1. Department of Biology, McGill University, Montreal, Quebec H3B 1A1, Canada
2. Facility for Electron Microscopy Research, McGill University, Montreal, Quebec H3A 0C7, Canada
3. Department of Anatomy and Cell Biology, McGill University, Montreal, Quebec H3A 0C7, Canada
4. INRS-Institut Armand-Frappier, Laval, Quebec H7V 1B7, Canada