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Ruth Schippert, Josh Wallman; Effects Of Lens-wear On Fgf Receptor Isoform Expression In The Chick Scleral Layers. Invest. Ophthalmol. Vis. Sci. 2011;52(14):6305.
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© ARVO (1962-2015); The Authors (2016-present)
The chick, like most vertebrates other than eutherian mammals, has a sclera consisting of a fibrous layer and a cartilaginous layer. When the eye elongates towards myopia, the cartilaginous layer increases its thickness and its synthesis of proteoglycans while the fibrous layer does the opposite; when the eye slows its elongation growing hyperopic, the situation is reversed. Because we have found that, in vitro, exogenous FGF causes the synthesis of proteoglycans to be increased in the fibrous sclera and decreased in the cartilaginous layer (Zhu et al., ARVO 2009), we investigated whether the opposite growth-response of the two scleral layers of the chick might be related to differences in mRNA expression levels of the several FGF receptor isoforms.
Five two-day-old chicks were treated for 1day (12h light/dark cycle) with a positive lens (+5.5D) on one eye. Relative mRNA expression levels of FGFR1b, FGFR1c, FGFR2b, FGFR2c, FGFR3b, FGFR3c, FREK and CFR1 in the fibrous and the cartilaginous sclera were determined via semi-quantitative real-time PCR. Ct-levels were normalized against 18SrRNA as a reference gene.
All FGF receptor isoforms were expressed in both tissues. Although the small number of animals tested limits our ability to make any statistical inferences at this point, if we average across the 2 scleral layers and the 8 receptor isoforms, treatment with positive lenses for 1 day caused a trend toward increased expression in the lens-wearing eye (mean 38% greater expression in lens-wearing eye; p<0.0001 by paired t-test; 62% of samples showed higher expression in lens-wearing eye). There was a consistent, but not statistically significant, tendency for the increase in the lens-wearing eye to be greater in the fibrous layer than in the cartilaginous layer (58% vs. 19% increase in lens-wearing eye), especially in FGFR3a and FGFR3b (82% increase vs. 5% increase and 80% increase vs. 4% decrease, respectively).
On the basis of the present data, mRNA levels of the FGF receptors appear to be increased after 1 day of plus-lens wear. If the differential growth response of the two scleral layers to imposed myopic defocus (increased growth in the fibrous sclera and decreased growth in the cartilaginous layer) is related to FGF, the effect may be due to changes in the abundance of FGF receptors as well as any changes that might occur in FGF availability.
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