Search PubMed⌕ Search

Biomedical subjects

M W Young

Publications and source records attributed to M W Young.

At least 73 records · Page 4Linked to original sources
PubMed1985

Extrachromosomal DNA forms of copia-like transposable elements, F elements and middle repetitive DNA sequences in Drosophila melanogaster. Variation in cultured cells and embryos.

Drosophila melanogaster embryos and cells in culture were screened for the presence of unintegrated covalently closed circular DNA forms that hybridize to copia-like transposable elements, the F element and uncharacterized dispersed middle repetitive DNA elements. Our results indicate that the majority of copia-like elements (including copia, 297, 412, mdg1, mdg3 and gypsy), the F elements, and 9 of 12 middle repetitive DNA elements are present as free DNA forms in cultured cells and embryos. An 18 base-pair inverted repeat has been reported to flank the long direct repeat of mdg3, implying that mdg3 is not an orthodox copia-like element; however, we have sequenced two independently isolated mdg3 clones and shown that the inverted repeat is not part of the element. The relative abundance with which free DNA forms are found varies between the cultured cells used, and between cultured cells and embryos. This variation, which can be up to 20-fold for some elements, does not correlate well with either the amount of element-specific poly(A)+ RNA present per cell or the number of element-specific sequences integrated in the genome.

Animals↗
PubMed1985

A biological clock in Drosophila.

The per locus plays a central role in the organization and function of the Drosophila biological clock. The gene has been mapped to a 7-kb DNA segment by physically locating the breakpoints of several chromosomal rearrangements that disrupt per function. This DNA contains a single transcription unit which produces a 4.5-kb poly(A)+ RNA. No oscillation in the synthesis of this transcript is detected when per expression is followed over a 24-hour cycle of light and dark. When wild-type DNA containing only this transcription unit is transferred to the genome of a per0 (arrhythmic) fly by P-element-mediated transformation, the 4.5-kb RNA is produced and rhythmic behavior is restored with high penetrance of the rhythmic phenotype. This transforming DNA will also complement chromosomal deletions that include the per locus and adjoining transcription units, indicating that only one gene in this chromosomal interval plays a measureable role in the production of circadian rhythms. Transformed flies having rhythms with longer than wild-type periodicity underproduce the 4.5-kb RNA. We suggest that the periodicity of circadian rhythms in Drosophila is determined by the level of expression of a per locus protein encoded by the 4.5-kb transcript. We have found DNA homologous to the per locus in several species of vertebrates. DNA exhibiting very high homology to a portion of the per locus has been cloned from the mouse and the DNA sequence of the conserved segment has been determined. Mouse and fly DNAs both appear to code for long protein segments composed exclusively of alternating threonine and glycine or serine and glycine residues.

Animals↗
PubMed1984

Molecular genetics of a biological clock in Drosophila.

Ninety kilobase pairs (kb) of DNA have been isolated from the 3B region of the X chromosome of Drosophila melanogaster. Previous cytogenetic analyses have placed a gene required for rhythmic behavior (per) in this chromosomal interval. Physical characterization of a series of chromosomal rearrangements altering per locus activity indicates that DNA affecting behavioral rhythms is found in a 7.1-kb HindIII fragment. A single 4.5-kb poly(A)(+) RNA is transcribed from this DNA in wild-type pupae and adult flies. The transcript is eliminated by a per mutant that retains some rhythmic activity, but this mutant substitutes two novel transcripts, 11.5 kb and 0.9 kb. It is suggested that the new poly(A)(+) transcripts provide residual per locus activity.

Journal Article↗
PubMed1983

The Notch locus of Drosophila melanogaster.

The Notch locus appears to correspond to a 37 kb transcription unit. Homologous poly(A)+ RNA is about 11.7 kb. Nine RNA coding regions have been detected and localized within the transcription unit by S1 nuclease analyses. These range in size from 130 to 7250 bp. Sequences within the 3' coding region are variably used. Twenty-four Notch locus "point" mutations have been examined. Seven are associated with DNA insertions. Four insertions are associated with dominant mutations and are located within or very near RNA coding sequences of the 37 kb transcription unit. Three insertions are associated with recessive mutations and fall within intervening sequences. The positions of all insertions agree with the genetic map. It is estimated that, in the Notch region, one map unit corresponds to approximately 275 kb. On this basis, most of the 17 mutations that were not associated with DNA insertions can be placed within coding sequences of the 37 kb transcription unit.

Animals↗
PubMed1982

Differing levels of dispersed repetitive DNA among closely related species of Drosophila.

The genomic concentrations of certain middle repetitive DNA sequences vary considerably among closely related species of Drosophila. In fact, the chromosomes of D. melanogaster appear to carry approximately 3 times as much middle repetitive DNA as those of the sibling species D. simulans. Although most of the middle repetitive DNA of D. melanogaster consists of segments of "nomadic" DNA that occupy different dispersed chromosomal locations in different strains of flies, repeated DNA sequences recovered from the D. simulans genome are most often restricted to single chromosomal positions. Apparent differences in the total concentrations of middle repetitive DNA in the two species are most easily attributed to an approximately sevenfold difference in their dispersed repetitive and nomadic DNA contents. These differences may affect the relative mutation rates of these species or contribute to their reproductive isolation or both.

Animals↗
PubMed1982

A population genetic study of Goodenough Island, Papua New Guinea.

A sample of 105 coastal people and 82 mountain dwellers from Goodenough Island, off the eastern tip of Papua New Guinea have been tested for four blood group systems, haemoglobin, 17 enzyme systems and four serum proteins. Transferrins D1 and Blae were found in both populations and the frequency of almost 29% for PGDc in the mountain people is one of the highest for the region. Deficiency of G-6 PD and the presence of PGK4 were detected only in the coastal populations.

Adult↗
PubMed1981

Anomalous origin of the left coronary artery: angiographic and myocardial perfusion scintigraphic correlates.

We studied a patient with an anomalous left coronary artery arising from the pulmonary artery by using conventional angiographic and myocardial imaging techniques. Myocardial imaging with radioactive 201thallium confirmed the significance of resting Q waves, and the defect in anterior perfusion coupled with the presence of thallium in the pulmonary outflow tract during exercise underscored the dynamic nature of the ischemic response to exercise in this syndrome.

Adult↗
PubMed1980

Probable Pendred syndrome on Goodenough Island.

A large kindred from Bwaidoga village in south-eastern Goodenough Island is described, in which occur several cases of what appear to be the Pendred syndrome: deafness associated with goitre. It is possible that deviations from the more usual pattern of the syndrome may be due to its having arisen from a spontaneous mutation, not identical with the mutation seen elsewhere.

Adolescent↗
PubMed1979

Middle repetitive DNA: a fluid component of the Drosophila genome.

Most of the middle repetitive DNA of Drosophila melanogaster appears to be organized into families of 10-100 repeated elements that are found at scattered locations in the chromosome arms and occupy new chromosomal positions as populations of D. melanogaster diverge. These "nomadic" DNA segments can be identified by an analysis of cDm plasmids, hybrids of ColE1 and segments of randomly sheared D. melanogaster DNA. Eighty cDm plasmids were withdrawn, at random, from a library of approximately 17,000 cDm clones. Fifty-seven of these seem to contain either DNA that is not repeated in the D. melanogaster genome or DNA that has a low repetition frequency. The remaining 23 cDm plasmids contain repetitive sequences. Seventeen of these 23 plasmids contain repetitive sequences that are demonstrably scattered to many chromosomal sites that can be mapped in two D. melanogaster strains, g-1 and g-X11. The repeated elements hybridizing with each of the different Dm segments are at quite different chromosomal locations in these two strains. However, the size of each family of repeated sequences remains fairly constant in both strains. It is proposed that the number of elements in each family has been fixed by selection.

Animals↗