Novel requirements for HAP2/GCS1-mediated gamete fusion in Tetrahymena
Jennifer F. Pinello,
Josef Loidl,
Ethan S. Seltzer,
Donna Cassidy-Hanley,
Daniel Kolbin,
Anhar Abdelatif,
Félix A. Rey,
Rocky An,
Nicole J. Newberger,
Yelena Bisharyan,
Hayk Papoyan,
Haewon Byun,
Hector C. Aguilar,
Alex L. Lai,
Jack H. Freed,
Timothy Maugel,
Eric S. Cole,
Theodore G. Clark
Affiliations
Jennifer F. Pinello
Department of Cell Biology and Molecular Genetics, University of Maryland, College Park, MD 20742, USA; Department of Microbiology and Immunology, Cornell University, Ithaca, NY 14853, USA
Josef Loidl
Department of Chromosome Biology, Max Perutz Labs, University of Vienna, Vienna, Austria
Ethan S. Seltzer
Department of Microbiology and Immunology, Cornell University, Ithaca, NY 14853, USA
Donna Cassidy-Hanley
Department of Microbiology and Immunology, Cornell University, Ithaca, NY 14853, USA
Daniel Kolbin
Department of Microbiology and Immunology, Cornell University, Ithaca, NY 14853, USA
Anhar Abdelatif
Department of Microbiology and Immunology, Cornell University, Ithaca, NY 14853, USA
Félix A. Rey
Unité de Virologie Structurale, Institut Pasteur, 75724 Paris, France; CNRS UMR 3569, 75724 Paris, France
Rocky An
Department of Microbiology and Immunology, Cornell University, Ithaca, NY 14853, USA
Nicole J. Newberger
Department of Microbiology and Immunology, Cornell University, Ithaca, NY 14853, USA
Yelena Bisharyan
Office of Technology Development, Harvard University, Cambridge, MA 02138, USA
Hayk Papoyan
Department of Microbiology and Immunology, Cornell University, Ithaca, NY 14853, USA
Haewon Byun
Department of Microbiology and Immunology, Cornell University, Ithaca, NY 14853, USA
Hector C. Aguilar
Department of Microbiology and Immunology, Cornell University, Ithaca, NY 14853, USA
Alex L. Lai
Department of Chemistry and Chemical Biology, Cornell University, Ithaca, NY 14850, USA
Jack H. Freed
Department of Chemistry and Chemical Biology, Cornell University, Ithaca, NY 14850, USA
Timothy Maugel
Department of Biology, Laboratory for Biological Ultrastructure, University of Maryland, College Park, MD 20742, USA
Eric S. Cole
Biology Department, St. Olaf College, Northfield, MN 55057, USA
Theodore G. Clark
Department of Microbiology and Immunology, Cornell University, Ithaca, NY 14853, USA; Corresponding author
Summary: The ancestral gamete fusion protein, HAP2/GCS1, plays an essential role in fertilization in a broad range of taxa. To identify factors that may regulate HAP2/GCS1 activity, we screened mutants of the ciliate Tetrahymena thermophila for behaviors that mimic Δhap2/gcs1 knockout phenotypes in this species. Using this approach, we identified two new genes, GFU1 and GFU2, whose products are necessary for membrane pore formation following mating type recognition and adherence. GFU2 is predicted to be a single-pass transmembrane protein, while GFU1, though lacking obvious transmembrane domains, has the potential to interact directly with membrane phospholipids in the cytoplasm. Like Tetrahymena HAP2/GCS1, expression of GFU1 is required in both cells of a mating pair for efficient fusion to occur. To explain these bilateral requirements, we propose a model that invokes cooperativity between the fusion machinery on apposed membranes of mating cells and accounts for successful fertilization in Tetrahymena’s multiple mating type system.
