Organogenesis of the Caenorhabditis elegans intestine

The intestine of Caenorhabditis elegans is an epithelial tube consisting of only 20 cells and is derived clonally from a single embryonic blastomere called E. We describe the cellular events that shape the intestine. These events include cytoplasmic polarization of cells in the intestinal primordium, the intercalation of specific sets of cells, the generation of an extracellular cavity within the primordium, and adherens junction formation. The polarization of the intestinal primordium is associated with the generation of an asymmetric microtubule cytoskeleton, and microtubule function plays a role in subsequent cell polarity. We show that an isolated E blastomere is capable of generating polarized intestinal cells, indicating that some of the major events in intestinal organogenesis do not depend upon interactions with surrounding tissues. We compare and contrast intestinal organogenesis with some of the basic steps in development of a second epithelial organ, the pharynx, and suggest how these differences lead to organs with distinct shapes.     

Caenorhabditis elegans ubiquinone biosynthesis genes

Ubiquinone (coenzyme Q, Q) is an essential lipid electron carrier in the mitochondria respiratory chain, and also functions as antioxidant and participates as a cofactor of mitochondrial uncoupling proteins. Caernorhabditis elegans synthesize Q9, but both dietary Q8 intake and endogenous Q9 biosynthesis determine Q balance. Thus, it is of current interest to know the regulatory mechanisms of Q9 biosynthesis in this nematode. Here we review results that leaded to identification of genes involved in Q9 biosynthesis in this nematode using the RNA interference technology. C. elegans coq genes were silenced and depletion of Q content was observed, indicating that the genes related here participate in Q9 biosynthesis. Silenced populations showed an extension of adult life span, probably by the decrease of endogenous oxidative stress produced in mitochondria. We also report the heterologous complementation of C. elegans coq-5 and coq-7 genes in their homologue yeast coq null mutants, leading to restore its ability to growth in non-fermentable sugars. These complemented yeast strains accumulated Q6 but also the intermediate demethoxy-Q6. These findings support the conservative functional homology of these genes.     

Wild-type and mutant actin genes in Caenorhabditis elegans

We have sequenced the four actin genes of Caenorhabditis elegans. These four genes encode typical invertebrate actins and are highly homologous, differing from each other by, at most, three amino acid residues. As a first step toward an understanding of the developmental regulation of this gene set we have also sequenced mutant actin genes. The mutant genes were cloned from two independent revertants of a single dominant actin mutant. For both revertants, reversion was accompanied by an actin gene rearrangement. The accumulation of actin mRNA during development in these two revertants is different from that of wild-type animals. We present here a correlation between actin gene structure and expression in wild-type and mutant animals. The results, suggest that co-ordinate regulation of actin genes is not essential for wild-type muscle function. In addition, it appears that changes in the 3' region of at least one of the actin mRNA may affect its steady-state regulation during development.     

Expression of chimeric genes in Caenorhabditis elegans

We have shown the expression of transformed genes in the nematode Caenorhabditis elegans using a new gene fusion system. Vectors consisting of the flanking regions of a collagen gene (col-1) or a major sperm protein gene of C. elegans fused to the Escherichia coli uidA gene, encoding beta-glucuronidase, were microinjected into worms and found to be propagated as high-copy extrachromosomal tandem arrays. We have detected beta-glucuronidase activity in transformed lines, and have shown that the activity is dependent upon the correct reading frame of the construction and on the presence of the worm sequences. The enzyme activity was shown to be encoded by the chimeric beta-glucuronidase gene by co-segregation analysis and by inactivation with specific antisera. Expression is at a very low level, and seems to be constitutive. We have used histochemical techniques to visualize the enzyme activity in embryos.     

Thiamine pyrophosphate biosynthesis and transport in the nematode Caenorhabditis elegans

Thiamine (vitamin B1) is required in the diet of animals, and thiamine deficiency leads to diseases such as beri-beri and the Wernicke-Korsakoff syndrome. Dietary thiamine (vitamin B1) consists mainly of thiamine pyrophosphate (TPP), which is transformed into thiamine by gastrointestinal phosphatases before absorption. It is believed that TPP itself cannot be transported across plasma membranes in significant amounts. We have identified a partial loss-of-function mutation in the Caenorhabditis elegans gene (tpk-1) that encodes thiamine pyrophosphokinase, which forms TPP from thiamine at the expense of ATP inside cells. The mutation slows physiological rhythms and the phenotype it produces can be rescued by TPP but not thiamine supplementation. tpk-1 functions cell nonautonomously, as the expression of wild-type tpk-1 in one tissue can rescue the function of other tissues that express only mutant tpk-1. These observations indicate that, in contrast to expectation from previous evidence, TPP can be transported across cell membranes. We also find that thiamine supplementation partially rescues the phenotype of partial loss-of-function mutants of the Na/K ATPase, providing genetic evidence that thiamine absorption, and/or redistribution from the absorbing cells, requires the full activity of this enzyme.     

The Caenorhabditis elegans genes ced-3 and ced-4 act cell autonomously to cause programmed cell death

Mutations in the genes ced-3 and ced-4 prevent almost all of the programmed cell deaths that occur during Caenorhabditis elegans development. To determine the sites of action of these two genes, we performed genetic mosaic analyses. We generated C. elegans animals that carried a free chromosomal duplication bearing either ced-3(+) or ced-4(+) in an otherwise homozygous ced-3 or ced-4 genetic background. We used other genes on the duplication as markers to identify genetic mosaic animals in which the duplication was present in some but not all cells. The patterns of cell death survivors in these mosaic animals indicated that the products of both ced-3 and ced-4 function within dying cells to cause cell death.     

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.     

Trehalose metabolism genes in Caenorhabditis elegans and filarial nematodes

The sugar trehalose is claimed to be important in the physiology of nematodes where it may function in sugar transport, energy storage and protection against environmental stresses. In this study we investigated the role of trehalose metabolism in nematodes, using Caenorhabditis elegans as a model, and also identified complementary DNA clones putatively encoding genes involved in trehalose pathways in filarial nematodes. In C. elegans two putative trehalose-6-phosphate synthase (tps) genes encode the enzymes that catalyse trehalose synthesis and five putative trehalase (tre) genes encode enzymes catalysing hydrolysis of the sugar. We showed by RT-PCR or Northern analysis that each of these genes is expressed as mRNA at all stages of the C. elegans life cycle. Database searches and sequencing of expressed sequence tag clones revealed that at least one tps gene and two tre genes are expressed in the filarial nematode Brugia malayi, while one tps gene and at least one tre gene were identified for Onchocerca volvulus. We used the feeding method of RNA interference in C. elegans to knock down temporarily the expression of each of the tps and tre genes. Semiquantitative RT-PCR analysis confirmed that expression of each gene was silenced by RNA interference. We did not observe an obvious phenotype for any of the genes silenced individually but gas-chromatographic analysis showed >90% decline in trehalose levels when both tps genes were targeted simultaneously. This decline in trehalose content did not affect viability or development of the nematodes.     

Cuticle collagen genes. Expression in Caenorhabditis elegans

Collagen is a structural protein used in the generation of a wide variety of animal extracellular matrices. The exoskeleton of the free-living nematode, Caenorhabditis elegans, is a complex collagen matrix that is tractable to genetic research. Mutations in individual cuticle collagen genes can cause exoskeletal defects that alter the shape of the animal. The complete sequence of the C. elegans genome indicates upwards of 150 distinct collagen genes that probably contribute to this structure. During the synthesis of this matrix, individual collagen genes are expressed in distinct temporal periods, which might facilitate the formation of specific interactions between distinct collagens.     

Predicting aging/longevity-related genes in the nematode Caenorhabditis elegans

We present a novel mathematical/computational strategy for predicting genes/proteins associated with aging/longevity. The novelty of our method arises from the topological analysis of an organismal longevity gene/protein network (LGPN), which extends the existing cellular networks. The LGPN nodes represent both genes and corresponding proteins. Links stand for all known interactions between the nodes. The LGPN of C. elegans incorporated 362 genes/proteins, 160 connecting and 202 age-related ones, from a list of 321 with known impact on aging/longevity. A 'longevity core' of 129 directly interacting genes or proteins was identified. This core may shed light on the large-scale mechanisms of aging. Predictions were made, based upon the finding that LGPN hubs and centrally located nodes have higher likelihoods of being associated with aging/longevity than do randomly selected nodes. Analysis singled-out 15 potential aging/longevity-related genes for further examination: mpk-1, gei-4, csp-1, pal-1, mkk-4, 4O210, sem-5, gei-16, 1O814, 5M722, ife-3, ced-10, cdc-42, 1O776Co, and 1O690.     

Longevity determined by developmental arrest genes in Caenorhabditis elegans

The antagonistic pleiotropy theory of aging proposes that aging takes place because natural selection favors genes that confer benefit early on life at the cost of deterioration later in life. This theory predicts that genes that impact development would play a key role in shaping adult lifespan. To better understand the link between development and adult lifespan, we examined the genes previously known to be essential for development. From a pool of 57 genes that cause developmental arrest after inhibition using RNA interference, we have identified 24 genes that extend lifespan in Caenorhabditis elegans when inactivated during adulthood. Many of these genes are involved in regulation of mRNA translation and mitochondrial functions. Genetic epistasis experiments indicate that the mechanisms of lifespan extension by inactivating the identified genes may be different from those of the insulin/insulin-like growth factor 1 (IGF-1) and dietary restriction pathways. Inhibition of many of these genes also results in increased stress resistance and decreased fecundity, suggesting that they may mediate the trade-offs between somatic maintenance and reproduction. We have isolated novel lifespan-extension genes, which may help understand the intrinsic link between organism development and adult lifespan.