Gerald A Lincoln Centre for Reproductive Biology, University of Edinburgh Title OEClock genes and circannual timekeeping Abstract My talk will summarise the evidence that a circannual rhythm may be generated at the level of the pituitary gland through the interaction between melatonin-responsive timer cells in the pars tuberalis and the adjacent lactrotroph cells in the pars distalis that secrete prolactin. This may represent a ‘pacemaker-slave’ multicellular timer system. CV Gained a BSc degree at Imperial College, London in Zoology (honours. first class) 1970. PhD studies were at the Veterinary School, University of Cambridge under Prof Roger Short studying reproductive physiology and behaviour of red deer living wild on the Isle of Rhum, Scotland. This started a long research career devoted to understanding the physiological mechanisms underlying seasonal breeding in mammals. This has been pursued largely within the MRC Reproductive Biology Unit (later the Human Reproductive Sciences Unit) in Edinburgh, 1974-2005. A Unit directed by Prof Roger Short, and later Prof Dennis Lincoln and Prof Bob Miller. The highly seasonal Soay sheep has been developed as an animal model using specially designed light-controlled facilities at the Marshall Building at Roslin. Recently Dr Lincoln has joined the University of Edinburgh funded by a MRC Programme Grant to study the role of clock genes in long-term biological timing. He has long-standing collaborations with Professor Iain Clarke at Monash University in Melbourne who developed the HPD sheep model you will here about today, with Dr David Hazlerigg at the University of Aberdeen, Scotland, studying clock genes, and with Professor Andrew Loudon in Manchester searching for novel timer genes. The topic of today’s talk is circannual rhythms - based on a paper just about to be published in Science. Recent publications Lincoln GA, Clarke IJ, Hut RA, Hazlerigg DG. Characterizing a mammalian circannual pacemaker. Science 2006 (in press). Lincoln GA. Melatonin entrainment of circannual rhythms. Chronobiol Int 2006, 23:301-306. Lincoln GA. Decoding the nightly melatonin signal through circadian clockwork. Mol Cell Endocrinol 2006, 252: 69-73. Johnston JD, Tournier BB, Andersson H, Masson-Pevet M, Lincoln GA, Hazlerigg DG. Multiple effects of melatonin on rhythmic clock gene expression in the mammalian pars tuberalis. Endocrinology 2006, 147: 959-965. Lincoln GA, Johnston JD, Andersson H, Wagner G, Hazlerigg DG. Photorefractoriness in mammals: dissociating a seasonal timer from a circadian-based photoperiod response. Endocrinology 2005. 146: 3782-3790. Hazlerigg DG, Andersson H, Johnston JD, Lincoln GA. Molecular characterization of the long-day response in the Soay Sheep, a seasonal mammal. Curr Biol 2004 14: 334-339. Institution address Dr Gerald A Lincoln PhD ScD FRSE Centre for Reproductive Biology, University of Edinburgh Queen’s Medical Research Institute, Edinburgh g.lincoln@hrsu.mrc.ac.uk