Molecular cloning and characterization of chick sialoprotein associated with cones and rods, a developmentally regulated glycoprotein of interphotoreceptor matrix

PG-M/versican。该抗体特异性地染色感光层，我们最近报道了PG-M/多功能蛋白聚糖的缺乏。在这项研究中，我们重新表征了抗体，并确定了在感光层与MY-174反应的分子。免疫组织化学将抗原定位于光感受器周围的基质。各种糖苷酶双链反应表明，抗原是150 kDa的糖蛋白，具有唾液酸化的N-和O-连接的糖缀合物，分子量超过30 kDa。从纯化的MY-174抗原中获得的肽段序列表明，我们已经测序了全长cDNA，其开放阅读框为2787个碱基对，编码928个氨基酸的多肽，与人和小鼠的视锥和视杆相关唾液蛋白（SPACR）分别具有56%和54%的同源性，并具有SPACR的结构特征。此处的特异性唾液酸化O-糖缀合物涉及MY-174的表位结构。SPACR在胚胎15-16天开始出现，随着发育年龄的增长，SPACR的表达逐渐增加，与神经视网膜与视网膜色素上皮细胞之间的粘附平行。因此，我们得出结论，MY-174抗原在感光层，发育调节糖蛋白，是相同的小鸡SPACR，并可能参与一个新的系统介导的神经视网膜和视网膜色素上皮细胞之间的粘附。

PG-M/versican. The antibody specifically stains the photoreceptor layer, where we recently reported an absence of PG-M/versican. In this study, we re-characterized the antibody and identified the molecule that reacts to MY-174 at the photoreceptor layer. Immnohistochemistry localized the antigen to the matrix surrounding photoreceptors. A variety of glycosidase digestions showed that the antigen is the 150-kDa glycoprotein that has sialylated N- and O-linked glycoconjugates having a molecular mass of more than 30-kDa. The peptide sequences obtained from purified MY-174 antigen showed we had sequenced a full-length cDNA with an open reading frame of 2787 base pairs, encoding a polypeptide of 928 amino acids, with 56 and 54% identities to human and mouse sialoprotein associated with cones and rods (SPACRs), respectively, and with the structural features observed in SPACRs. The specific sialylated O-glycoconjugates here are involved in the epitope structure for MY-174. SPACR first appeared by embryonic days 15-16, and expression increased with developmental age, paralleling the adhesion between neural retina and retinal pigment epithelium. Thus, we concluded that the MY-174 antigen at the photoreceptor layer, a developmentally regulated glycoprotein, is identical to chick SPACR and may be involved in a novel system mediating adhesion between neural retina and retinal pigment epithelium.