Circadian Rhythm Gene Regulation in the Housefly Musca domestica

Abstract

The circadian mechanism appears remarkably conserved between Drosophila and mammals, with basic underlying negative and positive feedback loops, cycling gene products, and temporally regulated nuclear transport involving a few key proteins. One of these negative regulators is PERIOD, which in Drosophila shows very similar temporal and spatial regulation to TIMELESS. Surprisingly, we observe that in the housefly, Musca domestica, PER does not cycle in Western blots of head extracts, in contrast to the TIM protein. Furthermore, immunocytochemical (ICC) localization using enzymatic staining procedures reveals that PER is not localized to the nucleus of any neurons within the brain at any circadian time, as recently observed for several nondipteran insects. However, with confocal analysis, immunofluorescence reveals a very different picture and provides an initial comparison of PER/TIM-containing cells in Musca and Drosophila, which shows some significant differences, but many similarities. Thus, even in closely related Diptera, there is considerable evolutionary flexibility in the number and spatial organization of clock cells and, indeed, in the expression patterns of clock products in these cells, although the underlying framework is similar.

Roles of PER immunoreactive neurons in circadian rhythms and photoperiodism in the blow fly, Protophormia terraenovae

“…P. terraenovae may also have two clusters in DN m , but discrimination of the two is difficult without identification of fibre projections. Also fewer DN clusters have been reported in M. domestica than in D. melanogaster (Codd et al, 2007). Although there are some differences from D. melanogaster, it seems that P. terraenovae retains a homologous set of PER-ir neurons, as does M. domestica.…”

“…Also five s-LN v s, four of which were PDF-immunopositive were shown to be present in P. terraenovae as in D. melanogaster. Only one PDFimmunonegative s-LN v is present in P. terraenovae and D. melanogaster, whereas four PDF-immunonegative s-LN v s were found in the house fly Musca domestica (Codd et al, 2007). However, the numbers of l-LN v s and LN d s were similar in D. melanogaster, M. domestica and P. terraenovae.…”

“…per is an important circadian clock gene in D. melanogaster (Konopka and Benzer, 1971;Baylies et al, 1987), and circadian oscillation of per mRNA or distribution of per-expressing neurons has been shown in different insect orders (Frisch et al, 1996;Sauman and Reppert, 1996;Goto and Denlinger, 2002;Wise et al, 2002;Hodková et al, 2003;Závodská et al, 2005;Iwai et al, 2006;Codd et al, 2007;Moriyama et al, 2008). However, few studies have demonstrated that per or per-expressing neurons are functionally important for circadian behavioural rhythms or photoperiodism.…”

“…Although in D. melanogaster circadian clock genes and neurons are well known, photoperiodic responses in this species are very shallow and difficult to assay. Clock-gene-expressing neurons or their protein-immunoreactive neurons have been examined in many species (Frisch et al, 1996;Sauman and Reppert, 1996;Závodská et al, 2005;Codd et al, 2007); however, their roles in behavioural rhythms or photoperiodism have not been identified. Only in the hawk moth Manduca sexta, has the loss of photoperiodic control of pupal diapause been shown after ablation of per-expressing neurons (Wise et al, 2002;Shiga et al, 2003).…”

Sleep, arousal, and rhythms in flies

“…Another way to change activity/mating rhythms might be to ''tweak'' the arousal properties of the l-LNvs, perhaps by changing their number. Dif-ferences in the numbers of clock neurons within the various groups (although not the l-LNvs) have recently been identified between Drosophila and the housefly, which are both diurnal species (20). A comparative neuroanatomical analysis of clock gene expression in diurnal versus nocturnal flies might therefore prove interesting.…”