title: Light-Regulated Thyroid Hormone Signaling Is Required for Rod Photoreceptor Development in the Mouse Retina.
abstract: OBJECTIVE
  Ambient light is both a stimulus for visual function and a regulator of photoreceptor physiology. However, it is not known if light can regulate any aspect of photoreceptor development. The purpose of this study was to investigate whether ambient light is required for the development of mouse rod photoreceptors.
  
  
  METHODS
  Newborn mouse pups (C57BL/6) were reared in either cyclic light (LD) or constant dark (DD). Pups were collected at postnatal day (P)5, P10, P17, or P24. We performed retinal morphometric and cell death analysis at P5, P10, and P17. Rhodopsin expression was assessed using immunofluorescence, Western blot, and quantitative RT-PCR analysis. Electroretinograms were performed at P17 and P24. Radioimmunoassay and ELISA were used to follow changes in thyroid hormone levels in the serum and vitreous.
  
  
  RESULTS
  In the DD pups, the outer nuclear layer was significantly thinner at P10 and there were higher numbers of apoptotic cells at P5 compared to the LD pups. Rhodopsin expression was lower at P10 and P17 in DD pups. Electroretinogram a-waves were reduced in amplitude at P17 in the DD pups. The DD animals had lower levels of circulating thyroid hormones at P10. Light-mediated changes in thyroid hormones occur as early as P5, as we detected lower levels of total triiodothyronine in the vitreous from the DD animals. Drug-induced developmental hypothyroidism resulted in lower rhodopsin expression at P10.
  
  
  CONCLUSIONS
  Our data demonstrate that light exposure during postnatal development is required for rod photoreceptor development and that this effect could be mediated by thyroid hormone signaling.
authors.affiliation: Department of Ophthalmic Research, Cole Eye Institute, Cleveland Clinic, Cleveland, Ohio, United States.
authors.forename: Onkar
authors.initials: O
authors.lastname: Sawant
authors.affiliation: Department of Ophthalmic Research, Cole Eye Institute, Cleveland Clinic, Cleveland, Ohio, United States.
authors.forename: Amanda M
authors.initials: AM
authors.lastname: Horton
authors.affiliation: Department of Ophthalmic Research, Cole Eye Institute, Cleveland Clinic, Cleveland, Ohio, United States.
authors.forename: Meenal
authors.initials: M
authors.lastname: Shukla
authors.affiliation: Department of Ophthalmic Research, Cole Eye Institute, Cleveland Clinic, Cleveland, Ohio, United States.
authors.forename: Mary E
authors.initials: ME
authors.lastname: Rayborn
authors.affiliation: Department of Ophthalmic Research, Cole Eye Institute, Cleveland Clinic, Cleveland, Ohio, United States 2Department of Ophthalmology, Cleveland Clinic Lerner College of Medicine of Case Western Reserve University, Cleveland, Ohio, United States 3Louis Sto.
authors.forename: Neal S
authors.initials: NS
authors.lastname: Peachey
authors.affiliation: Department of Ophthalmic Research, Cole Eye Institute, Cleveland Clinic, Cleveland, Ohio, United States 2Department of Ophthalmology, Cleveland Clinic Lerner College of Medicine of Case Western Reserve University, Cleveland, Ohio, United States.
authors.forename: Joe G
authors.initials: JG
authors.lastname: Hollyfield
authors.affiliation: Department of Ophthalmic Research, Cole Eye Institute, Cleveland Clinic, Cleveland, Ohio, United States 2Department of Ophthalmology, Cleveland Clinic Lerner College of Medicine of Case Western Reserve University, Cleveland, Ohio, United States.
authors.forename: Sujata
authors.initials: S
authors.lastname: Rao
mesh_terms: D000818:Animals; D000831:Animals, Newborn; D015153:Blotting, Western; D016923:Cell Death; D004247:DNA / Q000235:genetics; D003623:Dark Adaptation; D004195:Disease Models, Animal; D004596:Electroretinography; D004797:Enzyme-Linked Immunosorbent Assay; D018507:Gene Expression Regulation, Developmental; D008027:Light; D055537:Light Signal Transduction; D051379:Mice; D008810:Mice, Inbred C57BL; D012162:Retinal Degeneration / Q000235:genetics / Q000378:metabolism* / Q000503:physiopathology; D017948:Retinal Rod Photoreceptor Cells / Q000378:metabolism* / Q000473:pathology / Q000528:radiation effects; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012243:Rhodopsin / Q000096:biosynthesis / Q000235:genetics / Q000528:radiation effects; D013963:Thyroid Hormones / Q000378:metabolism* / Q000528:radiation effects
chemical_list: D013963:Thyroid Hormones; D004247:DNA; D012243:Rhodopsin