paper by Zyss et al. from the November 28, 2011, issue of The Journal of Cell Biology...
Nov 28, 2011•7 min
Cofilin severs the ties between cytokinetic nodes Cytokinetic nodes are precursor structures that assemble into the actomyosin contractile ring that separates daughter cells in cytokinesis. Chen and Pollard describe how the actin-severing protein cofilin promotes the rapid formation of a complete contractile ring by limiting the actin-based connections between individual nodes. This biosights episode presents the paper by Chen and Pollard from the October 31, 2011, issue of The Journal of Cell B...
Oct 31, 2011•7 min
The ERM protein Moesin helps mitotic cells undergo a series of dramatic shape changes by linking the actin cytoskeleton to the plasma membrane. Roubinet et al. describe how Moesin's localization and activity is regulated over the course of the cell cycle by two different pathways that control Moesin phosphorylation and phosphoinositide synthesis. This biosights episode presents the paper by Roubinet et al. from the October 3, 2011, issue of The Journal of Cell Biology, and includes an interview ...
Oct 03, 2011•8 min
The actin cytoskeleton has been proposed to regulate exocytosis in many different ways. Nightingale et al. use a two-color, live-cell imaging assay to reveal two contrasting functions of actin in distinct stages of Weibel–Palade body secretion: actin-based anchors inhibit the fusion of these secretory granules with the plasma membrane but, post-fusion, a contractile actin ring squeezes granule content out of the cell. This biosights episode presents the paper by Nightingale et al. from the Augus...
Sep 05, 2011•8 min
At the start of mitosis, the nuclear envelope and nuclear pore complexes break down and disperse into the endoplasmic reticulum and cytoplasm. Lu et al. use rapid, 3D live cell imaging to reveal that, in contrast to previous models, the nuclear envelope reforms directly from ER cisternae after mitosis and that this happens before nuclear pore complexes start to reassemble. This biosights episode presents the paper by Lu et al. from the August 8, 2011, issue of the Journal of Cell Biology , and i...
Aug 08, 2011•7 min
Several mRNAs are specifically transported to the anterior and posterior regions of Drosophila oocytes by microtubule-based motor proteins, but the organization of microtubules in these cells is unclear. Parton et al. reveal that oocyte microtubules are highly dynamic and display a PAR-1-dependent bias in polarity that facilitates transport of oskar mRNA to the oocyte posterior. This biosights episode presents the paper by Parton et al. from the July 11, 2011, issue of The Journal of Cell Biolog...
Jul 11, 2011•9 min
