中文摘要：

主要组织相容性复合体（Major histocompatibility complex,MHC）是有颌脊椎动物基因组中的一个高度多态性的基因家族,与免疫系统密切相关,MHC基因特征在哺乳类、鸟类、两栖类和鱼类中已被较好地描述.为了解爬行动物MHC基因的序列特征,通过PCR技术从胎生种密点麻蜥（Eremias multiocellata）、荒漠麻蜥（Eremias przewalskii）及卵生种山地麻蜥（Eremias brenchleyi）的肝脏中克隆了MHC I类基因外显子3和4的DNA片段,采用RT-PCR（逆转录-PCR）从这3种麻蜥的妊娠期子宫组织克隆了这两个外显子的cDNA片段.结果表明,3种麻蜥MHC I类基因均发生基因重复,密点麻蜥和山地麻蜥至少有4个基因座位,荒漠麻蜥至少有5个基因座位.在山地麻蜥获得的其中一条DNA片段中编码氨基酸的密码子突变为终止密码子,推测其为MHC I类基因的假基因.在外显子3编码的α2结构域中检测到多个多肽结合位点和β-2微球蛋白结合位点以及一个保守的半胱氨酸位点.在外显子4编码的α3结构域中检测到多个β-2微球蛋白结合位点和CD8分子结合位点以及一个保守的半胱氨酸位点.基于氨基酸的系统发育分析提示3种麻蜥的子宫均表达经典的MHC I类基因,可能有一些MHC基因座位未在子宫中表达.DNA系统发育重建揭示3种麻蜥MHC I类基因谱系没有表现出物种特异性进化,而表现出跨种多态性.上述结果为进一步研究胎生繁殖方式与母体免疫系统的协同进化及有鳞目MHC的演化奠定了基础.

英文摘要：

The major histocompatibility complex（MHC） genes have been well characterized in mammals, birds, amphibians and fishes, but little is known about their organization in reptiles, despite the fact that reptiles occupy an important phylogenetic position for understanding the evolutionary history of vertebrates MHC genes. In this study we used polymerase chain reaction（PCR） and reverse transcription- polymerase chain reaction（RT-PCR） to amplify the genomic exon 3 and exon 4 fragments of MHC class I genes in three racerunner lizards, including viviparous Multiocellated Racerunner（Eremias multiocellata）, viviparous Gobi Racerunner（Eremias przewalskii）, and oviparous Ordos Racerunner（Eremias brenchleyi）. We also presented the molecular characterization of class I sequences for racerunner lacertids. Gene duplication was detected in the three Eremias species, at least four MHC class I loci in Multiocellated Racerunners and Ordos Racerunners, and at least five in Gobi Racerunners. A putative class I pseudogene was inferred in Ordos Racerunner for a premature stop codon in a segment of socalled exon 3. The peptide binding region, β2-microglobulin interaction sites and a conserved cysteine residue were recognized in α2 domain encoded by exon 3. The β2-microglobulin interaction sites, CD8 molecule interaction sites and a conserved cysteine residue were recognized in α3 domain encoded by exon 4. Putative classical class I genes were expressed in the uterus of both oviparous and viviparous racerunners during pregnancy, along with some alleles unexpressed in uterine. In addition, phylogenetic reconstruction suggested the existence of trans-species polymorphism in MHC class I genes in Eremias. These findings provide clues for further investigations of co-evolution of viviparity and maternal immune system, as well as evolution of squamate MHC.