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Vol. 18, Issue 4, 1153-1166, April 2007

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Genetic Control of Fusion Pore Expansion in the Epidermis of Caenorhabditis elegans

Tamar Gattegno^*,, Aditya Mittal^,,, Clari Valansi^*, Ken C.Q. Nguyen^||, David H. Hall^||, Leonid V. Chernomordik, and Benjamin Podbilewicz^*,

*Department of Biology, Technion-Israel Institute of Technology, Haifa 32000, Israel; Section on Membrane Biology, Laboratory of Cellular and Molecular Biophysics, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892; and ^||Center for C. elegans Anatomy, Department of Neuroscience, Albert Einstein College of Medicine, Bronx, NY 10461

Submitted September 25, 2006; Revised January 2, 2007; Accepted January 8, 2007
Monitoring Editor: Peter Walter

Developmental cell fusion is found in germlines, muscles, bones, placentae, and stem cells. In Caenorhabditis elegans 300 somatic cells fuse during development. Although there is extensive information on the early intermediates of viral-induced and intracellular membrane fusion, little is known about late stages in membrane fusion. To dissect the pathway of cell fusion in C. elegans embryos, we use genetic and kinetic analyses using live-confocal and electron microscopy. We simultaneously monitor the rates of multiple cell fusions in developing embryos and find kinetically distinct stages of initiation and completion of membrane fusion in the epidermis. The stages of cell fusion are differentially blocked or retarded in eff-1 and idf-1 mutants. We generate kinetic cell fusion maps for embryos grown at different temperatures. Different sides of the same cell differ in their fusogenicity: the left and right membrane domains are fusion-incompetent, whereas the anterior and posterior membrane domains fuse with autonomous kinetics in embryos. All but one cell pair can initiate the formation of the largest syncytium. The first cell fusion does not trigger a wave of orderly fusions in either direction. Ultrastructural studies show that epidermal syncytiogenesis require eff-1 activities to initiate and expand membrane merger.

The online version of this article contains supplemental material at MBC Online (http://www.molbiolcell.org).

These authors contributed equally to this work.

Present address: Department of Biochemical Engineering and Biotechnology, Indian Institute of Technology-Delhi, Hauz Khas, New Delhi 110016, India.

Address correspondence to: Benjamin Podbilewicz (podbilew{at}tx.technion.ac.il)

Abbreviations used: AJ, apical junction; eff-1, epithelial fusion failure-1; idf-1,, irregular dorsal fusion-1; TEM, transmission electron microscopy.

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