Liquid-liquid phase transitions in cell biology


Richard Neher
Biozentrum, University of Basel


slides at neherlab.org/20171121_theoretical_biophysics_slides.html

The cytosol is structured

Many organelles are not membrane bound

Micrograph of a nucleolus. wikipedia.org.
Nucleoli are few um in diameter.
Cajal bodies, described in 1903.
About 0.3-1um sized structures in the nucleus

Potential roles of sub-cellular non-membrane bound compartments

  • Function generally poorly described
  • Nucleoli: involved in rRNA production and processing
  • Cajal bodies: possibly involved in splicing
  • Generally: structure helps spatio-temporal organisation of 1000s of reactions
  • Locally increase concentration of reaction partners
  • Buffer concentrations in the cytosol

P granules in C. elegans

Jennifer T Wang et al. The top row shows a schematic of the assymetric cell division in a C. elegans embryo.
The bottom panels show the distribution of P granules in the wild type and different mutants.

P granules in C. elegans

Organelles resemble liquid droplets

Yongdae Shin and Clifford P. Brangwynne, Science 2017
  • droplets drip and deform in shear flow
  • droplets coalesce
  • droplets round up in absense of shear
  • droplets require nucleation
  • droplets exchange material with their surroundings
  • behavior reminiscent of vinaigrette