A novel C-terminal sequence from barley polyamine oxidase is a vacuolar sorting signal

Barley contains two different isoforms of flavin-containing polyamine oxidase (BPAO1 and BPAO2). We have previously demonstrated that BPAO2 is a symplastic protein in barley leaves. On the contrary, maize polyamine oxidase (MPAO), the best characterized member of this enzyme class, is apoplastic. Comparison of the derived amino-acid sequences of BPAO2 and MPAO has revealed that both precursor proteins include a cleavable N-terminal signal peptide of 25 amino acid residues, but the barley enzyme shows an extra C-terminal extension of eight amino acids. By means of MPAO engineering with BPAO2 C-terminal tail (MPAO-T) and exploiting transient expression in Nicotiana tabacum protoplasts, we demonstrate that this oligopeptide is a signal for protein sorting to the plant vacuole. The vacuolar sorting of MPAO-T was saturable. Specific mutations of the C-terminal tail were constructed to determine which amino acid residues of this novel propeptide affect proper protein sorting. No consensus sequence or common structural determinant is required for the intracellular retention of the MPAO-T protein, but a gradual lowering of the efficiency was observed as a result of progressive deletion of the C-terminus.     

Increasing biomass in Amazonian forest plots

A previous study by Phillips et al. of changes in the biomass of permanent sample plots in Amazonian forests was used to infer the presence of a regional carbon sink. However, these results generated a vigorous debate about sampling and methodological issues. Therefore we present a new analysis of biomass change in old-growth Amazonian forest plots using updated inventory data. We find that across 59 sites, the above-ground dry biomass in trees that are more than 10 cm in diameter (AGB) has increased since plot establishment by 1.22 +/- 0.43 Mg per hectare per year (ha(-1) yr(-1), where 1 ha = 10(4) m2), or 0.98 +/- 0.38 Mg ha(-1) yr(-1) if individual plot values are weighted by the number of hectare years of monitoring. This significant increase is neither confounded by spatial or temporal variation in wood specific gravity, nor dependent on the allometric equation used to estimate AGB. The conclusion is also robust to uncertainty about diameter measurements for problematic trees: for 34 plots in western Amazon forests a significant increase in AGB is found even with a conservative assumption of zero growth for all trees where diameter measurements were made using optical methods and/or growth rates needed to be estimated following fieldwork. Overall, our results suggest a slightly greater rate of net stand-level change than was reported by Phillips et al. Considering the spatial and temporal scale of sampling and associated studies showing increases in forest growth and stem turnover, the results presented here suggest that the total biomass of these plots has on average increased and that there has been a regional-scale carbon sink in old-growth Amazonian forests during the previous two decades.     

Redundancy, insult-specific sensors and thresholds: unlocking the S-phase checkpoint response

DNA damage that is not properly repaired during genomic replication is a major source of gross chromosomal rearrangements and sequence loss during cell proliferation. In higher eukaryotes such mutations increase the risk of cancer. Eukaryotic cells have multiple checkpoint responses activated by DNA damage and stalled replication forks. We focus here on fork-associated events that activate and respond to S-phase checkpoint kinases.     

A cytosolic NAD-dependent deacetylase, Hst2p, can modulate nucleolar and telomeric silencing in yeast

In budding yeast, the silent information regulator Sir2p is a nuclear NAD-dependent deacetylase that is essential for both telomeric and rDNA silencing. All eukaryotic species examined to date have multiple homologues of Sir two (HSTs), which share a highly conserved globular core domain. Here we report that yeast Hst2p and a mammalian Hst2p homologue, hSirT2p, are cytoplasmic in yeast and human cells, in contrast to yHst1p and ySir2p which are exclusively nuclear. Although yHst2p cannot restore silencing in a sir2 deletion, overexpression of yHst2p influences nuclear silencing events in a SIR2 strain, derepressing subtelomeric silencing while increasing repression in the rDNA. In contrast, a form of ySir2p carrying a point mutation in the conserved core domain disrupts both telomeric position effect (TPE) and rDNA repression at low expression levels. This argues that non-nuclear yHst2p can compete for a substrate or ligand specifically required for telomeric, and not rDNA repression.     

Deforestation in Lacandonia (southeast Mexico): evidence for the declaration of the northernmost tropical hot-spot

To assess the conservation status of Lacandonia, a megadiversity area in Mexico, rates of deforestation were calculated for the periods 1974–1981 and 1981–1991, using a random sample of 38 5 × 5km sites. We evaluated: (i) the overall magnitude of, and spatial and temporal variation in deforestation; (ii) how spatial variation relates to human population density, terrain slope and the presence of the Montes Azules Biosphere Reserve; (iii) the magnitude of potential plant species loss associated with deforestation. Overall deforestation was greater in the former than in the second period (1412 vs. 744ha/year), although mean rates (2.1 and 1.6%/year) were statistically indistinguishable due to a considerable spatial variation. The greatest spatial variation was related to the presence of the Montes Azules Reserve: deforestation outside the reserve was 20 and 6 times greater in the first and second period, respectively. Population density and terrain slope were related to deforestation but the relationship was considerably poor. Estimates of plant species committed to extinction (out of the expected total flora of 4314 species) were as high as 22% by year 2035, and 55% by year 2135. Such levels of potential species extinction associated to deforestation, and the great biological diversity of Lacandonia provide evidence to declare it as the northernmost tropical hot-spot and a priority goal in conservation efforts.     

Isolation, propagation and characterisation of Cryptosporidium

This review consists of 11 papers presented at the Consensus Conference on Cryptosporidium in Water (Parasitology Stream), held in Melbourne, Australia, from 5 to 6th October 1998. The conference was sponsored by the Water Services Association of Australia, the Australian Water and Wastewater Association, and the Collaborative Research Centre for Water Quality and Treatment. The papers summarise the advantages and disadvantages of various contemporary technologies applicable to parasite propagation and biochemical/molecular characterisation. Studies have detected distinct genetic differences between clinical isolates from humans and animals, and it is hoped that comprehensive documentation studies will facilitate the identification of environmental isolates in the not too distant future.     

Inhibition of "tissue" transglutaminase increases cell survival by preventing apoptosis

Treatment of the human promonocytic cell line U937 with all-trans-retinoic acid (RA) commits these cells to apoptosis, which can be triggered by simply increasing intracellular calcium levels by the ionophore A23187. RA treatment of U937 cells is characterized by a decrease in Bcl-2 and marked induction of "tissue" transglutaminase (tTG) gene expression. In this study, we show that the inhibition of tTG expression in U937 cells undergoing apoptosis prevents their death. In fact, U937 cell-derived clones transfected with the human tTG gene in the antisense orientation showed a pronounced decrease in apoptosis induced by several stimuli. These findings demonstrate that the Ca(2+)-dependent irreversible cross-linking of intracellular proteins catalyzed by tTG represents an important biochemical event in the gene-regulated cell death in monoblasts. In addition, our data indicate that the apoptotic program in promonocytic cells is strictly regulated by RA and that a key role is played by the free intracellular calcium concentration.     

Recurrent neural tube defects associated with partial trisomy 2p22-pter: report of two siblings and review of the literature

We report on two male siblings with partial trisomy 2p22-pter and partial monosomy 15q26-qter resulting from a maternally derived translocation t(2;15)(p22;q26). Both fetuses had different neural tube defects (craniorachischisis in the first fetus and anencephaly in the second fetus) which were detected by sonographic examination at the end of the first trimester of pregnancy. This report demonstrates the importance of chromosomal analysis in the etiologic exploration of neural tube defects and supports the importance of 2p24 triplication in neural tube development.     

Iron release in erythrocytes and plasma non protein-bound iron in hypoxic and non hypoxic newborns

Iron is released in a desferrioxamine (DFO)-chelatable form (DCI) when erythrocytes are challenged by an oxidative stress. In β-thalassemic erythrocytes, both DCI content and release (after aerobic incubation for 24 h) are increased and correlated with the fetal hemoglobin (HbF) levels. Since erythrocytes from newborns have an extremely high content of HbF and are exposed to conditions of oxidative stress, the release of iron in these erythrocytes was investigated. The erythrocyte DCI content was increased in preterm but not in term newborns as compared to adults, while the release was increased in both preterm and term erythrocytes. The level of plasma non protein-bound iron (NPBI), which was not detectable in adults, was much higher in preterm than in term newborns. When term plus preterm newborns were divided in two groups, normoxic and hypoxic, according to cord blood pH, it was found that both iron release and NBPI were markedly higher in the hypoxic newborns compared to normoxic ones. Similar results were also obtained when the preterm and term infants were considered separately on the basis of cord blood pH. Therefore, iron release and NPBI are higher when conditions of hypoxia occur. In fact, when the values for iron release and NPBI were separately plotted against cord blood pH values, significant negative correlations were seen in both cases. NPBI was correlated with iron release seen in all the newborns and a significant part of the released iron could be recovered into the incubation medium at the end of the incubation.