Circadian period integrates network information through activation of the BMP signaling pathway

CERIANI, MF

Newport, LI

Congreso; Gordon Research Conference on Chronolobiology.; 2013

Living organisms use biological clocks to maintain internal temporal order and anticipate daily environmental changes. Clocks employ self‐sustained biochemical oscillators that express at molecular, physiological and behavioral levels. In Drosophila, over 150 neurons are implicated in circadian regulation of locomotor behavior but the small ventral lateral neurons (sLNvs) are clearly central. They express and release the neuropeptide Pigment Dispersing Factor (PDF) and set the period of locomotor behavior under free running conditions (in constant darkness, DD). To identify additional components involved in sending or receiving information relevant for synchronization of the circadian network a missexpression screen was carried out through deregulation of gene expression specifically in PDF+ cells. As a result a fly strain that causes period lengthening of daily activity rhythms was singled out. The transposon landed within schnurri (shn), a nuclear component of the BMP signalling pathway. During development, activation of the BMP pathway acts as a retrograde signal to define synaptic properties according to the requirement of specific stages. We found that shn overexpression in the PDF circuit is necessary and sufficient to generate a 25.5h period of locomotor behavior, while downregulation of shn levels resulted in deconsolidated activity rhythms. Deregulation of canonical components of the BMP pathway triggered similar (though more pronounced) phenotypes, underscoring that the entire pathway plays a role in defining this essential property of the molecular clock. Strikingly, adult‐specific activation of BMP signalling in PDF+ cells is sufficient for period lengthening. To gain insight into the molecular mechanism a detailed analysis of PERIOD (PER) subcellular localization was carried out during the transition from DD3 to DD4. As predicted from the behavioral phenotype, PER nuclear entry was delayed upon shn overexpression, suggesting that pathway activation leads to downregulation of PER protein levels; in support of this possibility concomitant overexpression of PER (and CLOCK) rescued the long period shn phenotype. Additional experiments including transcriptional reporter lines supported the notion that shn overexpression (i.e., pathway activation) results in reduced CLOCK levels. We propose that controlled activation of the BMP pathway through the postsynaptic release of specific ligands is required to fine‐tune circadian period in the adult brain. Thus, adult circadian period would integrate both, the pace of the cell autonomous molecular clock and information derived by other circadian relevant clusters to ensure coherence in the network.