title: A regulatory sequence from theretinoid X receptor γ genedirects expression to horizontal cells and photoreceptors in the embryonic chicken retina.
abstract: Combining techniques of episomal vector gene-specific Cre expression and genomic integration using the piggyBac transposon system enables studies of gene expression-specific cell lineage tracing in the chicken retina. In this work, we aimed to target the retinal horizontal cell progenitors.
  
  
  
  A 208 bp gene regulatory sequence from the chickenretinoid X receptor γgene(RXRγ208) was used to drive Cre expression. RXRγ is expressed in progenitors and photoreceptors during development. The vector was combined with a piggyBac "donor" vector containing a floxed STOP sequence followed by enhanced green fluorescent protein (EGFP), as well as a piggyBac helper vector for efficient integration into the host cell genome. The vectors were introduced into the embryonic chicken retina with in ovo electroporation. Tissue electroporation targets specific developmental time points and in specific structures.
  
  
  
  Cells that drove Cre expression from the regulatory RXRγ208 sequence excised the floxed STOP-sequence and expressed GFP. The approach generated a stable lineage with robust expression of GFP in retinal cells that have activated transcription from the RXRγ208 sequence. Furthermore, GFP was expressed in cells that express horizontal or photoreceptor markers when electroporation was performed between developmental stages 22 and 28. Electroporation of a stage 12 optic cup gave multiple cell types in accordance withRXRγ geneexpression in the early retina.
  
  
  
  In this study, we describe an easy, cost-effective, and time-efficient method for testing regulatory sequences in general. More specifically, our results open up the possibility for further studies of theRXRγ-generegulatory network governing the formation of photoreceptor and horizontal cells. In addition, the method presents approaches to target the expression of effector genes, such as regulators of cell fate or cell cycle progression, to these cells and their progenitor.
authors.affiliation: Department of Neuroscience, Faculty of Medicine, Uppsala University, Uppsala, Sweden.
authors.forename: Maria K E
authors.initials: MK
authors.lastname: Blixt
authors.affiliation: Department of Neuroscience, Faculty of Medicine, Uppsala University, Uppsala, Sweden.
authors.forename: Finn
authors.initials: F
authors.lastname: Hallböök
mesh_terms: D000818:Animals; D019070:Cell Lineage; D002642:Chick Embryo; D002645:Chickens; D018274:Electroporation; D018507:Gene Expression Regulation, Developmental / Q000502:physiology*; D005822:Genetic Vectors; D049452:Green Fluorescent Proteins; D019426:Integrases / Q000235:genetics; D051857:Otx Transcription Factors / Q000235:genetics; D000071841:PAX6 Transcription Factor / Q000235:genetics; D020419:Photoreceptor Cells, Vertebrate / Q000378:metabolism*; D016133:Polymerase Chain Reaction; D050436:Regulatory Elements, Transcriptional; D012045:Regulatory Sequences, Nucleic Acid / Q000235:genetics*; D012160:Retina / Q000196:embryology*; D051248:Retinal Horizontal Cells / Q000378:metabolism*; D047491:Retinoid X Receptor gamma / Q000235:genetics*
chemical_list: D051857:Otx Transcription Factors; D000071841:PAX6 Transcription Factor; D047491:Retinoid X Receptor gamma; C485184:enhanced green fluorescent protein; D049452:Green Fluorescent Proteins; C045073:Cre recombinase; D019426:Integrases