title: Discrimination of DNA and RNA in cells by a vital fluorescent probe: lifetime imaging of SYTO13 in healthy and apoptotic cells.
abstract: BACKGROUND
  Of the few vital DNA and RNA probes, the SYTO dyes are the most specific for nucleic acids. However, they show no spectral contrast upon DNA or RNA binding. We show that fluorescence lifetime imaging using two-photon excitation of SYTO13 allows differential and simultaneous imaging of DNA and RNA in living cells, as well as sequential and repetitive assessment of staining patterns.
  
  
  METHODS
  Two-photon imaging of SYTO13 is combined with lifetime contrast, using time-gated detection. We focus on distinguishing DNA and RNA in healthy and apoptotic Chinese hamster ovary cells.
  
  
  RESULTS
  In healthy cells, SYTO13 has a fluorescence lifetime of 3.4 +/- 0.2 ns when associated with nuclear DNA. Bound to RNA, its lifetime is 4.1 +/- 0.1 ns. After induction of apoptosis, clusters of SYTO13 with fluorescence lifetime of 3.4 +/- 0.2 ns become apparent in the cytoplasm. They are identified as mitochondrial DNA on the basis of colocalization experiments with the DNA-specific dye, DRAQ5, and the mitochondrial-specific dye, CMXRos. Upon progression of apoptosis, the lifetime of SYTO13 attached to DNA shortens significantly, which is indicative of changes in the molecular environment of the dye.
  
  
  CONCLUSIONS
  We have characterized SYTO13 as a vital lifetime probe, allowing repetitive and differential imaging of DNA and RNA.
authors.affiliation: Department of Biophysics, Cardiovascular Research Institute Maastricht, University of Maastricht, Maastricht, The Netherlands. MAMJ.vanZandvoort@BF.unimaas.nl
authors.forename: Marc A M J
authors.initials: MA
authors.lastname: van Zandvoort
authors.forename: Cees J
authors.initials: CJ
authors.lastname: de Grauw
authors.forename: Hans C
authors.initials: HC
authors.lastname: Gerritsen
authors.forename: Jos L V
authors.initials: JL
authors.lastname: Broers
authors.forename: Mirjam G A
authors.initials: MG
authors.lastname: oude Egbrink
authors.forename: Frans C S
authors.initials: FC
authors.lastname: Ramaekers
authors.forename: Dick W
authors.initials: DW
authors.lastname: Slaaf
mesh_terms: D000818:Animals; D000880:Anthraquinones; D017209:Apoptosis / Q000235:genetics*; D016466:CHO Cells; D002451:Cell Compartmentation / Q000235:genetics; D002467:Cell Nucleus / Q000737:chemistry; D048429:Cell Size / Q000502:physiology; D006224:Cricetinae; D003593:Cytoplasm / Q000737:chemistry; D004247:DNA / Q000032:analysis*; D005057:Eukaryotic Cells / Q000737:chemistry* / Q000166:cytology; D005456:Fluorescent Dyes; D007091:Image Processing, Computer-Assisted / Q000295:instrumentation / Q000379:methods*; D008856:Microscopy, Fluorescence / Q000295:instrumentation / Q000379:methods*; D008928:Mitochondria / Q000737:chemistry / Q000648:ultrastructure; D009589:Nitrogen Oxides; D009930:Organic Chemicals; D012313:RNA / Q000032:analysis*; D013194:Staining and Labeling / Q000295:instrumentation / Q000379:methods*
chemical_list: D000880:Anthraquinones; C406029:DRAQ5NO; D005456:Fluorescent Dyes; D009589:Nitrogen Oxides; D009930:Organic Chemicals; C461159:SYTO 13; C107472:red dye CMXRos; D012313:RNA; D004247:DNA