CR-PSOC researchers define role of chromatin mechanics in nuclear stiffness

In the paper “Chromatin and lamin A determine two different mechanical response regimes of the cell nucleus”, recently published in the journal Molecular Biology of the Cell (http://www.molbiolcell.org/cgi/doi/10.1091/mbc.E16-09-0653), Dr. Andrew Stephens and collaborators from the Northwestern CR-PS-OC report experiments establishing differential roles played by the nuclear lamin proteins of the nuclear envelope and chromatin in the mechanics of the cell nucleus. By directly stretching nuclei of human cells, the team of researchers from the labs of Robert Goldman and John Marko at Northwestern University showed that chromatin – the chromosomes themselves – control the initial small-strain (< 30% lengthening) mechanics of the cell nucleus, with the lamin network coming into play for deformations of more than 30%.  Dr. Ed Banigan showed that the experimental results are well-explained by a model in which the nuclear envelope is treated as a polymer “shell” and where the interior chromatin is modeled as a crosslinked polymer network.

The team also reports experiments showing that the state of the chromatin – whether it is more heterochromatic or euchromatic – affects nuclear stiffness.  Given that the balance of heterochromatin and euchromatin, along with nuclear morphology and stability, are altered in many diseases, this new paper suggests that chromatin mechanics may play a much larger role in controlling nuclear stiffness and shape than has been previously appreciated.