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M Ashburner

Publications and source records attributed to M Ashburner.

At least 73 records · Page 4Linked to original sources
PubMed1991

Effects of juvenile hormone mimics on larval development and metamorphosis of Drosophila melanogaster.

To determine if prolonged larval exposure to juvenile hormone (JH) could influence the decision to metamorphose, Drosophila melanogaster larvae were reared from hatching on medium containing either of the JH mimics, methoprene or 2-[1-methyl-2-(4-phenoxyphenoxy)-ethoxy]-pyridine (S31183). The latter was 23 times more active as a JH mimic in the white puparial assay (ED50 = 0.22 pmole). Larval development and pupariation were unaffected except at 1000 ppm methoprene and 10 ppm or higher S31183 where larval life was prolonged with increased mortality in the second instar. Adult eclosion was prevented by concentrations greater than 1 ppm methoprene and 0.1 ppm S31183. At low concentrations only adult abdominal development was affected, but at the higher concentrations an increasing percentage was blocked at the pupal stage. This latter effect was considerably diminished when the treatment was begun in the mid second instar. The methoprene-resistant mutations, Met1 and Met2, were 10 and 6 times more resistant to S31183 in the white puparial assay and about 20 times more resistant in the larval feeding experiments than the wild-type, indicating that the effects seen are typical of JH. These studies suggest that excess JH may affect adult development of imaginal structures if present at the onset of postembryonic cell proliferation of the imaginal discs or histoblasts. Thus, commitment for adult differentiation must occur early during this proliferative phase.

Abdomen↗
PubMed1991

Integrated maps of the Drosophila genome: progress and prospects.

A physical map of the Drosophila melanogaster genome is being assembled, consisting of ordered overlapping cosmid clones. The map is constructed in steps, separately for each chromosomal division. Gaps in this map are to be bridged with yeast artificial chromosome clones. Hybridization to previously cloned genes and extensive use of in situ hybridization to polytene chromosomes ensure that the cosmid map is firmly anchored to the wealth of available genetic and cytogenetic information. The intention is to make the physical map widely available as part of an overall, integrated genetic resource for the Drosophila research community.

Animals↗
PubMed1991

The molecular structure of TE146 and its derivatives in Drosophila melanogaster.

TE146 is a giant transposon of Drosophila melanogaster. It carries two copies of the white and roughest genes, normally found on the X chromosome. The structure of this transposon has been studied at the molecular level. TE146 may transpose to new chromosome positions, excise and be lost from the genome or undergo internal rearrangements. The termini of TE146 are foldback DNA elements (FB); the transposon also carries two internal FB elements. Loss or internal rearrangement of TE146 involves recombination between different FB elements. These events have been mapped molecularly, by taking advantage of the fact that the FB sequences are composed largely of a regular 155-bp repeat sequence that is cut by the restriction enzyme TaqI, and are shown to be nonrandom. We suggest that these FB-FB exchange events occur by mitotic sister-chromatid exchange in the premeiotic germ line.

Animals↗
PubMed1990

Towards a physical map of the Drosophila melanogaster genome: mapping of cosmid clones within defined genomic divisions.

A physical map of the D. melanogaster genome is being constructed, in the form of overlapping cosmid clones that are assigned to specific polytene chromosome sites. A master library of ca. 20,000 cosmids is screened with probes that correspond to numbered chromosomal divisions (ca. 1% of the genome); these probes are prepared by microdissection and PCR-amplification of individual chromosomes. The 120 to 250 cosmids selected by each probe are fingerprinted by Hinfl digestion and gel electrophoresis, and overlaps are detected by computer analysis of the fingerprints, permitting us to assemble sets of contiguous clones (contigs). Selected cosmids, both from contigs and unattached, are then localized by in situ hybridization to polytene chromosomes. Crosshybridization analysis using end probes links some contigs, and hybridization to previously cloned genes relates the physical to the genetic map. This approach has been used to construct a physical map of the 3.8 megabase DNA in the three distal divisions of the x chromosome. The map is represented by 181 canonical cosmids, of which 108 clones in contigs and 32 unattached clones have been mapped individually by in situ hybridization to chromosomes. Our current database of in situ hybridization results also includes the beginning of a physical map for the rest of the genome: 162 cosmids have been assigned by in situ hybridization to 129 chromosomal subdivisions elsewhere in the genome, representing 5 to 6 megabases of additional mapped DNA.

Animals↗
PubMed1990

A genetic basis for the inviability of hybrids between sibling species of Drosophila.

A mutation of Drosophila melanogaster whose only known effect is the rescue of otherwise lethal interspecific hybrids has been characterized. This mutation, Hmr, maps to 1-31.84 (9D1-9E4). Hmr may be the consequence of a P element insertion. It rescues hybrid males from the cross of D. melanogaster females to males of its three sibling species, D. simulans, D. mauritiana and D. sechellia. This rescue is recessive, since hybrid males that carry both Hmr and a duplication expected to be Hmr+ are not rescued. Hmr also rescues the otherwise inviable female hybrids from the cross of compound-X D. melanogaster females to males of its sibling species. This rescue is also recessive, since a compound-X heterozygous for Hmr does not rescue. Another mutation, discovered on the In(1)AB chromosome of D. melanogaster, is also found to rescue normally inviable species hybrids: unlike Hmr, however, In(1)AB rescues hybrid females from the cross of In(1)AB/Y males to sibling females, as well as hybrid males from the cross of In(1)AB females to sibling males. These data are interpreted on the basis of a model for the genetic basis of hybrid inviability of complementary genes.

Animals↗
PubMed1990

The molecular analysis of the el-noc complex of Drosophila melanogaster.

The el-noc complex spans a distance of about 200 kb on chromosome 2L. It consists of three discrete genetic regions el, l(2)35Ba and noc, each of which has a distinct phenotype when mutant. The noc locus itself is complex, including three separate regions. The el locus has been characterized by mapping 30 aberration breakpoints to the DNA. It extends over a distance of about 80 kb. It can be divided into two parts by the aberrations In(2LR)DTD128 and T(Y;2)A80. These break between two sets of el alleles yet are both phenotypically wild type for elbow. The simplest explanation is that el consists of two transcription units elA and elB. The locus pu, which appears to be unrelated to the el-noc complex, is found to map between the two el loci very close to elB (the distal el locus). The loci l(2)35Ba and nocA have been separated by only two l(2)35Ba+nocA- deletions and a nocA- inversion. No l(2)35Ba-nocA+ aberrations have been found. At the molecular level these loci are found to occupy almost the same region, and are probably identical.

Animals↗
PubMed1990

A novel transvection phenomenon affecting the white gene of Drosophila melanogaster.

The zeste mutation of Drosophila melanogaster suppresses the expression of white genes in the eye. This suppression is normally dependent on there being two copies of w+ located close to each other in the genome--they may either be in cis (as in a tandem duplication of w+) or in trans, i.e. on homologous chromosomes. Duplicated w+ genes carried by a giant transposing element, TE146(Z), are suppressed by z whether they are in direct (tandem) or inverted order. The tandem form of the TE is very sensitive to a rearrangement on the homologous chromosome--many rearrangements with breakpoints "opposite" the TE's insertion site prevent the interaction between the white genes on a z background. These aberrations act as dominant suppressors of zeste that are specific to the tandemly duplicated form of TE146(Z). The inverted form of the TE146(Z) presumably pairs as a hairpin loop; this is more stable than the tandem form by the criterion that its zeste phenotype is unaffected by any of the aberrations. This effect of rearrangements has been used as the basis for a screen, gamma-ray induced aberrations with at least one breakpoint opposite the TE site were recovered by their suppression of the zeste phenotype.

Animals↗
PubMed1990

Characterization of the FB-NOF transposable element of Drosophila melanogaster.

FB-NOF is a composite transposable element of Drosophila melanogaster. It is composed of foldback sequences, of variable length, which flank a 4-kb NOF sequence with 308-bp inverted repeat termini. The NOF sequence could potentially code for a 120-kD polypeptide. The FB-NOF element is responsible for unstable mutations of the white gene (wc and wDZL) and is associated with the large TEs of G. Ising. Although most strains of D. melanogaster have 20-30 sites of FB insertion, FB-NOF elements are usually rare, many strains lack this composite element or have only one copy of it. A few strains, including wDZL and Basc have many (8-21) copies of FB-NOF, and these show a tendency to insert at "hot-spots." These strains also have an increased number of FB elements. The DNA sequence of the NOF region associated with TE146(Z) has been determined.

Amino Acid Sequence↗
PubMed1990

The genetics of a small autosomal region of Drosophila melanogaster containing the structural gene for alcohol dehydrogenase. VII. Characterization of the region around the snail and cactus loci.

The genetic interval 35C to 36A on chromosome arm 2L of Drosophila melanogaster has been saturated for mutations with visible or lethal phenotypes. 38 loci have been characterized, including several maternal-effect lethals (vasa, Bic-C, chiffon, cactus and cornichon) and several early embryonic lethals, including snail and fizzy. About 130 deletions have been used to order these loci. Complex interactions between mutant alleles have been uncovered in the immediate genetic environs of the snail gene, as has further evidence for an interaction between this region and that including the nearby genes no-ocelli and elbow.

Alcohol Dehydrogenase↗
PubMed1990

Posterior localization of vasa protein correlates with, but is not sufficient for, pole cell development.

The protein product of the Drosophila maternal-effect posterior group gene vasa is localized to the posterior pole of the oocyte and is sequestered by the pole cells as they form. It is, however, present at easily detectable levels throughout the oocyte and pre-blastoderm embryo. The protein is present in the pole cells and their germ line derivatives throughout all stages of development. An antiserum against this protein recognizes a pole-cell-specific antigen in seven other Drosophila species. Of six other maternal-effect loci essential for embryonic pole cell development, none affects expression of vasa, mutations in four abolish vasa protein localization, and mutations in two, tudor and valois, have little, if any, effect on vasa expression or localization. This indicates that vasa protein, when properly localized, is not sufficient for induction of pole cell development, and that at least the tudor and valois wild-type functions are also required specifically for this process. These results are discussed with respect to the multiple functions of the vasa gene.

Animals↗
PubMed1990

The Adh gene promoters of Drosophila melanogaster and Drosophila orena are functionally conserved and share features of sequence structure and nuclease-protected sites.

The sibling species Drosophila melanogaster and D. orena show similar patterns of alcohol dehydrogenase expression, both spatially and temporally. These two species diverged from a common ancestor 6 million to 15 million years ago, and the DNA sequences of the promoter regions of their Adh genes show a mosaic pattern of conservation and change. By interspecific transformation of D. orena sequences into D. melanogaster, we demonstrate a functional equivalence between these sequences. Using both D. melanogaster embryo extracts and purified transcription factor Adf-1, we compare the protection of these promoter sequences from nuclease, demonstrating considerable conservation.

Alcohol Dehydrogenase↗
PubMed1989

PCR amplification of DNA microdissected from a single polytene chromosome band: a comparison with conventional microcloning.

A novel alternative to microcloning for the production of region specific chromosomal DNA is described. In this method, 'microamplification', single bands are dissected from polytene chromosomes and digested with Sau3A. Oligonucleotide adaptors are ligated to these fragments to provide convenient priming sites for polymerase chain reaction amplification. In this way, as much as 1 microgram of DNA can be amplified from a single band. Probes made from PCR amplified DNA from two such dissections have been used to probe cloned DNA form a 100 kb chromosome walk. Whereas conventional microcloning has generated cloned EcoRI fragments corresponding to 3-4 kb of the walk, the PCR probes cover greater than 90% of this chromosomal region. Thus microamplification is significantly more effective than microcloning in providing probes for establishing chromosomal walks.

Animals↗
PubMed1989

Chaotic names.

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Animals↗
PubMed1989

Temporal and spatial utilization of the alcohol dehydrogenase gene promoters during the development of Drosophila melanogaster.

The enzyme alcohol dehydrogenase of Drosophila melanogaster is encoded by a single structural gene (Adh) with two promoters, distal and proximal (PD and PP). During development these two promoters are used differently: the major Adh transcript of larvae is from PP, the major transcript of adult flies is from PD. At a few discrete times in development transcription occurs simultaneously from both promoters. In situ hybridization has been used to investigate the spatial and temporal aspects of promoter activity at these stages of development. Maternally inherited Adh transcripts are not localized in the embryo; they decay very rapidly after fertilization. Zygotic expression of Adh RNA begins after germ-band retraction, 10.5 hr after fertilization. Expression is confined to the fat body, but occurs from both distal and proximal promoters. By 15 hr expression is first seen in the gut, from PP. By the same time fat body expression from PD has ceased, and transcription in this tissue is exclusively from PP for the next 4 days. The steady-state level of Adh transcript begins to decline at the end of larval development. There is then the transient accumulation of transcripts from PD, but predominantly in the larval fat body, rather than in the gut. These data illustrate a surprising complexity in the tissue and temporal regulation of Adh expression in D. melanogaster. Moreover, they show that transcripts from two different promoters of the same gene can, at certain well-defined stages of development, accumulate in the same cells.

Alcohol Dehydrogenase↗
PubMed1989

Genetic resistance to viral infection: the molecular cloning of a Drosophila gene that restricts infection by the rhabdovirus sigma.

The ref(2)P gene of Drosophila melanogaster has two common alleles, ref(2)Po which permits the infection of flies by the rhabdovirus sigma (sigma), and ref(2)Pp which is restrictive for sigma infection. This gene has been cloned by P element tagging and shown to code for two RNAs in adult flies. These RNAs are expressed in both males and females, but only the larger is expressed in ovaries. Both transcripts are shorter, by about 50 nucleotides, in flies carrying the ref(2)Pp allele than in those carrying ref(2)Po. The dominance relationships of these two alleles, and the fact that ref(2)Pnull alleles are permissive to sigma infection, suggest that the ref(2)Po product is antimorphic to that of the ref(2)Pp allele.

Alleles↗