Transport kinetics of maltotriose in strains ofSaccharomyces

Summary Maltotriose transport was studied in two brewer's yeast strains, an ale strain 3001 and a lager strain 3021, using laboratory-synthesized¹⁴C-maltotriose. The maltotriose transport systems preferred a lower pH (pH 4.3) to a higher pH (pH 6.6). Two maltotriose transport affinity systems have been indentified. The high affinity system hasK _m values of 1.3 mM for strain 3021 and 1.4 mM for strain 3001. The low affinity competitively inhibited by maltose and glucose withK _i values of 58 mM and 177 mM. respectively, for strain 3021, and 55 mM and 147 mM, respectively, for strain 3001. Cells grown in maltotriose and maltose had higher maltotriose and maltose transport rates, and cells grown in glucose had lower maltortriose and maltose transport rates. Early-logarithmic phase cells transported glucose faster than either maltose or maltotriose. Cells harvested later in the growth phase had increased maltotriose and maltose transport activity. Neither strain exhibited significant differences with respect to maltose and maltotriose transport activity.     

Environmental DNA reveals a mismatch between diversity facets of Amazonian fishes in response to contrasting geographical,environmental and anthropogenic effects

Freshwater ecosystems are among the most endangered ecosystem in the world. Understanding how human activities affect these ecosystems requires disentangling and quantifying the contribution of the factors driving community assembly. While it has been largely studied in temperate freshwaters, tropical ecosystems remain challenging to study due to the high species richness and the lack of knowledge on species distribution. Here, the use of eDNA-based fish inventories combined to a community-level modelling approach allowed depicting of assembly rules and quantifying the relative contribution of geographic, environmental and anthropic factors to fish assembly. We then used the model predictions to map spatial biodiversity and assess the representativity of sites surveyed in French Guiana within the EU Water Framework Directive (WFD) and highlighted areas that should host unique freshwater fish assemblages. We demonstrated a mismatch between the taxonomic and functional diversity. Taxonomic assemblages between but also within basins were mainly the results of dispersal limitation resulting from basin isolation and natural river barriers. Contrastingly, functional assemblages were ruled by environmental and anthropic factors. The regional mapping of fish diversity indicated that the sites surveyed within the EU WFD had a better representativity of the regional functional diversity than taxonomic diversity. Importantly, we also showed that the assemblages expected to be the most altered by anthropic factors were the most poorly represented in terms of functional diversity in the surveyed sites. The predictions of unique functional and taxonomic assemblages could, therefore, guide the establishment of new survey sites to increase fish diversity representativity and improve this monitoring program.     

Causal inference and large-scale expert validation shed light on the drivers of SDM accuracy and variance

Aim

To develop a causal understanding of the drivers of Species distribution model (SDM) performance.

Location

United Kingdom (UK).

Methods

We measured the accuracy and variance of SDMs fitted for 518 species of invertebrate and plant in the UK. Our measure of variance reflects variation among replicate model fits, and taxon experts assessed model accuracy. Using directed acyclic graphs, we developed a causal model depicting plausible effects of explanatory variables (e.g. species' prevalence, sample size) on SDM accuracy and variance and quantified those effects using a multilevel piecewise path model.

Results

According to our model, sample size and niche completeness (proportion of a species' niche covered by sampling) directly affect SDM accuracy and variance. Prevalence and range completeness have indirect effects mediated by sample size. Challenging conventional wisdom, we found that the effect of prevalence on SDM accuracy is positive. This reflects the facts that sample size has a positive effect on accuracy and larger sample sizes are possible for widespread species. It is possible, however, that the omission of an unobserved confounder biased this effect. Previous studies, which reported negative correlations between prevalence and SDM accuracy, conditioned on sample size.

Main conclusions

Our model explicates the causal basis of previously reported correlations between SDM performance and species/data characteristics. It also suggests that niche completeness has similarly large effects on SDM accuracy and variance as sample size. Analysts should consider niche completeness, or proxies thereof, in addition to sample size when deciding whether modelling is worthwhile.     

The distribution of coastal fish eDNA sequences in the Anthropocene

Aim

Coastal fishes have a fundamental role in marine ecosystem functioning and contributions to people, but face increasing threats due to climate change, habitat degradation and overexploitation. The extent to which human pressures are impacting coastal fish biodiversity in comparison with geographic and environmental factors at large spatial scale is still under scrutiny. Here, we took advantage of environmental DNA (eDNA) metabarcoding to investigate the relationship between fish biodiversity, including taxonomic and genetic components, and environmental but also socio-economic factors.

Location

Tropical, temperate and polar coastal areas.

Time period

Present day.

Major taxa studied

Marine fishes.

Methods

We analysed fish eDNA in 263 stations (samples) in 68 sites distributed across polar, temperate and tropical regions. We modelled the effect of environmental, geographic and socio-economic factors on α- and β-diversity. We then computed the partial effect of each factor on several fish biodiversity components using taxonomic molecular units (MOTU) and genetic sequences. We also investigated the relationship between fish genetic α- and β-diversity measured from our barcodes, and phylogenetic but also functional diversity.

Results

We show that fish eDNA MOTU and sequence α- and β-diversity have the strongest correlation with environmental factors on coastal ecosystems worldwide. However, our models also reveal a negative correlation between biodiversity and human dependence on marine ecosystems. In areas with high dependence, diversity of all fish, cryptobenthic fish and large fish MOTUs declined steeply. Finally, we show that a sequence diversity index, accounting for genetic distance between pairs of MOTUs, within and between communities, is a reliable proxy of phylogenetic and functional diversity.

Main conclusions

Together, our results demonstrate that short eDNA sequences can be used to assess climate and direct human impacts on marine biodiversity at large scale in the Anthropocene and can further be extended to investigate biodiversity in its phylogenetic and functional dimensions.     

Treatment-resistant depression: definition,prevalence, detection,management, and investigational interventions

Treatment-resistant depression (TRD) is common and associated with multiple serious public health implications. A consensus definition of TRD with demonstrated predictive utility in terms of clinical decision-making and health outcomes does not currently exist. Instead, a plethora of definitions have been proposed, which vary significantly in their conceptual framework. The absence of a consensus definition hampers precise estimates of the prevalence of TRD, and also belies efforts to identify risk factors, prevention opportunities, and effective interventions. In addition, it results in heterogeneity in clinical practice decision-making, adversely affecting quality of care. The US Food and Drug Administration (FDA) and the European Medicines Agency (EMA) have adopted the most used definition of TRD (i.e., inadequate response to a minimum of two antidepressants despite adequacy of the treatment trial and adherence to treatment). It is currently estimated that at least 30% of persons with depression meet this definition. A significant percentage of persons with TRD are actually pseudo-resistant (e.g., due to inadequacy of treatment trials or non-adherence to treatment). Although multiple sociodemographic, clinical, treatment and contextual factors are known to negatively moderate response in persons with depression, very few factors are regarded as predictive of non-response across multiple modalities of treatment. Intravenous ketamine and intranasal esketamine (co-administered with an antidepressant) are established as efficacious in the management of TRD. Some second-generation antipsychotics (e.g., aripiprazole, brexpiprazole, cariprazine, quetiapine XR) are proven effective as adjunctive treatments to antidepressants in partial responders, but only the olanzapine-fluoxetine combination has been studied in FDA-defined TRD. Repetitive transcranial magnetic stimulation (TMS) is established as effective and FDA-approved for individuals with TRD, with accelerated theta-burst TMS also recently showing efficacy. Electroconvulsive therapy is regarded as an effective acute and maintenance intervention in TRD, with preliminary evidence suggesting non-inferiority to acute intravenous ketamine. Evidence for extending antidepressant trial, medication switching and combining antidepressants is mixed. Manual-based psychotherapies are not established as efficacious on their own in TRD, but offer significant symptomatic relief when added to conventional antidepressants. Digital therapeutics are under study and represent a potential future clinical vista in this population.     

Artificial induction of exocytosis in bull sperm.

We have investigated an exocytotic event, the acrosome reaction (AR), induced by treatment of bovine sperm with vesicles composed of dilauroyl phosphatidylcholine (PC12). Cell membrane permeability barriers (dye exclusion), acrosomal status (pisum sativum (PSA) lectin binding), and intracellular Ca2+ (Fluo3 fluorescence) were evaluated utilizing flow cytometry and fluorescence microscopy. By these methods the AR is resolved into four kinetically distinct steps: (a) PC12 transfer to the sperm plasma membrane (PM); (b) increased permeability of the PM to extracellular Ca2+; (c) localized leakage of acrosomal contents at the anterior tip of the sperm; and (d) vesiculation of sperm membranes and complete exposure of acrosomal contents. Evidence for PC12 transfer to sperm includes transfer of a fluorescent PC12 analogue from vesicles to cells and the absence of detectable vesicle--cell fusion. The fusion inducing properties of PC12 appear to reside in the lipid head group as neither dilauroylphosphatidylethanolamine nor dilauroylphosphatidylglycerol stimulated the AR. The effect of PC chain length on AR induction closely parallels the aqueous phase solubility of the lipid tested. The rate and extent of the AR depend on the extracellular calcium concentration. Cells treated in the absence of calcium do not undergo the AR, but do so rapidly (less than 1 min) upon subsequent addition of calcium. This role of Ca2+ is partially filled by Sr2+, but not by Ba2+ or Mg2+. The rate of the AR decreases with decreasing temperature and the AR occurs very slowly below 27 degrees C. Simultaneous evaluation of intracellular calcium and acrosomal status reveals the kinetic relationship between Ca2+ influx and the exposure of acrosomal contents. N-Ethylmaleimide preincubation arrests PC12-treated sperm at an intermediate stage in the AR, characterized by punctate PSA binding over the tip of the sperm head. The AR, a developmentally regulated, receptor-mediated fusion event, synchronously induced here in vitro, provides a useful model for mechanistic studies of exocytosis.     

Plate 457. Mutisia Subspinosa Compositae

Mutisia subspinosa Cav. is described and illustrated and its relationships with other members of Mutisia sect. Guariruma (Cass.) Cabrera discussed. Notes on its cultivation are provided along with a historical insight into the collections of Née, made on the Malaspina expedition.     

Experimental dissociation of the effects of diet, age and breeding experience on primary reproductive effort in zebra finches Taeniopygia guttata

Reproductive performance varies with age in a wide range of organisms, and increasingly such patterns are interpreted in terms of state-dependent models. We sought to characterise 'state' with regards to age-related variation in clutch size, egg mass and timing of breeding in captive zebra finches Taeniopygia guttata , focusing on the roles of diet quality, age and breeding experience. Females on a high-quality diet laid larger clutches of larger eggs than did females on a low-quality diet. The effect of age on reproductive performance was examined by comparing females breeding (i.e. paired) for the first time at either 3- and/or 6-months of age. Clutch size increased with age but on the low-quality diet only, not on the high-quality diet. Furthermore, clutch size decreased between 3- and 6-months of age in birds bred first on the high-quality diet and then on the low-quality diet. Age did not affect egg mass but older birds had shorter laying intervals. Reproductive performance did not differ between females breeding at 6-months of age for the first or second time: the effects of age were not due to 'training' effects or experience specific to breeding (e.g. undergoing the physiological process of egg formation). In conclusion, nutritional condition (diet) emerged as a central component of state that could strongly influence, and even reverse, any age-dependent increase in primary reproductive performance.     

Effect of platelet-derived growth factor on DNA synthesis and gene expression in bone marrow stromal cells derived from adult and old rats

The effects of platelet-derived growth factor (PDGF) on DNA synthesis and mRNA expression of osteoblast markers in marrow stromal cells derived from adult (6 months) and old (24 months) rats were examined. Treatment of stromal cells from adult rats with dexamethasone induced the appearance of osteoblast-like cells. PDGF partially also inhibited the differentiation of stromal cells induced by dexamethasone. In cultures of serum-starved stromal cells, PDGF stimulated [³H]-thymidine incorporation into DNA in a dose-dependent manner with a maximum stimulation of 15-fold at 500 ng/ml. By comparison, insulin-like growth factor (IGF-I) has a small effect on [³H] -thymidine incorporation. The effect of PDGF and IGF-I on DNA synthesis was additive. Treatment of the confluent stromal cells from adult rats with PDGF increased the mRNA level of osteopontin fourfold without any significant effect on alkaline phosphatase and type I collagen mRNAs. In contrast, dexamethasone stimulated the mRNA expression of alkaline phosphatase, type I collagen, and osteopontin 2.1-, 2.3-, and 14-fold, respectively. Addition of PDGF to dexamethasone-treated cells failed to induce any further increase in osteopontin expression whereas the expression of alkaline phosphatase and type I collagen was partially reduced. The expression of osteocalcin mRNA was negligible in stromal cells but stimulated several fold by dexamethasone and 1,25(OH)₂D₃. PDGF inhibited drastically the elevation of osteocalcin mRNA. In contrast, IGF-I stimulated type I collagen expression 100% without any appreciable effect on the expression of osteopontin and alkaline phosphatase. The stimulatory effect of PDGF on osteopontin expression was augmented by IGF-I. Furthermore, PDGF attenuated the stimulatory effect of IGF-I on type I collagen expression. The responses of cultured cells from old rats to growth factors were also examined. PDGF or PDGF plus IGF-I increased [³H]-thymidine incorporation in stromal cells from old rats but to a lesser extent. However, PDGF was equally effective in stimulating osteopontin expression in cells from both adult and old rats. We concluded that PDGF is a potent mitogen but that the response of stromal cells from old rats is impaired. In addition, PDGF stimulates osteopontin expression in stromal cells and this effect is not age dependent. © 1995 Wiley-Liss, Inc.