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A Coulson

Publications and source records attributed to A Coulson.

At least 55 records · Page 3Linked to original sources
PubMed1990

HIV risk difference between condom users and nonusers among U.S. heterosexual women.

Using data from the National Survey of Family Growth, we estimate that among 3,498,060 U.S. reproductive-age women least likely to be protected from HIV, 12% rely on condoms for birth control. We have modeled the risk difference between condom users and nonusers and projected the number of preventable and nonpreventable HIV infections likely to occur among the 419,201 condom users as a function of 50 HIV-incidence/relative risk assumptions. Results of the attributable-risk model suggest that at the current low HIV-incidence level in U.S. women, condom-user failure rates will be less than 1% per year, substantially lower than the 10% condom-user failure rate for pregnancy. As few as 1% but up to 11% of all new HIV cases may be prevented by the current low level of condom use, depending on the exact degree of condom effectiveness in this population at risk. However, the model further projects that up to 45% of all new HIV cases may be prevented if condoms are maximally effective and far more widely used. Women with seropositive partners may enjoy the same protective benefits of condoms, but the costs in terms of condom-user failures will be much higher than in the remainder of the population at risk. Among serious and reliable users, condom-user failure rates for HIV may approach those for pregnancy, but only in women who have known seropositive partners.

Adolescent↗
PubMed1989

Caenorhabditis elegans has scores of homoeobox-containing genes.

Homoeobox-containing genes control cell identities in particular spatial domains, cell lineages, or cell types during the development of Drosophila and Caenorhabditis elegans, and they probably control similar processes in vertebrates. More than 80 genes with homoeoboxes that have sequence similarities ranging from 25 to 100% have been isolated by genetic means or by DNA hybridization to previously isolated genes. We synthesized 500-2,000-fold degenerate oligonucleotides corresponding to a set of well-conserved eight amino acid sequences from the helix-3 region of the homoeodomain. We screened C. elegans genomic libraries with these probes and identified 49 putative homoeobox-containing loci. DNA sequencing confirmed that eight out of ten selected loci had sequences corresponding to the conserved helix-3 region plus additional flanking sequence similarity. One of these genes contained a sequence corresponding to a complete pou-domain and another was closely related to the homoeobox-containing genes caudal/cdx-1. The putative homoeobox loci were mapped to the physical contig map of C. elegans, allowing the identification of potentially corresponding genes from the correlated genetic map. We estimate that the number of homoeobox-containing genes in C. elegans is at least 60, constituting approximately 1% of the estimated total number of genes.

Amino Acid Sequence↗
PubMed1989

Molecular genetics of the Caenorhabditis elegans heterochronic gene lin-14.

We describe a general strategy for the genetic mapping in parallel of multiple restriction fragment length polymorphism (RFLP) loci. This approach allows the systematic identification for cloning of physical genetic loci within about 100 kb of any gene in Caenorhabditis elegans. We have used this strategy of parallel RFLP mapping to clone the heterochronic gene lin-14, which controls the timing and sequence of many C. elegans postembryonic developmental events. We found that of about 400 polymorphic loci in the C. elegans genome associated with the Tc1 family of repetitive elements, six are within 0.3 map unit of lin-14. The three closest lin-14-linked Tc1-containing restriction fragments were cloned and used to identify by hybridization an 830-kb region of contiguous cloned DNA fragments assembled from cosmid and yeast artificial chromosome libraries. A lin-14 intragenic recombinant that separated a previously cryptic lin-14 semidominant mutation from a cis-acting lin-14 suppressor mutation was used to map the location of the lin-14 gene to a 25-kb region of this 830-kb contig. DNA probes from this region detected lin-14 allele-specific DNA alterations and a lin-14 mRNA. Two lin-14 semi-dominant alleles, which cause temporally inappropriate lin-14 gene activity and lead to the reiterated expression of specific early developmental events, were shown to delete sequences from the lin-14 gene and mRNA. These deletions may define cis-acting sequences responsible for the temporal regulation of lin-14.

Alleles↗
PubMed1989

mec-7 is a beta-tubulin gene required for the production of 15-protofilament microtubules in Caenorhabditis elegans.

In the nematode Caenorhabditis elegans, microtubules with 15 protofilaments are a specialized feature of six touch-receptor neurons; microtubules found in other C. elegans neurons have 11 protofilaments. Mutations in the gene mec-7 result in touch-insensitive animals whose touch cells lack the 15-protofilament microtubules. We have characterized 54 mutations in the mec-7 gene. The absence of mec-7 activity results selectively in the recessive loss of touch sensitivity. Partial loss-of-function alleles result in a partial loss of touch sensitivity. Dominant mutations, which are isolated at an unusually high proportion, may encode abnormal products. We have cloned the mec-7 gene; it encodes a beta-tubulin which is 90-93% identical to vertebrate beta-tubulin. Our results are consistent with the hypothesis that tubulin heterogeneity contributes to the formation of structurally and functionally distinct sets of microtubules.

Amino Acid Sequence↗
PubMed1988

Posterior pattern formation in C. elegans involves position-specific expression of a gene containing a homeobox.

During postembryonic development in C. elegans, posterior-specific pattern formation requires the gene mab-5. Within the posterior body region, mab-5 activity controls epidermal, neuronal, and mesodermal cell differentiation, and also the direction of cell migration. Here, we show that mab-5 RNA is localized in the posterior body region, indicating that mab-5 activity is targeted to posterior cells, at least in part, by a mechanism that operates at the level of mab-5 RNA synthesis or stabilization. We also show that mab-5 contains a homeobox similar to that of the Drosophila Antennapedia gene. This suggests that mab-5 influences cell differentiation and cell migration by regulating gene expression, and clearly demonstrates that genes containing homeoboxes influence global aspects of pattern formation in organisms other than Drosophila.

Amino Acid Sequence↗
PubMed1988

Genome linking with yeast artificial chromosomes.

The haploid genome of Caenorhabditis elegans consists of some 80 x 10(6) base pairs of DNA contained in six chromosomes. The large number of interesting loci that have been recognized by mutation, and the accuracy of the genetic map, mean that a physical map of the genome is highly desirable, because it will facilitate the molecular cloning of chosen loci. The first steps towards such a map used a fingerprinting method to link cosmid clones together. This approach reached its practical limit last year, when 90-95% of the genome had been cloned into 17,500 cosmids assembled into some 700 clusters (contigs), but the linking clones needed were either non-existent or extremely rare. Anticipating this, we had planned to link by physical means--probably by hybridization to NotI fragments separated by pulse field gel electrophoresis. NotI recognizes an eight base sequence of GC pairs; thus the fragments should be large enough to bridge regions that clone poorly in cosmids, and, with no selective step involved, would necessarily be fully representative. However, with the availability of a yeast artificial chromosome (YAC) vector, we decided to use this alternative source of large DNA fragments to obtain linkage. The technique involves the ligation of large (50-1,000 kilobase) genomic fragments into a vector that provides centromeric, telomeric and selective functions; the constructs are then introduced into Saccharomyces cerevisiae, and replicate in the same manner as the host chromosomes.

Animals↗
PubMed1988

Evidence that insect embryogenesis is regulated by ecdysteroids released from yolk proteins.

That the yolk proteins (YPs), or vitellins, stored in the oocytes of insects are a nutritional store for subsequent embryogenesis has long been assumed. Exhaustive data base searching programs revealed highly significant sequence similarity between the three YPs of Drosophila melanogaster and part of the triacylglycerol lipase of the domestic pig. Based upon time of degradation of YPs during embryogenesis, existence of maternally stored ecdysteroid conjugates in embryos, location of these conjugates in locust embryos, and the fact that free active ecdysteroid hormones are released at a specific time in embryogenesis to trigger cuticle deposition, we postulate that the similarity reflects a common property of Drosophila YPs--the ability to bind the fatty acid ecdysteroid conjugates. Our finding of conjugated ecdysteroids tightly bound to purified Drosophila YP supports this prediction.

Amino Acid Sequence↗
PubMed1988

Software for genome mapping by fingerprinting techniques.

A genome mapping package has been developed for reading and assembling data from clones analysed by restriction enzyme fragmentation and polyacrylamide gel electrophoresis. The package comprises: data entry; matching; assembly; statistical analysis; modelling. Data entry can be either manual or by a semiautomatic system based on a scanning densitometer. The primary emphasis in the analytical routines is on flexibility and interactive convenience, so that the operator has full knowledge of and control over the growing map, but a variety of automatic options are included. The package continually grows to meet the needs of the Caenorhabditis project.

Base Sequence↗
PubMed1987

Correlation of the physical and genetic maps in the lin-12 region of Caenorhabditis elegans.

We describe the assembly of a set of overlapping clones from the lin-12 III chromosomal region that spans approximately 600 kb, and the identification of two restriction fragment length polymorphisms, eP6 and eP7, that flank the lin-12 locus. A comparison of the physical map and the genetic map yields approximate measurements of 930 kb/map unit for the eP6--lin-12 interval and 830 kb/map unit for the lin-12--eP7 interval. We interpret these values as supporting the proposal that the apparent clustering of genes observed for C. elegans autosomes results from decreased recombination frequency in clusters and not from nonrandom distribution of genes on the physical map.

Animals↗
PubMed1986

Toward a physical map of the genome of the nematode Caenorhabditis elegans.

A technique for digital characterization and comparison of DNA fragments, using restriction enzymes, is described. The technique is being applied to fragments from the nematode Caenorhabditis elegans (i) to facilitate cross-indexing of clones emanating from different laboratories and (ii) to construct a physical map of the genome. Eight hundred sixty clusters of clones, from 35 to 350 kilobases long and totaling about 60% of the genome, have been characterized.

Journal Article↗
PubMed1982

AI regimes.

Explore the source record for details and available documents.

Animals↗
PubMed1981

Nasopharyngeal polyps in the cat.

The occurrence of inflammatory nasopharyngeal polyps is described in a series of four cats. Two of the cats presented with classical features of chronic upper respiratory tract infection, in a third gradual onset of coughing and retching were the only clinical signs, while in the fourth only noisy respiration accompanied the growth. In each cat the polyp was attached to the pharyngeal opening of the eustachian tube and it is suggested that such masses arise from either the lining of the tube itself or that they may even find origin within the tympanic bulla. However, anamnesis and the subsequent clinical and radiographic examinations did not indicate that the polyps were associated with external or middle ear disease. Removal by simple dissection was effected without the necessity of splitting the soft palate in any of the patients and, though expected, recurrence has not yet been seen.

Animals↗
PubMed1980

Effect of gonadotrophin releasing hormone on levels of luteinising hormone in cattle synchronised with dinoprost.

Synchronisation of oestrus was achieved in a group of three cows and two heifers with dinoprost. Sixty-six hours after the second injection of dinoprost, 0.125 mg synthetic gonadotrophin releasing hormone (GnRH) was given intramuscularly. Concentrations of luteinising hormone (LH) were monitored in peripheral blood and close grouping of preovulatory LH peaks was seen around 2.5 hours after injection of GnRH.

Animals↗
PubMed1979

Plasma progesterone and luteinising hormone levels in cattle after synchronisation of oestrus with dinoprost.

The plasma levels of progesterone and luteinising hormone (LH) were monitored in a group of cattle after pretreatment with two injections of 25 mg dinoprost. Close groupings of preovulatory LH peaks were observed and the possible significance of this is discussed. Based on the findings of this study, supporting evidence is provided for the timing of insemination after injection of cattle which have been synchronised for oestrus with dinoprost.

Animals↗