title: Temporal control of immediate early gene induction by light.
abstract: BACKGROUND
  The light-gated cation channel channelrhodopsin-2 (ChR2) is a powerful tool for the optical induction of action potentials in neurons. Mutations of the cysteine 128 (C128) residue have been shown to greatly extend the lifetime of the conducting state of ChR2. However, until now, only subthreshold depolarizations have been reported from C128 mutants.
  
  
  RESULTS
  Here we report the induction of long high-frequency spike trains by brief light pulses in ChR2(C128A)-transfected pyramidal cells in hippocampal slice culture. ChR2(C128A)-mediated spike bursts triggered expression of the immediate early gene c-fos in pyramidal neurons. Robust and cell-specific expression of c-Fos protein was detected after a single blue light pulse and depended on action potential firing, but not on synaptic activity. However, photocurrents diminished upon repeated stimulation and limited the number of action potential bursts that could be elicited.
  
  
  CONCLUSIONS
  We conclude that the C128A mutant is not suitable for chronic stimulation of neurons, but very useful for light-controlled induction of immediate early genes. This property of ChR2(C128A) could be harnessed to control the expression of proteins under control of the c-fos promoter with precise timing and single cell specificity.
authors.affiliation: Friedrich Miescher Institute for Biomedical Research, Basel, Switzerland.
authors.forename: Philipp
authors.initials: P
authors.lastname: Schoenenberger
authors.forename: Daniela
authors.initials: D
authors.lastname: Gerosa
authors.forename: Thomas G
authors.initials: TG
authors.lastname: Oertner
mesh_terms: D000200:Action Potentials / Q000528:radiation effects; D000818:Animals; D002448:Cell Adhesion / Q000528:radiation effects; D005786:Gene Expression Regulation / Q000528:radiation effects*; D017781:Genes, Immediate-Early / Q000235:genetics*; D015640:Ion Channel Gating / Q000528:radiation effects; D008027:Light; D051379:Mice; D009154:Mutation / Q000235:genetics; D009928:Organ Specificity / Q000528:radiation effects; D016760:Proto-Oncogene Proteins c-fos / Q000235:genetics / Q000378:metabolism; D017966:Pyramidal Cells / Q000166:cytology / Q000378:metabolism / Q000528:radiation effects; D051381:Rats; D012243:Rhodopsin / Q000235:genetics; D013997:Time Factors
chemical_list: D016760:Proto-Oncogene Proteins c-fos; D012243:Rhodopsin