哺乳动物体细胞核移植胚胎发育中表观重编程的研究进展

Research Progress of Epigenetic Reprogramming in Mammalian Somatic Cell Nuclear Transfer Embryo Development

体细胞核移植(somatic cell nuclear transfer,SCNT)是一种能将已分化的体细胞重编程为全能胚胎的繁殖生物技术,在良种扩繁、濒危物种保护和治疗性克隆等方面有着广泛的应用前景,但极低的克隆效率、克隆动物胎盘异常、出生后胎儿畸形等严重限制了该技术的实际应用。造成克隆效率低和胚胎发育异常的主要原因是供体核表观遗传重编程错误或不完全。1958年,将非洲爪蟾(Xenopus laevis)幼体肠细胞核移入去核卵母细胞,获得了第1例SCNT动物个体;1986年,通过电融合1个卵裂球与去核卵母细胞成功获得了3只存活的羔羊;1997年,将成年母羊的乳腺上皮细胞与去核卵细胞电融合,获得首个SCNT哺乳动物“多利”,开启了克隆时代,目前牛、小鼠、山羊、猪、欧洲盘羊、家兔、家猫、马、大鼠、骡子、狗、雪貂、狼、水牛、红鹿、单峰骆驼、食蟹猴等相继成功克隆,其中最引人瞩目的是2018年食蟹猴的成功克隆。作者通过将SCNT胚胎与受精胚胎的发育进行对比,阐述了SCNT过程中DNA甲基化、组蛋白修饰、基因组印迹、染色体状态等的重编程过程和缺陷,并从表观修饰剂、组蛋白去甲基化酶、抑制Xist表达、补充鱼精蛋白和精子RNA方面探讨单独或联合消除表观遗传重编程障碍对克隆效率的影响。随着低样本量测序技术的发展和完善,人们能够在SCNT胚胎中检测到更详细的全基因组表观遗传修饰图谱,进一步揭示SCNT胚胎表观遗传重编程中的缺陷,为提高克隆效率提供了线索。通过上述内容的阐述,希望为后续开发联合消除多种表观遗传障碍而提高克隆效率的策略和思路。

Somatic cell nuclear transfer(SCNT)is a reproductive biotechnology that can reprogram differentiated somatic cells into totipotent embryos.It has a wide range of application prospects in the propagation of excellent breeding livestock,protection of endangered species and therapeutic cloning,However,the extremely low cloning efficiency,abnormal placenta of cloned animals and fetal malformation after birth seriously limit the practical application of this technology.The low cloning efficiency and abnormal embryonic development are mainly due to errors or incomplete reprogramming of donor nuclear epigenetics.In 1958,the first SCNT animal individual was obtained by transferring the intestinal nucleus of Xenopus laevis larvae into enucleated oocytes;In 1986,three surviving lambs were successfully obtained by electrofusion of a blastomere and enucleated oocytes;In 1997,the mammary epithelial cells of adult ewes were fused with enucleated egg cells to obtain the first SCNT mammal“Dolly”,which opened the era of cloning.At present,cattle,mice,goats,pigs,European argali,rabbits,domestic cats,horses,rats,mules,dogs,ferrets,wolves,buffalo,red deer,humped camels,cynomolgus monkeys have been successfully cloned one after another.One of the most remarkable is the successful cloning of cynomolgus monkeys in 2018.By comparing the development of SCNT embryos with that of fertilized embryos,the author expounds the reprogramming process and defects of DNA methylation,histone modification,genomic imprinting and chromosome status in the process of SCNT.The effects of eliminating epigenetic reprogramming barriers,alone or in combination,on cloning efficiency are discussed in terms of epigenetic regulators,histone lysine demethylases,inhibition of Xist expression,supplementation of protamine and sperm RNA.With the development and improvement of low-sample-size sequencing technology,more detailed genome-wide epigenetic modification maps can be detected in SCNT embryos,further revealing defects in epigenetic reprogramming of SCNT embryos,and providing opportunities for improving cloning efficiency.Through the elaboration of the above content,hoping to provide strategies and ideas for the subsequent development of joint methods to eliminate multiple epigenetic barriers and improve cloning efficiency.