Biomedical subjects

Yinhui Lu

Publications and source records attributed to Yinhui Lu.

4 recordsLinked to original sources

PubMed2006

Actin filaments are required for fibripositor-mediated collagen fibril alignment in tendon.

Cells in tendon deposit parallel arrays of collagen fibrils to form a functional tissue, but how this is achieved is unknown. The cellular mechanism is thought to involve the formation of intracellular collagen fibrils within Golgi to plasma membrane carriers. This is facilitated by the intracellular processing of procollagen to collagen by members of the tolloid and ADAMTS families of enzymes. The carriers subsequently connect to the extracellular matrix via finger-like projections of the plasma membrane, known as fibripositors. In this study we have shown, using three-dimensional electron microscopy, the alignment of fibripositors with intracellular fibrils as well as an orientated cable of actin filaments lining the cytosolic face of a fibripositor. To demonstrate a specific role for the cytoskeleton in coordinating extracellular matrix assembly, cytochalasin was used to disassemble actin filaments and nocodazole or colchicine were used to disrupt microtubules. Microtubule disruption delayed procollagen transport through the secretory pathway, but fibripositor numbers were unaffected. Actin filament disassembly resulted in rapid loss of fibripositors and a subsequent disappearance of intracellular fibrils. Procollagen secretion or processing was not affected by cytochalasin treatment, but the parallelism of extracellular collagen fibrils was altered. In this case a significant proportion of collagen fibrils were found to no longer be orientated with the long axis of the tendon. The results suggest an important role for the actin cytoskeleton in the alignment and organization of the collagenous extracellular matrix in embryonic tendon.

Actins↗

PubMed2006

Tissue specific differences in fibrillin microfibrils analysed using single particle image analysis.

Fibrillin microfibrils endow mammalian connective tissues with elasticity and play a fundamental role in the deposition of elastin. The microfibrils are 57 nm periodic supramolecular protein polymers with a mass of 2.5 MDa per repeat. The organisation of molecules within a microfibril is still open to debate and structural studies are only just starting to unravel this issue. The contribution of microfibril associated proteins to microfibril ultrastructure and whether there are any tissue specific differences in microfibril structure is still unknown. Therefore, we have used low dose electron microscopy, single particle image analysis and atomic force microscopy to study the structure of fibrillin microfibrils from different tissues. EM images of microfibrils from aorta, ciliary zonules and vitreous humor were collected and more than 500 microfibril repeats from each sample were subjected to averaging. Averages from each sample were analysed using axial stain exclusion patterns and difference images to detect any variations between them. The overall morphology of fibrillin microfibrils was conserved between tissues and there were only very minor differences in the bead and shoulder region of microfibrils. These data suggest that the structure of isolated microfibrils represents the fibrillin scaffold, and either microfibril associated molecules are lost on purification or play only a minor role in microfibril structure.

Animals↗

PubMed2005

Evidence for the intramolecular pleating model of fibrillin microfibril organisation from single particle image analysis.

Fibrillin microfibrils endow mammalian connective tissues with elasticity and are fundamental for the deposition of elastin. The microfibrils are 57nm periodic supramolecular protein polymers with a mass of 2.4MDa per repeat. The detailed structure and organisation of most matrix assemblies is poorly understood due to their large size and complexity and it has proved a major challenge to define their structural organisation. Therefore, we have used low dose electron microscopy and single particle image analysis to study the structure of fibrillin microfibrils. Three novel features were detected: a globular feature that bridges the "arm" region, a double band of density crossing the microfibril and stain penetrating holes present in the interbead region, possibly produced by the removal of microfibril associated proteins in the purification procedure. Fine filaments of approximately 2.4nm diameter are resolved in the interbead region, which correspond to the reported diameter of the fibrillin molecule. Comparison of the stain exclusion pattern of microfibrils with the theoretical stain exclusion pattern of fibrillin packing models indicates that the intramolecular pleating model, where each fibrillin molecule is pleated within one microfibril period allowing extensibility by unpleating, has the best fit to the data.

Animals↗

PubMed2004

Coalignment of plasma membrane channels and protrusions (fibripositors) specifies the parallelism of tendon.

The functional properties of tendon require an extracellular matrix (ECM) rich in elongated collagen fibrils in parallel register. We sought to understand how embryonic fibroblasts elaborate this exquisite arrangement of fibrils. We show that procollagen processing and collagen fibrillogenesis are initiated in Golgi to plasma membrane carriers (GPCs). These carriers and their cargo of 28-nm-diam fibrils are targeted to previously unidentified plasma membrane (PM) protrusions (here designated "fibripositors") that are parallel to the tendon axis and project into parallel channels between cells. The base of the fibripositor lumen (buried several microns within the cell) is a nucleation site of collagen fibrillogenesis. The tip of the fibripositor is the site of fibril deposition to the ECM. Fibripositors are absent at postnatal stages when fibrils increase in diameter by accretion of extracellular collagen, thereby maintaining parallelism of the tendon. Thus, we show that the parallelism of tendon is determined by the late secretory pathway and interaction of adjacent PMs to form extracellular channels.

Animals↗