The ticking of the biological clock Biological rhythms have evolved so that organisms can anticipate both daily and seasonal changes in their environment and then adapt their behaviour accordingly. Researchers in the CINCHRON project are investigating the clock in a range of different insects, work that has relevance for understanding daily rhythms in humans, as Professor Charalambos Kyriacou explains. CINCHRON’s aim is to study the circadian and seasonal rhythms using a variety of insect models:
A lot of research into the circadian clock has historically focused on Drosophila, the fruit fly. Indeed, a Nobel Prize in Medicine/ Physiology was awarded in 2017 to the three US geneticists who identified the major clock genes in the fly. However, less is known about clocks in other insects, an issue that researchers in the CINCHRON project are addressing. “The aim of CINCHRON is to expand our knowledge of the biological clock into other species beyond Drosophila,” outlines Professor Charalambos Kyriacou, the project’s coordinator. The idea of the project is to study clocks in insects such as the pea aphid, which has a significant impact on crop productivity, as well as species like bees and silkmoths which have clear economic value. This research is being conducted against a backdrop of wider concern about the impact of climate change. “With climate change, the range of tropical insects is expanding – we’re already seeing that around the Mediterranean,” explains Professor Kyriacou. “We’re getting these insects – disease vectors – expanding their ranges. We want to understand their basic biology, including their circadian clock, which controls the timing of everything they do.”
Circadian and seasonal clock The circadian clock in these insects is typically localised in a very limited set of ‘clock’ neurons in the brain and these cells regulate rhythmic behaviour over the course of a day. Fruit flies tend to be crepuscular, meaning that they are very lively in the morning and just before dusk, but much less active in the middle of the day. “An insect wakes and has its morning burst of activity, then a siesta, then its evening behaviour. There is evidence that these neurons are divided into a ‘morning’ and an ‘evening’ oscillator, and they talk to each other. It’s important to be rhythmic, it’s a fitness character. An insect needs to anticipate when light’s coming on or off so they can get their physiology ready to meet the demands of the day or night. These rhythms are adaptive, and they can be adjusted,” explains Professor Kyriacou.
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Inner clock: the circadian rhythm changes according to the light-dark cycle. This is the clock that regulates behaviours and physiological processes that change with a period of 24 hrs. DNA (the hour hand of the clock) hosts the genes that control the circadian system and it is possible to study them using molecular biology techniques, symbolised by the pipette (the minute hand). Medial clock: the seasonal clock controls those behaviours and processes that cycle with a period of one year (migration, hibernation etc). The seasonal clock is controlled by the changes in temperature and length of daylight. Outer clock: the different insects that CINCHRON is exploiting as model organisms to study the clocks. There are 12 insects positioned along the circadian and seasonal clocks. If an insect is represented more than once, it means that more than one lab is working on it. The four fruit flies (at 1, 5, 7 and 11) are different from one another to show different mutations that are used in our studies. Figures created by Joanna Szramel, Terence Al Abaquita, and Giulia Manoli Early Stage Researchers of the CINCHRON project.
There are 15 different PhD projects within CINCHRON, focusing on both the circadian and seasonal clock in several insect species. The seasonal ‘clock’ is important for hibernation. “An insect’s hibernation is called diapause. In some insects it’s brought on by reduction in temperature, but in most it’s photoperiodic, so short days and long nights (there is evidence that the 24 hour timer can measure these day/night lengths in some insects) heralds the oncoming winter so that insects can hibernate till the longer days of spring arrive,” outlines Professor Kyriacou. The relationship between the circadian and seasonal clocks has long
been a subject of scientific debate; Professor Kyriacou says recent evidence suggests that they are closely related. “If you disrupt some of the clock genes that build the molecular oscillator, you get very strong changes in what we call the seasonal phenotype,” he says. “For example, our colleagues in Groningen are studying a parasitic wasp called Nasonia that can be used for the biological control of pests. With techniques like Crispr-cas9, you can now disrupt these 24 hour clock genes and examine the effects on seasonal hibernation.” This could open up new possibilities in the control of species like pea aphids or Drosophila
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