Photoinhibition of holly (Ilex aquifolium) in the field during the winter

The distribution of holly ( Ilex aquifolium ) and its habitat preferences indicate a sensitivity to low temperature, particularly when exposed to high light. Experiments were conducted to determine whether photoinhibition of photosynthesis occurs in holly leaves in the field in United Kingdom during the winter. Photosynthetic efficiency was assessed in holly leaves that were exposed to or shaded from direct sunlight using measurements of photosynthetic oxygen evolution and chlorophyll fluorescence. Field measurements were conducted over 3 weeks during January and February. Correlation of the measurements of photosynthetic efficiency with weather conditions indicated that holly was suffering photoinhibition, particularly in leaves exposed to direct sunlight. Controlled environment studies demonstrated that exposure of leaves to low temperature and high light resulted in reductions in photosynthetic efficiency; however, leaves recovered rapidly when exposed to a higher temperature and reduced light level.     

Microcirculatory pathways in normal human spleen, demonstrated by scanning electron microscopy of corrosion casts

Confusion regarding microcirculatory pathways in normal human spleen has arisen due to extrapolation from pathological material and from other mammalian spleens, not to mention difficulties in tracing intricate three-dimensional routes from the study of thin sections or cut surfaces of tissue. We examined microcirculatory pathways in normal human spleens freshly obtained from organ transplant donors. A modified corrosion casting procedure was used to obtain an open view of vessels and their connections. Our results demonstrate: 1) "arteriolar-capillary bundles" within lymphatic nodules and extensive branching of arterioles in the marginal zone (MZ); 2) the marginal sinus around lymphatic nodules; 3) the peri-marginal cavernous sinus (PMCS) outside the MZ or immediately adjacent to the nodule itself; the PMCS receives flow via ellipsoid sheaths and MZ, or directly from arterial capillaries, and drains into venous sinuses; 4) fast pathways for flow into venous sinuses via ellipsoid sheaths; 5) arterial capillary terminations in the reticular meshwork of the red pulp or MZ ("open" circulation); direct connections to venous sinuses also occur ("closed" circulation), although rarely; and 6) numerous open-ended venous sinuses in the MZ, allowing a large proportion of the splenic inflow to bypass the red cell filtration sites in the reticular meshwork and at venous sinus walls.     

Trimethoprim binds in a bacterial mode to the wild-type and E30D mutant of mouse dihydrofolate reductase

Previous crystallographic studies of the antibacterial trimethoprim in complexes with bacterial and avian dihydrofolate reductases have shown substantial differences in the mode of binding, providing plausible explanations for the origin of the remarkable species selectivity of this inhibitor (Matthews, D. A., Bolin, J. T., Burridge, J. M., Filman, D. J., Volz, K. W., Kaufman, B. T., Beddell, C. R., Champness, J. N., Stammers, D. K., and Kraut, J. (1985) J. Biol. Chem. 260, 381-391; Matthews, D. A., Bolin, J. T., Burridge, J. M., Filman, D. J., Volz, K. W., and Kraut, J. (1985) J. Biol. Chem. 260, 392-399). A major species difference between the active sites is that the only carboxylate present is always Glu in vertebrates and Asp in bacteria. Crystallographic studies of the wild-type and E30D mutant of the enzyme from mouse now reveal that in both cases trimethoprim is bound in an identical fashion to that observed with the bacterial enzyme, and there is no obvious single explanation for the origin of the 10(5)-fold selectivity of trimethoprim binding. In an earlier study of a mouse wild-type enzyme using more limited data it was proposed that trimethoprim bound in the avian mode (Stammers, D. K., Champness, J. N., Beddell, C. R., Dann, J. G., Eliopoulos, E. E., Geddes, A. J., Ogg, D., and North, A. C. T. (1987) FEBS Lett. 218, 178-184), but a re-examination indicates that the occupancy of the active site by trimethoprim is less than had been thought, and we are currently unable to make an unambiguous interpretation of the electron density maps and cannot confirm the avian mode of binding in those crystals.     

Fascioloides magna (Bassi, 1875) in feral swine from southern Texas.

Between 1971 and 1975, Fascioloides magna was found in 46 of 67 (69%) feral swine (Sus scrofa) in southern Texas. Flukes were recovered from swine in areas where F. magna commonly has been recovered from white-tailed deer and cattle. One to 12 flukes were recovered from each infected animal. Their presence was indicated by black hematin pigment on the liver and various other internal organs. Eggs were not detected in the gallbladder or feces of infected animals although mature flukes and eggs were recovered in the livers suggesting that, like cattle, feral swine can be infected but are aberrant hosts for the parasite and do not disseminate eggs.     

Genetic diversity and spatial genetic structure of African wild dogs (<Emphasis Type="Italic">Lycaon pictus</Emphasis>) in the Greater Limpopo transfrontier conservation area

The Greater Limpopo Transfrontier Conservation Area (GLTFCA) is one of the last refuges for the endangered African wild dog and hosts roughly one-tenth of the global population. Wild dogs in this area are currently threatened by human encroachment, habitat fragmentation and scarcity of suitable connecting habitat between protected areas. We derived genetic data from mitochondrial and nuclear markers to test the following hypotheses: (i) demographic declines in wild dogs have caused a loss of genetic variation, and (ii) Zimbabwean and South African populations in the GLTFCA have diverged due to the effects of isolation and genetic drift. Genetic patterns among five populations, taken with comparisons to known information, illustrate that allelic richness and heterozygosity have been lost over time, presumably due to effects of inbreeding and genetic drift. Genetic structuring has occurred due to low dispersal rates, which was most apparent between Kruger National Park and the Zimbabwean Lowveld. Immediate strategies to improve gene flow should focus on increasing the quality of habitat corridors between reserves in the GLTFCA and securing higher wild dog survival rates in unprotected areas, with human-mediated translocation only undertaken as a last resort.     

Ca2+ release through ryanodine receptors regulates skeletal muscle L-type Ca2+ channel expression

Skeletal muscle obtained from mice that lack the type 1 ryanodine receptor (RyR-1), termed dyspedic mice, exhibit a 2-fold reduction in the number of dihydropyridine binding sites (DHPRs) compared with skeletal muscle obtained from wild-type mice (Buck, E. D., Nguyen, H. T., Pessah, I. N., and Allen, P. D. (1997) J. Biol. Chem. 272, 7360-7367 and Fleig, A., Takeshima, H., and Penner, R. (1996) J. Physiol. (Lond.) 496, 339-345). To probe the role of RyR-1 in influencing L-type Ca(2+) channel (L-channel) expression, we have monitored functional L-channel expression in the sarcolemma using the whole-cell patch clamp technique in normal, dyspedic, and RyR-1-expressing dyspedic myotubes. Our results indicate that dyspedic myotubes exhibit a 45% reduction in maximum immobilization-resistant charge movement (Q(max)) and a 90% reduction in peak Ca(2+) current density. Calcium current density was significantly increased in dyspedic myotubes 3 days after injection of cDNA encoding either wild-type RyR-1 or E4032A, a mutant RyR-1 that is unable to restore robust voltage-activated release of Ca(2+) from the sarcoplasmic reticulum (SR) following expression in dyspedic myotubes (O'Brien, J. J., Allen, P. D., Beam, K., and Chen, S. R. W. (1999) Biophys. J. 76, A302 (abstr.)). The increase in L-current density 3 days after expression of either RyR-1 or E4032A occurred in the absence of a change in Q(max). However, Q(max) was increased 85% 6 days after injection of dyspedic myotubes with cDNA encoding the wild-type RyR-1 but not E4032A. Because normal and dyspedic myotubes exhibited a similar density of T-type Ca(2+) current (T-current), the presence of RyR-1 does not appear to cause a general overall increase in protein synthesis. Thus, long-term expression of L-channels in skeletal myotubes is promoted by Ca(2+) released through RyRs occurring either spontaneously or during excitation-contraction coupling.     

Ataxia-telangiectasia-like disorder (ATLD)-its clinical presentation and molecular basis

Comparison of the clinical and cellular phenotypes of different genomic instability syndromes provides new insights into functional links in the complex network of the DNA damage response. A prominent example of this principle is provided by examination of three such disorders: ataxia-telangiectasia (A-T) caused by lack or inactivation of the ATM protein kinase, which mobilises the cellular response to double strand breaks in the DNA; ataxia-telangiectasia-like disease (ATLD), a result of deficiency of the human Mre11 protein; and the Nijmegen breakage syndrome (NBS), which represents defective Nbs1 protein. Mre11 and Nbs1 are members of the Mre11/Rad50/Nbs1 (MRN) protein complex. MRN and its individual components are involved in different responses to cellular damage induced by ionising radiation and radiomimetic chemicals, including complexing with chromatin and with other damage response proteins, formation of radiation-induced foci, and the induction of different cell cycle checkpoints. The phosphorylation of Nbs1 by ATM would indicate that ATM acts upstream of the MRN complex. Consistent with this were the suggestions that ATM could be activated in the absence of fully functional Nbs1 protein. In contrast, the regulation of some ATM target proteins, e.g. Smc1 requires the MRN complex as well as ATM. Nbs1 may, therefore, be both a substrate for ATM and a mediator of ATM function. Recent studies that indicate a requirement of the MRN complex for proper ATM activation suggest that the relationship between ATM and the MRN complex in the DNA damage response is yet to be fully determined. Despite the fact that both Mre11 and Nbs1 are part of the same MRN complex, deficiency in either protein in humans does not lead to the same clinical picture. This suggests that components of the complex may also act separately.     

IL-11 and IL-11Rα immunolocalisation at primate implantation sites supports a role for IL-11 in placentation and fetal development

Embryo implantation, endometrial stromal cell decidualization and formation of a functional placenta are critical processes in the establishment and maintenance of pregnancy. Interleukin (IL)-11 signalling is essential for adequate decidualization in the mouse uterus and IL-11 promotes decidualization in the human. IL-11 action is mediated via binding to the specific IL-11 receptor α (IL-11Rα). The present study examined immunoreactive IL-11 and IL-11Rα in cycling rhesus monkey endometrium, at implantation sites in cynomolgus and rhesus monkeys and in human first trimester decidua and defined distinct spatial and temporal patterns. In cycling rhesus monkey endometrium, IL-11 and IL-11Rα increased in both basalis and functionalis regions during the secretory compared with the proliferative phase, with changing cellular locations in luminal and glandular epithelium and stroma. The patterns were similar overall to those previously described in human endometrium. Differences were seen in immunostaining during implantation in cynomologus and rhesus monkey. In the cynomolgus, very little staining for IL-11 or IL-11Rα was seen in syncytio- and cyto-trophoblast cells in the villi between days 12 and 150 of pregnancy although there was moderate staining in cytotrophoblast in the shell between days 12 and 17 and in subpopulations of cytotrophoblast cells invading the arteries at day 17. By contrast in the rhesus monkey between days 24 and 35 of pregnancy and in human first trimester placenta, cyto- and syncytio-trophoblast in the villi but not cytotrophoblast in the shell were positively stained. The most intense staining for both IL-11 and IL-11Rα was present within the decidua in the maternal component of implantation sites in all three primates but moderate staining was also present in maternal vascular smooth muscle and glands perivascular cells and epithelial plaques. These results are consistent with a role for IL-11 both during decidualization and placentation in primates.