Letters in 2011

Tunicates are the closest living relatives of the vertebrates. Many aspects of their lives and development are, however, poorly understood. It is generally thought that among ascidian tunicates such as Ciona, the superficially vertebrate-like central nervous system of the motile 'tadpole' larva degenerates and is completely replaced by an adult nervous system that develops from scratch. Here, state-of-the-art transgenesis and imaging techniques are used to show that this is not the case. There is continuity between the larval and adult nervous systems, with the adult nervous system developing from stem-cell-like ependymal cells found in the larva.

During mitosis, adherent cells change from a flattened to a rounded morphology, and this is thought to be necessary for the geometric requirements of cell division. Here, the forces that drive this shape change are studied. Mitotic rounding force depends both on the actomyosin cytoskeleton and the cell's ability to regulate osmolarity. The rounding force is generated by osmotic pressure and the actomyosin cortex maintains this rounding pressure against external forces. These results support the idea that in animal cells, the actomyosin cortex behaves like an internal cell wall that directs osmotic expansion to control cell shape.

The kinase JNK is known to stimulate c-Jun transcriptional activity, but the molecular mechanism has been unclear. Here, N-terminal phosphorylation of c-Jun is shown to antagonize the interaction of c-Jun with Mbd3, a component of the repressor complex NuRD. The interaction between c-Jun and Mbd3 is shown to be important in regulating the proliferation of intestinal progenitor cells in mice.