The endoplasmic reticulum consists of peripheral tubular networks connected to sheet-like domains surrounding the nucleus. Gerondopoulos et al. reveal that the Rab3GAP complex, which is mutated in the neurodevelopmental disorder Warburg Micro Syndrome, is a guanine nucleotide exchange factor that activates the small GTPase Rab18 (also mutated in Warburg Micro Syndrome) to control the balance between ER tubules and sheets. This biosights episode presents the paper by Gerondopoulos et al. from...

Early Drosophila embryos undergo 13 rounds of rapid nuclear division before enclosing each nucleus into an individual, membrane-bound cell. Reversi et al. describe how the phosphoinositides PI(4,5)P2 and PI(3,4,5)P3 control the resulting cell shapes by coordinating actomyosin contractility with plasma membrane expansion. This biosights episode presents the paper by Reversi et al. from the May 12, 2014, issue of The Journal of Cell Biology and includes an interview with senior author Stefano...

The lamella is a broad, flat region that forms at the front of migrating cells and adheres to the underlying substrate. Burnette et al. reveal that cells flatten out the lamella by mechanically coupling a contractile actomyosin network at the dorsal surface to ventral cell adhesions. This biosights episode presents the paper by Burnette et al. from the April 14, 2014, issue of The Journal of Cell Biology and includes an interview with authors Dylan Burnette (Vanderbilt University School of...

Membrane blebs can help the leading edge of migrating cells protrude forwards, but the contribution of blebs to the motility of Dictyostelium cells is unclear. Zatulovskiy et al. reveal that blebs form at the front of chemotaxing Dictyostelium cells, particularly when the cells are faced with a mechanically resistant environment, and that this process is guided by a PI3-kinase-dependent signaling pathway. This biosights episode presents the paper by Zatulovskiy et al. from the March 17,...

During development, the planar polarized distribution of Rho kinase and Myosin II helps Drosophila germ-band cells intercalate so that the embryo extends along its anterior-posterior axis. Simoes et al. reveal how Rho GTPase and the actin-binding protein Shroom combine to regulate the localization of Rho kinase and actomyosin contractility during axis elongation. This biosights episode presents the paper by Simoes et al. from the February 17, 2014, issue of The Journal of Cell Biology and...

The discoid shape of resting platelets is maintained by a peripheral ring of bundled microtubules called the marginal band. Diagouraga et al. reveal that, upon platelet activation, the motor protein dynein slides microtubules apart, inducing marginal band coiling and the conversion of platelets to a spherical shape. This biosights episode presents the paper by Diagouraga et al. from the January 20, 2014, issue of The Journal of Cell Biology and includes an interview with senior author Karin...

Tumor cells invade through extracellular matrices by forming actin-rich structures called invadopodia, which contain the transmembrane matrix metalloproteinase MT1-MMP. Monteiro et al. reveal that the Arp2/3 activating protein WASH works with the exocyst complex to deliver MT1-MMP from late endosomes to the invadopodial plasma membrane. This biosights episode presents the paper by Monteiro et al. from the December 23, 2013, issue of The Journal of Cell Biology and includes an interview with...

When a growing axon nears its target, it arborizes, or branches, to form numerous synaptic connections. Campbell and Okamoto reveal that localized caspase activation downstream of Slit-Robo signaling promotes arbor dynamics and restricts arbor growth. This biosights episode presents the paper by Campbell and Okamoto from the November 25, 2013, issue of The Journal of Cell Biology and includes an interview with lead author Douglas Campbell (formerly at the RIKEN Brain Science Institute,...

The microtubules of skeletal muscle fibers are arranged into an orthogonal grid, but how this network is formed is unknown. Oddoux et al. reveal that the network is built by dynamic microtubules nucleated from Golgi elements. This biosights episode presents the paper by Oddoux et al. from the October 28, 2013, issue of The Journal of Cell Biology and includes an interview with senior author Evelyn Ralston (NIH, Bethesda, MD). Produced by Caitlin Sedwick and Ben Short. See the associated...

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 al. from the...