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At least 127 records · Page 7Linked to original sources
PubMed1999

Cloning and characterization of two nuclear receptors from the filarial nematode Brugia pahangi.

Nuclear receptors (NRs) encompass a superfamily of cytoplasmic/nuclear localized receptors that on ligand binding (or by phosphorylation) directly regulate the transcription of target genes. NRs are involved in many developmental processes, including moulting in insects and dauer larva formation in Caenorhabditis elegans. Here we report the isolation of two genes related to NRs from the filarial nematode Brugia pahangi. Bp-nhr-1 is a member of the NGF1-B subfamily of NRs and is expressed at very low levels in post-infective larval stage 3 (L3) after their transmission to the mammalian host. The second gene, Bp-nhr-2, is related to XR78E/F of Drosophila, a gene involved in the ecdysone response, over the region of its DNA-binding domain. cDNA and genomic clones have been isolated that correspond to Bp-nhr-2. The most striking feature of the encoded protein is that, although there is a DNA-binding domain similar to that of other NRs, the ligand-binding domain is absent. To investigate the pattern of transcription of Bp-nhr-2 in the filarial life cycle, semi-quantitative reverse-transcriptase-mediated PCR was performed; this analysis demonstrated that the gene is expressed in early stages after infection and in the adult and microfilariae, and is up-regulated just before the moult between L3 and L4 but is not expressed during the moult between L4 and adult. Antibodies raised against a peptide corresponding to the transactivation domain of Bp-nhr-2 demonstrate that the protein is expressed in microfilariae and adult samples and that another cross-reactive protein is expressed in these life-cycle stages.

Amino Acid Sequence↗
PubMed2006

Targets of DAF-16 involved in Caenorhabditis elegans adult longevity and dauer formation.

The Forkhead Box O transcription factor DAF-16 regulates genes affecting dauer larva formation and adult life span. Expression profiling and genome-wide searches for DAF-16 binding sites in gene regulatory regions have identified thousands of potential DAF-16 targets. Some of these genes have been shown to alter longevity when their expression is attenuated by RNAi treatment. DAF-16 also associates with other transcription factors, allowing combinatorial modulation of gene expression. Although extensive descriptions of the gene network regulated by DAF-16 have been attempted, there remain many gaps in the understanding of how DAF-16 regulates dauer formation and longevity.

Aging↗
PubMed1999

Molecular cloning and demonstration of an aminopeptidase activity in a filarial nematode glycoprotein.

ES-62 is an abundant phosphorylcholine-containing secreted glycoprotein of the filarial nematode Acanthocheilonema viteae. Using an antiserum directed against the parasite molecule, 3 cDNAs of size, approximately 1.5-1.6 kbp were isolated from an A. viteae expression library. Sequence analysis in combination with N-terminal amino acid sequencing of purified ES-62 revealed that each clone contained a full-length cDNA for ES-62 corresponding to 474 amino acid residues but differed in their 5' and 3' untranslated regions. Characterisation of the 5' end of ES-62 mRNA using 5' rapid amplification of cDNA ends showed that it coded for a signal sequence. Several tryptic peptides were independently sequenced using quadruple-time-of-flight mass spectrometry and used to confirm the cDNA sequence. The mature protein was found to contain three potential N-linked glycosylation sites. Comparison of the derived amino acid sequence of ES-62 with the SwissProt database identified a sequence (between amino acid residues approximately 250 and 350 of mature ES-62) with significant similarity to several bacterial/fungal aminopeptidases. Incubation of ES-62 with leucine-7-amino-4-methylcoumarin as substrate confirmed that ES-62 possessed aminopeptidase activity.

Amino Acid Sequence↗
PubMed1999

SL1 trans splicing and 3'-end formation in a novel class of Caenorhabditis elegans operon.

Many Caenorhabditis elegans genes exist in operons in which polycistronic precursors are processed by cleavage at the 3' ends of upstream genes and trans splicing 100 to 400 nucleotides away, at the 5' ends of downstream genes, to generate monocistronic messages. Of the two spliced leaders, SL1 is trans spliced to the 5' ends of upstream genes, whereas SL2 is reserved for downstream genes in operons. However, there are isolated examples of what appears to be a different sort of operon, in which trans splicing is exclusively to SL1 and there is no intercistronic region; the polyadenylation signal is only a few base pairs upstream of the trans-splice site. We have analyzed the processing of an operon of this type by inserting the central part of mes-6/cks-1 into an SL2-type operon. In this novel context, cks-1 is trans spliced only to SL1, and mes-6 3'-end formation occurs normally, demonstrating that this unique mode of processing is indeed intrinsic to this kind of operon, which we herein designate "SL1-type." An exceptionally long polypyrimidine tract found in the 3' untranslated regions of the three known SL1-type operons is shown to be required for the accumulation of both upstream and downstream mRNAs. Mutations of the trans-splice and poly(A) signals indicate that the two processes are independent and in competition, presumably due to their close proximity, raising the possibility that production of upstream and downstream mRNAs is mutually exclusive.

Animals↗
PubMed2001

Isolation of a novel collagen gene (Mj-col-5) in Meloidogyne javanica and analysis of its expression pattern.

Mj-col-5, isolated from the plant parasitic nematode Meloidogyne javanica, has a longer carboxy-terminus than other members of the Caenorhabditis elegans COL-6 subfamily of cuticle collagen, including an extra tyrosine residue, and may form altered nonreducible cross-linkages. By semiquantitative determination at different life stages, Mj-col-5 transcript was shown to be more abundant in eggs than in juveniles/young females and adult females. To characterize further this gene's contribution to the changing cuticle of the nematode, we expressed a fusion protein containing a nonconserved 58-amino-acid sequence from the putative Mj-col-5 gene product and raised rabbit antiserum against the fusion protein. The antiserum detected a strongly reacting band (36 kDa, designated MJE36) on western blots of M. javanica eggs extracted with beta-mercaptoethanol. MJE36 was sensitive to collagenase and was not detected on western blots of extracts from M. javanica second-stage juveniles or adult females. A band of the same molecular size was detected in Meloidogyne incognita egg extracts but not in those of Heterodera avenae. Immunoblot indicated that MJE36 is not present in egg shells of M. javanica.

Amino Acid Sequence↗
PubMed1996

Genomic structure and 5' regulatory regions of the let-23 gene in the nematode C. elegans.

The let-23 gene in the nematode Caenorhabditis elegans encodes a receptor tyrosine kinase and is necessary for the induction of a vulva, survival past the L1 stage, hermaphrodite fertility and for male spicule development. We sequenced the entire let-23 genomic region of over 12 kb. The 5' end of the let-23 mRNA was mapped by sequencing polymerase chain reaction products, and two mRNAs were found which had alternative exons and were probably initiated at different sites. One transcript was trans-spliced to SL1. Expression of either cDNA rescued a let-23 vulvaless mutation in germline transformation. These results suggest that the let-23 gene encodes two proteins of 1323 or 1335 amino acid residues. We prepared various 5' deletion constructs of the let-23 gene, and examined their rescue activities for a let-23 lethal or vulvaless mutation. The results revealed that two regions were required for let-23 expression, one for larval survival and the other for vulva formation. We also cloned and analyzed a let-23 homologue from Caenorhabditis vulgaris. It can encode two proteins of 77% amino acid residue identity with the Let-23 proteins. The 12 kb fragment carrying the C. vulgaris gene rescued the let-23 vulvaless mutation in C. elegans. Seventeen sequences highly conserved between the two species were identified in the 5' upstream region or within an intron. Three of these sequences are contained in the two regions required for let-23 expression, suggesting that they are cis-acting elements for let-23 expression.

Amino Acid Sequence↗
PubMed1999

Origin and evolution of paralogous rRNA gene clusters within the flatworm family Dugesiidae (Platyhelminthes, Tricladida).

Analysis of the 18S rDNA sequences of five species of the family Dugesiidae (phylum Platyhelminthes, suborder Tricladida, infraorder Paludicola) and eight species belonging to families Dendrocoelidae and Planaridae and to the infraorder Maricola showed that members of the family Dugesiidae have two types of 18S rDNA genes, while the rest of the species have only one. The duplication event also affected the ITS-1, 5.8S, ITS-2 region and probably the 28S gene. The mean divergence value between the type I and the type II sequences is 9% and type II 18S rDNA genes are evolving 2.3 times more rapidly than type I. The evolutionary rates of type I and type II genes were calibrated from biogeographical data, and an approximate date for the duplication event of 80-120 million years ago was calculated. The type II gene was shown, by RT-PCR, to be transcribed in adult individuals of Schmidtea polychroa, though at very low levels. This result, together with the fact that most of the functionally important positions for small-subunit rRNA in prokaryotes have been conserved, indicates that the type II gene is probably functional.

Animals↗
PubMed1995

Characterization of the gene family encoding a host-protective antigen of the tapeworm Taenia ovis.

Genomic structure has been determined for a gene encoding a host-protective antigen of the parasitic platyhelminth Taenia ovis. An incomplete cDNA, known as 45W, encodes the protective antigen. Southern hybridisation experiments using 45W cDNA as a probe, revealed that the 45W gene was a member of a multigene family. Differential Southern hybridisation and rapid amplification of cDNA end (RACE) experiments were used to characterise the related genes, allowing the full-length coding region of the 45W encoded antigen to be determined. The gene family comprises a minimum of four members per haploid genome with each member showing varying degrees of 5' and 3' homology with respect to the 45W cDNA. A close homologue of the 45W gene, designated 45S, differed from 45W at 11 of 985 nt comprising the full-length mRNA. Sequencing of several independent RACE products for both 45W and 45S identified a cDNA which may be a product of homologous recombination between these genes, suggesting that the two genes may be alleles. Homologous recombination in genes which encode a host protective antigen such as 45W would provide a mechanism by which antigenic variants could arise.

Amino Acid Sequence↗
PubMed1994

Trans-splicing of a Meloidogyne incognita mRNA encoding a putative esophageal gland protein.

A monoclonal antibody, 7A9, specific for antigens in the subventral esophageal glands of adult female Meloidogyne incognita and for antigens in the longitudinal muscles of second-stage juveniles, was used to isolate a clone from a M. incognita cDNA expression library. The corresponding genomic DNA was isolated by hybridization and the gene designated sec-1. DNA sequence analysis of sec-1 revealed the presence of 9 introns having structural similarities to introns from the free-living nematode Caenorhabditis elegans. The sec-1 message was also trans-spliced and the leader sequence differed in one position from the sequence of the C. elegans trans-spliced leader SL1. Sequences analogous to sec-1 were specific to the genus Meloidogyne, and regulation of sec-1 expression did not involve differences in overall rates of transcript accumulation. The deduced amino acid sequence of the protein encoded by sec-1 had some similarities to the rod portions of several myosin heavy chains.

Amino Acid Sequence↗
PubMed2004

A genome sequence survey of the filarial nematode Brugia malayi: repeats, gene discovery, and comparative genomics.

Comparative nematode genomics has thus far been largely constrained to the genus Caenorhabditis, but a huge diversity of other nematode species, and genomes, exist. The Brugia malayi genome is approximately 100 Mb in size, and distributed across five chromosome pairs. Previous genomic investigations have included definition of major repeat classes and sequencing of selected genes. We have generated over 18,000 sequences from the ends of large-insert clones from bacterial artificial chromosome libraries. These end sequences, totalling over 10 Mb of sequence, contain just under 8 Mb of unique sequence. We identified the known Mbo I and Hha I repeat families in the sequence data, and also identified several new repeats based on their abundance. Genomic copies of 17% of B. malayi genes defined by expressed sequence tags have been identified. Nearly one quarter of end sequences can encode peptides with significant similarity to protein sequences in the public databases, and we estimate that we have identified more than 2700 new B. malayi genes. Importantly, 459 end sequences had homologues in other organisms, but lacked a match in the completely sequenced genomes of Caenorhabditis briggsae and Caenorhabditis elegans, emphasising the role of gene loss in genome evolution. B. malayi is estimated to have over 18,500 protein-coding genes.

Animals↗
PubMed2004

Stage-specific and species-specific differences in the production of the mRNA and protein for the filarial nematode secreted product, ES-62.

Previous studies have shown that the secreted phosphorylcholine-containing glycoprotein of filarial nematodes, ES-62, is only present in the post-infective life-cycle stages, but that the mRNA is transcribed throughout the worm's life-cycle. The aim of this current study was to investigate whether the presence or absence of protein expression simply reflects differences in mRNA abundance. To this end, we investigated the relative abundance of ES-62 using TaqMan real time RT-PCR, in different life-cycle stages of 2 model filarial nematode parasites, Acanthocheilonema viteae and Brugia pahangi. For B. pahangi, microfilariae, infective larvae and adult worms were each found to have approximately similar levels of ES-62 mRNA. However, the corresponding stages of A. viteae differed greatly from each other with a pattern of increased mRNA production with maturation. As a rule A. viteae had higher levels of ES-62 mRNA than B. pahangi, and this was particularly noticeable in the adult stage where the difference was approximately 3500-fold higher. However, this significant difference in mRNA abundance was not reflected in the quantity of ES-62 protein secreted by the adult worms of each species, as A. viteae only secreted approximately 3 times as much ES-62 as B. pahangi. Thus, overall, the results obtained from this study indicate that ES-62 protein production does not solely reflect mRNA levels, and also suggest that the 2 nematodes may employ different mechanisms for regulating protein production.

Animals↗
PubMed1995

18S rRNA data indicate that Aschelminthes are polyphyletic in origin and consist of at least three distinct clades.

The Aschelminthes is a collection of at least eight animal phyla, historically grouped together because the absence of a true body cavity was perceived as a pseudocoelom. Analyses of 18S rRNA sequences from six Aschelminth phyla (including four previously unpublished sequences) support polyphyly for the Aschelminthes. At least three distinct groups of Aschelminthes were detected: the Priapulida among the protostomes, the Rotifera-Acanthocephala as a sister group to the protostomes, and the Nematoda as a basal group to the triploblastic Eumetazoa.

Acanthocephala↗
PubMed1999

Launching the germline in Caenorhabditis elegans: regulation of gene expression in early germ cells.

One hundred years after Weismann's seminal observations, the mechanisms that distinguish the germline from the soma still remain poorly understood. This review describes recent studies in Caenorhabditis elegans, which suggest that germ cells utilize unique mechanisms to regulate gene expression. In particular, mechanisms that repress the production of mRNAs appear to be essential to maintain germ cell fate and viability.

Animals↗
PubMed2003

Molecular phylogeny of Haematoloechus Looss, 1899 (Digenea: Plagiorchiidae), with emphasis on North American species.

Phylogenetic hypothesis of 23 populations corresponding to 18 species of the digenean Haematoloechus from America, Europe, and Africa, based on ribosomal DNA 28S partial sequences (approximately 890 bp), is presented. Genetic divergence between the in-group and the out-groups ranged from 9.7 to 14.5% and within the in-group, from 0.9 to 12.2%. Eight most parsimonious trees 569 steps long were obtained, with a consistency index of 72%. Groups in the tree are not congruent with those in previous classification schemes of species in the genus, based on a small number of morphological characters. For this subset of Haematoloechus species, plesiomorphic hosts are species of Rana, with 2 colonizations to other amphibian groups. African species appear to have diverged after the separation of Gondwana and Laurasia. Therefore, South American species should appear as the closest relatives of African species when included in the analysis. The evidence presented suggests an ancestral wide distribution of North American representatives of the group, followed by successive contraction, amplification, and fragmentation of ranges and speciation events as a result of the intense volcanic activity in the central part of Mexico since the late Tertiary, the drying climate of western and central United States and northwestern Mexico from the early Eocene to the Pleistocene, and the glaciation during the Pleistocene.

Animals↗