Feric and Brangwynne Discover Importance of Gravity for Cell Size: UPDATED
CBE doctoral student Marina Feric, and her advisor, CBE Assistant Professor Clifford P. Brangwynne, have discovered that gravity can play an important role in cells. Feric and Brangwynne set out to understand how liquid-like RNA/protein (RNP) organelles are stabilized within the nucleus of large frog cells. By using small probe particles to make micro-rheological measurements in the cell nucleus, they found that an actin biopolymer scaffold constrains the motion of RNP droplets. Unexpectedly, when they disrupted the actin network, the RNP droplets underwent gravitational sedimentation to the bottom of the nucleus, where they coalesced into a few large droplets. Using the fluctuating motion of the probe particles to measure the viscosity within the nucleus, they could determine the mass density of the droplets from their sedimentation velocity. They were then able to develop a model that reveals how gravity becomes a significant force in cells larger than ~10 microns. Animal cells rarely grow much larger than this, which could be due to the increasingly disruptive effects of gravity on intracellular organization. For more information, see the research article, “A nuclear F-actin scaffold stabilizes ribonucleoprotein droplets against gravity in large cells”, published in the October 1 issue of the journal Nature Cell Biology, or the “News of the Week” story, “Why Are Cells the Size They Are?”, in the September 23 issue of Chemical and Engineering News (C&EN), or the October 24 story posted on the Princeton University homepage, or the October 28 article in The Atlantic.