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You are here: Home Research Units Former Working Groups Research Unit Rottner

Research interests

Research Unit Prof. Dr. Klemens Rottner

Please note that we have recently moved!
Our new address ist:

Division of Molecular Cell Biology
Zoological Institute
Technical University Braunschweig
Spielmannstrasse 7
38106 Braunschweig
Germany

 

Head of Research UnitProf. Dr. Klemens Rottner

Prof. Dr. Klemens Rottner
Actin Dynamics and Motility Unit

 

Phone: 0531-391-3255
Fax: 0228-73-4263
 

 

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Curriculum

  • Diploma:  Paris-Lodron-University, Salzburg/Austria (Biology/Zoology)
  • Ph.D.:  Institute of Molecular Biology of the Austrian Academy of Sciences and Paris-Lodron-University, Salzburg/Austria (Cell Biology/Immunology)
  • Postdoctoral Fellow:  EMBO-longterm-fellow: Gesellschaft für Biotechnlogische Forschung (GBF; now called Helmholtz Centre for Infection Research), Braunschweig
  • Groupleader:  Helmholtz Centre for Infection Research, Braunschweig
  • since 2010:  Professor, Institute of Genetics, Rhein.-Friedrich Wilhelms University, Bonn

 

Research Interests

  •  Molecular mechanisms of actin filament nucleation
  •  Actin assembly and turnover in lamellipodia and filopodia
  •  Regulation of the actin cytoskeleton and cell migration by Rho-family GTPases
  •  Interplay of actin dynamics, signalling and endocytosis
  •  Exploitation of the actin cytoskeleton by microbial pathogens

 

Technology and Methods

  •  advanced live-cell imaging techniques using widefield, confocal or TIRF optics
  •  functional interference with key regulators employing gene inactivation or RNAi
  •  dissection of actin turnover using photomanipulation and microinjection
  •  assessment of interactions, subcellular localizations and in vivo activities of actin regulators using state-of-the-art molecular and cell biology techniques

 

Research Summary

Our group is mainly interested in understanding the molecular mechanisms that drive the reorganization of different actin structures in cells. The actin cytoskeleton is responsible for building a diverse array of structures in cells, with multiple functions, ranging from contractile actin filament bundles pulling on attached matrix or cells to protrusive or invasive organelles such as lamellipodia, filopodia or the invadopodia of cancer cells. In recent years, our studies have mostly been focusing on trying to shed light on how cells assemble actin filaments at the plasma membrane, either upon stimulation by physiologic signals such as growth factors or induced for instance by selected bacterial pathogens.

The most prominent and best characterized factor driving the de novo formation or „nucleation“ of actin filaments is the Arp2/3-complex. This complex of seven proteins harbours two actin-related proteins (Arp 2 and 3), which together with an actin monomer form a nucleus of actin filament polymerization. However, the complex is mostly inactive in the absence of so called nucleation promoting factors (NPFs), the founding member of which is known as WASP, mutated in the rare, X-linked immunodeficiency Wiskott Aldrich Syndrome. The family in mammals comprises as classical members haematopoietic WASP, the more ubiquitous and neuronally enriched N-WASP and three WAVE isoforms (1,2,3). However, interesting additional family members have recently appeared on the scene, termed WASH, WHAMM and JMY.

Work by ourselves and our collaborators Giorgio Scita (Milan, Italy) and Theresia Stradal (University of Münster, Germany) have contributed to the notion that N-WASP and WAVEs have distinct subcellular localizations and functions. WAVEs are now commonly agreed to drive Arp2/3-complex activation at the tips of lamellipodia, whereas N-WASP appears to power actin assemly in various types of vesicle trafficking processes and endocytosis. Work by others has shown that N-WASP or WASP is essential for invadopodia and podosomes. Over the years, all these NPFs have also emerged as direct or indirect effector proteins of small GTPases of the Rho-family (Ras homology). Prominent Rho-GTPases include Cdc42 and Rac1, which signal the formation of filopodia and lamellipodia, respectively. Although N-WASP is potently activated by its direct interactor Cdc42, it does not operate in filopodia formation, as evidenced by N-WASP localization studies and gene removal. Arp2/3-complex is also dispensable for filopodia (but not lamellipodia) formation. The precise physiological relevance of Cdc42-induced N-WASP activation is currently unclear.

We have also begun to study so called type II NPFs, which are distinguished from aforementioned factors because besides Arp2/3-complex, they bind to actin filaments instead of monomers. Thus, how precisely these factors promote Arp2/3-dependent actin assembly is still unclear. Mammals express two type II NPFs, the Src-substrate cortactin and the haematopoietic HS1. Both proteins accumulate at sites of dynamic actin assembly, and show a great degree of co-localization in cells with Arp2/3-complex. We have recently generated a conditional cortactin mutant model, which is employed to dissect cortactin function in murine cells and tissues. Surprisingly, cortactin null fibroblasts still form lamellipodia, and problems in migration could be assigned to defective upstream signalling rather than diminished Arp2/3-complex activation in lamellipodia.

In current projects, we are trying to shed more light on the mechanistic function of cortactin in vivo. Are cortactin null phenotypes dependent on its interactions with actin filaments or Arp2/3-complex? In addition, we are trying to elucidate the relative contributions of filament nucleation, elongation and termination for the turnover of a given actin structure, such as the lamellipodium. We have also started to more systematically analyze the functions of different formins, another prominent class of actin nucleators/elongators, in lamellipodia and filopodia protrusion. Finally, we are keen to develop novel actin assembly assays that allow addressing directly specific biochemical activities or consequences of their manipulation in vivo.

We have active collaborations with numerous national and international experts in the field, including (besides the ones named above) Jan Faix (Hannover), Cord Brakebusch (Kopenhagen) and J. Victor Small (Vienna). Our research is funded in part by the Deutsche Forschungsgemeinschaft (DFG) through grants within Research Unit 629 („Molecular Mechanisms of Cell Motility“) and Priority Program 1464 („Principles and Evolution of Actin-nucleator Complexes“).

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