Garbayo J M, Green J A, Manikkam M, Beckers J F, Kiesling D O, Ealy A D, Roberts R M
Department of Animal Sciences, University of Missouri, Columbia, Missouri 65211, USA.
Mol Reprod Dev. 2000 Dec;57(4):311-22. doi: 10.1002/1098-2795(200012)57:4<311::AID-MRD2>3.0.CO;2-F.
Pregnancy-associated glycoproteins (PAG) are structurally related to aspartic proteinases and belong to an extensive, rapidly evolving family of recently duplicated genes expressed in the placentas of artiodactyl species. The aim of the present study was to clone PAG from the goat, study their temporal and cell-specific expression, and determine their phylogenetic relationship to PAG from other species. RT-PCR was used to generate PAG cDNA from pooled placental RNA obtained between days 45 and 115 of pregnancy. A total of 11 cDNA, which differed by > 5% from each other, were selected for complete bidirectional sequencing from 60 clones analyzed. A group of nine (caPAG1, caPAG3-7(var), caPAG9-11), which displayed > 80% sequence identity with each other, were expressed after day 45 of pregnancy and were localized to trophoblast binucleate cells. These PAG demonstrated an unusually high ratio of nonsynonymous (amino acid changing) to synonymous nucleotide differences. CaPAG2, by contrast, was detectable only in early pregnancy (days 18 and 19) and expressed throughout trophectoderm. It was of more ancient origin than the PAG1 group, but more recent than caPAG8. The latter was expressed at all stages examined (days 18 to 115). The data confirm that many PAG genes, with different patterns of temporal and spatial expression, are transcribed in the placenta of the goat. The data also suggest that the recently duplicated PAG genes are being selected for rapid diversification of function.
妊娠相关糖蛋白（PAG）在结构上与天冬氨酸蛋白酶相关，属于一个庞大且快速进化的基因家族，该家族由偶蹄目动物胎盘表达的近期重复基因组成。本研究的目的是从山羊中克隆PAG，研究它们的时空和细胞特异性表达，并确定它们与其他物种PAG的系统发育关系。采用逆转录聚合酶链反应（RT-PCR）从妊娠45至115天收集的胎盘RNA中生成PAG cDNA。从分析的60个克隆中选择了11个彼此差异大于5%的cDNA进行完整的双向测序。一组9个（caPAG1、caPAG3 - 7(var)、caPAG9 - 11）彼此间显示出大于80%的序列同一性，在妊娠45天后表达，并定位于滋养层双核细胞。这些PAG显示出非同义（氨基酸变化）与同义核苷酸差异的异常高比例。相比之下，CaPAG2仅在妊娠早期（第18和19天）可检测到，并在整个滋养外胚层表达。它的起源比PAG1组更古老，但比caPAG8更近。后者在所有检测阶段（第18至115天）均有表达。数据证实，许多具有不同时空表达模式的PAG基因在山羊胎盘中被转录。数据还表明，近期重复的PAG基因正被选择用于功能的快速多样化。
