Instability of a cryptic plasmid in Sinorhizobium meliloti P108 during symbiosis of it with alfalfa Medicago sativa

Instability of cryptic plasmids in Sinorhizobium meliloti laboratory strains SKhM1-188, DM7-R, and P108 as well as in their clones isolated from nodules of alfalfa grown during a long-term microvegetation experiment (120 days) was studied. The isolated clones of strains SKhM1-188 and DM7-R manifested stable inheritance of plasmids, whereas 12.7-14.0% of clones with changed plasmid profile were detected in a population of clones from strain P108. These segregants were designated as P108c. Segregants P108c exhibited significantly decreased symbiotic effectiveness, nitrogenase activity, and the competitiveness with respect to alfalfa, compared to the original strain P108. It was established that a 80-kb deletion occurred in a larger of two cryptic plasmids (240 and 230 kb) of segregants P108c. It was concluded that genetic rearrangements are possible in rhizobial clones that did not undergo structural transformation and retained viability in the nodule during the natural vegetation period of alfalfa.     

Correlation between thyroid hormone status and hepatic hyperplasia and hypertrophy caused by the peroxisome proliferator-activated receptor alpha agonist Wy-14,643

BACKGROUND: The metabolic inhibitor rotenone inhibits hepatocellular proliferation and the incidence of liver cancer resulting from exposure to the PPARalpha agonist Wy-14,643, via unknown mechanisms. Since the absence of thyroid hormones diminishes hepatomegaly, an early biomarker for the hepatocarcinogenicity induced by PPARalpha agonists, this study was undertaken to investigate whether rotenone might interference with the ability of Wy-14,643 to alter the animal thyroid status. METHODS: Male B6C3F1 mice were given Wy-14,643 (100 ppm), rotenone (600 ppm) or a mixture of both, in the feed for 7 days. Bromodeoxyuridine (BrDU), marker of cell replication, was delivered through subcutaneously implanted osmotic mini-pumps. At the end of the experiment, sera were collected and corticosterone and thyroid hormone levels were measured by solid-phase radioimmunoassay kits. In addition, liver tissue samples were stained immunohistochemically for BrDU to determine percentages of labeled cells. Further, cell surface area was determined from images generated by a Zeiss Axioplan microscope equipped with a plan Neofluar x40 0.75 na objective. Tracings of individual hepatocyte perimeters were then analyzed and cell-surface areas were calculated using MicroMeasure FL-4000. RESULTS: Wy-14,643 caused a significant increase in liver weights, hepatocyte BrDU labeling index (LI), and hepatocyte surface area. In animals which received both Wy-14,643 and rotenone simultaneously, all of these effects were significantly less pronounced compared with mice that received Wy-14,643 alone. Rotenone alone decreased liver weights, LI and surface area. The Free Thyroid Index (FTI), which provides an accurate reflection of the animal's thyroid status, was 5.0 +/- 0.3 in control mice. In animals exposed to rotenone, these values decreased to 2.0 +/- 0.9, but in animals which received Wy-14,643, levels increased significantly to 7.7 +/- 0.9. FTI values decreased to 3.4 +/- 0.8 in mice receiving both rotenone and Wy-14,643. CONCLUSION: A strong correlation was observed between the animal thyroid status and both, hepatocyte proliferation (r2 = 0.62), and hepatocyte surface area (r2 = 0.83). These results support the hypothesis that the thyroid status of the animal plays a role in PPARalpha-induced hepatocellular proliferation and liver cell enlargement. Both these events are known to contribute to the expression of liver cancer in response to the activation of PPARalpha.     

Distribution of MT1 Melatonin Receptor Promoter-Driven RFP Expression in the Brains of BAC C3H/HeN Transgenic Mice

The pineal hormone melatonin activates two G-protein coupled receptors (MT₁ and MT₂) to regulate in part biological functions. The MT₁ and MT₂ melatonin receptors are heterogeneously distributed in the mammalian brain including humans. In the mouse, only a few reports have assessed the expression of the MT₁ melatonin receptor expression using 2-iodomelatonin binding, in situ hybridization and/or polymerase chain reaction (PCR). Here, we described a transgenic mouse in which red fluorescence protein (RFP) is expressed under the control of the endogenous MT₁ promoter, by inserting RFP cDNA at the start codon of MTNR1a gene within a bacterial artificial chromosome (BAC) and expressing this construct as a transgene. The expression of RFP in the brain of this mouse was examined either directly under a fluorescent microscope or immunohistochemically using an antibody against RFP (RFP-MT₁). RFP-MT₁ expression was observed in many brain regions including the subcommissural organ, parts of the ependyma lining the lateral and third ventricles, the aqueduct, the hippocampus, the cerebellum, the pars tuberalis, the habenula and the habenula commissure. This RFP-MT₁ transgenic model provides a unique tool for studying the distribution of the MT₁ receptor in the brain of mice, its cell-specific expression and its function in vivo.     

Melanin in <Emphasis Type="Italic">Fonsecaea pedrosoi</Emphasis>: a trap for oxidative radicals

Background  

The pathogenic fungus Fonsecaea pedrosoi constitutively produces the pigment melanin, an important virulence factor in fungi. Melanin is incorporated in the cell wall structure and provides chemical and physical protection for the fungus.     

土壤低剂量芘污染对蚯蚓若干生化指标的影响

通过人工污染土壤的方法,设计芘的暴露浓度为0、60、120、240、480、960μg.kg-1.暴露实验进行1、3、7和14d后,分别检测蚯蚓内脏中细胞色素P450含量、谷胱甘肽转移酶(GST)、超氧化物歧化酶(SOD)、过氧化物酶(POD)、过氧化氢酶(CAT)活性和丙二醛(MDA)含量.结果表明,在供试浓度范围内,蚯蚓内脏中各生化指标对污染物暴露指示的敏感性存在差异:其中P450含量、GST和SOD活性最为敏感;POD和CAT活性次之;而MDA含量未对低剂量的芘暴露起到明显的指示作用.研究同时发现,低剂量污染物暴露的时间效应要强于剂量效应的影响.因而,在进行生态毒性诊断时,采用多指标和多时段的检测对增强指示的灵敏性和有效性尤为重要.     

Patch-clamp recording of charge movement, Ca(2+) current, and Ca(2+) transients in adult skeletal muscle fibers

Intramembrane charge movement (Q), Ca(2+) conductance (G(m)) through the dihydropyridine-sensitive L-type Ca(2+) channel (DHPR) and intracellular Ca(2+) fluorescence (F) have been recorded simultaneously in flexor digitorum brevis muscle fibers of adult mice, using the whole-cell configuration of the patch-clamp technique. The voltage distribution of Q was fitted to a Boltzmann equation; the Q(max), V(1/2Q), and effective valence (z(Q)) values were 41 +/- 3.1 nC/&mgr;F, -17.6 +/- 0.7 mV, and 2.0 +/- 0.12, respectively. V(1/2G) and z(G) values were -0.3 +/- 0.06 mV and 5.6 +/- 0.34, respectively. Peak Ca(2+) transients did not change significantly after 30 min of recording. F was fit to a Boltzmann equation, and the values for V(F1/2) and z(F) were 6.2 +/- 0.04 mV and 2.4, respectively. F was adequately fit to the fourth power of Q. These results demonstrate that the patch-clamp technique is appropriate for recording Q, G(m), and intracellular [Ca(2+)] simultaneously in mature skeletal muscle fibers and that the voltage distribution of the changes in intracellular Ca(2+) can be predicted by a Hodgkin-Huxley model.