Biology subjects

Gadsby, J. R.

Publications and source records attributed to Gadsby, J. R..

4 recordsLinked to original sources

bioRxiv2024

Membrane composition and curvature in SNX9-mediated actin polymerization

Membrane-binding adaptor protein Sorting nexin 9 (SNX9) contributes to viral uptake and inflammation and is associated with worse outcomes in several cancers. It is involved in endocytosis of epidermal growth factor receptors, {beta}1-integrin and membrane type 1 matrix metalloprotease and in mitochondrial-derived vesicles. Its BAR-PX domain binds phosphatidylinositol phosphates (PIPs) and its SH3 domain interacts with dynamin and N-WASP to stimulate Arp2/3 complex actin polymerization during vesicle scission. Recent complexities have arisen in SNX9s lipid specificity and its involvement both endocytic and filopodial membrane topologies. Here we use biolayer interferometry, cell-free reconstitution and superresolution microscopy to analyse the activities of SNX9. We find that more SNX9 binds membranes that contain PI(4,5)P2 and PI(3)P compared with PI(3,4)P2, despite having similar affinity, suggesting SNX9 can assemble into different macromolecular arrangements depending on the composition. Actin assembly requires the wider protein and lipid network provided by PX-BAR and SH3 interactions. 3D direct stochastic optical reconstruction microscopy on filopodia-like reconstitutions shows that SNX9 and related protein Transducer of Cdc42 activation-1 (TOCA-1) are competent to form both tubular and plaque-like organizations with the actin machinery. Finally, using cryo-electron tomography we show that SNX9 assembles both branched and bundled actin filaments demonstrating its multifunctional nature.

cell biology↗

bioRxiv2024

The open to closed D-loop conformational switch determines length in filopodia-like actin bundles

Filopodia, microspikes and cytonemes are implicated in sensing the environment and in dissemination of morphogens, organelles and pathogens across tissues. Their major structural component is parallel bundles of actin filaments that assemble from the cell membrane. Whilst the length of filopodia is central to their function, it is not known how their lengths are determined by actin bundle dynamics. Here, we identified a set of monoclonal antibodies that lengthen filopodia-like structures formed in a cell-free reconstitution system, and used them to uncover a key molecular switch governing length regulation. Using immunolabelling, enzyme-linked immunosorbent assays, immunoprecipitation and immunoblock experiments, we identified four antibodies that lengthen actin bundles by selectively binding the open DNase 1-binding loop (D-loop) of actin filaments. The antibodies inhibit actin disassembly and their effects can be alleviated by providing additional actin or cofilin. This work indicates that maintaining an open state of the actin filament D-loop is a mechanism of generating the long projections of filopodia-like actin bundles.

biochemistry↗

bioRxiv2019

A direct role for SNX9 in the biogenesis of filopodia

Filopodia are finger-like actin-rich protrusions that extend from the cell surface and are important for cell-cell communication and pathogen internalization. The small size and transient nature of filopodia combined with shared usage of actin regulators within cells confounds attempts to identify filopodial proteins. Here, we used phage display phenotypic screening to isolate antibodies that alter the actin morphology of filopodia-like structures in vitro. We found that all of the antibodies that cause shorter FLS interact with SNX9, an actin regulator that binds phosphoinositides during endocytosis and in invadopodia. In cells, we discover SNX9 at specialised filopodia in Xenopus development and that SNX9 is an endogenous component of filopodia that are hijacked by Chlamydia entry. We show the use of antibody technology to identify proteins used in filopodia-like structures, and a role for SNX9 in filopodia.

cell biology↗

bioRxiv2019

Constrained actin dynamics emerges from variable compositions of actin regulatory protein complexes

Assemblies of actin and its regulators underlie the dynamic morphology of all eukaryotic cells. To begin to understand how diverse regulatory proteins work together to generate actin-rich structures we tracked the assembly of actin regulators and their relative proportions in a cell-free system that generates filopodia-like structures (FLS). We found that heterogeneous mixtures of regulators could give rise to morphologically similar structures and that the FLS actin bundles exhibited simple dynamic behaviour of growth and shrinkage. To explain these observations, we combined experiment with theory, and found that stochastic fluctuations between redundant actin regulatory subcomplexes can account for the actin dynamics. Comparing the localizations of a variety of endogenous actin regulators in Drosophila embryos and distributions of filopodia lengths yielded similar conclusions of heterogenous actin regulatory complexes and filopodia lengths governed by a stochastic growth process. Our results explain how weakly-associating assemblies of regulatory proteins can produce robust functional outcomes.

cell biology↗