NAT1/DAP5/p97 and Atypical Translational Control in the Drosophila Circadian Oscillator

Abstract

Circadian rhythms are driven by gene expression feedback loops in metazoans. Based on the success of genetic screens for circadian mutants in Drosophila melanogaster, we undertook a targeted RNAi screen to study the impact of translation control genes on circadian locomotor activity rhythms in flies. Knockdown of vital translation factors in timeless protein-positive circadian neurons caused a range of effects including lethality. Knockdown of the atypical translation factor NAT1 had the strongest effect and lengthened circadian period. It also dramatically reduced PER protein levels in pigment dispersing factor (PDF) neurons. BELLE (BEL) protein was also reduced by the NAT1 knockdown, presumably reflecting a role of NAT1 in belle mRNA translation. belle and NAT1 are also targets of the key circadian transcription factor Clock (CLK). Further evidence for a role of NAT1 is that inhibition of the target of rapamycin (TOR) kinase increased oscillator activity in cultured wings, which is absent under conditions of NAT1 knockdown. Moreover, the per 59-and 39-UTRs may function together to facilitate cap-independent translation under conditions of TOR inhibition. We suggest that NAT1 and cap-independent translation are important for per mRNA translation, which is also important for the circadian oscillator. A circadian translation program may be especially important in fly pacemaker cells.

A Role for Drosophila ATX2 in Activation of PER Translation and Circadian Behavior

“…They support the emerging notion that translational control is critical for the function of circadian pacemaker neurons (8, 9). Our results also emphasize that ATX2 can function as a translational activator, as well as a translational repressor (12–14).…”

Cap-independent translation by DAP5 controls cell fate decisions in human embryonic stem cells

“…Considering previous reports showing that the 3 ′ UTR can also contribute to cap-independent translation (Izquierdo and Cuezva 2000;Martinez-Salas et al 2008;Bradley et al 2012;Bukhari et al 2016;Weingarten-Gabbay et al 2016), IRESs or elements that affect IRES activity may have been missed in this screen. Future screens can be conducted to include the 3 ′ UTR in the reporter plasmids and expand the number of targets assayed.…”

Translational Control of Entrainment and Synchrony of the Suprachiasmatic Circadian Clock by mTOR/4E-BP1 Signaling

“…Indeed, several studies have reported the roles of the eIF4E and its binding proteins in circadian clock physiology. For example, knockdown of the eIF4G homolog, NAT1, significantly reduces PER expression and lengthens the behavioral period in Drosophila (Bradley et al, 2012). Moreover, a recent study reported that the clock coordinates ribosomal biogenesis in the liver by rhythmic activation of the mTOR/4E-BP1/eIF4E pathway (Jouffe et al, 2013).…”