Spinal cord injury often results in permanent functional impairment. Neural stem cells present in the adult spinal cord can be expanded in vitro and improve recovery when transplanted to the injured spinal cord, demonstrating the presence of cells that can promote regeneration but that normally fail to do so efficiently. Using genetic fate mapping, we show that close to all in vitro neural stem cell potential in the adult spinal cord resides within the population of ependymal cells lining the central canal. These cells are recruited by spinal cord injury and produce not only scar-forming glial cells, but also, to a lesser degree, oligodendrocytes. Modulating the fate of ependymal progeny after spinal cord injury may offer an alternative to cell transplantation for cell replacement therapies in spinal cord injury. Spinal cord injuries occur in more than 30.000 individuals each year worldwide and result in significant morbidity, with patients requiring long physical and medical care. The recent identification of resident stem cells in the adult spinal cord has opened up for the possibility of pharmacological manipulation of these cells to produce cell types promoting recovery after injury. We have employed genetic tools to specifically address the identity and reaction to injury of a spinal cord subpopulation of cells known as ependymal cell. Genetic labeling of this putative stem cell population allows for the evaluation of stem cell activity in vitro and in vivo. We found that ependymal cells lining the central canal act as neural stem cells in vitro and contribute extensively to the glial scar in vivo. Interestingly, injury induces proliferation of ependymal cells and migration of ependyma-derived progeny towards the site of injury. Moreover, ependymal cell progeny differentiate and give rise to astrocytes as well as myelinating oligodendrocytes. In summary, our results point to ependymal cells as an attractive candidate population for non-invasive manipulation after injury.

Initiator for Coated Pit Assembly: During clathrin-mediated endocytosis, it has been thought that the sensing and binding of the clathrin adaptor protein AP2 to cargo and lipids leads to the recruitment of clathrin, nucleating the formation of a clathrin-coated pit. Henne et al. (p. 1281 , published online 6 May) have now found that this process of AP2 binding may not in fact represent either the first or the nucleation event of endocytosis. Instead, ubiquitous proteins called FCHo1/2 (F-BAR proteins) bind to the plasma membrane and define the sites of endocytosis independently of AP2. The F-BAR protein can generate very low curvature and, at higher concentration, generates higher curvature like those required at the neck of budding vesicles. The C terminus of the protein has a mu-homology domain (with homology to the mu domain of the AP2 complex) that interacts with Eps15 and intersectin, and via these proteins recruits AP2, which further recruits clathrin. Thus, a curvature-inducing protein can act to nucleate clathrin-coated pit assembly during endocytosis.

Regeneration of myelin is a dynamic, yet enigmatic process. Dombrowski et al. uncover a central role for regulatory T (Treg) cells in driving oligodendrocyte differentiation, in part via CCN3, a novel factor in Treg function and oligodendrocyte biology. This identifies Treg cells as key cellular players in efficient remyelination. Regeneration of CNS myelin involves differentiation of oligodendrocytes from oligodendrocyte progenitor cells. In multiple sclerosis, remyelination can fail despite abundant oligodendrocyte progenitor cells, suggesting impairment of oligodendrocyte differentiation. T cells infiltrate the CNS in multiple sclerosis, yet little is known about T cell functions in remyelination. We report that regulatory T cells (Treg) promote oligodendrocyte differentiation and (re)myelination. Treg-deficient mice exhibited substantially impaired remyelination and oligodendrocyte differentiation, which was rescued by adoptive transfer of Treg. In brain slice cultures, Treg accelerated developmental myelination and remyelination, even in the absence of overt inflammation. Treg directly promoted oligodendrocyte progenitor cell differentiation and myelination in vitro. We identified CCN3 as a Treg-derived mediator of oligodendrocyte differentiation and myelination in vitro. These findings reveal a new regenerative function of Treg in the CNS, distinct from immunomodulation. Although the cells were originally named 'Treg' to reflect immunoregulatory roles, this also captures emerging, regenerative Treg functions.

Shallow hydrophobic insertions and crescent-shaped BAR scaffolds promote membrane curvature. Here, we investigate membrane fission by shallow hydrophobic insertions quantitatively and mechanistically. We provide evidence that membrane insertion of the ENTH domain of epsin leads to liposome vesiculation, and that epsin is required for clathrin-coated vesicle budding in cells. We also show that BAR-domain scaffolds from endophilin, amphiphysin, GRAF, and β2-centaurin limit membrane fission driven by hydrophobic insertions. A quantitative assay for vesiculation reveals an antagonistic relationship between amphipathic helices and scaffolds of N-BAR domains in fission. The extent of vesiculation by these proteins and vesicle size depend on the number and length of amphipathic helices per BAR domain, in accord with theoretical considerations. This fission mechanism gives a new framework for understanding membrane scission in the absence of mechanoenzymes such as dynamin and suggests how Arf and Sar proteins work in vesicle scission.

Membrane scission is essential for intracellular trafficking. While BAR domain proteins such as endophilin have been reported in dynamin-independent scission of tubular membrane necks, the cutting mechanism has yet to be deciphered. Here, we combine a theoretical model, in vitro, and in vivo experiments revealing how protein scaffolds may cut tubular membranes. We demonstrate that the protein scaffold bound to the underlying tube creates a frictional barrier for lipid diffusion; tube elongation thus builds local membrane tension until the membrane undergoes scission through lysis. We call this mechanism friction-driven scission (FDS). In cells, motors pull tubes, particularly during endocytosis. Through reconstitution, we show that motors not only can pull out and extend protein-scaffolded tubes but also can cut them by FDS. FDS is generic, operating even in the absence of amphipathic helices in the BAR domain, and could in principle apply to any high-friction protein and membrane assembly.