Matthias Chiquet

A new nomenclature for the laminins

The authors have adopted a new nomenclature for the laminins. They are numbered with arabic numerals in the order discovered. The previous A, B1 and B2 chains, and their isoforms, are alpha, beta and gamma, respectively, followed by an arabic numeral to identify the isoform. For example, the first laminin identified from the Engelbreth-Holm-Swarm tumor is laminin-1 with the chain composition alpha 1 beta 1 gamma 1. The genes for these chains are LAMA1, LAMB1 and LAMC1, respectively.

Tenascin interferes with fibronectin action

Primary chick embryo fibroblasts attach to a tenascin substrate, but remain rounded and do not spread out. The proportion between tenascin and fibronectin in mixtures used to coat the substrate determines the shape of the cells. Tenascin inhibits integrin-mediated chick fibroblast attachment to fibronectin, laminin, and the GRGDS peptide. Rat fibroblast attachment to fibronectin, but not to laminin, is inhibited by tenascin. A monoclonal antibody against tenascin, as well as its Fab fragments, is able to neutralize the inhibitory activity on cell attachment and is therefore assumed to mask the cell-binding site of tenascin. On electron micrographs showing this monoclonal antibody bound to tenascin, its epitope can be localized to the terminal knob at the distal ends of the tenascin arms.

The integrin receptor α8β1 mediates interactions of embryonic chick motor and sensory neurons with tenascin-C

Summary This paper identifies a neuronal receptor for tenascin-C (tenascin/cytotactin), ~n extracellular matrix protein that has previously been detected in developing sensory and motor neuron pathways and has been shown to regulate cell migration in the developing CNS. Antibodies specific for each subunit of the integrin ~ are used to demonstrate that o~ mediates neurite outgrowth of embryonic sensory and motor neurons on this extrecellular matrix protein. In addition, expression of o~ in K562 cells results in surface expression of a.13~ heterodimers that are shown to promote attachment of this cell line to tenascin. The major domain in tenascin that mediates neurite outgrowth is shown to be localized to fibronectin type III repeats 6-8.

Interfering with the connection between the nucleus and the cytoskeleton affects nuclear rotation, mechanotransduction and myogenesis

Mechanical stress controls a broad range of cellular functions. The cytoskeleton is physically connected to the extracellular matrix via integrin receptors, and to the nuclear lamina by the LINC complex that spans both nuclear membranes. We asked here how disruption of this direct link from the cytoskeleton to nuclear chromatin affects mechanotransduction. Fibroblasts grown on flexible silicone membranes reacted to cyclic stretch by nuclear rotation. This rotation was abolished by inhibition of actomyosin contraction as well as by overexpression of dominant-negative versions of nesprin or sun proteins that form the LINC complex. In an in vitro model of muscle differentiation, cyclic strain inhibits differentiation and induces proliferation of C2C12 myoblasts. Interference with the LINC complex in these cells abrogated their stretch-induced proliferation, while stretch increased p38 MAPK and NFkappaB phosphorylation and the transcript levels of myogenic transcription factors MyoD and myogenin. We found that the physical link from the cytoskeleton to the nuclear lamina is crucial for correct mechanotransduction, and that disruption of the LINC complex perturbs the mechanical control of cell differentiation.

Collagen XII Interacts with Avian Tenascin-X through Its NC3 Domain

Large oligomeric proteins often contain several binding sites for different molecules and can therefore induce formation of larger protein complexes. Collagen XII, a multidomain protein with a small collagenous region, interacts with fibrillar collagens through its C-terminal region. However, no interactions to other extracellular proteins have been identified involving the non-collagenous N-terminal NC3 domain. To further elucidate the components of protein complexes present close to collagen fibrils, different extracellular matrix proteins were tested for interaction in a solid phase assay. Binding to the NC3 domain of collagen XII was found for the avian homologue of tenascin-X that in humans is linked to Ehlers-Danlos disease. The binding was further characterized by surface plasmon resonance spectroscopy and supported by immunohistochemical co-localization in chick and mouse tissue. On the ultrastructural level, detection of collagen XII and tenascin-X by immunogold labeling confirmed this finding.

Identification of Molecules in Leech Extracellular Matrix that Promote Neurite Outgrowth

The molecular composition of the substrate is of critical importance for neurite extension by isolated identified leech nerve cells in culture. One substrate upon which rapid growth occurs in defined medium is a cellfree extract of extracellular matrix (ECM) that surrounds the leech central nervous system (CNS). Here we report the co-purification of neurite-promoting activity with a laminin-like molecule. High molecular mass proteins from leech ECM purified by gel filtration exhibited increased specific activity for promoting neurite outgrowth. The most active fractions contained three major polypeptide bands of ca. 340, 250 and 220 kDa. Electron microscopy of rotary-shadowed samples showed three macromolecules, one of which had a cross-shaped structure similar to vertebrate laminin. A second six-armed molecule resembled vertebrate tenascin and a third rod-like molecule resembled vertebrate collagen type IV. The most active fractions contained a protein of ca. 1 MDa on non-reducing gels with disulphide-linked subunits of ca. 220 and 340 kDa, with cross-shaped laminin-like molecules. We conclude that a laminin-like molecule represents a major neurite promoting component present in leech ECM. The experiments represent a first step in determining the location of leech laminin within the CNS and assessing its role in neurite outgrowth during development and regeneration.

Structural Motifs of the Extracellular Matrix Proteins Laminin and Tenascin

Laminin and tenascin are two major extracellular matrix glycoproteins. They both consist of large disulphide-linked subunits composed of multiple structural and functional domains which are reflected in a distinct pattern of sequence motifs. These molecules belong to different protein families for which more and more members are being discovered. Members of these families have been discovered down to the level of Anthomedusae laminin (cf. Beck et al., 1990) and leech tenascin (Masuda-Nakagawa et al., 1989). The molecular structure not only varies considerably between species but for laminin also differences depending on the state of development and tissue origin have been elucidated. Varying numbers of tenascin isoforms generated by alternative splicing are found during development and in different tissues.

Ectopic expression of tenascin-C.

We read, with much interest, the recent Research Article by Jarvinen et al. ([Jarvinen et al., 2003][1]), in which the authors show that, after removing the cast from an immobilized rat hind leg, within 8 weeks tenascin-C (TN-C) expression is increased in tendon and the myotendinous junction, but

Functional Domains of Tenascin

Tenascin from chick embryos is an extracellular matrix protein with disulfide-linked subunits of Mr = 190–220,000 and a six-armed appearance in the electron microscope (EM) (cf. Chiquet-Ehrismann et al 1988). Its expression during development suggests a function in morphogenesis (Chiquet-Ehrismann et al 1986). Several activities of tenascin can be assayed in vitro: hemagglutination, interference with fibronectin-mediated cell spreading, promotion of neurite outgrowth, and stimulation of DNA synthesis (Chiquet-Ehrismann et al 1986, 1988, Chiquet 1989). We are trying to assign various functions to specific domains on the molecule.