involved in the sorting of lipids and membrane proteins to the apical plasma membrane and were key to the expansion of the apical domains required for intestinal lumen formation. -SMH Nat. Cell Biol. 13, 10.1038/ncb2328 (2011. BIOCHEMISTRY Synchronized Stepping Inside the cell, ensembles of different myosin proteins attached to a single cargo molecule allow for bidirectional transport along actin tracks. To gain insight into the coordination that must be required to deliver the cargo to its

more »

... ination, Ali et al. labeled myosin V (myoV) and myosin VI (myoVI), which move in opposite directions, with different colored quantum dots. They coupled the motors through a third quantum dot cargo and used total internal fl uorescence microscopy to determine the stepping dynamics of each individual motor. Though the motors have similar stall forces, myoV dominated ~80% of the time, probably because it has a higher unbinding force than myoVI. Regardless of which motor won, its movement was signifi cantly slowed by the losing motor which, interestingly, took continuous backward steps coincident with the forward steps of the winning motor. In the presence of micromolar concentrations of ADP, myoVI dominated by acting as an anchor that prevented myoV from stepping forward. The dominant motor could also be shifted by varying the myoV:myoVI:cargo conjugation ratio, consistent with regulation by varying the ratio of motor types bound to cargo. Such approaches that provide a mechanochemical understanding of motor coupling will be valuable in efforts to model the regulatory mechanisms that govern intracellular transport. -VV Proc. Natl. Acad. Sci. U.S.A. 108, E535 (2011). APPLIED PHYSICS Directing Single Photons Photons are ideal carriers of bits of information-they are fast, robust, and can travel long distances. For secure applications such as quantum key distribution for cryptography, the information is conveyed by single photons. Compared with classical keys, an attack on the communication channel by an eavesdropper that uses a quantum key is readily detected. Quantum dots are useful sources of single photons and can be integrated into on-chip waveguides that direct where the single CELL BIOLOGY Going Tubular Lipids provide the building blocks for cell membranes but can also play a role in intracellular membrane traffi cking and signaling. In nematodes, the gut develops from a tubular epithelium that has very distinct apical membranes that will be exposed to materials originating outside the organism, as compared with the ba-solateral membranes that communicate with the interior of the organism. Zhang et al. wanted to understand the role of lipids during the process of organ formation in C. elegans. By systematically targeting lipid biosynthetic pathways and examining changes in intestinal tubulogenesis, the authors confi rmed an essential role for glycosphingolipids in maintaining epithelial polarity and thereby the integrity of the central lumen of the developing gut. Glycosphingolipids were The myelin membrane that wraps around axons is essential for the speedy transmission of electrical signals in the nervous system. Myelin is produced by oligodendrocytes and differs from most cellular membranes because of its unusually high lipid content and exclusion of large proteins: a composition that is optimized for the transmission of nerve impulses. Using an in vitro culture system, Aggarwal et al. studied how oligodendrocytes are able to create these specialized membranes. The membrane sheets are so thin that most cellular organelles cannot encroach, keeping them restricted to the fatter parts of the cell body. With vesicle transport excluded as a mechanism, the authors found that the composition of the membranes is regulated within the membrane domain, by myelin basic protein (MBP), which acts as a regulator of diffusion. In the absence of MBP, the exclusion of proteins with an overlarge cytoplasmic domain from the membrane was disrupted. Thus MBP, which appears to be spread throughout the myelin sheet, is critical for restricting access so that only a few, primarily small proteins are integrated into the myelin sheet. -PJH Dev. Cell 21, 445 (2011).