Analysis for gene function of the XPG gene using Xpg-kockout mice.

利用基因靶向技术和胚胎干细胞技术，制备了携带无功能着色性干皮病G组基因（人类XPG基因的小鼠对偶体）的实验小鼠。这种常染色体隐性遗传病的纯合子动物表现出的体征和症状，如出生后生长迟缓、活动水平降低、进行性共济失调和过早死亡，与科凯恩综合征（CS）的临床表现相似。组织学分析显示，xpg纯合子的小脑浦肯野细胞层有多个缩缩细胞，胞体萎缩，细胞核萎缩。进一步免疫组化检测calbinin - d 28k （CaBP）显示，大量免疫反应性浦肯野细胞萎缩，其树突树比野生型仔鼠更小、更短。这些结果表明xpg突变体小脑浦肯野细胞明显变性。小脑皮层DNA片段原位检测研究表明，突变小鼠颗粒层中出现了一些脱氧核苷酸转移酶（TdT）介导的dutp -生物素原位缺口标记（TUNEL）阳性细胞，但浦肯野层中很少有细胞死亡。这些结果提示突变体小脑的浦肯野细胞变性正在进行，其中许多浦肯野细胞未出现死亡，xpg缺陷小鼠出现的一些异常小脑症状不仅是由于浦肯野细胞明显变性，还与其他细胞的损伤有关。

Laboratory mice carrying the nonfunctional xeroderma pigmentosum group G gene (the mouse counterpart of the human XPG gene) alleles have been generated by using gene-targeting and embryonic stem cell technology. Homozygote animals of this autosomal recessive disease exhibited signs and symptoms, such as postnatal growth retardation, reduced levels of activity, progressive ataxia and premature death, similar to the clinical manifestations of Cockayne syndrome(CS). Histological analysis of the cerebellum revealed multiple pyknotic cells in the Purkinje cell layer of the xpg homozygotes, which had atrophic cell bodies and shrunken nuclei. Further examination by an immunohistochemistry for calbindin-D 28k (CaBP) showed that a large number of immunoreactive Purkinje cells were atrophic and their dendritic trees were smaller and shorter than in wild-type littermates. These results indicated a marked degeneration of Purkinje cells in the xpg mutant cerebellum. Study by in situ detection of DNA fragmentation in the cerebellar cortex demonstrated that some deoxynucleotidyl transferase (TdT)-mediated dUTP-biotin in situ nick labeling (TUNEL)-positive cells appeared in the granule layer of the mutant mice, but few cell deaths were confirmed in the Purkinje layer. These results suggested Purkinje cell degeneration in the mutant cerebellum was underway, in which much Purkinje cell death had not appeared, and the appearance of some abnormal cerebellar symptoms in the xpg-deficient mice was not only due to a marked Purkinje cell degeneration, but also to damage of other cells.