Search PubMed⌕ Search

Biomedical subjects

S R West

Publications and source records attributed to S R West.

At least 19 recordsLinked to original sources
PubMed1995

Cell fate control in the Drosophila retina by the orphan receptor seven-up: its role in the decisions mediated by the ras signaling pathway.

Drosophila seven-up is an orphan receptor of the steroid receptor family that is required to specify photoreceptor neuron subtypes in the developing compound eye. Expression of seven-up is confined to four of the eight photoreceptor precursors, R3/R4/R1/R6. We show that misexpression of seven-up in any of the other cell types within the developing ommatidium interferes with their differentiation. Each cell type responds differently to seven-up misexpression. For example, ectopic expression in the non-neuronal cone cells using the sevenless promoter/enhancer (sev-svp) causes the cone cells to take on a neuronal identity. Ectopic expression of seven-up in R2/R5 using the rough enhancer (ro-svp) causes these neurons to lose aspects of their photoreceptor subtype identity while remaining neuronal. Each cell type appears to have a different developmental time window that is sensitive to misexpressed seven-up. The temporal order of responsiveness of each cell type to misexpressed seven-up is similar but not identical to the order of neuronal differentiation. This suggests that there are processes of specification that are distinct from the specification to become a photoreceptor neuron. We have identified members of the ras signaling pathway as suppressors of the cone cell to R7 neuron transformation caused by sev-svp. Suppression of the sev-svp phenotype can be achieved by decreasing the gene-dosage of any of the members of the ras-pathway. This suggests that the function of seven-up in the cone cells requires ras signaling. However, a decrease in ras signaling results in enhancement of the phenotype caused by the ro-svp transgene. We discuss the relationship between decisions controlled by seven-up and those controlled by ras signaling.

Animals↗
PubMed1993

Ectopic expression of seven-up causes cell fate changes during ommatidial assembly.

During Drosophila ommatidial development, a single cell is selected within the ommatidial cluster to become the R7 photoreceptor neuron. The seven-up gene has been shown to play a role in this process by preventing four other photoreceptor precursors, R3/R4/R1/R6, from adopting the R7 cell fate. The seven-up gene encodes a steroid receptor-like molecule that is expressed only in those four cells that require seven-up function in the developing Drosophila ommatidium. We have examined the functional significance of the spatially restricted expression of seven-up by misexpressing seven-up isoforms. As expected from the function that seven-up performs in R3/R4/R1/R6, ubiquitous expression of seven-up causes transformation of the R7 cell to an R1-R6 cell fate. In addition, depending on the timing and spatial pattern of expression, various other phenotypes are produced including the loss of the R7 cell and the formation of extra R7 cells. Ubiquitous expression of seven-up close to the morphogenetic furrow interferes with R8 differentiation resulting in failure to express the boss protein, the ligand for the sevenless receptor tyrosine kinase, and the R7 cell is lost consequently. Extra R7 cells are formed by recruiting non-neuronal cone cells as photoreceptor neurons in a sevenless and bride of sevenless independent way. Thus, the spatiotemporal pattern of seven-up expression plays an essential role in controlling the number and cellular origin of the R7 neuron in the ommatidium. Our results also suggest that seven-up controls decisions not only between photoreceptor subtypes, but also between neuronal and non-neuronal fates.

Animals↗
PubMed1986

Digital averaging to facilitate two-dimensional echocardiographic measurements.

A problem in quantitative two-dimensional echocardiography is myocardial dropout of still frame images. This study was designed to evaluate the ability of digital averaging to overcome myocardial dropout without distorting quantitative measurements. Forty-one percent of 80 digitally averaged images were thought to be improved by five independent observers, whereas 7% showed some deterioration. Measurements obtained from processed images were statistically identical (r greater than or equal to 0.9) to those from three arithmetically averaged, unprocessed images in 60 patients. Digital averaging can improve image quality without measurement distortion and should facilitate two-dimensional echocardiographic quantitation.

Analog-Digital Conversion↗
PubMed1986

Failure of fluosol DA to enhance the ultrasonic image of infarcted myocardium.

The perfluorocarbon Fluosol DA has been reported to increase the subjective echogenicity of infarcted myocardium. To investigate this phenomenon, two-dimensional echocardiograms were recorded in 20 closed-chest dogs before and 24,48,72, and 96 h following permanent coronary artery occlusion. Low-dose Fluosol, 10 ml/kg (LDF) (four dogs), high-dose Fluosol, 25 ml/kg (HDF) (eight dogs), or lactated Ringers 25 ml/kg (LR) (eight dogs) was administered 48 h after occlusion. Left ventricular sections corresponding to the short-axis echocardiographic examination plane were stained with nitroblue tetrazolium 48 h after Fluosol administration. Short-axis echocardiographic studies were evaluated by two blinded observers who found no consistent increase in the echogenicity of the infarcted area in any group. Videodensitometry of the infarcted area, normalized to the average value of two remote areas, confirmed mean post-Fluosol increases of 66% in LR dogs, 65% in LDF dogs, and 107% in HDF animals (p less than 0.001 for all dogs; all intergroup comparisons NS). The increase in videodensity observed in all groups may have occurred as a consequence of volume administration, although changes in infarct intensity occurring over time cannot be excluded.

Animals↗
PubMed1986

Quality assurance and patient care evaluation in the undergraduate curriculum.

To design a teaching and learning experience for medical students which would induce attitudes which would favourably influence their future involvement in patient care evaluation and quality assurance activities during their professional lives. A three hour seminar involving a minimal amount of didactic input and featuring role plays and analysis of reports of cases from real life in which the quality of care given had been unacceptable. An enjoyable seminar with some indication that the students had appreciated the objectives and--at least temporarily--become more positive in their attitudes towards Peer Review.

Curriculum↗
PubMed1984

Assessment of location and size of myocardial infarction with contrast-enhanced echocardiography. II. Application of digital imaging techniques.

Contrast echocardiography can be used to identify nonperfused regions of myocardium and localize and quantify infarcted myocardium. Analysis is usually undertaken by visual inspection of an analog two-dimensional echocardiographic image. The purpose of our study was to apply digital imaging techniques to contrast-enhanced echocardiograms for the determination of myocardial infarct size. Myocardial contrast was produced by an injection into the aortic root of a mixture of hydrogen peroxide and blood. Sixteen open chest dogs were studied 4 hours after coronary artery occlusion. Echocardiograms were evaluated by two independent observers. The results were compared with infarct location and size determined with nitro-blue tetrazolium staining of the corresponding slice of the left ventricle. Both the routine analog echocardiographic image and the digital subtraction image were analyzed. For the latter, three precontrast and three postcontrast echocardiographic enddiastolic fields were digitized in a 256 X 256 X 6 bit matrix and then averaged. Average pre- and postcontrast images were mathematically subtracted to form the digital subtraction image. There was excellent correlation between the percent of infarct determined with digital subtraction contrast echocardiography and results of nitro-blue tetrazolium staining (r = 0.97, SEE = 0.04, p less than 0.001). Using linear regression, the relation between infarct size by the two studies was best described by the equation DSI = 0.92 NBT + 0.03, where DSI = digital subtraction image and NBT = infarct size by nitro-blue tetrazolium. Inter- and intraobserver variability were also excellent (r = 0.93 and 0.96, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1983

The effect of personal characteristics on response levels in a health survey.

In a survey of everyday health in South Auckland, 207 mothers kept a diary of their families' health episodes and influences. Besides noting the problems of obtaining and maintaining respondent compliance, we found considerable variations in reporting levels between the main ethnic groups and between those willing to keep diaries for shorter or longer periods. The number of reports recorded varied on different days of the week and as time progressed. We quantified these variations and suggest correction processes which may be applied to research findings in multi-cultural areas.

Adult↗
PubMed1983

Audiometry and tympanometry in children throughout one school year.

One hundred children had audiometry and tympanometry testing every two to three weeks throughout 38 weeks of a school year. The results showed an average prevalence of some abnormality in 62% and that the abnormal group was constantly changing. Abnormal episodes had a median duration of three to four weeks and a mean of six weeks. Thirty-nine percent of the children had more than one episode. Comparisons were made between the different measures of hearing and middle-ear function and between these and educational tests of intelligence, language and school achievement. Educational deficit was related most closely to total decibel loss. Four screening models were designed to allow economical use of testers' time. Resultant test patterns were related to two to three week testing and to educational test results. The closest correlation with educational test results proved to be an audiogram pass/fail screen each school term.

Acoustic Impedance Tests↗
PubMed1983

Everyday health, South Auckland, 1980-81.

A morbidity diary was kept by 207 families in South Auckland. The subjects were known to the investigators from a previous study and much information about the families was already recorded. During two weeks records were requested on everyday health practices, disabilities, symptoms, health activities, upsets, and opinions on whether days were "good" or "bad". One hundred and fifty families gave information for two weeks and fifty-seven for one week. Data showed many significant relationships between demographic and socio-economic characteristics and health experiences and activities. These relationships are reported, and the importance of obtaining such information about communities and individuals discussed.

Adolescent↗