Category Archives: Publications

Chromatin in a marine picoeukaryote is a disordered assemblage of nucleosomes

by Lu Gan,  Mark S Ladinsky, and Grant J Jensen

Chromosoma 2013 Jul 3

Chromatin organization is central to many conserved biological processes, but it is generally unknown how the underlying nucleosomes are arranged in situ. Here, we have used electron cryotomography to study chromatin in the picoplankton Ostreococcus tauri, the smallest known free-living eukaryote.

By visualizing the nucleosome densities directly, we find that O. tauri chromosomes do not arrange into discrete, compact bodies or any other higher level of order. In contrast to the textbook 30-nm-fiber model, O. tauri chromatin resembles a disordered assemblage of nucleosomes akin to the polymer-melt model. This disorganized nucleosome arrangement has important implications for potentially conserved functions in tiny eukaryotes such as the clustering of non-homologous chromosomes at the kinetochore during mitosis and the independent regulation of closely positioned adjacent genes.

Read online: Springer.

Learn more about Lu Gan’s research.

Direct observation of stick-slip movements of water nanodroplets induced by an electron beam

by Utkur Mirsaidov, Haimei Zheng, Dipanjan Bhattacharya, Yosune Casana, Paul Matsudaira

Proc Natl Acad Sci USA 109(19), 7187-7190 (2012)

Dynamics of the first few nanometers of water at the interface are encountered in a wide range of physical, chemical, and biological phenomena. A simple but critical question is whether interfacial forces at these nanoscale dimensions affect an externally induced movement of a water droplet on a surface.

At the bulk-scale water droplets spread on a hydrophilic surface and slip on a nonwetting, hydrophobic surface. Here we report the experimental description of the electron beam-induced dynamics of nanoscale water droplets by direct imaging the translocation of 10- to 80-nm-diameter water nanodroplets by transmission electron microscopy. These nanodroplets move on a hydrophilic surface not by a smooth flow but by a series of stick-slip steps.

We observe that each step is preceded by a unique characteristic deformation of the nanodroplet into a toroidal shape induced by the electron beam. We propose that this beam-induced change in shape increases the surface free energy of the nanodroplet that drives its transition from stick to slip state. 

Pictured is a snapshot of 50nm-diameter water droplet formed by the electron beam of a TEM. When irradiated with electrons, the droplet moves by a stick-slip mechanism in which the dome-shape droplet deforms into a high-energy toroidal shape and then translocates by extending a thin lamella from one edge.

Read online: PNAS.

Learn more about Utkur Mirsaidov‘s and Paul Matsudaira‘s research.

Scrolling graphene into nanofluidic channels

by Utkur Mirsaidov,  VRSS Mokkapati,   Dipanjan Bhattacharya,   Henrik Andersen,  Michel Bosman,   Barbaros Özyilmazcd and  Paul Matsudaira

Lab Chip, 2013,13, 2874-2878

Scrolling of planar graphene induced by water as a result of the interplay between water capillarity and graphene elasticity leads to the formation of stable nanochannels that encapsulate water and nanoscale objects. These graphene nanochannels are potential nanofluidic platforms for dynamic imaging of nanoscale processes in liquids with Transmission Electron Microscopes (TEMs).

Read online: Royal Society Chemistry

Learn more about Utkur Mirsaidov‘s and Paul Matsudaira‘s research.