Most tissues are supported by a fibrous scaffold of collagen fibrils that accounts for 30% of total body mass. As a postdoc in the USA, I developed an in vitro system of assembling collagen fibrils in vitro by cleavage of procollagen with the procollagen N- and C-proteinases. With this system, I discovered the tip-mediated nucleation-propagation mechanism of collagen fibril assembly. I went on to discover how mutations in collagen genes that cause osteogenesis imperfecta (‘brittle bone disease’) and the Ehlers-Danlos syndrome (flexible joints and hyperextensible skin) alter procollagen structure, procollagen cleavage, fibril structure, and fibril assembly. This was the first demonstration that disease-causing mutations in collagens can change the structure and function of collagen molecules. On returning to the UK as a Wellcome Trust Senior Research Fellow, my own laboratory was the first to use serial block face-scanning electron microscopy (SBF-SEM) in the UK, and we developed methods that are now widely used to study tissues architecture. Using our SBF-SEM approach, we discovered that the collagen fibrils that are the majority of the mass of adult connective tissues are generated during embryogenesis and adolescence and remain unchanged during adulthood. Using SBF-SEM, we discovered that collagen fibrils assemble in vivo at the plasma membrane in structures we called fibripositors. My lab was the first to show that fibripositors are actin-based mechanosensors via which fibroblasts generate oscillatory tension on the extracellular matrix. The persistence of collagen fibrils throughout life implies the existence of a robust protection mechanism but none have been found. However, we have recently shown that the circadian clock regulates trafficking of procollagen through the secretory pathway to generate a rhythmic pulse of collagen that is generated and degraded each day to protect the permanent collagen from loss and damage.
We use a multidisciplinary approach to address our research questions including molecular biology (e.g. CRISPR/Cas9), protein biochemistry (e.g. mass spectrometry), light microscopy (e.g. confocal) and cell culture (e.g. 3D fibrous tissue). Historically we are known for our electron microscopy approaches to studying collagen fibril assembly, especially serial block face-scanning electron microscopy (SBF-SEM) using an FEI Quanta 250 environmental scanning electron microscope fitted with a Gatan 3View in-microscope ultamicrotome.