Department of Biomathematics, University of California, Los Angeles, David Geffen School of Medicine, Los Angeles, California, United States of America.|Department of Biomathematics, University of California, Los Angeles, David Geffen School of Medicine, Los Angeles, California, United States of America.|Department of Biology, University of Pennsylvania, Philadelphia, Pennsylvania, United States of America.|Department of Biomathematics, University of California, Los Angeles, David Geffen School of Medicine, Los Angeles, California, United States of America.