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At least 397 records · Page 22Linked to original sources
PubMed1993

An amplified mosquito dihydrofolate reductase gene: amplicon size and chromosomal distribution.

The dihydrofolate reductase amplicon in methotrexate-resistant mosquito cells provides an amplified gene in insects that can be compared directly to the corresponding amplified locus in mammalian cells. A cloned Aedes albopictus dihydrofolate reductase gene was used as a probe to examine the structure of dihydrofolate reductase alleles in sensitive and resistant cells. In wild type cells, two distinct alleles could be distinguished by restriction fragment length polymorphisms, one of which was amplified in methotrexate-resistant cells. Subsequent to amplification, an additional polymorphism at a ten base-pair XmnI recognition site indicated that the amplified mosquito gene is subject to genetic changes similar to those that have been described in amplified genes from mammalian cells. Pulsed-field gel electrophoresis was used to determine that the minimum size of the mosquito dihydrofolate reductase amplicon was 140 kilobases; ethidium bromide staining patterns suggested a size of at least 233 kilobases. Dihydrofolate reductase probes hybridized to distinct locations in five of the thirteen chromosomes in Mtx-5011-128 cells, indicating that the amplified DNA probably occurs as tandem direct or inverted repeats.

Aedes↗
PubMed2003

Construction of two BAC libraries from the wild Mexican diploid potato, Solanum pinnatisectum, and the identification of clones near the late blight and Colorado potato beetle resistance loci.

To facilitate isolation and characterization of disease and insect resistance genes important to potato, two bacterial artificial chromosome (BAC) libraries were constructed from genomic DNA of the Mexican wild diploid species, Solanum pinnatisectum, which carries high levels of resistance to the most important potato pathogen and pest, the late blight and the Colorado potato beetle (CPB). One of the libraries was constructed from the DNA, partially digested with BamHI, and it consists of 40328 clones with an average insert size of 125 kb. The other library was constructed from the DNA partially digested with EcoRI, and it consists of 17280 clones with an average insert size of 135 kb. The two libraries, together, represent approximately six equivalents of the wild potato haploid genome. Both libraries were evaluated for contamination with organellar DNA sequences and were shown to have a very low percentage (0.65-0.91%) of clones derived from the chloroplast genome. High-density filters, prepared from the two libraries, were screened with ten restriction fragment length polymorphism (RFLP) markers linked to the resistance genes for late blight, CPB, Verticillium wilt and potato cyst nematodes, and the gene Sr1 for the self-incompatibility S-locus. Thirty nine positive clones were identified and at least two positive BAC clones were detected for each RFLP marker. Four markers that are linked to the late blight resistance gene Rpi1 hybridized to 14 BAC clones. Fifteen BAC clones were shown to harbor the PPO (polyphenol oxidase) locus for the CPB resistance by three RFLP probes. Two RFLP markers detected five BAC clones that were linked to the Sr1 gene for self-incompatibility. These results agree with the library's predicted extent of coverage of the potato genome, and indicated that the libraries are useful resources for the molecular isolation of disease and insect resistance genes, as well as other economically important genes in the wild potato species. The development of the two potato BAC libraries provides a starting point, and landmarks for BAC contig construction and chromosome walking towards the map-based cloning of agronomically important target genes in the species.

Animals↗
PubMed1993

[Mutagenic effect of pindone on D. melanogaster].

A commercial grade Pindone was tested for the induction of genetic damage in male germ cells of Drosophila melanogaster by adult ingestion. Adults were starved for 4 days and then fed pindone at a concentration of 1 mM in ethyl alcohol 15% containing sucrose 5%. Pindone was found to increase the frequency of sex chromosome loss. Results were significant at the 1% level (Kastenbaum-Bowman test). However no significant results were obtained by the sex linked recessive lethal assay.

Animals↗
PubMed2000

Genetic mapping of two loci affecting DDT resistance in the malaria vector Anopheles gambiae.

Resistance to the insecticide DDT in the mosquito vectors of malaria has severely hampered efforts to control this disease and has contributed to the increase in prevalence of malaria cases seen in recent years. Over 90% of the 300-500 million annual cases of malaria occur in Africa, where the major vector is Anopheles gambiae. DDT resistance in the ZAN/U strain of An. gambiae is associated with an increased metabolism of the insecticide, catalysed by members of the glutathione S-transferase (GST) enzyme family, but the molecular mechanism underlying this metabolic resistance is not known. Genetic crosses show that resistance is autosomal and semidominant. We have used microsatellite markers to identify two quantitative trait loci (QTL), which together explain over 50% of the variance in susceptibility to DDT in the ZAN/U strain of An. gambiae. The first locus, rtd1, is on chromosome 3 between markers H341 and H88 and has a recessive effect with respect to susceptibility. The second locus, rtd2 is on chromosome 2L, close to marker H325 and has an additive genetic effect. The markers flanking these two QTL have been physically mapped to An. gambiae polytene chromosomes. They do not coincide with any of the GST genes that have been cloned and mapped in this species. Characterization of these QTL will lead to a clearer understanding of the mechanisms of metabolic resistance to DDT.

Animals↗
PubMed1997

[Genomic incompatibility in Drosophila virilis Sturt. X Drosophila lummei Hackman hybrids].

Genetic analysis of male sterility in Drosophila virilis x D. lummei hybrids was performed. It was shown that hybrid male sterility was caused mainly by incompatibility of sex chromosomes X and Y and homozygous chromosome 2 of D. virilis with other autosomes of D. lummei. Genes of chromosomes 3 and 5 enhanced sterility whereas genes of chromosome 4 suppressed its development. Factors controlling hybrid male sterility were demonstrated to have a recessive type of inheritance. At 17 degrees C, chromosome 6 of D. lummei was eliminated in F1 hybrids of the cross female D. virilis x male D. lummei. At 17 degrees C and 25 degrees C, sterility of the F1 hybrid males was 96% and 9%, respectively. Thus, two isolation mechanisms-elimination of chromosome 6 and male sterility-can simultaneously operate in F1. In addition to the region of the species-specific inversion In 1(a+b), factors controlling male sterility were mapped to the vermillion region of the X chromosome.

Animals↗
PubMed2002

Reconstitution of telomerase activity utilizing human catalytic subunit expressed in insect cells.

Telomerase is a specialized reverse transcriptase responsible for maintaining the termini of linear chromosomes. The human enzyme is a ribonucleoprotein complex minimally comprising a catalytic protein moiety (hTERT) and an RNA subunit (hTR) which acts as the template for the reverse transcriptase reaction. Here we report expression of recombinant hTERT protein in insect cells utilizing a baculovirus expression system. The recombinant hTERT protein reconstitutes telomerase activity in the presence of hTR, either when co-expressed in insect cells or when added in vitro. Reconstitution of telomerase activity using this system will facilitate further analysis of the biochemical and biophysical properties of this enzyme.

Animals↗
PubMed2002

Heterochromatin protein 1 is involved in control of telomere elongation in Drosophila melanogaster.

Telomeres of Drosophila melanogaster contain arrays of the retrotransposon-like elements HeT-A and TART. Their transposition to broken chromosome ends has been implicated in chromosome healing and telomere elongation. We have developed a genetic system which enables the determination of the frequency of telomere elongation events and their mechanism. The frequency differs among lines with different genotypes, suggesting that several genes are in control. Here we show that the Su(var)2-5 gene encoding heterochromatin protein 1 (HP1) is involved in regulation of telomere length. Different Su(var)2-5 mutations in the heterozygous state increase the frequency of HeT-A and TART attachment to the broken chromosome end by more than a hundred times. The attachment occurs through either HeT-A/TART transposition or recombination with other telomeres. Terminal DNA elongation by gene conversion is greatly enhanced by Su(var)2-5 mutations only if the template for DNA synthesis is on the same chromosome but not on the homologous chromosome. The Drosophila lines bearing the Su(var)2-5 mutations maintain extremely long telomeres consisting of HeT-A and TART for many generations. Thus, HP1 plays an important role in the control of telomere elongation in D. melanogaster.

Animals↗
PubMed2006

[Transposition of the hobo element in Drosophila melanogaster somatic cells].

Somatic mutation and recombination test on wing cells of Drosophila melanogaster showed that the recombination frequency in the somatic tissues of strains studied correlated with the presence of a full-length copy of the hobo transposable element in the genome. Transposition of hobo in somatic tissue cells at a frequency 3.5 x 10-2 per site per X chromosome was shown by fluorescence in situ hybridization with salivary gland polytene chromosomes of larvae of one of the D. melanogaster strains having a full-length hobo copy.

Animals↗
PubMed1993

Cytogenetical localization of Zygotic hybrid rescue (Zhr), a Drosophila melanogaster gene that rescues interspecific hybrids from embryonic lethality.

Hybrid females from crosses between Drsophila melanogaster males and females of its sibling species, D. simulans, D. mauritiana, or D. sechellia die as embryos. This lethality is believed to be caused by incompatibility between the X chromosome of D. melanogaster and the maternal cytoplasm. Zygotic hybrid rescue (Zhr) prevents this embryonic lethality and has been cytogenetically mapped to a proximal region of the X chromosome of D. melanogaster, probably in the centromeric heterochromatin. We have carried out high resolution cytological mapping of Zhr using deficiencies and duplications of the X heterochromatin. Deletions of the Zhr+ gene from the hybrid genome exhibit the Zhr phenotype. On the contrary, addition of the wild-type gene to the hybrid genome causes embryonic lethality, regardless of sex. The Zhr locus has been narrowed down to the region covered by Dp(1;f)1162 but not covered Dp(1;f)1205, a chromosome carrying a duplication of heterochromatin located slightly distal to the In(1)sc8 heterochromatic break-point.

Animals↗
PubMed2000

On the origin of metacentric, attached-X (A-X) chromosomes in Drosophila melanogaster males.

We describe here the isolation and cytogenetic characterization of a mutation inseparabile which generates in males a high frequency of A-X females. The mutation, segregating in low frequency in a laboratory stock, maps to cytological location 82F7-11 in the third chromosome. The mutation acts premeiotically in the male germ line. Disrupting the X chromosome centromeric heterochromatin suppresses the formation of A-X chromosome, implying that the mutation is involved in chromatid cohesion. The inseparabile mutation also affects disjunction of the chromosome 4 in males. We suspect that the mutation was responsible for the original A-X female found by L. V. Morgan in 1921.

Animals↗
PubMed1992

Degenerating Y chromosome of Drosophila miranda: a trap for retrotransposons.

In Drosophila miranda, the larval cuticle protein (Lcp) genes are located on the X2 and Y chromosomes, while in other Drosophila species the Lcp genes are inherited on the autosomes. We chose the D. miranda species as a model system to analyze the molecular bases of Y chromosome degeneration, a phenomenon observed in many species. DNA sequence analysis of the Y chromosomal Lcp gene locus reveals dense clustering of trapped retrotransposons. Once inserted at the Y chromosomal location they cannot easily be eliminated by unequal crossing-over, as recombination is a rare event in Drosophila males. In addition, we have uncovered an example of a completely inactive allele on the degenerating Y chromosome. The existence of such inactive Y-specific alleles was originally predicted in H. J. Muller's model for Y chromosome degeneration. We demonstrate that the Y chromosomal Lcp4 allele is no longer transcribed. From the divergence in DNA sequence organization of former homologous chromosome regions we conclude that changes in chromosome structure and destruction of genetic activity in degenerating Y chromosomes are based on one major mechanism, which operates by means of transposable elements.

Alleles↗
PubMed1966

The strandedness of meiotic chromosomes from Oncopeltus.

Meiotic chromosomes were isolated from male Oncopeltus fasciatus by dissecting the testes under insect Ringer's solution and spreading the living cells on the Langmuir trough. After being dried by the critical point method, preparations were examined under the electron microscope. Chromosomes at all stages of prophase prove to be multistranded. A significant increase in the number of parallel 250 A fibers in the chromosomes occurs between zygotene and diakinesis. Parallel folding, rather than true multistrandedness, is interpreted as the mechanism responsible for this observed increase in multistrandedness. It has not been possible to determine whether the multistrandedness observed at leptotene represents true multistrandedness or is the result of parallel folding. Apparent multistrandedness is lost at metaphase when the 250 A fibers of the chromosomes become coiled more tightly. In preparations isolated by these methods, no structures other than the 250 A chromosome fibers are visible in the chromomeres, which appear as regionally coiled or folded areas of the fibers along the arm of the chromosome.

Animals↗
PubMed1997

A new family of site-specific retrotransposons, SART1, is inserted into telomeric repeats of the silkworm, Bombyx mori.

The telomeres of the silkworm, Bombyx mori, consist of pentanucleotide repeats (TTAGG)n . We previously characterized the non-LTR element TRAS1, which terminates with oligo (A) in a head to tail orientation at the exact position (between A and C) of the (CCTAA) n repeats. Here we characterized another family of telomere-specific non-LTR retrotransposon named SART1. The SART1 family was inserted at another site of the (TTAGG) n in a reverse orientation from that of TRAS1. The complete unit of SART1, 6.7 kb in length with a poly (A) stretch, contains two open reading frames encoding putative gag and pol products, overlapping by 54 bp in the -1 reading frame. Most of the 600 SART1 copies in the silkworm haploid genome are completely conserved in structure without 5'truncation. All SART1 sequences analyzed were inserted at the same position (between T and A) within the (TTAGG) n repeats. Fluorescence in situ hybridization showed that many of the SART1 copies were localized in the chromosomal ends. A phylogenetic tree showed that the SART1, TRAS1 and two other site-specific elements, R1 and RT, which insert into 28S ribosomal RNA genes in insects, belong to the same group. Based on the orientation for the chromosomal insertion and structural similarities, these elements could be further classified into two subgroups, R1/TRAS1 and RT/SART1, suggesting that the target specificity of the two telomere-associated elements was changed independently.

Animals↗
PubMed2000

Nucleotide variation at the yellow gene region is not reduced in Drosophila subobscura: a study in relation to chromosomal polymorphism.

In contrast to Drosophila melanogaster and Drosophila simulans, the yellow (y) gene region of Drosophila subobscura is not located in a region with a strong reduction in recombination. In addition, this gene maps very close to the breakpoints of different inversions that segregate as polymorphic in natural populations of D. subobscura. Therefore, levels of variation at the y gene region in this species relative to those found in D. melanogaster and D. simulans may be affected not only by the change in the recombinational environment, but also by the presence of inversion polymorphism. To further investigate these aspects, an approximately 5.4-kb region of the A (=X) chromosome including the y gene was sequenced in 25 lines of D. subobscura and in the closely related species Drosophila madeirensis and Drosophila guanche. The D. subobscura lines studied differed in their A-chromosomal arrangements, A(st), A(2), and A(1). Unlike in D. melanogaster and D. simulans, levels of variation at the y gene region of D. subobscura are not reduced relative to those found at other genomic regions in the same species (rp49, Acp70A, and Acph-1). This result supports the effect of the change in the recombinational environment of a particular gene on the level of neutral variation. In addition, nucleotide variation is affected by chromosomal polymorphism. A strong genetic differentiation is detected between the A(1) arrangement and either A(st) or A(2), but not between A(st) and A(2). This result is consistent with the location of the y gene relative to the breakpoints of inversions A(1) and A(2). In addition, the pattern of nucleotide polymorphism in A(st)+A(2) and A(1) seems to point out that variation at the y gene region within these chromosomal classes is in the phase transient to equilibrium. The estimated ages of these arrangements assuming a star genealogy indicate that their origin cannot predate the D. madeirensis split. Therefore, the present results are consistent with a chromosomal phylogeny where Am(1), which is an arrangement present in D. madeirensis but absent in current populations of D. subobscura, would be the ancestral arrangement.

Animals↗
PubMed2004

[Genetic analysis of X-chromosome neurodegenerative mutants of Drosophila melanogaster induced by ethyl methansulfonate and nitrosoethylurea].

In a series of Drosophila mutants with changes in the brain structure, some characters (reduced life span, behavioral changes, and neuronal loss in various brain regions) resemble symptoms observed in human patients with neurodegenerative diseases. In addition, similar specific phenotypes shared by different species suggest that common mechanisms underlie degeneration of their nerve cell. This study reports the results of a genetic analysis of new X-chromosome mutants with neurodegenerative changes in brain structure, which were induced by chemical mutagenesis. According to complementation test, all mutants were divided into three complementation groups, in which the life span and dynamics of neurodegenerative changes were studied. The life span of Drosophila melanogaster flies was found to depend on the state of their nervous system.

Animals↗