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Xiuli Mao, Gary W. Conrad; Polysialylation in Cornea During Chick Embryonic Development. Invest. Ophthalmol. Vis. Sci. 2011;52(14):1095.
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© ARVO (1962-2015); The Authors (2016-present)
Polysialic acid (PSA) and neural cell adhesion molecule (NCAM) play important roles in nerve growth and development, fertilization, and as biomarkers of such diseases as small cell lung cancer. The purpose of this study was to assay for NCAM and PSA in the cornea, determining their expression levels during embryonic development, and localizing them in cornea and eye.
RT-QPCR was used on 1ug total mRNA samples extracted from the corneas of embryos, hatched and adult chicks to determine the expression levels of NCAM, and two relevant polysialytransferases. Western blotting was conducted to detect changes in the levels of NCAM and polysiaylation. NCAM and PSA also were localized using immunofluorescence on frozen sections of embryonic and adult corneas.
RT-QPCR analysis revealed that mRNAs for NCAM, ST8SiaII and ST8SiaIV were in chick cornea. NCAM and ST8SiaII mRNAs expression increased slightly by E9 and decreased thereafter. Both showed dramatic declines in adult corneas. ST8SiaIV mRNA expression kept decreasing by E19, but then rose back to the E12 level in adult cornea. This suggests that ST8SiaIV may be involved in attaching PSA on other proteins than NCAM. Western blotting analysis revealed very strong staining from E9 to E20, but then beginning at E20 and continued after hatching, NCAM protein staining became much fainter, whereas PSA staining in the same MW region and higher became more intense. Several new polysiaylated proteins appeared at E18 and their expressions increased as the embryos developed and after hatching. These results suggest that there are other polysialylated proteins, whose expression starts at hatching. Immunofluorescence analysis revealed that both NCAM and PSA were found in epithelium, stroma and endothelium of embryonic and adult chick cornea. Significantly, NCAM also was found in extracellular matrix (ECM) of embryonic cornea stroma.
Both NCAM and PSA are expressed in embryonic and adult chick corneas. Their expression levels undergo significant changes during the transition from embryo to adulthood. There are other polysialylated proteins in cornea than NCAM and at least NCAM is localized in the stromal ECM.
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