Mechanotransduction in Caenorhabditis elegans

One of the looming mysteries in signal transduction today is the question of how mechanical signals, such as pressure or mechanical force delivered to a cell, are interpreted to direct biological responses. All living organisms, and probably all cells, have the ability to sense and respond to mechanical stimuli. At the single-cell level, mechanical signaling underlies cell-volume control and specialized responses such as the prevention of poly-spermy in fertilization. At the level of the whole organism, mechanotransduction underlies processes as diverse as stretch-activated reflexes in vascular epithelium and smooth muscle; gravitaxis and turgor control in plants; tissue development and morphogenesis; and the senses of touch, hearing, and balance. Intense genetic, molecular, and elecrophysiological studies in organisms ranging from nematodes to mammals have highlighted members of the recently discovered DEG/ENaC family of ion channels as strong candidates for the elusive metazoan mechanotransducer. Here, we discuss the evidence that links DEG/ENaC ion channels to mechanotransduction and review the function of Caenorhabiditis elegans members of this family called degenerins and their role in mediating mechanosensitive behaviors in the worm.     

Globins in Caenorhabditis elegans

Extensive in silico search of the genome of Caenorhabditis elegans revealed the presence of 33 genes coding for globins that are all transcribed. These globins are very diverse in gene and protein structure and are localized in a variety of cells, mostly neurons. The large number of C. elegans globin genes is assumed to be the result of multiple evolutionary duplication and radiation events. Processes of subfunctionalization and diversification probably led to their cell-specific expression patterns and fixation into the genome. To date, four globins (GLB-1, GLB-5, GLB-6, and GLB-26) have been partially characterized physicochemically, and the crystallographic structure of two of them (GLB-1 and GLB-6) was solved. In this article, a three-dimensional model was designed for the other two globins (GLB-5 and GLB-26), and overlays of the globins were constructed to highlight the structural diversity among them. It is clear that although they all share the globin fold, small variations in the three-dimensional structure have major implications on their ligand-binding properties and possibly their function. We also review here all the information available so far on the globin family of C. elegans and suggest potential functions.     

Coccidian assemblages in the Wyoming ground squirrel, Spermophilus elegans elegans.

One thousand nineteen Wyoming ground squirrels (Spermophilus elegans elegans) from 4 populations in southern Wyoming were examined for intestinal parasites. The most prevalent parasites were 6 species of coccidia: Eimeria beecheyi, Eimeria bilamellata, Eimeria callospermophili, Eimeria larimerensis, Eimeria morainensis, and Eimeria spermophili. Most ground squirrels harbored 2 or more species. This eimerian assemblage was present across populations and over years. Differences in the prevalence of infection were not found among host age classes or between sexes. The presence or absence of helminths was independent of the presence and absence of Eimeria. A log-linear model to test the independence of the distribution of Eimeria spp. among hosts revealed 3 significant positive associations, for E. bilamellata and E. beecheyi, E. morainesis and E. callospermophili, and E. larimerensis and E. bilamellata.     

Sex Determination in Caenorhabditis elegans

In Caenorhabditis elegans, the decision to develop as a hermaphrodite or male is controlled by a cascade of regulatory genes. These genes and other tissue-specific regulatory genes also control sexual fate in the hermaphrodite germline, which makes sperm first and then oocytes. In this review, we summarize the genetic and molecular characterization of these genes and speculate how they mutually interact to specify sexual fate.     

Cryoprotectant toxicity in Caenorhabditis elegans

We have looked at the effects of the cryoprotectant M22 upon viability in the model organism C. elegans. M22 is a well-known vitrification solution which has been successfully used in the laboratory to preserve organs destined for transplantation. M22 reduces survival of C. elegans in a concentration-dependent manner. M22 at concentrations of 10% (v/v) or higher inhibits progeny production and development. A few mutants in the ILS (insulin-like signaling) pathway of C. elegans are more resistant to the toxic effect of M22 compared to wild-type worms. Afatinib, an anti-cancer drug, protects against M22 toxicity. Afatinib by itself does not increase longevity.     

State-dependency in C. elegans

Memory and the expression of learned behaviors by an organism are often triggered by contextual cues that resemble those that were present when the initial learning occurred. In state-dependent learning, the cue eliciting a learned behavior is a neuroactive drug; behaviors initially learned during exposure to centrally acting compounds such as ethanol are subsequently recalled better if the drug stimulus is again present during testing. Although state-dependent learning is well documented in many vertebrate systems, the molecular mechanisms underlying state-dependent learning and other forms of contextual learning are not understood. Here we demonstrate and present a genetic analysis of state- dependent adaptation in Caenorhabditis elegans. C. elegans normally exhibits adaptation, or reduced behavioral response, to an olfactory stimulus after prior exposure to the stimulus. If the adaptation to the olfactory stimulus is acquired during ethanol administration, the adaptation is subsequently displayed only if the ethanol stimulus is again present. cat-1 and cat-2 mutant animals are defective in dopaminergic neuron signaling and are impaired in state dependency, indicating that dopamine functions in state-dependent adaptation in C. elegans.     

Innexins in C. elegans

Innexins are functionally analogous to the vertebrate connexins, and the innexin family of gap junction proteins has been identified in many invertebrates, including Drosophila and C. elegans. The genome sequencing project has identified 25 innexins in C. elegans. We are particularly interested in the roles that gap junctions may play in embryonic development and in wiring of the nervous system. To identify the particular C. elegans innexins that are involved in these processes, we are examining their expression patterns using specific antibodies and translational GFP fusions. In addition we are investigating mutant, RNAi and overexpression phenotypes for many of these genes. To date, we have generated specific antibodies to the non-conserved carboxyl termini of 5 innexins. We have constructed GFP translational fusions for 17 innexins and observed expression patterns for 13 of these genes. In total we have characterized expression patterns representing 14 innexins. Mutations have been identified in 5 of these genes, and at least 3 others have RNAi mutant phenotypes. Generalities emerging from our studies include: 1) most tissues and many individual cells express more than one innexin, 2) some innexins are expressed widely, while others are expressed in only a few cells, and 3) there is a potential for functional pairing of innexins.     

Deciphering endocytosis in Caenorhabditis elegans

We discuss in this review recent studies using the worm Caenorhabditis elegans to decipher endocytic trafficking in a multicellular organism. Recent advances, including in vivo assay systems, new genetic screens, comparative functional analysis of conserved proteins, and RNA-mediated interference (RNAi) in C. elegans, are being used to study the functions of known membrane trafficking factors and to identify new ones. The ability to monitor endocytosis in vivo in worms allows one to test current endocytosis models and to demonstrate the physiological significance of factors identified by genetic and biochemical methods. The available human genome sequence facilitates comparative studies where human homologs of new factors identified in C. elegans can be quickly assayed for similar function using traditional cell biological methods in mammalian cell systems. New studies in C. elegans have used a combination of these techniques to reveal novel metazoan-specific trafficking factors required for endocytosis. Many more metazoan-specific trafficking factors and insights into the mechanisms of endocytosis are likely to be uncovered by analysis in C. elegans .     

Touch sensation in Caenorhabditis elegans

The nematode C. elegans exhibits a variety of reponses to touch. When specific sets of mechanosensory neurons are killed with a laser, specific touch responses are abolished. Many mutations that result in defective mechanosensation have been identified. Some of the mutations define genes that specify the fate of a set of mechanoreceptors called the touch cells, which mediate response to light touch to the body of the worm. Genes specifying touch cell fate appear to regulate genes that encode touch-cell differentiation proteins, including apparent subunits of a touch-cell-specific ion channel, rare mutant forms of which lead to swelling and lysis of the touch cells. Molecular attachments of the ion channel, both to extracellular matrix components and, intracellularly, to a special large-diameter microtubule, may be required for mechanical gating of the channel. A mechanoreceptor-interneuron-motorneuron reflex circuit for response to light touch has been proposed.     

7Beta-oxygenated limonoids from Trichilia elegans ssp. elegans

Five 7beta- and 7alpha-oxygenated obacunone-type limonoids were obtained on reinvestigation of the seeds of Trichilia elegans ssp. elegans: 7-deoxo-7beta-acetoxykihadanins A and B, 7-deoxo-7beta-hydroxykihadanins A and B and 7-deoxo-7alpha-hydroxykihadanin A, the last three being isolated after acetylation procedures as their mono- and/or diacetate derivatives. This is the first report of the natural occurrence of C-7 beta-substituted limonoids without any oxygenated function at C-6. The structures of these compounds have been established on the basis of 1D- and 2D-NMR spectral techniques, ESI-mass spectrum and X-ray crystallographic data.     

UeberRoylea elegans Wall

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UeberRoylea elegans Wall

Ohne Zusammenfassung     

UeberRoylea elegans Wall

Ohne Zusammenfassung