Spatial and temporal expression of short, long/medium, or both opsins in human fetal cones.
Human cone photoreceptors are characterized by long (L), medium (M), or short (S) wavelength-specific opsin. No reports have described the developmental pattern of human cone opsin expression, nor has the existence of human cones containing more than one opsin been tested. Single-and double-label immunocytochemistry and in situ hybridization have been used to determine the developmental pattern of opsin appearance and to investigate the presence of double-labeled cones in sections and wholemounts of human fetal, neonatal, infant, and adult retina. S opsin protein appears in and around the fovea at fetal week (Fwk) 10.9, whereas L/M opsin first appears in the fovea at Fwk 14-15. S opsin mRNA and protein are consistently detected much farther into peripheral retina than L/M opsin, indicating that S appears before L/M opsin. S cones cover 90% of the retina by Fwk 19. L/M cones appear outside the central retina by Fwk 21.5 and reach the retinal edge by Fwk 34-37. The spatial pattern of mRNA expression closely matches that for protein, but mRNA appears slightly earlier than protein at a given retinal point, indicating that only short delays occur between mRNA expression and translation into protein. Cones containing both S and L/M opsin (S+L/M) appear around the fovea shortly after L/M opsin is expressed, are found in more peripheral retina at older ages, and decrease in number after birth. Some S+L/M cones are still detected in adult retina. Both S opsin protein and mRNA appear significantly earlier than L/M mRNA or protein across the human retina, suggesting that the two cone types differentiate under independent controlling factors. However, the presence of single cones containing both S and L/M opsin during development suggests that human cones can respond to the factors controlling expression of each opsin.
Xiao
M
M
Department of Biological Structure, University of Washington, Seattle, Washington 98195, USA.
Hendrickson
A
A
D000375:Aging / Q000378:metabolism*; D005314:Embryonic and Fetal Development; D005333:Fetus / Q000378:metabolism; D005629:Frozen Sections; D005865:Gestational Age; D006801:Humans; D020033:Protein Isoforms / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism; D017949:Retinal Cone Photoreceptor Cells / Q000196:embryology* / Q000378:metabolism*; D017299:Rod Opsins / Q000235:genetics / Q000378:metabolism*; D013997:Time Factors; D014018:Tissue Distribution
D020033:Protein Isoforms; D012333:RNA, Messenger; D017299:Rod Opsins