C. elegans Demonstrates Distinct Behaviors within a Fixed and Uniform Electric Field

C. elegans will orient and travel in a straight uninterrupted path directly towards the negative pole of a DC electric field. We have sought to understand the strategy worms use to navigate to the negative pole in a uniform electric field that is fixed in both direction and magnitude. We examined this behavior by quantifying three aspects of electrotaxis behavior in response to different applied field strengths: the mean approach trajectory angles of the animals’ tracks, turning behavior (pirouettes) and average population speeds. We determined that C. elegans align directly to the negative pole of an electric field at sub-preferred field strength and alter approach trajectories at higher field strengths to maintain taxis within a preferred range we have calculated to be ~ 5V/cm. We sought to identify the sensory neurons responsible for the animals’ tracking to a preferred field strength. eat-4 mutant animals defective in glutamatergic signaling of the amphid sensory neurons are severely electrotaxis defective and ceh-36 mutant animals, which are defective in the terminal differentiation of two types of sensory neurons, AWC and ASE, are partially defective in electrotaxis. To further elucidate the role of the AWC neurons, we examined the role of each of the pair of AWC neurons (AWCOFF and AWCON), which are functionally asymmetric and express different genes. nsy-5/inx-19 mutant animals, which express both neurons as AWCOFF, are severely impaired in electrotaxis behavior while nsy-1 mutants, which express both neurons as AWCON, are able to differentiate field strengths required for navigation to a specific field strength within an electric field. We also tested a strain with targeted genetic ablation of AWC neurons and found that these animals showed only slight disruption of directionality and turning behavior. These results suggest a role for AWC neurons in which complete loss of function is less disruptive than loss of functional asymmetry in electrotaxis behavior within a uniform fixed field

The Parallel Worm Tracker: A Platform for Measuring Average Speed and Drug-Induced Paralysis in Nematodes

Background Caenorhabditis elegans locomotion is a simple behavior that has been widely used to dissect genetic components of behavior, synaptic transmission, and muscle function. Many of the paradigms that have been created to study C. elegans locomotion rely on qualitative experimenter observation. Here we report the implementation of an automated tracking system developed to quantify the locomotion of multiple individual worms in parallel. Methodology/Principal Findings Our tracking system generates a consistent measurement of locomotion that allows direct comparison of results across experiments and experimenters and provides a standard method to share data between laboratories. The tracker utilizes a video camera attached to a zoom lens and a software package implemented in MATLAB®. We demonstrate several proof-of-principle applications for the tracker including measuring speed in the absence and presence of food and in the presence of serotonin. We further use the tracker to automatically quantify the time course of paralysis of worms exposed to aldicarb and levamisole and show that tracker performance compares favorably to data generated using a hand-scored metric. Conclusions/Signficance Although this is not the first automated tracking system developed to measure C. elegans locomotion, our tracking software package is freely available and provides a simple interface that includes tools for rapid data collection and analysis. By contrast with other tools, it is not dependent on a specific set of hardware. We propose that the tracker may be used for a broad range of additional worm locomotion applications including genetic and chemical screening

Transcriptional analysis of the response of \u3ci\u3eC. elegans\u3c/i\u3e to ethanol exposure

Ethanol-induced transcriptional changes underlie important physiological responses to ethanol that are likely to contribute to the addictive properties of the drug. We examined the transcriptional responses of Caenorhabditis elegans across a timecourse of ethanol exposure, between 30 min and 8 h, to determine what genes and genetic pathways are regulated in response to ethanol in this model. We found that short exposures to ethanol (up to 2 h) induced expression of metabolic enzymes involved in metabolizing ethanol and retinol, while longer exposure (8 h) had much more profound effects on the transcriptome. Several genes that are known to be involved in the physiological response to ethanol, including direct ethanol targets, were regulated at 8 h of exposure. This longer exposure to ethanol also resulted in the regulation of genes involved in cilia function, which is consistent with an important role for the effects of ethanol on cilia in the deleterious effects of chronic ethanol consumption in humans. Finally, we found that food deprivation for an 8-h period induced gene expression changes that were somewhat ameliorated by the presence of ethanol, supporting previous observations that worms can use ethanol as a calorie source

Multiple novel prostate cancer susceptibility signals identified by fine-mapping of known risk loci among Europeans

Genome-wide association studies (GWAS) have identified numerous common prostate cancer (PrCa) susceptibility loci. We have fine-mapped 64 GWAS regions known at the conclusion of the iCOGS study using large-scale genotyping and imputation in 25 723 PrCa cases and 26 274 controls of European ancestry. We detected evidence for multiple independent signals at 16 regions, 12 of which contained additional newly identified significant associations. A single signal comprising a spectrum of correlated variation was observed at 39 regions; 35 of which are now described by a novel more significantly associated lead SNP, while the originally reported variant remained as the lead SNP only in 4 regions. We also confirmed two association signals in Europeans that had been previously reported only in East-Asian GWAS. Based on statistical evidence and linkage disequilibrium (LD) structure, we have curated and narrowed down the list of the most likely candidate causal variants for each region. Functional annotation using data from ENCODE filtered for PrCa cell lines and eQTL analysis demonstrated significant enrichment for overlap with bio-features within this set. By incorporating the novel risk variants identified here alongside the refined data for existing association signals, we estimate that these loci now explain ∼38.9% of the familial relative risk of PrCa, an 8.9% improvement over the previously reported GWAS tag SNPs. This suggests that a significant fraction of the heritability of PrCa may have been hidden during the discovery phase of GWAS, in particular due to the presence of multiple independent signals within the same regio

Electric field stimuli suppress pirouette probability.

<p>(A) Probability of pirouette behaviors in wild-type animals tracking at different electric field strengths. A single pirouette event was identified if the angular speed equaled or exceeded 110°/second in an individual track. The pirouette probability is suppressed with electric field stimuli of 1.5, 3, and 6 V/cm in comparison to non-stimulus (0 V/cm; <i>p</i> < 0.002). (B) Field stimulus and pirouette suppression in different strains. <i>eat-4(ky5)</i>, <i>nsy-5</i>/<i>inx-19</i> (AWC^{<i>OFF/OFF</i>}) <i>ceh-36(ky646)</i> and AWC::<i>eat-4</i> mutant animals display defects in suppression of local search behavior with application of an electric field stimulus compared to wild type (<i>p</i> ≤ 0.00005). <i>nsy-1</i> (AWC^ON/ON) animals display significant suppression of local search behavior (<i>p</i> ≤ 0.00005). AWC::caspase exhibited small, but statistically significant deficits in the suppression of search behavior (<i>p</i> = 0.0002). For all trials, error bars represent SEM; number of individual animal tracks per genotype (<i>N</i>) ≥ 154. <i>P</i>-values were determined from post-hoc pairwise comparisons of estimates obtained via general linear mixed-models. Significance was assessed using a false discovery rate of 0.05.</p

Mean trajectory angles and speeds at different field strengths.

<p>(A) Mean trajectory angles of <i>eat-4(ky5)</i>, <i>ceh-36(ky646)</i> and <i>nsy-5/inx-19</i> (AWC^OFF/OFF) mutant animals are significantly different from wild type at 1.5 and 3 V/cm (<i>p</i> ≤ 0.0001). <i>nsy-1</i> (AWC^ON/ON) mutant animals’ mean trajectory angle are slightly wider than that of wild-type animals at 1.5 and 3 V/cm (Fig 4A; <i>p</i> ≥ 0.0035). <i>eat-4(</i>+<i>)</i> rescue in AWC neurons (AWC::<i>eat-4</i>) results in a slight lowering of mean trajectory angle compared to <i>eat-4</i> mutant animals at 3 V/cm (<i>p</i> ≥ 0.0057). (B) Mean speed of different strains. <i>eat-4</i> and <i>ceh-36</i> mutant animals fail to increase speeds upon application of an electric field stimuli (1.5-6V/cm) when compared to wild type (<i>p</i> ≤ 0.007 and <i>p</i> ≤ 0.0067,respectively). <i>nsy-5/inx-19</i> (AWC^OFF/OFF) animals do not differ statistically from non-stimulus speeds (0 V/cm) at 1.5V/cm and 3V/cm (<i>p</i> ≥ 0.0702). <i>nsy-1</i> (AWC^ON/ON) animals have a significant increase in speed at all field strengths compared to non-stimulus (0 V/cm) speeds (<i>p</i> ≤ 0.0005). <i>eat-4(</i>+<i>)</i> rescue in AWC neurons (AWC::<i>eat-4</i>) results in increased speeds at all field strengths (1.5–6 V/cm; <i>p</i> ≤ 0.007). Error bars represent SEM; number of individual animal tracks per genotype (<i>N</i>) ≥ 154 per calculated average. Data points for different strains were staggered for better visualization. <i>P</i>-values were determined from post-hoc pairwise comparisons of estimates obtained via general linear mixed-models. Significance was assessed using a false discovery rate of 0.05.</p

Electrotaxis behavior in wild-type animals at multiple field strengths.

<p>(A) Trajectories of individual animals within a population at applied field strengths of 0, 1.5, 3, 6 and 9 V/cm. (B) Orientation of trajectory angles. Angle coordinates were assigned in 1° increments from 0 to ± 180°. Negative and positive angles represent direction above and below X-axis. (C-D) Distribution of trajectory angles for different electric field strengths. Lines are smoothed using a seven point moving average. (E) Mean trajectory angles of wild-type animals are significantly different at all electric field strengths in comparison to non-stimulus at 0 V/cm (<i>p</i> ≤ 0.0001). The trajectory angles above (+) and below the X-axis (-) were combined and plotted as absolute values. (F) Mean speed of wild-type animals increases significantly at electric field strengths of 1.5–9 V/cm relative to non-stimulus speed (<i>p</i> < 0.0001). For (E) and (F), error bars represent SEM; number of individual animal tracks per genotype (<i>N</i>) ≥ 154. <i>P</i>-values were determined from post-hoc pairwise comparisons of estimates obtained via general linear mixed-models. Significance was assessed using a false discovery rate of 0.05.</p

Role of AWC, ASH or ASJ on electrotaxis behavior.

<p>(A-C) Trajectory paths of individual animals at 3 V/cm for AWC::caspase, ASH::caspase and ASJ::caspase strains. (D-F) Distribution of animal trajectory angles for different electric field strengths in AWC::caspase, ASH::caspase and ASJ::caspase strains.</p