Circadian rhythms in Drosophila.

We discuss some historical features of the circadian in Drosophila melanogaster. We then describe some recent progress from our laboratory in three different areas. First, we discuss the regulation of circadian gene expression as assayed with microarrays. Results are discussed that verify and extend published data, both with respect to the previously identified cycling mRNAs as well as some clustering within the genome of some of the genes that give rise to these circadian transcripts. Also discussed are experiments that attempt to identify transcripts that are enriched in lateral neurons, the key circadian pacemaker cells in the Drosophila brain. Second, the issue of damping within the brain is addressed, by assaying molecular oscillations after many days in constant darkness. Third, the identification of a new circadian mutant is described, which is a fully recessive allele of the gene Clock. The previous allele in flies, as well as the single mutant allele in mice, is a dominant allele. This limits the conclusions that can be drawn from the genetic and molecular analyses in these mutant strains. Results with the new recessive allele not only support the notion that Clock is an important clock gene but also indicate that it contributes more to the amplitude of the rhythm rather than the period.