Peripheral clocks entrainment

Sassone-Corsi We know that the transplanted SCN doesn t receive normal input from the retina. Is it possible that the transplanted SCN is not communicating with the rest of peripheral tissues in the same way I am not sure that the experiment of Bert van der Horst will teU us whether the transplanted SCN is able to entrain a non-functioning peripheral clock. 

Use of the Per-luc rat model made possible studies on the role of food in the entrainment of these and other peripheral clocks (Stokkan et al 2001). Rats were fed under restriction during the day. Organ explants from these rats were then cultured and the phases of the Per-luc rhythm were shifted by 12 hours in the liver (Fig. 3), and somewhat lesser amounts in stomach and colon (Fig. 4B). The SCN was completely unaffected by the feeding schedule. 

FIG. 4. Diagram of a circadian system in mammals. The master clock in the SCN entrains all non-SCN clocks in the brain and peripheral organs. Light information enters into the SCN, and non-photic information such as restriction feeding and maternal care enter into the peripheral clocks. Additionally, this scheme proposes the existence of non-photic entrainment from information from non-SCN clocks. 

Cermakian We have done almost the reverse experiments with fibroblast implants from Clock l mutants whose clock is quite impaired. When we put these fibroblast implants into mice whose SCN is functional, the SCN was not able to entrain them. So I don t think that a grafted SCN will be able to entrain peripheral tissues of these Crj double mutants. 

The relationship between central and peripheral oscillators is different in flies and mammals. In mammals, these oscillators form a hierarchy in which the central oscillator, which resides in the suprachiasmatic nucleus (SCN), functions as a master clock that is entrained by photic signals from the eye, and in turn drives subservient peripheral oscillators via humoral signals (Moore et al 1995, Yamazaki et al 2000, Kramer et al 2001, Cheng et al 2002). In contrast, both central and peripheral oscillators operate autonomously and are directly entrainable by light in Drosophila (Plautz et al 1997), thus obviating the need for a hierarchical system. Our results support the concept of independent oscillators in flies since central (sUN ) oscillators are not necessary for olfaction rhythms and local oscillators in antennae appear to be sufficient. 

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