Using Drosophila eclosion to genetically dissect how central and peripheral clocks and the endocrine system interact to time behaviour

• Applicant: Professor Dr. Christian Wegener
• Subject Area: Cognitive, Systems and Behavioural Neurobiology ; Animal Physiology and Biochemistry
• Term: from 2018 to 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 398112454

• Final Report Year: 2023

Final Report Abstract

Animals time and synchronise development and physiological activity of the different body systems in order to survive. Similarly, they adjust behaviour and physiological activity to the temporal structure of the environment. Timing and synchronisation of different body systems and behaviour requires a timer (central and peripheral endogenous clocks) and an integrating communication system (the neuroendocrine system). Yet, we know astonishingly little about the complex pathways and underlying molecular and cellular mechanisms by which endogenous clocks and neuroendocrine systems interact with each other. Here, we used the timing of eclosion in the fruit fly Drosophila as a model to dissect the interactions between central and peripheral clocks, developmental and circadian timers and the neuroendocrine system. Previous work showed that eclosion timing requires the central clock in the brain and a peripheral clock in the prothoracic gland (PG) which produces ecdysteroids. Neurons producing the peptide PTTH couple those two clocks, and receive input from small ventral lateral neurons (sLNvs), pace-maker neurons of the central clock. In the project, we successfully defined when during development and during the day PTTH signalling is active. We found that for rhythmic eclosion, PTTH signalling is required at the end of pupal development. PTTH signalling seems inactive in early pupal development, but becomes active with a circadian activity pattern two days prior to eclosion. These findings provide strong evidence that PTTH, besides its known role in developmental timing, in fact also represents a circadian signal in Drosophila. We further found strong evidence that the previously established connection from sLNv to PTTH neurons to the PG is the only required neuroendocrine pathway that couples the central and PG clock for eclosion timing. Juvenile hormone and insulin, other major endocrine developmental signals besides ecdysteroids, seem not to be involved. Also the transient PDF-expressing Trineurons seem not to be involved in eclosion rhythmicity. While we found that PTTH neurons express receptors for further clock-derived peptides, none of these peptides influenced eclosion rhythmicity. Eclosion hormone (EH) is a key signal to initiate and maintain eclosion motor patterns. We tested the role of the EH neurons as a hub between developmental and circadian timing. Recently developed transsynaptic tracer methodols allowed us to comprehensively characterise the connectivity of clock neurons with EH neurons. We found that sLNvs and several other clock neuron subgroups are presynaptic to EH neurons. Moreover, EH neurons express receptors for various peptides expressed by clock neurons. The identified connections may be important for eclosion rhythmicity as silencing the whole central clock network or the PDF-positive neurons led to arrhythmic eclosion. Silencing of other individual clock cell subclusters, however, had little effect on eclosion rhythmicity. Using the same approach, we also identified peripheral sensory neurons as modulators of EH neuron activity. Our results emphasise the key role of the sLNv for eclosion rhythmicity, and define a role for PTTH as a circadian timer in Drosophila. Importantly, we were able to identify a clock-expressed peptide as a potential key signal by which the brain can inhibit or delay eclosion; a result that we would like to follow up in the future.

Publications

• Natural Zeitgebers Under Temperate Conditions Cannot Compensate for the Loss of a Functional Circadian Clock in Timing of a Vital Behavior in Drosophila. Journal of Biological Rhythms, 36(3), 271-285.
  Ruf, Franziska; Mitesser, Oliver; Mungwa, Simon Tii; Horn, Melanie; Rieger, Dirk; Hovestadt, Thomas & Wegener, Christian
  
• A rhythmic temporal pattern of PTTH signaling and its modulation during pupal-adult transition in Drosophila. 114. Annual Meeting of the German Zoological Society Bonn.
  Amini E. & Wegener C.
  
• Chemoconnectomics and timing of PTTH signaling during eclosion gating in Drosophila. Neurofly 2022, St. Malo, France.
  Amini E., Stanewsky R., Zandawala M. & Wegener C.
  
• The tracheal dendrite neurons of Drosophila modulate eclosion behaviour but not its rhythmicity. 114. Annual Meeting of the German Zoological Society Bonn.
  Grimm S., Amini E., Zandawala M. & Wegener C.
  
• Timed receptor tyrosine kinase signaling couples the central and a peripheral circadian clock inDrosophila. Cold Spring Harbor Laboratory.
  Cavieres-Lepe, Javier; Amini, Emad; Nässel, Dick R.; Stanewsky, Ralf; Wegener, Christian & Ewer, John