Molecular Cell Glycobiology of the Retinal Degeneration

(1)利用原位杂交组织化学方法，在不同类型的视网膜变性过程中，通常观察到参与n链糖缀合物末端唾液化的alpha2,6-唾液基转移酶mrna表达的进行性降低。α 2,3-唾液基转移酶的mrna表达，涉及0-连接糖缀合物的末端唾液化，仅在出生后第16和18天被检测到。这可能是在正常成熟的光感受器中检测到的0连接的涎糖缀合物在大鼠的光感受器内段从P16到P18被积极地合成，这表明在成熟的视网膜中，光感受器层的0连接的涎糖缀合物是稳定的，很少翻转。这表明异常的n链糖缀合物可能导致视网膜变性，而0链糖缀合物的遗传缺陷可能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段游离核糖体的电镜检查，分离型核糖体和聚集型核糖体分别对应于活性型和非活性型。(3)以Bam H1-Bg1 ii酶切的大鼠alpha2,6-唾液基转移酶cDNA片段为探针，分离出小鼠alpha2,6-唾液基转移酶的两个基因组DNA克隆。确定克隆序列，用于基因靶向制备视网膜变性动物模型。(4)采用pcr -异双工法分析视网膜色素变性患者外周血中编码人α 2,6-唾液基转移酶的基因组DNA外显子6的序列。到目前为止，还没有发现任何点突变。

(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.