Dear Editor,
Histone lysine methylation plays an essential role in regulating chromatin functions such as transcription and heterochromatin formation. Histone H3 lysine 4 (H3K4) methylation is linked to active transcription [1, 2]. Recent findings in mammals have demonstrated that histone methylation is reversible by a family of Jumonji C (JmjC) domain-containing proteins. KDMS/ JARID1 family proteins have been shown to be able to demethylate H3K4me1,2,3 in mammals [3].