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MicroRNA–184 Is a Highly Enriched Corneal Epithelial–Specific MicroRNA: Implications for Corneal Epithelial Homeostasis

Dermatology, Northwestern, Chicago, IL

Commercial Relationships: D.G. Ryan, None; R.M. Lavker, None.

Support: NIH Grant EY06769

Abstract

Purpose: MicroRNAs (miRNA’s) are a family of endogenous, small (21–27 nt) RNAs, that regulate the expression of complementary messenger RNAs by acting as repressors of translation. Recent studies have identified roles for miRNAs in stem cell regulation, developmental timing, differentiation, and the initiation and progression of cancer. To date there is no information on the miRNA profiles in self–renewing epithelia such as the limbal/corneal epithelium.

Methods: We isolated corneal epithelium from adult mice eyes (n=100) and footpad epithelium (n=6). Total RNA was extracted from both epithelia, and low molecular weight (LMW) RNA was purified using miRNA purification columns. LMW RNAs from adult corneal and footpad epithelia were analyzed using microarrays (Bionomics Research and Technology Center, Rutgers University) that contain all known mammalian miRNA genes. Corneal epithelial miRNA microarrays were validated using Northern blots for short RNAs. Using locked nucleic acid–modified oligonucleotide probes and in situ hybridization we elucidated the distribution of miRNAs in the corneal epithelium.

Results: After subtracting out background hybridization and restricting analysis to those miRNAs showing a >4 fold enrichment, a total of 7 miRNAs were found to be corneal epithelial– enriched. One miRNA (mir–184) was 89–fold higher in corneal epithelium than footpad. Northern blots showed a very intense signal for mir–184 in the corneal epithelium and no detectable signal in the footpad sample, confirming the microarray data. The expression pattern for mir–184 was consistent with the microarray and Northern data, as a strong signal for mir–184 was detected in the basal and immediately suprabasal cells in the corneal epithelium; little signal was detected in the superficial cells. In contrast, mir–184 expression was absent in the limbal and conjunctival epithelia, mucocutaneous junctional epithelium, meibomian gland and the eyelid epidermis. Little if any change in mir–184 expression was noted in the peripheral corneal epithelium during re–epithelization following a central corneal epithelial wound.

Conclusions: Mir–184 is mainly restricted to the corneal epithelium and is expressed in abundant amounts. This expression pattern reflects the unique lateral heterogeneity of the corneal/limbal epithelial basal layer. Expression of mir–184 appears to be independent of the proliferative status of the corneal epithelium. Potential target mRNAs that could be regulated by mir–184, suggest that this miRNA might function in the maintenance of glycogen synthesis necessary for the homeostasis of corneal epithelium.

Keywords: cornea: basic science • gene/expression • differentiation

© 2006, The Association for Research in Vision and Ophthalmology, Inc., all rights reserved. For permission to reproduce any part of this abstract, contact the ARVO Office at arvo{at}arvo.org.