Ubiquitin‐specific protease‐like 1 (USPL1) is a SUMO isopeptidase with essential,non‐catalytic functions

Isopeptidases are essential regulators of protein ubiquitination and sumoylation. However, only two families of SUMO isopeptidases are at present known. Here, we report an activity‐based search with the suicide inhibitor haemagglutinin (HA)‐SUMO‐vinylmethylester that led to the identification of a surprising new SUMO protease, ubiquitin‐specific protease‐like 1 (USPL1). Indeed, USPL1 neither binds nor cleaves ubiquitin, but is a potent SUMO isopeptidase both in vitro and in cells. C13orf22l—an essential but distant zebrafish homologue of USPL1—also acts on SUMO, indicating functional conservation. We have identified invariant USPL1 residues required for SUMO binding and cleavage. USPL1 is a low‐abundance protein that colocalizes with coilin in Cajal bodies. Its depletion does not affect global sumoylation, but causes striking coilin mislocalization and impairs cell proliferation, functions that are not dependent on USPL1 catalytic activity. Thus, USPL1 represents a third type of SUMO protease, with essential functions in Cajal body biology.     

Evaluation of gene prediction software using a genomic data set: application to Arabidopsis thaliana sequences

MOTIVATION: The annotation of the Arabidopsis thaliana genome remains a problem in terms of time and quality. To improve the annotation process, we want to choose the most appropriate tools to use inside a computer-assisted annotation platform. We therefore need evaluation of prediction programs with Arabidopsis sequences containing multiple genes. RESULTS: We have developed AraSet, a data set of contigs of validated genes, enabling the evaluation of multi-gene models for the Arabidopsis genome. Besides conventional metrics to evaluate gene prediction at the site and the exon levels, new measures were introduced for the prediction at the protein sequence level as well as for the evaluation of gene models. This evaluation method is of general interest and could apply to any new gene prediction software and to any eukaryotic genome. The GeneMark.hmm program appears to be the most accurate software at all three levels for the Arabidopsis genomic sequences. Gene modeling could be further improved by combination of prediction software. AVAILABILITY: The AraSet sequence set, the Perl programs and complementary results and notes are available at http://sphinx.rug.ac.be:8080/biocomp/napav/. CONTACT: Pierre.Rouze@gengenp.rug.ac.be.     

Organization and possible origin of the Bari-1 cluster in the heterochromatic h39 region of Drosophila melanogaster

The molecular organization of the heterochromatic h39 region of the Drosophila melanogaster second chromosome has been investigated by studying two BAC clones identified both by Southern blotting and by FISH experiments as containing tandem arrays of Bari1, a transposable element present only in this region. Such BAC clones appear to contain different portions of the h39 region since they differ in the DNA sequences flanking the Bari1 repeats on both sides. Thus, the 80 Bari1 copies estimated to be present in the h39 region are split into at least two separated subregions. On the basis of the analysis of the flanking sequences a possible mechanism depending on an aberrant activity of the Bari1 transposase is proposed for the genesis of the heterochromatic tandem arrays of the element.     

Quantifying the evidence for ecological synergies

There is increasing concern that multiple drivers of ecological change will interact synergistically to accelerate biodiversity loss. However, the prevalence and magnitude of these interactions remain one of the largest uncertainties in projections of future ecological change. We address this uncertainty by performing a meta-analysis of 112 published factorial experiments that evaluated the impacts of multiple stressors on animal mortality in freshwater, marine and terrestrial communities. We found that, on average, mortalities from the combined action of two stressors were not synergistic and this result was consistent across studies investigating different stressors, study organisms and life-history stages. Furthermore, only one-third of relevant experiments displayed truly synergistic effects, which does not support the prevailing ecological paradigm that synergies are rampant. However, in more than three-quarters of relevant experiments, the outcome of multiple stressor interactions was non-additive (i.e. synergies or antagonisms), suggesting that ecological surprises may be more common than simple additive effects.     

Alloparental feeding in Adélie penguins: why is it uncommon?

We investigated alloparental interactions and conditions which could facilitate or prevent the expression of alloparental behaviours in Adélie penguins (Pygoscelis adeliae), a long-lived seabird which nests in high-density colonies around Antarctica. Observation sessions were carried out during the crèche stage on 48 identified pairs and 50 identified chicks in a 217-nest subcolony. As the season progressed, young were fed less often by their own parents because these were increasingly absent from the breeding site and less responsive to their offspring’s solicitations. As a consequence, young and particularly those with a low body mass, coming from a two-chick brood, opted for gradually soliciting more from other adults to obtain food, preferentially those nesting in their direct vicinity. Unsuccessful breeders represented a low and constant part of the adult population and were not specifically solicited by unrelated young. Despite the increasing chick demand, only 4.1% (3 out of 73) of alloparental solicitations resulted in feeding, which is negligible compared to parental feeding. To investigate factors that could trigger the appearance of alloparental care, we carried out comparisons with king (Aptenodytes patagonicus) and emperor penguins (Aptenodytes forsteri) which represent the closest species for which data on alloparental behaviour were available. Our results show different trends to those observed in these species and three factors may explain the low occurrence of alloparental behaviour in Adélie penguins: (1) the low and constant proportion of unsuccessful breeders, (2) the absence of chick selectivity towards unsuccessful breeders, and (3) the late period of chick accessibility for potential alloparents.     

Mitotracker Green Is a P-Glycoprotein Substrate

P-glycoprotein has a widespread expression on normal tissues. The protein has also been strongly associated with the multidrug resistance phenotype (MDR) on tumor cells. The employment of flow cytometry and confocal microscopy has contributed to the discovery and application of new particular fluorescent dyes. Nevertheless, several studies are being performed in different cellular types neglecting the expression/activity of MDR proteins. Because many fluorochromes have been reported as P-glycoprotein substrates, an especial attention must be given to the properties of new dyes in the presence of MDR proteins. Flow cytometric analyzes of Mitotracker Green (MTG) fluorescence profile were performed in a human erythroleukemic cell line and its resistant counterpart. In this report we demonstrated that MTG, a probe used to evaluate the mitochondrial mass, is a P-glycoprotein substrate and its staining profile is dependent on the activity of this protein. In vitro studies on a human erythroleukemic cell line and its resistant counterpart revealed that MDR modulators (Cyclosporin A, Verapamil, and Trifluoperazine) alter the MTG fluorescence pattern on a resistant cell line. The findings suggest that attention should be given to the expression of P-glycoprotein when performing an evaluation of mitochondria properties with MTG.     

Apolipoprotein A-II/A-I ratio is a key determinant in vivo of HDL concentration and formation of pre-beta HDL containing apolipoprotein A-II

Overexpression of human apolipoprotein A-II (apo A-II) in mice induced postprandial hypertriglyceridemia and marked reduction in plasma HDL concentration and particle size [Boisfer et al. (1999) J. Biol. Chem. 274, 11564-11572]. We presently compared lipoprotein metabolism in three transgenic lines displaying plasma concentrations of human apo A-II ranging from normal to 4 times higher, under ad libitum feeding and after an overnight fast. Fasting dramatically decreased VLDL and lowered circulating human apo A-II in transgenic mice; conversely, plasma HDL levels increased in all genotypes. The apo A-I content of HDL was inversely related to the expression of human apo A-II, probably reflecting displacement of apo A-I by an excess of apo A-II. Thus, the molar ratios of apo A-II/A-I in HDL were significantly higher in fed as compared with fasted animals of the same transgenic line, while endogenous LCAT activity concomitantly decreased. The number and size of HDL particles decreased in direct proportion to the level of human apo A-II expression. Apo A-II was abundantly present in all HDL particles, in contrast to apo A-I mainly present in large ones. Two novel findings were the presence of pre-beta migrating HDL transporting only human apo A-II in the higher-expressing mice and the increase of plasma HDL concentrations by fasting in control and transgenic mice. These findings highlight the reciprocal modifications of VLDL and HDL induced by the feeding-fasting transition and the key role of the molar ratio of apo A-II/A-I as a determinant of HDL particle metabolism and pre-beta HDL formation.     

What shapes the altitudinal range of a high mountain Mediterranean plant? Recruitment probabilities from ovule to seedling stage

Recruitment is a complex process consisting of sequential stages affected by biotic interactions and abiotic factors. Assessment of these sequential stages and corresponding subprocesses may be useful in identifying the most critical stages. Accordingly, to assess the factors that may determine the altitudinal range limits of the high mountain Mediterranean plant Silene ciliata, a set of demographic stages, from flower production to establishment of 2‐yr‐old plants, and their influence on recruitment probability were examined using a step‐by‐step approach. We integrated florivory, pollination and pre‐dispersal seed predation as pre‐dispersal factors, and seedling emergence and survival as post‐dispersal determinants of recruitment. Three populations were monitored at the southernmost margin of the species along its local altitudinal range. Previous studies suggest that seediness is strongly limited by summer drought especially at the lower boundary of the species, a situation that may worsen under current global warming. Our results showed that recruitment was mainly limited by low seed production in the pre‐dispersal stage and low seedling emergence and survival in the post‐dispersal stage, probably due to environmental harshness in summer. By contrast, biotic factors responsible for propagule loss, such as flower and fruit predation, had a minor effect on the probability of plant recruitment. Although the relative importance of transition probabilities was similar among populations along the altitudinal range, comparatively lower flower production significantly reduced the number of recruited plants at the lowest altitude population. This demographic bottleneck, together with increased competition with other species favoured by climate warming, might collapse population growth and limit persistence at the lower altitudinal range of the species, raising its low local altitudinal edge.