^aDepartment of Bioengineering and Therapeutic Sciences, University of California San Francisco, San Francisco

Departments of ^bGenetics

^cBioengineering, Stanford University, Palo Alto, California, USA

Correspondence to Teri E. Klein, PhD, Department of Genetics, Stanford University, 318 Campus Drive, Clark Center Room S221A, MC: 5448, Stanford CA 94305, USA Tel: +1 650 736 0156; fax:+1 650 725 3863; e-mail: [email protected]

Received December 3, 2013

Accepted March 4, 2014