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[
International Worm Meeting,
2013]
Well-fed, mate-deprived adult males make the risky choice to leave a plentiful source of food to explore their environment in search of mates. In contrast, recent experience with a mate while exposed to food produces a durable behavioral switch that restricts exploration within the limits of the food source. From a forward genetic screen for males that do not leave food (leaving assay defective -las), we isolated several mutants. We have recently shown that
las-1(
bx142) encodes a secretin-like G protein-coupled receptor for the neuropeptide pigment dispersing factor (
pdf-1). Male exploratory behavior results from the balance of two physiological needs -feeding and reproduction- that compete for the control of a distributed network for navigation. The phenotype of
pdfr-1 males reflects an imbalance in the relative contribution of the circuits that control exploration.
pdfr-1 is required in gender-shared sensory neurons PHA, PQR and URY to generate the state of arousal to leave food in search of mates. Thus,
pdfr-1 modulates a circuit that senses the internal environment of the animal and antagonizes the food-sensing circuit (Barrios et al., 2012, DOI 10.1038/nn.3253). We are currently identifying the molecular lesion responsible for the phenotype of
las-2(
bx143). We have mapped
bx143 to the distal left arm of chromosome I and through whole genome sequencing we have identified missense mutations in two candidate genes. Rescue experiments and complementation tests with these two candidates are under way.
bx143 males display normal locomotion on food but are strongly Las and mate response defective with no apparent morphological defects. These phenotypes suggest a role for
bx143 in the regulation of the neural circuits that convey male sex drive.
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Albertson, Donna G., Wang, Yi, Hall, David H., Xu, Meng, Thomson, Nicole, Emmons, Scott W., Jarrell, Travis
[
International Worm Meeting,
2009]
For many biological systems knowledge of structure is key to understanding function. It was Sydney Brenner''s insight that the structure of the C. elegans nervous system could be determined and analyzed by means of genetics that provided the inspiration for C. elegans research (Brenner, 1974). For over 20 years, the completed wiring diagram of the C. elegans hermaphrodite has afforded a unique basis for genetic studies of worm behavior. Among C. elegans behaviors, the most complex motor program is the multi-step mating behavior of the male. Reconstruction of the male nervous system was initiated along with that of the hermaphrodite in the 1970''s (Sulston, Albertson and Thomson, 1980), but its completion has awaited development of the modern PC. Using electron micrographs from the MRC we digitized and analyzed using a software platform for annotation of electron micrographs from the computer screen, we have determined the connectivity among the neurons and muscles in the male tail, the posterior connectome. Reconstruction of the anterior nervous system is underway. The male posterior connectome consists of the interconnections among the processes of 175 neurons (85 male-specific and 90 shared with the hermaphrodite) and 65 muscles (41 male-specific and 24 shared). These cells are joined together in a complex network by some 8000 synapses, 4000 chemical and 4000 electrical, more than are contained in the entire hermaphrodite nervous system. The networks of chemical and electrical synapses are largely overlapping, suggesting parallel routes of information transfer and processing. Male-specific and shared neurons and muscles are fully integrated together in the network. Many of the shared neurons are sexually dimorphic, not only in having a more branching architecture and having synapses with male-specific neurons and muscles, but also in lacking some and gaining other synaptic interactions amongst themselves. In spite of its complex network architecture, potential circuits for the various steps of the mating program can be discerned in the connectivity diagram, in some cases revealing previously unsuspected roles for individual neurons or classes of neurons. The results provide an unprecedented opportunity not only to understand how a decision-making, multifunctional neural network processes sensory information in a coherent manner, selecting a choice among alternate behavioral outputs in a goal-oriented behavior, but also an opportunity and a challenge to understand how this incredibly complex structure, the connectome, is specified by the genome.
-
[
WormBook,
2005]
The features that differentiate the C. elegans male from the hermaphrodite arise during postembryonic development. The major male mating structures, consisting of the blunt tail with fan and rays, the hook, the spicules and proctodeum, and the thin body, form just before the last larval molt. Male and hermaphrodite embryogenesis are similar but some essential male cell fates are already established at hatching. The male mating structures arise from three important sets of male-specific blast cells. These cells generate a total of 205 male-specific somatic cells, including 89 neurons, 36 neuronal support cells, 41 muscles, 23 cells involved in differentiating the hindgut, and 16 hypodermal cells associated with mating structures. Genetic and molecular studies have identified many genes required for male development, most of which also function in the hermaphrodite. Cell-cell interactions play a role in patterning all three of the generative tissues. Male-specific neurons, including sensory neurons of the rays, hook, post-cloacal sensilla, and spicules, differentiate at the end of the last larval stage and send out axons to make connections into the existing neuropil, greatly enlarging the posterior ganglia. The hindgut is highly differentiated to accommodate the spicules and the joining of the reproductive tract to the cloaca. A complex male-specific program generates many new muscles for copulation. The cell lineage and genetic program that gives rise to the one-armed male gonad appears to be a variation on that of the hermaphrodite.
-
[
International C. elegans Meeting,
2001]
In 1986, John White and coworkers published their reconstruction of connectivity in the nervous system of the C. elegans hermaphrodite. Since that time, only limited further reconstruction has been carried out. This has included determination of some posterior circuitry governing male mating behavior (Sulston et al., 1980) and outgrowth patterns in the developing embryonic nervous system (Norris et al., 1997 International Meeting). Complete connectivity remains unknown for the adult male and for all larval and embryonic stages. Full knowledge of connectivity is becoming increasingly important as studies of nervous system development and function advance and attempts are made to understand how the nervous system generates and controls complex behaviors. Sexual dimorphism of the nervous system is of particular interest. As part of the efforts in many areas to provide a complete description of the worm, we have undertaken to define additional circuitry within the nervous system. For nervous system reconstruction, the course of neuron processes and the chemical and electrical contacts that they make are determined by following processes through a series of electron micrographs of serial thin sections of fixed worms. In the original work, although a computerized system was developed for analyzing the electron microscopic images and compiling the data (J. White, PhD Thesis, 1974), it did not prove to be greatly superior to hand reconstructions, which were used for much of the analysis. Times have changed computerwise since the early 1970s, and we plan to return to a computer-aided approach and attempt to accelerate the reconstruction process by computerizing as many steps as possible. Serial thin sectioning and electron microscopy will continue to be carried out as before, and identification of neurite profiles and contacts in the images will also be done by visual inspection, but images will be digital and all steps subsequent to process and contact identification will be entirely in digital format. We hope that use of the computer will speed the reconstruction not only by promoting facile data storage, handling, and retrieval, but also by allowing simultaneous reconstruction and data entry that would make it possible for the computer to perform a kind of grammar checking on new data (e.g. no process can have greater than or less than one cell body) and consistency checking (e.g. with known pathways derived from previous reconstructions and GFP reporters). We plan to develop hardware and software and test it by attempting initially to reconstruct the preanal ganglion of the adult male. This ganglion contains circuitry serving to program male mating behavior that is as complex as that found in the nerve ring. The male tail contains 48 sensory neurons with axon processes targeted to this ganglion. Liu and Sternberg (1995) defined the relationship of inputs from these sensory neurons to the sequential steps of copulatory behavior. In our reconstruction, we hope to determine the targets of these sensory neurons and trace neuronal pathways to the copulatory muscles. If we are successful in making extensive additional reconstruction feasible with reasonable time and effort, our long term goal will be to trace male-specific interneurons into the nerve ring and determine how they influence central circuitry, as well as to undertake reconstruction of the L1 larva and other important stages.
-
[
East Coast Worm Meeting,
2002]
The original reconstruction of connectivity in the C. elegans hermaphrodite nervous system was mostly carried out by marking individual neuron profiles by hand on electron micrographic prints. This effort, undertaken primarily at the MRC Laboratory of Molecular Biology in Cambridge, England, involved a staff of 6-8 people and required 15 years. While some limited analysis of the developing nervous system and of mutants has been performed since that time, no further attempts have been made to define complete connectivity, which remains largely unknown in juvenile stages and in the adult male. To obtain further reconstructions, it is necessary to speed up the process of reconstruction many-fold. To achieve this, we have undertaken to develop computer aided methodology. Embedding, sectioning, and electron microscopy will be carried out as before. Digital analysis begins by scanning electron micrographic negatives. Neuron profiles are identified by an investigator and their positions marked by a single X,Y coordinate or their profiles may be traced. 3D reconstructions are then generated from the aligned series of images. Improved reconstruction methods will be applied to the original photographic images from Cambridge, which are now housed at the Albert Einstein College of Medicine, as well as to new images. On the Cambridge prints, which include a complete set of photographs of the adult male tail (1), as well as many valuable unpublished studies of mutants, corresponding profiles in adjacent sections are already marked by colored pen. For rapid analysis of new series, it will be essential to develop computer algorithms to aid the process of identifying correspondence between sections. As an objective to test our methodology, we have chosen to reconstruct the preanal ganglion of the adult male, which contains the circuitry that processes inputs from a variety of specialized sensillae, including the rays, hook and post-cloacal sensilla (1). Nematode neuron processes are very small (0.1-0.2m diameter), similar in size to the finest terminal branches in mammalian dendrites. They are mostly unbranched, synapses being formed at en passant swellings. In the male, the preanal ganglion is a cylindrical neuropil some 20m in diameter and 60m in length. A typical transverse section contains the profiles of 100-200 neurites, which here, atypically, form a significant number of branches. Our progress in reconstructing this circuitry from the available series of several thousand electron micrographs from the MRC will be reported.
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[
Worm Breeder's Gazette,
1993]
Cloning of the
lin-32 gene Connie Zhao and Scott W. Emmons, Department of Molecular Genetics, Albert Einstein College of Medicine, 1300 Morris Park Ave., Bronx, NY 10461
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[
International Worm Meeting,
2003]
A major effort was made in the late 1970s at the MRC Laboratory of Molecular Biology, Cambridge, England, to reconstruct the nervous system of the adult C. elegans male. This project has recently been resumed at the Albert Einstein College of Medicine. In the earlier work, a set of complete low-power and high-power prints were generated and partially analyzed (Sulston, J.E., Albertson, D.G., and Thomson, J.N. Dev. Biol. 78, 542-576, 1980). Not included in the earlier results were the postsynaptic targets of the rays. Thirty six ray sensory neurons with sensory endings in the nine bilateral pairs of rays provide major input signaling physical contact with the hermaphrodite during copulation. The ray neurons are of two ultrastructural types, but neurons of each type have different subtype properties in the different rays. For example, the neurotransmitters dopamine, serotonin, and multiple FMRFamides are each expressed in different subsets of the rays (see abstract by Lints and Emmons). This complexity raises the question whether each ray also has a unique set of postsynaptic targets. To examine this question, we compiled the axonal output of the rays from the existing data. Ray cell bodies are located in a bilateral pair of lumbar ganglia and extend axonal processes ventrally through circumferential commissures to the centrally-located, ventral preanal ganglion. There they branch and synapse with multiple postsynaptic target cells. Such branching is unusual for most C. elegans neurons but common for male-specific neurons in the preanal ganglion. Reconstruction of the neurons from most of the rays reveals that each ray neuron contacts from 3 to 8 postsynaptic target cells, and the pattern of targets is different for neurons from different rays. Thus the output of the rays to the circuitry generating copulatory behavior is complex. Computer software is being prepared to aid further reconstruction efforts. Our goal at this stage is to complete the analysis of the existing electron micrographs to provide a wiring diagram for the neurons and circuitry in the male tail.
-
[
Worm Breeder's Gazette,
1994]
C. elegans Molecular Genetics and Long PCR Scott R. Townsend, Cathy Savage, Alyce L. Finelli, Ting Xie, and Richard W. Padgett, Waksman Institute and Department of Molecular Biology and Biochemistry, Rutgers University, Piscataway, NJ 08855
-
[
Worm Breeder's Gazette,
1994]
Strain names for non-C. elegans species Scott W. Emmonst, Armand Leroit, and David Fitch, Department of Molecular Genetics, Albert Einstein College of Medicine, 1300 Morris Park Ave., Bronx, NY 10461, Department of Biology, New York University, RmlOO9 Main Bldg., Washington Square, New York, NY 10003
-
[
Worm Breeder's Gazette,
1983]
As starting points for the molecular cloning of
lin-12 III and
tra-1 III, we have identified several Tc1 polymorphisms linked to these genes. Genomic DNA was prepared from appropriate Bristol/Bergerac hybrid strains, cut with EcoRI, and probed with Tc1 (kindly provided by Scott Emmons). Our data are summarized in the maps below, which give the approximate map locations and EcoRI fragment sizes of the Bergerac-specific Tc1's. [See Figure 1]