Restricted chromosomal silencing in nucleolar dominance
Restricted chromosomal silencing in nucleolar dominance
复制标题
DOI：
10.1073/pnas.251424098
复制
发表时间：
2001-12-04
影响因子：
11.1
通讯作者：
Pikaard, CS
中科院分区：
文献类型：
--
作者：
Lewis, MS;Pikaard, CS
在种间杂交中，亲本一方染色体组织核仁的失败是一种被称为核仁显性的表观遗传现象。已知涉及数百万人的选择性基因沉默，但核仁组织者区（NOR）携带染色体在NORs之外失活的全部程度尚不清楚。借助拟南芥的基因组序列数据，我们绘制了拟南芥和砂南芥的异源四倍体杂交品种suidopsis suecica核仁显性诱导沉默的程度。利用灵敏的反转录PCR检测，我们发现4个大小约为4 Mbp的拟南芥NORs在suecica营养叶片中沉默了约99.5%，而从a.a arenosa遗传的NORs则保持完全活性。拟南芥的两个NORs （NOR2和NOR4）位于2号和4号染色体的端粒上，因此在NORs的远端没有基因。在着丝粒近端最接近NOR4的三个蛋白质编码基因（其中距离rRNA基因序列最近的只有3.1 kb）显示，尽管相邻的大约4 mbp的NOR沉默，但在杂交后代中仍被转录。这些数据反驳了NOR失活归因于邻近染色体区域沉默传播的假设，但支持NORs或rRNA基因是调控目标的模型。
Failure of one parent's chromosomes to organize nucleoli in an interspecific hybrid is an epigenetic phenomenon known as nucleolar dominance. Selective gene silencing on a scale of millions of by is known to be involved, but the full extent to which nucleolus organizer region (NOR)-bearing chromosomes are inactivated beyond the NORs is unknown. Aided by genome sequence data for Arabidopsis thaliana, we have mapped the extent of nucleolar dominance-induced silencing in Arabidopsis suecica, the allotetraploid hybrid of A. thaliana and Arabidopsis arenosa. Using a sensitive reverse transcription PCR assay, we show that the four A. thaliana NORs, each approximate to4 Mbp in size, are approximate to 99.5% silenced in A. suecica vegetative leaves, whereas the NORs inherited from A. arenosa remain fully active. The two A. thaliana NORs, NOR2 and NOR4, abut the telomeres on chromosomes 2 and 4, thus there are no genes distal to the NORs. The three protein-coding genes nearest NOR4 on its centromere-proximal side, the closest of which is only 3.1 kb from rRNA gene sequences, are shown to be transcribed in the hybrid despite the silencing of the adjacent approximate to 4-Mbp NOR. These data argue against hypotheses in which NOR inactivation is attributed to the spread of silencing from adjacent chromosomal regions, but favor models in which NORs or rRNA genes are the targets of regulation.