Cells were analyzed and sorted on a MoFlo cell sorter (Beckman Coulter, USA; former Cytomation, USA), equipped with a Coherent Enterprise 621 argon-ion laser tuned to 488 nm (used at 180 mW), and 635 nm Diode (25 mW). Two mg/ml propidium iodide -PI (Molecular Probes) were added to the samples before flow sorting to facilitate dead cell discrimination. The GFP and PI were excited at 488 nm and fluorescence was measured through 530/40 BP and 613/20 BP optical filters (all filters from Omega Optical, Brattleboro, VT, USA), respectively. Doublets were discriminated using a forward light scatter (FSC) versus pulse width. FL3 channel (in logarithmic mode) with FSC were used to display and gate out PI positive/dead cells. FSC and side light scatter (SSC) signals were detected and shown in linear mode. GFP+ cells were defined on SSC versus FL1 (in logarithmic mode) dot plot after exclusion of dead cells and debris as described above.