|Group leaders||Group members|
Prof. Dr. Thomas Raabe
One of the central challenges in neurobiological research is the elucidation of cellular and molecular mechanisms of brain development. Despite major anatomical differences between vertebrate and invertebrate nervous systems, the astounding similarity in their molecular mechanisms of development is becoming increasingly clear. Therefore, Drosophila melanogaster offers the opportunity to develop a general understanding of brain development through the use of genetic, molecular and functional studies.
Regulation of the number and proliferation pattern of neural stem cells during the development of the Drosophila melanogaster central nervous system
Neurogenesis involves proliferation and differentiation; both processes have to be tightly regulated in order to allow the formation of functional neuronal circuits. The major objective of our work is to uncover the roles of the protein kinase CK2 (Jauch et al., 2002, 2006; Akten et al., 2003) and the two nuclear proteins Mushroom body defect (Mud, Guan et al., 2000) and Mushroom body miniature (Mbm, Raabe et al., 2004) in regulation of cell proliferation of central brain neuroblasts of Drosophila. For Mud, recent experiments established two independent function of the protein in orientation of the mitotic spindle along the apical-basal axis of neuroblasts and in centrosome organisation (Izumi et al., 2007). However, the dynamic distribution of Mud at distinct subcellular sites during the cell cycle and the regulation of its function are not understood. In the case of Mbm, we want to use the recently identified null mutation of mbm for an extensive phenotypic analysis in the developing brain and eye. Based on preliminary studies, we propose that Mbm is part of a high molecular weight complex. Identification of the components will hopefully help to clarify the yet unknown molecular function of Mbm in the nucleus.
Figure 1: Visualisation of the mud brain phenotype. Gal4 driver line 17D labels a subset of mushroom bodies neurons in the central brain of adult flies. In the wild-type, four cell clusters can be seen in each brain hemisphere, each of which represents the progeny from a single mushroom body neuroblast. The axonal projections of the neurons bifurcate into a medial and dorsal projecting branch. In mud animals, the number of cell clusters is increased, which reflects the presence of additional mushroom body neuroblasts. In addition, Kenyon cell axons wind up below the cell body layer.
The role of p21-activated kinases in neurogenesis
The role of RhoGTPase mediated signalling pathways for many cellular processes, e.g. re-organisation of the cytoskeleton, cell cycle control and regulation of gene expression, which contribute to the control of cell growth and division, migration, cell adhesion and differentiation, is well established. RhoGTPases not only play important roles in neuronal development, including generation of neurons from neuronal precursor cells, differentiation of neurons (polarisation, neurite growth, axon pathfinding, dendrite formation), but also in the maintenance and function of the nervous system (synaptic plasticity, regeneration). P21-activated kinases (PAK) are a family of protein kinases, which act as downstream effectors of the RhoGTPases Cdc42 and/or Rac. Our major aim is to unravel the different roles of the three Drosophila PAK proteins D-PAK, Mbt (Melzig et al., 1998) and D-PAK3 (Mentzel et al., 2005) in generation and differentiation of neurons or in the maintenance of their physiological function. In the Drosophila eye, for instance, D-PAK is required for guidance of photoreceptor cell axons, whereas Mbt has an essential role in morphogenetic processes during the final differentiation of photoreceptor cells (Schneeberger et al., 2003). Recruitment of Mbt to adherens junctions (Figure 2) is dependent on binding to GTP-loaded RhoGTPases. Based on the finding that cadherin-mediated cell adhesion influences the activity of RhoGTPases, we postulate that Mbt as a downstream effector of RhoGTPases provides an additional link to the actin cytoskeleton. Although activation of Mbt has a dramatic influence on the actin cytoskeleton in the developing eye, recent biochemical and genetic experiments question the role of the LIM domain protein kinase (Limk) as a major link between Mbt and the actin depolymerisation factor Twinstar/Cofilin as it has been suggested for other PAK proteins (Menzel et al., 2007). On the other hand, we are pursuing a model, where Mbt phosphorylates components of the adherens junction complex to modulate cadherin-mediated cell adhesion. The project also aims to characterise other Mbt interaction substrates, which were identified by biochemical and genetic approaches.
Morphogenesis of photoreceptor cells during eye development of Drosophila. Shown are top and side views of eye imaginal discs at different developmental stages stained with an antibody against Mbt to visualize adherens junctions. After sequential recruitment and determination (left picture), the apical surfaces of the eight photoreceptor cells turn by 90° to point to the center of the ommatidium. The establishment of the final morphology involves expansion of the adherens junctions and apical membranes, which finally built up the light sensitive structures (rhabdomeres).
Various national and international collaborators
Cate, A.S., Gajendra,
S., Alsbury, S., Raabe, T., Tear, G., Mitchell, K.J. (2016) Mushroom body
defect is required in parallel to Netrin for midline axon guidance in
Drosophila. Development 143, 972-977.
Herter, E.K., Strauch, M., Gallant, M., Wolf, E., Raabe, T., Gallant, P. (2015) snoRNAs are a novel class of biologically relevant Myc targets. BMC Biol. 13(1):25.
Dusik, V., Senthilan,
P.R., Mentzel, B., Hartlieb, H,, Wülbeck, C., Yoshii, T., Raabe,
T., Helfrich-Förster, C. (2014) The MAP Kinase p38 Is Part of Drosophila
melanogaster's Circadian Clock. PLoS Genet.
Szabó A, Papin C, Zorn D, Ponien P, Weber F, Raabe T, Rouyer F. (2013) The CK2 Kinase Stabilizes CLOCK and Represses Its Activity in the Drosophila Circadian Oscillator. PLoS Biol. 11(8):e1001645.
Melzer, J., Kraft,
K.F., Urbach, R., Raabe, T. (2013) The p21-activated kinase Mbt is a component
of the apical protein complex in central brain neuroblasts and controls
cell proliferation. Development 140, 1871-1881.
Stark, F., Pfannstiel,
J., Klaiber, I., Raabe, T. (2011) Protein kinase CK2 links polyamine metabolism
to MAKK signalling in Drosophila. Cell. Signal. 23, 876-882.
Fischer, M., Raabe,
T., Heisenberg, M., Sendtner, M. (2009) Drosophila RSK negatively regulates
bouton number at the neuromuscular junction.
Akten, B., Tangredi, M.M., Jauch, E., Roberts, M.A., Ng, F., Raabe, T., Jackson, R.F. (2009) Ribosomal S6 kinase cooperates with casein kinase 2 to modulate the Drosophila circadian molecular oscillator. J. Neurosci. 29, 466-475.
Mentzel, B., Jauch,
E., Raabe, T. (2009) CK2beta interacts with regulates p21-activated kinases
in Drosophila. Biochem. Biophys. Res.
Menzel, N., Schneeberger, D., Raabe, T. (2007) The Drosophila p21 activated kinase Mbt regulates the actin cytoskeleton and adherens junctions to control photoreceptor cell morphogenesis. Mech. Dev. 124, 78-90.
Izumi, Y., Ohta, N., Hisata, K., Raabe, T., Matsuzaki, F. (2006) Drosophila Pins-binding protein Mud regulates spindle-polarity coupling and centrosome organization. Nature Cell Biol. 8, 586-593.
Jauch, E., Wecklein,
H., Stark, F., Jauch, M., Raabe, T. (2006) The CK2 transcription unit
encodes for functionally non-redundant protein isoforms. Gene 374, 142-152.
Mentzel, B., Raabe, T. (2005) Phylogenetic and structural analysis of the Drosophila melanogaster p21-activated kinase DmPAK3. Gene 349, 25-33.
Raabe, T., Clemens-Richter,
S., Twardzik, T., Ebert, A., Gramlich, G., Heisenberg, M. (2004) Identification
of Mushroom body miniature, a zinc-finger protein implicated in brain
development of Drosophila. PNAS 101, 14276-14281.
Schneeberger, D., Raabe, T. (2003). Mbt, a Drosophila PAK protein, combines with D-Cdc42 to regulate photoreceptor cell morphogenesis. Development 130, 427-437.
Scott, E. K., Raabe, T., Luo, L. (2002) Structure of the vertical and horizontal system neurons of the lobula plate in Drosophila. J. Comp. Neurol. 454, 470-481.
Jauch, E., Melzig, J., Brkulj, M., and Raabe, T. (2002) In vivo functional analysis of Drosophila protein kinase casein kinase 2 (CK2) beta-subunit. Gene 298, 29-39.
Raabe, T., Rapp, U.R. (2002) KSR-a regulator and scaffold protein of the MAP kinase pathway. Science STKE 136, pe28.
Feller, S.M., Wecklein, H., Lewitzky, M., Kibler, E., Raabe, T. (2002) SH3 domain-mediated binding of the Drk protein to Dos is an important step in signaling of Drosophila receptor tyrosine kinases.. Mech. Dev 116, 129-139.
Kerkhoff, E., Simpson, J.C., Leberfinger, C.B., Otto, I.M., Doerks, T., Bork, P., Rapp, U.R., Raabe, T., Pepperkok, R. (2001) The Spir actin organizers are involved in vesicle transport processes. Curr. Biol. 11, 1963-1968.
Bausenwein, B.S., Schmidt, M., Mielke, B., Raabe, T. (2000) In vivo functional analysis of the Daughter of Sevenless protein in receptor tyrosine kinase signaling. Mech. Dev. 90, 205-215.
Raabe, T. (2000) The Sevenless signaling pathway: variations of a common theme. Biochem. Biophys. Acta 1496, 151-163.
Otto, I.M., Raabe,
T., Rennefahrt, U.E.E., Bork, P., Rapp, U.R., Kerkhoff, E. (2000) The
p150-Spir protein provides a link between c-Jun N-terminal kinase function
and actin reorganization. Curr. Biol. 10, 345-348.
Melzig, J., Rein,
K.-H., Schäfer, U., Pfister, H., Jäckle, H., Heisenberg, M.,
and Raabe, T. (1998). A protein related to p21-activated kinase (PAK)
that is involved in neurogenesis in the Drosophila adult central nervous
system. Curr. Biol. 8, 1223-1226.
Liu,X., Bausenwein,B.S., Deak,P., Maröy,P., and Hafen,E. (1996) DOS,
a novel pleckstrin homology domain-containing protein required for signal
transduction between sevenless ans Ras1 in Drosophila. Cell 85,
Undergraduate and graduate students with a strong interest in developmental neurobiology are always welcome.
Im Rahmen der Studiengänge Genetik und Neurobiologie werden 8-wöchige F2-Praktikas angeboten.
Prof. Dr. Thomas Raabe / Institut für Medizinische Strahlenkunde und Zellforschung
Abteilung Molekulare Genetik
Biozentrum Am Hubland
Phone: (office Raabe): +49 (0)931 / 31 - 88548
Phone: (office): +49 (0)931 / 31 - 88668
Fax: +49 (0)931 / 201 - 45148
MSZ Universität Würzburg - Versbacher Strasse 5 - 97078 Würzburg - Germany
Phone: 0931 - 201 - 45 141 - Fax: 0931 - 201 - 45 835 - Email: firstname.lastname@example.org
Last update: 28. Februar 2018 - Copyright MSZ Würzburg 2003