About the Authors
Department of Biology, McGill University, Montreal, Quebec, Canada
Department of Cell and Systems Biology, University of Toronto, Toronto, Canada
The authors have declared that no competing interests exist.
The author(s) have made the following declarations about their contributions: Conceived and designed the experiments: FF RW. Performed the experiments: NR LC OL FF RW. Analyzed the data: NR LC OL FF RW. Wrote the paper: FF RW.