Imprinting in plants

This review discusses the modern issues in epigenetic regulation in plants related to the imprinting at the levels of genome, locus, and gene. The data described follow the historical order: from the beginning of research into non-crossability of plant forms with different ploidies to the recent communications about allelic imprinting at r1 locus of maize and the control of synthesis of storage proteins with a high forage value. The classical experiments of Kermicle and Lin on the cytogenetic confirmation of the role of parental genome ratio in the endosperm in a successful development of viable caryopses are described in detail. Uniqueness of the experimental technique used by these authors is emphasized. The variants for overcoming the effect of imprinted signal in apomicts and plants with a tetrasporic embryo sac are considered. A considerable attention is paid to the imprinting in the species with polyploid series and to the hypothesis of endosperm balance number. The issues of potential practical application of imprinting in breeding practice are discussed. The results obtained in this direction demonstrate the ways to increase the forage value of maize zeins.     

Imprinting in plants

This review discusses the modern issues in epigenetic regulation in plants related to the imprinting at the levels of genome, locus, and gene. The data described follow the historical order: from the beginning of research into non-crossability of plant forms with different ploidies to the recent communications about allelic imprinting at r1 locus of maize and the control of synthesis of storage proteins with a high forage value. The classical experiments of Kermicle and Lin on the cytogenetic confirmation of the role of parental genome ratio in the endosperm in a successful development of viable caryopses are described in detail. Uniqueness of the experimental technique used by these authors is emphasized. The variants for overcoming the effect of imprinted signal in apomicts and plants with a tetrasporic embryo sac are considered. A considerable attention is paid to the imprinting in the species with polyploid series and to the hypothesis of endosperm balance number. The issues of potential practical application of imprinting in breeding practice are discussed. The results obtained in this direction demonstrate the ways to increase the forage value of maize zeins.     

Genomic Imprinting in Mammals

Genomic imprinting affects a subset of genes in mammals and results in a monoallelic, parental-specific expression pattern. Most of these genes are located in clusters that are regulated through the use of insulators or long noncoding RNAs (lncRNAs). To distinguish the parental alleles, imprinted genes are epigenetically marked in gametes at imprinting control elements through the use of DNA methylation at the very least. Imprinted gene expression is subsequently conferred through lncRNAs, histone modifications, insulators, and higher-order chromatin structure. Such imprints are maintained after fertilization through these mechanisms despite extensive reprogramming of the mammalian genome. Genomic imprinting is an excellent model for understanding mammalian epigenetic regulation.     

Genomic Imprinting in Mammals

A review of the data on the mechanisms and effects of genomic imprinting, an epigenetic phenomenon regulating the development in placentate mammals, is presented. In contrast to the majority of gene loci with biallelic expression, the expression of imprinted loci is monoallelic. In humans and mice, more than 30 imprinted loci have been identified, in which maternal or paternal alleles may either be expressed or be found in a repressed state during ontogeny. Imprinting is established during gametogenesis, and the repression of an allele of the imprinted locus is determined by methylation of the key regulatory element of this allele. Both the maternal and paternal chromosome sets are required for normal development in mammals. This is why parthenogenesis and androgenesis in these animals are impossible in nature. As a result of differential gene expression of many imprinted loci, the balance of gene activity is established, which is necessary for normal proliferation and differentiation of various cell clones in embryogenesis. Many human developmental abnormalities and syndromes are determined by defective genomic imprinting. In particular, the loss of imprints, which is followed by the occurrence of biallelic expression of some imprinted loci, may cause malignant tumors.     

Parental Imprinting in Drosophila

Genetic imprinting is a form of epigenetic silencing. But with a twist. The twist is that while imprinting results in the silencing of genes, chromosome regions or entire chromosome sets, this silencing occurs only after transmission of the imprinted region by one sex of parent. Thus genetic imprinting reflects intertwined levels of epigenetic and developmental modulation of gene expression. Imprinting has been well documented and studied in Drosophila, however, these studies have remained largely unknown due to nothing more significant than differences in terminology. Imprinting in Drosophilais invariably associated with heterochromatin or regions with unusual chromatin structure. The imprint appears to spread from imprinted centers that reside within heterochromatin and these are, seemingly, the only regions that are normally imprinted in Drosophila. This is significant as it implies that while imprinting occurs in Drosophila, it is generally without phenotypic consequence. Hence the evolution of imprinting, at least in Drosophila, is unlikely to be driven by the function of specific imprinted genes. Thus, the study of imprinting in Drosophilahas the potential to illuminate the mechanism and biological function of imprinting, and challenge models based solely on imprinting of mammalian genes. This revised version was published online in July 2006 with corrections to the Cover Date.     

Imprinting and disease

Deregulation of imprinted genes has been observed in a number of human diseases such as Beckwith-Wiedemann syndrome, Prader-Willi/Angelman syndromes and cancer. Imprinting diseases are characterised by complex patterns of mutations and associated phenotypes affecting pre- and postnatal growth and neurological functions. Regulation of imprinted gene expression is mediated by allele-specific epigenetic modifications of DNA and chromatin. These modifications preferentially affect central regulatory elements that control in cis over long distances allele-specific expression of several neighbouring genes. Investigations of imprinting diseases have a strong impact on biomedical research and provide interesting models for function and mechanisms of epigenetic gene control.     

基因组印迹调节

虽然大多数哺乳动物基因都是双座位表达,但是有一少部分基因发生印迹,只有父母双方基因中的一个实际表达,这种表观遗传过程迁涉到发育不同阶段基因的表达调节,十分复杂,原则上印迹基因在生殖细胞中必须用表观遗传标记顺式标记,这些标记能够通过细胞分裂进行保存,在成熟生物分化细胞中能够指导多基因单座位表达,在生殖细胞形成早期两个座位上的表达差别必须消除,以便在成熟生殖细胞中重新设置印迹,在该文中,概述了目前所知介导这些过程的分子机制。     

Epigenetic Mosaicism in Genomic Imprinting Disorders

Russian Journal of Genetics - Differential gene expression during development is maintained by complex regulatory epigenetic mechanisms that provide the formation of different specialized cell...     

基因组印迹的起动与沉默

在配子中基因组印迹起动复合物的结合引发印迹现象,印迹起动复合物中有多种可鉴定成分,存在结合的精确时间和机制,印迹起动复合物似乎仅出现在生殖细胞系,而甲基CpG结合蛋白则能延续增殖印迹,因此基因组印迹调节着发育基因或组织特异性单等位基因的瞬时表达及大染色体结构域中基因之间的相互作用 。     

Genomisches Imprinting und Imprintingfehler

Genomic imprinting is an epigenetic process by which specific gene regions are marked by the male and the female germ lines by histone modifications and DNA methylation, so that only the paternal allele or only the maternal allele of a gene is active. Genomic imprints are erased in primordial germ cells, newly established during later stages of germ cell development and stably inherited through somatic cell divisions during postzygotic development. Defects in imprint erasure, establishment or maintenance result in aberrant epigenetic patterns and expression profiles and can cause specific diseases. Imprinting defects can occur spontaneously without any DNA sequence change (primary imprinting defect) or as the result of a mutation in a cis-regulatory element or a trans-acting factor (secondary imprinting defect). The distinction between primary and secondary imprinting defects is important for assessing the risk of recurrence in affected families.     

哺乳动物基因组印记的研究进展

基因组印记是由亲本来源不同而导致等位基因表达差异的一种遗传现象。基因组印记产生的原因及过程是现代遗传学的一个热点问题。哺乳动物的许多基因组印记特征都使其成为后基因组时代的一个热点生物学问题。进化的基因组印记在哺乳动物生殖、发育中起到了特定的作用。综述了基因组印记的特点、印记基因的印记机理、基因印记与克隆动物的发育、印记基因与疾病的研究进展。     

雏鸡听觉印记学习

雏鸡听觉印记学习是研究新生个体在早期发育阶段学习与记忆形成的神经机制的良好实验模型.听觉刺激对印记学习有很好的强化作用,作用效果依赖于频率、强度和持续时间等声音特征.从声音的选择、听觉刺激所引起的分子水平和组织水平改变等方面综述雏鸡听觉印记学习的研究进展.     

拟南芥的印记基因和印记表达调控

基因组印记是指后代仅表达亲本之一基因拷贝的现象。印记基因的发生是防止孤雌生殖发生的有效手段之一。拟南芥FIS(Fertilisation-independent seed)印记基因mea、fis2和fie在中央细胞分裂抑制和早期胚乳发育调节中发挥重要作用。fis突变体具有两种表型:当受精缺失时二倍体胚乳自主发育,而当受精发生时形成非细胞化的胚乳。FIS多梳蛋白复合体(Polycomb protein complex)包括上述3种FIS蛋白,在目标位点催化组蛋白H3第27位赖氨酸的tri-甲基化(H3K27 tri-methylation)。DME(DEMETER)和AtMET1(Methyltransferase1)参与了mea和fis2的印记表达控制。最近研究结果表明,开花植物中转座子的插入影响邻近基因的表达,是基因组印记进化的主要驱动力量。本文综述了10年来拟南芥中FIS印记基因和相关基因的发现及其调控机理,期望能为水稻、玉米等重要作物中印记基因的研究提供借鉴和参考。     

Imprinting on time-structured acoustic stimuli in ducklings

Filial imprinting is a dedicated learning process that lacks explicit reinforcement. The phenomenon itself is narrowly heritably canalized, but its content, the representation of the parental object, reflects the circumstances of the newborn. Imprinting has recently been shown to be even more subtle and complex than previously envisaged, since ducklings and chicks are now known to select and represent for later generalization abstract conceptual properties of the objects they perceive as neonates, including movement pattern, heterogeneity and inter-component relationships of same or different. Here, we investigate day-old Mallard (Anas platyrhynchos) ducklings’ bias towards imprinting on acoustic stimuli made from mallards’ vocalizations as opposed to white noise, whether they imprint on the temporal structure of brief acoustic stimuli of either kind, and whether they generalize timing information across the two sounds. Our data are consistent with a strong innate preference for natural sounds, but do not reliably establish sensitivity to temporal relations. This fits with the view that imprinting includes the establishment of representations of both primary percepts and selective abstract properties of their early perceptual input, meshing together genetically transmitted prior pre-dispositions with active selection and processing of the perceptual input.     

Imprinting evolution and human health

Genomic imprinting results in parent-of-origin-dependent, monoallelic expression of genes. The functional haploid state of these genes has far-reaching consequences. Not only has imprinting been implicated in accelerating mammalian speciation, there is growing evidence that it is also involved in the pathogenesis of several human conditions, particularly cancer and neurological disorders. Epigenetic regulatory mechanisms govern the parental allele-specific silencing of imprinted genes, and many theories have attempted to explain the driving force for the evolution of this unique form of gene control. This review discusses the evolution of imprinting in Therian mammals, and the importance of imprinted genes in human health and disease.