Changes to social feeding behaviors are not sufficient for fitness gains of the Caenorhabditis elegans N2 reference strain.

The standard reference Caenorhabditis elegans strain, N2, has evolved marked behavioral changes in social feeding behavior since its isolation from the wild. We show that the causal, laboratory-derived mutations in two genes, npr-1 and glb-5, confer large fitness advantages in standard laboratory conditions. Using environmental manipulations that suppress social/solitary behavior differences, we show the fitness advantages of the derived alleles remained unchanged, suggesting selection on these alleles acted through pleiotropic traits. Transcriptomics, developmental timing, and food consumption assays showed that N2 animals mature faster, produce more sperm, and consume more food than a strain containing ancestral alleles of these genes regardless of behavioral strategies. Our data suggest that the pleiotropic effects of glb-5 and npr-1 are a consequence of changes to O2 -sensing neurons that regulate both aerotaxis and energy homeostasis. Our results demonstrate how pleiotropy can lead to profound behavioral changes in a popular laboratory model.

Regulatory changes in two chemoreceptor genes contribute to a Caenorhabditis elegans QTL for foraging behavior.

Natural isolates of C. elegans differ in their sensitivity to pheromones that inhibit exploratory behavior. Previous studies identified a QTL for pheromone sensitivity that includes alternative alleles of srx-43, a chemoreceptor that inhibits exploration through its activity in ASI sensory neurons. Here we show that the QTL is multigenic and includes alternative alleles of srx-44, a second chemoreceptor gene that modifies pheromone sensitivity. srx-44 either promotes or inhibits exploration depending on its expression in the ASJ or ADL sensory neurons, respectively. Naturally occurring pheromone insensitivity results in part from previously described changes in srx-43 expression levels, and in part from increased srx-44 expression in ASJ, which antagonizes ASI and ADL. Antagonism between the sensory neurons results in cellular epistasis that is reflected in their transcription of insulin genes that regulate exploration. These results and genome-wide evidence suggest that chemoreceptor genes may be preferred sites of adaptive variation in C. elegans.

Balancing selection shapes density-dependent foraging behaviour.

The optimal foraging strategy in a given environment depends on the number of competing individuals and their behavioural strategies. Little is known about the genes and neural circuits that integrate social information into foraging decisions. Here we show that ascaroside pheromones, small glycolipids that signal population density, suppress exploratory foraging in Caenorhabditis elegans, and that heritable variation in this behaviour generates alternative foraging strategies. We find that natural C. elegans isolates differ in their sensitivity to the potent ascaroside icas#9 (IC-asc-C5). A quantitative trait locus (QTL) regulating icas#9 sensitivity includes srx-43, a G-protein-coupled icas#9 receptor that acts in the ASI class of sensory neurons to suppress exploration. Two ancient haplotypes associated with this QTL confer competitive growth advantages that depend on ascaroside secretion, its detection by srx-43 and the distribution of food. These results suggest that balancing selection at the srx-43 locus generates alternative density-dependent behaviours, fulfilling a prediction of foraging game theory.

Roles of p75(NTR), long-term depression, and cholinergic transmission in anxiety and acute stress coping.

BACKGROUND: Stress is causally associated with anxiety. Although the underlying cellular mechanisms are not well understood, the basal forebrain cholinergic neurons have been implicated in stress response. p75(NTR) is a panneurotrophin receptor expressed almost exclusively in basal forebrain cholinergic neurons in adult brain. This study investigated whether and how p75(NTR), via regulation of the cholinergic system and hippocampal synaptic plasticity, influences stress-related behaviors. METHODS: We used a combination of slice electrophysiology, behavioral analyses, pharmacology, in vivo microdialysis, and neuronal activity mapping to assess the role of p75(NTR) in mood and stress-related behaviors and its underlying cellular and molecular mechanisms. RESULTS: We show that acute stress enables hippocampal long-term depression (LTD) in adult wild-type mice but not in mice lacking p75(NTR). The p75(NTR) mutant mice also exhibit two distinct behavioral impairments: baseline anxiety-like behavior and a deficit in coping with and recovering from stressful situations. Blockade of stress-enabled LTD with a GluA2-derived peptide impaired stress recovery without affecting baseline anxiety. Pharmacological manipulations of cholinergic transmission mimicked the p75(NTR) perturbation in both baseline anxiety and responses to acute stress. Finally, we show evidence of misregulated cholinergic signaling in animals with p75(NTR) deletion. CONCLUSIONS: Our results suggest that loss of p75(NTR) leads to changes in hippocampal cholinergic signaling, which may be involved in regulation of stress-enabled hippocampal LTD and in modulating behaviors related to stress and anxiety.

Critical role of promoter IV-driven BDNF transcription in GABAergic transmission and synaptic plasticity in the prefrontal cortex.

Transcription of Bdnf is controlled by multiple promoters, which drive expression of multiple transcripts encoding for the same protein. Promoter IV contributes significantly to activity-dependent brain-derived neurotrophic factor (BDNF) transcription. We have generated promoter IV mutant mice (BDNF-KIV) by inserting a GFP-STOP cassette within the Bdnf exon IV locus. This genetic manipulation results in disruption of promoter IV-mediated Bdnf expression. BDNF-KIV animals exhibited significant deficits in GABAergic interneurons in the prefrontal cortex (PFC), particularly those expressing parvalbumin, a subtype implicated in executive function and schizophrenia. Moreover, disruption of promoter IV-driven Bdnf transcription impaired inhibitory but not excitatory synaptic transmission recorded from layer V pyramidal neurons in the PFC. The attenuation of GABAergic inputs resulted in an aberrant appearance of spike-timing-dependent synaptic potentiation (STDP) in PFC slices derived from BDNF-KIV, but not wild-type littermates. These results demonstrate the importance of promoter IV-dependent Bdnf transcription in GABAergic function and reveal an unexpected regulation of STDP in the PFC by BDNF.

Multiple, novel biologically active endophytic actinomycetes isolated from upper Amazonian rainforests.

Microbial biodiversity provides an increasingly important source of medically and industrially useful compounds. We have isolated 14 actinomycete species from a collection of approximately 300 plant stem samples from the upper Amazonian rainforest in Peru. All of the cultured isolates produce substances with inhibitory activity directed at a range of potential fungal and bacterial pathogens. For some organisms, this activity is very broad in spectrum while other organisms show specific activity against a limited number of organisms. Two of these organisms preferentially inhibit bacterial test organisms over eukaryotic organisms. rDNA sequence analysis indicates that these organisms are not equivalent to any other cultured deposits in GenBank. Our results provide evidence of the untapped biodiversity in the form of biologically active microbes present within the tissues of higher plants.

Bioactive endophytes warrant intensified exploration and conservation.

BACKGROUND: A key argument in favor of conserving biodiversity is that as yet undiscovered biodiversity will yield products of great use to humans. However, the link between undiscovered biodiversity and useful products is largely conjectural. Here we provide direct evidence from bioassays of endophytes isolated from tropical plants and bioinformatic analyses that novel biology will indeed yield novel chemistry of potential value. METHODOLOGY/PRINCIPAL FINDINGS: We isolated and cultured 135 endophytic fungi and bacteria from plants collected in Peru. nrDNAs were compared to samples deposited in GenBank to ascertain the genetic novelty of cultured specimens. Ten endophytes were found to be as much as 15-30% different than any sequence in GenBank. Phylogenetic trees, using the most similar sequences in GenBank, were constructed for each endophyte to measure phylogenetic distance. Assays were also conducted on each cultured endophyte to record bioactivity, of which 65 were found to be bioactive. CONCLUSIONS/SIGNIFICANCE: The novelty of our contribution is that we have combined bioinformatic analyses that document the diversity found in environmental samples with culturing and bioassays. These results highlight the hidden hyperdiversity of endophytic fungi and the urgent need to explore and conserve hidden microbial diversity. This study also showcases how undergraduate students can obtain data of great scientific significance.