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Eukaryotic Cell, December 2007, p. 2419-2428, Vol. 6, No. 12
1535-9778/07/$08.00+0     doi:10.1128/EC.00204-07
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

Regulation of Ammonia Homeostasis by the Ammonium Transporter AmtA in Dictyostelium discoideum

Ryuji Yoshino,^1,5* Takahiro Morio,¹ Yoko Yamada,^2, Hidekazu Kuwayama,^1,3 Masazumi Sameshima,^2,4 Yoshimasa Tanaka,¹ Hiromi Sesaki,⁵ and Miho Iijima^5*

Graduate School of Life and Environmental Sciences, University of Tsukuba, Tsukuba, Ibaraki, Japan 305-8572,¹ Electron Microscopy Center, The Tokyo Metropolitan Institute of Medical Science, Bunkyo-ku, Tokyo, Japan 113-8613,² Graduate School of Frontier Biosciences, Osaka University, Suita, Osaka, Japan 565-0871,³ Department of Biofunctional Science Faculty of Agriculture and Life Science, Hirosaki University, Bunkyo-cho, Hirosaki, Aomori, Japan 036-8561,⁴ Department of Cell Biology, Johns Hopkins University, School of Medicine, Baltimore, Maryland 21205⁵

Received 11 June 2007/ Accepted 3 October 2007

Ammonia has been shown to function as a morphogen at multiple steps during the development of the cellular slime mold Dictyostelium discoideum; however, it is largely unknown how intracellular ammonia levels are controlled. In the Dictyostelium genome, there are five genes that encode putative ammonium transporters: amtA, amtB, amtC, rhgA, and rhgB. Here, we show that AmtA regulates ammonia homeostasis during growth and development. We found that cells lacking amtA had increased levels of ammonia/ammonium, whereas their extracellular ammonia/ammonium levels were highly decreased. These results suggest that AmtA mediates the excretion of ammonium. In support of a role for AmtA in ammonia homeostasis, AmtA mRNA is expressed throughout the life cycle, and its expression level increases during development. Importantly, AmtA-mediated ammonia homeostasis is critical for many developmental processes. amtA^– cells are more sensitive to NH₄Cl than wild-type cells in inhibition of chemotaxis toward cyclic AMP and of formation of multicellular aggregates. Furthermore, even in the absence of exogenously added ammonia, we found that amtA^– cells produced many small fruiting bodies and that the viability and germination of amtA^– spores were dramatically compromised. Taken together, our data clearly demonstrate that AmtA regulates ammonia homeostasis and plays important roles in multiple developmental processes in Dictyostelium.

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* Corresponding author. Mailing address: Department of Cell Biology, Johns Hopkins University School of Medicine, 725 N. Wolfe St., Hunterian 107, Baltimore, MD 21205. Phone: (410) 502-6836. Fax: (410) 502-7826. E-mail for Ryuji Yoshino: ryoshino{at}jhmi.edu. E-mail for Miho Iijima: miijima{at}jhmi.edu

Published ahead of print on 19 October 2007.

Present address: University of Dundee, MSI/WTB Complex, Dow Street, Dundee DD1 5EH, United Kingdom.

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Eukaryotic Cell, December 2007, p. 2419-2428, Vol. 6, No. 12
1535-9778/07/$08.00+0     doi:10.1128/EC.00204-07
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

This article has been cited by other articles:

• Gross, J. D. (2009). Acidic Ca2+ Stores, Excitability, and Cell Patterning in Dictyostelium discoideum. Eukaryot Cell 8: 696-702 [Full Text]