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KM Bumsted O'Brien, D Schulte, AE Hendrickson; Expression of Photoreceptor-Associated Genes During Human Embryonic Eye Development . Invest. Ophthalmol. Vis. Sci. 2002;43(13):2683.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose:Human photoreceptor topography is centered on the fovea, which contains the highest density of cones and lacks rods. How are these photoreceptor types specified during embryogenesis? Human retinal development begins centrally with the first cells in the fovea being morphologically defined at Fetal week (Fwk) 10.5-11. Bibb et al., 2001 reported that the photoreceptor specific genes cone/rod homeobox (Crx), interphotoreceptor binding protein (IRBP), and phosphodiesterase-beta (PDEB) were first expressed at Fwk 13.5. We have examined a wide range of factors believed important in photoreceptor development by correlating mRNA and protein expression using PCR, in situ hybridization (ish) and immunocytochemistry (imcyt). Methods: mRNA extracted from human fetal eyes between Fwk 12.5-18.5 underwent reverse transcription and PCR was performed with primers specific to actin, PDEB, Crx, short (S) and long/medium (L/M) wavelength cone opsin, rod opsin (R), Nrl, and photoreceptor nuclear antigen (PNR). Paired retinas were stained for ish and imcyt using standard methods. Results:From Fwk12.5 onward, there was detectable expression of PDEB, Crx and PNR. IRBP was detected between Fwk12.5 and Fwk14.5. Between Fwk 14.5 and 16.5, S, L/M and R opsin expression was detected. Nrl was not detected until Fwk 18.5. This expression profile correlated well with imcyt or insitu labeling for IRBP, L/M, and R, but S cones were detected at Fwk13 near the fovea by both methods. Imcyt labeling for Nrl also found nuclear staining in rods near the fovea by Fwk 16. Conclusion:The data indicate that some genes associated with the differentiation of photoreceptors like Crx and PNR are expressed before opsins. The late PCR detection of S opsin and Nrl compared to morphological methods suggests caution in constructing temporal developmental schemes based on a single methodology. By comparing expression patterns using multiple methods, we will gain a better insight into developmental mechanisms underlying the establishment of human photoreceptor phenotypes.
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