Liu Yalin, Su Handong, Pang Junling, Gao Zhi, Wang Xiu-Jie, Birchler James A, Han Fangpu
State Key Laboratory of Plant Cell and Chromosome Engineering, University of Chinese Academy of Sciences, Beijing 100049, China.
University of Chinese Academy of Sciences, Beijing 100049, China State Key Laboratory of Plant Genomics, Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, Beijing 100101, China;
Proc Natl Acad Sci U S A. 2015 Mar 17;112(11):E1263-71. doi: 10.1073/pnas.1418248112. Epub 2015 Mar 2.
The ability of centromeres to alternate between active and inactive states indicates significant epigenetic aspects 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 further derivatives with new centromeres being formed elsewhere on each chromosome. Our results suggest that de novo centromere initiation is quite common and can persist on chromosomal fragments without a canonical centromere. However, we hypothesize that when de novo centromeres are initiated in opposition to a larger normal centromere, they are cleared from the chromosome by inactivation, thus maintaining karyotype integrity.
着丝粒在活跃和非活跃状态之间转换的能力表明，存在着控制着丝粒组装和功能的重要表观遗传因素。在玉米（Zea mays）中，B染色体着丝粒在与9号染色体短臂的易位（TB-9Sb）上发生错分，可产生许多着丝粒大小和着丝粒DNA序列各异的变体。在TB-9Sb的这类衍生物中，我们在染色体衍生物3-3上发现了一个新生着丝粒，它没有典型的着丝粒重复序列。这个着丝粒源自9号染色体短臂上的一个288 kb区域，距离TB-9Sb中9号染色体的易位断点有19兆碱基（Mb）。祖细胞telo2-2中的功能性B着丝粒在衍生物3-3中缺失，但仍保留一些B重复序列。衍生物3-3的新生着丝粒在另外三个衍生物中变得不活跃，每个染色体上的其他位置形成了新的着丝粒。我们的结果表明，新生着丝粒的起始相当普遍，并且可以在没有典型着丝粒的染色体片段上持续存在。然而，我们推测，当新生着丝粒与一个更大的正常着丝粒相对立起始时，它们会通过失活从染色体上清除，从而维持核型的完整性。
