Isaac Edery
	Associate Professor Department of Molecular Biology and Biochemistry Rutgers, The State University of New Jersey Ph.D., 1988, McGill University Tel:  [732] 235-5550 Fax: [732] 235-5318 edery@cabm.rutgers.edu

Clocks, behavior, adaptation and evolution, photic and temperature signals, PAS-containing transcription factors, pre-mRNA splicing.

The main goal of our laboratory is to understand the molecular and biochemical bases of circadian (@ 24 hour) rhythms. To achieve this goal, we are using the powerful genetics available in Drosophila in combination with biochemical, molecular and histochemical approaches. Daily fluctuations in biochemical, physiological and behavioral phenomena are governed by endogenous circadian clocks that can be synchronized (entrained) by external time cues (zeitgebers), most notably the daily changes in light/dark and temperature. This adaptive feature of circadian clocks enables organisms to temporally align their physiology and behavior such that they occur at biologically advantageous times during the day.

The isolation of "clock genes" has provided significant insights into the molecular underpinnings governing circadian rhythms. The best-characterized animal model system for a circadian clock is Drosophila melanogaster, where four clock proteins termed PERIOD (PER), TIMELESS (TIM), dCLOCK (CLK) and CYCLE (CYC/dBMAL1) function in a negative transcriptional autoregulatory loop. dCLOCK and CYC are members of the basic-helix-loop-helix (bHLH)/PAS (PER-ARNT-SIM) superfamily of transcription factors and are required for the daily stimulation of per and tim expression. PER and TIM form a complex in the cytoplasm that enters the nucleus in a temporally gated manner where they bind the dCLOCK-CYC heterodimer blocking its DNA binding activity. In the absence of denovo synthesis, the concentrations of PER and TIM in the nucleus decrease below threshold levels relieving autoinhibition which "jump starts" the next round of per and tim transcript accumulation.

In addition to this core transcriptional feedback loop, posttranscriptional mechanisms play an important role because they introduce "biochemical time constraints" that stretch the transcriptional feedback loop to ~24 hr. For example, the cytoplasmic phosphorylation of PER by the kinase DOUBLE-TIME (DBT) renders PER unstable. Because per mRNA levels are increasing during this time threshold levels of cytoplasmic PER are eventually reached that favor its dimerization with TIM, an interaction that stabilizes PER. The slow accumulation of this bimolecular interaction ensures that the nuclear entry of the inhibitory PER-TIM complex is a slow process, possibly creating a time-window for daily increases in the levels of per and tim transcripts.

A hallmark feature of circadian clocks is that they can be synchronized by light. In Drosophila, a blue-light photoreceptor called CRYPTOCHROME (CRY) has been implicated in the rapid light-induced degradation of TIM, a key early step in synchronizing the clock to local time. Besides light, temperature is the most important environmental regulator of circadian clocks. In general, diurnal animals respond to colder temperatures by displaying a greater proportion of their activity during day-time hours, whereas night-time activity predominates at warmer temperatures. This directional response has a clear adaptive value, ensuring that the activity of an organism is maximal at a time of day when the temperature would be expected to be optimal for activity. We recently showed that a thermosensitive splicing event in the 3’ untranslated region (UTR) of the mRNA from the per gene plays an important role in how a circadian clock in Drosophila melanogaster adapts to low temperatures and short day-lengths (photoperiod), environmental conditions that are typical of seasonally cold days (see figure). Our findings are beginning to reveal how a clock integrates seasonal variations in temperature and photoperiod.

Ongoing studies are geared towards isolating all the components that comprise a circadian timekeeping device and understanding how the daily changes in visible light and ambient temperature modulate the oscillatory mechanism. The recent sequencing of the entire genome of Drosophila melanogaster promises to keep this organism at the forefront of discoveries in circadian rhythms.

Recent evidence shows a remarkable conservation in the clock proteins that are part of the circadian timing machinery in Drosophila and mammals. As a result, studies using Drosophila as a model system may help in developing more efficient treatments for several human disorders associated with altered clock function, such as manic depression, seasonal affective disorders (winter depression), jet-lag and chronic sleep problems. Nonetheless, despite the high degree of conservation at the structural level, some of the putative orthologs in Drosophila and mammals appear to have different functions in the oscillatory mechanism. Our working hypothesis is that these differences reflect important aspects of the unique dynamic relationship between a particular biosystem and its natural habitat. Thus, comparative studies should reveal a rich diversity of molecular circuits used to keep biological phenomena in sync with the daily environmental changes imposed by the rotation of the Earth on its axis.

Cold temperatures stimulate splicing of the 3'-terminal per intron leading to an earlier accumulation of per mRNA and protein. The earlier per cycles lead to preferential daytime activity whereas the opposite occurs with delayed molecular rhythms. As a result flies avoid the hot sun on warm days (they are more nocturnal; see right bottom panel) but are more active during the warmer daytime hours typical of the autumn/winter seasons (left bottom panel).

Selected Publications1