TRITHORAX-dependent arginine methylation of HSP68 mediates circadian repression by PERIOD in the monarch butterfly

• Published in: Proceedings of the National Academy of Sciences - PNAS Vol. 119; no. 4; p. 1
• Main Authors: Zhang, Ying, Iiams, Samantha E, Menet, Jerome S, Hardin, Paul E, Merlin, Christine
• Format: Journal Article
• Language: English
• Published: United States National Academy of Sciences 25.01.2022
• Subjects: Amino Acid Sequence; Animals; Arginine - metabolism; Binding; Biological clocks; Biological Sciences; BMAL1 protein; Butterflies - physiology; Catalytic activity; Chromosomal Proteins, Non-Histone - metabolism; Circadian rhythm; Circadian Rhythm - genetics; Circadian rhythms; Conserved Sequence; Danaus plexippus; Deoxyribonucleic acid; DNA; Eukaryotes; Exons; Feedback loops; Gene silencing; Heat shock proteins; Heat-Shock Proteins - genetics; Heat-Shock Proteins - metabolism; Histone methyltransferase; Homology; Intracellular Signaling Peptides and Proteins; Mammals; Methylation; Models, Biological; Muscles; Period Circadian Proteins - metabolism; Transcription activation; Transcriptional Activation; insect; heat shock protein; arginine methylation; PERIOD; TRITHORAX
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.2115711119

Transcriptional repression drives feedback loops that are central to the generation of circadian (∼24-h) rhythms. In mammals, circadian repression of circadian locomotor output cycles kaput, and brain and muscle ARNT-like 1 (CLOCK:BMAL1)-mediated transcription is provided by a complex formed by PERIOD (PER) and CRYPTOCHROME (CRY) proteins. PER initiates transcriptional repression by binding CLK:BMAL1, which ultimately results in their removal from DNA. Although PER's ability to repress transcription is widely recognized, how PER binding triggers repression by removing CLK:BMAL1 from DNA is not known. Here, we use the monarch butterfly as a model system to address this problem because it harbors a simplified version of the CLK:BMAL1-activated circadian clock present in mammals. We report that an intact CLOCK mouse exon 19 homologous region (CLKe19r) and the histone methyltransferase TRITHORAX (TRX) are both necessary for monarch CLK:BMAL1-mediated transcriptional activation, CLK-PER interaction, and PER repression. Our results show that TRX catalytic activity is essential for CLK-PER interaction and PER repression via the methylation of a single arginine methylation site (R45) on heat shock protein 68 (HSP68). Our study reveals TRX and HSP68 as essential links between circadian activation and PER-mediated repression and suggests a potential conserved clock function for HSPs in eukaryotes.