Post-embryonic development of circadian oscillations within and outside the optic lobe in the cricket, gryllus bimaculatus

The adult cricket Gryllus bimaculatus has a central clock in the optic lobe that regulates overt activity rhythms and secondary oscillators in the tissue outside the optic lobe. Here we investigated properties of the rhythmic expression of clock genes in the optic lobe and extra-optic lobe tissues in nymphs, and compared them with those of adults. In the optic lobe, mRNA of the clock genes period (per), timeless (tim), cycle (cyc) and Clock (Clk) were expressed in patterns similar to those in adult profiles, but at significantly lower levels. Among the extra-optic lobe tissues, the brain and TAG showed a rhythmic expression of per and tim, the mid-gut only in tim, and the anterior-stomach in none of the genes studied. The mRNA levels of clock genes were again significantly lower than those in adults. Unlike in adults, the brain and mid-gut lost their rhythms of clock gene expression in DD, and when the optic lobes were bilaterally removed. These results suggest that the rhythms outside the optic lobe are weak in nymphs, and may become robust after the imaginal molt.