The Lysine Demethylase dKDM2 Is Non-essential for Viability, but Regulates Circadian Rhythms in Drosophila.

Yani Zheng,Jian-Quan Ni,Yu Jia,Xiao Li,Mengmeng Liu,Xingjie Ren,Jun-Yuan Ji,Yong Zhang,Ye Niu,Yongbo Xue

doi:10.3389/fgene.2018.00354

Abstract

Post-translational modification of histones, such as histone methylation controlled by specific methyltransferases and demethylases, play critical roles in modulating chromatin dynamics and transcription in eukaryotes. Misregulation of histone methylation can lead to aberrant gene expression, thereby contributing to abnormal development and diseases such as cancer. As such, the mammalian lysine-specific demethylase 2 (KDM2) homologs, KDM2A and KDM2B, are either oncogenic or tumor suppressive depending on specific pathological contexts. However, the role of KDM2 proteins during development remains poorly understood. Unlike vertebrates, Drosophila has only one KDM2 homolog (dKDM2), but its functions in vivo remain elusive due to the complexities of the existing mutant alleles. To address this problem, we have generated two dKdm2 null alleles using the CRISPR/Cas9 technique. These dKdm2 homozygous mutants are fully viable and fertile, with no developmental defects observed under laboratory conditions. However, the dKdm2 null mutant adults display defects in circadian rhythms. Most of the dKdm2 mutants become arrhythmic under constant darkness, while the circadian period of the rhythmic mutant flies is approximately 1 h shorter than the control. Interestingly, lengthened circadian periods are observed when dKDM2 is overexpressed in circadian pacemaker neurons. Taken together, these results demonstrate that dKdm2 is not essential for viability; instead, dKDM2 protein plays important roles in regulating circadian rhythms in Drosophila. Further analyses of the molecular mechanisms of dKDM2 and its orthologs in vertebrates regarding the regulation of circadian rhythms will advance our understanding of the epigenetic regulations of circadian clocks.

Highlights

Covalent histone modifications, methylation and acetylation of lysine (K) residues on the N-terminal tails of histones H3 and H4, play fundamental roles in epigenetic regulation of gene expression in eukaryotes
The Drosophila has only one KDM2 homolog (dKDM2) protein is not detectable from the mutant larvae as assayed by a Western blot (Figure 1E). These analyses demonstrate that dKdm21 and dKdm22 disrupt the dKdm2 locus
The mRNA level of beag, a neighboring gene of dKdm2, is reduced in the dKdm22 mutants, as assayed by multiple repeats. Our analyses with both these alleles did not reveal any difference between them. These results show that both dKdm21 and dKdm22 are null alleles

Summary

Introduction

Methylation and acetylation of lysine (K) residues on the N-terminal tails of histones H3 and H4, play fundamental roles in epigenetic regulation of gene expression in eukaryotes. The addition or removal of methyl groups to lysine residues is dynamically modulated by specific lysine methyltransferases (KMTs) and lysine demethylases dKDM2 Regulates Circadian Rhythms (KDMs), respectively (Shi and Whetstine, 2007; Black et al, 2012). These enzymes are highly conserved in the evolution of eukaryotes (Zhou and Ma, 2008; Zhang and Ma, 2012; Qian et al, 2015). The in vivo function and regulation of these enzymes in developmental, physiological, and pathological contexts are still not fully understood (Nottke et al, 2009; Dimitrova et al, 2015)

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