Chronobiology research

 

Behavioural Neurogenetics Research

 

Drosophila chronotype populations

We use laboratory selection protocols to derive populations of flies with widely diverged phasing of adult emergence from pupal cases to understand how properties of their underlying clocks evolve.  These early and late populations have been subjected to selection for ~340 generations and have revealed very interesting aspects of chronotype evolution.

Drosophila reared in semi-natural conditions

A unique resource developed here is a set of fly populations that are reared in an outdoor enclosure, enabling us to ask how circadian clocks evolve in presence of natural environmental time cues where levels and spectral composition of light, temperature, humidity etc., change in ways very different from typical laboratory rearing conditions.

            Constant condition and              T-cycle populations

Circadian clocks have evolved on Earth’s cyclic environment of exactly 24 hour period. We ask how circadian clocks are affected when flies are maintained under constant light or darkness. Further we ask how circadian clocks would evolve if exposed to non-Earth-like cycles such as 20 hour or 28 hour periods.

Plasticity of circadian waveform

Cycling light and temperature affect behavioural and physiological processes, internal clocks help organisms synchronise these processes optimally. However, environmental conditions change across the year which demands that the circadian clock and its output be flexible. Light and temperature regimes can be used to probe plasticity of circadian waveforms (behavioural and molecular).  We aim to understand genetic and cellular aspects of circadian organization underlying this flexibility. 

Neurogenetics of oviposition rhythm

Mechanistic details of regulation of timing have been elucidated by decades of research on fly locomotor activity rhythms. The canonical notions that arise from that research breakdown in case of egg laying rhythm of flies. We attempt to understand the molecular and neural basis of this very important but unusual circadian rhythm.

Previous research in chronobiology

The Chronobiology Laboratory was established by Prof MK Chandrashekaran (1996-1999) and subsequently headed by Prof Vijay Kumar Sharma (2000-2016).  Several distinct questions related to circadian rhythms, the underlying oscillators and their modulation by geophysical and biological factors have been examined, in addition to studies examining their adaptive significance. The findings that have emerged from those studies can be found here.

Temperature circuits

Modulation of circadian behaviour due to light has been studied in great detail. However, very little is known about temperature input to the clock and how temperature affects circadian behaviour. Studies from other labs and our have commended the role of an ion channel, the Drosophila Transient Receptor Potential channel A1 (dTRPA1) in modulating activity rest behaviour in response to rhythmic thermal cues. We aim to identify neuronal circuits (the communicating neurons and their neurotransmitters) which mediate rhythmic activity in response to changing thermal cues.

Electrical synapses

The pacemaker circuit of the fruit fly comprises of ~150 neurons in its brain. These neurons communicate and function as a network to bring about circadian behaviour. Neuropeptides and chemical transmission have been studied for their role in communication within this circuit and also as its output. However, electrical synapses/gap junctions may also contribute to communication within the circuit and in generating a robust output. We find evidence for the role of gap junction proteins in determining both period and phase of activity rhythms of the fly.   

Sleep and circadian clock

Sleep-wake cycles are a well-studied output of the clock. However, sleep is regulated by two components: a clock that regulating the timing aspect of sleep and a homeostat which regulates how much and how well the organism sleeps. Studies in the lab have been able to identify the role of a critical circadian clock component to be part of the sleep circuit, a unidirectional influence of the clock over the homeostat.

Across species comparisons

To address the question of functional significance of circadian organization using a comparative approach we compared several aspects of activity/rest rhythm of different Drosophilid species under various environmental conditions along with natural conditions.  We have found that a closely related species D. ananassae likely occupies a distinct temporal niche as compared to its more well-studied relative D melanogaster and that its underlying circadian clock enables this behaviour.

Feeding and circadian clocks

Previous studies have posited the role of peripheral clock in maintaining rhythmic feeding in animals, thus classifying feeding as an input to the clock in addition to being an output.  We ask if cyclic food availability can synchronise rhythms in locomotion and whether that also alters the underlying molecular clocks.  We also examine whether individual flies exhibit rhythmicity in feeding and whether presence of conspecifcs may influence this rhythmicity.

 

Social interaction in fruit flies

The tendency of organisms to gather in space and time is called aggregation. Organisms form aggregates in the presence of resources, to avoid predation but also to socialize. Previous research showed that flies will form non-random clusters even in the absence of resources. Our studies attempt to develop robust methods to quantify aggregation and understand whether differences in inter-fly relationships and social interactions modulate aggregation patterns.

Modelling neurodegeneration in fruit flies

Huntington’s disease is a neurodegenerative condition marked by the loss of neurons in specific brain regions.  We can express the mutated form of the human gene responsible for the disease in a subset of circadian clock neurons in the fly which recapitulated major phenotypes of the disease. We are exploring cellular and molecular processes that can accelerate or slow down the progression of the condition in our fly model.