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A role for casein kinase 2α in the Drosophila circadian clock


Circadian clocks drive rhythmic behaviour in animals and are regulated by transcriptional feedback loops1,2. For example, the Drosophila proteins Clock (Clk) and Cycle (Cyc) activate transcription of period (per) and timeless (tim). Per and Tim then associate, translocate to the nucleus, and repress the activity of Clk and Cyc. However, post-translational modifications are also critical to proper timing. Per and Tim undergo rhythmic changes in phosphorylation1, and evidence supports roles for two kinases in this process: Doubletime (Dbt) phosphorylates Per3,4, whereas Shaggy (Sgg) phosphorylates Tim5. Yet Sgg and Dbt often require a phosphoserine in their target site6,7, and analysis of Per phosphorylation in dbt mutants3,8 suggests a role for other kinases. Here we show that the catalytic subunit of Drosophila casein kinase 2 (CK2α) is expressed predominantly in the cytoplasm of key circadian pacemaker neurons. CK2α mutant flies show lengthened circadian period, decreased CK2 activity, and delayed nuclear entry of Per. These effects are probably direct, as CK2α specifically phosphorylates Per in vitro. We propose that CK2 is an evolutionary link between the divergent circadian systems of animals, plants and fungi.

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Figure 1: Biochemical activity of wild-type and mutant CK2α.
Figure 2: Drosophila CK2α is primarily expressed in circadian pacemaker cells.
Figure 3: Circadian regulation of Per and Tim in CK2α mutants.
Figure 4: Nuclear entry of Per in homozygous CK2α mutants. +, wild type; T, Tik/Tik homozygotes; R, TikR/TikR homozygotes.
Figure 5: Phosphorylation by CK2α is period-specific.


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We thank J. Rutila for assistance and guidance in conducting the genetic screen; J. Biswas for assistance with sequencing; A. McElvaine for cloning; L. McCarty for western blots; R. Scharnweber for helping to set up the CK2 activity assays; Bloomington Stock Center for fly stocks; C. Glover for CK2 antibodies; and the Northwestern University Biological Imaging Facility for assistance with confocal microscopy.

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Correspondence to Ravi Allada.

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Lin, JM., Kilman, V., Keegan, K. et al. A role for casein kinase 2α in the Drosophila circadian clock. Nature 420, 816–820 (2002).

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