Reversible and irreversible unfolding of mitotic newt chromosomes by applied force

Michael Poirier, Sertac Eroglu, Didier Chatenay, John F. Marko*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

73 Scopus citations

Abstract

The force-extension behavior of individual mitotic newt chromosomes was studied, using micropipette surgery and manipulation, for elongations up to 80 times native length. After elongations up to five times, chromosomes return to their native length. In this regime chromosomes have linear elasticity, requiring ~1 nN of force to be stretched to two times native length. After more than five times stretching, chromosomes are permanently elongated, with force hysteresis during relaxation. If a chromosome is repeatedly stretched to ~10 times native length and relaxed, a series of hysteresis loops are obtained that converge to a single reversible elastic response. For further elongations, the linear dependence of force on extension terminates at a force 'plateau' of ~15-20 nN, near 30 times extension. After >30 times extensions, the elastic moduli of chromosomes can be reduced by more than 20-fold, and they appear as 'ghosts': swollen, elongated, and with reduced optical contrast under both phase and differential interference contrast imaging. Antibody labeling indicates that histone proteins are not being lost during even extreme extensions. Results are interpreted in terms of extension and failure of chromatin-tethering elements; the force data allow estimates of the number and size of such connectors in a chromosome.

Original languageEnglish (US)
Pages (from-to)269-276
Number of pages8
JournalMolecular biology of the cell
Volume11
Issue number1
DOIs
StatePublished - Jan 2000

ASJC Scopus subject areas

  • Molecular Biology
  • Cell Biology

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