Developmental control of late replication and S phase length

Curr Biol. 2010 Dec 7;20(23):2067-77. doi: 10.1016/j.cub.2010.10.021. Epub 2010 Nov 11.

Abstract

Background: Fast, early embryonic cell cycles have correspondingly fast S phases. In early Drosophila embryos, forks starting from closely spaced origins replicate the whole genome in 3.4 min, ten times faster than in embryonic cycle 14 and a hundred times faster than in a wing disc. It is not known how S phase duration is regulated. Here we examined prolongation of embryonic S phases, its coupling to development, and its relationship to the appearance of heterochromatin.

Results: Imaging of fluorescent nucleotide incorporation and GFP-PCNA gave exquisite time resolution of S phase events. In the early S phases, satellite sequences replicated rapidly despite a compact chromatin structure. In S phases 11-13, a delay in satellite replication emerged in sync with modest and progressive prolongation of S phase. In S phase 14, major and distinct delays ordered the replication of satellites into a sequence that occupied much of S phase. This onset of late replication required transcription. Satellites only accumulated abundant heterochromatin protein 1 (HP1) after replicating in S phase 14. By cycle 15, satellites clustered in a compact HP1-positive mass, but replication occurred at decondensed foci at the surface of this mass.

Conclusions: The slowing of S phase is an active process, not a titration of maternal replication machinery. Most sequences continue to replicate rapidly in successive cycles, but increasing delays in the replication of satellite sequences extend S phase. Although called constitutively heterochromatic, satellites acquire the distinctive features of heterochromatin, compaction, late replication, HP1 binding, and aggregation at the chromocenter, in successive steps coordinated with developmental progress.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Animals
  • Chromosomal Proteins, Non-Histone / genetics
  • Chromosomal Proteins, Non-Histone / metabolism
  • DNA Replication*
  • DNA, Satellite / genetics
  • DNA, Satellite / metabolism
  • Drosophila Proteins / genetics
  • Drosophila Proteins / metabolism
  • Drosophila melanogaster / embryology*
  • Drosophila melanogaster / genetics*
  • Heterochromatin / metabolism
  • Proliferating Cell Nuclear Antigen / genetics
  • Proliferating Cell Nuclear Antigen / metabolism
  • Recombinant Fusion Proteins / genetics
  • Recombinant Fusion Proteins / metabolism
  • S Phase*

Substances

  • Chromosomal Proteins, Non-Histone
  • DNA, Satellite
  • Drosophila Proteins
  • Heterochromatin
  • Proliferating Cell Nuclear Antigen
  • Recombinant Fusion Proteins
  • heterochromatin protein 1, Drosophila