1. W. M. Keck Science Department, Claremont McKenna, Pitzer, and Scripps Colleges, Claremont, CA 91711, USA.
2. Division of Biological Sciences, Section of Cell and Developmental Biology, University of California, San Diego, La Jolla, CA 92093, USA.
3. Division of Biology and Biological Engineering (BBE), California Institute of Technology, Pasadena, CA 91125, USA.
4. Tata Institute for Genetics and Society–UCSD, La Jolla, CA 92093, USA.