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First published online January 13, 2009
doi: 10.1242/10.1242/dev.027599

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no poles encodes a predicted E3 ubiquitin ligase required for early embryonic development of Drosophila

¹ Department of Cell and Developmental Biology, Vanderbilt University Medical Center, U-4200 MRBIII, 465 21st Avenue South, Nashville, TN 37232, USA.
² Center for Biosystems Research, University of Maryland Biotechnology Institute, 5115 Plant Sciences Building, College Park, MD 20742, USA.

^* Author for correspondence (e-mail: laura.a.lee{at}vanderbilt.edu)

Accepted 25 November 2008

In a screen for cell-cycle regulators, we identified a Drosophila maternal effect-lethal mutant that we named `no poles' (nopo). Embryos from nopo females undergo mitotic arrest with barrel-shaped, acentrosomal spindles during the rapid S-M cycles of syncytial embryogenesis. We identified CG5140, which encodes a candidate RING domain-containing E3 ubiquitin ligase, as the nopo gene. A conserved residue in the RING domain is altered in our EMS-mutagenized allele of nopo, suggesting that E3 ligase activity is crucial for NOPO function. We show that mutation of a DNA checkpoint kinase, CHK2, suppresses the spindle and developmental defects of nopo-derived embryos, revealing that activation of a DNA checkpoint operational in early embryos contributes significantly to the nopo phenotype. CHK2-mediated mitotic arrest has been previously shown to occur in response to mitotic entry with DNA damage or incompletely replicated DNA. Syncytial embryos lacking NOPO exhibit a shorter interphase during cycle 11, suggesting that they may enter mitosis prior to the completion of DNA replication. We show that Bendless (BEN), an E2 ubiquitin-conjugating enzyme, interacts with NOPO in a yeast two-hybrid assay; furthermore, ben-derived embryos arrest with a nopo-like phenotype during syncytial divisions. These data support our model that an E2-E3 ubiquitination complex consisting of BEN-UEV1A (E2 heterodimer) and NOPO (E3 ligase) is required for the preservation of genomic integrity during early embryogenesis.

Key words: Drosophila, Embryogenesis, Cell cycle, Mitosis, DNA checkpoint, E3 ubiquitin ligase

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