4.7 Article

Integrative analysis of gene amplification in Drosophila follicle cells: parameters of origin activation and repression

Journal

GENES & DEVELOPMENT
Volume 25, Issue 13, Pages 1384-1398

Publisher

COLD SPRING HARBOR LAB PRESS, PUBLICATIONS DEPT
DOI: 10.1101/gad.2043111

Keywords

DNA replication; ORC; transcription; H4 acetylation; chorion; oogenesis

Funding

  1. Mathers Charitable Foundation
  2. NIH [1U01HG004279, GM57960]
  3. American Cancer Society

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In metazoans, how replication origins are specified and subsequently activated is not well understood. Drosophila amplicons in follicle cells (DAFCs) are genomic regions that undergo rereplication to increase DNA copy number. We identified all DAFCs by comparative genomic hybridization, uncovering two new amplicons in addition to four known previously. The complete identification of all DAFCs enabled us to investigate these in vivo replicons with respect to parameters of transcription, localization of the origin recognition complex (ORC), and histone acetylation, yielding important insights into gene amplification as a metazoan replication model. Significantly, ORC is bound across domains spanning 10 or more kilobases at the DAFC rather than at a specific site. Additionally, ORC is bound at many regions that do not undergo amplification, and, in contrast to cell culture, these regions do not correlate with high gene expression. As a developmental strategy, gene amplification is not the predominant means of achieving high expression levels, even in cells capable of amplification. Intriguingly, we found that, in some strains, a new amplicon, DAFC-22B, does not amplify, a consequence of distant repression of ORC binding and origin activation. This repression is alleviated when a fragment containing the origin is placed in different genomic contexts.

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