Endocrine Abstracts

Two major timing systems control all living organisms. The first is the “circadian” clock, which drives a vast array of internal physiological systems. This includes timing of hormone secretion, and interaction with intra-cellular signalling pathways. The second system is the less understood photoperiodic clock, in which virtually all life forms adapt to the passage of the seasons. Here, processes as diverse as reproduction, sexual behaviour, parental care, metabolism and fattening, hibernation, and seasonal migration are all driven by internal timers, entrained to daylength changes. The two systems (circadian and seasonal) are actually driven by common genetic mechanisms, such that some hormones (ie melatonin) are sculpted by the light dark cycle but interpreted by the clock. A major step forwards here has been the rapid increase in knowledge of the core genetic mechanisms driving the circadian clockwork in cells. With this, we have been able to explore how specific elements couple to and engage with key output circuits driving rhythmic physiology. I will illustrate this by offering two examples as a perspective. First, how the circadian clockwork is used to drive responses to the hormone melatonin, and links from this to how thyroid hormone signalling is employed to drive annual cycles. Secondly, we will touch on how the clock-work is used to tune inflammatory responses, and the cross-talk with anti-inflammatory glucocorticoids. In this session, my goal is to emphasise how little we yet still know, and offer options for interested young researchers to join this fast-growing field, with its untapped potential for application in medicine and beyond.