Hirsh DI et al. (1977) "Expression of genes essential for early development in the nematode, C. elegans."

Hirsh DI, Hecht RM, Vanderslice R, Carr SH, Wood WB

[1977]

Genetic tests for maternal effects have been performed on 25 temperature-sensitive zygote-defective mutants of the nematode Caenorhabditis elegans. For most of the genes defined by these mutants (22 out of 25), maternal expression is sufficient for zygote survival, even if the gene is not expressed in the zygote. Twelve of these 22 genes must be expressed in the mother for zygote survival (strict maternals). For the remaining ten, expression either in the mother or in the zygote is sufficient for survival. One mutant shows a paternal effect in which wild-type sperm cytoplasm appears to rescue mutant zygotes. Maternal effect tests on mutants that block as late as the second larval stage after hatching indicate that in 3 of 11 mutants maternal contributions still can rescue mutant progeny. Temperature shift experiments on the zygote-defective embryos show that all but one of the strict maternal mutants are temperature sensitive only before gastrulation. One of the mutants that can be rescued by gene expression in the zygote is temperature sensitive prior to gastrulation, suggesting that some zygote genes can function in early embryogenesis.

Siddiqui SS (1989) "Axonal outgrowth and process placement of sensory lumbar neurons in the nematode Caenorhabditis elegans."

Siddiqui SS

[1989]

One of the most remarkable features of the brain is the degree of precision with which neurons are interconnected. As the neural circuitry of the nematode Caenorhabditis elegans has been completely established through serial section electron micrographs, and because the nematode is amenable to genetic analysis, it is an excellent system to study the genetic basis of axonal outgrowth and process placement in the formation of a neural network. Here, I will describe the identification of 11 genes which affect the axonal outgrowth and guidance of five pairs of lumbar neurons in C. elegans. A pair of bilaterally symmetric luumbar ganglia are situated in the tail of C. elegans, each consisting of 12 neurons. We have examined the morphology and pattern of axonal processes of three embryonic (PHA, PHB, and PLM) and two postembryonic (PHC and PVN) lumbar neurons on the wild type and existing uncoordinated (unc) mutants, immunocytochemically. We have earlier shown that antibodies against horseradish peroxidase (HRP) stain PHA, PHB, PHC and PVN neurons, and monoclonal antibodies specific to different tubulin isotypes stain the mechanosensory neuron PLM. A monoclonal antibody TY21, raised against C. elegans crude homogenate is specific for phasmid neurons PHA, and PHB. In the wild type, PHA, PHB, PHC, and PVN send anteriorly directed processes ventrally via the lumbar commissures to targets in the ventral cord; whereas, PLM sends a process anteriorly in a subventral position, sending a branch ventrally to the ventral cord near the vulva. PHA, PHN, PHC, and PLM are bipolar neurons, extend a backward process into the tail spike. Mutations in nine genes (unc-6, unc-13, unc-33, unc-44, unc-51, unc-61, unc-71, unc-73, and unc-98) result in abnormal axonal outgrowth and process placement of PHC, PCN and PLM neurons. Four (unc-6, unc-33, unc-44, and unc-51) of the nine genes identified above, and unc-76 were previously shown to affect the growth of PHA and PHB neurons. Mutants in unc-53, which are apparently normal in the growth of PHA, PHB, PHC, and PVN neurons, and unc-76, harbor defects in PLM axonal outgrowth and guidance. In summary, we have identified a set of 11 genes, which exert overlapping, but distinct effects on the axonal outgrowth and process placement of embryonic (PHA, PHB, and PLM), and postembryonic (PHC and

Ward S (1977) "Use of nematode behavioral mutants for analysis of neural function and development."

Ward S

[1977]

The soil nematode Caenorhabditis elegans was selected 11 years ago by Sydney Brenner as an experimental organism suitable for the isolation of many behavioral mutants and small enough for anatomical analysis of such mutants with the electron microscope. Two distinct goals motivated the initial studies of this organism: first, the hope that some of the mutants would have simple anatomical alterations that could be directly correlated with their behavioral defects, allowing the assignment of specific functions to specific neurons, and second, the hope that the detailed analysis of the kinds of alterations induced by individual mutations and the classes of cells affected by given mutations would reveal general features of the genetic program that specifies the development of the organism. Over the past 11 years the number of investigators working on C. elegans has increased to about 75 and is still growing. Nearly 3,000 different mutants have been isolated and different investigators are pursuing their effects on different cells. My own research is in the development of the nervous system. In particular, I would like to learn something about the workings of the complex black box that connects individual genes to the determination of the morphology of developing neurons. Are there gene products whose specific function is to determine the morphology of cells? If so, what are these gene products and how do they act in the developing cell? One would anticipate that mutations in such hypothetical genes would cause specific morphological alterations in cells. Because the morphology of a neuron determines its function, by selecting behavioral mutants altered in the function of the nervous system one might commonly find mutants that alter the morphology of neurons, and some of these might be in specific morphological genes. It is my hope that it will be possible to compare such mutants to the wild type in order to identify the defective gene products and thereby learn something about the role of normal gene products in determining the development of neurons. In this paper I will first summarize the results of several years' work on one specific class of mutants in the nematode, sensory mutants, work performed both in my laboratory and that of my colleagues Jim Lewis and Jonathan Hodgkin. Second, I will discuss frankly some of the difficulties and frustrations we have experienced in trying to interpret the effects of these specific mutants. Some of these difficulties illustrate problems endemic to genetic studies of development. Third, I will describe the more recent work performed in my labortory that is being directed toward genetic analysis of the structure and function of a

Marks NJ et al. (2010) Adv Exp Med Biol "Neuropeptides in helminths: occurrence and distribution."

Marks NJ, Maule AG

[Adv Exp Med Biol, 2010]

Nematode neuropeptide systems comprise an exceptionally complex array of approximately 250 peptidic signaling molecules that operate within a structurally simple nervous system of approximately 300 neurons. A relatively complete picture of the neuropeptide complement is available for Caenorhabditis elegans, with 30 flp, 38 ins and 43 nlp genes having been documented; accumulating evidence indicates similar complexity in parasitic nematodes from clades I, III, IV and V. In contrast, the picture for parasitic platyhelminths is less clear, with the limited peptide sequence data available providing concrete evidence for only FMRFamide-like peptide (FLP) and neuropeptide F (NPF) signaling systems, each of which only comprises one or two peptides. With the completion of the Schmidtea meditteranea and Schistosoma mansoni genome projects and expressed sequence tag datasets for other flatworm parasites becoming available, the time is ripe for a detailed reanalysis ofneuropeptide signalingin flatworms. Although the actual neuropeptides provide limited obvious value as targets for chemotherapeutic-based control strategies, they do highlight the signaling systems present in these helminths and provide tools for the discovery of more amenable targets such as neuropeptide receptors or neuropeptide processing enzymes. Also, they offer opportunities to evaluate the potential of their associated signaling pathways as targets through RNA interference (RNAi)-based, target validation strategies. Currently, within both helminth phyla, theflp signaling systems appear to merit further investigation as they are intrinsically linked with motor function, a proven target for successful anti-parasitics; it is clear that some nematode NLPs also play a role in motor function and could have similar appeal. At this time, it is unclear if flatworm NPF and nematode INS peptides operate in pathways that have utility for parasite control. Clearly, RNAi-based validation could be a starting point for scoring potential target pathways within neuropeptide signaling for parasiticide discovery programs. Also, recent successes in the application of in planta-based RNAi control strategies for plant parasitic nematodes reveal a strategy whereby neuropeptide encoding genes could become targets for parasite control. The possibility of developing these approaches for the control of animal and human parasites is intriguing, but will require significant advances in the delivery of RNAi-triggers.

Paul W. Sternberg (2005) WormBook "Vulval development."

Paul W. Sternberg

[WormBook, 2005]

C. elegans vulval development is an intensively studied example of animal organogenesis. A network of intercellular signaling, signal transduction, and transcriptional regulation underlies the precise formation of this organ, which is the connection between the hermaphrodite uterus and the outside of the nematode. A single cell of the somatic gonad, the anchor cell, organizes the development of the vulva from epidermal precursors as well as the physical connection of the epidermis with the uterus. WNT signaling acting via the HOX gene lin-39 renders six epidermal precursor cells competent to respond to other developmental signals. The anchor cell induces nearby epidermal precursor cells to generate vulval cells via an epidermal growth factor (EGF) signaling pathway. The precise pattern of vulval precursor cell fates involves the graded action of the EGF signaling and LIN-12 (Notch) mediated lateral signaling. EGF promotes the 1 fate while LIN-12 promotes the 2 fate. Both EGF and LIN-12 prevent precursor cells from adopting the 3 fate, which generates non-specialized epidermis. EGF-receptor and Notch signaling are antagonistic: EGF-receptor signaling leads to down-regulation of the Notch-like receptor LIN-12 , while LIN-12 signaling induces negative regulators of EGF-receptor signaling such as MAP kinase phosphatase LIP-1 and the tyrosine kinase ARK-1. The 1 precursor cell generates vulE and vulF mature vulval cells; the pattern of vulE and vulF cells requires an additional signal from the anchor cell as well as WNT signaling. The two 2 precursor cells generate vulA, vulB1, vulB2, vulC and vulD cells but in mirror symmetric polar patterns: ABCD and DCBA. The reversed polarity of the posterior 2 precursor cell lineage requires WNT signaling mediated by both Frizzled class and Ryk class WNT-receptors LIN-17 and LIN-18 , respectively. A network of transcription factors controls the seven mature adult cell types; these include the LIM domain protein LIN-11 , the Pax2/5/8 protein EGL-38 , the zinc finger protein LIN-29 , and the Nkx6.1/6.2 protein COG-1. The anchor cell also patterns nearby uterine cells, via the DSL ligand LAG-2 and LIN-12 , to generate the four uv1 cells that form the tight connection with the vulva. This connection is initiated by the anchor cell, which invades between the vulF cells in a process analogous to invasive behavior of metastatic tumor cells. During this invasion process, the basement membranes between the gonad and body wall are degraded. The extensive information about vulval development in C. elegans has helped it become a paradigmatic case for identifying and studying a variety of regulatory pathways.

Luo Y et al. (2009) "Caenorhabditis elegans Model for Initial Screening and Mechanistic Evaluation of Potential New Drugs for Aging and Alzheimers Disease."

Link CD, Luo Y, Wu Y, Brown M

[2009]

Although the worms may not be universally accepted as having a direct relevance for AD pathology, they are well suited for validation of target A toxicity in vivo [12,21]. The absence of endogenous A production in the worms offers an opportunity to find a direct role of the A involvement in pathological behaviors [22]. In addition, predominantly intracellular expression of A provides another tool to address specific roles of intracellular A in relation to its toxicity. Substantial evidence implicates intracellular A oligomers in early events related to AD [16]. Intracellular A has also been observed in human brain neurons [23] and in triple transgenic AD mouse models, where its accumulation preceded neurofibrillary tangle formation [24]. This evidence supports the notion that A toxicity assayed in the worm model reflects A toxicity in mammalian neurons. A recent study indicates that the transgenic C. elegans model may be generally relevant to the proteotoxicity underlying neurodegenerative diseases [25]. Additionally, the strain has been used to investigate the role of insulin-like signaling and heat-shock factor in A proteotoxicity [26,27], providing excellent examples for the relevance of the C. elegans model to AD. There are several advantages of C. elegans over the mouse model for initial drug screening and target characterization. First, there are highly conserved biochemical pathways between worms and humans. Second, established transgenic mutant linking of human A expression with pathological behavioral phenotypes are easy to score. The worms have a relatively low cost of cultivation because of their small size, rapid life cycle, and short life span [28], which allow screening of thousands of animals over multiple generations on microtiter plates. The simple structure of its nervous system, consisting of only 302 neurons in an adult nematode, makes it valuable for screening drugs against age-associated neurodegeneration and the ease of genetic manipulations, which is evident in the availability of mutants and application of RNA interference (RNAi) knockdown. Several examples illustrate the power of C. elegans in screening for new drugs [29], including many known human drugs [30,31]. Some lead molecules originating from worm-based screening assays are in advanced stages of drug discovery [11]. Using the C. elegans model in the past years, we have uncovered effects of natural compounds on extension of the worms' life span; [32] on a stress response protein, the small heat-shock protein hsp-16.2; [33] on age-related behavioral declines; [34] on muscle degeneration; [35] and on A-expression-induced pathological behaviors [22]. Most of those experiments would be difficult and might be impossible to perform in mice. In this chapter, we describe methods we have employed for compound screening and pharmacological evaluations of potential AD drugs using the C. elegans model.