Altered telomeres in tumors with ATRX and DAXX mutations

The proteins encoded by ATRX and DAXX participate in chromatin remodeling at telomeres and other genomic sites. Because inactivating mutations of these genes are common in human pancreatic neuroendocrine tumors (PanNETs), we examined the telomere status of these tumors. We found that 61% of PanNETs displayed abnormal telomeres that are characteristic of a telomerase-independent telomere maintenance mechanism termed ALT (alternative lengthening of telomeres). All of the PanNETs exhibiting these abnormal telomeres had ATRX or DAXX mutations or loss of nuclear ATRX or DAXX protein. ATRX mutations also correlate with abnormal telomeres in tumors of the central nervous system. These data suggest that an alternative telomere maintenance function may operate in human tumors with alterations in the ATRX or DAXX genes.     

Synaptic changes in layer 2/3 underlying map plasticity of developing barrel cortex

The functional and anatomical rearrangements of cortical sensory maps accompanying changes in experience are not well understood. We examined in vivo and in vitro how the sensory map and underlying synaptic connectivity of the developing rat barrel cortex are altered when the sensory input to the cortex is partially deprived. In the nondeprived cortex, both the sensory responses and synaptic connectivity between columns were strengthened through an increase in the synaptic connection probability between L2/3 pyramids in adjacent columns. This was accompanied by a selective growth of L2/3pyramid axonal arbors between spared columns. In contrast, deprived and nondeprived cortical columns became weakly connected in their L2/3 pyramid connections.     

Mutations in CIC and FUBP1 contribute to human oligodendroglioma

Oligodendrogliomas are the second most common malignant brain tumor in adults and exhibit characteristic losses of chromosomes 1p and 19q. To identify the molecular genetic basis for this alteration, we performed exomic sequencing of seven tumors. Among other changes, we found that the CIC gene (homolog of the Drosophila gene capicua) on chromosome 19q was somatically mutated in six cases and that the FUBP1 gene [encoding far-upstream element (FUSE) binding protein] on chromosome 1p was somatically mutated in two tumors. Examination of 27 additional oligodendrogliomas revealed 12 and 3 more tumors with mutations of CIC and FUBP1, respectively, 58% of which were predicted to result in truncations of the encoded proteins. These results suggest a critical role for these genes in the biology and pathology of oligodendrocytes.     

Methylmercury in runoff from the Svartberget Catchment in northern Sweden during a stormflow episode

The dynamics of MeHg during rain-driven runoff episodes are important in calculating the output of MeHg from forested catchments. These dynamics may also provide insight into the processes controlling MeHg output from soils to surface waters. The concentrations of MeHg, Hg-tot, TOC and associated chemistry were observed during a rain-driven, July runoff episode on two forested tributaries of the Svartberget Catchment, as well as at the outlet of a mire in the headwaters of that catchment. TOC concentrations in runoff increased during the episode. Hg-tot concentrations also tended to increase (from 3 to between 4 and 7 ng L^?1), though the timing of that increase varied. MeHg concentrations, on the other hand, tended to decrease. The decrease was slight in the two forested tributaries (ca. 0.1 ng L^?1), but greater in the mire runoff (from 0.8 to ca 0.3 ng L^?1). These data are set in relation to a hypothesis about the processes which control MeHg output.     

The impact of rising CO2 on ecosystem production

A fundamental property of green plants is that the rate of photosynthesis is dependent in the ambient CO₂ concentration. There is overwhelming experimental evidence that this effect increases plant production in most C₃ plants: hundreds of experiments with many species show that plant growth increases an average 30% to 40% for a doubling of the present normal ambient CO₂ concentration (Kimball, 1986). External environmental factors, such as temperature and the availability of nutrients, modify this response. The greatest stimulation of photosynthesis and growth can be expected to occur at high temperatures and much smaller responses at low temperature. Factors which restrict growth, such as low nutrients, will reduce but usually do not eliminate the stimulation of production with increasing CO₂ even when nitrogen is severly limiting. There are also reports of direct effects of ambient CO₂ concentration on dark respiration which show that there is an immediate reduction in the rate of CO₂ efflux or O₂ consumption when the CO₂ around plant tissues is increased. There have been very few longterm field studies of the effects of increased CO₂ on whole plants and ecosystem processes but the data from these studies are consistent in showing an increase in plant production with an increase in CO₂ concentration of the ambient air.     

Transient gene expression in transformed banana (Musa cv. Bluggoe) protoplasts and embryogenic cell suspensions

Summary In order to introduce currently-available genes with agronomical value into banana, two genetic transformation protocols have been optimized.Firstly, regenerable protoplasts isolated from embryogenic cell suspensions of the cultivar Bluggoe have been used for the introduction of several chimaeric uidA gene constructs by electroporation. With the inclusion of polyethylene glycol and heat shock, the frequency of transiently expressing protoplasts reached 1.8% as shown by an in situ -glucuronidase assay. A duplicated 35S promoter with an alfalfa mosaic virus leader sequence (pBI-426) induced the highest expression rate among the constructs tested.Embryogenic cell suspensions of cv. Bluggoe have also been bombarded with accelerated particles coated with a high expression uidA gene construct (pEmuGN) using a biolistic gun. After a partial optimization of the procedure, transient GUS assays reproducibly demonstrated the presence of 400 blue foci in 30 l of settled cell volume (approximately 25 mg cells). Selection and characterization of antibiotic-resistant transformed cultures is in progress.Abbreviations AMV alfalfa mosaic virus - GUS -glucuronidase - TGE transient GUS expression - uidA gene for -glucuronidase