Discovery of a novel 2,4-dimethylquinoline-6-carboxamide M4 positive allosteric modulator (PAM) chemotype via scaffold hopping

This Letter details our efforts to replace the 3-amino moiety, an essential pharmacophore for M₄ PAM activity in most M₄ PAMs to date, within the thieno[2,3-b]pyridine core, as the β-amino carboxamide motif has been shown to engender poor solubility, varying degrees of P-gp efflux and represents a structural alert. A scaffold hopping exercise identified a novel 2,4-dimethylquinoline carboxamide core that provided M₄ PAM activity and good CNS penetration without an amino moiety. In addition, MacMillan photoredox catalysis chemistry was essential for construction of the 2,4-dimethylquinoline core.     

Distribution and socio-ecological impacts of the invasive alien cactus <Emphasis Type="Italic">Opuntia stricta</Emphasis> in eastern Africa

Many cactus species have been introduced around the world and have subsequently become major invaders, inducing social and ecological costs. We recorded the distribution of Opuntia stricta in eastern Africa, and conducted 200 household interviews using semi-structured questionnaires to assess local perceptions of O. stricta in Laikipia County, Kenya. Opuntia stricta was widespread and abundant in parts of Kenya, Tanzania and Ethiopia and present at low densities in Uganda. In Laikipia County, pastoralists identified that O. stricta had been present for more than 10 years, and were of the opinion that it was still spreading and increasing in density. Two-thirds of respondents estimated that 50–75% of valuable grazing land had been invaded, and all felt that it contributed to the ill-health and death of livestock. Other negative impacts included reductions in native plant populations, rangeland condition, human health, and mobility of humans and animals. These negative impacts resulted in economic losses of US$ 500–1000 per household per year for 48% of households. Only 20% of respondents reported actively managing O. stricta, yet all respondents believed a reduction in the abundance of this weed would improve well-being. Management interventions are needed to reduce negative impacts.     

Inferring infection hazard in wildlife populations by linking data across individual and population scales

Our ability to infer unobservable disease‐dynamic processes such as force of infection (infection hazard for susceptible hosts) has transformed our understanding of disease transmission mechanisms and capacity to predict disease dynamics. Conventional methods for inferring FOI estimate a time‐averaged value and are based on population‐level processes. Because many pathogens exhibit epidemic cycling and FOI is the result of processes acting across the scales of individuals and populations, a flexible framework that extends to epidemic dynamics and links within‐host processes to FOI is needed. Specifically, within‐host antibody kinetics in wildlife hosts can be short‐lived and produce patterns that are repeatable across individuals, suggesting individual‐level antibody concentrations could be used to infer time since infection and hence FOI. Using simulations and case studies (influenza A in lesser snow geese and Yersinia pestis in coyotes), we argue that with careful experimental and surveillance design, the population‐level FOI signal can be recovered from individual‐level antibody kinetics, despite substantial individual‐level variation. In addition to improving inference, the cross‐scale quantitative antibody approach we describe can reveal insights into drivers of individual‐based variation in disease response, and the role of poorly understood processes such as secondary infections, in population‐level dynamics of disease.     

Digestive parameters and water turnover of the leopard tortoise

Leopard tortoises (Stigmochelys pardalis) experience wide fluctuations in environmental conditions and unpredictable availability of food and water within the Nama-Karoo biome. It was hypothesised that tortoises fed two diets differing in preformed water and fibre content would have differing food intake, gut transit rate, assimilation efficiency, faecal and urinary water loss, and urine concentrations. It was predicted that tortoises fed these contrasting diets would attempt to maintain energy and water balance by altering their digestive parameters. Leopard tortoises fed lucerne (Medicago sativa) had a low food intake coupled with long gut transit times, which resulted in the lowest amount of faecal energy and faecal water lost. Tortoises fed tomatoes (Solanum lycopersicum) had higher food intake and faster gut transit times, but more energy and water was lost in the faeces. However, daily energy assimilated and assimilation efficiency were comparable between tortoises fed the two diets. Urine osmolality was significantly different between tortoises on the two diets. Results indicate that leopard tortoises can adjust parameters such as transit rate, food intake, water loss and urine osmolality to maintain body mass, water and energy balance in response to a high fibre, low water content and a low fibre, high water content diet. This study suggests that this digestive flexibility allows leopard tortoises in the wild to take advantage of unpredictable food and water resources.     

Down but not out: marine turtles of the British Virgin Islands

We present the result of a multi-annual assessment of the spatio-temporal patterns of marine turtle nesting, and foraging in the Eastern Caribbean archipelago state of the British Virgin Islands. Despite exploitation over several centuries, three species (leatherback Dermochelys coriacea , green Chelonia mydas and hawksbill Eretmochelys imbricata turtles) are still nesting and green and hawksbill turtles are found foraging. Leatherback turtles are showing signs of a recovery co-incident with the implementation of an effective moratorium on adult take. When compared with historical data we demonstrate an apparent reduction in nesting levels in green and hawksbill turtles and a nesting range contraction in green turtles. Despite current conservation steps, it will be a decade or more before evidence of recovery can be expected in the two hard-shelled species. Coupled with wider biological knowledge, our findings offer insights into the relative resilience of the different species to exploitation pressure. Additionally, the intra-annual temporal and spatial spread of nesting demonstrated underlines the difficulties of monitoring such a multi-species assemblage in such a diffuse archipelago.     

Ionic mechanisms of endogenous bursting in CA3 hippocampal pyramidal neurons: a model study

A critical property of some neurons is burst firing, which in the hippocampus plays a primary role in reliable transmission of electrical signals. However, bursting may also contribute to synchronization of electrical activity in networks of neurons, a hallmark of epilepsy. Understanding the ionic mechanisms of bursting in a single neuron, and how mutations associated with epilepsy modify these mechanisms, is an important building block for understanding the emergent network behaviors. We present a single-compartment model of a CA3 hippocampal pyramidal neuron based on recent experimental data. We then use the model to determine the roles of primary depolarizing currents in burst generation. The single compartment model incorporates accurate representations of sodium (Na(+)) channels (Na(V)1.1) and T-type calcium (Ca(2+)) channel subtypes (Ca(V)3.1, Ca(V)3.2, and Ca(V)3.3). Our simulations predict the importance of Na(+) and T-type Ca(2+) channels in hippocampal pyramidal cell bursting and reveal the distinct contribution of each subtype to burst morphology. We also performed fast-slow analysis in a reduced comparable model, which shows that our model burst is generated as a result of the interaction of two slow variables, the T-type Ca(2+) channel activation gate and the Ca(2+)-dependent potassium (K(+)) channel activation gate. The model reproduces a range of experimentally observed phenomena including afterdepolarizing potentials, spike widening at the end of the burst, and rebound. Finally, we use the model to simulate the effects of two epilepsy-linked mutations: R1648H in Na(V)1.1 and C456S in Ca(V)3.2, both of which result in increased cellular excitability.     

Agrin and neuregulin, expanding roles and implications for therapeutics

Agrin and neuregulin are broadly expressed molecules that have significant developmental roles. Here we review the diverse temporal and spatial expression patterns and functions of these molecules and the impact that dysregulation may have on a number of disease states. Many know agrin as a modulator of synaptogenesis and the neuregulins for their prominent role in breast cancer; this review elaborates on many of the other proposed functions for these molecules both in the nervous system and elsewhere. In several instances we discuss the possible use of agrin, neuregulin and related molecules as therapeutic agents.     

Lateral symbiont acquisition in a maternally transmitted chemosynthetic clam endosymbiosis

Deep-sea clams of the family Vesicomyidae live in symbiosis with intracellular chemosynthetic bacteria. These symbionts are transmitted maternally (vertically) between host generations and should therefore show a pattern of genetic variation paralleling that of the cotransmitted host mitochondrion. However, instances of lateral (nonvertical) symbiont acquisition could still occur, thereby decoupling symbiont and mitochondrial phylogenies. Here, we provide the first evidence against strict maternal cotransmission of symbiont and mitochondrial genomes in vesicomyids. Analysis of Vesicomya sp. mt-II clams from hydrothermal vents on the Juan de Fuca Ridge (northeastern Pacific) revealed a symbiont phylotype (designated symB(VII)) highly divergent from previously described symbionts of the same host lineage. SymB(VII)-hosting clams occurred at low frequency (0.02) relative to individuals hosting the dominant symbiont phylotype. Phylogenetic analysis of 16S rRNA genes from a wide range of symbionts and free-living bacteria clustered symB(VII) within the monophyletic clade of vesicomyid symbionts. Further analysis of 3 symbiont loci (23S, dnaK, and soxA) across 11 vesicomyid taxa unambiguously placed symB(VII) as sister to the symbiont of a distantly related host lineage, Vesicomya sp. from the Mid-Atlantic Ridge (98.9% median nucleotide identity across protein-coding loci). Using likelihood and Bayesian model discrimination methods, we rejected the strict maternal cotransmission hypothesis by showing a significant decoupling of symbiont and host mitochondrial (COI and mt16S genes) phylogenies. Indeed, decoupling occurred even when symB(VII) was excluded from phylogenetic reconstructions, suggesting a history of host switching in this group. Together, the data indicate a history of lateral symbiont transfer in vesicomyids, with symB(VII) being the most conspicuous example. Interpreted alongside previous studies of the vesicomyid symbiosis, these results suggest a mixed mode of symbiont transmission characterized by predominantly vertical transmission punctuated with instances of lateral symbiont acquisition. Lateral acquisition may facilitate the exchange of genetic material (recombination) among divergent symbiont lineages, rendering the evolutionary history of vesicomyid symbiont genomes much more complex than previously thought.     

The relative sensitivity of different alignment methods and character codings in sensitivity analysis

Sensitivity analysis provides a way to measure robustness of clades in sequence‐based phylogenetic analyses to variation in alignment parameters rather than measuring their branch support. We compared three different approaches to multiple sequence alignment in the context of sensitivity analysis: progressive pairwise alignment, as implemented in MUSCLE; simultaneous multiple alignment of sequence fragments, as implemented in DCA; and direct optimization followed by generation of the implied alignment(s), as implemented in POY. We set out to determine the relative sensitivity of these three alignment methods using rDNA sequences and randomly generated sequences. A total of 36 parameter sets were used to create the alignments, varying the transition, transversion, and gap costs. Tree searches were performed using four different character‐coding and weighting approaches: the cost function used for alignment or equally weighted parsimony with gap positions treated as missing data, separate characters, or as fifth states. POY was found to be as sensitive, or more sensitive, to variation in alignment parameters than DCA and MUSCLE for the three empirical datasets, and POY was found to be more sensitive than MUSCLE, which in turn was found to be as sensitive, or more sensitive, than DCA when applied to the randomly generated sequences when sensitivity was measured using the averaged jackknife values. When significant differences in relative sensitivity were found between the different ways of weighting character‐state changes, equally weighted parsimony, for all three ways of treating gapped positions, was less sensitive than applying the same cost function used in alignment for phylogenetic analysis. When branch support is incorporated into the sensitivity criterion, our results favour the use of simultaneous alignment and progressive pairwise alignment using the similarity criterion over direct optimization followed by using the implied alignment(s) to calculate branch support.