GENETIC VARIATION AND THE EVOLUTION OF EPIGENETIC REGULATION

Epigenetic variation has been observed in a range of organisms, leading to questions of the adaptive significance of this variation. In this study, we present a model to explore the ecological and genetic conditions that select for epigenetic regulation. We find that the rate of temporal environmental change is a key factor controlling the features of this evolution. When the environment fluctuates rapidly between states with different phenotypic optima, epigenetic regulation may evolve but we expect to observe low transgenerational inheritance of epigenetic states, whereas when this fluctuation occurs over longer time scales, regulation may evolve to generate epigenetic states that are inherited faithfully for many generations. In all cases, the underlying genetic variation at the epigenetically regulated locus is a crucial factor determining the range of conditions that allow for evolution of epigenetic mechanisms.     

Biochemical studies on malathion resistance,inheritance and association of carboxylesterase activity in brown planthopper,Nilaparvata lugens complex in Peninsular Malaysia

Abstract Two sympatric populations of brown planthopper (BPH), one from rice and the other from Leersia hexandra were collected from each of five locations in Malaysia. All the tested malathion-resistant individuals of the rice BPH population and F₁ generation (cross between malathion-resistant [usually caught on rice] and malathion-susceptible [usually caught on Leersia]) showed high esterase activity, while all malathion-susceptible individuals on L. hexandra showed low esterase activity. In the F₂ generation, all the individuals tested against malathion were approximately 75% resistant and 25% susceptible and the inheritance pattern of esterase activity (high and low esterase activity) segregated in the same manner to a 3: 1 ratio. This confirms that resistance to malathion is mono-factorial and inheritance pattern of esterase activity is also linked to malathion resistance. Carboxylesterase or total esterase activity in BPH is inherited in a simple Mendelian fashion that is encoded by a single dominant gene. For the total esterase assay, average esterase activity levels in the rice-infesting population ranged from 17.64 to 19.37 nmoles 1-napthol/mg protein while that in the Leersia-infesting population ranged from 5.29 to 6.11 nmoles 1-napthol/mg protein. In terms of esterase activity, the two sympatric Nilaparvata lugens populations separated into two distinct groups. Results based on the tube color intensity test showed 96% and 98% resistant and susceptible individuals were present in the rice- and Leersia-infesting populations, respectively. In a filter paper test, the rice-infesting population had 94% with high esterase activity while the Leersia-infesting population had 96% with low esterase activity.     

Maternal effects on phase characteristics in the desert locust, Schistocerca gregaria: a review of current understanding

Desert locusts demonstrate pronounced density-dependent polyphenism: a complex suite of traits shifts over the lifetime of an individual in response to crowding or isolation. These changes also accumulate across generations through a maternal effect. Female desert locusts alter the developmental trajectory of their offspring in response to their own experience of crowding. The mother possesses a memory of both the recency and extent of crowding and shifts the phase state of her hatchlings accordingly. Extensive experimental work has shown that offspring behaviour is controlled by a low molecular weight, polar compound (or compounds) released from the mother's accessory glands. The chemical identity of this agent is not yet known.     

Paternal, maternal, and biparental inheritance of the chloroplast genome in Passiflora (Passifloraceae): implications for phylogenetic studies

Patterns of inheritance of the chloroplast genome in Passiflora were analyzed by examining the progeny from both interspecific and intraspecific crosses. Artificial crosses of field-collected material were performed in greenhouses at The University of Texas at Austin. DNA from fresh leaf material was analyzed by Southern blot techniques to identify the donor of the chloroplast genome. Initially, single progeny were analyzed for 11 crosses; two intraspecific crosses demonstrated maternal inheritance, whereas the nine interspecific crosses had paternal inheritance. Subsequently, the donor of the chloroplast genome was determined for multiple progeny in seven crosses. Passiflora oerstedii × P. retipetala showed strict paternal inheritance in all of 17 progeny. A series of five crosses and backcrosses between P. oerstedii and P. menispermifolia demonstrated strictly paternal inheritance. Finally, when 15 progeny were analyzed for the P. costaricensis × P. costaricensis cross, 12 of the 15 showed maternal inheritance, whereas the remaining three were biparental. Interestingly, all interspecific crosses had primarily paternal inheritance, whereas all intraspecific crosses had primarily maternal inheritance. The implications of heteroplasmy on phylogenetic analyses of chloroplast DNA are discussed.     

Epigenetic inheritance in rice plants

BACKGROUND AND AIMS: Epigenetics is defined as mechanisms that regulate gene expression without base sequence alteration. One molecular basis is considered to be DNA cytosine methylation, which reversibly modifies DNA or chromatin structures. Although its correlation with epigenetic inheritance over generations has been circumstantially shown, evidence at the gene level has been limited. The present study aims to find genes whose methylation status directly correlates with inheritance of phenotypic changes. METHODS: DNA methylation in vivo was artificially reduced by treating rice (Oryza sativa ssp. japonica) seeds with 5-azadeoxycytidine, and the progeny were cultivated in the field for > 10 years. Genomic regions with changed methylation status were screened by the methylation-sensitive amplified polymorphysm (MSAP) method, and cytosine methylation was directly scanned by the bisulfite mapping method. Pathogen infection with Xanthomonas oryzae pv. oryzae, race PR2 was performed by the scissors-dip method on mature leaf blades. KEY RESULTS: The majority of seedlings were lethal, but some survived to maturity. One line designated as Line-2 showed a clear marker phenotype of dwarfism, which was stably inherited by the progeny over nine generations. MSAP screening identified six fragments, among which two were further characterized by DNA blot hybridization and direct methylation mapping. One clone encoding a retrotransposon gag-pol polyprotein showed a complete erasure of 5-methylcytosines in Line-2, but neither translocation nor expression of this region was detectable. The other clone encoded an Xa21-like protein, Xa21G. In wild-type plants, all cytosines were methylated within the promoter region, whereas in Line-2, corresponding methylation was completely erased throughout generations. Expression of Xa21G was not detectable in wild type but was constitutive in Line-2. When infected with X. oryzae pv. oryzae, against which Xa21 confers resistance in a gene-for-gene manner, the progeny of Line-2 were apparently resistant while the wild type was highly susceptible without Xa21G expression. CONCLUSIONS: These results indicated that demethylation was selective in Line-2, and that promoter demethylation abolished the constitutive silencing of Xa21G due to hypermethylation, resulting in acquisition of disease resistance. Both hypomethylation and resistant trait were stably inherited. This is a clear example of epigenetic inheritance, and supports the idea of Lamarckian inheritance which suggested acquired traits to be heritable.     

Genomic prediction of seedling root length in maize (Zea mays L.)

Genotypes with extreme phenotypes are valuable for studying ‘difficult’ quantitative traits. Genomic prediction (GP) might allow the identification of such extremes by phenotyping a training population of limited size and predicting genotypes with extreme phenotypes in large sequences of germplasm collections. We tested this approach employing seedling root traits in maize and the extensively genotyped Ames Panel. A training population made up of 384 inbred lines from the Ames Panel was phenotyped by extracting root traits from images using the software program aria . A ridge regression best linear unbiased prediction strategy was used to train a GP model. Genomic estimated breeding values for the trait ‘total root length’ (TRL) were predicted for 2431 inbred lines, which had previously been genotyped by sequencing. Selections were made for 100 extreme TRL lines and those with the predicted longest or shortest TRL were validated for TRL and other root traits. The two predicted extreme groups with regard to TRL were significantly different (P = 0.0001). The difference in predicted means for TRL between groups was 145.1 cm and 118.7 cm for observed means, which were significantly different (P = 0.001). The accuracy of predicting the rank between 1 and 200 of the validation population based on TRL (longest to shortest) was determined using a Spearman correlation to be ρ = 0.55. Taken together, our results support the idea that GP may be a useful approach for identifying the most informative genotypes in sequenced germplasm collections to facilitate experiments for quantitative inherited traits.     

成骨不全及其分子机制

成骨不全作为罕见性遗传性结缔组织疾病,具有临床异质性与遗传异质性,迄今已经分为15个亚型.有常染色体显性遗传与常染色体隐性遗传两种遗传方式.常染色体显性遗传以Ⅰ型胶原蛋白结构基因COL1A1、COL1A2突变为主.非Ⅰ型胶原蛋白突变的常染色体隐性遗传的成骨不全患者数量少,但致病基因种类多,涉及到胶原合成后异常修饰,胶原蛋白分子伴侣及羧基端前肽剪切酶缺陷、成骨细胞与破骨细胞分化及转录因子异常、钙离子通道与Wnt信号通路分子等诸多方面.致病基因及其机制的研究,对于成骨不全的基因确诊及个体化药物治疗意义重大.     

综述: DNA甲基化在动物胚胎和生殖细胞发育过程中的重编程

表观遗传信息DNA甲基化在动物的发育、细胞分化和器官形成过程中,起着至关重要的作用．近期,关于DNA甲基化在脊椎动物胚胎发育和生殖细胞发育过程重编程的研究取得了重要的进展．发现斑马鱼的早期胚胎完整地继承了精子的DNA甲基化图谱,而哺乳动物的早期胚胎和原始生殖细胞发育过程则经历了整体去甲基化并重新建立甲基化图谱的过程,但胚胎发育过程中基因的印迹区未发生DNA去甲基化,而生殖细胞发育过程中印迹区的甲基化修饰被消除．     

When to rely on maternal effects and when on phenotypic plasticity?

Existing insight suggests that maternal effects have a substantial impact on evolution, yet these predictions assume that maternal effects themselves are evolutionarily constant. Hence, it is poorly understood how natural selection shapes maternal effects in different ecological circumstances. To overcome this, the current study derives an evolutionary model of maternal effects in a quantitative genetics context. In constant environments, we show that maternal effects evolve to slight negative values that result in a reduction of the phenotypic variance (canalization). By contrast, in populations experiencing abrupt change, maternal effects transiently evolve to positive values for many generations, facilitating the transmission of beneficial maternal phenotypes to offspring. In periodically fluctuating environments, maternal effects evolve according to the autocorrelation between maternal and offspring environments, favoring positive maternal effects when change is slow, and negative maternal effects when change is rapid. Generally, the strongest maternal effects occur for traits that experience very strong selection and for which plasticity is severely constrained. By contrast, for traits experiencing weak selection, phenotypic plasticity enhances the evolutionary scope of maternal effects, although maternal effects attain much smaller values throughout. As weak selection is common, finding substantial maternal influences on offspring phenotypes may be more challenging than anticipated.