Interplay between phosphorylation and palmitoylation mediates plasma membrane targeting and sorting of GAP43.

Phosphorylation and lipidation provide posttranslational mechanisms that contribute to the distribution of cytosolic proteins in growing nerve cells. The growth-associated protein GAP43 is susceptible to both phosphorylation and S-palmitoylation and is enriched in the tips of extending neurites. However, how phosphorylation and lipidation interplay to mediate sorting of GAP43 is unclear. Using a combination of biochemical, genetic, and imaging approaches, we show that palmitoylation is required for membrane association and that phosphorylation at Ser-41 directs palmitoylated GAP43 to the plasma membrane. Plasma membrane association decreased the diffusion constant fourfold in neuritic shafts. Sorting to the neuritic tip required palmitoylation and active transport and was increased by phosphorylation-mediated plasma membrane interaction. Vesicle tracking revealed transient association of a fraction of GAP43 with exocytic vesicles and motion at a fast axonal transport rate. Simulations confirmed that a combination of diffusion, dynamic plasma membrane interaction and active transport of a small fraction of GAP43 suffices for efficient sorting to growth cones. Our data demonstrate a complex interplay between phosphorylation and lipidation in mediating the localization of GAP43 in neuronal cells. Palmitoylation tags GAP43 for global sorting by piggybacking on exocytic vesicles, whereas phosphorylation locally regulates protein mobility and plasma membrane targeting of palmitoylated GAP43

Extraction of pure cellular fluorescence by cell scanning in a single-cell microchip

A 3-dimensional liquid flow control method has been developed to manipulate and retain a single yeast cell freely in a microchip. This method allows us to carry out single-cell experiments by selecting any desired single cell from a group, retaining the cell for cellular signal detection, and delivering reagents to the cell during continual detection and observation without any negative impact from the liquid flow on the live cell. The cell was scanned back and forth across an observation window in order to extract pure cellular fluorescent signals. Different scanning methods were discussed for effective collection of the cellular fluorescent signal. The cell scanning technique results in many advantages, such as distinguishing a small part of a cell, allowing for background correction and monitoring the switch of reagents. In addition, it is possible to evaluate the photobleaching effects on both the background and cellular fluorescence, with the latter found to be less significant in a restricted cellular environment

Enhanced photoprotection pathways in symbiotic dinoflagellates of shallow-water corals and other cnidarians

Photoinhibition, exacerbated by elevated temperatures, underlies coral bleaching, but sensitivity to photosynthetic loss differs among various phylotypes of Symbiodinium, their dinoflagellate symbionts. Symbiodinium is a common symbiont in many cnidarian species including corals, jellyfish, anemones, and giant clams. Here, we provide evidence that most members of clade A Symbiodinium, but not clades B–D or F, exhibit enhanced capabilities for alternative photosynthetic electron-transport pathways including cyclic electron transport (CET). Unlike other clades, clade A Symbiodinium also undergo pronounced light-induced dissociation of antenna complexes from photosystem II (PSII) reaction centers. We propose these attributes promote survival of most cnidarians with clade A symbionts at high light intensities and confer resistance to bleaching conditions that conspicuously impact deeper dwelling corals that harbor non-clade A Symbiodinium