多倍体植物的表观遗传现象

表观遗传现象是指基因表达发生改变但不涉及DNA序列的变化, 它存在于许多植物的多倍体化过程中,而且能够在代与代之间传递。表观遗传变异包括基因沉默、DNA甲基化、核仁显性、休眠转座子激活和基因组印记等方面。这种现象可能是由于基因组间的相互作用直接诱发基因沉默或基因表达改变所致;也可能由DNA甲基化之外的组蛋白编码的改变引起;或者与甲基化不足、染色质重组或转座子激活等有关。表观遗传变异在提高基因表达的多样性,引起遗传学和细胞学上的二倍化,以及促进基因组间的相互协调等方面起着重要作用。文章综述了植物多倍体化过程中的表观遗传现象及其在多倍体植物基因组进化中的作用,并在此基础上提出了今后在这方面的研究途径。     

Trophic structure of macrobenthos in the Tagus estuary and adjacent coastal shelf

The trophic structure of benthic communities in the Tagus estuary and adjacent coastal shelf was characterized according to a functional guild approach, based on sampling surveys conducted between 1987 and 2000. Macrobenthic organisms were assigned to seven distinct trophic groups (herbivorous, filter feeders, surface deposit feeders, subsurface deposit feeders, carnivores, filter feeders/detritivores, carnivores/detritivores) and the dominance of these groups was related to environmental variables using multivariate ordination techniques. Surface-deposit feeders were numerically dominant in the Tagus estuary, making up 52% of the benthic communities, while in the adjacent coastal shelf the assemblage was dominated by both surface-deposit feeders and filter feeders (37% and 33%, respectively). When biomass was considered, filter feeders and filter feeders/detritivores were the dominant groups in the estuary, while for the adjacent coastal shelf filter feeders represented 83% of the total biomass. Salinity, depth and sediment composition were the main factors structuring spatial distribution. Surface-deposit feeders were the most abundant macrobenthos of the upper estuary. Surface deposit feeders also dominated the middle and the lower estuary but the proportion of filter feeders as well as other trophic groups increased with salinity. Generally, a more even distribution of trophic structure was found at stations with high salinity. In the adjacent coastal shelf, the trophic diversity decreased with depth. The trophic structure revealed that filter feeders dominated in abundance and biomass in shallow sandy sediments (<25 m), while in deeper sandy mud and muddy habitats (>50 m to 260 m), deposit feeders and carnivores were the most important groups in abundance and biomass, respectively.     

Effects of environmental fluctuation on plankton allelopathy

 This paper studies a two-dimensional system that arises in plankton allelopathy involving discrete time delays and environmental fluctuations. The environmental parameters are assumed to be perturbed by white noise characterized by a Gaussian distribution with mean zero and unit spectral density. The dynamic behaviour of the stochastic system is studied and the fluctuations in population are measured both analytically and numerically by computer simulation. Received: 7 September 1998 / Revised version: 14 October 1998     

A geographical model of high species diversity

Several cases of high species diversity, for example in tropical rain forests, imply that speciation has been frequent or rapid. However, how speciation could proceed so frequently as to generate extraordinary diversity still remains unsolved, despite recent advancements of diverse theories of allopatric and sympatric speciation. This paper presents a theoretical model that demonstrates the process of frequent speciation by means of geographical fragmentation. We focus on allopatric speciation and explore the evolutionary effect of fragmentation and extinction of demes (subpopulations) in a widespread species or species group. After a large contagious population of a single species is fragmented into demes, extinction of some demes could result in isolation of multiple demes. Thus, several demes could become good species simultaneously through the process of allopatric speciation. We apply the random extinction method to this fragmentation process where demes become randomly extinct. The present model illustrates that frequent speciation could occur in communities where large environmental changes frequently take place.     

贵州龙洞和万家洞内部分环境因子与动物群落结构的相关性

分别在2005年的10月和2006年的2月赴遵义龙洞和万家洞对肉眼见到的软体动物、节肢动物和脊索动物进行了观察和采集,在龙洞共获标本454号,隶属3门6纲13目20科29种或类群;在万家洞共获标本1726号,隶属3门7纲11目18科22种或类群。根据两洞内各光带中动物种类和数量组成不同,将其划分为6个动物群落,经群落多样性分析,物种丰富度、群落多样性、最大多样性、均匀度、优势度和相似性指数最高的分别是群落A(3.1932)、C(2.0788)、A(2.8332)、B(0.7828)、E(0.3789)和B-E(1.7854)。此外还研究了部分环境因子与群落多样性的相关性。结果显示,土壤中有机质的含量与群落多样性指数呈极显著正相关,相关系数为0.828(双尾显著性检验≤0.05);空气中CO2的含量与物种数、物种丰富度指数、群落多样性指数、群落最大多样性指数和群落优势度指数都成不显著负相关,相关系数分别为-0.160、-0.263、-0.072、-0.117和-0.031。由此证明土壤有机质的含量和空气中CO2的含量是影响洞穴动物群落变化的重要因子。     

Use of maize pollen by adult Chrysoperla carnea (Neuroptera: Chrysopidae) and fate of Cry proteins in Bt-transgenic varieties

We investigated the use of maize pollen as food by adult Chrysoperla carnea under laboratory and field conditions. Exposure of the insects to insecticidal Cry proteins from Bacillus thuringiensis (Bt) contained in pollen of transgenic maize was also assessed. Female C. carnea were most abundant in a maize field when the majority of plants were flowering and fresh pollen was abundant. Field-collected females contained an average of approximately 5000 maize pollen grains in their gut at the peak of pollen shedding. Comparable numbers were found in females fed ad libitum maize pollen in the laboratory. Maize pollen is readily used by C. carnea adults. When provided with a carbohydrate source, it allowed the insects to reach their full reproductive potential. Maize pollen was digested mainly in the insect's mid- and hindgut. When Bt maize pollen passed though the gut of C. carnea, 61% of Cry1Ab (event Bt176) and 79% of Cry3Bb1 (event MON 88017) was digested. The results demonstrate that maize pollen is a suitable food source for C. carnea. Even though the pollen grains are not fully digested, the insects are exposed to transgenic insecticidal proteins that are contained in the pollen.     

Demethylation of the aryl hydrocarbon receptor repressor as a biomarker for nascent smokers

Epigenetic modifications to peripheral white blood cell DNA occur in response to a wide variety of exposures. In prior work, we and others have shown that broad changes in DNA methylation, particularly at the aryl hydrocarbon receptor repressor (AHRR) locus, occur in samples from subjects with long histories of smoking. However, given the large number of epigenetic changes that occur in response to prolonged smoking, the primacy of the response at AHRR and the sensitivity of these changes to low levels of smoking are not known. Therefore, we examined the association of smoking to genome lymphocyte DNA methylation status in a representative sample of 399 African American youths living in the rural South that includes 72 subjects with less than one half-pack year of exposure. Consistent with our prior findings, we found a stepwise effect of smoking on DNA methylation among youth with relatively brief exposure histories at a CpG residue in AHRR (cg05575921) (FDR corrected p values; 3 × 10⁻⁷ and 0.09 in the male and female samples, respectively) that was identified in previous studies and at which the effects of smoking were significant, even in those subjects with less than one half pack year exposure. We conclude that AHRR demethylation at cg05575921 in peripheral cells may serve as an early, sensitive biomarker for even low levels of exposure to tobacco smoke, providing a non-self-report alternative for nascent exposure to tobacco smoke. We also suggest that the AHRR/AHR pathway may be functional in the response of peripheral white blood cells to tobacco smoke exposure.     

细胞重编程中的表观遗传分子机制

成体细胞可以通过核移植、细胞融合或者特定因子导入的方式实现重编程回到多能性状态。在重编程的过程中,表观遗传水平的调控机制起到了非常关键的作用。通过回顾重编程的研究进展来探讨表观遗传学在重编程中的调控机制。     

DNA甲基转移酶的表达调控及主要生物学功能

DNA甲基化是表观遗传学的重要部分, 同组蛋白修饰相互作用, 通过改变染色质结构, 调控基因表达。在哺乳类细胞或人体细胞中, DNA甲基化与细胞的增殖、衰老、癌变等生命现象有着重大关系。对催化DNA甲基化的DNA甲基转移酶(DNA methyltransferase, Dnmt)的研究可以揭示DNA甲基化对基因表达调控的机制, 从而研究与之相关的重要生命活动。文章以DNA甲基转移酶作为切入点, 探讨DNA甲基转移酶在基因表达调控中发挥的作用及其主要生物学功能。