Drosophilaclock cells use multiple mechanisms to transmit time-of-day signals in the brain

Abstract

Regulation of circadian behavior and physiology by the Drosophila brain clock requires communication from central clock neurons to downstream output regions, but the mechanism by which clock cells regulate downstream targets is not known. We show here that the pars intercerebralis (PI), previously identified as a target of the morning cells in the clock network, also receives input from evening cells. We determined that morning and evening clock neurons have time of day dependent connectivity to the PI, which is regulated by specific peptides as well as by fast neurotransmitters. Interestingly, PI cells that secrete the peptide DH44, and control rest:activity rhythms, are inhibited by clock inputs while insulin-producing cells are activated, indicating that the same clock cells can use different mechanisms to drive cycling in output neurons. Inputs of morning cells to the DILP2+ neurons are relevant for the circadian rhythm of feeding, reinforcing the role of the PI as a circadian relay that controls multiple behavioral outputs. Our findings provide mechanisms by which clock neurons signal to non-clock cells to drive rhythms of behavior.

Dorsal clock neurons in Drosophila sculpt locomotor outputs but are dispensable for circadian activity rhythms

“…Indeed, the pace of DN1 molecular clock cycling is dictated by the speed of cycling in lateral clock cells ( Chatterjee et al., 2018 ; Stoleru et al., 2005 ; Yao et al., 2016 ; Zhang et al., 2010a ). Also consistent with an output function for DN1 cells is the fact that they are synaptically and functionally connected to multiple groups of non-clock output cells ( Barber et al., 2021 ; 2016 ; Cavanaugh et al., 2014 ; Guo et al., 2018 ; Jin et al., 2021 ; Lamaze et al., 2018 ; Tabuchi et al., 2018 ; Zhang et al., 2021a , 2021b ). Together, these results suggest a hierarchical organization, with DN1s lying downstream of the lateral clock neurons and serving as intermediaries that propagate pacemaker-derived circadian information to output regions that control behaviors.…”

“…In support of this model, we also demonstrated that DN1p axons make close anatomical contact with PI output cells. Recently, this connectivity has been functionally confirmed through calcium imaging of PI cells during genetic activation of DN1p neurons ( Barber et al., 2021 ; Jin et al., 2021 ). However, given our current results that indicate that rest:activity rhythms persist in the face of Kir2.1 eGFP -mediated silencing of DN1p cells, it is clear that this DN1p to PI connection is not strictly necessary for circadian regulation of behavior.…”

Synaptic connectome of theDrosophilacircadian clock

“…While recent work has unraveled some clock output pathways to endocrine cells, our collective understanding of the circadian regulation of endocrine rhythms is poor (Nagy et al, 2019, King and Sehgal, 2020, Barber et al, 2021, Hidalgo et al, 2023. To address this knowledge gap, we first identified and classified all endocrine or NSC in the brain which are a major source of circulating hormones.…”

“…Nonetheless, given the rich array of neuropeptides expressed in clock neurons, both synaptic and paracrine signaling appear crucial in mediating the connectivity between clock neurons as well as their output pathways. While recent work has begun to uncover some of this connectivity (Cavanaugh et al, 2014, Nagy et al, 2019, Barber et al, 2021, Reinhard et al, 2022a, Reinhard et al, 2022b, Shafer et al, 2022, Hidalgo et al, 2023, Kurogi et al, 2023, global analyses encompassing entire neuronal networks across both brain hemispheres are lacking.…”

“…While recent work has begun to uncover some of this connectivity (Nagy et al, 2019, Barber et al, 2021, Reinhard et al, 2022a, Reinhard et al, 2022b, Shafer et al, 2022, Hidalgo et al, 2023, global analyses encompassing entire neuronal networks across both brain hemispheres are lacking.…”