Author information:
(1)Department of Cellular and Molecular Medicine, University of California, San 
Diego, 9500 Gilman Drive, La Jolla, CA, USA.
(2)Howard Hughes Medical Institute, Department of Medicine, University of 
California, San Diego, 9500 Gilman Drive, La Jolla, CA, USA.
(3)Howard Hughes Medical Institute, Department of Medicine, University of 
California, San Diego, 9500 Gilman Drive, La Jolla, CA, USA. Electronic address: 
mrosenfeld@ucsd.edu.
(4)Department of Cellular and Molecular Medicine, University of California, San 
Diego, 9500 Gilman Drive, La Jolla, CA, USA; Howard Hughes Medical Institute, 
Department of Medicine, University of California, San Diego, 9500 Gilman Drive, 
La Jolla, CA, USA. Electronic address: ckg@ucsd.edu.