[
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.
[
1985]
Since the last review in this series, several important projects relating to aging research in Caenorhabditis elegans have been completed. A more detailed review of the field is available. A major focus of research in Caenorhabditis elegans over the last few years has been on development, particularly the cell lineage. The entire cell lineage of the adult hermaphrodite has been described. The genetic loci coding for myosin, for rRNA, for actin, collagen, and oocyte yolk proteins, and a major family of proteins synthesized in the sperm have been isolated using recombinant DNA techniques. A transposable element has been identified, and studies aimed at using this element as a mutagen are underway. A good start has been made in generating an ordered series of overlapping recombinant clones of the entire genome; several labs are developing techniques for transformation of the worm. Aging research has also made progress over the last few years. Single-gene mutants and selectively bred stocks displaying longer lifespans have been isolated. A number of new markers of senescence have been described. Programmed cell death during development of the worm has been a major focus of research, and mutants altering this process have been isolated. There are still a few problems for aging research: there is not a single agreed-upon method of culturing biochemical quantities of worms that also gives lifespans comparable to those of small-scale cultures; and observed differences in aging parameters that are general versus those that are due to culture conditions are still under dispute. Two methods of growth (axenic and monoxenic) are still commonly used, for the most part always in distinct laboratories. All of these findings will be described within.