Transposons, RNA Interference and Heterochromatin

描述(申请人提供)：植物和动物的种系经历基因组重新编程，以重置表观遗传标记，否则将干扰受精卵的多能性。这些标记中最主要的可能是转座元件(TE)的表观遗传修饰，它构成了大多数真核基因组的大部分。我们发现，来自异染色质的小干扰RNA在植物生殖系重编程中发挥着关键作用，越来越多的证据表明动物中也存在类似的现象。植物中的生殖细胞是由有丝分裂的减数分裂产物产生的，一些伴生细胞也会分化，类似于动物的哺乳细胞和其他支持细胞。我们发现，花粉粒伴核(营养核或VN)的重新编程导致转座子的激活，并在精子细胞中积累了一类新的“表观遗传激活的”小干扰RNA(Easy RNA)。在胚珠中，同样的小RNA途径中的突变导致额外的无融合二倍体生殖细胞的分化，以及卵子中TE的激活。异常的生殖细胞规格对植物繁殖有深远的影响，包括产生克隆的不还原种子(无融合生殖)。我们将研究植物生殖系重编程的机制，以及小RNA在生殖细胞鉴定中的作用。我们还将研究重编程出错时表观等位基因的跨代遗传。我们有初步证据表明，系统可移动的小RNA在配子中积累，并从配子传递到受精卵，为跨代遗传提供了一种机制。 与公共健康相关：越来越多的证据表明，环境因素可以对人类健康产生跨代影响。然而，表观遗传传递的机制及其对下一代基因表达的影响仍不清楚。基因组重编程是生殖系和早期胚胎正常发育的基础。原始生殖细胞和胚胎都失去了转座子的DNA甲基化，并获得了印记基因的甲基化。癌症基因组的类似重新编程可以导致肿瘤抑制基因的沉默。专注于植物，我们发现了来自转座子的移动小RNA信号，这些信号是在种系重新编程后产生的。这些小RNA依赖于DNA甲基化1染色质重构体的减少，就像它在小鼠和人类中的同源物一样，在精子细胞中表达，最近在哺乳动物生殖系中出现了类似的小RNA、转座子沉默和基因组重编程之间的相互作用。我们将确定这些小RNA是否与零星基因甲基化和表观遗传有关。我们还将研究它们在减数分裂和生殖细胞命运中的作用。

DESCRIPTION (provided by applicant): The germlines of plants and animals undergo genome reprogramming in order to reset epigenetic marks that would otherwise interfere with pluripotency of the zygote. Perhaps chief among these marks are epigenetic modifications of transposable elements (TE), which make up a majority of most eukaryotic genomes. We have found that small interfering RNA derived from heterochromatin plays a key role in germline reprogramming in plants, and there is mounting evidence for a similar phenomenon in animals. Germ cells in plants arise from the products of meiosis by mitotic division, and a number of companion cells also differentiate resembling nurse cells and other support cells in animals. We have found that reprogramming of the pollen grain companion cell nucleus (the vegetative nucleus or VN) results in transposon activation, and that a new class of "epigenetically activated" small interfering RNA (easiRNA) accumulate in sperm cells. In ovules, mutants in this same small RNA pathway result in differentiation of additional ameiotic diploid germ cells, as well as TE activation in the egg. Aberrant germ cell specification has profound implications for plant reproduction, including the production of clonal unreduced seeds (apomixis). We will investigate the mechanism of germline reprogramming in plants, and the function of small RNA in specification of germ cell identity. We will also investigate the transgenerational inheritance of epialleles when reprogramming goes awry. We have preliminary evidence that systemically mobile small RNA accumulate in the gametes, from which they are passed into the fertilized zygote, providing a mechanism for transgenerational inheritance. PUBLIC HEALTH RELEVANCE: There is a growing body of evidence that environmental factors can have transgenerational effects on human health. However, the mechanism of epigenetic transmission and its impact on gene expression in the next generation is still unknown. Genome reprogramming is fundamental to normal development of the germline and early embryo. Both primordial germ cells and embryos lose DNA methylation from transposons, and gain methylation of imprinted genes. Similar reprogramming of the cancer genome can lead to silencing of tumor suppressor genes. Focusing on plants, we have found mobile small RNA signals from transposons that arise following reprogramming in the germline. These small RNA depend on the chromatin remodeler Decrease in DNA Methylation1 which, like its homologs in mouse and humans, is expressed in sperm cells, and a similar interaction between small RNA, transposon silencing and genome reprogramming has recently emerged in the mammalian germline. We will determine whether these small RNA are responsible for sporadic gene methylation and epigenetic inheritance. We will also investigate their role in meiosis and germ cell fate.