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《Current biology : CB》2020,30(18):3544-3555.e6
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随着核移植技术和干细胞技术的逐渐成熟,目前已获得牛、小鼠核移植胚胎干细胞,以及人 - 兔异种间核移植胚胎干细胞,这些细胞在体外可分化成多种细胞形态 . 已经进行的实验性动物克隆性治疗,显示了诱人的潜力,但人核移植胚胎干细胞研究还面临着许多问题,如建系效率低、卵母细胞来源有限以及伦理学和安全性问题等 . 长远地看,随着克隆效率的提高,在道德与法律之间达成共识,核移植胚胎干细胞必将造福人类 . 相似文献
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Plant myxodiasporous species have the ability to release a polysaccharidic mucilage upon imbibition of the seed (myxospermy) or the fruit (myxocarpy). This is a widespread capacity in angiosperms providing multiple ecological functions including higher germination efficiency under environmental stresses. It is unclear whether myxodiaspory has one or multiple evolutionary origins and why it was supposedly lost in several species. Here, we summarize recent advances on three main aspects of myxodiaspory. (a) It represents a combination of highly diverse traits at different levels of observation, ranging from the dual tissular origin of mucilage secretory cells to diverse mucilage polysaccharidic composition and ultrastructural organization. (b) An asymmetrical selection pressure is exerted on myxospermy-related genes that were first identified in Arabidopsis thaliana. The A. thaliana and the flax intra-species mucilage variants show that myxospermy is a fast-evolving trait due to high polymorphism in a few genes directly acting on mucilage establishment. In A. thaliana, these actors are downstream of a master regulatory complex and an original phylogenetic overview provided here illustrates that this complex has sequentially evolved after the common ancestor of seed plants and was fully established in the common ancestor of the rosid clade. (c) Newly identified myxodiaspory ecological functions indicate new perspectives such as soil microorganism control and plant establishment support. 相似文献
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Vassili V. Velkov 《Journal of biosciences》1999,24(4):529-559
This review is focused on the physiological and evolutionary strategies of the processes occurring during the entry of microbial
cells into stationary phase and the subsequent period of stasis. The molecular mechanisms adapting microorganisms from exponential
growth to a static state involve activation and complex regulation of the stationary factor Sigma-S, which directs RNA polymerase
to the specific promoters. As a result the static cells acquire general resistance (simultaneous tolerances) to different
environmental stresses. In parallel with the physiological adaptation to stasis, diverse genetical processes are aimed towards
resuming the growth of the static cells. Different types of mutagenesis occur: (i) in cells entering stasis and (ii) in static
cells (adaptive mutagenesis). Cessation of growth induces the transient hypermutator state resulting in the accumulation of
random mutations in the subpopulation of the static cells. If by chance, one or a few of such mutations lead to resumption
of division, the growing cell will return to a normal mechanism of spontaneous mutagenesis.
Another mechanism for generating genetical variability in stressed cells involves transposons and conjugative plasmids. Stresses
can stimulate the excision of some transposons, which, in turn, can generate chromosomal mutations and activate intracellular
mechanisms of mutagenesis. Under stress some conjugative plasmids activate genes encoding antirestriction proteins that repress
restriction-modification systems of the recipient cells. Moreover, under stress special cellular mechanisms decrease (alleviate)
the activity of restriction-modification systems which, in turn, enhance the probability of gene transfer into the stressed
cells.
Under stress, the efficiency of inter-species genetical barriers also decreases. This, stimulates inter-species gene transfer
and may lead to a burst of incipient speciation in the population of non-growing cells. After resumption of growth the genetical
barriers leading to isolation will be restored.
In general, the cessation of growth “switches on”, and resumption of growth “switches off”, a set of special processes that
are responsible for generating bursts of genetical variability in populations of microorganisms.
This article is dedicated to the memory of Nikolai V Timofeev-Ressovsky (1900–1981). 相似文献
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对3种C3木本植物丁香(Syringa meyeri)、杨树(Populus alba)、落叶松(Larix gmelinii)叶片和树枝绿色组织相关指标分析发现:3种植物叶片Chl.a+b含量均显著高于树枝,但是树枝较叶片Chl.a/b比值差异不明显(丁香、落叶松)(p>0.05)或显著高(杨树)(p<0.05)。单位叶绿素内各酶活性显示,丁香树枝PEPC、PEPCK、PPDK、NADP-ME、NADP-MDH酶活性分别是叶片的2.4、4.1、3.2、4.5和1.9倍;杨树树枝分别是叶片的2.1、15、6.3、6.3和2.8;落叶松树枝分别是叶片的6.8、6.3、4.3、4和5.5倍,而单位鲜重内各酶活性显示出的树枝与叶片的差异均小于单位叶绿素的相应结果。种间比较发现,杨树叶片和树枝5种酶活性均显著高于丁香和落叶松。树枝绿色组织内C4酶活性普遍高于相应叶片的事实说明,木质化绿色组织内可能存在C4酶相关的生化过程。丁香与落叶松树枝的电子传递速率、PSⅡ效率大于叶片,杨树叶片的相应值大于树枝,相关分析表明,这种高的C4酶活性并没有显著影响叶绿素荧光参数(p>0.05),显示出树枝绿色组织和C3植物叶片内C4酶对光合影响的复杂性。 相似文献
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Ji Jingjuan Guo Tonghang Tong Xianhong Luo Lihua Zhou Guixiang Fu Yingyun Liu Yusheng 《Frontiers of Biology in China》2007,2(1):80-84
Therapeutic cloning, which is based on human somatic cell nuclear transfer, is one of our major research objectives. Though
inter-species nuclear transfer has been introduced to construct human somatic cell cloned embryos, the effects of type, passage,
and preparation method of donor cells on embryo development remain unclear. In our experiment, cloned embryos were reconstructed
with different passage and preparation methods of ossocartilaginous cell, skin fibroblast, and cumulus cells. The cumulus
cell embryos showed significantly higher development rates than the other two (P < 0.05). The development rate of embryos reconstructed with skin fibroblasts of different passage number and somatic cells
of different chilling durations showed no significant difference. Also, fluorescence in situ hybridization (FISH) was conducted to detect nuclear derivation of the embryos. The result showed that the nuclei of the
inter-species cloned embryo cells came from human. We conclude that (1) cloned embryos can be constructed through human-rabbit
interspecies nuclear transfer; (2) different kinds of somatic cells result in different efficiency of nuclear transfer, while
in vitro passage of the donor does not influence embryo development; (3) refrigeration is a convenient and efficient donor
cell preparation method. Finally, it is feasible to detect DNA genotype through FISH.
Translated from Zoological Research, 2005, 26(4): 416–421 [译自: 动物学研究] 相似文献
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The proper detection of orthologs is crucial for evolutionary studies of genes and species. Despite large efforts to solve this problem the methodological situation appears unsettled to a large extent and the “quest for orthologs” is still an ongoing task in large-scale genome comparisons.Here, we introduce a simple operational framework for the detection of orthologs and their classification. The operational framework relies on well-established principles, optimizing their implementation for the considered purposes, and chaining components in coherent procedures: 1) We take advantage of the efficiency and simplicity of the Reciprocal Best Hit (RBH) detections, remedying (by design) the drawback concerning the limitations in terms of 1:1 detections. The procedure is based on the partitioning of Reciprocal Best Hits, with the further merging of partitions including members of the same paralogous classes (“SuperPartition of Orthologs” (SPOs)). 2) We then resort to the conservation profiles of the obtained clusters, allowing simple detection of SPOs containing duplicated members. Based on accepted evolutionary principles, such members can be further tagged as in-paralogs (co-orthologs) or out-paralogs.The method is illustrated and validated by extensive genomic analyses. The performances of the overall approach are characterized in global terms for three sets of species (Chlamydiae, Mycobacteria, Aspergilli), showing that at least 75% of the sets of orthologs contain at most one protein from a given species. The sets including more than one protein from a given species are shown to contain in-paralogs in proportions varying from 28% to 58%. The characterizations also show that the large majority of SPOs are associated with ancestral motifs, and accordingly not prone to chaining effects that might be triggered by multi-domain proteins. Further the SPO formulation is compared to other similarity based ortholog detection methods. Beyond core common results, significant differences are observed between various methods, which can be accounted for to a large extent on conceptual grounds, relative to the different merging schemes involved. Such comparisons highlight a major advantage of the SPO approach concerning the proper clustering of associated paralogs, which appear to be often dispatched spuriously into distinct orthologous classes.Finally the perspectives for future applications and elaborations of SPO-based compositional analyses are discussed. 相似文献
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P. Reis-Santos † R. P. Vasconcelos M. Ruano C. Latkoczy ‡ D. Günther ‡ M. J. Costa § H. Cabral § 《Journal of fish biology》2008,72(10):2595-2614
Otolith chemical composition differed between juveniles of five fish species ( Solea solea , Solea senegalensis , Platichthys flesus , Diplodus vulgaris and Dicentrarchus labrax ) in nursery areas of six estuaries along the Portuguese coast (Douro, Ria de Aveiro, Mondego, Tejo, Sado and Mira). Spatially consistent patterns in the concentration of some elements were responsible for differences between species. Discrimination of estuaries using data from all species simultaneously averaged 44·7% of correctly classified cases, whilst discrimination of species averaged 76·2%. Moreover, species-related patterns in otolith fingerprints were highlighted when comparing species for each estuarine nursery area, with intra estuarine species discrimination averages ranging from 86·2 to 100·0%. Similarities in the otolith elemental fingerprints were larger between species with close phylogeny and ecology, particularly between flatfish and perciform species. In addition to the differences in physiological regulation of species, specific microhabitat use in a common environment was suggested as a relevant factor for the differentiation of otolith chemistry among species occurring in the same locations. Despite positive results in specific estuaries, variation in otolith composition limited the use of species as proxies to classify others to their system of origin. 相似文献
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漫长历史时期的气候条件对生物多样性的现代分布格局产生了深远影响,分析以孑遗植物为优势种群落的分布格局、种群更新类型与适应策略,可揭示气候变化下孑遗植物的残存机制.本文以孑遗植物的群落生态学研究为视角,在综述孑遗落叶阔叶树种的定义、分布与生境特征、种间关系、种群更新与群落维持、植物性状与生境响应的基础上,提出在区域孑遗植物多样性研究中,应从微地形-植被关系入手,应用微地形单元的分类体系与手法,以微地形单元上斑块状植物群落为对象,分析其生境特征、种群结构、群落动态以及植物性状,揭示微地形梯度孑遗植物群落的分异格局,阐明区域内多种孑遗落叶阔叶树种的共存机制;结合植物群落谱系结构分析,进一步阐明孑遗植物群落的残存机制,有助于丰富我国亚热带山地植物多样性研究及保护生态学理论. 相似文献