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R.E. Hausman, C. Chu, M. Daher, H.P. Pariser; Tissue-Specific Requirement for Cell Surface Disulfide Exchange in Embryonic Retinal Cell Adhesion . Invest. Ophthalmol. Vis. Sci. 2003;44(13):1664.
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Purpose: Disulfide exchange is involved in many cell surface activities, especially for cells in culture. These include, the uptake of bacterial toxins and viruses such as HIV. Additionally, there are three vertebrate tissues where cell surface disulfide exchange is involved in differentiation or physiological function: platelets, B lymphocytes and embryonic retina. We have shown that retina cognin is a protein disulfide isomerase (PDI) and participates in embryonic chick retinal cell adhesion via disulfide isomerase activity. There is a family of PDI-like proteins in all vertebrates, the question is whether similar proteins might mediate cell adhesion in other chick embryo tissues. Methods: Chick embryo tissues from embryonic ages E7-E15 (retina, forebrain, heart and liver) were dispersed into cell suspensions with trypsin and gyratory reaggregated according to standard procedures and allowed to reaggregate in either balanced salt or calcium-magnesium free balanced salt solutions. In experimental flasks, cell surface disulfide exchange activity was blocked with DTNB [5,5'-dithio-bis (2-nitro-benzoic acid)], an inhibitor of disulfide exchange on the cell surface. It binds to the active site of PDI. At selected intervals samples of each of the suspensions were counted for the number of single cells, those not in aggregates, remaining. Results: DTNB caused a significant decrease in reaggregation of retina cells and this effect decreased with increasing embryonic age. It was approximately 45% of the control (without DTNB) level by hours of reaggregation at E7-8, 69% at E9-10, 94% at E11-12 and 99% at E13-15. Forebrain cell suspensions were 96% of the controls at E7-8, 98% at E9-10, 95% at E11-12 and 99% at E13-15. There were no significant effects of DTNB on the reaggregation of heart or liver cells at the ages tested. During the 2 hour reaggregation there were no significant differences between those cells from any tissue suspended in balanced salt solution or calcium-magnesium free balanced salt solution. Conclusions: The finding that DTNB affects the reaggregation of retinal cells in vitro confirms previous results and establishes the dependence on embryonic age. We have previously shown that DTNB binds to retinal cognin and blocks its disulfide exchange activity. The failure of DTNB to affect the reaggregation of the other chick embryo cells suggests that PDI family proteins do not participate widely in embryonic cell adhesion. Thus, their role in cell to cell interactions might be limited to a limited number of developmental or physiological processes.
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