Reevaluation ofDrosophila melanogaster's neuronal circadian pacemakers reveals new neuronal classes

Abstract

In the brain of the fly Drosophila melanogaster, ∼150 clock-neurons are organized to synchronize and maintain behavioral rhythms, but the physiological and neurochemical bases of their interactions are largely unknown. Here we reevaluate the cellular properties of these pacemakers by application of a novel genetic reporter and several phenotypic markers. First, we describe an enhancer trap marker called R32 that specifically reveals several previously undescribed aspects of the fly's central neuronal pacemakers. We find evidence for a previously unappreciated class of neuronal pacemakers, the lateral posterior neurons (LPNs), and establish anatomical, molecular, and developmental criteria to establish a subclass within the dorsal neuron 1 (DN1) group of pacemakers. Furthermore, we show that the neuropeptide IPNamide is specifically expressed by this DN1 subclass. These observations implicate IPNamide as a second candidate circadian transmitter in the Drosophila brain. Finally, we present molecular and anatomical evidence for unrecognized phenotypic diversity within each of four established classes of clock neurons. Indexing termsDrosophila; circadian clock; neuropeptides; PDF receptor; IPNamide; nplp1; glass Overt biological rhythms such as the predictable daily leaf movements of plants and the sleep/ wake cycle of animals are ultimately driven by molecular oscillations. Throughout the living world such oscillations are sustained by intracellular transcriptional/translational feedback loops (reviewed by Dunlap, 1999). In Drosophila many components of the molecular clock are known in detail. Products of the clock genes period (per), timeless (tim), Clock, cycle, vrille, and PAR domain protein 1 (Pdp1) form two interconnected and self-sustained transcriptional feedback loops, the kinetics of which are regulated by clock protein interactions and attendant kinases (recently reviewed by Hardin, 2004;Schöning and Staiger, 2005;Taghert and Lin, 2005). Although the core clock genes are expressed rhythmically throughout the fly's body, only a few small groups of clock-expressing neurons in the central brain (termed pacemakers) are necessary and sufficient for the organization and maintenance of rhythmic locomotor activity (reviewed by Hall, 2005;Helfrich-Förster, 2005). When these pacemaker *Correspondence to: Paul Taghert, Dept. Anatomy and Neurobiology, Washington University School of Medicine, 660 S. Euclid Ave., St. Louis, MO 63110. E-mail: taghertp@pcg.wustl.edu. Current address for S.C.P. Renn: Bauer Center for Genomics Research, Harvard University, 7 Divinity Ave., Rm. 249, Cambridge, MA 02138. NIH Public Access NIH-PA Author ManuscriptNIH-PA Author Manuscript NIH-PA Author Manuscript neurons of Drosophila are electrically silenced their molecular oscillations are lost under constant conditions, suggesting that electrical activity at the cell membrane is required for the endogenous molecular clockwork (Nitabach et al., 2002).Approximately 150 neurons express the dynamic molecular clockwork in the adult ...

Moonlight shifts the endogenous clock of Drosophila melanogaster

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Clk post-transcriptional control denoises circadian transcription both temporally and spatially

“…However, a group of B150 neurons in the brain drives circadian rhythms in locomotor activity 18 . These neurons have been divided into several subgroups based on their anatomical location and expression of the core clock genes 19,20 . These groups are small and large ventral lateral (sLNvs and lLNvs), dorsal lateral (LNds), and dorsal (DN1s, DN2s and DN3s) neurons.…”

Impaired clock output by altered connectivity in the circadian network

“…The one best understood encompasses the small ventral lateral neurons (LNvs), comprised of five cells, of which four rhythmically release the neuropeptide pigment dispersing factor (PDF) at their dorsal terminals. Other oscillators within the fly brain include the dorsal lateral neurons (LNds) together with the dorsal neurons (DN1-3) (2). Ablation of all LNvs by overexpression of proapoptotic genes, as well as null mutations on the pdf gene or its receptor, cause behavioral arrhythmicity a few days upon transfer to constant conditions (3)(4)(5)(6) likely through the gradual loss of synchronization among the components of the small LNv cluster (7).…”