关于体细胞的全能性问题

体细胞的全能性问题是生物学的重要问题之一。自Ｗｅｉｓｍａｎｎ在１９世纪中期提出这个问题后,已在学术界争论了一百多年。最近由于基因工程方面的突破,对这一问题的研究也获得很大进展。现在看来,全能性与全能性表达不是一回事。细胞具全能性基础以后,还需某种因子的启动才能开始全能性的表达。     

动物细胞全能性的研究

在植物细胞全能性研究的基础上引出动物细胞全能性这一热点研究课题.介绍了动物细胞全能性的表现,分析了细胞全能性表现程度差异的原因,最后对动物细胞全能性的广泛应用及存在的问题进行探讨,并对细胞命运及其调控进行了展望.     

Nanog基因的功能与调控

胚胎干细胞的无限增殖能力和亚全能性决定了它在再生医学、新药开发及发育生物学基础研究中具有巨大的应用前景。探索维持胚胎干细胞亚全能性的因子及其网络的调控功能成为胚胎干细胞生物学研究的热点。已研究发现多个与维持胚胎干细胞亚全能性相关的基因如Oct4,Nanog,Sox2等,其中Nanog是2003年5月末发现的一个基因,它对维持胚胎干细胞亚全能性起关键性作用,能够独立于LIF／Stat3维持ICM和胚胎干细胞的亚全能性。几年来,Nanog的生物学功能及其与Oct4,Sox2等亚全能性维持基因之间的相互作用关系已有较为深入的研究,并发现多个调控Nanog表达的转录因子,从而进一步明晰Nanog与已知调控胚胎发育的信号通路之间的关系。在综述Nanog基因的表达特征和功能的基础上、重点探讨Nanog基因表达调控以及Oct4,Sox2等亚全能性维持基因之间的相互作用关系,并对未来的研究趋势予以展望。     

干细胞命运决定的分子调控网络

来源于囊胚期胚胎内细胞团的胚胎干细胞具有独特的生物学特性,包括无限自我更新的能力以及分化为内胚层、中胚层和外胚层各种细胞的潜能.阐明胚胎干细胞全能性维持以及向各种特定细胞分化的分子机制,不仅有助于我们了解胚胎发育过程,而且将促进胚胎干细胞尽早应用于疾病治疗.本文主要就干细胞的一种命运决定过程,维持胚胎干细胞全能性或失去全能性开始分化,结合最新的研究进展讨论该过程中的分子调控网络,包括信号转导通路、表达调控网络以及表观遗传调控.     

植物细胞的全能性

简述了植物细胞全能性理论的创立和实验论证,介绍了近年来植物细胞全能性在细胞学和分子生物学方面的研究,对植物组织培养有一定的参考作用。     

培养的胡萝卜细胞的体细胞胚胎发生

培养的植物细胞的体细胞胚胎发生,是研究从单个细胞到完整植株的分化和发育全过程的理想系统,对全能性表达的分子机制更是如此。本综述报告有关体细胞胚胎发生研究的最新进展。     

“细胞分化”一节基于资料和探究的教学思路

通过层层递进的问题引导和资料分析,帮助学生理解“细胞分化”和“细胞全能性”这2个核心概念的要素,并在此基础上引导学生构建概念图,宏观掌握概念的内涵和外延。     

关于胚乳的几个问题

胚乳是植物种子的重要组成部分,在种子的萌发过程中有重要作用。简要介绍了胚乳的来源、遗传、发育、全能性几个方面的知识。     

维持胚胎干细胞生物学特性的分子调控机制

胚胎干(embryonic stem,ES)细胞来源于植入前的胚胎.在体外培养条件下,可保持分化成机体各种类型细胞的能力,即全能性.因此,胚胎干细胞被广泛用作研究胚胎发生、发育的细胞模型,也是目前开展细胞移植性治疗研究的重要来源.揭示维持ES细胞自我更新和全能性的分子调控机制,是ES细胞基础研究和临床治疗基础研究的重要领域.目前研究发现,不同的信号通路、转录因子及其通过激活ES细胞特异性表达谱对维持ES细胞多能性、自我更新发挥关键作用。     

“细胞分化”教学设计

“细胞分化”的教学既要解决细胞分化的定义、意义、原因．使学生能从现象深入到本质理解细胞分化,同时,又需要进一步阐明细胞分化的影响因素,揭示细胞分化与细胞全能性的关系。本节课用大量感性材料形成概念,以实验探究形式突破细胞分化原因和细胞全能性教学。     

The initiation of senescence and its relationship to embryonic cell differentiation

Mouse embryonic stem cells have an unlimited lifespan in cultures if they are prevented from differentiating. After differentiating, they produce cells which divide only a limited number of times. These changes seen in cultures parallel events that occur in the developing embryo, where immortal embryonic cells differentiate and produce mortal somatic ones. The data strongly suggest that differentiation initiates senescence, but this view entails additional assumptions in order to explain how the highly differentiated sexual gametes manage to remain potentially immortal. Cells differentiate by blocking expression from large parts of their genome and it is suggested that losses or gains of genetic totipotency determine cellular lifespans. Cells destined to be somatic do not regain totipotency and senesce, while germ-line cells regain complete genome expression and immortality after meiosis and gamete fusions. Losses of genetic totipotency could induce senescence by lowering the levels of repair and maintenance enzymes.     

Mechanisms of somatic embryogenesis in cell cultures: Physiology,biochemistry, and molecular biology

Summary One of the most characteristic cell functions in plants is totipotency. Somatic embryogenesis can be regarded as a model system for the investigation of mechanisms of totipotency, because a high frequency and synchronous embryogenic system from single somatic cells has been established in carrot suspension cultures. Four phases are recognized in this process, and several molecular markers, viz. polypeptides, mRNAs, antigens against monoclonal antibodies, can be detected during the expression of totipotency, but they disappear during its loss. Four organ-specific genes have been isolated from hypocotyls and roots by differential screening. They were expressed preferentially after the globular-heart stages of embryogenesis, and were strongly suppressed by auxin. A CEM 1 gene was isolated by differential screening of embryogenic cell clusters. This gene was expressed strongly and transiently during the proglobular and globular stages. The sequence of CEM 1 was found to encode a polypeptide showing high homology to the elongation factor isolated from eucaryotic cells. Thus good progress is being made in understanding the basic mechanisms of somatic embryogenesis. Presented in the Session-in-Depth Developmental Biology of Embryogenesis at the 1991 World Congress on Cell and Tissue Culture, Anaheim, California, June 16–20, 1991.     

Somatic Embryogenesis in Cultured Carrot Cells

Somatic embryogenesis in cultured plant cells is an ideal system for investigating the whole process of differentiation and development from single cells to whole plants, and especially the molecular mechanism of expression of totipotency. This review reports recent progress the studies on somatic embryogenesis.     

Epigenetic reprogramming in early mammalian development and following somatic nuclear transfer

Epigenetic modifications of the genome play a significant role in the elaboration of the genetic code as established at fertilisation. These modifications affect early growth and development through their influence on gene expression especially on imprinted genes. Genome-wide epigenetic reprogramming in germ cells is essential in order to reset the parent-of-origin specific marking of imprinted genes, but may have a more general role in the restoration of totipotency in the early embryo. In a similar way, on somatic nuclear cloning, a differentiated cell must become 'reprogrammed' restoring totipotency in order to undergo development. Here we discuss the dynamic epigenetic reprogramming that takes place during normal development and highlight those areas with relevance to somatic nuclear cloning and the possibility of improving the efficiency of this process. We propose the concept of 'epigenetic checkpoints' for normal progression of development and the loss of totipotency.     

Acquisition of embryogenic competency does not require cell division in carrot somatic cell

Totipotency is the ability of a cell to regenerate the entire organism, even after previous differentiation as a specific cell. When totipotency is coupled with active cell division, it was presumed that cell division is essential for this expression. Here, using the stress-induction system of somatic embryos in carrots, we show that cell division is not essential for the expression of totipotency in somatic/embryonic conversion. Morphological and histochemical analyses showed that the cell did not divide during embryo induction. Inhibitors of cell division did not affect the rate of somatic embryo formation. Our results indicate that the newly acquired trait of differentiation appears without cell division, but does not arise with cell division as a newborn cell.     

Toti "potent" repressors

A fascinating property of germ cells is their ability to maintain totipotency throughout development. At fertilization, this totipotency is unleashed and the egg generates all the cell types needed to make a brand new organism. Occasionally, germ cells differentiate precociously in the embryo or in the gonads and form teratomas, tumors containing many differentiated somatic cell types. Until recently, the genetic basis for teratoma formation was not known. The unexpected discovery of a teratoma in a C. elegans double mutant points to translational control as a key mechanism to maintain totipotency in developing germ cells.     

Genomic multipotentiality of differentiated somatic cells

Nuclear transplantations from several differentiated somatic cell types into amphibian oocytes and eggs revealed that their genome contains the genes required for the development of prefeeding tadpoles. In addition, erythrocyte nuclei directed the formation of feeding tadpoles (independent organisms) that advanced to larval stages with hind limb buds. Thus, the genome of several differentiated somatic cell types can undergo widespread activation and specify a multiplicity of cell types. Although evidence for the genetic totipotency of differentiated somatic cells is lacking, we speculate that the genetic totipotency of at least some differentiated somatic cell types still remains a tenable hypothesis.