Originally published as Genetics Published Articles Ahead of Print on October 18, 2007.

Genetics, Vol. 177, 1539-1551, November 2007, Copyright © 2007
doi:10.1534/genetics.107.079160

Circadian Rhythm Gene Regulation in the Housefly Musca domestica

Veryan Codd^*,,1,2, David Dolezel^,,1, Jan Stehlik^,, Alberto Piccin^*,3, Karen J. Garner^*, Seth N. Racey^*,4, Kornelis R. Straatman^*, Edward J. Louis^*,5, Rodolfo Costa^**, Ivo Sauman, Charalambos P. Kyriacou^*,6 and Ezio Rosato^*

^* Department of Genetics, University of Leicester, Leicester LE1 7RH, United Kingdom, Department of Biology, University of Leicester, Leicester LE1 7RH, United Kingdom, Institute of Entomology, Academy of Sciences of the Czech Republic, 370 05 Ceske Budejovice, Czech Republic, Faculty of Biological Sciences, University of South Bohemia, 370 05 Ceske Budejovice, Czech Republic and ^** Department of Biology, University of Padova, 35131 Padova, Italy

⁶ Corresponding author: Department of Genetics, University of Leicester, Leicester LE1 7RH, United Kingdom.
E-mail: cpk{at}leicester.ac.uk

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.

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