Transposons, RNA Interference and Heterochromatin

描述（由申请人提供）：植物和动物的生殖系经过基因组重编程，以重置表观遗传标记，否则会干扰受精卵的多能性。也许这些标记中最主要的是转座元件（TE）的表观遗传修饰，它构成了大多数真核生物基因组。我们已经发现来自异染色质的小干扰RNA在植物种系重编程中起着关键作用，并且有越来越多的证据表明动物中也有类似的现象。植物中的生殖细胞是由有丝分裂产生的减数分裂的产物，许多伴侣细胞也分化成类似于动物中的哺乳细胞和其他支持细胞。我们发现花粉粒伴细胞核（营养核或VN）的重编程导致转座子激活，并且在精子细胞中积累了一类新的“表观遗传激活”小干扰RNA （easiRNA）。在胚珠中，同样的小RNA途径的突变导致额外的无卵分裂二倍体生殖细胞的分化，以及卵子中的TE激活。异常的生殖细胞规格对植物生殖具有深远的影响，包括克隆未还原种子（无融合）的产生。我们将研究植物种系重编程的机制，以及小RNA在生殖细胞身份规范中的作用。我们还将研究重编程出错时外显子的跨代遗传。我们有初步的证据表明，系统移动的小RNA在配子中积累，并从配子中传递到受精卵中，为跨代遗传提供了一种机制。

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.