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Biomedical subjects

R D Ward

Publications and source records attributed to R D Ward.

At least 37 records · Page 2Linked to original sources
PubMed1999

Analysis of TFIIA function In vivo: evidence for a role in TATA-binding protein recruitment and gene-specific activation.

Activation of transcription can occur by the facilitated recruitment of TFIID to promoters by gene-specific activators. To investigate the role of TFIIA in TFIID recruitment in vivo, we exploited a class of yeast TATA-binding protein (TBP) mutants that is activation and DNA binding defective. We found that co-overexpression of TOA1 and TOA2, the genes that encode yeast TFIIA, overcomes the activation defects caused by the TBP mutants. Using a genetic screen, we isolated a new class of TFIIA mutants and identified three regions on TFIIA that are likely to be involved in TBP recruitment or stabilization of the TBP-TATA complex in vivo. Amino acid replacements in only one of these regions enhance TFIIA-TBP-DNA complex formation in vitro, suggesting that the other regions are involved in regulatory interactions. To determine the relative importance of TFIIA in the regulation of different genes, we constructed yeast strains to conditionally deplete TFIIA levels prior to gene activation. While the activation of certain genes, such as INO1, was dramatically impaired by TFIIA depletion, activation of other genes, such as CUP1, was unaffected. These data suggest that TFIIA facilitates DNA binding by TBP in vivo, that TFIIA may be regulated by factors that target distinct regions of the protein, and that promoters vary significantly in the degree to which they require TFIIA for activation.

DNA-Binding Proteins↗
PubMed1998

Sugar feeding and fluid destination control in the phlebotomine sandfly Lutzomyia longipalpis (Diptera: Psychodidae).

Sandfly feeding behaviour and destination of coloured sugar meals in the gut of Lutzomyia longipalpis were investigated with particular attention to the role of the crop. Sandflies were able to ingest sugar from liquid drops, microcapillaries, a slice of pear and even sugar powder. In most cases the flies adopted a 'sugar feeding mode' with raised palps. As the fruit dried, flies of both sexes fed by piercing the tissue with the proboscis. All sugar-fed flies had a full crop plus a small amount of sugary fluid in the thoracic mid-gut, i.e. past the stomodaeal valve. Dissections of flies interrupted during feeding showed that the very first trace of sugar passed through the stomodaeal valve, but that the rest of the meal was diverted into the crop. This suggests that closure of the stomodaeal valve is initiated only after a small volume of sugar solution has passed through it.

Animals↗
PubMed1998

Stomodaeal valve ultrastructure in the sandfly Lutzomyia longipalpis (Diptera: Psychodidae).

The stomodaeal valve and adjacent cardia region of the alimentary canal of the phlebotomine sandfly Lutzomyia longipalpis have been studied using electron microscopy. With the scanning electron microscope (SEM), numerous pit-like structures of different sizes were found in the surface of the valve of male and female flies. Under the transmission electron microscope (TEM), the cells adjacent to the pores were shown to have numerous mitochondria and to lack neural innervation. It is suggested that the pit-like structures are probably secretory. A typical basiconic sensilla was found on the inner side of the oesophagus at the junction with the stomodaeal valve, with at least one dendrite which extended to the tip, indicating a chemosensory role. It is likely that this type of sensilla may control the movement of the stomodaeal valve after contact with fluids entering the mid-gut and may be responsible for diverting the sugar meal to the crop by closure of the valve.

Animals↗
PubMed1997

Phlebotomine sandflies in a focus of visceral leishmaniasis in a border area of eastern Sudan.

A field study was carried out in eastern Sudan, near the Ethiopian border, to investigate the abundance, seasonality, man-biting behaviour and resting sites of sandflies in two areas where visceral leishmaniasis (kala-azar) is endemic: Umsalala village, Galabat Province; and the adjacent Dinder National Park (DNP), Dinder Province. Abundance of the different species was determined from collections made, using light and sticky-paper traps, in various habitats between November 1993 and February 1995. Man-biting sandflies were collected as they landed on human bait. The habitats investigated for day-resting sandflies were thatched huts, chicken coops, tree-holes, termite mounds and soil cracks. Animal burrows were not investigated. The species found were Phlebotomus (Larroussius) orientalis, P. (Phlebotomus) papatasi, P. (Paraphlebotomus) saevus, P. (Anaphlebotomus) rodhaini, Sergentomyia (Sintonius) clydei, S. (Sergentomyia) antennata, S. (Sergentomyia) sckwetzi, S. (Parrotomyia) africana and S. (Grassomyia) squamipleuris. Phlebotomus orientalis was the only man-biting sandfly species found in the DNP whereas P. papatasi, P. orientalis and P. saevus were all found in Umsalala. Abundance of each species varied with the habitat. In Umsalala and a camp for game wardens in the DNP, Sergentomyia spp. predominated over Phlebotomus. In the DNP, the most abundant sandfly in a thicket dominated by Acacia seyal trees was P. orientalis, followed by Sergentomyia spp. Significant habitat 'preferences' were observed for most sandfly species in the area. In attempts to find resting flies, P. orientalis was only found resting in the mounds made by the termite Macrotermes herus and P. papatasi was only found inside huts; no resting sites were detected for other Phlebotomus spp. but Sergentomyia spp. were observed in all the sites investigated. The P. orientalis in the DNP showed a clear seasonal variation in abundance, which was closely correlated with the mean monthly temperature and relative humidity of the area. A remarkable increase in the abundance of this vector occurred at the beginning of the rainy season.

Animals↗
PubMed1997

The sandfly Lutzomyia longipalpis shows specific humoral responses to bacterial challenge.

The presence of immune molecules induced by microorganisms in the haemolymph of Lutzomyia longipalpis sandflies has been investigated. Injections of Escherichia coli and Micrococcus luteus into female sandflies induced anti-bacterial activity in the haemolymph. Inhibition zone assays showed that haemolymph from E. coli and M.luteus injected sandflies differentially inhibited M.luteus growth. This differential effect was specific to M.luteus infection since anti-E.coli activity was similar in haemolymph from both E.coli or M.luteus injected sandflies. Haemolymph following injection of either bacteria showed the induction of a 4 kDa peptide. Haemolymph from M.luteus injected sandflies also contained a 33 kDa polypeptide which was absent in haemolymph from E.coli and control uninfected insects. Sandflies, in common with other insects, were shown to possess general and specific humoral immune responses to the presence of microorganisms.

Animals↗
PubMed1997

IMGs set goals for AMA section.

International medical graduates have become an important part of the American health care structure in recent decades, but too often they remain second-class citizens within the medical community. Increasingly, voices within medicine have called for formal recognition of the unique needs of IMG physicians.

American Medical Association↗