NOVEL SPLICE VARIANTS OF HUMAN TENASCIN-C MRNA IDENTIFIED IN NORMAL AND BULLOUS KERATOPATHY CORNEAS

PURPOSE: Pseudophakic/aphakic bullous keratopathy (PBK/ABK) human corneas accumulate an extracellular matrix glycoprotein tenascin-C (TN-C), an important modulator of cell adhesion and migration. Here, the purpose was to identify specific TN-C mRNA splice variants in normal and PBK/ABK human corneas. METHODS: Conventional and semiquantitative reverse transcription-polymerase chain reaction (RT-PCR) with primers to alternatively spliced (insertional) and constitutive fibronectin type II-like repeats of TN-C was used. Splice variants were identified by cloning and sequencing of RT-PCR products or by Southern blot analysis. RESULTS: The majority of corneal TN-C mRNA species corresponded to relatively small forms of the protein. Four previously unidentified TN-C mRNA splice variants were found in normal and PBK/ABK corneas that contained insertional repeats A1+A2+B+D, A1+A2+D, A1+B+D, or A1+D. Variants with insertional repeats A1+A2 or A1, previously described in mouse and rat, were also identified in human corneas. Semiquantitative RT-PCR showed that novel TN-C mRNA variants were dramatically elevated in PBK/ABK compared to normal corneas. CONCLUSION: TN-C protein was found in PBK/ABK but not in normal corneas; however, both normal and diseased corneas contained mRNA for 15 different TN-C isoforms. PBK/ABK corneas had elevated levels of six relatively small TN-C mRNA variants including five novel ones. These specific isoforms may adversely affect adhesion and migration of corneal cells thus contributing to the exacerbation of PBK/ABK.