Genetic dissection of seasonal timing in Drosophila

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Seasonal timing is a key process for survival for most organisms, especially in temperate regions. In broad ranges of species, from plants to mammals, the annual change in day-length is monitored the so-called a photoperiodic clock, allowing the accurate timing of the seasonal response. Many insects for example, including numerous agricultural pests, detect the shortening of the day during the autumn and switch to diapause (a developmental arrest), which allow them to survive the winter. Despite intensive study of the photoperiodic clock for the last 80 years, the underlying molecular mechanism is still largely unknown. This is in marked contrast to our understanding of the circadian clock that regulates daily rhythms, where studies in various model organisms, particularly Drosophila, have established firm principles and rich mechanistic detail, including genes conserved across diverse phyla. In Drosophila, the genetic basis of the seasonal clock has focused on female diapause, manifested as a developmental arrest of the ovaries induced by short days and low temperatures. Unfortunately, this phenotype is not very robust, and practically is not amenable for large genetic screens. Recently, research in our laboratory has corroborated previous observations that flies developed under short days become significantly cold-resistant compared with flies raised in long-days. The difference in cold response can be easily quantified using the chill-coma recovery (CCR) assay, in which flies exposed to freezing temperatures enter reversible narcosis . The recovery time reflects how cold-adaptive the flies are, and our recent work has demonstrated that this response is largely regulated by the photoperiod (i.e. flies exposed to short photoperiods during development exhibit shorter recovery times). We have devised an automated system, allowing the monitoring of hundreds of flies, and here we propose to use this system for high-throughput genetic screen for genes involved in the photoperiodicresponse.