A col10a1: nlGFP transgenic line displays putative osteoblast precursors at the medaka notochordal sheath prior to mineralization

by Joerg Renn, Anita Büttner, Thuy Thanh To, Sherlynn Jin Hui Chan and Christoph Winkler

Dev Biol 2013 Sep 1;381(1):134-43

In teleosts, such as medaka, ossification of the vertebral column starts with the mineralization of the notochordal sheath in a segmental pattern. This establishes the chordal centrum, which serves as the basis for further ossifications by sclerotome derived osteoblasts generating the vertebral body.

So far, it is unclear which cells produce the notochordal sheath and how a segmental pattern of mineralization is established in teleosts. Here, we use a transgenic medaka line that expresses nlGFP under the control of the col10a1 promoter for in vivo analysis of vertebral body formation. We show that col10a1:nlGFP expression recapitulates endogenous col10a1 expression.

In the axial skeleton, col10a1:nlGFP cells appear prior to the mineralization of the notochordal sheath in a segmental pattern. These cells remain on the outer surface of the chordal centra during mineralization as well as subsequent perichordal ossification of the vertebral bodies. Using twist1a1:dsRed and osx:mCherry transgenic lines we show that a subset of col10a1:nlGFP cells is derived from sclerotomal precursors and differentiates into future osteoblasts.

For the first time, this shows a segmental occurrence of putative osteoblast precursors in the vertebral centra prior to ossification of the notochordal sheath. This opens the possibility that sclerotome derived cells in teleosts are implicated in the establishment of the mineralized vertebral column in a similar manner as previously described for tetrapods.

Read online: Pubmed.

Learn more about Christoph Winkler’s research.

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.