A Role for the Segment Polarity Gene shaggy/GSK-3 in the Drosophila Circadian Clock

Abstract

Tissue-specific overexpression of the glycogen synthase kinase-3 (GSK-3) ortholog shaggy (sgg) shortens the period of the Drosophila circadian locomotor activity cycle. The short period phenotype was attributed to premature nuclear translocation of the PERIOD/TIMELESS heterodimer. Reducing SGG/GSK-3 activity lengthens period, demonstrating an intrinsic role for the kinase in circadian rhythmicity. Lowered sgg activity decreased TIMELESS phosphorylation, and it was found that GSK-3 beta specifically phosphorylates TIMELESS in vitro. Overexpression of sgg in vivo converts hypophosphorylated TIMELESS to a hyperphosphorylated protein whose electrophoretic mobility, and light and phosphatase sensitivity, are indistinguishable from the rhythmically produced hyperphosphorylated TIMELESS of wild-type flies. Our results indicate a role for SGG/GSK-3 in TIMELESS phosphorylation and in the regulated nuclear translocation of the PERIOD/TIMELESS heterodimer.

Lithium- and Valproate-Induced Alterations in Circadian Locomotor Behavior in Drosophila

“…By studying double mutants of doubletime and shaggy, it could be possible to define the epistatic relationships of these two genes with relationship to circadian period changes induced by lithium. Based on the circadian phenotype of Drosophila mutants lacking GSK-3b activity (Martinek et al, 2001), and based on our data and that of others (Padiath et al, 2004), we propose that lithium increases the circadian period by inhibiting GSK-3b. These experiments strongly suggest that the fly's response to lithium is similar to that of rodents as reported before (Abe et al, 2000;Iwahana et al, 2004).…”

“…GSK-3b (shaggy) mutants were isolated through an EPelement insertion screen using timeless-GAL4 as a driver, which misexpressed many genes in the neurons that expressed the timeless clock gene (Martinek et al, 2001). We tested flies heterozygous for a null GSK-3b mutation, flies that expressed GSK-3b ubiquitously when given heat treatments, and flies that expressed GSK-3b under pdf promoter control.…”

“…Since GSK-3b null mutations produce lethality in flies, it is not possible to test the homozygous loss-of-function phenotype of this mutation directly. Young and co-workers (Martinek et al, 2001) devised a recovery design with which they rescued GSK-3b expression during metamorphosis. These flies subsequently had very little GSK-3b function left and they displayed very long periods.…”

“…It is significant that Drosophila shaggy mutants lacking GSK-3b activity display lengthening of the circadian period (Martinek et al, 2001). In humans, a single nucleotide polymorphism in the GSK-3b promoter region has been reported to correlate with the onset of bipolar disorder (Benedetti et al, 2004).…”

Assessment of circadian function in fibroblasts of patients with bipolar disorder

“…52 In addition, the PAR-leucine zipper transcription factor albumin D element-binding protein (DBP) is a first-order clock-controlled gene directly regulated by BMAL1/ CLOCK; 53 it also plays a role in the core clock by activating Per1 transcription. 54 Kinases such as CKId, 55,56 CKIe 57,58 and GSK3b 25,59 play an important role in phosphorylation of clock proteins, thus regulating the activity, nuclear entry and degradation of various core clock components. Among these kinases, GSK3b is of particular interest here because it was reported to be one of the direct targets of lithium, 60 which is an effective therapy for bipolar disorder.…”