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A role for microRNAs in the Drosophila circadian clock.

ABSTRACT: Little is known about the contribution of translational control to circadian rhythms. To address this issue and in particular translational control by microRNAs (miRNAs), we knocked down the miRNA biogenesis pathway in Drosophila circadian tissues. In combination with an increase in circadian-mediated transcription, this severely affected Drosophila behavioral rhythms, indicating that miRNAs function in circadian timekeeping. To identify miRNA-mRNA pairs important for this regulation, immunoprecipitation of AGO1 followed by microarray analysis identified mRNAs under miRNA-mediated control. They included three core clock mRNAs-clock (clk), vrille (vri), and clockworkorange (cwo). To identify miRNAs involved in circadian timekeeping, we exploited circadian cell-specific inhibition of the miRNA biogenesis pathway followed by tiling array analysis. This approach identified miRNAs expressed in fly head circadian tissue. Behavioral and molecular experiments show that one of these miRNAs, the developmental regulator bantam, has a role in the core circadian pacemaker. S2 cell biochemical experiments indicate that bantam regulates the translation of clk through an association with three target sites located within the clk 3' untranslated region (UTR). Moreover, clk transgenes harboring mutated bantam sites in their 3' UTRs rescue rhythms of clk mutant flies much less well than wild-type CLK transgenes.

SUBMITTER: Kadener S

PROVIDER: S-EPMC2751990 | biostudies-literature | 2009 Sep

REPOSITORIES: biostudies-literature

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A role for microRNAs in the Drosophila circadian clock.

Kadener Sebastian S Menet Jerome S JS Sugino Ken K Horwich Michael D MD Weissbein Uri U Nawathean Pipat P Vagin Vasia V VV Zamore Phillip D PD Nelson Sacha B SB Rosbash Michael M

Genes & development 20090820 18

Little is known about the contribution of translational control to circadian rhythms. To address this issue and in particular translational control by microRNAs (miRNAs), we knocked down the miRNA biogenesis pathway in Drosophila circadian tissues. In combination with an increase in circadian-mediated transcription, this severely affected Drosophila behavioral rhythms, indicating that miRNAs function in circadian timekeeping. To identify miRNA-mRNA pairs important for this regulation, immunoprec ...[more]

PMID: 19696147

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Project description:Cell-autonomous feedback loops underlie the molecular oscillations that define circadian clocks. In Drosophila the transcription factor Clk activates multiple clock components of feedback loops many of which feed back and regulate Clk expression or activity. Previously the authors evoked similar molecular oscillations in putatively naïve neurons in Drosophila by ectopic expression of a single gene, Clk, suggesting a master regulator function. Using molecular oscillations of the core clock component PERIOD (PER), the authors observed dramatic and widespread molecular oscillations throughout the brain in flies expressing ectopic Clk. Consistent with the master regulator hypothesis, they found that Clk is uniquely capable of inducing ectopic clocks as ectopic induction of other clock components fails to induce circadian rhythms. Clk also induces oscillations even when expression is adult restricted, suggesting that ectopic clocks can even be induced in differentiated cells. However, if transgene expression is discontinued, PER expression disappears, indicating that Clk must be continually active to sustain ectopic clock function. In some cases Clk-mediated PER induction was observed without apparent synchronous cycling, perhaps due to desynchronization of rhythms between clocks or truly cell autonomous arrhythmic PER expression, indicating that additional factors may be necessary for coherent rhythms in cells ectopically expressing Clk. To determine minimal requirements for circadian clock induction by Clk, the authors determined the genetic requirements of ectopic clocks. No ectopic clocks are induced in mutants of Clk's heterodimeric partner cyc. In addition, noncycling PER is observed when ectopic Clk is induced in a cryb mutant background. While other factors may contribute, these results indicate that persistent Clock induction is uniquely capable of broadly inducing ectopic rhythms even in adults, consistent with a special role at the top of a clock gene hierarchy.

Project description:BackgroundTranscriptional feedback loops are central to circadian clock function. However, the role of neural activity and membrane events in molecular rhythms in the fruit fly Drosophila is unclear. To address this question, we expressed a temperature-sensitive, dominant negative allele of the fly homolog of dynamin called shibire(ts1) (shi(ts1)), an active component in membrane vesicle scission.Principal findingsBroad expression in clock cells resulted in unexpectedly long, robust periods (>28 hours) comparable to perturbation of core clock components, suggesting an unappreciated role of membrane dynamics in setting period. Expression in the pacemaker lateral ventral neurons (LNv) was necessary and sufficient for this effect. Manipulation of other endocytic components exacerbated shi(ts1)'s behavioral effects, suggesting its mechanism is specific to endocytic regulation. PKA overexpression rescued period effects suggesting shi(ts1) may downregulate PKA pathways. Levels of the clock component PERIOD were reduced in the shi(ts1)-expressing pacemaker small LNv of flies held at a fully restrictive temperature (29 degrees C). Less restrictive conditions (25 degrees C) delayed cycling proportional to observed behavioral changes. Levels of the neuropeptide PIGMENT-DISPERSING FACTOR (PDF), the only known LNv neurotransmitter, were also reduced, but PERIOD cycling was still delayed in flies lacking PDF, implicating a PDF-independent process. Further, shi(ts1) expression in the eye also results in reduced PER protein and per and vri transcript levels, suggesting that shibire-dependent signaling extends to peripheral clocks. The level of nuclear CLK, transcriptional activator of many core clock genes, is also reduced in shi(ts1) flies, and Clk overexpression suppresses the period-altering effects of shi(ts1).ConclusionsWe propose that membrane protein turnover through endocytic regulation of PKA pathways modulates the core clock by altering CLK levels and/or activity. These results suggest an important role for membrane scission in setting circadian period.

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A role for microRNAs in the Drosophila circadian clock.

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A role for microRNAs in the Drosophila circadian clock.

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