Nelson, Charles et al. (2017) International Worm Meeting "Post-transcriptional regulation of the microRNA let-7 in C. elegans."

Ambros, Victor, Nelson, Charles

[International Worm Meeting, 2017]

let-7 is a microRNA whose sequence, function, and regulation are well conserved throughout the animal kingdom. LIN-28 is an RNA binding protein that negative regulates let-7 biogenesis. In mammals, biochemical and crystal structure studies show that LIN-28 achieves this negative regulation by binding the let-7/let-7* stem loop of either primary-let-7 or pre-let-7. Interestingly, the post-transcriptional repression that LIN-28 imposes upon let-7 biogenesis is conserved in C. elegans, but the stem-loop sequence is not. Recent studies have demonstrated that in C. elegans LIN-28 binds to the primary-let-7 transcript downstream of the let-7/let-7* stem loop to repress let-7 biogenesis. In addition to LIN-28 repression, two other mechanisms of post-transcriptional regulation of let-7 biogenesis have also been described. First, let-7 complimentary sequences in its primary transcript have been described to promote its own biogenesis. Second, trans-splicing of pri-let-7 has been shown to remodel its secondary structure to facilitate processing. This work aims to further characterize how these various modes of post-transcriptional control of let-7 biogenesis are integrated to achieve robustly regulated expression of let-7 in the context of the heterochronic pathway.

Nelson, Dru Charles et al. (2013) International Worm Meeting "A new imaging system for high-throughput C. elegans analysis of temperature-entrained rhythmic gene expression."

Nelson, Dru Charles, van der Linden, Alexander, Winbush, Ari

[International Worm Meeting, 2013]

Temperature is a universal entrainment signal for the circadian clock, but relatively little is known about temperature entrainment, even though temperature plays a central role in the synchronization of clocks in many species including mammals and flies. The complex architecture of the fly and mammalian nervous system makes it difficult to understand how temperature signals reach the clock to fine tune circadian rhythms in behavior and physiology at an organismal level. Studying these processes in C. elegans, an extensively used animal model with a small and completely mapped nervous system, has the potential to functionally dissect the pathways from the temperature input to the circadian-driven behavioral output. These properties combined with our recent discovery of temperature entrained circadian molecular rhythms in C. elegans could provide fundamental information for how temperature signals entrain the clock(s). To examine how temperature input entrains the clock, we have developed a new in vivo automated imaging system for long-term recording and quantification of rhythmic gene expression in C. elegans. Using this system, we can robustly measure and quantify fluorescence levels emanating from a circadian reporter during temperature cycles. This imaging system gives us the opportunity to identify genes and neurons that function in the temperature entrained clock of C. elegans. We show that the tax-2 cGMP-gated ion channel, previously implicated in responses to temperature signals and thermotaxic behavior in C. elegans, is required for temperature entrainment of rhythmic gene expression. These results suggest that sensory signals are necessary to transmit temperature information to the C. elegans clock(s), a pathway that appears to be conserved in Drosophila. Our data establishes C. elegans as a new and experimentally amenable model system for understanding the temperature-entrained clock(s). This work was made possible by NIH 1P20GM103650 and 1R21NS078617.

Miller DM et al. (1992) Worm Breeder's Gazette "unc-4 LacZ Expression in A-Type Motor Neurons"

Miller DM, Niemeyer CJ

[Worm Breeder's Gazette, 1992]

unc-4 LacZ expression in A-type motor neurons David M. Miller and Charles J. Niemeyer, Dept. of Cell Biology, Duke Univ. Medical Ctr, Durham, NC 27710

Opperman CH et al. (1992) Parasitol Today "Nematode acetylcholinesterases--molecular forms and their potential role in nematode behavior."

Chang S-H, Opperman CH

[Parasitol Today, 1992]

Nematode movement is reliant upon the somatic musculature that runs longitudinally along the body wall. Neuromuscular synapses occur in the ventral and dorsal cords and employ the excitatory neurotransmitter, acetylcholine (ACh), for modulation of muscle activity. Acetylcholine activity is terminated by hydrolysis by acetylcholinesterase (AChE). Here, Charles Opperman and Stella Chang discuss the molecular forms and potential role of this enzyme.

Duan, Ye et al. MicroPubl Biol

Duan, Ye, Choi, Sungwook, Ambros, Victor, Nelson, Charles

[MicroPubl Biol, 2020]

The application of CRISPR/Cas9 genome editing has revolutionized the genetic analysis of gene function in vivo by enabling highly efficient and precise in loco mutagenesis of defined genomic loci (Adli, 2018). In particular, CRISPR/Cas9 mediated homologous directed recombination (HDR) permits the introduction of complex genetic modifications at single nucleotide resolution (Cong et al., 2013; Dickinson et al., 2013). However, the targeted mutagenesis of essential genes using CRISPR/Cas9 can be challenging since the recovery of deleterious mutations of an essential gene may require a genetic balancer with a wild type copy of the gene (or alternatively a genetic suppressor locus) that can be later outcrossed for phenotypic analysis of novel targeted mutations. Genetic balancers are commonly available for model organisms such as worms or flies, but in the context of CRISPR/Cas9 genome editing, the balancer itself can be edited along with the targeted genomic locus, dramatically reduce the efficiency of recovering the desired loss of function alleles. Therefore, editing of essential genes would be facilitated by a strategy where the targeted genomic locus is efficiently edited, whilst the balancer locus is resistant to editing.

DeFelice LJ et al. (1993) Worm Breeder's Gazette "Preliminary Biophysical Characterization of Ion Channels in C. elegans Sperm Membranes"

DeFelice LJ, L'Hernault SW, Machaca KA

[Worm Breeder's Gazette, 1993]

Biochemical and pharmacological studies have revealed that ion transport across the C. elegans sperm plasma membrane probably accompanies formation of spermatozoa (Nelson and Ward, Cell 19: 457-464, 1980; Ward, Hogan and Nelson, Dev. Biol. 98: 70-79, 1983). We have been examining these phenomena by patch clamping techniques. Spermatids were prepared from him-5 (e1490)males in Sperm Medium (SM; see Nelson and Ward, ibid.) and the patch pipette was filled with SM (for cell attached recordings) or various other solutions (for cell detached recordings). The small size (~5-6 microns for spermatids) of this cell required narrow tipped pipettes, which were fire polished so that the tips had an internal diameter of about 1 micron and had a resistance of 4-10 megaohm. Utilization of these narrow tipped pipettes allowed formation of high resistance (greater than 20 gigaohm) membrane seals to patch pipettes on both cell attached and broken cell detached (inside out) preparations, as measured on a List EPC-7 ,bandlimited at 1000 Hz by standard techniques (Wellis et al., Biophys. J. 57: 41-48, 1990). Cell attached patches, which have an area of about 5 microns (2) (by capacitive measurement), do not seem to affect cell viability for at least 30 minutes and can be obtained routinely on either spermatids or spermatocytes. Distinct levels of current appear at each applied voltage, indicating at least four types of ion channels in spermatid plasma membrane. In figure 1, the lowest conductance level observed is about 15 pS and the highest is 95 pS. These currents reverse between 10 and 15 mV negative to rest (arbitrarily set to 0 mV). A 200 pS ion channel is also occasionally observed (not shown in Fig. 1). These results indicate that it is feasible to study C. elegans sperm differentiation by patch clamping. Our first investigations will involve patch clamping spermatids and inducing their differentiation into spermatozoa while monitoring ion channel activities.

Sterling P et al. (2023) Anim Cogn "Why an animal needs a brain."

Sterling P, Laughlin S

[Anim Cogn, 2023]

In Principles of Neural Design (2015, MIT Press), inspired by Charles Darwin, Sterling and Laughlin undertook the unfashionable task of distilling principles from facts in the technique-driven, data-saturated domain of neuroscience. Their starting point for deriving the organizing principles of brains are two brainless single-celled organisms, Escherichia coli and Paramecium, and the 302-neuron brain of the nematode Caenorhabditis elegans. The book is an exemplar in how to connect the dots between simpler and (much) more complex organisms in a particular area. Here, they have generously agreed to republish an abridged version of Chapter 2 (Why an Animal Needs a Brain), in which many of their principles are first described.

Kimble JE et al. (1984) Dev Biol "Specification of male development in Caenorhabditis elegans: the fem genes."

Hirsh DI, Edgar LG, Kimble JE

[Dev Biol, 1984]

Mutation of the gene fem-2 causes feminization of both sexes: hermaphrodites make no sperm, and males produce oocytes in an intersexual somatic gonad. A double mutant harboring ts alleles of both fem-1 (formerly named isx-1; G. A. Nelson, K. K. Lew, and S. Ward, 1978, Dev. Biol. 66, 386-409) and fem-2 causes transformation of XO animals (normally male) into spermless hermaphrodites at restrictive temperature. The phenotypes, temperature-sensitive periods, and maternal effects observed in mutants of each fem gene are found to be similar. It is suggested that the fem genes are centrally involved in specification of male development in Caenorhabditis elegans--both in the germ line of hermaphrodites and in somatic and germ line tissues of

Soto, Rony et al. (2020) MicroPubl Biol

Van Buskirk, Cheryl, Soto, Rony

[MicroPubl Biol, 2020]

Across species, sleep is increased following exposure to damaging conditions, a phenomenon known as stress-induced sleep (SIS) (Hill et al. 2014; Lenz et al. 2015; Zada et al. 2019). In C. elegans, SIS is dependent on the ALA interneuron (Hill et al. 2014; Nelson et al. 2014), which promotes a coordinated quiescent state through the collective action of several neuropeptides (Nelson et al. 2014; Nath et al. 2016). Recently it has been shown that ALA ablation can suppress phenotypes associated with loss of the cephalic sensilla sheath (CEPsh) glia, such as prolonged larval development and locomotor pausing in adults (Katz et al. 2018), indicating that these glia attenuate certain aspects of ALA function. The CEPsh glia form a tubular structure surrounding the sensory endings of the CEP neurons and also extend thin processes that sheath the nerve ring, including the synapse between ALA and the postsynaptic AVE, a major locomotor interneuron. While the ALA is likely to promote SIS via peptidergic rather than synaptic signaling (Nelson et al. 2014; Nath et al. 2016), we wished to determine whether CEPsh glia ablation may impact the SIS-promoting function of ALA. To this end, we examined three independent lines that genetically ablate the four CEPsh glial cells (Katz et al. 2018), and compared the SIS responses of these strains to wild type and to ALA specification-defective ceh-17(np1) mutant animals. We examined three conditions known to trigger ALA-dependent sleep: noxious heat, pore-forming Cry5B toxin, and ultraviolet light exposure (Figure 1). We found that while the glia-ablated (GA) lines displayed a trend toward enhanced heat-SIS at the 15min time point, there were no significant differences in heat-SIS between the GA lines and wild-type. The GA lines also showed wild-type Cry5B-SIS. Surprisingly, two of the GA lines showed reduced UV-SIS, rather than the enhanced sleep that would be predicted if the CEPsh glia attenuate ALAs peptidergic function. Our data indicate that CEPsh glia are largely dispensable for stress-induced sleep, but may modulate the UVSIS response. As UV exposure elicits a delayed sleep response relative to other SIS triggers, we speculate that UV damage may activate ALA in a manner that is distinct, and partially supported by glial function.

Chavez-Perez, Carlos et al. (2021) MicroPubl Biol

Rohacek, Alex M, Raizen, David M, Jafari, Niusha, Chavez-Perez, Carlos, Keenan, Brendan T

[MicroPubl Biol, 2021]

Like other animals, the nematode C. elegans exhibits reduced movement and sleep in response to sickness, which can be induced by exposure to high temperatures (Hill et al. 2014; Nelson et al. 2014) ultraviolet light (DeBardeleben et al. 2017), and other stressful exposures (Hill et al. 2014; Goetting et al. 2020). This response has been termed Stress/Sickness-Induced Sleep (SIS) (Hill et al. 2014; Trojanowski and Raizen 2016). Exposure to the stressor leads to quiescence in part via release of the cytokine Epidermal Growth Factor (EGF) (Hill et al. 2014; Konietzka et al. 2020), which is encoded by the gene lin-3 (Hill and Sternberg 1992). EGF activates the ALA and RIS neurons, which then release their respective neuropeptides to effect reduced movement and behavioral quiescence (Konietzka et al. 2020).