Our recent progress in epigenetic research using the model ciliate, Tetrahymena thermophila

Epigenetic research focuses on heritable changes beyond the DNA sequence, which has led to a revolution in biological studies and benefits in many other fields. The well-known model ciliate, Tetrahymena thermophila offers a unique system for epigenetic studies due to its nuclear dimorphism and special mode of sexual reproduction (conjugation), as well as abundant genomic resources and genetic tools. In this paper, we summarize recent progress made by our research team and collaborators in understanding epigenetic mechanisms using Tetrahymena. This includes: (1) providing the first genome-wide base pair-resolution map of DNA N⁶-methyladenine (6mA) and revealed it as an integral part of the chromatin landscape; (2) dissecting the relative contribution of cis- and trans- elements to nucleosome distribution by exploring the unique nuclear dimorphism of Tetrahymena; (3) demonstrating the epigenetic controls of RNAi-dependent Polycomb repression pathways on transposable elements, and (4) identifying a new histone monomethyltransferase, TXR1 (Tetrahymena Trithorax 1), that facilitates replication elongation through its substrate histone H3 lysine 27 monomethylation (H3K27me1).