title: Circadian molecular clocks tick along ontogenesis.
abstract: The circadian system controls the timing of behavioral and physiological functions in most organisms studied. The review addresses the question of when and how the molecular clockwork underlying circadian oscillations within the central circadian clock in the suprachiasmatic nuclei of the hypothalamus (SCN) and the peripheral circadian clocks develops during ontogenesis. The current model of the molecular clockwork is summarized. The central SCN clock is viewed as a complex structure composed of a web of mutually synchronized individual oscillators. The importance of development of both the intracellular molecular clockwork as well as intercellular coupling for development of the formal properties of the circadian SCN clock is also highlighted. Recently, data has accumulated to demonstrate that synchronized molecular oscillations in the central and peripheral clocks develop gradually during ontogenesis and development extends into postnatal period. Synchronized molecular oscillations develop earlier in the SCN than in the peripheral clocks. A hypothesis is suggested that the immature clocks might be first driven by external entraining cues, and therefore, serve as "slave" oscillators. During ontogenesis, the clocks may gradually develop a complete set of molecular interlocked oscillations, i.e., the molecular clockwork, and become self-sustained clocks.
authors.affiliation: Institute of Physiology, Academy of Sciences of the Czech Republic, Prague, Czech Republic. sumova@biomed.cas.cz
authors.forename: A
authors.initials: A
authors.lastname: Sumová
authors.forename: Z
authors.initials: Z
authors.lastname: Bendová
authors.forename: M
authors.initials: M
authors.lastname: Sládek
authors.forename: R
authors.initials: R
authors.lastname: El-Hennamy
authors.forename: K
authors.initials: K
authors.lastname: Matejů
authors.forename: L
authors.initials: L
authors.lastname: Polidarová
authors.forename: S
authors.initials: S
authors.lastname: Sosniyenko
authors.forename: H
authors.initials: H
authors.lastname: Illnerová
mesh_terms: D000818:Animals; D030801:Animals, Genetically Modified; D001683:Biological Clocks / Q000235:genetics / Q000502:physiology*; D002940:Circadian Rhythm / Q000235:genetics; D005260:Female; D015870:Gene Expression; D008297:Male; D009474:Neurons / Q000502:physiology; D013493:Suprachiasmatic Nucleus / Q000196:embryology / Q000254:growth & development / Q000502:physiology*