鱼类培养细胞核发育潜能的研究

本文用细胞核连续移植方法,从鲫鱼囊胚细胞的继代培养细胞,获得一尾存活达三年之久的移核鱼,但性腺未分化,不育。并从性成熟的鲫鱼短期培养肾细胞,获得一尾完成发育的性成熟的成鱼。实验结果提示鱼类囊胚细胞的继代培养细胞核和已分化的成鱼体细胞核仍具发育的全能性,为用细胞核移植方法进行鱼类体细胞育种的可能性提供了依据。     

Brood development into sexual females depends on the presence of a queen but not on temperature in an ant dispersing by colony fission,Aphaenogaster senilis

Abstract. 1. In eusocial insects, colony fission is a mode of dispersal by which a young queen leaves her nest with some workers to found a new colony. In these species, adult females (workers and the queen) should allocate most resources to increasing their colony size, which constrains the possibility of fission. In contrast, developing diploid larvae should have a preference for becoming a queen and having their own offspring, rather than becoming workers and rearing the offspring of other females. 2. In the ant Aphaenogaster senilis, queens are produced in very small numbers, suggesting that adult females control larval development. We used a 6‐year series of data on more than 300 nests to determine the annual cycle of worker and queen production. Although both overlapped, the latter mostly occurred in the second half of the summer, after a major peak of worker emergence. Young queens were also often produced in nests whose reproductive queen had died, thus allowing her replacement. Overall, we estimate that only 0.07% of diploid larvae actually develop into gynes. 3. Laboratory experiments indicated that brood is bipotent until the second larval instar. Diploid larval development into queen was favoured by the removal of the mother queen, but was not affected by rearing temperature. 4. Our data suggest that most diploid broods are forced by the adults to develop into workers rather than into gynes. However, when the queen is not present due to death or after a fission event, a few larvae are allowed to develop into gynes. One way for workers to limit the development of larvae might be by controlling the amount of food they receive.     

DNA methylation as a key process in regulation of organogenic totipotency and plant neoplastic progression?

Summary Progressive loss of organogenic totipotency appears to be a common event in long-term plant tissue culture. This loss of totipotency, which has been proposed to be a typical trait of plant neoplastic progression, is compared to some mechanisms that occur during the establishment of animal differentiation-resistant cancer lines in vitro. Evidence is presented that alteration in DNA methylation patterns and expression of genes occur during long-term callus culture. An effect of the auxin, 2,4-dichlorophenoxyacetic acid, in the progressive methylation, is moreover suggested. Methylation of genes relevant to cell differentiation and progressive elimination of cells capable of differentiation is proposed as being responsible for this progressive loss of organogenic potential. Finally, the epigenetic alteration (DNA methylation) that occurs during prolonged periods of culture may induce other irreversible genetic alterations that ultimately make the loss of totipotency irreversible.     

Organelle inheritance in plant cell division: the actin cytoskeleton is required for unbiased inheritance of chloroplasts, mitochondria and endoplasmic reticulum in dividing protoplasts

Nuclear inheritance is highly ordered, ensuring stringent, unbiased partitioning of chromosomes before cell division. In plants, however, little is known about the analogous cellular processes that might ensure unbiased inheritance of non-nuclear organelles, either in meristematic cell divisions or those induced during the acquisition of totipotency. We have investigated organelle redistribution and inheritance mechanisms during cell division in cultured tobacco mesophyll protoplasts. Quantitative analysis of organelle repositioning observed by autofluorescence of chloroplasts or green fluorescent protein (GFP), targeted to mitochondria or endoplasmic reticulum (ER), demonstrated that these organelles redistribute in an ordered manner before division. Treating protoplasts with cytoskeleton-disrupting drugs showed that redistribution depended on actin filaments (AFs), but not on microtubules (MTs), and furthermore, that an intact actin cytoskeleton was required to achieve unbiased organelle inheritance. Labelling the actin cytoskeleton with a novel GFP-fusion protein revealed a highly dynamic actin network, with local reorganisation of this network itself, appearing to contribute substantially to repositioning of chloroplasts and mitochondria. Our observations show that each organelle exploits a different strategy of redistribution to ensure unbiased partitioning. We conclude that inheritance of chloroplasts, mitochondria and ER in totipotent plant cells is an ordered process, requiring complex interactions with the actin cytoskeleton.     

Sepecial symposium: In vitro plant recalcitrance in vitro plant recalcitrance: An introduction

Summary In vitro recalcitrance is the inability of plant cells, tissues and organs to respond to tissue culture manipulations. With respect to plant regeneration, recalcitrance can be a major limiting factor for the biotechnological exploitation of economically important plant species and it can also impair the wider application of in vitro conservation techniques. This first paper introduces a compilation of Symposium papers, collectively entitled “Do we understand in vitro plant recalcitrance?”, presented at the 1999 Congress of the Society for In Vitro Biology. The Symposium reviewed recalcitrance in the context of genetic predeterminism, molecular markers and gene expression patterns, whole and explant physiology, stress physiology, habituation, neoplastic progression and plant cancer. The symposium contributors present fundamental and applied investigative approaches which have the potential to enhance our current understanding of in vitro recalcitrance and to assist in overcoming the problems associated with nonresponsive plant cultures. This introductory paper presents the general concept of recalcitrance in relation to whole-plant and explant physiology and considers basic aspects of tissue culture manipulations in the context of recalcitrance problems.     

Insights into the regenerative property of plant cells and their receptivity to transgenesis: Wheat as a research case study

From a holistic perspective, the discovery of cellular plasticity, a very interesting property of totipotency, underlies many topical issues in biology with important medical applications, while transgenesis is a core research tool in biology. Partially known, some basic mechanisms involved in the regenerative property of cells and in their receptivity to transgenesis are common to plant and animal cells and highlight the principle of the unity of life. Transgenesis provides an important investigative instrument in plant physiology and is regarded as a valuable tool for crop improvement. The economic, social, cultural and scientific importance of cereals has led to a rich stream of research into their genetics, biology and evolution. Sustained efforts to achieve the results obtained in the fields of genetic engineering and applied biotechnology reflect this deep interest. Difficulties encountered in creating genetically modified cereals, especially wheat, highlighted the central notions of tissue culture regeneration and transformation competencies. From the perspective of combining or encountering these competencies in the same cell lineage, this reputedly recalcitrant species provides a stimulating biological system in which to explore the physiological and genetic complexity of both competencies. The former involves two phases, dedifferentiation and redifferentiation. Cells undergo development switches regulated by extrinsic and intrinsic factors. The re-entry into the cell division cycle progressively culminates in the development of organized structures. This is achieved by global chromatin reorganization associated with the reprogramming of the gene expression pattern. The latter is linked with surveillance mechanisms and DNA repair, aimed at maintaining genome integrity before cells move into mitosis, and with those mechanisms aimed at genome expression control and regulation. In order to clarify the biological basis of these two physiological properties and their interconnectedness, we look at both competencies at the core of defense/adaptive mechanisms and survival, between undifferentiated cell proliferation and organization, constituting a transition phase between two different dynamic regimes, a typical feature of critical dynamic systems. Opting for a candidate-gene strategy, several gene families could be proposed as relevant targets for investigating this hypothesis at the molecular level.     

Stem cells in reproductive strategy of asexually reproducing invertebrates

Original and literature data supporting the evolutionary conservation of the morphofunctional organization of totipotent cells of germ and stem lineages in metazoan animals are reviewed. We studied stem cells of the colonial rhizocephalans, Peltogasterella gracilis, Polyascus polygenea and Thylacoplethus isaevae, the turbellarian Dugesia tigrina, the colonial hydroid Obelia longissima, and cultured embryonic stem cells of mouse. The typical germinal granules of germ plasm, selective expression of the activity of alkaline phosphatase and of proliferating cell nuclear antigen (PCNA), which are known as markers of stem and primary germ cells of vertebrates, and the specific expression of the protein product of the vasa gene in cells of rhizocephalans, which is a marker of cells of germ and stem lineages of various metazoans, specified the stem cells of invertebrates of such different taxa. The self-renewing pool of totipotent stem cells is the cellular basis of the reproductive strategy, including sexual and asexual reproduction; such cells share morphofunctional features of embryonic stem and germline cells of Metazoa.