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Gordon W. Laurie, Diane E. Laurie, Robert L. McKown; Immunodetection of a Lacritin-like Protein in Non-Primate Tears Primarily as a C-Terminal Fragment. Invest. Ophthalmol. Vis. Sci. 2012;53(14):4234.
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The human proscretory mitogen lacritin displays cross-species activity. It promotes sustained basal tearing when added topically to rabbit eyes, and non-stimulated tear protein secretion by rat lacrimal acinar cells. The implication is that the co-receptor/receptor targeting mechanism is likely conserved, but whether lacritin is present in non-primate tears is unknown. Here we assay for lacritin in normal horse tears as part of a larger understanding of lacritin function in mammals.
Ensembl genomic alignment of the human ‘LACRT’ gene with horse genome EquCab2.0 served as the source of sequence for analysis. Normal horse tears were collected using an ophthalmic sponge at Virgina Tech’s MARE Center. Tear blots were analyzed using polyclonal antibodies respectively specific for the N- and C-terminus of human lacritin. Parallel analysis was performed by ELISA.
Nucleotide identity of human LACRT’s five exons with the apparently ortholgous region in horse chromosome 6 was 74%. This compares to 68% and 98% identity respectively with cat and chimp LACRT orthologues. Blotting using anti-C terminal antibodies readily detected a 13 kDa band in horse tears that was also apparent by Coomassie blue staining. The same antibody detected uncleaved lacritin (24 kDa) strongly and C-terminal fragments of 13 and 11 kDa weakly in human tears. Anti-N-terminal antibodies were slightly reactive with a 24 kDa horse antigen and showed no reaction with the anti-C-teminal reactive 13 kDa species. ELISA displayed a similar respective difference between horse C-terminal and N-terminal immunoreactivity.
These data suggest that lacritin-like proteins are present in horse tears, most likely as a C-terminal fragment. The human lacritin C-terminus is both mitogenic and bactericidal. Conservation of this activity in horses might contribute to corneal wound repair.
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