Fibrous components of the extracellular matrix are light-microscopically classified into three types of fibers: collagen, reticular and elastic. The present study reviews the ultrastructure of these fibrous components as based on our previous studies by light, electron, and atomic force microscopy. Collagen fibers present a cord- or tape-shape 1-20 microm wide and run a wavy course in tissues. These fibers consist of closely packed thin collagen fibrils (30-100 nm thick in ordinary tissues of mammals), and exhibit splitting and joining in altering the number of the fibrils to form a three-dimensional network as a whole. Individual collagen fibrils (i.e., unit fibrils) in collagen fibers have a characteristic D-banding pattern whose length is ranges from 64 to 67 nm, depending on tissues and organs. During fibrogenesis, collagen fibrils are considered to be produced by fusing short and thin fibrils with tapered ends. Reticular fibers are usually observed as a delicate meshwork of fine fibrils stained black by the silver impregnation method. They usually underlie the epithelium and cover the surface of such cells of muscle cells, adipose cells and Schwann cells. Electronmicroscopically, reticular fibers are observed as individual collagen fibrils or a small bundle of the fibrils, although the diameter of the fibrils is thin (about 30 nm) and uniform. Reticular fibers are continuous with collagen fibers through the exchange of these collagen fibrils. In silver-impregnated specimens, individual fibrils in reticular fibers are densely coated with coarse metal particles, probably due to the high content of glycoproteins around the fibrils. Elastic fibers and laminae are composed of microfibrils and elastin components. Observations of the extracted elastin have revealed that elastin components are comprised of elastin fibrils about 0.1-0.2 microm thick. Elastic fibers and laminae are continuous with networks and/or bundles of microfibrils (or oxytalan fibers), and form an elastic network specific to individual tissues. The fibrous components of the extracellular matrix are thereby morphologically categorized into two systems: the collagen fibrillar system as a supporting framework of tissues and cells, and the microfibrilelastin system for uniformly distributing stress to maintain the resilience adapted to local tissue requirements.

Proteolytic cleavage of the cohesin subunit Scc1 is a consistent feature of anaphase onset, although temporal differences exist between eukaryotes in cohesin loss from chromosome arms, as distinct from centromeres. We describe the effects of genetic deletion of Scc1 in chicken DT40 cells. Scc1 loss caused premature sister chromatid separation but did not disrupt chromosome condensation. Scc1 mutants showed defective repair of spontaneous and induced DNA damage. Scc1-deficient cells frequently failed to complete metaphase chromosome alignment and showed chromosome segregation defects, suggesting aberrant kinetochore function. Notably, the chromosome passenger INCENP did not localize normally to centromeres, while the constitutive kinetochore proteins CENP-C and CENP-H behaved normally. These results suggest a role for Scc1 in mitotic regulation, along with cohesion.

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Reactive oxygen species (ROS) are toxic but essential molecules responsible for host defense and cellular signaling. Conserved NADPH oxidase (NOX) family enzymes direct the regulated production of ROS. Hydrogen peroxide (H2O2) generated by dual oxidases (DUOXs), a member of the NOX family, is crucial for innate mucosal immunity. In addition, H2O2 is required for cellular signaling mediated by protein modifications, such as the thyroid hormone biosynthetic pathway in mammals. In contrast to other NOX isozymes, the regulatory mechanisms of DUOX activity are less understood. Using Caenorhabditis elegans as a model, we demonstrate that the tetraspanin protein is required for induction of the DUOX signaling pathway in conjunction with the dual oxidase maturation factor (DUOXA). In the current study, we show that genetic mutation of DUOX (bli-3), DUOXA (doxa-1), and peroxidase (mlt-7) in C. elegans causes the same defects as a tetraspanin tsp-15 mutant, represented by exoskeletal deficiencies due to the failure of tyrosine cross-linking of collagen. The deficiency in the tsp-15 mutant was restored by co-expression of bli-3 and doxa-1, indicating the involvement of tsp-15 in the generation of ROS. H2O2 generation by BLI-3 was completely dependent on TSP-15 when reconstituted in mammalian cells. We also demonstrated that TSP-15, BLI-3, and DOXA-1 form complexes in vitro and in vivo. Cell-fusion-based analysis suggested that association with TSP-15 at the cell surface is crucial for BLI-3 activation to release H2O2. This study provides the first evidence for an essential role of tetraspanin in ROS generation.