Immune Cells as Model Cell Types for Molecular & Cell Biology. The immune system consists of an elaborate orchestration of various cell types specialized for different molecular processes. Due to the spectrum of these specializations, immune cells represent an intriguing cellular model to identify general molecular and cell biological principles. We employ immune cells to unravel the basic mechanisms and principles of cell motility such as during cell migration, macropinocytosis and leukocyte trafficking. Our lab interdisciplinary combines advanced live-cell microscopy, genetic-engineering (e.g. CRISPR), custom-made micro-environments (e.g. microfluidics, 3D collagen matrices) and unbiased system-wide approaches. Thereby we aim to identify fundamental molecular principles of immune cell motion and their misregulation in disease.
Cellular Navigation during Immune Cell Migration. Leukocytes are very fast moving cells. On their journey, these migratory cells have to find their way through crowded three-dimensional mazes. Whereas certain cell types such as mesenchymal cells proteolytically digest the environment on their path, leukocytes typically migrate without digesting or remodelling their environment (given the cumulative distance of all leukocytes in the human body of more than 100,000 km per hour, they otherwise would perforate the body with more than two million kilometers of tunnels per day). To discover how these extremely fast cells navigate through the dense meshwork of interstitial connective tissue fibers without harming other cells, we built obstacle course for leukocytes in reconstituted environments. Thereby, we identified that leukocytes use their nucleus as a ruler to probe their surroundings for the largest pores—and thereby find the path of least resistance.
Renkawitz et al, Nature 2019
Dendritic cell in a 3D collagen network (Imaged by Meghan K. Driscoll, University of Texas Southwestern Medical Center)
Cytoskeletal Dynamics during Immune Cell Migration. We discovered that amoeboid cells (such as dendritic cells) adapt their actin cytoskeleton dynamics to the adhesiveness of the migratory substrate (Renkawitz et al, Nature Cell Biology). Thereby we could show that not tracks of adhesive substrates but gradients of chemoattractants dictate the path of amoeboid cells, endowing these cells with extraordinary flexibility and enabling them to traverse almost every type of tissue (Renkawitz & Sixt, EMBOreports).
Renkawitz et al, Nature Cell Biology 2009
Renkawitz & Sixt, EMBOreports 2010 (Review)
Hons et al, Nature Immunology 2018
3D Microenvironments. Whereas in vivo experiments are truly physiological, they do not allow for precise manipulation of environmental parameters and are elaborate for the discovery of detailed molecular mechanisms of immune cell biology such as during cell motility. In contrast, in vitro 2D experiments enable faster manipulations, but increasing knowledge points to substantial differences of cellular mechanisms in 2D and 3D environments (see e.g. Friedl, Sahai, Weiss & Yamada Nat Rev Mol Cell Biol 2012). To bridge this gap, we and others developed micro-engineered tissue-mimetic assays to combine the advantage of precise manipulations in 2D assays with the presence of complex 3D microenvironments. Specifically, we implemented the methodology of micro-engineered ”pillar-forests’ to study cell migration in vitro in 3D with precisely defined microenvironmental parameters (Renkawitz et al., Methods in Cell Biology). Shortly, these devices provide a 3D migration environment made of PDMS (polydimethylsiloxane), in which two closely adjacent surfaces are interconnected by micron-sized structures such as pillars (or micro-channels). Thereby, these devices represent a flattened approximation of collagen matrices with the advantage of cellular confinement in one plane (XY) close to the imaging surface, enabling high-resolution single-cell imaging. We complement these assays with experimentation in collagen matrices, ex vivo tissue explants, and in vivo approaches.
Renkawitz et al, Methods in Cell Biology 2018
Frick et al, PLoS One 2018
Lämmermann et al, Blood 2009
Genetic Engineering in Immune Cells. Current knowledge on the molecular mechanisms and cell biological principles of immune cell biology (such as cell migration) is often based on studies utilizing knockout mice, which however hampers screening of large numbers of candidate components due to its time and resource consuming nature. To circumvent this bottleneck, conditionally immortalized hematopoietic precursor cells (Hoxb8 cells) with myeloid and lymphoid potential have been established by the Häcker Lab (Redecke et al, Nature Methods 2013). We recently contributed in showing that Hoxb8 cells can be differentiated into migratory DCs functionally indistinguishable from their primary counterparts (bone-marrow derived DCs) (Leithner et al, Eur J Immunol). Importantly, Hoxb8-FL cells can be efficiently targeted via CRISPR mediated gene editing (Leithner et al, Eur J Immunol).
Leithner et al, Eur J Immunol 2018
Earlier Work on Homology Search during DNA Recombination. We visualized homology search during DSB repair in vivo, using genome-wide analysis of chromatin immunoprecipitation of DSB repair factors in yeast. Thereby we could show that homology search is strongly influenced by the chromosomal architecture and nuclear organization (Renkawitz et al, Mol Cell). This led to a model, in which homology search during DSB repair proceeds by an accelerated random probing mechanism guided by genomic
proximity (Renkawitz et al, Nat Rev Mol Cell Biol).
Lademann et al, Cell Reports 2017
Renkawitz, Lademann & Jentsch, Nature Reviews Molecular Cell Biology 2014
Renkawitz, Lademann & Jentsch, Cell Cycle 2013 (Comment)
Renkawitz et al, Molecular Cell 2013