PERIOD-controlled deadenylation of the timeless transcript in the Drosophila circadian clock

Abstract

The Drosophila circadian oscillator relies on a negative transcriptional feedback loop, in which the PERIOD (PER) and TIMELESS (TIM) proteins repress the expression of their own gene by inhibiting the activity of the CLOCK (CLK) and CYCLE (CYC) transcription factors. A series of posttranslational modifications contribute to the oscillations of the PER and TIM proteins but few posttranscriptional mechanisms have been described that affect mRNA stability. Here we report that down-regulation of the POP2 deadenylase, a key component of the CCR4-NOT deadenylation complex, alters behavioral rhythms. Downregulating POP2 specifically increases TIM protein and tim mRNA but not tim pre-mRNA, supporting a posttranscriptional role. Indeed, reduced POP2 levels induce a lengthening of tim mRNA poly(A) tail. Surprisingly, such effects are lost in per 0 mutants, supporting a PERdependent inhibition of tim mRNA deadenylation by POP2. We report a deadenylation mechanism that controls the oscillations of a core clock gene transcript. circadian rhythms | clock genes | mRNA poly(A) tail | CAF1/POP2 | CCR4-NOT complex

Drosophila PSI controls circadian period and the phase of circadian behavior under temperature cycle via tim splicing

“…Interestingly, two genes implicated in mRNA decapping triggered by deadenylation, were also identified, with long periods observed when these genes were downregulated. Moreover, POP2, a CCR4-NOT component, was recently shown to regulate tim mRNA and protein levels (Grima et al, 2019). Another gene isolated in our screen, SMG5, was also recently found to impact circadian behavior (Ri et al, 2019).…”

“…Future work will be required to determine whether these factors directly target mRNAs encoding for core clock components, or whether their effect on circadian period is indirect. Interestingly, the POP2 deadenylase, which is part of the CCR4-NOT complex, was recently shown to regulate tim mRNA levels post-transcriptionally (Grima et al, 2019). It should be noted that while our screen targeted 364 proteins binding or associated with RNA, it did not include all of them.…”

Roles of peripheral clocks: lessons from the fly

“…miRNAs emerged as an important regulator of core clock genes in Drosophila: Clk is regulated by miRNA bantam [15], cwo by lethal-7 (let-7) [16], tim by miR-276a [17] and miR-375 [18]. The repressors per and tim are under further posttranscriptional regulation, including activation of per translation by Ataxin 2 (ATX2) [19,20], Twenty-four (TYF) [21] and LSM12, a component of ATX2-TYF complex [22], and control of tim mRNA poly(A) tail length by POP2 deadenylase [23]. Finally, posttranslational modifications (glycosylation, acetylation, sumoylation, and phosphorylation) regulate numerous aspects of clock protein function and metabolism, including, stability, nuclear translocation, DNA binding, potency of transcription and repression, and interaction with other core clock proteins (reviewed in [24]).…”

“…Co/posttranscriptional and translational regulation mechanisms, such as alternative splicing, alternative polyadenylation, regulation of polyA tail length, RNA editing, and miRNA-mediated silencing, are tissue-specific [155][156][157][158]. Remarkably, these mechanisms are either regulated by circadian clocks [123,159,160], or directly target the core clock and/or its output [23,66,80,161,162] and may further diversify tissue-specific circadian transcriptomes and proteomes.…”

CK2 Inhibits TIMELESS Nuclear Export and Modulates CLOCK Transcriptional Activity to Regulate Circadian Rhythms

“…During the day, CLK-CYC heterodimers activate the transcription of per, tim, and other clock-controlled genes (ccgs). 5 The accumulation of PER and TIM proteins is delayed by a number of post-transcriptional and post-translational mechanisms [6][7][8][9][10] until early night, when PER and TIM attain high enough levels to form heterodimeric complexes in the cytoplasm prior to nuclear entry. 11,12 Nuclear PER, likely still in complex with TIM, promotes the repression of the circadian transcriptome by inhibiting CLK-CYC transcriptional activity and removing them from clock genes before its degradation in the late night and early day.…”