Precise cell division with proper chromosome orientation is the prerequisite for genomic stability, growth and development of all organisms. Defects during cell division can result in diseases such as Down’s syndrome, Edwards’ syndrome and Patau’s syndrome in humans and crop reductions in plants. The advent of technology and a renewed focus on chromosome biology means there are many interesting questions left to investigate in the field of centromere biology. For instance, what is the role for centromere in sister kinetochore mono-orientation in meiosis I, bi-orientation in meiosis II and mitosis, what is the role that centromere has in chromosome segregation?
Recently, Dr. HAN Fangpu’s group in the Institute of Genetics and Developmental Biology (IGDB), Chinese Academy of Sciences, found the relationship between H2AThr133ph and CENH3 (A centromeric histone H3 variant) nucleosome in plants during cell division, and revealed the potential temporal and spatial regulation roles for H2A phosphorylation in chromosome segregation.
In order to understand the mechanism of centromere structure on chromosome orientation and segregation in plant, Dr. HAN’s group focuses on the genetics and epigenetics of plant centromere. They have established many dicentric chromosome lines in maize and wheat, of which one centromere is inactive (Gao et al. 2011; Fu et al. 2012). They also generate a series of different sized minichromosomes from break-fusion-bridge cycles, it was observed that some minichromosomes displayed bi-orientation in metaphase I, where the sister chromatids separated precociously in anaphase I and differs from the normal A chromosome (Han et al. 2007). They was the first to discover that phosphorylation of histone H2AThr133 was associated with centromere function and maintenance in plants (Dong and Han. 2012). They currently focus on the mechanism of centromere structure and its role in segregation and orientation during plant meiosis.
In this study, they worked on the poorly detailed mechanisms of H2AThr133ph and its kinases on chromosome orientation during cell division. They discovered that most CENH3 nucleosomes contain phosphorylated H2AThr133 in the centromeric regions, and H2AThr133ph expands to the entail centromeric regions during (pro)metaphase, and are currently looking into the temporal and spatial regulatory roles for H2A phosphorylation during chromosome segregation.
They also studied the Bub1-H2AT133ph-Sgo1 pathway and spindle assembly checkpoint (SAC) components in maize meiosis, which is rarely investigated in plants. They found that the ZmBub1-ZmSgo1-H2AThr133ph and ZmBub3 signals loads well on minichromosomes, afd1 mutants and Mis12 RNAi transgenic lines all with special orientation in meiosis I. These results indicating these pathways have no direct impact on function with sister centromere orientation during the meiosis I in maize.
The work entitled “Dynamic Location changes of Bub1-phosphorylated-H2AThr133 with CENH3 Nucleosome in Maize Centromeric Regions” was published in New Phytologiston January 12, 2017 (DOI:10.1111/nph.14415).
This work was supported by grants from the National Natural Science Foundation of China (31320103912).
Dynamic Location Changes of Histone H2A Phosphorylation in Centromeric Regions for Plant Chromosome Orientation and Segregation (Image by IGDB)
Dr. HAN Fangpu