ATX-1, an Arabidopsis homolog of trithorax,activates flower homeotic genes

BACKGROUND: The genes of the trithorax (trxG) and Polycomb groups (PcG) are best known for their regulatory functions in Drosophila, where they control homeotic gene expression. Plants and animals are thought to have evolved multicellularity independently. Although homeotic genes control organ identity in both animals and plants, they are unrelated. Despite this fact, several plant homeotic genes are negatively regulated by plant genes similar to the repressors from the animal PcG. However, plant-activating regulators of the trxG have not been characterized. RESULTS: We provide genetic, molecular, functional, and biochemical evidence that an Arabidopsis gene, ATX1, which is similar to the Drosophila trx, regulates floral organ development. The effects are specific: structurally and functionally related flower homeotic genes are under different control. We show that ATX1 is an epigenetic regulator with histone H3K4 methyltransferase activity. This is the first example of this kind of enzyme activity reported in plants, and, in contrast to the Drosophila and the yeast trithorax homologs, ATX1 can methylate in the absence of additional proteins. In its ability to methylate H3K4 as a recombinant protein, ATX1 is similar to the human homolog. CONCLUSIONS: ATX1 functions as an activator of homeotic genes, like Trithorax in animal systems. The histone methylating activity of the ATX1-SET domain argues that the molecular basis of these effects is the ability of ATX1 to modify chromatin structure. Our results suggest a conservation of trxG function between the animal and plant kingdoms despite the different structural nature of their targets.     

Essential role of NKT cells producing IL-4 and IL-13 in the development of allergen-induced airway hyperreactivity

Using natural killer T (NKT) cell-deficient mice, we show here that allergen-induced airway hyperreactivity (AHR), a cardinal feature of asthma, does not develop in the absence of V(alpha)14i NKT cells. The failure of NKT cell-deficient mice to develop AHR is not due to an inability of these mice to produce type 2 T-helper (Th2) responses because NKT cell-deficient mice that are immunized subcutaneously at non-mucosal sites produce normal Th2-biased responses. The failure to develop AHR can be reversed by the adoptive transfer of tetramer-purified NKT cells producing interleukin (IL)-4 and IL-13 to Ja281(-/-) mice, which lack the invariant T-cell receptor (TCR) of NKT cells, or by the administration to Cd1d(-/-) mice of recombinant IL-13, which directly affects airway smooth muscle cells. Thus, pulmonary V(alpha)14i NKT cells crucially regulate the development of asthma and Th2-biased respiratory immunity against nominal exogenous antigens. Therapies that target V(alpha)14i NKT cells may be clinically effective in limiting the development of AHR and asthma.     

Identification of the blood group Lewis(a) determinant in the oviducal mucins of Xenopus tropicalis

The amphibian Xenopus tropicalis appears an increasingly appealing model for both genetic and developmental biology studies, compared to the related species Xenopus laevis. Study of the glycosylation pattern of its secreted glycoproteins revealed that this species synthesizes large amounts of Lewis(a) epitope, whereas this motif has previously only been identified in animals within the primate lineage. The use of (1)H-nuclear magnetic resonance spectroscopy enabled us to resolve the sequence of three Lewis(a)-bearing O-linked glycans associated with oviducal secretions, out of which one contained the novel sequence Gal(beta 1-3)GlcNAc(beta 1-6)GalNAc-ol. These structural data suggested the emergence of an alpha 1,4-fucosyltransferase activity in animals outside the primate lineage. On this basis, the screening of a X. tropicalis GenBank database with human Lewis-fucosyltransferase sequences revealed the occurrence of a putative fucosyltransferase gene that presented an unusual acceptor motif.     

Biochemical identification of proteasome-associated endonuclease activity in sunflower

Proteasomes have been purified from sunflower hypocotyles. They elute with a molecular mass of 600 kDa from gel filtration columns and two-dimensional gel electrophoresis indicates that the complex contains at least 20 different protein subunits. Peptide microsequencing revealed the presence of four subunits homologous to subunits Beta2, Beta6, Alpha5 and Alpha6 of plant proteasomes. These proteasomes have chymotrypsin-like activity and the highly purified fraction of this complex is associated with an endonuclease activity hydrolyzing Tobacco mosaic virus RNA and Lettuce mosaic virus RNA with a cleavage pattern showing fragments of well-defined size. This is the first evidence of a RNA endonuclease activity associated with plant proteasomes.     

Regulation of bone resorption and osteoclast survival by nitric oxide: possible involvement of NMDA-receptor

Nitric oxide has been shown to play an important role in regulation of bone resorption. However, the role of endogenous nitric oxide on osteoclast activity remains still controversial. In this work, using RT-PCR amplification, we demonstrated that rabbit mature osteoclasts express mRNA encoding for neuronal nitric oxide synthase suggesting that this enzyme could be involved in basal nitric oxide production in these cells. Then we assessed the effect of carboxy-PTIO, a nitric oxide scavenger, on in vitro bone resorption and osteoclast survival. Carboxy-PTIO (10-100 microM) inhibited osteoclastic bone resorption in a dose dependent manner and induced osteoclast apoptosis by a mechanism involving caspase 3 activation. These results suggest that basal concentration of endogenous nitric oxide may be essential for normal bone resorption by supporting osteoclast survival. Because osteoclasts express N-methyl-d-aspartate-receptor (NMDA-R), we hypothesized that in osteoclasts NMDA-R may be involved in nitric oxide production as in neuronal cells. We confirmed that blockade of NMDA-R with specific non-competitive antagonists, MK801 and DEP, strongly inhibited bone resorption. As for carboxy-PTIO, we showed that blockade of NMDA-R by both antagonists induced osteoclast apoptosis in a dose dependent manner by a mechanism dependent on caspase 3 activation. Intracellular calcium concentration in osteoclasts decreased within minutes in the presence of both antagonists. Finally, MK801-induced osteoclast apoptosis was partially reversed in the presence of small amount of SNAP (100 nM), a nitric oxide donor, suggesting that the effect of NMDA-R on osteoclast apoptotic cell death could be due to a decrease in nitric oxide production. Taken together, our results are consistent with the hypothesis that NMDA-R on osteoclasts could have a similar function as those in neuronal cells, i.e., to allow a calcium influx, which in turn activates a constitutive neuronal nitric oxide synthase. Nitric oxide generated by this pathway may be essential for osteoclast survival and hence for normal bone resorption.     

Spatial variation in springtime food resources influences the winter body mass of roe deer fawns

It is well established that the dynamics of mammalian populations vary in time, in relation to density and weather, and often in interaction with phenotypic differences (sex, age and social status). Habitat quality has recently been identified as another significant source of individual variability in vital rates of deer, including roe deer where spatial variations in fawn body mass were found to be only about a tenth of temporal variations. The approach used was to classify the habitat into blocks a priori, and to analyse variation in animal performance among the predefined areas. In a fine-grained approach, here we use data collected over 24 years on 1,235 roe deer fawns captured at known locations and the plant species composition sampled in 2001 at 578 sites in the Chizé forest to determine the spatial structure at a fine scale of both vegetation and winter body mass of fawns, and then to determine links between the two. Space and time played a nearly equal role in determining fawn body masses of both sexes, each accounting for about 20% of variance and without any interaction between them. The spatial distribution of fawn body mass was perennial over the 24 years considered and predicted values showed a 2 kg range according to location in the reserve, which is much greater than suggested in previous work and is enough to have strong effects on fawn survival. The spatial distribution and the range of predicted body masses were closely similar in males and females. The result of this study is therefore consistent with the view that the life history traits of roe deer are only weakly influenced by sexual selection. The occurrence of three plant species that are known to be important food items in spring/summer roe deer diets, hornbeam (Carpinus betulus), bluebell (Hyacinthoides sp.) and Star of Bethlehem (Ornithogalum sp.) was positively related to winter fawn body mass. The occurrence of species known to be avoided in spring/summer roe deer diets [e.g. butcher's broom (Ruscus aculeatus) and beech (Fagus sylvatica)], was negatively related to fawn body mass. We conclude that the spatial variation in the body mass of fawns in winter in this forest is as important as the temporal variation, and that the distribution of plant species that are actively selected during spring and summer is an important determinant of spatial variation in winter fawn body mass. The availability of these plants is therefore likely to be a key factor in the dynamics of roe deer populations.     

The focal adhesion and nuclear targeting capacity of the LIM-containing lipoma-preferred partner (LPP) protein

Targeting of proteins to a particular cellular compartment is a critical determinant for proper functioning. LPP (LIM-containing lipoma-preferred partner) is a LIM domain protein that is localized at sites of cell adhesion and transiently in the nucleus. In various benign and malignant tumors, LPP is present in a mutant form, which permanently localizes the LIM domains in the nucleus. Here, we have investigated which regions in LPP target the protein to its subcellular locations. We found that the LIM domains are the main focal adhesion targeting elements and that the proline-rich region of LPP, which harbors binding sites for alpha-actinin and vasodilator-stimulated phosphoprotein (VASP), has a weak targeting capacity. All of the LIM domains of LPP cooperate in order to provide robust targeting to focal adhesions, and the linker between LIM domains 1 and 2 plays a pivotal role in this targeting. When overexpressed in the cytoplasm of cells, the LIM domains of LPP can deplete endogenous LPP and vinculin from focal adhesions. The proline-rich region of LPP contains targeting sites for focal adhesions and stress fibers that are distinct from the alpha-actinin and VASP binding sites, and the LPP LIM domains are dispensable for targeting LPP to the nucleus. Our studies have defined novel functional domains in the LPP protein.     

Effect of habitat fragmentation on dispersal in the butterfly Proclossiana eunomia

Comparison of dispersal rates of the bog fritillary butterfly between continuous and fragmented landscapes indicates that between patch dispersal is significantly lower in the fragmented landscape, while population densities are of the same order of magnitude. Analyses of the dynamics of the suitable habitat for the butterfly in the fragmented landscape reveal a severe, non linear increase in spatial isolation of patches over a time period of 30 years (i.e. 30 butterfly generations), but simulations of the butterfly metapopulation dynamics using a structured population model show that the lower dispersal rates in the fragmented landscape are far above the critical threshold leading to metapopulation extinction. These results indicate that changes in individual behaviour leading to the decrease of dispersal rates in the fragmented landscape were rapidly selected for when patch spatial isolation increased. The evidence of such an adaptive answer to habitat fragmentation suggests that dispersal mortality is a key factor for metapopulation persistence in fragmented landscapes. We emphasise that landscape spatial configuration and patch isolation have to be taken into account in the debate about large-scale conservation strategies.     

Effects of the Diadromus pulchellus ascovirus,DpAV-4, on the hemocytic encapsulation response and capsule melanization of the leek-moth pupa,Acrolepiopsis assectella

DpAV-4 is a symbiotic ascovirus found in natural populations of the solitary endoparasitoid wasp Diadromus pulchellus. The female wasp injects this virus into the pupae of the leek-moth Acrolepiopsis assectella during oviposition. The ascovirus replicates in the pupal tissues and the consequent lysis of the cells occurs synchronously with egg hatching and the development of the wasp larva. We show here that encapsulation and capsule melanization were activated when minute nylon monofilaments were implanted into the hemocoel of non parasitized leek-moth pupae and that encapsulation and melanization were inhibited in pupae parasitized by D. pulchellus. When the pupae were infected by DpAV-4, melanization of the nylon monofilaments was abolished, but a capsule was still always formed. These results indicate that DpAV-4 is a free virus able to alter the defence system of the parasitized host so as to improve the development of the parasitoid wasp, D. pulchellus.