Entry characteristics and performance in a Masters module in Tropical Medicine: a 5-year analysis.

OBJECTIVES: Postgraduate courses can contribute to better-qualified personnel in resource-limited settings. We aimed to identify how entry characteristics of applicants predict performance in order to provide support measures early. METHODS: We describe demographic data and end-of-module examination marks of medical doctors who enrolled in a first semester module of two one-year MSc programmes between 2010 and 2014. We used t-tests and one-way anova to compare, and post hoc tests to locate differences of mean marks between categories of entry characteristics in univariate analysis. After exclusion of collinear variables, multiple regression examined the effect of several characteristics in multivariable analysis. RESULTS: Eighty-nine students (47% male) with a mean age of 32 (SD 6.4) years who received their medical degree in the UK (19%), other European (22%), African (35%) or other countries (24%) attended the 3-months module. Their mean mark was 69.1% (SD 10.9). Medical graduates from UK universities achieved significantly higher mean marks than graduates from other countries. Students' age was significantly negatively correlated with the module mark. In multiple linear regression, place of medical degree (ß = -0.44, P < 0.001) and time since graduation (ß = -0.28, P = 0.007) were strongest predictors of performance, explaining 32% of the variation of mean marks. CONCLUSION: Students' performance substantially differs based on their entry criteria in this 1st semester module. Non-UK graduates and mature students might benefit from early support.

Dp44mT targets the AKT, TGF-ß and ERK pathways via the metastasis suppressor NDRG1 in normal prostate epithelial cells and prostate cancer cells.

BACKGROUND: Effective treatment of prostate cancer should be based on targeting interactions between tumour cell signalling pathways and key converging downstream effectors. Here, we determined how the tumourigenic phosphoinositide 3-kinase/protein kinase B (PI3K/AKT), tumour-suppressive phosphatase and tensin homologue deleted on chromosome 10 (PTEN) and transforming growth factor-ß (TGF-ß) pathways are integrated via the metastasis suppressor, N-myc downstream-regulated gene-1 (NDRG1). Moreover, we assessed how the novel anti-tumour agent, Dp44mT, may target these integrated pathways by increasing NDRG1 expression. METHODS: Protein expression in Dp44mT-treated normal human prostate epithelial cells and prostate cancer cells (PC-3, DU145) was assessed by western blotting. The role of NDRG1 was examined by transfection using an NDRG1 overexpression vector or shRNA. RESULTS: Dp44mT increased levels of tumour-suppressive PTEN, and decreased phosphorylation of ERK1/2 and SMAD2L, which are regulated by oncogenic Ras/MAPK signalling. Importantly, the effects of Dp44mT on NDRG1 and p-SMAD2L expression were more marked in prostate cancer cells than normal prostate epithelial cells. This may partly explain the anti-tumour selectivity of these agents. Silencing NDRG1 expression increased phosphorylation of tumourigenic AKT, ERK1/2 and SMAD2L and decreased PTEN levels, whereas NDRG1 overexpression induced the opposite effect. Furthermore, NDRG1 silencing significantly reduced the ability of Dp44mT to suppress p-SMAD2L and p-ERK1/2 levels. CONCLUSION: NDRG1 has an important role in mediating the tumour-suppressive effects of Dp44mT in prostate cancer via selective targeting of the PI3K/AKT, TGF-ß and ERK pathways.

Acute exposure of adult male rats to dietary phytoestrogens reduces fecundity and alters epididymal steroid hormone receptor expression.

Phytoestrogens are plant-derived compounds with oestrogenic activity. They are common in both human and animal diets, particularly through soy-based foods. This study assessed whether exposure of adult male rats to a high phytoestrogen diet for 3-25 days affected their fertility, and assessed possible mechanisms through which phytoestrogens may disrupt fertility. Adult males, fed a high phytoestrogen diet for 3 days, demonstrated significantly reduced fecundity. This effect was transient, with fecundity returning to control levels by day 12. The expression of oestrogen receptor-alpha and androgen receptor mRNA was increased in the initial segment of the epididymis, but decreased in the cauda epididymis following 3 days on the high phytoestrogen diet. Epididymal sperm counts cannot account for the reduction in fertility at day 3. However, lipid peroxidation of epididymal sperm was significantly increased in animals fed a high phytoestrogen diet for 3 days. Disruption of the steroid regulation of the epididymis by phytoestrogens may alter its function, resulting in decreased quality of sperm, and thereby reducing fecundity.

Sequence analysis of the L1 metallo-beta-lactamase from Xanthomonas maltophilia.

The amino acid sequence deduced from the L1 beta-lactamase gene of Xanthomonas maltophilia shows a significant variation from that of the CphA and Blm metallo-beta-lactamases of Aeromonas hydrophila and Bacillus cereus, respectively. Whilst the N-terminus of the L1 protein shows some similarity, particularly at the histidine residues previously suggested as a zinc-binding motif, the C-terminus of the protein demonstrates very little similarity. Such differences amongst this group of enzymes would argue for at least three subclasses within the Group 3 beta-lactamases. However, in order to predict their phylogenetic ancestry more sequence data are required from other possible metallo-beta-lactamases.

Regulation of 5alpha-reductase isoforms by oxytocin in the rat ventral prostate.

Oxytocin (OT) is present in the male reproductive tract, where it is known to modulate contractility, cell growth, and steroidogenesis. Little is known about how OT regulates these processes. This study describes the localization of OT receptor in the rat ventral prostate and investigates if OT regulates gene expression and/or activity of 5alpha-reductase isoforms I and II. The ventral prostates of adult male Wistar rats were collected following daily sc administration of saline (control), OT, a specific OT antagonist or both OT plus antagonist for 3 d. Expression of the OT receptor was identified in the ventral prostate by RT-PCR and Western blot, and confirmed to be a single active binding site by radioreceptor assay. Immunohistochemistry localized the receptor to the epithelium of prostatic acini and to the stromal tissue. Real-time RT-PCR determined that OT treatment significantly reduced expression of 5alpha-reductase I but significantly increased 5alpha-reductase II expression in the ventral prostate. Activity of both isoforms of 5alpha-reductase was significantly increased by OT, resulting in increased concentration of prostatic dihydrotestosterone. In conclusion, OT is involved in regulating conversion of testosterone to the biologically active dihydrotestosterone in the rat ventral prostate. It does so by differential regulation of 5alpha-reductase isoforms I and II.

Inhibition of acid production in Streptococcus mutans R9 by formic acid.

Both lactic and acetic acids cause mixed inhibition of acid production in mutans streptococci. This inhibition is partly irreversible due to cell death, an important factor when considering acidogenicity and aciduricity of these organisms, and their role in the caries process. Other monocarboxylic end-products may be present and may also be important inhibitors of acid production in dental plaque. This study considered the effects of varying concentrations of the end-product formic acid on acid production rates in Streptococcus mutans R9, measured using the pH-stat. Undissociated formic acid caused mixed inhibition with constants of Kiu (uncompetitive) of 6.07 +/- 1.27 mmol-1 and Kic (competitive) of 0.2 +/- 0.11 mmol l-1. Inhibition was found to be fully reversible, with no loss of cell viability. It is concluded that at those concentrations found in vivo, formate is not a significant inhibitor of acid production by S. mutans in dental plaque at any time, and is not important in determining the acidogenicity or aciduricity of this organism.

Inhibition of acid production in Streptococcus mutans R9: inhibition constants and reversibility.

End-product inhibition of acid production in Streptococcus mutans R9 was investigated by measuring effects of varying concentrations of H+ and of undissociated lactic or acetic acids on acid production rates in the pH stat. H+ caused purely uncompetitive inhibition (inhibition constant Kiu 0.018 mmol 1(-1). Lactic acid caused mixed inhibition with inhibition constants of Kiu 4.24 mmol 1(-1) and Kic 4.55 mmol 1(-1). Reversibility of inhibition by H+ showed only a statistically significant reduction only at pH < 4.5. Reversibility of inhibition by lactic and acetic acids decreased with increasing inhibitor concentration. In all cases, reversibility correlated with the extent to which viability was retained, suggesting that loss of reversibility was due to cell death. These results suggest that, after a low-pH episode in dental plaque, caused by fermentation of dietary carbohydrate, the ability of plaque organisms to produce acid in subsequent exposures to carbohydrate may be reduced.

Mitotic aneuploidy induced by sodium deoxycholate in Aspergillus nidulans.

Sodium deoxycholate is shown to induce aneuploidy in a heterozygous diploid strain of Aspergillus nidulans. It is suggested that this is the result of interference with the normal functioning of the mitotic apparatus through disruption of the nuclear membrane. This effect limits the value of sodium deoxycholate as a paramorphogenic agent in the estimation of the genotoxic effects of environmental and genetic factors.

Paramorphogenic and genotoxic activity of Triton X-100 and sodium dodecyl sulphate in Aspergillus nidulans.

The genotoxic activities of Triton X-100 and sodium dodecyl sulphate in Aspergillus nidulans were assessed in order to evaluate their relative merits as paramorphogenic agents. Triton X-100 was found to be ideally suited to this purpose due to its efficient paramorphogenic effect and lack of genotoxicity. Sodium dodecyl sulphate was considered unsuitable since it reduced viability and was inconsistent in its paramorphogenic action.

Oxytocin increases 5alpha-reductase activity of human prostate epithelial cells, but not stromal cells.

BACKGROUND: Oxytocin is known to modulate 5-alpha-reductase expression and has, therefore, been implicated in the etiology and novel pharmacological treatments of benign prostatic hyperplasia (BPH). These suggestions have been made in the absence of any direct evidence that oxytocin regulates expression or activity of 5-alpha-reductase isoenzymes in the human prostate. This study evaluated the effects of oxytocin on the activity and expression of 5-alpha-reductase isoenzymes I and II of human prostate stromal (PrSC; primary site of BPH development) and epithelial (PrEC) cells. METHODS: Cell cultures were incubated with oxytocin, or oxytocin plus a specific oxytocin antagonist for 24 hr, and conversion of (3)H-Testosterone to dihydrotestosterone used to estimate total 5-alpha-reductase activity and to determine activity of both type I and type II isoenzymes. Fully quantitative real-time RT-PCR determined levels of expression of both isoenzymes following treatments. RESULTS: Oxytocin significantly increased the total 5-alpha-reductase activity of PrEC but not of PrSC. 5-alpha-Reductase I gene expression and enzyme activity were also increased (P<0.05) in PrEC by oxytocin. Oxytocin significantly increased type II activity, but not expression, in PrEC. Oxytocin did not significantly affect 5-alpha-reductase activity or expression in PrSC. CONCLUSION: Both 5-alpha-reductase I and II are expressed in normal human prostate stromal and epithelial cells. Only 5-alpha-reductase isoenzymes of prostate epithelium are modulated by oxytocin.

Yeast flocculation: Flo1 and NewFlo phenotypes and receptor structure.

Flocculation characteristics of 42 flocculent strains of Saccharomyces cerevisiae were examined. Two entirely distinct 'lectin-like' mechanisms of flocculation were distinguished by sugar, salt, and low pH inhibitions, protease sensitivity, and selective expression of flocculation. One group, termed Flo1 phenotype, was inhibited by mannopyranoses and contained all strains bearing known genes affecting flocculation. The other group, termed NewFlo phenotype, contained the majority of brewery ale stains and was inhibited by manno- and glucopyranoses. Detailed sugar-inhibition work revealed the probable receptor identity of both Flo1 and NewFlo flocculation, as being non-reducing termini of alpha-(1-3)-linked mannan side branches, two or three mannopyranose residues in length.

Comparison of the meta pathway operons on NAH plasmid pWW60-22 and TOL plasmid pWW53-4 and its evolutionary significance.

The regulated meta pathway operon for the catabolism of salicylate on the naphthalene plasmid pWW60-22 was cloned into the broad-host-range vector pKT230 on a 17.5 kbp BamHI fragment. The recombinant plasmid conferred the ability to grow on salicylate when mobilized into plasmid-free Pseudomonas putida PaW130. A detailed restriction map of the insert was derived and the locations of some of the genes were determined by subcloning and assaying for their gene products in Escherichia coli and P. putida hosts. The existence of a regulatory gene was demonstrated by the induction of enzyme activities in the presence of salicylate. DNA-DNA hybridization indicated a high degree of structural homology between the pWW60-22 operon and the analogous meta pathway operon on TOL plasmid pWW53-4. The data are consistent with the structural genes being arranged in an identical linear array and suggest an evolutionary link between the two catabolic systems.

Effects of steroids on oxytocin secretion by the human prostate in vitro.

Oxytocin (OT) concentrations are elevated in prostate tissue of patients with benign prostatic hyperplasia (BPH). Oxytocin specifically increases growth, 5 alpha-reductase activity and contractility in the prostate. In the rat prostatic OT concentrations are regulated by gonadal steroids, with androgens reducing but oestrogens increasing OT concentrations. The regulation of prostatic oxytocin in man is not understood. This study investigates the effects of gonadal steroids on oxytocin production by the human prostate. Primary explants (approx. 1 mm3) of prostate tissue from patients with BPH were incubated in Dulbecco's modified Eagle's media in the absence or presence of 10 nmol/L testosterone (T), 10 nmol/L dihydrotestosterone (DHT), T or DHT plus 100 nmol/L of the anti-androgen cyproterone acetate (CPA), 55 pmol/L diethylstilbestrol (DES), or DES plus DHT. The amount of oxytocin secreted into the media after 3 days was measured by radioimmunoassay. Testosterone and DHT significantly increased oxytocin concentrations secreted into the media from 0.86 +/- 0.11 ng/g of tissue (control) to 1.51 +/- 0.14 ng/g (p < 0.01) and 1.54 +/- 0.13 ng/g (p < 0.05), respectively. Incubation of tissue samples with CPA resulted in oxytocin concentrations similar to control levels. Treatment with DES caused a significant increase from 1.99 +/- 0.71 to 3.98 +/- 1.36 ng/g (p < 0.05). A similar increase was measured in media of tissue incubated in DES plus DHT (p < 0.001). The results demonstrate that, unlike the rat where androgens decrease oxytocin, in hyperplastic human prostate tissue both androgens and oestrogens increase oxytocin. This imbalance in the regulation of oxytocin may result in promoting prostatic overgrowth in the pathogenesis of BPH.

Mitotic recombination in stable and unstable chromosome III disomics of Aspergillus nidulans.

Approximately 2% of the haploid breakdown sectors of heterozygous chromosome III disomics of Aspergillus nidulans are the result of recombination between the homologous chromosomes. The exchanges are concentrated between the two mutations spanning the centromere. Comparisons are made between disomics hemizygous for the sodIII A1 mutation (Upshall et al. 1979) which are stable when grown at 37 degrees C, and disomics carrying the wild type allele of the sodIII A1 locus, which are unstable under all conditions. It is shown that neither temperature nor the sodIII A1 mutation affect the frequency or pattern of recombination between the homologues.

Oxytocin promotes spermiation and sperm transfer in the mouse.

Spermatogenesis is a complex process during which developing germ cells move from the base of the seminiferous tubule towards the lumen where they are shed. Studies in the rat suggest that seminiferous tubule contraction, induced by exogenous oxytocin, promotes spermiation. This study examines the role of testicular oxytocin in development of the testes, spermatogenesis and spermiation in the mouse. Groups of wild-type (WT) mice, oxytocin knockout mice (OTKO) deficient in testicular oxytocin and mice containing an oxytocin transgene (bOT4.2) that over express testicular oxytocin were killed between days 5 and 45 post partum. The testes and epididymides were removed weighed and prepared either for histological and morphometric study by light microscopy, for sperm counts (epididymis), or extracted for determination of oxytocin content (testis - day 45 only). Testicular oxytocin concentrations were significantly greater (p < 0.05) in bOT4.2 mice than in WT or OTKO mice. No differences in testicular and epididymal weight, or in diameter and area of seminiferous tubules between the mice genotypes were found at any given time. Germ cell development was similar in all genotypes and was comparable with previous studies. The timing of spermiation between the groups was significantly different (p < 0.001) with bOT4.2 < WT < OTKO and the appearance of epididymal sperm was significantly different (p < 0.05) with bOT4.2 < WT < OTKO. There were significant correlations between the percentage of tubules containing residual bodies and epididymal sperm count (p < 0.05) and between the percentage of animals containing residual bodies and the percentage of animals containing epididymal sperm (p < 0.01). These data suggest that in the mouse oxytocin, whilst not involved in germ cell development, is important in the process of spermiation and sperm transfer in the mouse.

Construction of hybrid xylE genes between the two duplicate homologous genes from TOL plasmid pWW53: comparison of the kinetic properties of the gene products.

The two xylE genes for catechol 2,3-oxygenase, encoded by TOL plasmid pWW53, carry a common SalI restriction site within the reading frame. Each gene was cut at the SalI site and the 5' end of each gene spliced to the 3' end of the other to form hybrid genes, from both of which catalytically active catechol 2,3-oxygenase activities were expressed. The kinetic parameters were determined for the gene products of both the hybrid and the wild-type xylE genes with catechol, 3-methylcatechol and 4-methylcatechol as substrates. Comparison of the results suggested firstly, that the C-terminal regions of the enzymes determined both the binding and the catalytic specificity, and, secondly, that the N-terminal region of one of the enzymic gene products contained a secondary binding site which caused inhibition by excess substrate for methylcatechol substrates but not for catechol. One of the wild-type enzymes appeared to have an intrinsically higher activity for all three substrates than the other. This higher activity depended on the presence of both its C- and N-terminal regions, and in both hybrid enzymes, which contained only one of these regions, activity was significantly reduced.

Cloning, sequencing, temporal expression and tissue-specificity of two serine proteases from the midgut of the blood-feeding fly Stomoxys calcitrans.

Using highly degenerate, serine-protease-specific PCR primers on a midgut-specific cDNA library it was estimated that a minimum of 24 independent serine proteases were expressed in the midgut of Stomoxys calcitrans. The relative abundance of these 24 independent serine proteases has been estimated by restriction analysis of PCR products, showing that 69% fall into six almost equally abundant groups. Two highly abundant serine protease cDNAs (Ssp1 and Ssp2) were isolated and sequenced. They encode preproenzymes of 272 amino acids (Mr 28521) and 255 amino acids (Mr 27097) with putative signal peptides of 17 amino acids and 16 amino acids, putative activation peptides of 15 amino acids and 10 amino acids and mature enzymes of 239 amino acids (Mr 25322; pI 4.89) and 228 amino acids (Mr 24182; pI 7.59), respectively. Both deduced amino acid sequences contain the Asp/His/Ser catalytic triad and the highly conserved sequences surrounding it. Ssp2 also has the aspartate and two glycine residues in the specificity pocket, marking this as a typical trypsin. The positioning of the residues in the specificity pocket of Sspl is unusual; aspartate and glycine residues are present, which is typical of trypsin, but both are separated from surrounding conserved residues by additional amino acids; the second glycine found in the specificity pocket of trypsin is replaced by a serine, which is typical of chymotrypsin. Although a serine protease, the precise substrate specificity of Sspl remains to be determined. Northern analysis shows that both serine proteases are expressed constitutively with only a 20% change in the levels of expression of Ssp1 and Ssp2 through the digestive cycle, and that expression occurs predominantly in the opaque region of the midgut, the region responsible for secretion of digestive enzymes.

Mitotic crossing over in chromosome I disomics of Aspergillus nidulans.

The frequency and pattern of homologous recombination in chromosome I disomics of Aspergillus nidulans is presented. Approximately 6% of randomly selected haploid breakdown sectors are recombinant. Most of these arise from double exchange events, one of which is located in the centromere region, the other distal on the left arm. Other marked regions are rarely involved in a recombination event. Reciprocal genotypes arise in approximately equal frequencies indicating that exchange results in reciprocally recombined non-sister chromatids at the four strand stage of mitosis. Possible theories for the extreme localisation of exchange events are discussed.

Function and localization of oxytocin receptors in the reproductive tissue of rams.

Oxytocin is present in the male reproductive tract and has been shown to increase contractility in the epididymis and to modulate steroidogenesis. This study investigated the effects of oxytocin in the testis in vivo, and the presence and cellular localization of oxytocin receptors in the reproductive tract of rams. During the breeding season, mature rams underwent efferent duct ligation before injection of either oxytocin (20 microg) or oxytocin plus an oxytocin antagonist (20 microg) into the testicular artery; the contralateral testicular artery received saline. Injection of oxytocin caused a significant increase (P < 0.05) in the concentration of spermatozoa collected from the rete testis. This effect was not observed after treatment with the oxytocin antagonist plus oxytocin. Western blot analysis performed using a specific oxytocin receptor antibody (020) identified a single immunoreactive band of 66 kDa in testicular and epididymal tissue. This band was present in uterine tissue but not in liver or muscle. Immunocytochemistry identified oxytocin receptors on Leydig and Sertoli cells of the testis, on epithelial cells throughout the epididymis, on peritubular smooth muscle cells in the cauda epididymidis, and on the epithelial cells and circular smooth muscle layer of the ductus deferens. These findings indicate that oxytocin can modulate sperm transport in the ram testis. A role for oxytocin in promoting sperm transit is supported by the localization of oxytocin receptors in the cauda epididymis and ductus deferens, and the presence of receptors on Leydig, Sertoli and epididymal epithelial cells provides further evidence that oxytocin may be involved in the local regulation of steroidogenesis.