In Strongylocentrotus purpuratus the hyalins are a set of three to four rather large glycoproteinsud(hereafter referred to as ???hyalin???), which are the major constituents of the hyaline layer, theuddeveloping sea urchin embryo???s extracellular matrix. Recent research from our laboratories hasudshown that hyalin is a cell adhesion molecule involved in sea urchin embryo specific cellularudinteractions. Other laboratories have shown it to consist of 2-3% carbohydrate, and a cloned,udsequenced fragment demonstrated repeat domains (HYR) and non-repeat regions. Interest in thisudmolecule has increased because HYR has been identified in organisms as diverse as bacteria, flies,udworms, mice and humans, as well as sea urchins. Our laboratories have shown that hyalin appearsudto mediate a specific cellular interaction that has interested investigators for over a century,udarchenteron elongation/attachment to the blastocoel roof. We have done this by localizing hyalin onudthe two components of the cellular interaction and by showing that hyalin and anti-hyalin antibodyudblock the cellular interaction using a quantitative microplate assay. The microplate assay, however,udhas limitations because it does not directly assess hyalin???s effects on the adhesion of the twoudcomponents of the interaction. Here we have used an elegant direct assay that avoids the limitations,udwhere we microdissected the two components of the adhesive interaction and tested their readhesionudto each other, thereby avoiding possible factors in the whole embryos that could confound or confuseudresults. Using both assays, we found that mild periodate treatment (6 h to 24 h in sodium acetateudbuffer with 0.2M sodium periodate at 4 ??C in the dark) of hyalin eliminates its ability to block theudcellular interaction, suggesting that the carbohydrate component(s) may be involved in hyalin???sudspecific adhesive function. This is an important first step in identifying the molecular mechanismsudof a well known cellular interaction in the NIH designated sea urchin embryo model, a system thatudhas led to the discovery of scores of physiological mechanisms, including those involved in humanudhealth and disease.
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