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Ilene K Gipson, Sandra Spurr-Michaud, Ann Tisdale, Christina Marko; Conjunctival Goblet Cells Produce MUC16. Invest. Ophthalmol. Vis. Sci. 2014;55(13):2760.
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© ARVO (1962-2015); The Authors (2016-present)
MUC16 is a membrane spanning mucin expressed by apical cells of the corneal and conjunctival epithelium. Its ectodomain, which can be constitutively shed, has been considered the source of MUC16 present in tears. The purpose of this study was to determine if conjunctival goblet cells express MUC16 mucin.
Tissue used for these studies was discarded human conjunctival tissue obtained at the time of either lid resection surgery or following cataract surgery. In situ hybridization using probes to an ectodomain sequence of MUC16, and immunofluorescence microscopy using three different antibodies that recognize the protein core of the ectodomain of MUC16, were used to assay MUC16 message and protein in human goblet cells. Immunoelectron and confocal microscopy were used to localize MUC16 within mucin granules of goblet cells. To determine if there is a correlation between tear levels of MUC16 and the goblet cell mucin MUC5AC, Spearman rank correlation tests were performed, using levels of the non-goblet cell-derived mucin MUC1, a membrane-spanning mucin expressed by apical cells of the cornea and conjunctival epithelium as comparator. Laser capture microdissection was used to obtain goblet cell mRNA from sections of mouse conjunctiva for PCR analysis of MUC16 expression. Primers containing the sequence for both the Muc16 ectodomain as well as the Muc16 cytoplasmic tail were used.
In situ hybridization and immunohistochemistry demonstrate conclusively that human conjunctival goblet cells produce MUC16. Immunoelectron and confocal microscopy demonstrate that the mucin is present within mucin granules of goblet cells. The amount of MUC16 in tears correlates to the amount of MUC5AC in tears (Spearman r value=0.49, p<0.001, N=45), but not to MUC1 levels (Spearman r value = 0.28, p>0.1, N=30). Preliminary PCR data indicate that mouse goblet cells express Muc16, but that only the ectodomain and not the cytoplasmic domain are transcribed.
Conjunctival goblet cells in both human and mouse express and secrete the mucin MUC16. The amount of MUC16 correlates to the amount of goblet cell derived MUC5AC in human tears. Compared to MUC16 mRNA in apical cells of the corneal and conjunctival epithelium, goblet cell MUC16 mRNA appears to lack the sequence that transcribes the cytoplasmic tail.
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