The clock gene period of the housefly, Musca domestica, rescues behavioralrhythmicity in Drosophila melanogaster: Evidence for intermolecular coevolution?

In Drosophila, the clock gene period (per), is an integral component of the circadian clock and acts via a negative autoregulatory, feedback loop. Com parative analyses of per genes in insects and mammals have revealed that th ey may function in similar ways. However in the giant silkmoth, Antheraea p ernyi, per expression and that of the partner gene, tim, is not consistent with the negative feedback role. As an initial step in developing an altern ative dipteran model to Drosophila, we have identified the per orthologue i n the housefly, Musca domestica. The Musca po sequence highlights a pattern of conservation and divergence similar to other insect per genes. The PAS dimerization domain shows an unexpected phylogenetic relationship in compar ison with the corresponding region of other Drosophila species, and this ap pears to correlate with a functional assay of the Musca per transgene in Dr osophila melanogaster per-mutant hosts. A simple hypothesis based on the co evolution of the PERIOD and TIMELESS proteins with respect to die PER PAS d omain can explain the behavioral data gathered from transformants.