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R.M. Lavker, D.G. Ryan; MicroRNAs of the Mammalian Eye Display Distinct and Overlapping Tissue Specificity . Invest. Ophthalmol. Vis. Sci. 2006;47(13):5410.
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© ARVO (1962-2015); The Authors (2016-present)
A new class of endogenous, noncoding RNAs has recently been identified and designated as microRNAs (miRNAs). MicroRNAs can regulate gene expression at many levels, giving rise to the idea that RNA is capable of performing similar regulatory roles as proteins. In mammals, miRNAs inhibit the translation of a target messenger RNA, thereby silencing protein production. A great deal of attention has been directed towards understanding the role of miRNAs in embryonic development, differentiation and stem cell regulation. Surprisingly, little attention has been directed towards characterizing the expression of miRNAs in mammalian ocular tissues.
Total RNA from mouse whole eyes, footpad, tongue, liver, brain, kidney, heart and spleen were analyzed by Northern blots using oligonucleotides complementary to mature miRNAs. The following miRNAs were examined: mir–129, –181, –182, –183, –184, –204 and –205. The distribution of these miRNAs in tissues of the eye was determined through in situ hybridization using locked nucleic acid–modified oligonucleotides, labeled with digoxygenin, as probes.
In addition to the eye, most of the miRNAs were expressed in other tissues. Many were particularly enriched in the brain. Within the eye, the miRNA expression patterns exhibited regional specificity. In the anterior segmental epithelia, expression was noted for mir–129, 181, 182, 184, and 205. The expression pattern of mir–184 was particularly striking since it was solely restricted to the corneal epithelium, and absent from all other tissues examined. Other corneal miRNAs exhibited broader expression patterns that varied not only by zone (e.g., conjunctival, limbal) but by cell type (e.g., basal vs. wing cells). Within the ciliary epithelium, a strong expression pattern was noted for mir–204. Retinal tissues expressed mir–181, 182, 183, 204 and 205. As was seen in the anterior segment, expression patterns of these miRNAs were both distinct (e.g., outer segment– mir–183 vs. ganglion cell layer – mir–181) and overlapping – mir–182. In a manner reminiscent of the corneal epithelial specificity of mir–184, mir–183 was restricted to the outer nuclear layer of the retina as well as the brain.
The tissue and cell specificity for ocular miRNAs suggests that these RNAs may be regulating various aspects of development and differentiation. That mir–183 and 184 were restricted to the retina and corneal epithelium, respectively, suggests that these two miRNAs might provide cell type specific function such as controlling metabolism and/or development.
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