[
WormBook,
2006]
A distinctive feature of polarized epithelial cells is their specialized junctions, which contribute to cell integrity and provide platforms to orchestrate cell shape changes. The chapter discusses the composition and assembly of C. elegans cell-cell and cell-extracellular matrix junctions, proteins that anchor the cytoskeleton and mechanisms involved in establishing epithelial polarity. The focus remains cellular and does not properly deal with epithelial cells in the context of the developing embryo.
[
WormBook,
2006]
Sarcomeres within body wall muscle in C. elegans include attachments to the sarcolemma that are remarkably similar in structure to vertebrate adhesion complexes. Crucial early steps in muscle sarcomere assembly, a highly orchestrated affair involving many proteins, involve the assembly of these sarcomere attachments. The steps involved in initiating the correct placement of these attachments and other sarcomere substructures are poorly understood. Using mutants in C. elegans we are attempting to dissect the various steps in this process. We review what has been discovered to date and present a model of sarcomere assembly that initiates at the plasma membrane and involves proteins within muscle, the hypodermis and within the extracellular matrix.
[
WormBook,
2007]
The nematode cuticle is an extremely flexible and resilient exoskeleton that permits locomotion via attachment to muscle, confers environmental protection and allows growth by molting. It is synthesised five times, once in the embryo and subsequently at the end of each larval stage prior to molting. It is a highly structured extra-cellular matrix (ECM), composed predominantly of cross-linked collagens, additional insoluble proteins termed cuticlins, associated glycoproteins and lipids. The cuticle collagens are encoded by a large gene family that are subject to strict patterns of temporal regulation. Cuticle collagen biosynthesis involves numerous co- and post-translational modification, processing, secretion and cross-linking steps that in turn are catalysed by specific enzymes and chaperones. Mutations in individual collagen genes and their biosynthetic pathway components can result in a range of defects from abnormal morphology (dumpy and blister) to embryonic and larval death, confirming an essential role for this structure and highlighting its potential as an ECM experimental model system.
[
WormBook,
2005]
Basement membranes are thin, specialized extracellular matrices surrounding most tissues in all metazoans. The compositions and functions of basement membranes have generally been well conserved throughout the subkingdom. Genetic analyses of basement membrane components in C. elegans have provided insights into their assembly and functions during development. Immuno- or GFP-tagged localization studies have shown that basement membranes on different tissues, or even sub-regions of tissues, contain different sets of proteins or alternatively spliced isoforms of them. Several components, including laminin, perlecan, type IV collagen and possibly osteonectin/SPARC, are essential for completion of embryogenesis, being necessary for tissue organization and structural integrity. In contrast, type XVIII collagen and nidogen are not required for viability but primarily influence organization of the nervous system. All of these proteins, with the exception of nidogen and the addition of fibulin, have roles of varying degree in morphogenesis of the gonad. A major family of cellular receptors for basement membrane proteins, the integrins, have also been characterized in C. elegans. As one might expect, integrins have been shown to function in many of the same processes as their potential ligands, the basement membrane components. While much remains to be explored, studies of basement membranes in C. elegans have been highly informative and hold great promise for improving our understanding of how these structures are assembled and how they function in development.