Peripheral clocks in Drosophila

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For several decades, biorhythm researchers in the two main animal model system, the fruitfly and the mouse have believed that behavioural rhythms are determined exclusively by central brain clock neurons. These neurons act as pacemakers and can generate the 24 hour locomotor cycles that are so important for allowing the animal to interact with its environment at the optimum time of day. In the fly, the pacemaker cells are called the sLNvs and in the mouse, the SCN. In the fly, the peripheral nervous system and non-neural organs have independent clocks, whereas in the mammal, the SCN synchronises the rhythms in the periphery via a number of signalling factors. Recently we have observed that clocks in the antennae or the eyes, which lie outside the central brain of the fruitfly, can nevertheless generate behavioural rhythms even though the central clock neurons are made genetically arrhythmic. This means there are pacemaker cells in these two peripheral tissues that can mediate rhythmic behaviour, so it is not all about the sLNvs. However, the clock cells in the antennae need the central brain network to be intact, even though it is clockless, in order for these behavioural rhythms to be expressed. These results will come as something of a shock to fly clock researchers as it overturns current dogma.We shall carefully examine the antennae and identify the clock cells that act as behavioural pacemakers. We know that these cells are involved in temperature, wind and gravity sensing as well as hearing, but is it particular subsets of these or is it all of them ? The antennae as also full of smell receptors, so we shall ask whether these too can act as pacemaker cells. We shall manipulate these cells genetically in a number of ways, for example by stopping their clocks, hyperexciting these cells, or speeding them up or slowing them down to see what happens to the rhythmic behaviour. We will also examine how 'normal' these rhythms are, do they respond to light and temperature in the usual ways that clocks do, or are they abnormal? We shall also find out how the antennal pacemaker cells might connect to the central brain circuit that is required for rhythms to be expressed. We will extend our studies to the eye in a similar way and finally we shall ask whether non-neural tissue, the fly's liver called the fat body, can also drive behavioural rhythms. While this might seem unlikely, given the surprising results that we have already obtained, we take nothing for granted.