title: Regulation of ammonia homeostasis by the ammonium transporter AmtA in Dictyostelium discoideum.
abstract: 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 NH(4)Cl 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.
authors.affiliation: Graduate School of Life and Environmental Sciences, University of Tsukuba, Tsukuba, Ibaraki, Japan 305-8572. ryoshino@jhmi.edu
authors.forename: Ryuji
authors.initials: R
authors.lastname: Yoshino
authors.forename: Takahiro
authors.initials: T
authors.lastname: Morio
authors.forename: Yoko
authors.initials: Y
authors.lastname: Yamada
authors.forename: Hidekazu
authors.initials: H
authors.lastname: Kuwayama
authors.forename: Masazumi
authors.initials: M
authors.lastname: Sameshima
authors.forename: Yoshimasa
authors.initials: Y
authors.lastname: Tanaka
authors.forename: Hiromi
authors.initials: H
authors.lastname: Sesaki
authors.forename: Miho
authors.initials: M
authors.lastname: Iijima
mesh_terms: D000641:Ammonia / Q000378:metabolism*; D000818:Animals; D001692:Biological Transport; D027682:Cation Transport Proteins / Q000235:genetics / Q000378:metabolism* / Q000502:physiology*; D002450:Cell Communication; D005786:Gene Expression Regulation; D006706:Homeostasis; D008954:Models, Biological; D009696:Nucleic Acids / Q000737:chemistry; D010766:Phosphorylation; D010802:Phylogeny; D000644:Quaternary Ammonium Compounds / Q000737:chemistry*; D015398:Signal Transduction
chemical_list: D027682:Cation Transport Proteins; D009696:Nucleic Acids; D000644:Quaternary Ammonium Compounds; D000641:Ammonia