Abstract
The suprachiasmatic nucleus (SCN) is a mammalian central circadian pacemaker. This nucleus develops in the last stage of fetal life and matures to make strong synaptic connections within 2 weeks of postnatal life to establish strong oscillation characteristics. To identify factors that initiate the circadian oscillation, we applied a differential display PCR method to developing SCN, and isolated a gene with seven zinc-finger motifs, Lot1, which encodes a gene that appeared at a very high level in the SCN during the early postnatal days. Lot1 mRNA first appeared at postnatal day 1 (P1) at a very high level, and the signal in the SCN continued to be very high until P10 and thereafter rapidly decreased until P20 and was expressed at a very faint level during adulthood. Lot1 mRNA expression was observed only in neurons of the dorsomedial SCN throughout the course of development. During the developmental stage, Lot1 mRNA expression shows a circadian rhythm with a peak in the day time and a trough at night time in both light-dark and constant dark conditions. These observations imply that Lot1 is the first identified putative transcription factor expressed only in the period of active synaptogenesis in the SCN, where Lot1 might play a role in establishing autonomous oscillation.