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T M Mason

Publications and source records attributed to T M Mason.

8 recordsLinked to original sources
PubMed1997

The complete genome sequence of the hyperthermophilic, sulphate-reducing archaeon Archaeoglobus fulgidus.

Archaeoglobus fulgidus is the first sulphur-metabolizing organism to have its genome sequence determined. Its genome of 2,178,400 base pairs contains 2,436 open reading frames (ORFs). The information processing systems and the biosynthetic pathways for essential components (nucleotides, amino acids and cofactors) have extensive correlation with their counterparts in the archaeon Methanococcus jannaschii. The genomes of these two Archaea indicate dramatic differences in the way these organisms sense their environment, perform regulatory and transport functions, and gain energy. In contrast to M. jannaschii, A. fulgidus has fewer restriction-modification systems, and none of its genes appears to contain inteins. A quarter (651 ORFs) of the A. fulgidus genome encodes functionally uncharacterized yet conserved proteins, two-thirds of which are shared with M. jannaschii (428 ORFs). Another quarter of the genome encodes new proteins indicating substantial archaeal gene diversity.

Archaeoglobus fulgidus↗
PubMed1994

Characterization of regulatory volume decrease in the THP-1 and HL-60 human myelocytic cell lines.

Exposure to hypotonic stress produces a transient increase in cell volume followed by a regulatory volume decrease (RVD) in both THP-1 and HL-60 cells. In contrast, cells exposed to hypotonic stress in a high K/low Na Hanks' solution not only failed to volume regulate, but displayed a secondary swelling. Thus, while an outward K gradient was required for RVD, the secondary swelling indicated that hypotonic stress increased permeability in the absence of a negative membrane potential. The K channel blocker quinine (1-4 mM) blocked RVD in both cell types. Gramicidin's ability to overcome the quinine block of RVD indicated that RVD is mediated by a quinine-sensitive cation transport mechanism that is independent of the swelling-induced anion transport mechanism. Barium (1-4 mM), another K channel blocker, slowed the rate of RVD, while 4-aminopyridine, charybdotoxin, tetraethylammonium chloride, tetrabutylammonium chloride, and gadolinium had no effect on RVD. Furthermore, RVD was not mediated by calcium-activated conductances, since it occurred normally in Ca-free medium, in medium containing cadmium, and in BAPTA-loaded cells. Gramicidin produced little or no volume change in isotonic medium, suggesting that basal C1 permeability of both THP-1 and HL-60 cells is low. However, swelling induced an anion efflux pathway that is permeable to both chloride and bromide, but is impermeable to methanesulfonate and glutamate. The anion channel blocker 3,5-diiodosalicylic acid (DISA) antagonized RVD in both cell types. In conclusion, RVD in THP-1 and HL-60 cells is mediated by independent anion and cation transport mechanisms that involve both a DISA-sensitive anion pathway and a quinine-inhibitable K efflux pathway, neither of which requires increases in intracellular calcium to be activated.

Anions↗
PubMed1992

Alpha-irradiation of haemopoietic tissue in pre- and postnatal mice: 2. Effects of mid-term contamination with 239Pu in utero.

The distribution of 239Pu in various tissues of foetal and postnatal offspring of pregnant mice, injected i.v. at 13 days gestation with 30 kBq 239Pu/kg (in some cases with 10 or 100 kBq/kg), together with the numbers of haemopoietic progenitors in the bone marrow, spleen and liver, were measured through to 1 year post-partum. The quality of the haemopoietic microenvironment in these mice was also measured using the renal-capsule implant method. The largest radiation dose received by any haemopoietic organ was that in the liver, amounting to 10-14 mGy, as reported previously. In spite of normal numbers of haemopoietic spleen colony-forming cells (CFC-S) in the liver and seeding, at birth, into the bone marrow where the level of plutonium was minimal, a long-term deficit in their number rapidly developed. The development of the stromal microenvironment, however, was also deficient, suggesting that the dose of alpha-irradiation to the foetal liver was sufficient to cause sublethal damage in those cells destined to become the precursors of the supportive haemopoietic microenvironment in bone marrow and spleen. The results of this study suggest that although the placenta affords significant shielding to the tissues of the developing foetus from maternal contamination, the long-term effects on haemopoiesis are comparable to those in mice contaminated as adults. This further implies that the developing haemopoietic tissues are exquisitely sensitive to 239Pu contamination.

Alpha Particles↗
PubMed1991

Alpha-particle irradiation of haemopoietic tissue in pre- and postnatal mice. 1: Distribution of plutonium-239 after mid-term contamination.

Pregnant mice (at 13 days gestation) and age-matched controls were injected with 30 kBq 239Pu/kg and the distribution of plutonium in maternal and foetal tissues measured. Approximately 2% of the activity injected into the mother reached each foetus in 24 h, 95% of which was contained in membranes and placenta. The concentration of plutonium in foetal liver was 3 times the average foetal body concentration; both liver and body concentrations in the foetus increased by the end of gestation. Each pup accumulated only 0.01% extra injected activity after 9 days lactation and, as the resulting concentrations in the neonatal skeleton were low, we conclude that the greatest haemopoietic risk to the offspring from mid-term contamination in utero is in the foetal liver (which received an average dose of 10-14 mGy between the time of mid-term contamination and birth). By the end of gestation about one-quarter of the original activity was transferred to foetal tissues from the maternal liver and skeleton. No significant changes in maternal distribution were detected as a result of lactation. The results of this study are discussed, along with a compilation of previously published data.

Animals↗
PubMed1989

The development of spatial distributions of CFU-S and in-vitro CFC in femora of mice of different ages.

The radial distributions of spleen colony forming units (CFU-S) and in-vitro colony forming cells (in-vitro-CFC) were measured in the diaphyseal marrow cavity of femora removed from 3-, 5- and 11-week-old mice. The distributions observed in 11-week-old mice confirm earlier findings that the highest concentrations of CFU-S exist near bone surfaces whereas the concentration of in-vitro-CFC increases to a peak value approximately 300 microns from the femoral axis with a low value at the bone surface. The gradients of the distributions in all three age groups are very similar suggesting that spatial organization in marrow is established by 3 weeks at the latest and, as the marrow cavities grow, so the distributions extend into the new space following their respective gradients. The peak of CFU-S concentration at the bone surfaces in all age groups coincides with increased rates of DNA synthesis and a low self-renewal capacity. Conversely, CFU-S nearer the centre of the cavity maintain a low turnover but have a high self-renewal capacity. Measurements made on 1-week-old mice show that the marrow contains a lower average concentration of CFU-S in the femoral cavity compared to older mice. However, these CFU-S have both a high rate of turnover and a high self-renewal capacity. It appears that these better quality CFU-S remain in a central location while the rest of the population ages and expands in association with growing bone regions.

Aging↗
PubMed1988

Long-term haemopoietic injury in mice after repeated irradiation: precursor-cell cycling and its regulation.

The cycling rate of haemopoietic stem cells (day 9 CFU-S) and granulocyte-macrophage colony forming cells (GM-CFC) in mouse femora was, in response to reduced numbers, elevated at all times of sampling between 3 weeks and 10 months after 4 repeated doses of 4.5 Gy X-rays (3 wk between doses). The level of a stimulator of CFU-S cycling was also elevated, and this was observed in both axial and marginal regions of the marrow inside the shaft. However, the rate of production of the stimulator was low; lower than previously reported in marrow regenerating after a single dose of 4.5 Gy, indicating damage to the regulatory stromal cells. The distribution of CFU-S across the axial and marginal zones of femoral marrow was changed from that in normal mice, where higher concentrations were found near the bone surface, to a more uniform distribution.

Animals↗