Translational Regulation of the DOUBLETIME/CKIδ/ε Kinase by LARK Contributes to Circadian Period Modulation

Abstract

The Drosophila homolog of Casein Kinase I δ/ε, DOUBLETIME (DBT), is required for Wnt, Hedgehog, Fat and Hippo signaling as well as circadian clock function. Extensive studies have established a critical role of DBT in circadian period determination. However, how DBT expression is regulated remains largely unexplored. In this study, we show that translation of dbt transcripts are directly regulated by a rhythmic RNA-binding protein (RBP) called LARK (known as RBM4 in mammals). LARK promotes translation of specific alternative dbt transcripts in clock cells, in particular the dbt-RC transcript. Translation of dbt-RC exhibits circadian changes under free-running conditions, indicative of clock regulation. Translation of a newly identified transcript, dbt-RE, is induced by light in a LARK-dependent manner and oscillates under light/dark conditions. Altered LARK abundance affects circadian period length, and this phenotype can be modified by different dbt alleles. Increased LARK delays nuclear degradation of the PERIOD (PER) clock protein at the beginning of subjective day, consistent with the known role of DBT in PER dynamics. Taken together, these data support the idea that LARK influences circadian period and perhaps responses of the clock to light via the regulated translation of DBT. Our study is the first to investigate translational control of the DBT kinase, revealing its regulation by LARK and a novel role of this RBP in Drosophila circadian period modulation.

Transcriptome dynamics over a lunar month in a broadcast spawning acroporid coral

“…The identified rbm38 gene has not previously been shown to function in clocks, but a related RRM gene, rbm4/lark , regulates circadian phase periodicity in Drosophila (Huang et al . ) and likely functions in the Acropora clock. Other highly significant differences were observed in genes driving skeletogenesis and those producing components of the extracellular matrix/skeletogenic organic matrix (ECM/SOM; Fig.…”

TRAP-seq Profiling and RNAi-Based Genetic Screens Identify Conserved Glial Genes Required for Adult Drosophila Behavior

“…We utilized methods identical to our published studies (Huang et al, 2013, 2014, 2015) to isolate ribosomes and translating RNAs from adult fly astrocytes; the protocols are outlined in detail in a recent review (Jackson et al, 2015). The current study utilized a Gal4 driver ( alrm-Gal4 ) that expresses in fly astrocytes but not in CNS neurons or other glial cell types (Doherty et al, 2009) to drive expression of a characterized UAS-EGFP-L10a transgene (Huang et al, 2013; encoding an EGFP-tagged L10a ribosomal subunit).…”

The molecular ticks of the Drosophila circadian clock

“…This protein is required for normal eclosion and locomotor activity rhythms [51], and is expressed rhythmically with a peak late during the day [52]. A recent study has shown that LARK promotes DBT expression by binding to dbt mRNAs, and indicates that this interaction controls circadian period length [53]. …”