Thèse de doctorat en Neurosciences
Soutenue en 2006
à Strasbourg 1 en cotutelle avec Copenhagen - Danemark .
A la recherche de gènes saisonniers : Implication du système KiSS-1/GPR54 dans le contrôle saisonnier de la reproduction
Anticipation and adaptation of individuals to the upcomming daily and seasonal variations are a prerequisite for species survival, particulary mammals. Life has developed the ability to measure and manage time, using light as the most reliable environmental time cue. These timing processes involve a photoneuroendocrine axis comprising the retina, various hypothalamic structures of which is the suprachiasmatic nucleus (SCN - seat of the master circadian clock), and the pineal gland which rhythmically releases the hormone melatonin to distribute timing information to the whole organism. Recently, major advances have been made in the understanding of the molecular events underlying circadian rhythms, with the discovery of specific "clock genes" working in double positive and negative transcriptional feedback loops. In contrast, much less is known about the molecular mechanisms operating on a seasonal time-scale and regulating yearly functions such as reproduction, hibernation, weight regulation, or seasonal pathologies in humans. This project initially aimed at identify genes underpinning the seasonal adaptations of animals for which several functions are regulated by photoperiod (i. E. Day length). The approach involved two steps: 1) To identify unknown genes which display photoperiodic or melatonin-dependent changes of expression within the photoneuroendocrine system; 2) To determine how these genes and their products may regulate the seasonal functions. For this research, we have used a well defined photoperiodic model, the Syrian hamster (Mesocricetus auratus), in which photoperiod greatly influences physiology and behaviours, in particular the reproductive activity. Hamsters maintained under long summer days (LD) are sexually active, while reproduction is dramatically inhibited after a few weeks in hamsters kept under short winter days (SD).
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