PubMed Health⌕ Search

Biomedical subjects

T J Davies

Publications and source records attributed to T J Davies.

At least 19 recordsLinked to original sources
PubMed2005

An investigation of the origin and significance of bilateral symmetry of the pronuclear zygote in the mouse.

BACKGROUND: Preliminary observations revealed that advanced zygotes of the PO strain mouse are often bilaterally symmetrical, and suggested that both the plane of first cleavage and features of the blastocyst bear a consistent relationship to the zygote's bilateral plane. METHODS: Spaced oil drops were injected into the zona pellucida to delineate the bilateral plane in pronuclear zygotes, and a distinct cluster of drops then placed over the second polar body. Such non-invasive marking was combined with gelation of the perivitelline space to prevent rotation of the zygotes within the zona pellucida. RESULTS: Nearly two-thirds of advanced pronuclear stage zygotes were bilaterally symmetrical and, regardless of whether first cleavage was meridional, it was almost invariably orthogonal to the bilateral plane. Moreover, both the axis of polarity and bilateral plane of the blastocyst bore a consistent relationship to the zygote's bilateral plane. Haploid parthenotes also exhibited bilateral symmetry, although in the absence of fertilization, first cleavage was less consistently orthogonal to the bilateral plane. CONCLUSIONS: Bilateral symmetry may be an intrinsic property of the oocyte that is induced by its activation and, from the reproducible way it maps on both the 2-cell conceptus and blastocyst, seems to play a role in early patterning.

Animals↗
PubMed2002

Trophectoderm growth and bilateral symmetry of the blastocyst in the mouse.

BACKGROUND: The present study was undertaken to ascertain whether the polarized flow of cells from polar to mural trophectoderm is related to the axis of bilateral symmetry of the blastocyst in the mouse, and whether trophectoderm cells can initiate new cycles once they have left the polar region. METHODS AND RESULTS: Two different approaches were used to investigate the relationship of polar to mural flow of trophectoderm cells to the bilateral axis. One was to mark peripheral polar trophectoderm cells at one or both ends of the bilateral axis in early blastocysts and examine the distribution of their clonal descendants after further growth in culture. The other was to mark the two ends of the bilateral axis with small oil drops in the zona pellucida in blastocysts whose polar trophectoderm was then labelled globally with fluorescent latex microspheres before culture. In both cases, marking of additional blastocysts orthogonal to the bilateral axis was also done. The results show that the direction of polar to mural flow of cells is not random, and that the most distal mural trophectoderm cell could yield up to eight descendants during 45 h of culture. CONCLUSION: The findings are consistent with the polar to mural flow of trophectoderm cells being aligned with the bilateral axis. Moreover, trophectoderm cells can embark on new cycles even when remote from the inner cell mass.

Animals↗
PubMed2002

The plane of first cleavage is not related to the distribution of sperm components in the mouse.

BACKGROUND: Marking experiments using phytohaemagglutinin (PHA) and Concanavalin A (ConA) have suggested that the first cleavage plane is related to the point of sperm entry. Because of concerns about the specificity of lectin binding, the distribution of sperm components has been investigated directly. METHODS AND RESULTS: The sperm tail could be identified in cleaving zygotes and early 2-cell stages following their permeabilization and exposure to Oregon Green Paclitaxel. At neither stage did the anterior end of the tail, which lies initially at the site of sperm entry, bear a consistent relationship to the first cleavage plane, even when it had clearly retained its original location. Moreover, using artificial insemination with MitoTracker-labelled sperm, the midpiece was found to remain associated with anterior end of the tail through to the 2-cell stage. Lectins showed no discernible binding to the fertilization cone of mechanically denuded zygotes and very strong binding to the zona pellucida. Moreover, after general labelling of zygotes with either ConA or PHA, persisting surface lectin tended to be concentrated towards the cleavage plane. CONCLUSION: The present findings challenge the claim that the sperm specifies the plane of first cleavage, and also question the methodology on which it was based.

Animals↗
PubMed1998

Translational inhibition of cyclin B1 and appearance of cyclin D1 very early in the differentiation of mouse trophoblast giant cells.

Investigation of the basis of uncoupling of replication of the genome from mitosis in the mouse trophoblast has so far been neglected despite its significance for understanding both placental development and cell cycle control. In order to obtain clues about the molecular basis of the switch from proliferation to endoreduplication, we have investigated changes in the expression of cyclins and cyclin-dependent kinases in diploid versus giant trophoblast cells. Interestingly, while cyclin B1 transcripts were found in both diploid and giant cells, the protein was found exclusively in diploid cells. This could be explained by either inhibition of translation or by constitutive degradation of the protein. The latter was ruled out by examining blastocysts which had been cultured in the presence of the proteasome inhibitor N-acetyl-leu-leu-norleucinal followed by immunostaining for cyclin B1. In these experiments cyclin B1 protein accumulated in diploid but not in giant cells. Fusion of trophoblast giant cells with secondary oocytes, which are rich in maturation promoting factor (MPF) activity, revealed that an exogenous source of active MPF could cause chromosome condensation and nuclear envelope breakdown in endocycling cells; therefore endoreduplication via polyteny evidently requires the suppression of MPF activity. In addition, cyclin D1 transcripts were found only in giant cells and, interestingly, the beginning of its expression was evident prior to that of placental lactogen I, an early marker of trophoblast differentiation. The results suggest that supression of MPF activity, by inhibition of translation of cyclin B1, is a key mechanism for the establishment of the endocycle in the mouse trophoblast.

Animals↗
PubMed1996

Constitutive expression of the machinery for programmed cell death.

In the presence of cycloheximide (CHX) to inhibit protein synthesis, a high concentration of staurosporine (STS) induces almost all cells in explant cultures of 8/8 types of newborn mouse organs and 3/3 types of adult mouse organs to die with the characteristic features of apoptosis. Eggs and blastomeres also die in this way when treated with STS and CHX, although they are less sensitive to this treatment than trophectoderm or inner cell mass cells whose sensitivity resembles that of other developing cells. Human red blood cells are exceptional in being completely resistant to treatment with STS and CHX. As (STS plus CHX)-induced cell deaths have been shown to display the characteristic features of programmed cell death (PCD), we conclude that all mammalian nucleated cells are capable of undergoing PCD and constitutively express all the proteins required to do so. It seems that the machinery for PCD is in place and ready to run, even though its activation often depends on new RNA and protein synthesis.

Alkaloids↗
PubMed1993

Lack of coupling between onset of giant transformation and genome endoreduplication in the mural trophectoderm of the mouse blastocyst.

Prominent among the various types of cell that differentiate from the trophectoderm of the mouse blastocyst are trophoblastic giant cells. Repeated endoreduplication of the genome accompanies the growth of these cells, which have been shown to be polytene rather than polyploid. Early stages in giant transformation have been examined, mainly in the mural trophectoderm of the implanting blastocyst which gives rise to the primary trophoblastic giant cells. One confusing issue is whether these early stages include the onset of endoreduplication of the genome. This issue has been addressed in the present study by comparing the DNA content of nuclei in isolated trophectoderm and ICM tissue rather than, as previously, by relating measurements on air-dry preparations of entire blastocysts to those of adult liver. The results, particularly those from delayed and reactivated blastocysts, show that genome endoreduplication is not an obligatory early event in the transformation of mural trophectoderm cells.

Animals↗
PubMed1992

Observations of H2O2 and PAN in a rural atmosphere.

Measurements of gaseous H2O2 and peroxyacetyl nitrate (PAN) concentrations in air are given for a site in rural southern England over an approximately 4-year period. In both cases the data show both diurnal and seasonal patterns. Temperature and wind direction had clear influences on the recorded concentrations of both species. There was an indication of increasing H2O2 concentrations with time. The use of a two-dimensional global model confirmed that this would be expected to occur alongside growth in ozone formation. It is suggested that, during photochemical episodes, the sequential build-up of ozone, PAN and H2O2 could be important in influencing the ability of vegetation to resist the effects of aggressive pollutants.

Journal Article↗
PubMed1992

The immediate- and medium-term effects of Meswak on the composition of mixed saliva.

Chewing sticks or Meswaks are used for teeth cleaning in many parts of the world. They contain substances that may reduce caries and periodontal disease. The present study consisted of 2 parts. In a short-term experiment, volunteers chewed on an inert eliciting agent (pyrogen-free rubber) and then a piece of Meswak, each for 5 min. For the medium-term experiment, volunteers brushed with either Meswak or a conventional toothbrush 5 x a day for 2 weeks. Saliva produced immediately after chewing Meswak showed statistically significant increases in calcium and chloride, but decreases in phosphate and pH as compared with controls. In the medium-term experiment, saliva samples collected 4 h after the last use of Meswak or toothbrush showed no significant differences in any of the components examined (calcium, magnesium, chloride, phosphate, IgA, IgG, lactate dehydrogenase and aspartate transaminase). Gingival and plaque indices, however, were significantly lower after brushing with Meswak. Salivary calcium promotes mineralization of tooth enamel and chloride inhibits calculus formation. Our results thus indicate that Meswak releases substances into saliva that could improve oral health. Calcium and chloride values were similar to those of controls after 4 h and thus frequent use of Meswak may be necessary to maintain a favorable salivary environment.

Bacteria↗
PubMed1991

Antimitogenic and mitogenic actions of interleukin-1 in diverse cell types are associated with induction of gro gene expression.

Interleukin-1 (IL-1) is an antiproliferative factor for growing human melanoma A375-C6 cells. To define the molecular basis for the action of IL-1, we set out to identify early genes induced by the cytokine in the absence of de novo protein synthesis. cDNA libraries were constructed from A375-C6 cells that were exposed or unexposed to IL-1 plus cycloheximide. Subtractive hybridization was used to prepare a library that was enriched for IL-1-induced clones. Two of these clones were shown by Northern analysis to represent IL-1-inducible genes. Nucleotide sequencing identified these genes as gro/melanoma growth stimulatory activity, which encodes a cell secretory product, and c-jun, which encodes a transcription factor. IL-1 caused persistent steady state elevation of gro mRNA but only transient induction of c-jun. Northern analysis using gene probes for the transcription factors c-fos and Egr-1 revealed that IL-1 induced c-fos but not Egr-1 expression in these cells. This indicates that differential early gene expression characterizes the growth-inhibitory action of IL-1. In contrast, serum, which is mitogenic for these cells, induces c-jun, c-fos, and Egr-1, but not gro expression. These data imply that in A375-C6 cells, both growth-inhibitory and stimulatory signals can channel their action through c-fos and c-jun genes. As gro induction was specifically associated with the antimitogenic action of IL-1, we studied the effect of the cytokine on gro gene expression in other types of cells. IL-1 was mitogenic for human glioblastoma and monkey kidney epithelial cells and induced gro whereas other mitogens did not. Thus, IL-1 can induce gro gene expression in diverse cell types, whether it acts to stimulate or inhibit proliferation. Like other cytokines gro may play diverse cell-specific roles in growth control.

Animals↗
PubMed1990

A comparison of serum mucoprotein with serum alpha 1 acid glycoprotein, haptoglobin, and alpha 1 antitrypsin assays in monitoring inflammatory bowel disease.

Serum mucoprotein level is a monitor for inflammatory bowel disease activity although its method of measurement is laborious. An easier assay of alpha 1 acid glycoprotein is described. The ability of the two proteins to differentiate active from non-active cases was evaluated and the results compared with acute inflammatory reactants such as alpha 1 antitrypsin and haptoglobin. Amongst 79 patients with inflammatory bowel disease linear discriminant analysis was used to segregate overlapping ranges for patients with and without active disease and thus enabling the evaluation of sensitivity and specificity of each test. Predictive values of 78.6% for mucoprotein and 76.7% for alpha 1 acid glycoprotein were achieved and were due to the fact that there is a very strong linear correlation between these two proteins (r = 0.83, p less than 0.01). Furthermore the mucoprotein fraction is predominantly comprised of alpha 1 acid glycoprotein by as much as 91.5%. alpha 1 antitrypsin and haptoglobin showed poor predictive values. Pairing up all the proteins each with mucoprotein improved the sensitivity, specificity, and predictive value slightly. As a single test alpha 1 acid glycoprotein gave highest specificity, proved easy to assay and was automatable. It was therefore recommended as a substitute for serum mucoprotein in routine assays and as an effective monitor and predictor of inflammatory bowel disease.

Colitis, Ulcerative↗
PubMed1987

Factors that affect the induction of gamma glutamyltransferase in epileptic patients receiving anti-convulsant drugs.

Serum samples from 335 epileptic patients receiving one or more anticonvulsant drugs, phenobarbitone, primidone and phenytoin, have been analysed for biochemical liver profile (BLP) and serum drug concentration. The results show that the induction of serum gamma glutamyltransferase (GGT) is affected by the sex and age of the patient, type of anti-convulsant drug prescribed and duration of treatment. It is less affected by serum drug concentration. It is suggested that these factors must be considered when interpreting results involving serum GGT activity as the index of microsomal enzyme induction.

Adolescent↗
PubMed1981

Effects of rest, exercise and warming on serum creatine kinase levels in primary hypothyroidism.

1. Serum creatine kinase and oral temperature were measured in 20 patients with primary hypothyroidism before and after 48 h bed rest. Fifteen of these patients were heated during the 48 h period. The remaining five acted as control subjects. In addition, creatine kinase and oral temperature were measured in five control subjects after a 30 min period of exercise and again after a 30 min period of resting. 2. The oral temperature rose and the serum creatine kinase levels fell only in those patients who were actively warmed. In the control subjects the period of exercise followed by resting caused no significant change in creatine kinase levels. 3. A subnormal body temperature appears to be an important determinant of the raised serum creatine kinase levels seen in patients with primary hypothyroidism.

Body Temperature↗
PubMed1981

Accelerated hypertriglyceridemia in patients on continuous ambulatory peritoneal dialysis - a preventable abnormality.

Increasing hypertriglyceridemia is a recognised complication of CAPD. To investigate the etiology lipid clearance studies using the intravenous fat tolerance test were performed in control subjects and in uremic patients before and after six months CAPD treatment. Oral carbohydrate intake was restricted and the use of hypertonic dialysate kept to a minimum. Although serum triglycerides were elevated in the uremic patients before CAPD (3.1 +/- 0.3 mMol/L) no further increase occurred during therapy. Oral carbohydrate intake was restricted to 240-250 Gms/24 hrs and hypertonic dialysate to 5.7 +/- 4.1% of the total. There were no significant changes in fractional removal rate of lipid. Therefore further increases in serum triglycerides in CAPD may be prevented by simple dietary manoeuvres.

Adult↗
PubMed1980

Pancreatic juice gamma-glutamyltransferase, alanine transaminase, and alkaline phosphatase in pancreatic disease.

Pancreatic juice gamma-glutamyltransferase (GGT, EC 2.3.2.2) has been proposed as a marker of pancreatic disease. We have collected pancreatic juice endoscopically from 24 control patients and 43 patients with a variety of hepatic, pancreatic, and biliary disorders. Pancreatic juice GGT, alanine transaminase (ALT, EC 2.6.1.2), and alkaline phosphatase (ALP, EC 3.1.3.1) were measured and found to be present in all samples. GGT was significantly higher in patients with pancreatic cancer (range 21-1175 IU/liter, P less than 0.005) compared with controls (range 2-52 IU/liter). Of 17 patients with pancreatic juice GGT concentrations greater than 52 IU/liter, eleven had definite pancreatic disease (seven pancreatic cancer, four chronic pancreatitis) and, in the remaining six, pancreatitis was possible although not proven. Pancreatic juice ALT and ALP provided no useful diagnostic criteria. GGT in pancreatic juice seems to be a nonspecific marker of pancreatic disease and merits further study.

Alanine Transaminase↗