From single molecules to embryos in living color: Animation defines life, and the three-dimensional (3D) imaging of dynamic biological processes occurring within living specimens is essential to understand life. However, in vivo imaging, especially in 3D, involves inevitable tradeoffs of resolution, speed, and phototoxicity. Chen et al. describe a microscope that can address these concerns. They used a class of nondiffracting beams, known as 2D optical lattices, which spread the excitation energy across the entire field of view while simultaneously eliminating out-of-focus excitation. Lattice light sheets increase the speed of image acquisition and reduce phototoxicity, which expands the range of biological problems that can be investigated. The authors illustrate the power of their approach using 20 distinct biological systems ranging from single-molecule binding kinetics to cell migration and division, immunology, and embryonic development. Science , this issue 10.1126/science.1257998

Adding to the super-resolution arsenal: Structured illumination microscopy (SIM) uses light intensities that are orders of magnitude lower than other super-resolution methods. SIM is also far faster over cellular-sized fields of view. Li et al. used two approaches to improve the resolution of SIM to allow live cell imaging of dynamic cellular processes, including endocytosis and cytoskeleton remodeling. The contrast in performance between SIM and other techniques is due to a few key differences. Defining the practical resolution at the limited signal-to-noise ratios necessary for live cell imaging will require better imaging metrics. Science , this issue 10.1126/science.aab3500

RNA granules have been likened to liquid droplets whose dynamics depend on the controlled dissolution and condensation of internal components. The molecules and reactions that drive these dynamics in vivo are not well understood. In this study, we present evidence that a group of intrinsically disordered, serine-rich proteins regulate the dynamics of P granules in C. elegans embryos. The MEG (maternal-effect germline defective) proteins are germ plasm components that are required redundantly for fertility. We demonstrate that MEG-1 and MEG-3 are substrates of the kinase MBK-2/DYRK and the phosphatase PP2A^PPTR−½. Phosphorylation of the MEGs promotes granule disassembly and dephosphorylation promotes granule assembly. Using lattice light sheet microscopy on live embryos, we show that GFP-tagged MEG-3 localizes to a dynamic domain that surrounds and penetrates each granule. We conclude that, despite their liquid-like behavior, P granules are non-homogeneous structures whose assembly in embryos is regulated by phosphorylation.

Stem cells orient cell division and generate a distinct cell fate based on position relative to the Wnt source.