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Stephen C. Pflugfelder, Zuguo Liu, Dagoberto Monroy, De–Quan Li, Maria E. Carvajal, Shari A. Price–Schiavi, Nebila Idris, Abraham Solomon, Amyee Perez, Kermit L. Carraway; Detection of Sialomucin Complex (MUC4) in Human Ocular Surface Epithelium and Tear Fluid. Invest. Ophthalmol. Vis. Sci. 2000;41(6):1316-1326.
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purpose. To evaluate human ocular surface epithelium and tear fluid for the
presence of sialomucin complex (MUC4), a high-molecular-weight
heterodimeric glycoprotein composed of mucin (ASGP-1) and transmembrane
methods. Reverse transcription–polymerase chain reaction (RT–PCR) and Northern
blot analysis assays were used to identify sialomucin complex RNA in
ocular surface epithelia. Immunoprecipitation and immunoblot analysis
were used to identify immunoreactive species in human tears and in the
corneal and conjunctival epithelia using antibodies specific for
carbohydrate and peptide epitopes on the sialomucin complex subunits.
Immunofluorescence staining was used to detect sialomucin complex in
frozen sections and impression cytology specimens of human cornea and
results. ASGP-1– and ASGP-2–specific sequences were amplified from RNA
extracted from both conjunctival and corneal epithelial biopsies by
RT–PCR. Sialomucin complex transcripts were also detected in these
tissues by Northern blot analysis, with a greater level of RNA detected
in the peripheral than the central corneal epithelium. Sialomucin
complex was immunoprecipitated from tear fluid samples and both corneal
and conjunctival epithelia and detected by immunoblot analysis with
specific anti–ASGP-1 and anti–ASGP-2 antibodies. The ASGP-1 peptide
antibody HA-1 stained the full thickness of the corneal and
conjunctival epithelia. In contrast, antibody 15H10, which reacts
against a carbohydrate epitope on ASGP-1, stained only the superficial
epithelial layers of these tissues. No staining was observed in the
conjunctival goblet cells.
conclusions. Sialomucin complex was originally identified in rat mammary
adenocarcinoma cells and has recently been shown to be produced by the
ocular surface epithelia of rats. Furthermore, it has been identified
as the rat homologue of human MUC4 mucin. The present studies show that
it is expressed in the stratified epithelium covering the surface of
the human eye and is present in human tear fluid. Expression of a
carbohydrate-dependent epitope on the mucin subunit (ASGP-1) of
sialomucin complex occurs in a differentiation-dependent fashion.
Sialomucin complex joins MUC1 as another membrane mucin produced by the
human ocular surface epithelia but is also found in the tear fluid,
presumably in a soluble form, as found on the rat ocular
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