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At least 829 records · Page 46Linked to original sources
PubMed2006

Genetically engineered underdominance for manipulation of pest populations: a deterministic model.

We theoretically investigate the potential for introgressing a desired engineered gene into a pest population by linking the desired gene to DNA constructs that exhibit underdominance properties. Our deterministic model includes two independently segregating engineered constructs that both carry a lethal gene, but suppress each other. Only genotypes containing both or neither construct are viable. Both constructs also carry the desired gene with an independent regulatory mechanism. We examine the minimal number of individuals of an engineered strain that must be released into a natural population to successfully introgress the desired gene. We compare results for strains carrying single and multiple insertions of the constructs. When there are no fitness costs associated with the inserted constructs (when the lethal sequences are not expressed), the number of individuals that must be released decreases as the number of insertions in the genome of the released strain increases. As fitness costs increase, the number of individuals that must be released increases at a greater rate for release strains with more insertions. Under specific conditions this results in the strain with only a single insertion of each construct being the most efficient for introgressing the desired gene. We discuss practical implications of our findings.

Animals↗
PubMed2003

Reflections on the Anopheles gambiae genome sequence, transgenic mosquitoes and the prospect for controlling malaria and other vector borne diseases.

The completion of the Anopheles gambiae Giles genome sequencing project is a milestone toward developing more effective strategies in reducing the impact of malaria and other vector borne diseases. The successes in developing transgenic approaches using mosquitoes have provided another essential new tool for further progress in basic vector genetics and the goal of disease control. The use of transgenic approaches to develop refractory mosquitoes is also possible. The ability to use genome sequence to identify genes, and transgenic approaches to construct refractory mosquitoes, has provided the opportunity that with the future development of an appropriate genetic drive system, refractory transgenes can be released into vector populations leading to nontransmitting mosquitoes. An. gambiae populations incapable of transmitting malaria. This compelling strategy will be very difficult to achieve and will require a broad substantial research program for success. The fundamental information that is required on genome structure, gene function and environmental effects on genetic expression are largely unknown. The ability to predict gene effects on phenotype is rudimentary, particularly in natural populations. As a result, the release of a refractory transgene into natural mosquito populations is imprecise and there is little ability to predict unintended consequences. The new genetic tools at hand provide opportunities to address an array of important issues, many of which can have immediate impact on the effectiveness of a host of strategies to control vector borne disease. Transgenic release approaches represent only one strategy that should be pursued. A balanced research program is required.

Animals↗
PubMedDate not supplied

Duplication of the genome in normal and cancer cell cycles.

It is critical to discover the mechanisms of normal cell cycle regulation if we are to fully understand what goes awry in cancer cells. The normal eukaryotic cell tightly regulates the activity of origins of DNA replication so that the genome is duplicated exactly once per cell cycle. Over the last ten years much has been learned concerning the cell cycle regulation of origin activity. It is now clear that the proteins and cell cycle mechanisms that control origin activity are largely conserved from yeast to humans. Despite this conservation, the composition of origins of DNA replication in higher eukaryotes remains ill defined. A DNA consensus for predicting origins has yet to emerge, and it is of some debate whether primary DNA sequence determines where replication initiates. In this review we outline what is known about origin structure and the mechanism of once per cell cycle DNA replication with an emphasis on recent advances in mammalian cells. We discuss the possible relevance of these regulatory pathways for cancer biology and therapy.

Animals↗
PubMed1996

Genetic exchange as a possible source of genomic diversity in sylvatic populations of Trypanosoma cruzi.

Thirty six stocks of Trypanosoma cruzi isolated from sylvatic mammals (32 Didelphis marsupialis and one Philander opossum) and triatomine bugs (Rhodnius robustus and one unidentified bug) in the Amazonian forest by Carajas, Brazil were characterized by isoenzyme and random amplified polymorphic DNA (RAPD) analysis as belonging to principal zymodeme '1 (Z1). Two different homozygous phenotypes and the corresponding heterozygous phenotype were found for phosphoglucomutase with an observed frequency almost identical with that predicted by the theoretical Hardy-Weinberg distribution. Parental and hybrid profiles were also suggested by RAPD analysis, which allowed exclusion of mixed parental strains from the hybrids: isoenzyme and RAPD profiles of biological clones were also indistinguishable from those of uncloned stocks. Trypanosoma cruzi stocks from widely separated geographic origins in Central and South America gave similar RAPD profiles that allowed them to be recognized as being Z1. These results indicate that genetic exchange could contribute to the generation of genetic diversity during the sylvatic cycle of T. cruzi, and this may have epidemiologic and taxonomic implications.

Animals↗
PubMed1997

Genetic variability and geographic differentiation among three species of Triatomine bugs (Hemiptera-Reduviidae).

Three species of triatomine bugs, Triatoma sordida, T. guasayana, and T. patagonica, were examined by cytogenetic (C-banded karyotypes and male meiotic process) and isoenzymatic studies. These three species, with different importance as Chagas' disease vectors, were found to be closely related according to their known ethologic, ecologic, and morphologic traits. Although they have the same diploid chromosome number (2n = 22 constituted by 20 autosomes and an XY male/XX female sex mechanism), each species has a distinct chromosomal behavior during male meiosis and a specific amount and localization of C-heterochromatic blocks. Moreover, these chromosome characteristics allowed us to differentiate two T. sordida populations. Isoenzymatic data confirmed the taxonomic status of the three species and together with our cytogenetic results questioned the species homogeneity of T. sordida.

Animals↗
PubMed1998

Species-specific repeat units in the intergenic spacer of the ribosomal RNA cistron of Anopheles aquasalis Curry.

A genomic DNA library of Anopheles aquasalis Curry was screened for clones that hybridized more intensely to DNA from A. aquasalis than to DNA from A. benarrochi Gabaldon, Cova Garcia, and Lopez, A. konderi Galvao and Damasceno, A. nuneztovari Gabaldon cytotypes A, B, and C, A. oswaldoi (Peryassu), A. rangeli Gabaldon, Cova Garcia, and Lopez, or A. trinkae Faran. Two specific clones (2.5 kilobasepairs [kbp] and 3.0 kbp) from A. aquasalis were isolated. Both A. aquasalis-specific clones were from the intergenic spacer region of the ribosomal RNA (rRNA) cistron. Upon digestion with Rsa I, a 900-bp fragment from the clone AA-1 hybridized specifically to A. aquasalis DNA. Analysis of the DNA sequence of this fragment revealed four tandemly repeated 36-bp units. Three of these repeat units were identical, and the fourth was 94% identical to the others. The DNA sequence of a highly conserved region of these repeats was used to synthesize an oligonucleotide probe specific to A. aquasalis.

Animals↗
PubMed2006

Expression and characterization of RNA-dependent RNA polymerase of Dendrolimus punctatus tetravirus.

Dendrolimus punctatus tetravirus (DpTV) has been identified as a new member of the genus Omegatetravirus of the family Tetraviridae that may be related serologically to Nudaurelia capensis virus (NomegaV). To establish the function of DpTV RNA genome and to better understand the mechanism of viral replication, the putative RNA-dependent RNA polymerase (RdRp) domain has been cloned and expressed in Escherichia coli. The recombinant protein was purified on a Ni-chelating HisTrap affinity column and demonstrated to initiate viral RNA synthesis in a primer-independent manner but not by terminal nucleotidyle transferase activity in the presence of Mg2+ and RNA template. Mutation of the GDD to GAA interferes with the residues at the polymerase active site and metal ions, and thus renders the polymerase inactive.

Amino Acid Sequence↗
PubMed2003

[Cotransformation of rice by bar and cecropin B gene expression cassettes lacking vector backbone sequences].

Whole plasmids are used in both Agrobacterium-mediated transformation and direct DNA transfer, generally leading to the integration of vector backbone sequences into the host genome along with the transgene(s). The undesirable vector backbone sequences may not only promote transgene rearrangements and affect transgene or endogenous gene expression negatively, but have disadvantage on the safe assessment of the transformants as "desert DNA". The direct DNA transforming systems can transfer minimal gene expression cassettes (promoter, open reading frame, terminator) into plant genome and generate "safer" transformants, also it can delivery multiple genes of agronomic relevance to economically-important crop plants. But there is seldom researching reports on the topic till now. The present paper studied some factors that affecting the transforming efficiency of liner gene expression cassettes to rice varieties by particle bombardment, and the integration patterns of the gene expression cassettes in rice genome were compared with that of the whole plasmids. The results showed: (1) The transforming frequency of gene expression cassettes to rice via particle bombardment is 0.1%-0.5%, the cotransforming frequency of non-selectable gene is about 50%-60% when two separate gene expression cassettes were used for transformation. Increasing the DNA mole content can increase the transforming frequency and the beside sequences of gene constructs may play an important role on the variation of transforming efficiency between different rice varieties. (2) It's reported that the selectable and non-selectable transgene expression cassettes generated low-copy-number transgenic plants with simple integration patterns. While our results showed that the non-selectable cecropin B gene cassette generated simple integration patterns with 1-3 copies in the rice genome, but the selectable bar gene cassette which got 4-14 copies had much more complex integration patterns than that of the whole plasmids which got 1-3 copies only. As the bar gene is promoted by the CaMV35 promoter, in which there is a 19 bp palindromic sequence could act as recombination hot spot and lead to DNA rearrangement, we presumed that the transgene recombination events happened during the integration course have generated the complex Southern patterns of bar gene expression cassette. The recombination character, the heredity behavior and the expression law of gene expression cassettes in the rice genomes will be reported in our future papers.

Acetyltransferases↗
PubMed1996

A purified mariner transposase is sufficient to mediate transposition in vitro.

Mariners are a widespread and diverse family of animal transposons. Extremely similar mariners of the irritans subfamily are present in the genomes of three divergent insect host species, which strongly suggests that species-specific host factors are unnecessary for mobility. We tested this hypothesis by examining the activity of a purified transposase from one of these elements (Himar1) present in the horn fly, Haematobia irritans. Himar1 transposase was sufficient to reproduce transposition faithfully in an in vitro inter-plasmid transposition reaction. Further analyses showed that Himar1 transposase binds to the inverted terminal repeat sequences of its cognate transposon and mediates 5' and 3' cleavage of the element termini. Independence of species-specific host factors helps to explain why mariners have such a broad distribution and why they are capable of horizontal transfer between species.

Animals↗
PubMed2001

Nucleotide sequence of 3'-end of the genome of Taura syndrome virus of shrimp suggests that it is related to insect picornaviruses.

Taura syndrome disease, caused by Taura syndrome virus (TSV), is one of the most important viral diseases of penaeid shrimp in the Western Hemisphere resulting in catastrophic disease epidemics in farmed shrimp. We have cloned and sequenced a 3278 bp cDNA representing the 3' end of the TSV genome. Sequence analyses revealed that frame + 2 had the longest open reading (ORF) frame. This frame contained a 5'-terminal 19 non-coding bases followed by an ORF from nucleotides 20 to 3053 (encoding 1011 amino acids, aa) and a 3' untranslated region of 225 nts. The deduced aa sequence of TSV showed significant similarities with those of the coat proteins of insect picornaviruses, Rhopalosiphum padi virus, Plautia stali intestine virus, Drosophila C virus, Triatoma virus of Triatoma infestans and Himetobi P virus of brown plant hopper. A single transcript of approximately 10 kb was detected by Northern blot hybridization suggesting that the TSV coat protein gene is not expressed as a subgenomic RNA. We concluded that the genome organization of TSV is similar to insect picornaviruses. This is the first molecular evidence of occurrence of a picornavirus in the class Decapoda.

Amino Acid Sequence↗
PubMed2001

Homology-based annotation yields 1,042 new candidate genes in the Drosophila melanogaster genome.

The approach to annotating a genome critically affects the number and accuracy of genes identified in the genome sequence. Genome annotation based on stringent gene identification is prone to underestimate the complement of genes encoded in a genome. In contrast, over-prediction of putative genes followed by exhaustive computational sequence, motif and structural homology search will find rarely expressed, possibly unique, new genes at the risk of including non-functional genes. We developed a two-stage approach that combines the merits of stringent genome annotation with the benefits of over-prediction. First we identify plausible genes regardless of matches with EST, cDNA or protein sequences from the organism (stage 1). In the second stage, proteins predicted from the plausible genes are compared at the protein level with EST, cDNA and protein sequences, and protein structures from other organisms (stage 2). Remote but biologically meaningful protein sequence or structure homologies provide supporting evidence for genuine genes. The method, applied to the Drosophila melanogaster genome, validated 1,042 novel candidate genes after filtering 19,410 plausible genes, of which 12,124 matched the original 13,601 annotated genes. This annotation strategy is applicable to genomes of all organisms, including human.

Animals↗
PubMed2006

Immune pathways and defence mechanisms in honey bees Apis mellifera.

Social insects are able to mount both group-level and individual defences against pathogens. Here we focus on individual defences, by presenting a genome-wide analysis of immunity in a social insect, the honey bee Apis mellifera. We present honey bee models for each of four signalling pathways associated with immunity, identifying plausible orthologues for nearly all predicted pathway members. When compared to the sequenced Drosophila and Anopheles genomes, honey bees possess roughly one-third as many genes in 17 gene families implicated in insect immunity. We suggest that an implied reduction in immune flexibility in bees reflects either the strength of social barriers to disease, or a tendency for bees to be attacked by a limited set of highly coevolved pathogens.

Animals↗
PubMed2000

Infectious disease. Research (genomics) is crucial to attacking malaria.

Solving the enormous problem of malaria worldwide will require a balance between investments in research and control. In this point-counterpoint, two scientists describe the rationales for these very different strategies. Steve Hoffman believes that genomics research is the best investment in the future if we have the vision of malaria eradication. Chris Curtis presents an opposing viewpoint, that low-tech control approaches are the practical ones under current conditions.

Animals↗
PubMed2005

Analysis of cytochrome P450 genes in silkworm genome (Bombyx mori).

We have searched the Bombyx mori genome for members of the major enzyme family, the Cytochrome P450s, which carry out multiple reactions to enable organisms to rid themselves of foreign compounds. As a result, 86 putative P450s were discovered in silkworm genome, which are thought to belong to 32 subfamilies. A comparative genomic analysis with Drosophila melanogaster reveals that the two insects have some similar P450 distribution patterns but still have some obvious differences. Especially, the diverse distribution exists in 7 p450 subfamilies, which are CYP4A, CYP4C, CYP4D, CYP6A, CYP6AE, CYP6B and CYP9A. Furthermore, we collected expression sequence tag (EST) evidence for 49 putative P450s genes, which are expressed at the transcriptional level and more likely to be true P450s.

Animals↗
PubMed2000

Infectious disease. The case for deemphasizing genomics in malaria control.

Solving the enormous problem of malaria worldwide will require a balance between investments in research and control. In this point-counterpoint, two scientists describe the rationales for these very different strategies. Steve Hoffman believes that genomics research is the best investment in the future if we have the vision of malaria eradication. Chris Curtis presents an opposing viewpoint, that low-tech control approaches are the practical ones under current conditions.

Animals↗