PNAS：中科院遗传所发表表观遗传学新成果

着丝粒是与有丝分裂和减数分裂有关的重要染色体结构，是纺锤丝微管的附着之处，也是姐妹染色单体在分开前相互连接的地方。着丝粒能够在激活和失活状态之间交替变化，其装配和功能不依赖于DNA序列，而是受到表观遗传学调控。

日前，中科院和密苏里大学的科学家们在美国国家科学院PNAS杂志上发表文章，向人们展示了染色体片段上发生的着丝粒从头形成(de novo centromere formation)。文章的通讯作者是中科院遗传所的韩方普(Fangpu Han)和密苏里大学的James A. Birchler。

在玉米中(Zea mays)，B染色体着丝粒发生错分裂(misdivision)会生成不同大小和序列的着丝粒。研究人员在这样的片段中(该片段缺乏标准的着丝粒重复序列)先后观察到了着丝粒的从头形成和失活。

研究表明，着丝粒从头起始是一种很常见的现象，能够在缺乏标准着丝粒的染色体片段上持续存在并遗传下去。不过当大着丝粒和小着丝粒出现在一起的时候，小着丝粒会被失活。因此这种从头形成的着丝粒遇到较大的常规着丝粒时，就会被失活并清除出染色体，以便维持核型的完整性。

原文链接：Sequential de novo centromere formation and inactivation on a chromosomal fragment in maize

The ability of centromeres to alternate between active and inactive states indicates significant epigeneticaspects controlling centromere assembly and function. In maize (Zea mays), misdivision of the B chromosome centromere on a translocation with the short arm of chromosome 9 (TB-9Sb) can produce many variants with varying centromere sizes and centromeric DNA sequences. In such derivatives of TB-9Sb, we found a de novo centromere on chromosome derivative 3-3, which has no canonical centromeric repeat sequences. This centromere is derived from a 288-kb region on the short arm of chromosome 9,and is 19 megabases (Mb) removed from the translocation breakpoint of chromosome 9 in TB-9Sb. The functional B centromere in progenitor telo2-2 is deleted from derivative 3-3, but some B-repeat sequences remain. The de novo centromere of derivative 3-3 becomes inactive in three furtherderivatives with new centromeres being formed elsewhere on each chromosome. Our results suggest thatde novo centromere initiation is quite common and can persist on chromosomal fragments without acanonical centromere. However, we hypothesize that when de novo centromeres are initiated inopposition to a larger normal centromere, they are cleared from the chromosome by inactivation, thus maintaining karyotype integrity.

作者：Yalin Liu