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ForC lacks canonical formin activity but bundles actin filaments and is required for multicellular development of Dictyostelium cells

  • Diaphanous-related formins (DRFs) drive the nucleation and elongation of linear actin filaments downstream of Rho GTPase signalling pathways. Dictyostelium formin C (ForC) resembles a DRF, except that it lacks a genuine formin homology domain 1 (FH1), raising the questions whether or not ForC can nucleate and elongate actin filaments. We found that a recombinant ForC-FH2 fragment does not nucleate actin polymerization, but moderately decreases the rate of spontaneous actin assembly and disassembly, although the barbed-end elongation rate in the presence of the formin was not markedly changed. However, the protein bound to and crosslinked actin filaments into loose bundles of mixed polarity. Furthermore, ForC is an important regulator of morphogenesis since ForC-null cells are severely impaired in development resulting in the formation of aberrant fruiting bodies. Immunoblotting revealed that ForC is absent during growth, but becomes detectable at the onset of early aggregation when cells chemotactically stream together to form aDiaphanous-related formins (DRFs) drive the nucleation and elongation of linear actin filaments downstream of Rho GTPase signalling pathways. Dictyostelium formin C (ForC) resembles a DRF, except that it lacks a genuine formin homology domain 1 (FH1), raising the questions whether or not ForC can nucleate and elongate actin filaments. We found that a recombinant ForC-FH2 fragment does not nucleate actin polymerization, but moderately decreases the rate of spontaneous actin assembly and disassembly, although the barbed-end elongation rate in the presence of the formin was not markedly changed. However, the protein bound to and crosslinked actin filaments into loose bundles of mixed polarity. Furthermore, ForC is an important regulator of morphogenesis since ForC-null cells are severely impaired in development resulting in the formation of aberrant fruiting bodies. Immunoblotting revealed that ForC is absent during growth, but becomes detectable at the onset of early aggregation when cells chemotactically stream together to form a multicellular organism, and peaks around the culmination stage. Fluorescence microscopy of cells ectopically expressing a GFP-tagged, N-terminal ForC fragment showed its prominent accumulation in the leading edge, suggesting that ForC may play a role in cell migration. In agreement with its expression profile, no defects were observed in random migration of vegetative mutant cells. Notably, chemotaxis of starved cells towards a source of cAMP was severely impaired as opposed to control. This was, however, largely due to a marked developmental delay of the mutant, as evidenced by the expression profile of the early developmental marker csA. In line with this, chemotaxis was almost restored to wild type levels after prolonged starvation. Finally, we observed a complete failure of phototaxis due to abolished slug formation and a massive reduction of spores consistent with forC promoter-driven expression of beta-galactosidase in prespore cells. Together, these findings demonstrate ForC to be critically involved in signalling of the cytoskeleton during various stages of development.show moreshow less

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Metadaten
Author:Alexander Junemann, Moritz Winterhoff, Benjamin Nordholz, Klemens Rottner, Ludwig Eichinger, Ralph Graef, Jan Faix
DOI:https://doi.org/10.1016/j.ejcb.2013.07.001
ISSN:0171-9335 (print)
Parent Title (English):European journal of cell biology
Publisher:Elsevier
Place of publication:Jena
Document Type:Article
Language:English
Year of first Publication:2013
Year of Completion:2013
Release Date:2017/03/26
Tag:Actin bundles; Cell migration; Chemotaxis; Development; Dictyostelium; Formin; Morphogenesis; Phototaxis; Spore formation
Volume:92
Issue:6-7
Pagenumber:12
First Page:201
Last Page:212
Funder:German Research Council (DFG) priority programme "Principles and evolution of actin nucleator complexes" [FA330/6-1, RO2414/3-1, SPP1464]
Organizational units:Mathematisch-Naturwissenschaftliche Fakultät / Institut für Biochemie und Biologie
Peer Review:Referiert