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Vol. 19, Issue 4, 1439-1449, April 2008

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The Tip Growth Apparatus of Aspergillus nidulans

Naimeh Taheri-Talesh^*, Tetsuya Horio^*,, Lidia Araujo-Bazán, Xiaowei Dou^*,, Eduardo A. Espeso, Miguel A. Peñalva, Stephen A. Osmani^*, and Berl R. Oakley^*

*Department of Molecular Genetics, The Ohio State University, Columbus, OH 43210; Institute of Health Biosciences, University of Tokushima Graduate School, Tokushima 770-8503, Japan; and Departamento de Microbiología Molecular, Centro de Investigaciones Biológicas, Consejo Superior de Investigaciones Científicas, Madrid 28040, Spain

Submitted May 18, 2007; Revised December 11, 2007; Accepted January 16, 2008
Monitoring Editor: David Drubin

Hyphal tip growth in fungi is important because of the economic and medical importance of fungi, and because it may be a useful model for polarized growth in other organisms. We have investigated the central questions of the roles of cytoskeletal elements and of the precise sites of exocytosis and endocytosis at the growing hyphal tip by using the model fungus Aspergillus nidulans. Time-lapse imaging of fluorescent fusion proteins reveals a remarkably dynamic, but highly structured, tip growth apparatus. Live imaging of SYNA, a synaptobrevin homologue, and SECC, an exocyst component, reveals that vesicles accumulate in the Spitzenkörper (apical body) and fuse with the plasma membrane at the extreme apex of the hypha. SYNA is recycled from the plasma membrane by endocytosis at a collar of endocytic patches, 1–2 µm behind the apex of the hypha, that moves forward as the tip grows. Exocytosis and endocytosis are thus spatially coupled. Inhibitor studies, in combination with observations of fluorescent fusion proteins, reveal that actin functions in exocytosis and endocytosis at the tip and in holding the tip growth apparatus together. Microtubules are important for delivering vesicles to the tip area and for holding the tip growth apparatus in position.

Present address: Department of Neurology, Harvard Medical School, VA Boston Healthcare System, 1400 VFW Pkwy., Bldg. 3 RM 2C130, West Roxbury, MA 02134.

Address correspondence to: Berl R. Oakley (oakley.2{at}osu.edu)

Abbreviations used: ABPA, actin-binding protein A; DMSO, dimethyl sulfoxide; GFP, green fluorescent protein; mRFP, monomeric red fluorescent protein; PCR, polymerase chain reaction; SNARE, soluble N-ethylmaleimide-sensitive-factor attachment protein receptor.