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

通过基因打靶和胚胎干细胞技术，已经产生了携带无功能着色性干皮病G组基因(相当于人类XPG基因的小鼠)等位基因的实验室小鼠。这种常染色体隐性遗传病的纯合子动物具有与Cockayne综合征(CS)相似的临床症状和体征，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。小脑的组织学分析显示，XPG纯合子的浦肯野细胞层有多个固缩细胞，胞体萎缩，核缩小。进一步的Calbindin-D28k(CABP)免疫组织化学检查显示，大量免疫反应阳性的浦肯野细胞萎缩，其树突比野生型仔猪的树突更小更短。这些结果表明，XPG突变型小脑中的浦肯野细胞明显变性。通过对小脑皮质DNA片段化的原位检测发现，突变小鼠的小脑颗粒层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，而浦肯野细胞层中几乎没有细胞死亡。这些结果提示突变的小脑浦肯野细胞正在变性，没有出现大量的浦肯野细胞死亡，XPG基因缺陷小鼠出现一些异常的小脑症状，不仅是由于浦肯野细胞的显著变性，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.