Adaptation of the Drosophila circadian clock to seasonal changes in temperature and photoperiod

In Drosophila melanogaster, splicing of an intron in the 3' untranslated region of the period (per) mRNA (herein referred to as dmpi8) is enhanced at cold temperatures, leading to more rapid daily increases in per transcript levels and earlier "evening" activity. We show that shortening the photoperiod (day length) enhances daily fluctuations in the splicing of dmpi8 and advances its cycle, whereas the amplitude of the clock-regulated daytime decline in splicing increases as temperatures rise. Our results identify a novel non-photic role for NORPA in the temperature regulated repression of dmpi8 splicing.;In related work I found that two haplotypes (termed VT1.1 and VT1.2) in the per 3' UTR with six natural polymorphisms showed differential splicing efficiency in inbred flies, transgenic flies, and S2 cells. The VT1.1 haplotype leads to better dmpi8 splicing and earlier evening activity. Splicing assays in S2 cells also suggest that efficient dmpi8 splicing promotes per mRNA export. Our results suggest that splicing of dmpi8 plays a major role for Drosophila in adapting to local climates.;This dissertation also shows that light acutely stimulates the expression of tim at cold but not warm temperatures and that this is regulated at the transcriptional level. Cold-specific stimulation of tim RNA abundance requires CLK or CYC but not PER, TIM, CRY, or the canonical phototransduction pathway. The photoinduction of tim is temporally restricted to the daily rising phase in tim mRNA levels, likely ensuring that sunrise does not prematurely stimulate tim expression during unseasonably cold long days.;My work suggests a model whereby temperature and day length are integrated to set the phase of the clock in a seasonably appropriate manner. Namely, during cold short days, stimulation of per dmpi8 splicing and photoinduction of tim mRNA transcription ensures that both per and tim transcripts accumulate more rapidly, leading to Drosophila exhibiting preferential activity during the warmer daytime hours despite the earlier onset of dusk. Conversely, during warm long days, the inefficient splicing of dmpi8 and lack of light stimulated tim transcription delay evening activity such that flies avoid the deleterious effects of the hot midday hours.