Conservation of Epigenetic Regulation, ORC Binding and Developmental Timing of DNA Replication Origins in the Genus Drosophila

B. R. Calvi¹, B. A. Byrnes and A. J. Kolpakas

Department of Biology, Syracuse University, Syracuse, New York 13244

^¹ Corresponding author: Department of Biology, Syracuse University, 130 College Pl., BRL 703, Syracuse, NY 13244.
E-mail: bcalvi{at}syr.edu

There is much interest in how DNA replication origins are regulatedso that the genome is completely duplicated each cell divisioncycle and in how the division of cells is spatially and temporallyintegrated with development. In the Drosophila melanogasterovary, the cell cycle of somatic follicle cells is modifiedat precise times in oogenesis. Follicle cells first proliferatevia a canonical mitotic division cycle and then enter an endocycle,resulting in their polyploidization. They subsequently entera specialized amplification phase during which only a few, selectorigins repeatedly initiate DNA replication, resulting in genecopy number increases at several loci important for eggshellsynthesis. Here we investigate the importance of these modifiedcell cycles for oogenesis by determining whether they have beenconserved in evolution. We find that their developmental timinghas been strictly conserved among Drosophila species that havebeen separate for $~$ 40 million years of evolution and provideevidence that additional gene loci may be amplified in somespecies. Further, we find that the acetylation of nucleosomesand Orc2 protein binding at active amplification origins isconserved. Conservation of DNA subsequences within amplificationorigins from the 12 recently sequenced Drosophila species genomesimplicates members of a Myb protein complex in recruiting acetylasesto the origin. Our findings suggest that conserved developmentalmechanisms integrate egg chamber morphogenesis with cell cyclemodifications and the epigenetic regulation of origins.