All metazoans possess extracellular matrices (ECM) composed of complex assemblies of molecules with generally well conserved structures and functions. ECM play structural roles, providing scaffolds that organize and strengthen tissues, and instructional roles, influencing differentiation and development. Major ECM components include the collagens, a diverse family of fibrous proteins distinguished by their triple-helical coiled coil structure, other large glycoproteins, such as laminin, fibronectin and nidogen, and proteoglycans, proteins with attached glycosaminoglycan chains. For most ECM components, cell surface receptors have been identified that can mediate interactions between the cell and its ECM. The nematode Caenorhabditis elegans is an excellent system for studies of the structures and functions of ECM components, and their roles in development. C. elegans is the simplest metazoan in which detailed genetic analysis of the ECM can be performed. The complete cell lineage and detailed anatomical structure of the organism have been described. The simple life style of C. elegans allows animals with severe morphological and/or motility defects to survive and, because they are internally self-fertilizing hermaphrodites, even reproduce. These properties can simplify mutational analyses of genes encoding ECM components. Two major forms of ECM have been identified in C. elegans, the cuticle and basement membranes. The cuticle, or exoskeleton, covers the outside of the animal and lines the lumen of the pharynx. Basement membranes cover the pseudocoelomic faces of the pharynx, intestine, gonad, and hypodermis. There is no visible interstitial matrix between the cells within tissues, possibly because nearly all cells are adjacent to the cuticle or a basement membrane. This review focuses on studies of the ECM in C. elegans. The reader is referred to excellent recent reviews concerning related topics: collagens in other nematodes; mutations in human fibrillar collagens; mutations in human type IV collagen; composition

Affiliation:
- Department of Cell, Molecular and Structural Biology, Northwestern University Medical School, Chicago, Illinois 60611.