The clock gene period in the housefly, Musca domestica : a molecular analysis

Abstract

The period gene (per) of Drosophila melanogaster, which lies at the core of the fly's circadian clock, controls a number of biological rhythms, including the circadian periodicity of locomotor activity and adult emergence from the pupal case. Levels of per gene products cycle with a 24 hour period, as required for a clock molecule. Furthermore, a temporal delay between the peak expression of per mRNA and protein suggests the existence of a negative feedback loop through which Per protein regulates the synthesis of its own mRNA.;In an attempt to determine the extent to which clock molecules and mechanisms are conserved among dipterans, I cloned the per homologue from the housefly, Musca domestica. The Musca per gene encodes a protein of 1072 amino acids in which areas of high similarity with Drosophila per are interspersed by non-conserved stretches. Areas of high conservation include the amino terminus, the PAS domain and the region surrounding the per5 mutation site of D. melanogaster. Successively I assessed Musca per functionality in the D. melanogaster circadian machinery. Behavioural analysis of transgenic per0 fruit flies expressing the Musca per homologue, demonstrates that the housefly per is able to replace endogenous per functions in the host's clock system.;Expression of per products was investigated in both housefly and transgenic fruitfly. Housefly per transcript levels display daily changes in abundance, similar to those observed in wild-type D. melanogaster. Circadian oscillations were also found in per levels in D. melanogaster transformants, albeit with a lower amplitude than those described for wild type. Expression of Per protein in both housefly and D. melanogaster transformants does not show the daily fluctuation characteristic of wild type D. melanogaster Per.;This comparative study suggests that the current model based on the negative feedback loop may be inadequate to explain the molecular mechanism underlying the circadian clock