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EE G Cornish, AM Hales, AE Hendrickson, JM Provis; A Gradient in Fgf-2 Expression During Formation of the Foveal Depression Correlates With Cone Morphology . Invest. Ophthalmol. Vis. Sci. 2002;43(13):2684.
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Purpose:FGF-2 and the receptors flg and bek are expressed by cone photoreceptors during development. Foveal cones go through a period of delayed maturation during formation of the foveal depression1 but are transformed into a narrow and elongated phoenotype, postnatally. In this study we examined expression of FGF-2, flg and bek in relation to the morphological differentiation of foveal cones. Methods:Macaque retinae aged between foetal day (Fd) 65 and 4 months postnatal, were fixed in Methyl Carnoy's, embedded in paraffin and sectioned parallel to the horizontal meridian. DIG-labelled riboprobes were prepared from rat FGF-2, FGFR1 (flg) and R2 (bek) cDNAs (≷88% homology) for in situ hybridisation. Levels of mRNA expression were compared within sections using NIH Image and the Kruskal-Wallace and Dunnett-like statistical tests. Antibodies to the splice variants of R1 (flg) and R2 (bek) were used to demonstrate the post-translation distribution of R1 and R2. Results:In the post-mitotic monkey retina FGF-2 mRNA is virtually restricted to ganglion cells and cone photoreceptors. Immunoreactivity to flg (flg-IR) and bek-IR is present on cones, each with a distinctive distribution. Early in the formation of the foveal depression (Fd 115) there is a significant downregulation of FGF-2 mRNA within the foveal cone mosaic; morphologically, foveal cones are shorter and broader than in the parafovea at this age. In the same period flg-IR is intense on the foveal rim at the cone/RPE interface and at the level of the synapses, but is almost completely absent within the foveal cone mosaic. Bek-IR is maintained during early formation of the fovea and there is no evidence of bek mRNA downregulation. Postnatally FGF2 and both receptor mRNAs are expressed uniformly throughout the foveal cone mosaic. Conclusion:FGF receptor activation has a role in the morphological differentation of foveal cones. 1. Abramov et al.Science (1982)217:265-7.
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