SciCombinator

Discover the most talked about and latest scientific content & concepts.

Concept: Caenorhabditis briggsae

260

The ability to acquire large-scale recordings of neuronal activity in awake and unrestrained animals is needed to provide new insights into how populations of neurons generate animal behavior. We present an instrument capable of recording intracellular calcium transients from the majority of neurons in the head of a freely behaving Caenorhabditis elegans with cellular resolution while simultaneously recording the animal’s position, posture, and locomotion. This instrument provides whole-brain imaging with cellular resolution in an unrestrained and behaving animal. We use spinning-disk confocal microscopy to capture 3D volumetric fluorescent images of neurons expressing the calcium indicator GCaMP6s at 6 head-volumes/s. A suite of three cameras monitor neuronal fluorescence and the animal’s position and orientation. Custom software tracks the 3D position of the animal’s head in real time and two feedback loops adjust a motorized stage and objective to keep the animal’s head within the field of view as the animal roams freely. We observe calcium transients from up to 77 neurons for over 4 min and correlate this activity with the animal’s behavior. We characterize noise in the system due to animal motion and show that, across worms, multiple neurons show significant correlations with modes of behavior corresponding to forward, backward, and turning locomotion.

Concepts: Nervous system, Neuron, Caenorhabditis elegans, Animal, Caenorhabditis, Rhabditidae, Caenorhabditis briggsae, Calcium in biology

204

The self-assembly of α-synuclein is closely associated with Parkinson’s disease and related syndromes. We show that squalamine, a natural product with known anticancer and antiviral activity, dramatically affects α-synuclein aggregation in vitro and in vivo. We elucidate the mechanism of action of squalamine by investigating its interaction with lipid vesicles, which are known to stimulate nucleation, and find that this compound displaces α-synuclein from the surfaces of such vesicles, thereby blocking the first steps in its aggregation process. We also show that squalamine almost completely suppresses the toxicity of α-synuclein oligomers in human neuroblastoma cells by inhibiting their interactions with lipid membranes. We further examine the effects of squalamine in a Caenorhabditis elegans strain overexpressing α-synuclein, observing a dramatic reduction of α-synuclein aggregation and an almost complete elimination of muscle paralysis. These findings suggest that squalamine could be a means of therapeutic intervention in Parkinson’s disease and related conditions.

Concepts: Cancer, Caenorhabditis elegans, Caenorhabditis, Rhabditidae, In vivo, In vitro, Paralysis, Caenorhabditis briggsae

50

Longevity mechanisms increase lifespan by counteracting the effects of aging. However, whether longevity mechanisms counteract the effects of aging continually throughout life, or whether they act during specific periods of life, preventing changes that precede mortality is unclear. Here, we uncover transcriptional drift, a phenomenon that describes how aging causes genes within functional groups to change expression in opposing directions. These changes cause a transcriptome-wide loss in mRNA stoichiometry and loss of co-expression patterns in aging animals, as compared to young adults. Using Caenorhabditis elegans as a model, we show that extending lifespan by inhibiting serotonergic signals by the antidepressant mianserin attenuates transcriptional drift, allowing the preservation of a younger transcriptome into an older age. Our data are consistent with a model in which inhibition of serotonergic signals slows age-dependent physiological decline and the associated rise in mortality levels exclusively in young adults, thereby postponing the onset of major mortality.

Concepts: Gene expression, RNA, Caenorhabditis elegans, Animal, Caenorhabditis, Model organism, Rhabditidae, Caenorhabditis briggsae

42

How do very small animals with limited long-distance dispersal abilities move between locations, especially if they prefer ephemeral micro-habitats that are only available for short periods of time? The free-living model nematode Caenorhabditis elegans and several congeneric taxa appear to be common in such short-lived environments, for example decomposing fruits or other rotting plant material. Dispersal is usually assumed to depend on animal vectors, yet all current data is based on only a limited number of studies. In our project we performed three comprehensive field surveys on possible invertebrate vectors in North German locations containing populations of C. elegans and two related species, especially C. remanei, and combined these screens with an experimental analysis of persistence in one of the vector taxa.

Concepts: Caenorhabditis elegans, Animal, Caenorhabditis, Nematode, Model organism, Rhabditidae, Sydney Brenner, Caenorhabditis briggsae

29

Moderate stress can increase lifespan by hormesis, a beneficial low-level induction of stress response pathways. 5'-fluorodeoxyuridine (FUdR) is commonly used to sterilize Caenorhabditis elegans in aging experiments. However, FUdR alters lifespan in some genotypes and induces resistance to thermal and proteotoxic stress. We report that hypertonic stress in combination with FUdR treatment or inhibition of the FUdR target thymidylate synthase, TYMS-1, extends C. elegans lifespan by up to 30%. By contrast, in the absence of FUdR, hypertonic stress decreases lifespan. Adaptation to hypertonic stress requires diminished Notch signaling and loss of Notch co-ligands leads to lifespan extension only in combination with FUdR. Either FUdR treatment or TYMS-1 loss induced resistance to acute hypertonic stress, anoxia, and thermal stress. FUdR treatment increased expression of DAF-16 FOXO and the osmolyte biosynthesis enzyme GPDH-1. FUdR-induced hypertonic stress resistance was partially dependent on sirtuins and base excision repair (BER) pathways, while FUdR-induced lifespan extension under hypertonic stress conditions requires DAF-16, BER, and sirtuin function. Combined, these results demonstrate that FUdR, through inhibition of TYMS-1, activates stress response pathways in somatic tissues to confer hormetic resistance to acute and chronic stress. C. elegans lifespan studies using FUdR may need re-interpretation in light of this work.

Concepts: Nervous system, Caenorhabditis elegans, Caenorhabditis, Rhabditidae, Nucleotide excision repair, Caenorhabditis briggsae, Osmosis

25

The locomotion behavior of Caenorhabditis elegans has been studied extensively to understand the respective roles of neural control and biomechanics as well as the interaction between them. Constructing a mathematical model is helpful to understand the locomotion behavior in various surrounding conditions that are difficult to realize in experiments. In this study, we built three hidden Markov models (HMMs) for the crawling behavior of C. elegans in a controlled environment with no chemical treatment and in a formaldehyde-treated environment (0.1 and 0.5 ppm). The organism’s crawling activity was recorded using a digital camcorder for 20 min at a rate of 24 frames per second. All shape patterns were quantified by branch length similarity (BLS) entropy and classified into four groups using the self-organizing map (SOM). Comparison of the simulated behavior generated by HMMs and the actual crawling behavior demonstrated that the HMM coupled with the SOM was successful in characterizing the crawling behavior. In addition, we briefly discussed the possibility of using the HMM together with BLS entropy to develop bio-monitoring systems to determine water quality.

Concepts: Nervous system, Neuron, Caenorhabditis elegans, Caenorhabditis, Model organism, Rhabditidae, Hidden Markov model, Caenorhabditis briggsae

24

Animals respond to predators by altering their behavior and physiological states, but the underlying signaling mechanisms are poorly understood. Using the interactions between Caenorhabditis elegans and its predator, Pristionchus pacificus, we show that neuronal perception by C. elegans of a predator-specific molecular signature induces instantaneous escape behavior and a prolonged reduction in oviposition. Chemical analysis revealed this predator-specific signature to consist of a class of sulfolipids, produced by a biochemical pathway required for developing predacious behavior and specifically induced by starvation. These sulfolipids are detected by four pairs of C. elegans amphid sensory neurons that act redundantly and recruit cyclic nucleotide-gated (CNG) or transient receptor potential (TRP) channels to drive both escape and reduced oviposition. Functional homology of the delineated signaling pathways and abolishment of predator-evoked C. elegans responses by the anti-anxiety drug sertraline suggests a likely conserved or convergent strategy for managing predator threats.

Concepts: Nervous system, Neuron, Predation, Caenorhabditis elegans, Animal, Caenorhabditis, Rhabditidae, Caenorhabditis briggsae

23

Correlating molecular labeling at the ultrastructural level with high confidence remains challenging. Array tomography (AT) allows for a combination of fluorescence and electron microscopy (EM) to visualize subcellular protein localization on serial EM sections. Here, we describe an application for AT that combines near-native tissue preservation via high-pressure freezing and freeze substitution with super-resolution light microscopy and high-resolution scanning electron microscopy (SEM) analysis on the same section. We established protocols that combine SEM with structured illumination microscopy (SIM) and direct stochastic optical reconstruction microscopy (dSTORM). We devised a method for easy, precise, and unbiased correlation of EM images and super-resolution imaging data using endogenous cellular landmarks and freely available image processing software. We demonstrate that these methods allow us to identify and label gap junctions in Caenorhabditis elegans with precision and confidence, and imaging of even smaller structures is feasible. With the emergence of connectomics, these methods will allow us to fill in the gap-acquiring the correlated ultrastructural and molecular identity of electrical synapses.

Concepts: Electron, Neuron, Caenorhabditis elegans, Caenorhabditis, Rhabditidae, Scanning electron microscope, Caenorhabditis briggsae, Image processing

22

Cell intercalation is a highly directed cell rearrangement that is essential for animal morphogenesis. As such, intercalation requires orchestration of cell polarity across the plane of the tissue. CDC-42 is a Rho family GTPase with key functions in cell polarity, yet its role during epithelial intercalation has not been established because its roles early in embryogenesis have historically made it difficult to study. To circumvent these early requirements, in this paper we use tissue-specific and conditional loss-of-function approaches to identify a role for CDC-42 during intercalation of the Caenorhabditis elegans dorsal embryonic epidermis. CDC-42 activity is enriched in the medial tips of intercalating cells, which extend as cells migrate past one another. Moreover, CDC-42 is involved in both the efficient formation and orientation of cell tips during cell rearrangement. Using conditional loss-of-function we also show that the PAR complex functions in tip formation and orientation. Additionally, we find that the sole C. elegans Eph receptor, VAB-1, functions during this process in an Ephrin-independent manner. Using epistasis analysis, we find that vab-1 lies in the same genetic pathway as cdc-42 and is responsible for polarizing CDC-42 activity to the medial tip. Together, these data establish a previously uncharacterized role for polarized CDC-42, in conjunction with PAR-6, PAR-3 and an Eph receptor, during epithelial intercalation.

Concepts: DNA, Developmental biology, Caenorhabditis elegans, Animal, Caenorhabditis, Rhabditidae, Eph receptor, Caenorhabditis briggsae

21

Despite technological advances, the survival records from longevity experiments remain the most indispensable tool in ageing-related research. A variety of interventions, including medications, genetic manipulations and calorie restriction (CR), have been demonstrated to extend the lifespan of several species. Surprisingly, few systematic studies have investigated the differences among these anti-ageing strategies using survival data. Here, we conduct a comprehensive and comparative meta-analysis of numerous published studies on Caenorhabditis elegans and Drosophila. We found that CR and genetic manipulations are generally more effective than medications at extending the total lifespan in both models, and CR can improve the ageing pattern of C. elegans. We further analysed the survival variation for different anti-ageing medications and determined that hypoglycaemic agents and antioxidants are advantageous despite only moderately increasing the overall lifespan; therefore, these two types of medications are promising CR mimetics. Analysis of genetic manipulations also indicated that the genes or pathways that extend lifespan in a healthier pattern are associated with CR. These results suggest that CR or CR mimetics may be the most reasonable and potentially beneficial anti-ageing strategy.

Concepts: DNA, Genome, RNA, Caenorhabditis elegans, Caenorhabditis, Model organism, Rhabditidae, Caenorhabditis briggsae