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Eukaryotic Cell, June 2005, p. 1125-1136, Vol. 4, No. 6
1535-9778/05/$08.00+0     doi:10.1128/EC.4.6.1125-1136.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.

Class I and Class II Chitin Synthases Are Involved in Septum Formation in the Filamentous Fungus Aspergillus nidulans

Masayuki Ichinomiya,^1, Emi Yamada,^1, Shuichi Yamashita,² Akinori Ohta,¹ and Hiroyuki Horiuchi^1*

Department of Biotechnology,¹ Department of Agricultural and Environmental Biology, The University of Tokyo, Tokyo 113-8657, Japan²

Received 25 November 2004/ Accepted 29 March 2005

The class II and class I chitin synthases of the filamentous fungus Aspergillus nidulans are encoded by chsA and chsC, respectively. Previously, we presented several lines of evidence suggesting that ChsA and ChsC have overlapping functions in maintaining cell wall integrity. In order to determine the functions of these chitin synthases, we employed electron and fluorescence microscopy and investigated in detail the cell wall of a chsA chsC double mutant (AC mutant) along with the localization of ChsA and ChsC. In the lateral cell wall of the AC mutant, electron-transparent regions were thickened. Septa of the AC mutant were aberrantly thick and had a large pore. Some septa were located abnormally close to adjacent septa. A functional hemagglutinin (HA)-tagged ChsA (HA-ChsA) and a functional FLAG-tagged ChsC (FLAG-ChsC) were each localized to a subset of septation sites. Comparison with the localization pattern of actin, which is known to localize at forming septa, suggested that ChsA and ChsC transiently exist at the septation sites during and shortly after septum formation. Double staining of HA-ChsA and FLAG-ChsC indicated that their localizations were not identical but partly overlapped at the septation sites. Fluorescence of FLAG-ChsC, but not of HA-ChsA, was also observed at hyphal tips. These data indicate that ChsA and ChsC share overlapping roles in septum formation.

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* Corresponding author. Mailing address: 1-1-1 Yayoi, Bunkyo-ku, Tokyo 113-8657, Japan. Phone: 81-3-5841-5170. Fax: 81-3-5841-8015. E-mail: ahhoriu{at}mail.ecc.u-tokyo.ac.jp.

M.I. and E.Y. contributed equally to this work.

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Eukaryotic Cell, June 2005, p. 1125-1136, Vol. 4, No. 6
1535-9778/05/$08.00+0     doi:10.1128/EC.4.6.1125-1136.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.

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