Expression of clock genes RNAs in teeth and brain at post-natal (PN) day 1. Conventional RT-PCR showed that Bmal1, Clock, Per1, and Per2 RNAs are expressed in mouse teeth as well as in the brain. No amplification bands are detected in negative control samples (omission of cDNA) (A). β-actin was also amplified using the same cDNA and served as a positive RT-PCR control (A). Real time PCR was performed to quantify the relative expression levels of Bmal1, Clock, Per1 and Per2 in teeth versus the brain (B–E). Of interest, Bmal1, Clock and Per1 RNA expression levels were relative higher in teeth than in brain (B–D). In contrast, Per2 expression was higher in brain (E). All data were normalized to β-actin. Data were expressed as means ± SD at four determinations. NC, negative control.