title: Egr-1 mRNA expression is a marker for the direction of mammalian ocular growth.
abstract: OBJECTIVE
  The immediate early gene Egr-1 is thought to form part of the pathway that mediates abnormal ocular growth. This study investigated whether the mRNA expression levels of Egr-1 in a mammalian retina are modulated differentially, depending on the direction of ocular growth.
  
  
  METHODS
  To induce accelerated growth and myopia, guinea pigs wore a -5 diopter (D) lens over one eye from 4 to 11 days of age. To induce inhibited growth, the lens was removed after 7 days of -5 D lens wear, and the eye allowed to recover from myopia for 3 days. Ocular parameters and Egr-1 mRNA levels were subsequently assessed, and compared to untreated fellow eyes and eyes from untreated littermates. Possible circadian changes in Egr-1 mRNA levels were also determined in 18 additional animals by taking measures every 4 hours during a 24-hour cycle.
  
  
  RESULTS
  Ocular compensation to a -5 D lens occurred after 7 days (Δ -4.8 D, Δ +147 μm growth, N = 20). In 5 highly myopic eyes (Δ -7.4 D), Egr-1 mRNA levels in the retina were significantly downregulated relative to contralateral control (51%) and age-matched untreated (47%) eyes. Three days after the -5 D lens was removed, eyes had recovered from the myopia (Δ -0.5 D, relative change of +2.9 D, N = 4) and Egr-1 mRNA levels were significantly elevated relative to contralateral (212%) and untreated (234%) eyes, respectively. Normal Egr-1 mRNA expression was higher in the middle of the day than in the middle of the night. Immunolabeling showed strong Egr-1 reactivity in cell bodies in the inner nuclear and ganglion cell layers.
  
  
  CONCLUSIONS
  Egr-1 mRNA levels in a mammalian retina show a bi-directional persistent response to opposing ocular growth stimuli. This suggests retinal Egr-1 might act as a signal for the direction of ocular growth in different species.
authors: Vision Sciences Group, School of Psychology, Faculty of Science and IT, The University of Newcastle, New South Wales, Australia.
authors: Regan S
authors: RS
authors: Ashby
authors: Vision Sciences Group, School of Psychology, Faculty of Science and IT, The University of Newcastle, New South Wales, Australia Department of Ophthalmology, Daqing Oilfield General Hospital, Saertu, Daqing, China.
authors: Guang
authors: G
authors: Zeng
authors: Vision Sciences Group, School of Psychology, Faculty of Science and IT, The University of Newcastle, New South Wales, Australia.
authors: Amelia J
authors: AJ
authors: Leotta
authors: Vision Sciences Group, School of Psychology, Faculty of Science and IT, The University of Newcastle, New South Wales, Australia School of Optometry, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong.
authors: Dennis Y
authors: DY
authors: Tse
authors: Vision Sciences Group, School of Psychology, Faculty of Science and IT, The University of Newcastle, New South Wales, Australia.
authors: Sally A
authors: SA
authors: McFadden
mesh_terms: D000704:Analysis of Variance; D000818:Animals; D015415:Biomarkers / Q000378:metabolism; D002940:Circadian Rhythm / Q000502:physiology; D004195:Disease Models, Animal; D051766:Early Growth Response Protein 1 / Q000378:metabolism*; D005123:Eye / Q000254:growth & development*; D006168:Guinea Pigs; D007150:Immunohistochemistry; D009216:Myopia / Q000378:metabolism*; D012333:RNA, Messenger / Q000378:metabolism; D012160:Retina / Q000378:metabolism*
chemical_list: D015415:Biomarkers; C497325:EGR1 protein, human; D051766:Early Growth Response Protein 1; D012333:RNA, Messenger
keywords: Egr-1; guinea pig; myopia; refractive error; retina