title: Insulin, insulin-like growth factor-1, insulin receptor, and insulin-like growth factor-1 receptor expression in the chick eye and their regulation with imposed myopic or hyperopic defocus.
abstract: OBJECTIVE
  Insulin stimulates eye growth in chicks and this effect is greatly enhanced if the retinal image is degraded by the defocus of either sign. However, it is unclear whether the insulin receptor (IR) is expressed at all in the chicken retina in animals 1-2 weeks post-hatching. We have investigated IR expression and whether IR transcript abundance varies in the fundal layers. To elucidate the possible role of insulin and insulin-like growth factor (IGF)-1 signaling in eye growth regulation, mRNA (mRNA) levels were measured for insulin, IGF-1, IR, and IGF-1 receptor (IGF-1R) during imposed negative or positive defocus.
  
  
  METHODS
  Chicks were treated binocularly with positive or negative spectacle lenses for 4 or 24 h, or they remained untreated (n=6, for each treatment group). Northern blot analyses were performed to screen for transcription variants in the different fundal layers of untreated animals. Real-time PCR was used to quantify IR, IGF-1R, IGF-1, and insulin mRNA levels in the different fundal layers of the chick eye in the three treatment groups.
  
  
  RESULTS
  IR mRNA was found in all the studied tissues, although there is evidence of tissue-specific transcript variations. Three major transcripts were detected for IR. The brain, retina, and choroid showed the longest transcript (4.3 kb), which was not present in the liver. Nevertheless, the liver and brain showed a second transcript (2.6 kb) not present in the retina and choroid. A short transcript (1.3 kb) was the predominant form in the liver and choroid, and it seems to be present in the retinal pigment epithelium (RPE) and sclera as well. In the retina, no significant gene expression changes were found when defocus was imposed. Interestingly, in the RPE, both IR and IGF-1R were already downregulated after short periods (4 h) of positive lens wear. In contrast, IR and IGF-1R were upregulated in the choroid and fibrous sclera during treatment with negative, but not positive, lenses.
  
  
  CONCLUSIONS
  Differences observed in the IR transcript length in different tissues suggest possibly different functions. The differential regulation of IR and IGF-1R in the RPE, choroid, and fibrous sclera is consistent with their involvement in a signaling cascade for emmetropization.
authors.affiliation: University Eye Hospital, Institute for Ophthalmic Research, Section of Neurobiology of the Eye, Tuebingen, Germany.
authors.forename: Alexandra Marcha
authors.initials: AM
authors.lastname: Penha
authors.forename: Frank
authors.initials: F
authors.lastname: Schaeffel
authors.forename: Marita
authors.initials: M
authors.lastname: Feldkaemper
mesh_terms: D017398:Alternative Splicing; D000818:Animals; D001921:Brain / Q000378:metabolism; D002645:Chickens / Q000235:genetics / Q000378:metabolism*; D002829:Choroid / Q000378:metabolism; D058453:Emmetropia / Q000502:physiology*; D015870:Gene Expression; D006956:Hyperopia / Q000235:genetics / Q000378:metabolism*; D007328:Insulin / Q000235:genetics / Q000378:metabolism*; D007334:Insulin-Like Growth Factor I / Q000235:genetics / Q000378:metabolism*; D008099:Liver / Q000378:metabolism; D009216:Myopia / Q000235:genetics / Q000378:metabolism*; D012333:RNA, Messenger / Q000032:analysis; D017526:Receptor, IGF Type 1 / Q000235:genetics / Q000378:metabolism*; D011972:Receptor, Insulin / Q000235:genetics / Q000378:metabolism*; D012160:Retina / Q000737:chemistry / Q000378:metabolism; D055213:Retinal Pigment Epithelium / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012590:Sclera / Q000378:metabolism; D014785:Vision, Ocular / Q000502:physiology
chemical_list: D007328:Insulin; D012333:RNA, Messenger; D007334:Insulin-Like Growth Factor I; D017526:Receptor, IGF Type 1; D011972:Receptor, Insulin