Measuring optimality of a neural system by a logic gate model

The nematode worm, Caenorhabditis elegans, is a relatively simple neural system model for measuring the efficiency of information transmission from sensory organ to muscle fiber. With the potential to measure this efficiency, a method is proposed to compare the organization of an idealized neural circuit with a logic gate design. This approach is useful for analysis of a neural circuit that is not tractable to a strictly biological model, and where the assumptions of a logic gate design have applicability. Also, included in the results is an abstract perspective of the electrical-specific synaptic network in the somatic system of the nematode worm.

Presynaptic Gαo (GOA-1) signals to depress command neuron excitability and allow stretch-dependent modulation of egg laying in Caenorhabditis elegans

Egg laying in the nematode worm Caenorhabditis elegans is a two-state behavior modulated by internal and external sensory input. We have previously shown that homeostatic feedback of embryo accumulation in the uterus regulates bursting activity of the serotonergic HSN command neurons that sustains the egg-laying active state. How sensory feedback of egg release signals to terminate the egg-laying active state is less understood. We find that Gαo, a conserved Pertussis Toxin-sensitive G protein, signals within HSN to inhibit egg-laying circuit activity and prevent entry into the active state. Gαo signaling hyperpolarizes HSN, reducing HSN Ca2+ activity and input onto the postsynaptic vulval muscles. Loss of inhibitory Gαo signaling uncouples presynaptic HSN activity from a postsynaptic, stretch-dependent homeostat, causing precocious entry into the egg-laying active state when only a few eggs are present in the uterus. Feedback of vulval opening and egg release activates the uv1 neuroendocrine cells which release NLP-7 neuropeptides which signal to inhibit egg laying through Gαo-independent mechanisms in the HSNs and Gαo-dependent mechanisms in cells other than the HSNs. Thus, neuropeptide and inhibitory Gαo signaling maintains a bi-stable state of electrical excitability that dynamically controls circuit activity in response to both external and internal sensory input to drive a two-state behavior output.

The structural basis of Bcl-2 mediated cell death regulation in hydra

Apoptosis is regulated by evolutionarily conserved signaling pathways to remove damaged, diseased or unwanted cells. Proteins homologous to the B-cell lymphoma 2 (Bcl-2) family of proteins, the primary arbiters of mitochondrially mediated apoptosis, are encoded by the cnidarian Hydra vulgaris. We mapped interactions between pro-survival and pro-apoptotic Bcl-2 proteins of H. vulgaris by affinity measurements between Hy-Bcl-2-4, the sole confirmed pro-survival Bcl-2 protein, with BH3 motif peptides of two Bcl-2 proteins from hydra that displayed pro-apoptotic activity, Hy-Bak1 and Hy-BH3-only-2, and the BH3 motif peptide of the predicted pro-apoptotic protein Hy-Bax. In addition to peptides from hydra encoded pro-apoptotic proteins, Hy-Bcl-2-4 also engaged BH3 motif peptides from multiple human pro-apoptotic Bcl-2 proteins. Reciprocally, human pro-survival Bcl-2 proteins Bcl-2, Bcl-xL, Bcl-w, Mcl-1 and A1/Bfl-1 bound to BH3 spanning peptides from hydra encoded pro-apoptotic Hy-Bak1, Hy-BH3-only and Hy-Bax. The molecular details of the interactions were determined from crystal structures of Hy-Bcl-2-4 complexes with BH3 motif peptides of Hy-Bak1 and Hy-Bax. Our findings suggest that the Bcl-2 family in hydra may function in a manner analogous to the Bcl-2 family in humans, and less like the worm Caenorhabditis elegans where evolutionary gene deletion has simplified the apoptotic program. Combined, our results demonstrate the powerful conservation of the interaction pattern between hydra and human Bcl-2 family members. Furthermore, our data reveal mechanistic differences in the mode of binding between hydra and sponges such as Geodia cydonium, with hydra encoded Bcl-2 resembling the more promiscuous pro-apoptotic Bcl-2 members found in mammals compared with its sponge counterpart.

Sonic stimulation at certain frequencies can confer limited protection on nematode host infected with Serratia marcescens

Different mono-frequency and poly-frequency sounds were investigated for their possible therapeutic effect on infected worm (Caenorhabditis elegans) population. Sound corresponding to the frequency of 700 Hz and 2,000 Hz were found to confer 11-27% survival benefit on worm population challenged with multi-drug resistant gram-negative bacterial pathogen Serratia marcescens.

Comment on "Magnetosensitive neurons mediate geomagnetic orientation in Caenorhabditis elegans"

A diverse array of species on the planet employ the Earth's magnetic field as a navigational aid. As the majority of these animals are migratory, their utility to interrogate the molecular and cellular basis of the magnetic sense is limited. Vidal-Gadea and colleagues recently argued that the worm Caenorhabditis elegans possesses a magnetic sense that guides their vertical movement in soil. In making this claim, they relied on three different behavioral assays that involved magnetic stimuli. Here, we set out to replicate their results employing blinded protocols and double wrapped coils that control for heat generation. We find no evidence supporting the existence of a magnetic sense in C. elegans. We further show that the Vidal-Gadea hypothesis is problematic as the adoption of a correction angle and a fixed trajectory relative to the Earth's magnetic inclination does not necessarily result in vertical movement.

The Role of Netrins and Their Receptors in Epithelial Mesenchymal Plasticity during Development

Transitions between mesenchymal and epithelial cells are underpinned by changes in motility, adhesion, and polarity. Netrins and their receptors can control each of these cellular properties, and are emerging as important regulators of epithelial mesenchymal plasticity (EMP). Netrins were first identified in the worm Caenorhabditis elegans as secreted chemoattractants/repellents that could guide migrating mesodermal cells and axonal growth cones. Orthologues were subsequently found to play conserved roles in vertebrates and in the vinegar fly Drosophila. In the years that have followed it has become clear that, in addition to chemotaxis, netrin pathways have a number of other biological roles, many of which are directly relevant to the processes of EMP. Netrins and their receptors regulate morphogenesis of epithelial branched structures in the lung, mammary gland, pancreas, and vasculature, and can also promote the loss of epithelial structure. More recently they have been shown to drive apicobasal cell polarization events in vertebrates, flies, and worms. Given these many and varied roles in regulating epithelial morphogenetic events, together with their well-established roles in cell motility, netrins are likely to remain an important future avenue for EMP research.

Model super-organisms: Can the biochemical genetics of E. coli help us understand aging?

Escherichia coli is a powerful model organism to help us understand biochemical pathways and enzyme function. In E. coli, biosynthetic pathway mutants are conditionally viable depending on the composition of the nutrient media. Genetic analysis allows enzyme function to be linked to gene sequences. E. coli is used in the lab as a food source for the nematode worm Caenorhabditis elegans, a model organism for the understanding of basic animal biology. Recent work has shown that specific biosynthetic pathways in E. coli can influence C. elegans aging. Careful experimentation is needed to determine whether E. coli biochemistry influences aging by altering C. elegans nutrition or through changes to bacterial functions, such as toxin production. Understanding these interactions in the C. elegans–E. coli model “super-organism” will inform studies of how bacteria of the human microbiota interact with the host.