Identification and characterization of han, a drosophila gene encoding GPCR, that mediates circadian rhythm and temperature preference

Abstract

A wide range of organisms, from bacteria to humans, manifest circadian rhythms in biochemical, physiological, and behavioral phenomena. Recent progress had been made by using Drosophila model system, and several transcription factors began to be known for playing a central oscillator mastering daily rhythms of the organism. However, the mechanisms through which output from the circadian clock controls rhythmic behavior are poorly understood. Here I describe the characteristics of the newly identified Drosophila gene, han, that encodes GPCR. han alleles were originally isolated for a P-insertion mutant that preferred different temperatures during the day and night. In situ histochemistry and immunohistochemistry reveal that han is expressed in 13 pairs of circadian clock neurons including ventro-lateral neurons(LNvs), which are known to be important for downstream effect of central oscillator. In addition to the altered temperature preference compared with wild type flies, the flies mutated in han show abnormal circadian locomotor behavior in 12 hour light-dark cycles and rapidly loose their rhythmicity in constant dark condition. The behavioral characteristics of han null mutants and han/pdf double mutants were similar to those of pdf null mutants, suggesting that Han and PDF lie in same circadian output signaling pathways. I also found that PDF binds specifically to S2 cells expressing Han and results in the elevation of cAMP synthesis. Therefore it is proposed that that Han is a PDF receptor regulating circadian behavioral rhythm through coordination of activities of clock neurons. Further investigating any specific interaction with other known circadian clock factors, I found that han/cry double mutant shows abnormal morning and evening peak in circadian locomotor behavior, not observed in either han or cry single mutant. Closer examination of each morning and evening clock neurons reveals that core central clock proteins, Per and Tim, in evening clock neu...