1. Department of Molecular Physiology and Biophysics, Baylor College of Medicine,Houston, TX 77030, USA.
2. Department of Chemical Engineering, California Institute of Technology,Pasadena, CA 91125, USA.
3. Department of Medicine, School of Medicine, University of California-San Diego, 9500 Gilman Drive, La Jolla, CA 92093-0641, USA.
4. Biological Imaging Center, Department of Biology, California Institute of Technology, Pasadena, CA 91125, USA.