Abstract
Abstract: :
Purpose: Mucin glycoproteins are important constituents of the precorneal tear film, providing lubrication, stabilization and protection against foreign objects and pathogens. Previous studies have shown that human ocular epithelia express both membrane-associated (MUC1, MUC4) and secreted (MUC2, MUC5AC, MUC7) mucins. Recently, the family of membrane-associated mucins has expanded to include MUC1, MUC3, MUC4, MUC12, MUC13, MUC15, MUC16 and MUC 17. The present study was undertaken to evaluate the expression of these newly identified transmembrane mucins in human cornea and conjunctiva. Methods: Total RNA was isolated from human donor corneal and conjunctival tissues obtained from the Kentucky Lions Eye Bank. Specific mucin gene expression was evaluated by semi-quantitative RT-PCR using primers based on cDNA sequences in the Genbank database and normalized to ß2 microglobulin transcripts. As positive controls, cDNA from non-ocular tissues expressing each mucin type was analyzed in parallel. PCR products were sequenced to confirm their identities. Results: Both human cornea and conjunctiva expressed transcripts for MUC1, MUC4, MUC13, MUC15 and MUC16, whereas MUC3, MUC12 and MUC17 were not detected in either tissue. The relative levels of mucin mRNA expression were similar in both tissues with exception of MUC13 transcripts which were more abundant in conjunctiva than in cornea. Conclusion: The results provide evidence for the expression of three newly identified transmembrane mucins - MUC13, MUC15 and MUC16 - in human cornea and conjunctiva. Although the patterns of mucin gene expression are qualitatively similar in the two tissues, the relatively high level of MUC13 transcripts in conjunctiva may reflect the presence lymphoid cells which were recently reported to express this mucin. The precise cellular locations, distribution and functions of MUC13, MUC15 and MUC16 mucins in relation to previously characterized ocular mucins remain to be explored.
Keywords: cornea: surface mucins • gene/expression