DPP signaling contributes to set basic properties of the circadian clock

BECKWITH, EJ; BERNI, J; CERIANI, MF

NY

Congreso; Neurobiology of Drosophila; 2011

Cold Spring Harbor Laboratories

Virtually all living organisms are exposed to cyclic changes in their environment and the ability to anticipate these changes has obvious adaptive value, as it is indicated by the widespread distribution of biological clocks. Circadian rhythms maintain internal temporal order with a period close to that of the environmental cycle they are synchronized to and regulate the timing of physiological and behavioral processes. Thus, circadian clocks oscillate with ~24-h periods and are usually entrained by the 24h light-dark (LD) cycle. In Drosophila, a group of neurons expressing the Pigment Dispersing Factor (PDF) represent the “central oscillator” of the fly brain.As a result of a miss-expression screen using the GAL4/UAS system we identified a fly strain that causes period lengthening of the daily activity rhythms. The transposon landed within schnurri (shn), a nuclear component of the decapentaplegic (dpp) pathway. shn overexpression within the PDF circuit was necessary and sufficient to generate a 25.5h period of locomotor behavior in adult flies. At the same time, specific shn RNAi expression restricted to PDF neurons triggers loss of rhythmicity. Interestingly, shn overexpression in adult flies has no effect in the PDF circuit structure or PDF inmunoreactivity at the dorsal termini, ruling out a developmental effect of the pathway over the circuit.Constitutive overexpression of activated receptors that initiate the signalling cascade also gave rise to long period phenotypes, underscoring the DPP pathway itself might be involved. In contrast, downregulation of the endogenous receptors also impacted circadian rhythmicity leading to arrhythmicity. A detailed analysis of PERIOD (PER) subcelular localization indicated a delayed PER nuclear entry in the mutant compared to that of wild type flies, pointing to a specific effect of shn deregulation on the core clock mechanism. To further investigate this possibility we modulated the expression of several clock components in a shn overexpression background; surprisingly, PER overexpression led to a phenotypic rescue of the long period, similarly to what was observed upon deregulation of SHAGGY. In summary, the DPP pathway modulates the availability of functional PER providing an alternative delay mechanism within the molecular clockwork.