Keynes R et al. (1996) Neuron "Axons turn as netrins find their receptor."

Keynes R, Cook GMW

[Neuron, 1996]

The idea of chemoattraction as a guiding mechanism for growing axons was originally suggested by Ramon y Cajal as a result of earlier work on leucocytes. Discussing the ventral navigation of commissural axons toward the midline floor plate in the developing spinal cord, he wrote: ...The oblique direction assumed by these axons would be explained if chemoattractants produced by the ventral half of the neuroepithelium were stronger than those produced by the rest of the epithelium...a sufficiently extended period of chemoattractant secretion by the floor plate could explain the relatively long period of time over which the ventral commissure is formed". Chemoattraction is well established at the molecular level in leucocyte biology, but good evidence was lacking in the vertebrate nervous system until collagen gels were used to assay for chemoattractants, allowing the purification and cloning of netrins. The homology then revealed between netrins and UNC-6, a laminin-related protein required for circumferential dorsal and ventral migrations of axons in the body wall of Caenorhabditis elegans, further suggested that netrins may provide highly conserved midline guidance cues for axons, operating in organisms ranging from nematode worms to higher vertebrates. This appealing view is now amply confirmed with an impressive group of studies using worms, flies, and rodents to analyze neural development in the face of netrin loss- and gain-of-function, and the story has simultaneously taken a significant step forward with the identification of the structure and function of netrin receptors.

Basset D et al. (1991) J Fr Ophtalmol "[Allergic granulomatous nodule of the conjunctiva disclosing onchocerciasis]."

Basset D, D'Hermies F, Lagrange PH, Pouliquen Y

[J Fr Ophtalmol, 1991]

A new case of conjunctival allergic nodule is reported in a Guinean man. This lesion was first described by Ashton and Cook in 1979. Histologically, this nodule consists of amorphous eosinophilic material surrounded by epithelioid and giant cells arranged in a pallisade; some eosinophils are often found in the inflammatory reaction. This lesion usually resolves spontaneously. In documented cases, nematodes and particularly filaria such as Mansonella perstans are usually isolated. Our observation is the first documented case with Onchocerca volvulus. Microfilariae were detected by examination of normal saline containing the biopsy specimen. The new major antifilarial treatment ivermectin was associated.

Morimoto RI et al. (2024) Autophagy "Proteostasis in health and disease: a conversation with Professor Rick Morimoto."

Ktistakis NT, Morimoto RI

[Autophagy, 2024]

Professor Richard (Rick) Morimoto is the Bill and Gayle Cook Professor of Biology and Director of the Rice Institute for Biomedical Research at Northwestern University. He has made foundational contributions to our understanding of how cells respond to various stresses, and the role played in those responses by chaperones. Working across a variety of experimental models, from <i>C</i>. <i>elegans</i> to human neuronal cells, he has identified a number of important molecular components that sense and respond to stress, and he has dissected how stress alters cellular and organismal physiology. Together with colleagues, Professor Morimoto has coined the term "proteostasis" to signify the homeostatic control of protein expression and function, and in recent years he has been one of the leaders of a consortium trying to understand proteostasis in healthy and disease states. I took the opportunity to talk with Professor Morimoto about proteostasis in general, the aims of the consortium, and how autophagy is playing an important role in their research effort.

Goldman, Gal et al. (2021) International Worm Meeting "The role of network topology in the performance of the circuit for nociceptive behaviors in C. elegans"

Pechuk, Vladyslava, Schneidman, Elad, Oren-Suissa, Meital, Goldman, Gal

[International Worm Meeting, 2021]

The nature of the relationship between neural circuits and the resulting animal behavior is a key question in neurobiology. It was previously established that the specific synaptic and cellular properties of neural networks can be widely disparate, yet maintain similar function (Prinz et al., 2004). It is therefore clear that some features of a network's structure are important to retain certain functional features. The sensitivity of such networks to changes in the topology have not been characterized. To explore the contribution of topology to the network's performance, we focused here on the circuit for nociceptive behaviors in C. elegans. The neurons of the circuit are shared between the two sexes, but their connectivity is different (Cook et al., 2019). The behaviors that result from these circuits are sexually dimorphic as well. The distinct network topologies and behavioral outputs make this circuit a good example for exploring the relationship between structure and function in neural networks. We simulated the response of the nociceptive circuits to external stimuli, in males and in hermaphrodites, using a wide range of realistic values for the circuit's biophysical parameters (synaptic strengths, conductivity, membrane time constants, etc.). We then searched for the parameters' space in which the activity of the motor output neurons in the simulation would match the worms' behaviors in experimental observations. We found an overlap between the sexes in terms of the synaptic and cellular parameters that allow for the correct behavior of the network. Moreover, our results suggest that the connectivity alone might be sufficient to explain the behavioral differences between the sexes. Notably, more stringent requirements of the models' performance suggests that the connections in this network cannot be all excitatory, as has been commonly assumed, or that additional inhibitory neurons must play an important role in shaping the circuit's response to tail stimulation. Future analysis will further explore the relations between the network's topology and the joint activity patterns of the neurons as measured by calcium imaging.

Jarrell, Travis A. et al. (2013) International Worm Meeting "The connectome of the anterior nervous system of the C. elegans adult male."

Nguyen, Kenneth, Bloniarz, Adam E., Brittin, Christopher A., Cook, Steven J., Hall, David H., Emmons, Scott W., Xu, Meng, Jarrell, Travis A., Wang, Yi

[International Worm Meeting, 2013]

The innate behavioral repertoires of the two sexes of a species are guided by differing reproductive priorities. C. elegans male copulation is controlled by a neural network in the tail in which a majority of the neurons and muscles are specific to the male. But known differences in olfactory preferences and exploratory tendencies emanate from behaviors controlled by circuits in the head, where the complement of neurons is nearly identical in the two sexes. We determined connectivity in the anterior nervous system of the adult male from a 1,500 section-long thin section EM series extending from near the tip of the nose, through the nerve ring, and part way into the retrovesicular ganglion. This region contains the bulk of the synapses, excluding ventral cord nmj's. To make a comparison to the hermaphrodite, we re-reconstructed legacy Cambridge micrographs using our software, which allows us to score synaptic weights (see abstract by Cook et al). While our analysis is at an early stage, we can already see the essential result: in the adjacency matrices that display the connectivity, it is difficult to spot differences that appear greater than would be expected given the inherent variability of neuronal wiring. Known circuits in navigation and other responses are conserved. Thus behavioral differences likely emerge from differing circuit properties rather than differing connectivity. There are two possible exceptions: AIM synapses onto AIB and RIA synapses onto RIB in the male only. One set of male-specific synapses expected involves the male-specific head CEM sensory neurons, and the tail EF interneurons, which receive extensive input from the copulatory circuits in the tail and extend processes through the ventral nerve cord into the nerve ring. Both of these neuron classes have as their strongest targets the AVB command interneurons for forward locomotion. This suggests one of their functions may be to inhibit forward locomotion when a hermaphrodite is sensed or during copulation. They make additional connections to be further explored.

Pechuk, Vladyslava et al. (2021) International Worm Meeting "Sexually-dimorphic responses to noxious stimuli in C. elegans result from differences in interneuron connectivity rather than in sensory processing"

Pechuk, Vladyslava, Salzberg, Yehuda, Oren-Suissa, Meital

[International Worm Meeting, 2021]

Sexually reproducing animals display sexually dimorphic behaviors, geared towards reproductive success. Are there differences in the way the two sexes interpret and respond to the same aversive input? To address this question we analyzed the worm's avoidance responses to hazardous conditions. C. elegans generates an escape response to aversive stimuli by integrating sensory information from the polymodal nociceptive ASH head neurons and tail neurons, and conveying it to the main reversal interneuron AVA. The recent full mapping of the male connectome (Cook et al. 2019) suggests that the sex-shared neurons in the avoidance circuit are dimorphically connected, e.g. ASH to AVA connection is predicted to exist only in hermaphrodites. We measured the response of both sexes to the aversive stimuli SDS and glycerol using a behavioral tail-drop assay. We found that the two sexes exhibit dose-dependent sexually dimorphic responses to the aversive stimuli - across multiple nociceptive modalities, hermaphrodites exhibited a lower pain threshold than males. The behavioral differences and the suggested anatomical maps prompted us to functionally deconstruct the avoidance circuit. To examine potential sexual dimorphism at the sensory level, we compared ASH receptor expression levels (OCR-2, OSM-9, OSM10, QUI-1, ODR-3, GPA-3), ASH glutamatergic secretion by imaging the pHluorin sensor, and neuronal activation by calcium imaging in both sexes. We found that the ASH sensory neuron is non-dimorphic for all these parameters and responds similarly in the two sexes. Furthermore, we activated ASH optogenetically, thus bypassing the sensory input level, and found that hermaphrodites responded with a reversal at a lower LED intensity compared to males, in agreement with the tail-drop assay. Lastly, imaging of the downstream AVA interneuron revealed a stronger and longer response to the stimulus in hermaphrodites compared to males, further pointing to the connectivity and interneuron levels as the key sources for dimorphism in the circuit. Together, our results suggest that dimorphic responses to noxious cues arise due to neuronal circuit dimorphism downstream of sensory processing. We hypothesize that differences in circuit connectivity, rather than sensory perception per se, allow for sex-specific behavioral adaptation.

Vidal , B. et al. (2019) International Worm Meeting "Decoding pharyngeal neuron fate specification."

Hobert, O., Gulez, B., Vidal , B., Reilly, M.

[International Worm Meeting, 2019]

The pharyngeal nervous system is composed of only 20 neurons belonging to 14 different types, which form a self-contained circuit that is almost independent from the somatic nervous system. This simplicity makes it possible to analyze it in a comprehensive way. Moreover, all pharyngeal neurons directly connect to end organs and can be considered polymodal with sensory-motor characteristics (see abstract by S.J. Cook and S.W.Emmons), a feature that is reminiscent of primitive nervous systems. Thus, understanding how pharyngeal neurons are specified during development might shed light on fundamental aspects of neuronal development. ceh-34, a homeodomain transcription factor of the Six family, is continuously expressed in all pharyngeal neurons and no other neurons outside of the pharynx. Remarkably, we have found that in ceh-34 mutants, pharyngeal neurons are generated, but fail to express a wide array of terminal identity genes, including neurotransmitter pathway genes, indicating that ceh-34 acts as a pharyngeal neuron master regulator ("terminal selector"). Moreover, a conditional AID-based allele demonstrates that ceh-34 is continuously required during the life of the worm to maintain pharyngeal neuron identity. We hypothesize that ceh-34 acts together with other transcription factors to form a combinatorial code that gives each pharyngeal neuron its unique identity. We have found several other homeodomain transcription factors expressed in subsets of pharyngeal neurons (see abstract by M. Reilly and O.Hobert) and we are doing a mutant analysis to test whether they also play a role in the pharyngeal nervous system specification. Moreover, we are performing forward genetic screens to find additional factors in an unbiased way. So far we have identified four mutants that appear to affect I2 neuron identity. We are in the process of pinpointing the causal molecular lesions and further characterizing these new mutants. We hope our efforts will lead to a comprehensive understanding of the regulatory code that dictates pharyngeal neuron development.

Loer, Curtis et al. (2021) International Worm Meeting "Characterizing the nervous system of the nematode Pristionchus pacificus - similarities and differences with C. elegans"

Hobert, Oliver, Cook, Steve, Witte, Hanh, Loer, Curtis, Sommer, Ralf

[International Worm Meeting, 2021]

The nervous systems of many nematodes are remarkably similar despite considerable divergence of their genomes. We are examining the evolution of nematode nervous systems by characterizing the nervous system of the nematode Pristionchus pacificus (Ppa) to compare with that of the highly described C. elegans (Cel), which boasts a complete cell lineage, and a complete set of neurons and their connectivities in both sexes (Sulston &amp; Horvitz, 1977; Sulston et al., 1983; White et al., 1986; Cook et al., 2019, Nature 571: 63-71). Within a few years, we and others seek to approach a similar level of characterization for Ppa. For example, the connectivity and likely homologies for head sensory neurons in Ppa have been determined, demonstrating considerable similarities plus a few striking differences, such as the absence of amphid 'winged' cilia found in Cel (Hong et al., 2019, eLife 2019;8:e47155). Considerable progress has been made in transgenics, traditional reporters and CRISPR generation of mutants and short knock-ins. To study neuronal specification in Ppa, we have epitope-tagged transcription factor genes to examine their expression patterns, including Ppa orthologs of unc-3, unc-86 and unc-42. We have also found that an antiserum to C. elegans unc-86 works in Ppa, showing a pattern identical to that of the epitope-tagged locus. The pattern of Ppa-unc-86 expression is remarkably similar to that of Cel; one difference is in the absence of clear HSN homologs in hermaphrodites. This is consistent with the absence of HSNs in Ppa seen with anti-serotonin. Other differences in serotonergic neurons suggest possible differences in the role of Ppa-unc-86 in Ppa vs. Cel. In Cel, the 'terminal selector' unc-86 plays a role in specifying serotonergic fate (Zhang et al., 2014, Development 141: 422-435). For example, in Cel, the AIM neurons express both unc-86 and serotonin; in Ppa presumptive AIM neurons lack serotonin but still express unc-86. We will present these and other results of our analysis of nervous system similarities and difference in C. elegans and P. pacificus.

Garrigues, Jacob et al. (2021) International Worm Meeting "C. elegans transposable elements harbor diverse transcription factor DNA-binding motifs"

Pasquinelli, Amy, Garrigues, Jacob

[International Worm Meeting, 2021]

Transposable elements (TEs) are powerful agents of evolution that can rewire transcriptional programs by mobilizing and distributing transcription factor (TF) DNA-binding motifs throughout genomes. To investigate the extent that TEs provide TF-binding motifs in C. elegans, we determined the genomic positions of DNA-binding motifs for over 200 different TFs (1). Surprisingly, we found that almost all of the examined TFs have binding motifs that reside within TEs, and all types of TEs have at least one instance of a TF motif, demonstrating that TEs provide previously unappreciated numbers of TF-binding motifs to the C. elegans genome. After determining the occurrence of TF motifs in TEs relative to the rest of the genome, we identified numerous TF-binding motifs that are highly enriched within TEs compared to what would be expected by chance. Consistent with potential functional roles for these TE-enriched TF-binding sequences, we found that significantly more TEs with TF motifs display evidence for selection compared to those lacking motifs through the use of publicly available genome variation data (2). We also compared the locations of TE-residing TF motifs to published ATAC-seq (3) and ChIP-seq (4) data, which identify regions of open chromatin associated with TF DNA binding and regions bound by TFs of interest, respectively. Strikingly, we found that all of the TF motif types that occur in TEs have instances of residing within accessible chromatin, and the overwhelming majority of TF-binding motifs located within TEs associate with their cognate TFs, suggesting extensive binding of TFs to sequences within TEs. Additionally, TEs with accessible or TF-bound motifs reside in the putative promoter regions of ~14% of all protein-coding genes, providing widespread possibilities for influencing gene expression. Taken together, our work shows that TE-provided TF-binding sites are ubiquitous in C. elegans and have broad potential to rewire gene expression. 1. Weirauch et al. (2014) Cell 158:1431-1443. 2. Cook et al. (2016) Nucleic Acids Research 45:D650-D657. 3. Daugherty et al. (2017) Genome Research 27:2096-2107. 4. Kudron et al. (2018) Genetics 208:937-949.

Hong, Ray et al. (2019) International Worm Meeting "Evolution of neuronal anatomy in two divergent nematode species."

Hong, Ray, Hobert, Oliver, Sieriebriennikov, Bogdan, Carstensen, Heather, Riebesell, Metta, Castrejon, Jessica, Sommer, Ralf, Cook, Steven, Sarpolaki, Tahmineh, Cochella, Luisa, Moreno, Eduardo, Bumbarger, Daniel

[International Worm Meeting, 2019]

The nematodes C. elegans and P. pacificus, havingdiverged more than 100 million years ago, now inhabit different habitats and display distinct patterns of behavior, including odor-mediated paralysis and predation in P. pacificus. To understand how the nervous systems of these two species have diverged, we undertook a detailed examination of the neuroanatomy of the chemosensory system of P. pacificus. Using several independent features such as cell body position, axon projections and lipophilic dye uptake, we have assigned homologies between the amphid neurons, their first-layer interneurons, and several internal receptor neurons of P. pacificusand C. elegans. We found that neuronal count and soma position are highly conserved. However,the morphological elaborations of several amphid cilia are different between these two nematodes and show less diversity among each other in P. pacificus, most notably in the absence of 'winged' cilia morphology. To assess potential divergences in gene expression patterns, we considered three phylogenetically conserved genes that encode for regulatory and signaling factors. We found that Ppa-che-1p::rfp (zinc finger TF) animals expressed the reporter in two neuron pairs in the head region of the worm, with one of the two pairs of amphid neurons being the ASE. Interestingly, the P. pacificusAS5(ASE) axons do not cross each other at the dorsal midline, as they do in C. elegans, but instead terminate at the dorsal midline, suggesting the left and right ASE neurons are electrically coupled in P. pacificus. Furthermore, the differences in the existence of molecular regulators (lsy-6) and effectors (gcy genes) of C. elegans ASE laterality suggest that the ASE neurons of P. pacificus may not be functionally lateralized. In contrast, the expression of the Ppa-odr-3p::rfp (G-protein subunit) and Ppa-odr-7p::rfp (nuclear hormone receptor) appear to have switched expression patterns in the P. pacificussuch that they are expressed inthe AD3(AWA) and AS7(AWC) counterparts, respectively.When combined with neural circuitry analysis (see abstract by S. Cook et al), these findings indicate that the major substrate for evolutionary divergence does not lie in changes in neuronal cell number or neuronal process targeting, but rather in sensory perception, cilia morphology, and synaptic partner choice within inherent constraints in neuronal processes.