Insight into molecular core clock mechanism of embryonic and early postnatal rat suprachiasmatic nucleus

All studied clock genes were expressed in the rat suprachiasmatic nucleus (SCN) as early as embryonic day 19, but no rhythmic expression was detected.

• At embryonic day 19 (E19), Per1, Per2, Cry1, Bmal1, and Clock mRNA were present in the SCN, but their expression levels varied.
• Low levels of Per1, Cry1, and Clock mRNA were observed, while Bmal1 mRNA levels were high and Per2 mRNA levels were medium.
• No detectable rhythms in mRNA or protein levels of PER1, PER2, and CRY1 were found at E19.
• By postnatal day 3 (P3), rhythmic expression of Per1, Per2, Cry1, and Bmal1 mRNA was detected, but not for Clock mRNA.
• The rhythmicity of Per1, Per2, and Bmal1 mRNA increased in amplitude by postnatal day 10 (P10) compared to P3.
• The findings indicate a gradual development of the molecular clockwork from no rhythmicity at E19 to established rhythms by P10.

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