C57BL/6 Mice Lacking Muc1 Show No Ocular Surface Phenotype

PURPOSE. To test the hypothesis that a membrane-spanning mucin, Muc1, facilitates the spread of tear film and protects against bacterial adherence. METHODS. Age-matched, Mucl null mice and wild-type mice of C57BL/6 genetic background were used for comparison. Eyes were examined by slit lamp biomicroscopy with fluorescein solution to assess epithelial damage and tear film stability. Structure of the ocular surface epithelia was examined by light microscopy, scanning and transmission electron microscopy, and wholemount confocal microscopy. Bacterial adherence assay was performed on in vivo corneas with Pseudomonas aeruginosa containing a plasmid encoding green fluorescent protein, followed by wholemount confocal microscopy. Real-time reverse transcription-polymerase chain reaction was performed using Muc4-specific primers to quantitate Muc4 mRNA expression in ocular surface tissues. RESULTS. No differences were found between Mucl null and control mice in any parameter tested. Ocular surface epithelia of Mucl null mice of the C57BL/6 strain had a normal appearance of surface microplicae, a well-developed glycocalyx on the apical cell membrane, and a normal appearance of goblet cell mucin packets. There was no convincing evidence that bacterial adherence on the cornea was increased in Muc1 null mice. Muc4 mRNA expression was not upregulated in Mucl null mice compared with control. No ocular surface infections were observed in Mucl null mice of the C57BL/6 strain (n = 204), which were housed in the animal facility over a period of 26 months. CONCLUSIONS. Mucl null mice of C57BL/6 background appeared normal in all respects tested. These data differ from the reported phenotype in the mice of the C57BL/6 x SVJ129 background, which show development of blepharitis and conjunctivitis.