Dear Editor,
Histone methylation is a reversible histone posttranslational modification that plays an important role in various chromatin-based processes,including chromatin structure remodeling,transcription,and DNA repair [1,2].LSD1 (also known as KDM1A) is the first identified histone lysine demethylase.It converts mono-or dimethylated histone H3 (H3K4mel/me2) to unmodified H3 [3].LSD1 is highly conserved in eukaryotes and plays important roles in various biological processes,such as development and tumorgenesis.LSD2 (also known as KDM1B or AOF1) is the only other mammalian paralogue of the LSD1 family.Similar to LSD1,LSD2 is also a histone H3K4mel/me2 demethylase [4-7].LSD1 has been shown to be enriched at promoter regions;in contrast,LSD2 mainly associates with the gene body regions of actively transcribed genes [5].LSD2 is highly expressed in oocytes,and is required for de novo DNA methylation of some imprinted genes,a function dependent on its H3K4 demethylase activity [4].Thus,LSD2 is an important player in epigenetic regulation and has functions distinct from those of LSD1.