@article{johnson_haugh_2016, title={Are Filopodia Privileged Signaling Structures in Migrating Cells?}, volume={111}, ISSN={["1542-0086"]}, DOI={10.1016/j.bpj.2016.09.022}, abstractNote={Filopodia are thin, fingerlike structures that contain bundled actin filaments and project from the cell periphery. These structures are dogmatically endowed with the ability to sense cues in the microenvironment, implying that filopodia foster local signal transduction, yet their small diameter hampers the imaging of dynamic processes therein. To overcome this challenge, we analyzed total internal reflection fluorescence images of migrating fibroblasts coexpressing either a plasma membrane marker or tagged AktPH domain, a translocation biosensor for signaling through the phosphoinositide 3-kinase pathway, along with a cytosolic volume marker. We devised a scheme to estimate the radii of filopodia using either the membrane marker or volume marker data, and we used that information to account for geometry effects in the biosensor data. With conservative estimates of relative target molecule abundance, it is revealed that filopodia typically harbor higher densities of 3' phosphoinositides than adjacent regions at the cell periphery. In this context at least, the analysis supports the filopodial signaling hypothesis.}, number={9}, journal={BIOPHYSICAL JOURNAL}, publisher={Elsevier BV}, author={Johnson, Heath E. and Haugh, Jason M.}, year={2016}, month={Nov}, pages={1827–1830} }
 @article{king_asokan_haynes_zimmerman_rotty_alb_tagliatela_blake_lebedeva_marston_et al._2016, title={Lamellipodia are crucial for haptotactic sensing and response}, volume={129}, ISSN={["1477-9137"]}, DOI={10.1242/jcs.184507}, abstractNote={ABSTRACT Haptotaxis is the process by which cells respond to gradients of substrate-bound cues, such as extracellular matrix proteins (ECM); however, the cellular mechanism of this response remains poorly understood and has mainly been studied by comparing cell behavior on uniform ECMs with different concentrations of components. To study haptotaxis in response to gradients, we utilized microfluidic chambers to generate gradients of the ECM protein fibronectin, and imaged the cell migration response. Lamellipodia are fan-shaped protrusions that are common in migrating cells. Here, we define a new function for lamellipodia and the cellular mechanism required for haptotaxis – differential actin and lamellipodial protrusion dynamics lead to biased cell migration. Modest differences in lamellipodial dynamics occurring over time periods of seconds to minutes are summed over hours to produce differential whole cell movement towards higher concentrations of fibronectin. We identify a specific subset of lamellipodia regulators as being crucial for haptotaxis. Numerous studies have linked components of this pathway to cancer metastasis and, consistent with this, we find that expression of the oncogenic Rac1 P29S mutation abrogates haptotaxis. Finally, we show that haptotaxis also operates through this pathway in 3D environments. Highlighted Article: Haptotaxis (directed migration) on a substrate-bound gradient is perhaps the least-well understood form of directed migration. We show that differential lamellipodial dynamics are crucial for this process.}, number={12}, journal={JOURNAL OF CELL SCIENCE}, publisher={The Company of Biologists}, author={King, Samantha J. and Asokan, Sreeja B. and Haynes, Elizabeth M. and Zimmerman, Seth P. and Rotty, Jeremy D. and Alb, James G., Jr. and Tagliatela, Alicia and Blake, Devon R. and Lebedeva, Irina P. and Marston, Daniel and et al.}, year={2016}, month={Jun}, pages={2329–2342} }
 @article{johnson_king_asokan_rotty_bear_haugh_2015, title={F-actin bundles direct the initiation and orientation of lamellipodia through adhesion-based signaling}, volume={208}, ISSN={["1540-8140"]}, DOI={10.1083/jcb.201406102}, abstractNote={During cell migration, F-actin bundles/filopodia serve as templates for formation and orientation of lamellipodia and prime their stabilization by adhesion-based PI3K signaling.}, number={4}, journal={JOURNAL OF CELL BIOLOGY}, publisher={Rockefeller University Press}, author={Johnson, Heath E. and King, Samantha J. and Asokan, Sreeja B. and Rotty, Jeremy D. and Bear, James E. and Haugh, Jason M.}, year={2015}, month={Feb}, pages={443–455} }
 @article{haynes_asokan_king_johnson_haugh_bear_2015, title={GMF beta controls branched actin content and lamellipodial retraction in fibroblasts}, volume={209}, ISSN={["1540-8140"]}, DOI={10.1083/jcb.201501094}, abstractNote={The primary activity of GMFβ in vivo is actin branch disassembly (and not inhibition of Arp2/3 activation), and this activity plays an important role in lamellipodial dynamics and directional migration toward ECM cues.}, number={6}, journal={JOURNAL OF CELL BIOLOGY}, publisher={Rockefeller University Press}, author={Haynes, Elizabeth M. and Asokan, Sreeja B. and King, Samantha J. and Johnson, Heath E. and Haugh, Jason M. and Bear, James E.}, year={2015}, month={Jun}, pages={803–812} }
 @article{rotty_wu_haynes_suarez_winkelman_johnson_haugh_kovar_bear_2015, title={Profilin-1 Serves as a Gatekeeper for Actin Assembly by Arp2/3-Dependent and -Independent Pathways}, volume={32}, ISSN={["1878-1551"]}, DOI={10.1016/j.devcel.2014.10.026}, abstractNote={Cells contain multiple F-actin assembly pathways, including the Arp2/3 complex, formins, and Ena/VASP, which have largely been analyzed separately. They collectively generate the bulk of F-actin from a common pool of G-actin; however, the interplay and/or competition between these pathways remains poorly understood. Using fibroblast lines derived from an Arpc2 conditional knockout mouse, we established matched-pair cells with and without the Arp2/3 complex. Arpc2(-/-) cells lack lamellipodia and migrate more slowly than WT cells but have F-actin levels indistinguishable from controls. Actin assembly in Arpc2(-/-) cells was resistant to cytochalasin-D and was highly dependent on profilin-1 and Ena/VASP but not formins. Profilin-1 depletion in WT cells increased F-actin and Arp2/3 complex in lamellipodia. Conversely, addition of exogenous profilin-1 inhibited Arp2/3 complex actin nucleation in vitro and in vivo. Antagonism of the Arp2/3 complex by profilin-1 in cells appears to maintain actin homeostasis by balancing Arp2/3 complex-dependent and -independent actin assembly pathways.}, number={1}, journal={DEVELOPMENTAL CELL}, publisher={Elsevier BV}, author={Rotty, Jeremy D. and Wu, Congying and Haynes, Elizabeth M. and Suarez, Cristian and Winkelman, Jonathan D. and Johnson, Heath E. and Haugh, Jason M. and Kovar, David R. and Bear, James E.}, year={2015}, month={Jan}, pages={54–67} }
 @article{asokan_johnson_rahman_king_rotty_lebedeva_haugh_bear_2014, title={Mesenchymal Chemotaxis Requires Selective Inactivation of Myosin II at the Leading Edge via a Noncanonical PLC gamma/PKC alpha Pathway}, volume={31}, ISSN={["1878-1551"]}, DOI={10.1016/j.devcel.2014.10.024}, abstractNote={Chemotaxis, migration toward soluble chemical cues, is critical for processes such as wound healing and immune surveillance and is exhibited by various cell types, from rapidly migrating leukocytes to slow-moving mesenchymal cells. To study mesenchymal chemotaxis, we observed cell migration in microfluidic chambers that generate stable gradients of platelet-derived growth factor (PDGF). Surprisingly, we found that pathways implicated in amoeboid chemotaxis, such as PI3K and mammalian target of rapamycin signaling, are dispensable for PDGF chemotaxis. Instead, we find that local inactivation of Myosin IIA, through a noncanonical Ser1/2 phosphorylation of the regulatory light chain, is essential. This site is phosphorylated by PKCα, which is activated by an intracellular gradient of diacylglycerol generated by PLCγ. Using a combination of live imaging and gradients of activators/inhibitors in the microfluidic chambers, we demonstrate that this signaling pathway and subsequent inhibition of Myosin II activity at the leading edge are required for mesenchymal chemotaxis.}, number={6}, journal={DEVELOPMENTAL CELL}, publisher={Elsevier BV}, author={Asokan, Sreeja B. and Johnson, Heath E. and Rahman, Anisur and King, Samantha J. and Rotty, Jeremy D. and Lebedeva, Irina P. and Haugh, Jason M. and Bear, James E.}, year={2014}, month={Dec}, pages={747–760} }
 @article{welf_johnson_haugh_2013, title={Bidirectional coupling between integrin-mediated signaling and actomyosin mechanics explains matrix-dependent intermittency of leading-edge motility}, volume={24}, ISSN={["1939-4586"]}, DOI={10.1091/mbc.e13-06-0311}, abstractNote={A physicochemical model is used to describe the coupling of adhesion, cytoskeletal, and signaling dynamics during cell migration. Analysis of stochastic simulations predicts relationships between measurable quantities that reflect partitioning of stress between F-actin–bound adhesions, which act as a molecular clutch, and retrograde F-actin flow.}, number={24}, journal={MOLECULAR BIOLOGY OF THE CELL}, publisher={American Society for Cell Biology (ASCB)}, author={Welf, Erik S. and Johnson, Heath E. and Haugh, Jason M.}, year={2013}, month={Dec}, pages={3945–3955} }
 @article{welf_ahmed_johnson_melvin_haugh_2012, title={Migrating fibroblasts reorient directionality by a metastable, PI3K-dependent mechanism}, volume={197}, ISSN={["1540-8140"]}, DOI={10.1083/jcb.201108152}, abstractNote={Migrating fibroblasts reorient directionality by PI3K-dependent branching and pivoting of protrusions, a mechanism that allows fibroblasts to align with an external chemotactic gradient.}, number={1}, journal={JOURNAL OF CELL BIOLOGY}, publisher={Rockefeller University Press}, author={Welf, Erik S. and Ahmed, Shoeb and Johnson, Heath E. and Melvin, Adam T. and Haugh, Jason M.}, year={2012}, month={Apr}, pages={105–114} }