Output from the central clock controlling Drosophila circadian behavior [electronic resource].

Su, Henry.
130 p.
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The Drosophila central clock, located in ventral lateral neurons (LNvs), endogenously keeps time and generates a wide range of circadian rhythms. Molecular basis of the central oscillator depends on rhythmic expression of period and timeless which dictates expression of cycling outputs. period and timeless mutants affect rhythmic levels of Pigment Dispersing Factor (PDF), an important neuropeptide secreted by the LNvs. Absence of pdf results in behavioral arrhythmicity. This dissertation attempts to address issues pertaining to control of circadian output by elucidating mechanisms of PDF signal transmission, determining neuroanatomical regions downstream of the clock, and searching for novel output genes.
Conditions controlling PDF release from lateral neurons are unclear. Using an ex vivo system, we altered extracellular ionic concentrations of larval lateral neuron (LN) explants and immunostained for PDF. Levels of PDF were dependent on the presence of extracellular Ca2+ and depolarizing conditions. This observation was seen in LN cell bodies but not terminals indicating extrasynaptic PDF release.
Neuroanatomical regions that communicate with the central clock have not yet been identified. Utilizing the recent discovery that Ras/MAPK signaling is an output pathway from the central clock, we localized activation of MAPK (phosphoMAPK) to CNS regions with PDF positive terminals. We also demonstrated cycling of phosphoMAPK in dorsal protocerebral CNS neurons adjacent to dorsal PDF termini (the only LNv projections with PDF cycling). Identification of these phosphoMAPK cycling neurons was pursued utilizing mosaic technology. Mosaic mutants for Nfl (an upstream effector of MAPK output), failed to localize specific neuroanatomical regions for Nfl/Ras/MAPK signaling indicating that MAPK activation may exist in many CNS regions to control circadian behaviors.
Finally, employing a screen for novel candidate genes associated with MAPK activation, we identified P11, a putative G-protein coupled receptor. Pan-neuronal P11 overexpression leads to locomotor and eclosion arrhythmia, which is preceded by a period of rhythmic behavior. Restricted overexpression in tim expressing neurons did not affect rhythmic locomotor activity suggesting that P11 interferes with output and not central clock function. P11 overexpression induced arrhythmia appears not to directly involve MAPK activation, but instead affects levels and cycling of a CRE-luciferase reporter construct.
Source: Dissertation Abstracts International, Volume: 64-04, Section: B, page: 1642.
Supervisor: Amita Sehgal.
Thesis (Ph.D.)--University of Pennsylvania, 2003.
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School code: 0175.
University of Pennsylvania.
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Dissertation Abstracts International 64-04B.
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