Cheng NN et al. (1987) International C. elegans Meeting "further studies of par-2."

Kemphues KJ, Cheng NN

[International C. elegans Meeting, 1987]

Cheng NN et al. (1995) International C. elegans Meeting "IN SEARCH OF rec-1, A GENE REQUIRED FOR MAINTAINING PROPER DISTRIBUTION OF CROSSOVERS DURING MEIOSIS"

Cheng NN, Rose AM, Vijayaratnam V

[International C. elegans Meeting, 1995]

The rec-1 mutation has been shown to alter the distribution of crossovers on chromosome I and to increase the frequency of recombination across certain genetic intervals. We are attempting to clone this gene in order to understand the mechanism by which the distribution of meiotic crossovers is established. Genetic mapping has located rec-1 gene to the right end of the LG I, uncovered by the ribosomal deletion eDf24 but to the right of unc-54 (M. Zetka & A. Rose, unpublished data). We are taking several approaches to try to correlate the rec-1 mutation to a coding region, including rescuing the rec-1 mutation with cosmids and searching for RFLP in the region. Cosmids spanning the region have been tested for rescue of the rec-1 phenotype, and a partial rescue observed. To aid the identification of rec-1 gene, we are also characterizing some genes in the region. One of these is a homolog of the yeast RAD3 gene which encodes a DNA repair helicase. This gene is required for excision repair of UV-damaged DNA and plays a role in mitotic recombination and RNA pol II transcription in yeast. The C.elegans homolog encodes a protein which contains a DEAH motif and is a member of the DEAD box family of RNA helicase-like proteins. We are testing the possibility that the RAD3 homolog corresponds to the rec-1 gene.

Cheng NN et al. (1996) West Coast Worm Meeting "rec-1 ENCODES A PUTATIVE HELICASE REQUIRED FOR ESTABLISHING THE NON-RANDOM DISTRIBUTION OF MEIOTIC EXCHANGES"

Rose AM, Cheng NN

[West Coast Worm Meeting, 1996]

The distribution of sites of meiotic exchanges is regulated in C. elegans, as evidenced by the presence of a gene cluster in the middle of the autosomes on the genetic map. The recombination frequency in the gene cluster is considerably lower, possibly due to suppression of recombination, while regions outside are highly recombinogenic. Previous genetic analyses have shown that the rec-1 mutation affects the placement of exchanges along the chromosome without apparently disrupting the recombination process per se ( Zetka and Rose, 1995). Thus the distribution of genes on the genetic map in the rec-1 mutant background approaches that on the physical map. We report here the molecular identification of the rec-1 gene through germ line transformation rescue of the mutant. Our data show that rec-1 encodes a predicted protein containing a DEAH motif that is present in a variety of DNA/RNA helicases from yeast to mammals. In addition, REC-1 shares sequence similarity to proteins involved in nucleotide excision repair and chromosome segregation, such as RAD3 and CHL1 in yeast and ERCC2/XPD in humans. Data base searches have revealed that there is another gene in C. elegans closely related to rec-1 as well as to the yeast CHL1 gene. We will discuss the possible role of REC-1 in establishing the proper distribution of crossovers during meiosis. (We gratefully acknowledge Dr. Y. Kohara for providing a cDNA clone, Dr. D. Baillie and D. Janke for the transgenic strains, and V. Vijayaratnam for some of the rescue data. --Supported by NSERC of Canada)

Shen X et al. (2010) Neuronal Development, Synaptic Function and Behavior, Madison, WI "Biomechanical analysis of C. elegans motility"

Arratia P E, Krajacic P, Lamitina T, Purohit P, Shen X

[Neuronal Development, Synaptic Function and Behavior, Madison, WI, 2010]

Previous studies of C. elegans motility have focused mainly on simple quantitative assays, such as the ''thrashing'' assay. More recently, quantitative approaches have been used to study nematode kinematics. Such quantitative approaches could provide a new level of phenotypic resolution to the study of C. elegans motility. We recently developed a simple mathematical model to describe the C. elegans swim gait. This model provides estimates for the biomechanical properties of motility including force, power, tissue viscosity, and Young''s modulus. Here, we used high-speed video as well as image analysis and particle tracking methods to experimentally measure the forces imparted on the surrounding fluid by a swimming C. elegans. Analysis of the local forces (propulsive and lateral) over the wave period is computed by performing a simple force balance and by coupling the fluid velocity field with the nematode body postures. The propulsive force shows a sharp peak as the lateral force approaches zero. The magnitude of the peak propulsive force (i.e. thrust) and the average mechanical power of a swimming nematode in M9 solution are approximately 3.0 nN and 2.0 pW. By comparison, values of force and power estimated using theoretical models are approximately 3.5 nN and 5.0 pW. These data provide experimental validation for our model of motility and demonstrate that biomechanical phenotyping can provide a sensitive and quantitative phenotypic metric for the analysis of C. elegans motility.

Petzold, Bryan C. et al. (2011) International Worm Meeting "Influence of Body Mechanics on Force Thresholds for Touch Sensation in C. elegans."

Park, Sung-Jin, Pruitt, Beth L., Goodman, Miriam B., Petzold, Bryan C.

[International Worm Meeting, 2011]

We assessed the interplay between body mechanics and touch sensitivity by modulating muscle tone with Channelrhodopsin-2 and measuring force thresholds with a novel force-clamp metrology. Touch sensation is poorly understood despite the prevalence of disrupted touch and associated pain in pervasive diseases like diabetes. C. elegans is an ideal model for touch with its six touch receptor neurons (TRNs) and behavioral response to gentle touch. Force applied to the body results in stress/strain of nearby TRNs, triggering opening of force-gated ion channels, cellular depolarization, and an avoidance response for sufficiently large forces. Previously, we developed a behavioral force-clamp metrology capable of applying nN-mN forces to moving L4/young adult animals (Park et al, Rev Sci Instr, in press). Using this metrology, we showed that wild-type (N2) animals respond to forces ³ 100 nN, revealing unprecedented mechanical sensitivity. Previously, we showed that the three-layered outer shell (cuticle, hypodermis, and body wall muscle) plays a crucial role in filtering and transmitting applied forces (Park et al, PNAS 104:17376, 2007) and that body wall muscle tone regulates body mechanics (Petzold et al, Biophys J, in press). Now, we are testing the hypothesis that changes in body mechanics modulate touch sensitivity. To do this, we compare force-response curves in un-stimulated and hyper-contracted animals. Preliminary results show that larger forces are needed to evoke avoidance responses in hyper-contracted animals. We used light to manipulate body wall muscle contraction in transgenic animals expressing ChR2 under the control of a body wall muscle-specific promoter. This study provides a way to study the interplay between body mechanics and touch sensitivity in C. elegans and will further our understanding of the role of the outer shell in filtering and transmitting loads to the TRNs.

How, J.J. et al. (2019) International Worm Meeting "Graph-theoretic analysis of whole-brain imaging reveals stimulus-specific changes in patterns of neural activity."

How, J.J., Navlakha, S., Chalasani, S.H.

[International Worm Meeting, 2019]

Patterned neural activity has been shown to underlie the perception of olfactory stimuli. However, most work to date has focused on early stages of sensory processing, and thus it is unclear how the rest of the nervous system interprets information transduced at the sensory periphery. Here, we used whole-brain calcium imaging of thirty immobilized Caenorhabditis elegans to study how different chemical stimuli induce unique patterns of neural activity. We exposed groups of three worms to one of ten conditions: benzaldehyde (BZ), diacetyl (DA), isoamyl alcohol (IAA), 2-nonanone (NN), or NaCl, at either high or low concentrations. We generated networks that describe the functional interactions between neurons using mutual information, and extracted 22 graph-theoretic properties that characterize the network's functional integration, segregation, and resilience. We identified a few properties that can distinguish between low and high stimulus concentrations, one between attractants (BZ, DA, IAA, and a low concentration of NaCl) and repellents (NN and a high concentration of NaCl), and a third set of properties that can accurately classify the attractants. High concentrations of chemical stimuli tend to induce a network that is more functionally segregated, while repellents induce a network with a shorter path between any two neurons. Furthermore, attractants can be grouped by three different properties - the centrality of an average neuron, how often a strongly connected neuron is connected to weakly connected neurons, and the distance between the furthest apart pair of neurons. Importantly, all of these properties have values that are different from those obtained by analyzing the structural connectivity between neurons in the head of the worm. Thus, we conclude that the structural connectome provides a rich substrate that is employed in very distinct ways to support perception and, ultimately, behavior. Many of these graph-theoretic features deal with how efficiently information is transmitted throughout the C. elegans nervous system, and may reflect the saliency of the stimulus in question.

G Kao et al. (1999) International C. elegans Meeting "Characterization of Laminin beta and gamma Genes."

G Kao, C Huang, WG Wadsworth

[International C. elegans Meeting, 1999]

We have characterized laminin b (lam-1) and laminin g (lam-2) genes. The sequencing project has uncovered genes for one isoform each of the two subunits and two isoforms of laminin a , epi-1 and lam-3. (See abstract by Cheng et al.). This indicates that two types of trimers likely are form in basement membranes : a A bg and a B bg . A hypomorphic mutation (rh219) exists in lam-1, whose phenotypes we have described in previous meetings (IWM 1997). Both lam-1(RNAi) and lam-2(RNAi) animals arrest development during morphogenesis. Significantly, this phenotype is identical to the arrest seen in double knockout of epi-1 and lam-3, and is more severe than either knockout alone. We examined the expression patterns of lam-1 and lam-2 using promoter:GFP fusions. Both genes are expressed in body wall muscles, pharynx, vulval muscles, the rectal muscle group and the distal tip cells. The expression patterns of b and g subunit genes overlap with and are more widespread than either epi-1 or lam-3 alone. Taken together these results suggest that lam-1 and lam-2 are found in all basement membranes and indicate that trimers a A bg and a B bg are formed.

Cho, Jihye et al. (2021) International Worm Meeting "Identify the function of mechanosensitive channel PEZO-1 in C. elegans males"

Cho, Jihye, Kim, Kyuhyung

[International Worm Meeting, 2021]

The conversion of mechanical force to biological signals is crucial for the survival of animals. Mechanosensitive ion channels play a direct role in sensing physical stimuli and are evolutionarily conserved from bacteria to mammals. In mammals, PIEZO channels have been identified as ion channels that directly detect mechanical stimuli (Coste et al., 2010, Gnanasambandam et al., 2015, Syeda et al., 2015). C. elegans genome has a single PIEZO gene, pezo-1, which encodes 14 isoforms (Bai X et al., 2020). However, the function of PEZO-1 in C. elegans has not been fully understood yet. To investigate its function, we first grouped 14 isoforms into short or long isoforms depending on the mRNA length and observed their expression patterns. We found that the promoter region of short isoforms is expressed in several tail neurons, including the 6th ray neurons of C. elegans males. Nine pairs of male ray neurons appear to have functional specialization and have been implicated to be involved in mating behavior (Zhang H, Yue X, Cheng H, et al., 2018). Interestingly, sensory endings of ray 6 neurons, but not other ray neurons, are not exposed to the external environment (Sulston and Horvitz, 1977), suggesting a distinct role in mechanotransduction during C. elegans mating. We are currently examining the contribution of PEZO-1 to mating behavior in males.

Riga, Amalia et al. (2019) International Worm Meeting "The role of basolateral polarity regulators in epithelial tissue homeostasis."

Boxem, Mike, Pires, Helena, Riga, Amalia

[International Worm Meeting, 2019]

Polarization of epithelial cells into apical and basolateral domains is essential for the functioning of epithelia as selectively permeable barriers. The basolateral Scribble group proteins (Scrib, Lgl, Dlg) were originally identified as tumor suppressors in D. melanogaster and were later shown to play key roles in the establishment and maintenance of polarity in a broad range of cell types. In addition to promoting basolateral identity, Scribble group proteins regulate diverse processes including tissue growth, differentiation and directed cell migration, and therefore are major regulators of tissue development and homeostasis. In C. elegans, loss of LET-413/Scrib and DLG-1/Dlg results in defects in epithelial polarization and junction formation during embryonic development, resulting in embryonic lethality. However, their importance in larval epithelia is less well understood. To study the role of LET-413 in larval epithelia, we generated an allele that allows inducible protein degradation using the auxin-inducible system recently developed for C. elegans (1). We find that ubiquitous degradation of LET-413 in larval tissues results in a developmental arrest. Tissue-specific degradation of LET-413 in the larval intestine does not cause defects in development. In contrast, degradation of LET-413 in the seam cells and hypodermis mimics the developmental arrest seen upon ubiquitous LET-413 degradation. Live-cell imaging of seam cells shows a severe effect on outgrowth and reattachment following the L1 asymmetric division. In addition, we observed that loss of LET-413 results in punctate and discontinuous localization pattern of DLG-1, similar to previous observations in C. elegans embryos. We are currently following the effects of LET-413 inactivation on cell recognition and migration pathways to understand the outgrowth defects of the seam cells. (1) Zhang L, Ward JD, Cheng Z, Dernburg AF. Development. 2015 Dec 15;142(24):4374-84.

Robert O'Hagan et al. (2003) International Worm Meeting "In vivo recordings of sensory transduction currents in C. elegans touch cells"

Robert O'Hagan, Martin Chalfie, Miriam B Goodman

[International Worm Meeting, 2003]

Genetic screens have identified 12 genes predicted to encode components of a mechanotransduction complex needed to sense touch along the body. We have recently shown that co-expression of the products of four of these genes (mec-4, mec-10, mec-2, mec-6) in Xenopus oocytes produces an amiloride-sensitive sodium current. However, evidence that these proteins are needed for an amiloride-sensitive channel that responds to mechanical perturbation in vivo has been lacking. We have now recorded from PLM cells in vivo and find that touch evokes an inwardly-rectifying current that is likely to be carried by sodium and appears to be blocked by amiloride. Forces as small as 100 nN are sufficient to elicit an inward current in PLM. This current is unlikely to be a mechanical artifact, since larger forces fail to evoke any obvious change in membrane current in other neurons in the tail. Transduction current adapts rapidly during sustained stimulation. In a manner reminiscent of receptor potentials in Pacinian corpuscles in mammals, both positive and negative changes in force produce an inward current. Preliminary studies also suggest that this current is abolished by mutation of mec-4. We are currently examining the response in cells that lack this and other proteins in the degenerin channel complex, as well as other proteins implicated in the function of these cells. These experiments should allow us to identify touch cell genes needed for the initial transduction event as well as those that act subsequently.