WormBook : the online review of C. elegans biology最新文献

The C. elegans genome contains sequences similar to a large number of mammalian genes implicated in the assembly, processing, and modification of glycans. In recent years, spectacular progress has been made in developing and refining tools to obtain structural information with small amounts of material, increasing our understanding of glycan structural complexity in this organism. These approaches have revealed novel N- and O-glycan structures in C. elegans, as well as a high degree of conservation in glycosaminoglycan structure. In parallel, studies in which glycan structure is perturbed by genetic manipulation have begun to reveal the roles of specific carbohydrate moieties in developmental and physiological processes. This review summarizes recent work elucidating the fine structure of complex carbohydrates in C. elegans as well as genetic studies that have uncovered novel roles for complex carbohydrates in developmental processes.

Clade I nematode species in the genus Trichinella can cause infections in humans that lead to mortality and serious morbidity. There are currently eight recognized species or genotypes that comprise this genus. The species display diverse biological characteristics, the evolutionary significance of which recently has been extensively clarified. Some of that diversity translates into variable importance as zoonotic pathogens, with T. spiralis having the highest significance. Trichinellosis has re-emerged as an important zoonotic infection in various parts of the world, reminding us that control of this infection depends on persistent vigilance. Trichinella species display unique and biologically interesting complexity in interactions with host cells that they inhabit. Significant progress has been made toward understanding details of these interactions. Progress on transcriptomics, proteomics and now genomics offers exciting prospects for accelerating advances in future research. An overview of these parasites regarding biology, significance as zoonotic pathogens and selected research topics is presented here.

C. elegans has a highly developed chemosensory system that enables it to detect a wide variety of volatile (olfactory) and water-soluble (gustatory) cues associated with food, danger, or other animals. Much of its nervous system and more than 5% of its genes are devoted to the recognition of environmental chemicals. Chemosensory cues can elicit chemotaxis, rapid avoidance, changes in overall motility, and entry into and exit from the alternative dauer developmental stage. These behaviors are regulated primarily by the amphid chemosensory organs, which contain eleven pairs of chemosensory neurons. Each amphid sensory neuron expresses a specific set of candidate receptor genes and detects a characteristic set of attractants, repellents, or pheromones. About 500-1000 different G protein-coupled receptors (GPCRs) are expressed in chemosensory neurons, and these may be supplemented by alternative sensory pathways as well. Downstream of the GPCRs, two signal transduction systems are prominent in chemosensation, one that uses cGMP as a second messenger to open cGMP-gated channels, and one that relies upon TRPV channels. These sensory pathways are modulated and fine-tuned by kinases and phosphatases. Chemosensory preferences can be modified by sensory adaptation, developmental history, and associative learning, allowing C. elegans to integrate context and experience into its behavior.

Heterotrimeric G proteins, composed of alpha, beta, and gamma subunits, are able to transduce signals from membrane receptors to a wide variety of intracellular effectors. In this role, G proteins effectively function as dimers since the signal is communicated either by the G alpha subunit or the stable G betagamma complex. When inactive, G alpha-GDP associates with G betagamma and the cytoplasmic portion of the receptor. Ligand activation of the receptor stimulates an exchange of GTP for GDP resulting in the active signaling molecules G alpha-GTP and free G betagamma, either of which can interact with effectors. Hydrolysis of GTP restores G alpha-GDP, which then reassociates with G betagamma and receptor to terminate signaling. The rate of G protein activation can be enhanced by the guanine-nucleotide exchange factor, RIC-8, while the rate of GTP hydrolysis can be enhanced by RGS proteins such as EGL-10 and EAT-16. Evidence for a receptor-independent G-protein-signaling pathway has been demonstrated in C. elegans early embryogenesis. In this pathway, the G alpha subunits GOA-1 and GPA-16 are apparently activated by the non-transmembrane proteins GPR-1, GPR-2, and RIC-8, and negatively regulated by RGS-7. The C. elegans genome encodes 21 G alpha, 2 G beta and 2 G gamma subunits. The alpha subunits include one ortholog of each mammalian G alpha family: GSA-1 (Gs), GOA-1 (Gi/o), EGL-30 (Gq) and GPA-12 (G12). The remaining C. elegans alpha subunits (GPA-1, GPA-2, GPA-3, GPA-4, GPA-5, GPA-6, GPA-7, GPA-8, GPA-9, GPA-10, GPA-11, GPA-13, GPA-14, GPA-15, GPA-16, GPA-17 and ODR-3) are most similar to the Gi/o family, but do not share sufficient homology to allow classification. The conserved G alpha subunits, with the exception of GPA-12, are expressed broadly while 14 of the new G alpha genes are expressed in subsets of chemosensory neurons. Consistent with their expression patterns, the conserved C. elegans alpha subunits, GSA-1, GOA-1 and EGL-30 are involved in diverse and fundamental aspects of development and behavior. GOA-1 acts redundantly with GPA-16 in positioning of the mitotic spindle in early embryos. EGL-30 and GSA-1 are required for viability starting from the first larval stage. In addition to their roles in development and behaviors such as egg laying and locomotion, the EGL-30, GSA-1 and GOA-1 pathways interact in a network to regulate acetylcholine release by the ventral cord motor neurons. EGL-30 provides the core signals for vesicle release, GOA-1 negatively regulates the EGL-30 pathway, and GSA-1 modulates this pathway, perhaps by providing positional cues. Constitutively activated GPA-12 affects pharyngeal pumping. The G alpha subunits unique to C. elegans are primarily involved in chemosensation. The G beta subunit, GPB-1, as well as the G gamma subunit, GPC-2, appear to function along with the alpha subunits in the classic G protein heterotrimer. The remaining G beta subunit, GPB-2, is thought to regulate the function of cer

Electrophysiology provides a quantifiable measure of synaptic activity useful in the functional analysis of synaptic proteins. Recent advances in the application of this technique to C. elegans provides a means of coupling genetics to electrophysiological analysis, providing new insights into the molecular mechanisms regulating neurotransmission. Here we describe a dissection technique that exposes the neuromuscular junctions of C. elegans for electrophysiological analysis. This technique can be adapted to record from virtually any excitable cell in the worm.

Despite the considerable advantages that C. elegans offers for studying gene function in vivo, this system is quite challenging for in vivo electrophysiological analysis of channel function, particularly in neurons. A major problem is that C. elegans neurons are confined in a pressurized and hard-to-penetrate cuticle. Recently, a method for culturing C. elegans embryonic cells has been developed and numerous researchers have already applied this option to study a variety of native ion channels and transporters using various configurations of the patch-clamp technique. C. elegans embryonic cells are obtained from eggs harvested from synchronized gravid adults and then are dissociated using a combination of enzymatic treatment and manual pipetting. Once plated on a surface covered with peanut lectin, cells adhere and differentiate into neurons, muscle and epithelial cells. Cultured embryonic cells recapitulate the expression of differentiation markers and are found in the culture in proportion to their cell type in the mature embryo. Differentiated cells survive well for at least 2 weeks. It should be noted that postembryonic cells do not appear to be generated in these cultures. Cultures can be used for electrophysiological study, testing of pharmacological sensitivities, and for RNAi. C. elegans cell culture thus constitutes the basis for the application of experimental procedures that are not easily applicable to the intact nematode.

Appropriate regulation of mRNA transcription is central to the differentiation and functions of eukaryotic cells, and to the development of complex organisms. mRNAs are synthesized by the coordinated action of a set of general transcription and mRNA modification factors. These factors and the fundamental mechanisms involved in transcription are conserved among eukaryotes, including C. elegans. Recent studies in various systems have revealed that this apparatus is not controlled through a simple on/off "switch" at the promoter, and that the factors and mechanisms involved in transcription are instead subject to regulation at a surprising number of different levels. In this chapter we will discuss examples in which regulation involving the general mRNA transcription apparatus or other transcription co-factors plays a central role in C. elegans development, and in which C. elegans studies have provided new insights into eukaryotic transcription mechanisms. Together, these studies have shown that regulatory mechanisms that involve the general Pol II machinery are a central participant in many aspects of C. elegans biology.

The architecture and dynamics of molecular networks can provide an understanding of complex biological processes complementary to that obtained from the in-depth study of single genes and proteins. With a completely sequenced and well-annotated genome, a fully characterized cell lineage, and powerful tools available to dissect development, Caenorhabditis elegans, among metazoans, provides an optimal system to bridge cellular and organismal biology with the global properties of macromolecular networks. This chapter considers omic technologies available for C. elegans to describe molecular networks--encompassing transcriptional and phenotypic profiling as well as physical interaction mapping--and discusses how their individual and integrated applications are paving the way for a network-level understanding of C. elegans biology.

Oscheius tipulae is a common soil nematode of the same family as C. elegans (Rhabditidae), which presents the same hermaphroditic mode of reproduction and is easily cultured in the same conditions. Oscheius tipulae has been used as a developmental genetic model system to study vulva formation. Compared to C. elegans, it has a simpler vulval cell lineage, a reduced competence group and a different mechanism of vulval cell fate patterning. The spectrum of vulval phenotypes obtained in genetic screens differs from that found in C. elegans. Its easy isolation from soil and the availability of numerous wild isolates of O. tipulae from all over the world facilitate population genetic and microevolutionary studies, especially of the evolution of cell lineage. The Oscheius genus also presents many species with interesting evolutionary changes in mode of reproduction, gonad development, body size, etc.