Harald Nüsse

Reversible Stabilization of Vesicles: Redox‐Responsive Polymer Nanocontainers for Intracellular Delivery

We present the self-assembly of redox-responsive polymer nanocontainers comprising a cyclodextrin vesicle core and a thin reductively cleavable polymer shell anchored via host-guest recognition on the vesicle surface. The nanocontainers are of uniform size, show high stability, and selectively respond to a mild reductive trigger as revealed by dynamic light scattering, transmission electron microscopy, atomic force microscopy, a quantitative thiol assay, and fluorescence spectroscopy. Live cell imaging experiments demonstrate a specific redox-responsive release and cytoplasmic delivery of encapsulated hydrophilic payloads, such as the pH-probe pyranine, and the fungal toxin phalloidin. Our results show the high potential of these stimulus-responsive nanocontainers for cell biological applications requiring a controlled delivery.

Controlled Light-Mediated Preparation of Gold Nanoparticles by a Norrish Type I Reaction of Photoactive Polymers.

Gold nanoparticles (AuNPs) are subjects of broad interest in scientific community due to their promising physicochemical properties. Herein we report the facile and controlled light-mediated preparation of gold nanoparticles through a Norrish type I reaction of photoactive polymers. These carefully designed polymers act as reagents for the photochemical reduction of gold ions, as well as stabilizers for the in situ generated AuNPs. Manipulating the length and composition of the photoactive polymers allows for control of AuNP size. Nanoparticle diameter can be controlled from 1.5 nm to 9.6 nm.

Light Mediated Preparation of Palladium Nanoparticles as Catalysts for Alkyne cis-Semihydrogenation

A bisacylphosphine oxide photoinitiator was used for the light mediated preparation of palladium nanoparticles (PdNPs) with a small diameter of 2.8 nm. All starting materials are commercially available, and PdNP synthesis is experimentally very easy to conduct. The PdNP-hybrid material was applied as catalyst for the semihydrogenation of various internal alkynes to provide the corresponding alkenes in excellent yields (up to 99%) and Z-selectivities (Z/E ratios up to 99/1).

Facile Light-Mediated Preparation of Small Polymer-Coated Palladium-Nanoparticles and Their Application as Catalysts for Alkyne Semi-Hydrogenation

A facile light-mediated preparation of small palladium nanoparticles (PdNPs) with a diameter of 1.3 nm and low dispersity by using low-priced and readily prepared photoactive polymers is presented. These polymers act as reagents for the photochemical reduction of Pd ions and they are also stabilizers for the PdNPs generated in situ. The PdNP-polymer hybrid materials prepared by this reliable approach are efficient hydrogenation catalysts that show high activity and Z-selectivity in the semi-hydrogenation of alkynes. These PdNP-catalyst hybrid materials can be readily recycled and reused up to five times.

Proteolytic processing of palmitoylated Hedgehog peptides specifies the 3-4 intervein region of the Drosophila wing

Cell fate determination during development often requires morphogen transport from producing to distant responding cells. Hedgehog (Hh) morphogens present a challenge to this concept, as all Hhs are synthesized as terminally lipidated molecules that form insoluble clusters at the surface of producing cells. While several proposed Hh transport modes tie directly into these unusual properties, the crucial step of Hh relay from producing cells to receptors on remote responding cells remains unresolved. Using wing development in Drosophila melanogaster as a model, we show that Hh relay and direct patterning of the 3–4 intervein region strictly depend on proteolytic removal of lipidated N-terminal membrane anchors. Site-directed modification of the N-terminal Hh processing site selectively eliminated the entire 3–4 intervein region, and additional targeted removal of N-palmitate restored its formation. Hence, palmitoylated membrane anchors restrict morphogen spread until site-specific processing switches membrane-bound Hh into bioactive forms with specific patterning functions.

Visible-Light-Enabled Preparation of Palladium Nanoparticles and Application as Catalysts for Suzuki–Miyaura Coupling

Silyl ketones were used for the preparation of palladium nanoparticles (PdNPs) starting with Pd(OAc)2 in dimethylformamide under irradiation with a visible light-emitting diode (LED). Variation of the silyl ketone structure allowed adjustment of the PdNP diameter (1.9 or 5.2 nm). The in situ-formed PdNPs were further stabilized with polyvinylpyrrolidone and then applied as recyclable catalysts in the Suzuki-Miyaura coupling of arylboronic acids with aryl iodides to obtain substituted biphenyls in excellent yields.

A Versatile High-Vacuum Cryo-transfer System for Cryo-microscopy and Analytics

Cryogenic microscopy methods have gained increasing popularity, as they offer an unaltered view on the architecture of biological specimens. As a prerequisite, samples must be handled under cryogenic conditions below their recrystallization temperature, and contamination during sample transfer and handling must be prevented. We present a high-vacuum cryo-transfer system that streamlines the entire handling of frozen-hydrated samples from the vitrification process to low temperature imaging for scanning transmission electron microscopy and transmission electron microscopy. A template for cryo-electron microscopy and multimodal cryo-imaging approaches with numerous sample transfer steps is presented.

Polarized microtubule dynamics directs cell mechanics and coordinates forces during epithelial morphogenesis

Coordinated rearrangements of cytoskeletal structures are the principal source of forces that govern cell and tissue morphogenesis1,2. However, unlike for actin-based mechanical forces, our knowledge about the contribution of forces originating from other cytoskeletal components remains scarce. Here, we establish microtubules as central components of cell mechanics during tissue morphogenesis. We find that individual cells are mechanically autonomous during early Drosophila wing epithelium development. Each cell contains a polarized apical non-centrosomal microtubule cytoskeleton that bears compressive forces, whereby acute elimination of microtubule-based forces leads to cell shortening. We further establish that the Fat planar cell polarity (Ft-PCP) signalling pathway3,4 couples microtubules at adherens junctions (AJs) and patterns microtubule-based forces across a tissue via polarized transcellular stability, thus revealing a molecular mechanism bridging single cell and tissue mechanics. Together, these results provide a physical basis to explain how global patterning of microtubules controls cell mechanics to coordinate collective cell behaviour during tissue remodelling. These results also offer alternative paradigms towards the interplay of contractile and protrusive cytoskeletal forces at the single cell and tissue levels.Studying early Drosophila wing epithelium development, Singh et al. find that individual cells are mechanically autonomous, and that their elongation along the proximal–distal axis is driven by polarized microtubule-mediated pushing forces.