Overview of Chemotaxis Behavior Assays in Caenorhabditis elegans

Abstract

Environmental pollution related to anthropogenic pressures, and the associated repercussions on public health, represent a worldwide problem. Thus, the study of the effects that environmental contaminants can pose to natural ecosystems and human health is of vital importance. Laboratory model organisms such as Caenorhabditis elegans have played a significant role in clarifying multilevel effects of those agents. Although the evaluation of contaminant effects at the behavioral level of organisms is an emerging approach in ecotoxicology, studies assessing chemotaxis behavior in C. elegans within the ecotoxicological research context are still scarce. Chemotaxis studies in C. elegans have contributed to the understanding of both the neuronal mechanisms involved in the behavioral effects triggered by environmental cues and the impact of contaminants on natural ecosystems. Its compact and well-characterized nervous system, as well as the availability of transgenic strains and molecular tools, allows a detailed examination of behavioral, molecular, and genetic chemosensation mechanisms. This overview provides a summary and general comparison of methods used to measure chemotaxis behavior in C. elegans, with the aim of helping researchers select the most suitable approach in their chemotaxis studies. We compare methods based on the type of chemical tested, advantages and drawbacks of the different approaches, and specific experimental goals. Lastly, we hope to encourage the evaluation of C. elegans chemotaxis behavior in ecotoxicology studies, as well as its potential integration in standardized protocols assessing environmental quality.

An efficient behavioral screening platform classifies natural products and other chemical cues according to their chemosensory valence inC. elegans

“…To expand knowledge of the nematode chemical-sensing repertoire and to spur efforts toward obtaining a general understanding of how chemical cues are encoded according to valence, we built an efficient platform for testing the ability of small molecules to attract or repel nematodes. Compared to classical C. elegans chemotaxis assays, which depend on manual assays and worm counts [4,21,74], our platform features liquid handling hardware for worm dispensing, flatbed scanners for rapid image acquisition, and modifications to optimize image quality and enable image de-multiplexing. Software to count animals, determine their position, and determine the strength and direction of chemotaxis and integrated data management completes the system.…”

“…To spur efforts toward obtaining a general understanding of how chemical cues are encoded according to valence, we built an efficient platform for testing compounds for the ability to attract or repel nematodes. Compared to classical C. elegans chemotaxis assays, which depend on manual assays and hand-counting worms [4,59,77], our platform features liquid handling hardware for worm dispensing, wetware to optimize image quality and enable image de-multiplexing, and software to count animals, determine their position, and determine the strength and direction of chemotaxis. The workflow presented here makes it possible to screen hundreds of compounds in a single week with improved rigor and reproducibility.…”

Worm-Based Diagnosis Combining Microfluidics toward Early Cancer Screening

“…Additionally, the slow diffusion of chemicals on agar plates leads to a time-consuming process for establishing specific concentration gradients [65]. Another drawback of traditional agar plates is the lack of clear demarcation, which can result in interactions between C. elegans and compromise the results' accuracy [66] In contrast, microfluidic systems offer precise control over fluid flow using micropumps and micro-valves, enabling the generation of time-and space-controlled concentration gradients in microchannels [67][68][69]. Microfluidic channels are designed with appropriate diameters to allow a single worm to pass through without encountering specific interactions [70,71].…”

An Undergraduate Laboratory Series Using C. elegans That Prepares Students for Independent Inquiry

“…To conduct the chemotaxis assay (Bargmann et al, 1993;Queirós et al, 2021), students worked in Plates were labeled for two test (T) and two control (C) sites in opposing quadrants, equidistant from the center. The test substance for the chemoattractant and chemorepellent tasks were 0.2% NaCl and 30% octanol in ethanol, respectively.…”