Genetic screens for Caenorhabditis elegans mutants defective in left/right asymmetric neuronal fate specification

We describe here the results of genetic screens for Caenorhabditis elegans mutants in which a single neuronal fate decision is inappropriately executed. In wild-type animals, the two morphologically bilaterally symmetric gustatory neurons ASE left (ASEL) and ASE right (ASER) undergo a left/right asymmetric diversification in cell fate, manifested by the differential expression of a class of putative chemoreceptors and neuropeptides. Using single cell-specific gfp reporters and screening through a total of almost 120,000 haploid genomes, we isolated 161 mutants that define at least six different classes of mutant phenotypes in which ASEL/R fate is disrupted. Each mutant phenotypic class encompasses one to nine different complementation groups. Besides many alleles of 10 previously described genes, we have identified at least 16 novel "lsy" genes ("laterally symmetric"). Among mutations in known genes, we retrieved four alleles of the miRNA lsy-6 and a gain-of-function mutation in the 3'-UTR of a target of lsy-6, the cog-1 homeobox gene. Using newly found temperature-sensitive alleles of cog-1, we determined that a bistable feedback loop controlling ASEL vs. ASER fate, of which cog-1 is a component, is only transiently required to initiate but not to maintain ASEL and ASER fate. Taken together, our mutant screens identified a broad catalog of genes whose molecular characterization is expected to provide more insight into the complex genetic architecture of a left/right asymmetric neuronal cell fate decision.     

Changing the substrate specificity of a chitooligosaccharide oxidase from Fusarium graminearum by model-inspired site-directed mutagenesis

Chitooligosaccharide oxidase (ChitO) catalyzes the oxidation of C1 hydroxyl moieties on chitooligosaccharides and in this way displays a different substrate preference as compared to other known oligosaccharide oxidases. ChitO was identified in the genome of Fusarium graminearum and a structural model revealed that one active site residue (Q268) was likely to be involved in the recognition of the N-acetyl moiety on the chitooligosaccharide substrates. The substrate specificity of wild type ChitO and the Q268R mutant were examined and confirmed that Q268 is indeed involved in N-acetyl recognition.     

Contrasting patterns of post‐fledging movements of two sympatric warbler species with different life‐history strategies

Broad‐scale movements of migrant songbirds during the post‐fledging period are hypothesized to aid in the development of navigational abilities, to allow individuals to prospect for future breeding territories (combined as regional exploration), or as representing the commencement of migration. Using an automated radio telemetry array, we compared broad‐scale post‐fledging movements of hatch‐year individuals from two closely related species: blackpoll warblers Setophaga striata and myrtle warblers Setophaga coronata coronata. These two species have contrasting migratory strategies (long‐distance vs short‐distance), and we studied populations from two different islands in Nova Scotia that have different geographical landscape features. Locally‐hatched individuals affixed with VHF radios in August were tracked throughout the Gulf of Maine region for up to 2.5 months after tagging. Departure date and direction, daily probability of initiating a flight, daily displacement, total displacement and net displacement were assessed to see if there was support for the commencement of migration or regional exploration hypotheses. We observed differences between both species and islands. Compared to blackpolls, myrtles departed later, had more variable timings and directions of departure, made fewer regional‐scale flights, were more directional in their movements, and had higher net displacement. Total displacement and daily flight distances were similar between species. Variability of departure behaviour of myrtles was observed on the island farther from the mainland and both species made longer flights from that island. These results are consistent with the hypothesis that hatch‐year blackpoll movements are a form of regional exploration and hatch‐year myrtle movements represent the initial stages of migration. Species differences may be related to migratory strategy (long‐distance vs short‐distance), where the need to acquire information during post‐fledging for navigational purposes is higher for blackpolls than myrtles. Island differences suggest that habitat quality and ecological barriers influence broad‐scale movements, and myrtles are more facultative in their behaviour than blackpolls.     

A need for recalibrating access and benefit sharing: How best to improve conservation,sustainable use of biodiversity,and equitable benefit sharing in a mutually reinforcing manner?

The upcoming UN Biodiversity Conference should address shortfalls of Access and Benefit Sharing systems inspired by the Nagoya Protocol to help improve sustainable use of biodiversity and equitable benefit sharing. Subject Categories: Economics, Law & Politics, Evolution & Ecology, Pharmacology & Drug Discovery

The 15^th UN Biodiversity Conference (COP‐15) in Kunming, China, presents an opportunity for transformative change to address the biodiversity crisis. However, a lack of consensus on two key issues—mobilization of the necessary resources; and the scope and functioning of regulatory regimes that govern access to genetic resources and the sharing of benefits resulting from their use—threaten progress under the next 10‐year strategic plan of the Convention on Biological Diversity. We highlight systemic misconceptions concerning the financing of biodiversity and the burden this places on the Access and Benefit Sharing (ABS) system. We caution that unworkable ABS regulatory frameworks and conflating ABS with resource mobilization could disrupt science policies built on open access, with potentially severe ramifications for research and innovation. To resolve these tensions, we call for a recalibration of ABS to maximize the value delivered by biodiversity for all of society, including indigenous peoples and local communities.     

Deciphering the molecular basis of memory failure in Alzheimer's disease

Acutely developing lesions of the brain have been highly instructive in elucidating the neural systems underlying memory in humans and animal models. Much less has been learned from chronic neurodegenerative disorders that insidiously impair memory. But the advent of a detailed molecular hypothesis for the development of Alzheimer's disease and the creation of compelling mouse models thereof have begun to change this situation. Experiments in rodents suggest that soluble oligomers of the amyloid beta protein (Abeta) may discretely interfere with synaptic mechanisms mediating aspects of learning and memory, including long-term potentiation. In humans, memory impairment correlates strongly with cortical levels of soluble Abeta species, which include oligomers. Local inflammatory changes, neurofibrillary degeneration, and neurotransmitter deficits all contribute to memory impairment, but available evidence suggests that these develop as a consequence of early Abeta accumulation. Accordingly, attempts to slow memory and cognitive loss by decreasing cerebral Abeta levels have entered human trials.     

Gene amplification and cold adaptation of pepsin in Antarctic fish. A possible strategy for food digestion at low temperature

Cold-adapted organisms have developed a number of adjustments at the molecular level to maintain metabolic functions at low temperatures. Among other features, they can produce enzymes characterized by a high turnover number or a high catalytic efficiency. The present work is aimed at investigating the process of food digestion at low temperature through the study of pepsins in Antarctic notothenioids. For such a purpose, we have cloned and sequenced three forms of pepsin A and a single form of gastricsin from the gastric mucosa of Trematomus bernacchii (rock cod). Phylogenetic analysis has suggested that the three pepsin A isotypes arose from two gene duplication events leading to the most ancestral pepsin A3 and to the most recent forms represented by pepsin A1 and pepsin A2. Molecular modeling has unraveled significant structural differences in these enzymes with respect to their mesophilic counterparts. Hydropathy and flexibility determined on the substrate-binding subsites of Antarctic and mesophilic pepsins have shown for pepsin A2 reduced hydropathy and increased flexibility at the level of the substrate cleft, features typical of cold-adapted enzymes. Northern blot analysis of RNA from rock cod gastric mucosa hybridized with molecular probes designed on specific regions of different pepsin forms has shown that rock cod pepsin genes are expressed at comparable levels. The present results suggest that the Antarctic rock cod adopted two different strategies to accomplish efficient protein digestion at low temperature. One mechanism is the gene duplication that increases enzyme production to compensate for the reduced kinetic efficiency, the other is the expression of a new enzyme provided with features typical of cold-adapted enzymes.     

Association of ARVCF with zonula occludens (ZO)-1 and ZO-2: binding to PDZ-domain proteins and cell-cell adhesion regulate plasma membrane and nuclear localization of ARVCF

ARVCF, an armadillo-repeat protein of the p120(ctn) family, associates with classical cadherins and is present in adherens junctions, but its function is poorly understood. Here, we show that ARVCF interacts via a C-terminal PDZ-binding motif with zonula occludens (ZO)-1 and ZO-2. ARVCF and ZO-1 partially colocalize in the vicinity of the apical adhesion complex in polarized epithelial Madin-Darby canine kidney cells. ARVCF, ZO-1, and E-cadherin form a complex and are recruited to sites of initial cell-cell contact in sparse cell cultures. E-cadherin binding and plasma membrane localization of ARVCF require the PDZ-binding motif. Disruption of cell-cell adhesion releases ARVCF from the plasma membrane and an increased fraction of the protein localizes to the nucleus. Nuclear localization of ARVCF also requires the PDZ-binding motif and can be mediated by the PDZ domains of ZO-2. Thus, the interaction of ARVCF with distinct PDZ-domain proteins determines its subcellular localization. Interactions with ZO-1 and ZO-2, in particular, may mediate recruitment of ARVCF to the plasma membrane and the nucleus, respectively, possibly in response to cell-cell adhesion cues.     

Nucleotide and haplotypic diversity of the<Emphasis Type="Italic"> NOS2A</Emphasis> promoter region and its relationship to cerebral malaria

To assess the hypothesis that nitric oxide is critical in the pathogenesis of cerebral malaria, we analysed genetic variation in the proximal promoter region of NOS2A, the gene encoding inducible nitric oxide synthase. Sequencing 72 Gambian chromosomes revealed 11 single nucleotide polymorphisms in 2.5 kB (theta=8.6 x 10(-4)). Genotyping 104 nuclear families identified six common haplotypes. A single haplotype, uniquely defined by the NOS2A-1659T allele, was associated with cerebral malaria by a transmission disequilibrium test of 334 affected children and their parents (P=0.02). An independent case-control study of 505 different children from the same population replicated the allelic association with cerebral malaria (odds ratio: 1.31, P=0.04). Taken together these data indicate a weak but significant association of the NOS2A locus with susceptibility to cerebral malaria. Despite high linkage disequilibrium across the region studied, this association would not have been detected without the initial construction of a dense marker set for haplotype tagging.     

Influence of oxygen partial pressures on protein synthesis in feeding crabs

Many water-breathing animals have a strategy that consists of maintaining low blood PO2 values in a large range of water oxygenation level (4-40 kPa). This study examines the postprandial changes in O2 consumption, arterial blood PO2, and tissue protein synthesis in the shore crab Carcinus maenas in normoxic, O2-depleted, and O2-enriched waters to study the effects of this strategy on the O2 consumption and peptide bond formation after feeding. In normoxic water (21 kPa), the arterial PO2 was 1.1 kPa before feeding and 1.2 kPa 24 h later. In water with a PO2 of 3 kPa (arterial PO2 0.6 kPa), postprandial stimulation of protein synthesis and O2 consumption were blocked. The blockade was partial at a water PO2 of 4 kPa (arterial PO2 0.8 kPa). An increase in environmental PO2 (60 kPa, arterial PO2 10 kPa) resulted in an increase in protein synthesis compared with normoxic rates. It is concluded that the arterial PO2 spontaneously set in normoxic Carcinus limits the rates of protein synthesis. The rationale for such a strategy is discussed.