Peroxisomes of the nematode Caenorhabditis elegans: distribution and morphological characteristics

We analyzed the distribution and morphological characteristics of peroxisomes in the nematode Caenorhabditis elegans by routine electron microscopy, immunoelectron microscopy, and morphometry. Peroxisomes were mainly contained in the epithelial cells of the digestive tract and pharyngeal gland, but some were observed in other cells. Their shape varied from round to twisted. The matrix of most peroxisomes was coarse and uneven, and contained electron-dense nucleoids and frequently tubular substructures. The diameter of peroxisomes in the gut (0.185 micro m) was smaller than that in pharyngeal gland (0.262 micro m). The volume density of peroxisomes per 100 micro m(2) of cytoplasm was 1.86 in the gut and 1.75 in the pharyngeal gland. After treatment with clofibrate, the diameter of peroxisomes increased approximately 1.11-fold in the gut and 1.2-fold in the pharyngeal gland. The volume density of peroxisomes also increased by 2.2-fold in the gut and 2.6-fold in the pharyngeal gland. The labeling density for catalase-2 was almost identical between gut and pharyngeal gland peroxisomes. The results show that in C. elegans peroxisomes mainly distribute in the epithelial cells of the gut and pharyngeal gland. Peroxisomes of the pharyngeal gland are larger than those of the gut, but peroxisomes of both tissues contain catalase-2 at similar concentrations.     

Touch receptor development and function in Caenorhabditis elegans

Mutations causing a touch-insensitive phenotype in the nematode Caenorhabditis elegans have been the basis of studies on the specification of neuronal cell fate, inherited neurodegeneration, and the molecular nature of mechanosensory transduction. © 1993 John Wiley & Sons, Inc.     

Caenorhabditis elegans development requires mitochondrial function in the nervous system

The mitochondrial respiratory chain (MRC) supplies the majority of the energy requirements of most eucaryotic cells. A null mutation in the Caenorhabditis elegans nuo-1 gene encoding a subunit of complex I (NADH-ubiquinone oxidoreductase) is lethal, leading to a developmental arrest at the third larval stage. To identify the tissues that regulate development in response to mitochondrial dysfunction, we restored nuo-1 expression with tissue-specific promoters. Only expression of nuo-1 ubiquitously or in the nervous system supported development to the adult stage. Pharyngeal expression of nuo-1 allowed development to proceed to the fourth larval stage. Expression of nuo-1 in the body muscles or in the germline had no effect. Furthermore, only ubiquitous or nervous system expression of nuo-1 allowed exit from the dauer state. Our results indicate that MRC function in the nervous system is needed to send and receive signals that control larval development and exit from dauer.     

Caenorhabditis elegans and the study of gene function in parasites.

The free-living nematode Caenorhabditis elegans is a tractable experimental model system for the study of both vertebrate and invertebrate biology. Its most significant advantages are its simplicity, both in anatomy and in genomic organization, and the elaborate methods that have been developed to attribute function to previously uncharacterized genes. Importantly, > 40% of parasitic nematode genes exhibit high levels of homology to genes within the C. elegans genome. Studying such genes using the C. elegans model should yield new insights into key molecules and their possible implications in parasite survival, leading to the discovery of new drug targets and vaccine candidates.     

Disease-related myotubularins function in endocytic traffic in Caenorhabditis elegans

MTM1, MTMR2, and SBF2 belong to a family of proteins called the myotubularins. X-linked myotubular myopathy, a severe congenital disorder characterized by hypotonia and generalized muscle weakness in newborn males, is caused by mutations in MTM1 (Laporte et al., 1996). Charcot-Marie-Tooth types 4B1 and 4B2 are severe demyelinating neuropathies caused by mutations in MTMR2 (Bolino et al., 2000) and SBF2/MTMR13 (Senderek et al., 2003), respectively. Although several myotubularins are known to regulate phosphoinositide-phosphate levels in cells, little is known about the actual cellular process that is defective in patients with these diseases. Mutations in worm MTM-6 and MTM-9, myotubularins belonging to two subgroups, disorganize phosphoinositide 3-phosphate localization and block endocytosis in the coelomocytes of Caenorhabditis elegans. We demonstrate that MTM-6 and MTM-9 function as part of a complex to regulate an endocytic pathway that involves the Arf6 GTPase, and we define protein domains required for MTM-6 activity.     

Mitochondrial expression and function of GAS-1 in Caenorhabditis elegans

A mutation in the gene gas-1 alters sensitivity to volatile anesthetics, fecundity, and life span in the nematode Caenorhabditis elegans. gas-1 encodes a close homologue of the 49-kDa iron protein subunit of Complex I of the mitochondrial electron transport chain from bovine heart. gas-1 is widely expressed in the nematode neuromuscular system and in a subcellular pattern consistent with that of a mitochondrial protein. Pharmacological studies indicate that gas-1 functions partially via presynaptic effects. In addition, a mutation in the gas-1 gene profoundly decreases Complex I-dependent metabolism in mitochondria as measured by rates of both oxidative phosphorylation and electron transport. An increase in Complex II-dependent metabolism also is seen in mitochondria from gas-1 animals. There is no apparent alteration in physical structure in mitochondria from gas-1 nematodes compared with those from wild type. These data indicate that gas-1 is the major 49-kDa protein of complex I and that the GAS-1 protein is critical to mitochondrial function in C. elegans. They also reveal the importance of mitochondrial function in determining not only aging and life span, but also anesthetic sensitivity, in this model organism.     

Molecular and functional analysis of apical junction formation in the gut epithelium of Caenorhabditis elegans

The Caenorhabditis elegans intestine is a simple and accessible model system to analyze the mechanism of junction assembly. In comparison to Drosophila and vertebrates, the C. elegans apical junction is remarkable because a single electron-dense structure is implicated in complex processes such as epithelial tightness, vectorial transport and cell adhesion. Here we present evidence in support of a heterogeneous molecular assembly of junctional proteins found in Drosophila and vertebrate epithelia associated with different junctions or regions of the plasma membrane. In addition, we show that molecularly diverse complexes participate in different aspects of epithelial maturation in the C. elegans intestine. DLG-1 (Discs large) acts synergistically with the catenin-cadherin complex (HMP-1-HMP-2-HMR-1) and the Ezrin-Radixin-Moesin homolog (ERM-1) to ensure tissue integrity of the intestinal tube. The correct localization of DLG-1 itself depends on AJM-1, a coiled-coil protein. Double depletion of HMP-1 (alpha-catenin) and LET-413 (C. elegans homolog of Drosophila Scribble) suggests that the catenin-cadherin complex is epistatic to LET-413, while additional depletion of subapically expressed CRB-1 (Crumbs) emphasizes a role of CRB-1 concerning apical junction formation in the C. elegans intestine.     

Cytoplasmic determination and distribution of developmental potential in the embryo of Caenorhabditis elegans

Development of the nematode Caenorhabditis elegans has been described completely on a cell-by-cell basis. In an invariant pattern five somatic founder cells and the primordial germ cell are generated within the first hour after the onset of cleavage. Using a laser microbeam for manipulation of individual blastomeres several aspects of early embryogenesis have been investigated, including the expression of cellular polarity, the localization of lineage-specific cleavage potential, the necessity for early cell-cell interaction, and the control of differential cell-cycle timing. The experiments demonstrate the central importance of a correct partitioning of cytoplasmic components during early embryogenesis and suggest a stepwise, binary segregation mechanism associated with the unequal cleavages in the germline.     

Species differentiation in Caenorhabditis briggsae and Caenorhabditis elegans

Identification of five laboratory strains (1-5) of putative Caenorhabditis briggsae was undertaken. Examination of the male bursal ray arrangement, mating tests with males of Caenorhabditis elegans, malate dehydrogenase zymograms, and SDS polyacrylamide electrophoresis demonstrated that strain 4 was C. briggsae and the others were C. elegans.     

A potassium channel-MiRP complex controls neurosensory function in Caenorhabditis elegans

MinK-related peptides (MiRPs) are single transmembrane proteins that associate with mammalian voltage-gated K(+) subunits. Here we report the cloning and functional characterization of a MiRP beta-subunit, MPS-1, and of a voltage-gated pore-forming potassium subunit, KVS-1, from the nematode Caenorhabditis elegans. mps-1 is expressed in chemosensory and mechanosensory neurons and co-localizes with kvs-1 in a subset of these. Inactivation of either mps-1 or kvs-1 by RNA interference (RNAi) causes partially overlapping neuronal defects and results in broad-spectrum neuronal dysfunction, including defective chemotaxis, disrupted mechanotransduction, and impaired locomotion. Inactivation of one subunit by RNAi dramatically suppresses the expression of the partner subunit only in cells where the two proteins co-localize. Co-expression of MPS-1 and KVS-1 in mammalian cells gives rise to a potassium current distinct from the KVS-1 current. Taken together these data indicate that potassium currents constitute a basic determinant for C. elegans neuronal function and unravel a unifying principle of evolutionary significance: that potassium channels in various organisms use MiRPs to generate uniqueness of function with rich variation in the details.     

Crossover distribution and frequency are regulated by him-5 in Caenorhabditis elegans

Mutations in the him-5 gene in Caenorhabditis elegans strongly reduce the frequency of crossovers on the X chromosome, with lesser effects on the autosomes. him-5 mutants also show a change in crossover distribution on both the X and autosomes. These phenotypes are accompanied by a delayed entry into pachytene and premature desynapsis of the X chromosome. The nondisjunction, progression defects and desynapsis can be rescued by an exogenous source of double strand breaks (DSBs), indicating that the role of HIM-5 is to promote the formation of meiotic DSBs. Molecular cloning of the gene shows that the inferred HIM-5 product is a highly basic protein of 252 amino acids with no clear orthologs in other species, including other Caenorhabditis species. Although him-5 mutants are defective in segregation of the X chromosome, HIM-5 protein localizes preferentially to the autosomes. The mutant phenotypes and localization of him-5 are similar but not identical to the results seen with xnd-1, although unlike xnd-1, him-5 has no apparent effect on the acetylation of histone H2A on lysine 5 (H2AacK5). The localization of HIM-5 to the autosomes depends on the activities of both xnd-1 and him-17 allowing us to begin to establish pathways for the control of crossover distribution and frequency.     

Mechanotransduction in Caenorhabditis elegans

One of the looming mysteries in signal transduction today is the question of how mechanical signals, such as pressure or mechanical force delivered to a cell, are interpreted to direct biological responses. All living organisms, and probably all cells, have the ability to sense and respond to mechanical stimuli. At the single-cell level, mechanical signaling underlies cell-volume control and specialized responses such as the prevention of poly-spermy in fertilization. At the level of the whole organism, mechanotransduction underlies processes as diverse as stretch-activated reflexes in vascular epithelium and smooth muscle; gravitaxis and turgor control in plants; tissue development and morphogenesis; and the senses of touch, hearing, and balance. Intense genetic, molecular, and elecrophysiological studies in organisms ranging from nematodes to mammals have highlighted members of the recently discovered DEG/ENaC family of ion channels as strong candidates for the elusive metazoan mechanotransducer. Here, we discuss the evidence that links DEG/ENaC ion channels to mechanotransduction and review the function of Caenorhabiditis elegans members of this family called degenerins and their role in mediating mechanosensitive behaviors in the worm.     

Globins in Caenorhabditis elegans

Extensive in silico search of the genome of Caenorhabditis elegans revealed the presence of 33 genes coding for globins that are all transcribed. These globins are very diverse in gene and protein structure and are localized in a variety of cells, mostly neurons. The large number of C. elegans globin genes is assumed to be the result of multiple evolutionary duplication and radiation events. Processes of subfunctionalization and diversification probably led to their cell-specific expression patterns and fixation into the genome. To date, four globins (GLB-1, GLB-5, GLB-6, and GLB-26) have been partially characterized physicochemically, and the crystallographic structure of two of them (GLB-1 and GLB-6) was solved. In this article, a three-dimensional model was designed for the other two globins (GLB-5 and GLB-26), and overlays of the globins were constructed to highlight the structural diversity among them. It is clear that although they all share the globin fold, small variations in the three-dimensional structure have major implications on their ligand-binding properties and possibly their function. We also review here all the information available so far on the globin family of C. elegans and suggest potential functions.     

WorfDB: the Caenorhabditis elegans ORFeome Database

WorfDB (Worm ORFeome DataBase; http://worfdb.dfci.harvard.edu) was created to integrate and disseminate the data from the cloning of complete set of approximately 19 000 predicted protein-encoding Open Reading Frames (ORFs) of Caenorhabditis elegans (also referred to as the 'worm ORFeome'). WorfDB serves as a central data repository enabling the scientific community to search for availability and quality of cloned ORFs. So far, ORF sequence tags (OSTs) obtained for all individual clones have allowed exon structure corrections for approximately 3400 ORFs originally predicted by the C. elegans sequencing consortium. In addition, we now have OSTs for approximately 4300 predicted genes for which no ESTs were available. The database contains this OST information along with data pertinent to the cloning process. WorfDB could serve as a model database for other metazoan ORFeome cloning projects.     

Anaerobiosis in the nematode Caenorhabditis elegans

In Caenorhabditis elegans, mortality rates and changes in concentrations of carbohydrate stores and anaerobic end products were determined in anoxic (test) and normoxic (control) animals at two different temperatures (10 and 20 degrees C). The anoxic tolerance of the free-living nematode proved to be well-developed: at 10 degrees C, about 50% of animals had survived a period of 50 h of anoxia. The carbohydrate stores (approximately 30 mmol glycosyl units kg-1 freshweight (FW)) were reduced by two-thirds within 24 h of anoxia at both temperatures. L-lactate, acetate, succinate, and propionate were identified as the main anaerobic end products. The amounts and proportions of the end products were dependent on temperature. They did not accumulate very much in the tissues, but were mainly excreted. During anoxia, the metabolism of C. elegans was depressed to 3-4% of the aerobic value. The food-source Escherichia coli was found to be at least partly alive in the gut of the animals. To separate between anaerobiosis in animals and bacteria, cleaning procedures were applied, and additional control measurements were made: anaerobic end products produced either by E. coli alone or by bacteria-free (axenic) bred nematodes were quantified at identical incubation conditions.