title: The origin recognition complex is dispensable for endoreplication in Drosophila.
abstract: The origin recognition complex (ORC) is an essential component of the prereplication complex (pre-RC) in mitotic cell cycles. The role of ORC as a foundation to assemble the pre-RC is conserved from yeast to human. Furthermore, in metazoans ORC plays a key role in determining the timing of replication initiation and origin usage. In this report we have produced and analyzed a Drosophila orc1 allele to investigate the roles of ORC1 in three different modes of DNA replication during development. As expected, ORC1 is essential for mitotic replication and proliferation in brains and imaginal discs, as well as for gene amplification in ovarian follicle cells. Surprisingly, however, ORC1 is not required for endoreplication. Decreased cell number in orc1 mutant salivary glands is consistent with the idea that undetectable levels of maternal ORC1 during embryogenesis fail to support further proliferation. Nevertheless, these cells begin endoreplicating normally and reach a final ploidy of >1000C in the absence of zygotic synthesis of ORC1. The dispensability of ORC is further supported by an examination of other ORC members, whereas Double-parked protein/Cdt1 and minichromosome maintenance proteins are apparently essential for endoreplication, implying that some aspects of initiation are shared among the three modes of DNA replication. This study provides insight into the physiologic roles of ORC during metazoan development and proposes that DNA replication initiation is governed differently in mitotic and endocycles.
authors: Department of Molecular Genetics and Microbiology, Duke University Medical Center, Durham, NC 27710, USA.
authors: So Young
authors: SY
authors: Park
authors: Maki
authors: M
authors: Asano
mesh_terms: D000483:Alleles; D000818:Animals; D002453:Cell Cycle; D018797:Cell Cycle Proteins; D004261:DNA Replication; D004268:DNA-Binding Proteins; D004330:Drosophila / Q000235:genetics*; D029721:Drosophila Proteins / Q000235:genetics; D008938:Mitosis; D051738:Origin Recognition Complex / Q000172:deficiency / Q000235:genetics*; D012469:Salivary Glands / Q000166:cytology
chemical_list: D018797:Cell Cycle Proteins; D004268:DNA-Binding Proteins; C411983:DUP protein, Drosophila; D029721:Drosophila Proteins; C489426:Mcm5 protein, Drosophila; D051738:Origin Recognition Complex