Molecular Cell Glycobiology of the Retinal Degeneration

(1)在各种类型的视网膜变性的过程中，使用原位杂交组织化学通常观察到参与N-连接糖缀合物的末端唾液酸化的α 2，6-唾液酸转移酶的mRNA表达的进行性降低。α 2，3-唾液酸转移酶的mRNA表达，涉及0-连接糖缀合物的末端唾液酸化，仅在出生后第16天和第18天检测到。在正常成熟的光感受器中检测到的0-连接的唾液酸糖缀合物可能在大鼠光感受器内节中从P16至P18活跃地合成，这表明光感受器层中的0-连接的唾液酸糖缀合物是稳定的，在成熟的视网膜中几乎没有翻转。这些结果表明，异常的N-连接糖缀合物可能会引起视网膜变性，而0-连接的遗传缺陷可能会导致先天性视网膜发育不良。(2)比较外周蛋白/rds mRNA的原位杂交组织化学和内节游离核糖体的电镜观察，聚集和聚集的核糖体分别对应于活性和非活性类型。(3)以大鼠α 2，6-唾液酸转移酶cDNA的BamH_1-Bg_1 Ⅱ酶切片段为探针，从小鼠α 2，6-唾液酸转移酶基因组DNA中分离到两个克隆。克隆的序列被确定用于通过基因打靶制备视网膜变性的动物模型。(4)应用PCR-异源双链法对视网膜色素变性患者外周血中编码人α 2，6-唾液酸转移酶基因组DNA第6外显子进行了序列分析。目前尚未发现任何点突变。

(1) A progressive decrease in the mRNA-expression of alpha2,6-sialyltransferase, involving in the terminal sialylation of N-linked glycoconjugates was commonly observed in the process of various types of retinal degeneration using in situ hybridization histochemistry. The mRNA-expression of alpha2,3-sialyltransferase, involving in the terminal sialylation of 0-linked glycoconjugates, was exclusively detected at post-natal day (p) 16 and p18. It is likely that 0-linked sialoglycoconjugates, which are detected in the normal mature photoreceptors, are actively synthesized from P16 to P18 in the rat photoreceptor inner segments, suggesting that the 0-linked sialoglycoconjugates in the photoreceptor layr are stable with little turn over in the mature retina. These suggest that abnormal N-linked glycoconjugates may induce retinal degeneration, whereas genetic defects of 0-linked ones may cause congenital retinal dysplasia.(2) Comparing the in situ hybridization histochemistry of the peripherin/rds mRNA and electron microscopic examination of free ribosomes in the inner segments, the disparsed and clustered ribosomes correspond to active and inactive types, respectively.(3) Two genomic DNA clones of mouse alpha2,6-sialyltransferase were isolated by using a Bam H1-Bg1 II-digested fragment of the cDNA of rat alpha2,6-sialyltransferase as a probe. The sequences of the clones were determined for preparing an animal model of retinal degeneration by gene targeting.(4) The sequence of the exon 6 of genomic DNA coding human alpha2,6-sialyltransferase in the peripheral blood of the patients of retinitis pigmentosa was analyzed using PCR-heteroduplex method. Any point mutation is not yet detected up to the present.