title: Identification of a retina-specific Otx2 enhancer element active in immature developing photoreceptors.
abstract: The homeodomain protein, Otx2, is a critical regulator of vertebrate photoreceptor genesis. However, the genetic elements that define the expression of Otx2 during photoreceptor development are unknown. Therefore, we sought to identify an Otx2 enhancer element that functions in photoreceptor development in order to better understand this specification event. Using the technique of electroporation, we tested a number of evolutionarily conserved elements (ECRs) for expression in the developing retina, and identified ECR2 as having robust activity in the retina. We have characterized this element using a number of assays, including Cre-fate mapping experiments. We found that ECR2 recapitulates expression/function of Otx2 primarily in newly postmitotic photoreceptor cells (PRs), as well as in a subset of retinal progenitor cells (RPCs). ECR2 was also found to be expressed in a subset of horizontal cells (HCs), in keeping with the role of Otx2 in HC development. Furthermore, we determined that the ECR2 element is not active in other Otx2-positive cells such as retinal bipolar cells (BPs), retinal pigmented epithelium (RPE), or the tectum, suggesting that the transcriptional networks controlling Otx2 expression in these cells are unique from those of developing PRs and HCs. These results reveal a distinct molecular state in dividing retinal cells and their newly postmitotic progeny, and provide genetic access to an early and critical transcriptional node involved in the genesis of vertebrate PRs.
authors.affiliation: Department of Genetics, Department of Ophthamology, Howard Hughes Medical Institute, Harvard Medical School, Boston, MA 02115, USA. mark_emerson@hms.harvard.edu
authors.forename: Mark M
authors.initials: MM
authors.lastname: Emerson
authors.forename: Constance L
authors.initials: CL
authors.lastname: Cepko
mesh_terms: D000818:Animals; D030801:Animals, Genetically Modified; D001483:Base Sequence; D002642:Chick Embryo; D017124:Conserved Sequence; D004247:DNA / Q000235:genetics; D004742:Enhancer Elements, Genetic; D019143:Evolution, Molecular; D018507:Gene Expression Regulation, Developmental; D051379:Mice; D008822:Mice, Transgenic; D008969:Molecular Sequence Data; D051857:Otx Transcription Factors / Q000235:genetics*; D020419:Photoreceptor Cells, Vertebrate / Q000166:cytology / Q000378:metabolism*; D010802:Phylogeny; D012160:Retina / Q000166:cytology / Q000201:enzymology* / Q000378:metabolism*; D012689:Sequence Homology, Nucleic Acid
chemical_list: D051857:Otx Transcription Factors; C497660:Otx2 protein, mouse; D004247:DNA