@article{9259,
  abstract     = {Gradients of chemokines and growth factors guide migrating cells and morphogenetic processes. Migration of antigen-presenting dendritic cells from the interstitium into the lymphatic system is dependent on chemokine CCL21, which is secreted by endothelial cells of the lymphatic capillary, binds heparan sulfates and forms gradients decaying into the interstitium. Despite the importance of CCL21 gradients, and chemokine gradients in general, the mechanisms of gradient formation are unclear. Studies on fibroblast growth factors have shown that limited diffusion is crucial for gradient formation. Here, we used the mouse dermis as a model tissue to address the necessity of CCL21 anchoring to lymphatic capillary heparan sulfates in the formation of interstitial CCL21 gradients. Surprisingly, the absence of lymphatic endothelial heparan sulfates resulted only in a modest decrease of CCL21 levels at the lymphatic capillaries and did neither affect interstitial CCL21 gradient shape nor dendritic cell migration toward lymphatic capillaries. Thus, heparan sulfates at the level of the lymphatic endothelium are dispensable for the formation of a functional CCL21 gradient.},
  author       = {Vaahtomeri, Kari and Moussion, Christine and Hauschild, Robert and Sixt, Michael K},
  issn         = {1664-3224},
  journal      = {Frontiers in Immunology},
  publisher    = {Frontiers},
  title        = {{Shape and function of interstitial chemokine CCL21 gradients are independent of heparan sulfates produced by lymphatic endothelium}},
  doi          = {10.3389/fimmu.2021.630002},
  volume       = {12},
  year         = {2021},
}

@article{275,
  abstract     = {Lymphatic endothelial cells (LECs) release extracellular chemokines to guide the migration of dendritic cells. In this study, we report that LECs also release basolateral exosome-rich endothelial vesicles (EEVs) that are secreted in greater numbers in the presence of inflammatory cytokines and accumulate in the perivascular stroma of small lymphatic vessels in human chronic inflammatory diseases. Proteomic analyses of EEV fractions identified > 1,700 cargo proteins and revealed a dominant motility-promoting protein signature. In vitro and ex vivo EEV fractions augmented cellular protrusion formation in a CX3CL1/fractalkine-dependent fashion and enhanced the directional migratory response of human dendritic cells along guidance cues. We conclude that perilymphatic LEC exosomes enhance exploratory behavior and thus promote directional migration of CX3CR1-expressing cells in complex tissue environments.},
  author       = {Brown, Markus and Johnson, Louise and Leone, Dario and Májek, Peter and Vaahtomeri, Kari and Senfter, Daniel and Bukosza, Nora and Schachner, Helga and Asfour, Gabriele and Langer, Brigitte and Hauschild, Robert and Parapatics, Katja and Hong, Young and Bennett, Keiryn and Kain, Renate and Detmar, Michael and Sixt, Michael K and Jackson, David and Kerjaschki, Dontscho},
  journal      = {Journal of Cell Biology},
  number       = {6},
  pages        = {2205 -- 2221},
  publisher    = {Rockefeller University Press},
  title        = {{Lymphatic exosomes promote dendritic cell migration along guidance cues}},
  doi          = {10.1083/jcb.201612051},
  volume       = {217},
  year         = {2018},
}

@article{402,
  abstract     = {During metastasis, malignant cells escape the primary tumor, intravasate lymphatic vessels, and reach draining sentinel lymph nodes before they colonize distant organs via the blood circulation. Although lymph node metastasis in cancer patients correlates with poor prognosis, evidence is lacking as to whether and how tumor cells enter the bloodstream via lymph nodes. To investigate this question, we delivered carcinoma cells into the lymph nodes of mice by microinfusing the cells into afferent lymphatic vessels. We found that tumor cells rapidly infiltrated the lymph node parenchyma, invaded blood vessels, and seeded lung metastases without involvement of the thoracic duct. These results suggest that the lymph node blood vessels can serve as an exit route for systemic dissemination of cancer cells in experimental mouse models. Whether this form of tumor cell spreading occurs in cancer patients remains to be determined.},
  author       = {Brown, Markus and Assen, Frank P and Leithner, Alexander F and Abe, Jun and Schachner, Helga and Asfour, Gabriele and Bagó Horváth, Zsuzsanna and Stein, Jens and Uhrin, Pavel and Sixt, Michael K and Kerjaschki, Dontscho},
  journal      = {Science},
  number       = {6382},
  pages        = {1408 -- 1411},
  publisher    = {American Association for the Advancement of Science},
  title        = {{Lymph node blood vessels provide exit routes for metastatic tumor cell dissemination in mice}},
  doi          = {10.1126/science.aal3662},
  volume       = {359},
  year         = {2018},
}

@article{672,
  abstract     = {Trafficking cells frequently transmigrate through epithelial and endothelial monolayers. How monolayers cooperate with the penetrating cells to support their transit is poorly understood. We studied dendritic cell (DC) entry into lymphatic capillaries as a model system for transendothelial migration. We find that the chemokine CCL21, which is the decisive guidance cue for intravasation, mainly localizes in the trans-Golgi network and intracellular vesicles of lymphatic endothelial cells. Upon DC transmigration, these Golgi deposits disperse and CCL21 becomes extracellularly enriched at the sites of endothelial cell-cell junctions. When we reconstitute the transmigration process in vitro, we find that secretion of CCL21-positive vesicles is triggered by a DC contact-induced calcium signal, and selective calcium chelation in lymphatic endothelium attenuates transmigration. Altogether, our data demonstrate a chemokine-mediated feedback between DCs and lymphatic endothelium, which facilitates transendothelial migration.},
  author       = {Vaahtomeri, Kari and Brown, Markus and Hauschild, Robert and De Vries, Ingrid and Leithner, Alexander F and Mehling, Matthias and Kaufmann, Walter and Sixt, Michael K},
  issn         = {22111247},
  journal      = {Cell Reports},
  number       = {5},
  pages        = {902 -- 909},
  publisher    = {Cell Press},
  title        = {{Locally triggered release of the chemokine CCL21 promotes dendritic cell transmigration across lymphatic endothelia}},
  doi          = {10.1016/j.celrep.2017.04.027},
  volume       = {19},
  year         = {2017},
}

@article{674,
  abstract     = {Navigation of cells along gradients of guidance cues is a determining step in many developmental and immunological processes. Gradients can either be soluble or immobilized to tissues as demonstrated for the haptotactic migration of dendritic cells (DCs) toward higher concentrations of immobilized chemokine CCL21. To elucidate how gradient characteristics govern cellular response patterns, we here introduce an in vitro system allowing to track migratory responses of DCs to precisely controlled immobilized gradients of CCL21. We find that haptotactic sensing depends on the absolute CCL21 concentration and local steepness of the gradient, consistent with a scenario where DC directionality is governed by the signal-to-noise ratio of CCL21 binding to the receptor CCR7. We find that the conditions for optimal DC guidance are perfectly provided by the CCL21 gradients we measure in vivo. Furthermore, we find that CCR7 signal termination by the G-protein-coupled receptor kinase 6 (GRK6) is crucial for haptotactic but dispensable for chemotactic CCL21 gradient sensing in vitro and confirm those observations in vivo. These findings suggest that stable, tissue-bound CCL21 gradients as sustainable “roads” ensure optimal guidance in vivo.},
  author       = {Schwarz, Jan and Bierbaum, Veronika and Vaahtomeri, Kari and Hauschild, Robert and Brown, Markus and De Vries, Ingrid and Leithner, Alexander F and Reversat, Anne and Merrin, Jack and Tarrant, Teresa and Bollenbach, Tobias and Sixt, Michael K},
  issn         = {09609822},
  journal      = {Current Biology},
  number       = {9},
  pages        = {1314 -- 1325},
  publisher    = {Cell Press},
  title        = {{Dendritic cells interpret haptotactic chemokine gradients in a manner governed by signal to noise ratio and dependent on GRK6}},
  doi          = {10.1016/j.cub.2017.04.004},
  volume       = {27},
  year         = {2017},
}

@article{1154,
  abstract     = {Cellular locomotion is a central hallmark of eukaryotic life. It is governed by cell-extrinsic molecular factors, which can either emerge in the soluble phase or as immobilized, often adhesive ligands. To encode for direction, every cue must be present as a spatial or temporal gradient. Here, we developed a microfluidic chamber that allows measurement of cell migration in combined response to surface immobilized and soluble molecular gradients. As a proof of principle we study the response of dendritic cells to their major guidance cues, chemokines. The majority of data on chemokine gradient sensing is based on in vitro studies employing soluble gradients. Despite evidence suggesting that in vivo chemokines are often immobilized to sugar residues, limited information is available how cells respond to immobilized chemokines. We tracked migration of dendritic cells towards immobilized gradients of the chemokine CCL21 and varying superimposed soluble gradients of CCL19. Differential migratory patterns illustrate the potential of our setup to quantitatively study the competitive response to both types of gradients. Beyond chemokines our approach is broadly applicable to alternative systems of chemo- and haptotaxis such as cells migrating along gradients of adhesion receptor ligands vs. any soluble cue. 
},
  author       = {Schwarz, Jan and Bierbaum, Veronika and Merrin, Jack and Frank, Tino and Hauschild, Robert and Bollenbach, Mark Tobias and Tay, Savaş and Sixt, Michael K and Mehling, Matthias},
  journal      = {Scientific Reports},
  publisher    = {Nature Publishing Group},
  title        = {{A microfluidic device for measuring cell migration towards substrate bound and soluble chemokine gradients}},
  doi          = {10.1038/srep36440},
  volume       = {6},
  year         = {2016},
}

@article{1597,
  abstract     = {Chemokines are the main guidance cues directing leukocyte migration. Opposed to early assumptions, chemokines do not necessarily act as soluble cues but are often immobilized within tissues, e.g., dendritic cell migration toward lymphatic vessels is guided by a haptotactic gradient of the chemokine CCL21. Controlled assay systems to quantitatively study haptotaxis in vitro are still missing. In this chapter, we describe an in vitro haptotaxis assay optimized for the unique properties of dendritic cells. The chemokine CCL21 is immobilized in a bioactive state, using laser-assisted protein adsorption by photobleaching. The cells follow this immobilized CCL21 gradient in a haptotaxis chamber, which provides three dimensionally confined migration conditions.},
  author       = {Schwarz, Jan and Sixt, Michael K},
  journal      = {Methods in Enzymology},
  pages        = {567 -- 581},
  publisher    = {Elsevier},
  title        = {{Quantitative analysis of dendritic cell haptotaxis}},
  doi          = {10.1016/bs.mie.2015.11.004},
  volume       = {570},
  year         = {2016},
}

@article{1599,
  abstract     = {The addition of polysialic acid to N- and/or O-linked glycans, referred to as polysialylation, is a rare posttranslational modification that is mainly known to control the developmental plasticity of the nervous system. Here we show that CCR7, the central chemokine receptor controlling immune cell trafficking to secondary lymphatic organs, carries polysialic acid. This modification is essential for the recognition of the CCR7 ligand CCL21. As a consequence, dendritic cell trafficking is abrogated in polysialyltransferase-deficient mice, manifesting as disturbed lymph node homeostasis and unresponsiveness to inflammatory stimuli. Structure-function analysis of chemokine-receptor interactions reveals that CCL21 adopts an autoinhibited conformation, which is released upon interaction with polysialic acid. Thus, we describe a glycosylation-mediated immune cell trafficking disorder and its mechanistic basis.
},
  author       = {Kiermaier, Eva and Moussion, Christine and Veldkamp, Christopher and Gerardy  Schahn, Rita and De Vries, Ingrid and Williams, Larry and Chaffee, Gary and Phillips, Andrew and Freiberger, Friedrich and Imre, Richard and Taleski, Deni and Payne, Richard and Braun, Asolina and Förster, Reinhold and Mechtler, Karl and Mühlenhoff, Martina and Volkman, Brian and Sixt, Michael K},
  journal      = {Science},
  number       = {6269},
  pages        = {186 -- 190},
  publisher    = {American Association for the Advancement of Science},
  title        = {{Polysialylation controls dendritic cell trafficking by regulating chemokine recognition}},
  doi          = {10.1126/science.aad0512},
  volume       = {351},
  year         = {2016},
}

@article{1285,
  abstract     = {Cell migration is central to a multitude of physiological processes, including embryonic development, immune surveillance, and wound healing, and deregulated migration is key to cancer dissemination. Decades of investigations have uncovered many of the molecular and physical mechanisms underlying cell migration. Together with protrusion extension and cell body retraction, adhesion to the substrate via specific focal adhesion points has long been considered an essential step in cell migration. Although this is true for cells moving on two-dimensional substrates, recent studies have demonstrated that focal adhesions are not required for cells moving in three dimensions, in which confinement is sufficient to maintain a cell in contact with its substrate. Here, we review the investigations that have led to challenging the requirement of specific adhesions for migration, discuss the physical mechanisms proposed for cell body translocation during focal adhesion-independent migration, and highlight the remaining open questions for the future.},
  author       = {Paluch, Ewa and Aspalter, Irene and Sixt, Michael K},
  journal      = {Annual Review of Cell and Developmental Biology},
  pages        = {469 -- 490},
  publisher    = {Annual Reviews},
  title        = {{Focal adhesion-independent cell migration}},
  doi          = {10.1146/annurev-cellbio-111315-125341},
  volume       = {32},
  year         = {2016},
}