In eukaryotes long sections of DNA in the genome can be tightly packed, which are called heterochromatin. These locally compacted heterochromatic loci are often further assembled into higher-order aggregates called heterochromatin bodies. Some examples like Chromocenters and Barr bodies, indicate that the heterochromatin bodies are important for the regulation of chromatin activities. However, the formation and function of these are only poorly understood.

In the protozoan Tetrahymena the formation of heterochromatin is accompanied by programmed DNA elimination. In a recent study, group leader Kazufumi Mochizuki and his postdoc Kensuke Kataoka from the Institute of Molecular Biotechnology (IMBA) showed that Jub1p, a novel heterochromatin body component, promotes heterochromatin body formation. Jub1p also promotes dephosphorylation of the Heterochromatin Protein 1 (HP1)-like protein Pdd1p. They as well demonstrated that Pdd1p dephosphorylation promotes the electrostatic interaction between Pdd1p and RNA, indicating that Pdd1p – RNA interaction underlies heterochromatin body formation.

Importantly Jub1p and Pdd1p dephosphorylation are required for DNA elimination. “We found that JUB1 KO cells as well as the cells expressing phosphor-mimetic PDD1 mutants show defects in heterochromatin body aggregation and DNA elimination without compromising local heterochromatin formation. These suggest that heterochromatin body per se plays a role in an essential biological process”, explains Mochizuki.  

Original Publication
Kataoka & Mochizuki. Phosphorylation of an HP1-like Protein Regulates Heterochromatin Body Assembly for DNA Elimination. Developmental Cell