Molecular clock: Molecular system that is able to maintain a given biological rhythm even under free-running conditions, i.e. in the absence of a zeitgeber.
On the other hand, the circadian secretion of cortisol is generated by an evolutionary conserved molecular 'clock', the circadian clock system, which consists of central and peripheral components [ 54, 55].
This finding is consistent with earlier literature suggesting the phasing of the molecular clock in the corticolimbic system and hippocampus are strongly influenced by the time of food availability (Amir, 2004; Ángeles-Castellanos et al., 2007; Wakamatsu et al., 2001).
However, the basic features of molecular clock components in the immune system and the role of clock genes in regulating host immune defenses remain uncharacterized.
Drosophilids are the best-analysed dipteran system concerning molecular clock analyses with rates of synonymous substitution per synonymous site per million years of 0.016 [ 49], 0.015 [ 50], and 0.011 [ 51].
Our results and future studies will help elucidate how the ancient system of molecular clock function has been co-opted for similar functions in social insects, providing a fascinating link between chronobiology and sociobiology.
The molecular phylogeny calibrated with the molecular clock data suggested that the developmental system of bilaterians was established before their divergence.
The PER2 and PER3 genes, key molecular clock components within the mammalian circadian timing system [ 79], had mean post-training increases in expression of +1.88-fold and +1.74 fold respectively.
In other words, the molecular clock seems to be the most robust feature of the clock system during Aβ pathology, being interrupted only by neuronal dysfunction and death.
To clarify the evolutionary process of the plant clock system, we recently reported the molecular phylogeny of LHY/CCA1 genes in angiosperms [ 9].
