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[
Genetics,
2020]
Differential gene expression across cell types underlies the development and cell physiology in multicellular organisms. <i>C. elegans</i> is a powerful, extensively used model to address these biological questions. A remaining bottleneck relates, however, to the difficulty to obtain comprehensive tissue-specific gene transcription data, since available methods are still challenging to execute and/or require large worm populations. Here, we introduce the <u>R</u>N<u>A</u><u>P</u>ol Dam<u>ID</u> (RAPID) approach, in which the Dam methyltransferase is fused to a ubiquitous RNA polymerase subunit in order to create transcriptional footprints <i>via</i> methyl marks on the DNA of transcribed genes. To validate the method, we determined the polymerase footprints in whole animals, sorted embryonic blastomeres and in different tissues from intact young adults by driving Dam fusion expression tissue-specifically. We obtained meaningful transcriptional footprints in line with RNA-seq studies in whole animals or specific tissues. To challenge the sensitivity of RAPID and demonstrate its utility to determine novel tissue-specific transcriptional profiles, we determined the transcriptional footprints of the pair of XXX neuroendocrine cells, representing 0.2% of the somatic cell content of the animals. We identified 2362 candidate genes with putatively active transcription in XXX cells, among which the few known markers for these cells. Using transcriptional reporters for a subset of new hits, we confirmed that the majority of them were expressed in XXX and identified novel XXX-specific markers. Taken together, our work establishes RAPID as a valid method for the determination of polymerase footprints in specific tissues of <i>C. elegans</i> without the need for cell sorting or RNA tagging.
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[
Nature,
1996]
What guides migrating nerve axons to their correct targets during development? This is one of the basic issues in developmental neurobiology, and chemoattraction has long been thought to be involved. A tangible answer began to emerge with the demonstration that explants of rat spinal floorplate promoted the outgrowth of axons from commissural neurons, and caused these axons to turn. Subsequently, the specific factors concerned in axon turning were identified. These factors, called netrin-1 and netrin-2, are phlogenetically conserved molecules related to the product of the
unc-6 gene in Caenorhabditis elegans.
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[
Proc Natl Acad Sci U S A,
2022]
In Darwin's and Mendel's times, researchers investigated a wealth of organisms, chosen to solve particular problems for which they seemed especially well suited. Later, a focus on a few organisms, which are accessible to systematic genetic investigations, resulted in larger repertoires of methods and applications in these few species. Genetic animal model organisms with large research communities are the nematode <i>Caenorhabditis elegans</i>, the fly <i>Drosophila melanogaster</i>, the zebrafish <i>Danio rerio,</i> and the mouse <i>Mus musculus.</i> Due to their specific strengths, these model organisms have their strongest impacts in rather different areas of biology. <i>C. elegans</i> is unbeatable in the analysis of cell-to-cell contacts by saturation mutagenesis, as worms can be grown very fast in very high numbers. In <i>Drosophila</i>, a rich pattern is generated in the embryo as well as in adults that is used to unravel the underlying mechanisms of morphogenesis. The transparent larvae of zebrafish are uniquely suited to study organ development in a vertebrate, and the superb versatility of reverse genetics in the mouse made it the model organism to study human physiology and diseases. The combination of these models allows the in-depth genetic analysis of many fundamental biological processes using a plethora of different methods, finally providing many specific approaches to combat human diseases. The plant model <i>Arabidopsis thaliana</i> provides an understanding of many aspects of plant biology that might ultimately be useful for breeding crops.
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[
Genes Nutr,
2006]
Beyond our inherited genetic make-up environmental factors are central for health and disease and finally determine our life span. Amongst the environmental factors nutrition plays a prominent role in affecting a variety of degenerative processes that are linked to aging. The exponential increase of non-insulin-dependent diabetes mellitus in industrialized nations as a consequence of a long-lasting caloric supernutrition is an expression of this environmental challenge that also affects aging processes. The most consistent effects along the environmental factors that slow down aging - from simple organisms to rodents and primates - have been observed for caloric restriction. In the yeast Saccharomyces cerevisiae, the fruit fly Drosophila melanogaster and the nematode Caenorhabditis elegans, sirtuins (silencing information regulators) have been identified to mediate as "molecular sensors" the effects of caloric restriction on aging processes. Sirtuins are NAD(+)-dependent deacetylases that are activated when e.g. cell energy status is low and the NAD(+) over NADH ratio is high. As a consequence transcription rates of a variety of genes including that of the apoptosis inducing p(53) gene are reduced. Moreover, in C. elegans, sirtuins were shown to interact with proteins of the insulin/IGF-1 signaling cascade of which several members are known to extend life span of the nematodes when mutated. Downstream targets of this pathway include genes that encode antioxidative enzymes such as Superoxide dismutase (SOD) whose transcription is activated when receptor activation by insulin/IGF is low or when sirtuins are active and the ability of cells to resist oxidative damage appears to determine their life span. Amongst dietary factors that activate sirtuins are certain polyphenols such as quercetin and resveratrol. Whereas their ability to affect life span has been demonstrated in simple organisms, their efficacy in mammals awaits proof of principle.
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[
Proc Natl Acad Sci U S A,
1978]
Embryogenesis of the free-living soil nematode Caenorhabditis elegans produces a juvenile having about 550 cells at hatching. We have determined the lineages of 182 cells by tracing the divisions of individual cells in living embryos. An invariant pattern of cleavage divisions of the egg generates a set of stem cells. These stem cells are the founders of six stem cell lineages. Each lineage has its own clock-i.e., an autonomous rhythm of synchronous cell divisions. The rhythms are maintained in spite of extensive cellular rearrangement. The rate and the orientation of the cell divisions of the cell lineages are essentially invariant among individuals. Thus, the destiny of cells seems to depend primarily on their lineage history. The anterior position of the site of origin of the stem cells in the egg relates to the rate of the cell cycle clock, suggesting intracellular preprogramming of the uncleaved egg. We used a technique that allows normal embryogenesis, from the fertilized egg to hatching, outside the parent under a cover glass. Embryogenesis was followed microscopically with Nomarski interference optics and high-resolution vidoe recording.
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[
Ecol Dis,
1983]
Medical records concerning filarial diseases in Ceylon date from the account of Davy[1], though there are hints as to the more obvious manifestations in the old chronicles of the country, too. A first survey was conducted in 1912/1913 concentrating on urban areas, followed by a second survey in the 1930s with emphasis on the rural parts. The results displayed a remarkable distribution pattern: Wuchereria bancrofti, the so-called "urban type", concentrated in Galle and Matara towns, whereas Brugia malayi, the "rural type", widespread along the southwest coast from Matara to Negombo, plus isolated pockets in the northwest, central north, east and south. The survey of the 1930s lead to the supposition that the occurrence of B. malayi must have something to do with the distribution of certain water plants, a suspicion later on confirmed in that Pistia stratiotes in particular--but other water plants as well--are essential for the survival of the vector (Taeniorhynchus (Mansonia) uniformis) during its early (submersed) stages of development. A determined effort to remove the water plants from tanks etc. reduced the rural type with encouraging results. At the same time, a combination of factors, in particular the war-time sojourn of masses of troops from Africa, already infected by filarial diseases, in the southwestern coastal areas triggered off an unexpected spread of the urban type out of its early "bridge-heads" in Galle and Matara towns to invade the southwest coastal areas, and, later on, supported by increased population mobility, to advance further inland too. At present, there is no remedy within sight to give some hope to come to grips with this problem as the vector, Culex pipiens fatigans, is ubiquitous and finds suitable breeding grounds practically everywhere. Research into the history of filarial diseases in Ceylon points as far as B. malayi is concerned, to an invasion by a Malayan army under the Kalinga kings during the days of close relations between Ceylon and southeast Asia, i.e. during the 12th and 13th centuries, and as far as W. bancrofti is concerned, a Chinese army, invading the southern coast in the early 15th century, is made responsible. Filarial diseases in Ceylon present a particular interesting case of geomedical research; but inspite of encouraging results in fighting the rural type, i.e. B. malayi, the urban type, W. bancrofti, seems to remain a problem of public health in the island for the forseeable future.
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[
Nat Cell Biol,
2003]
Chordate claudins are core components of tight junctions. By contrast, VAB-9, a nematode four-pass transmembrane protein related to claudins, localizes to adherens junctions and contributes to cell adhesion and actin - plasma membrane association.
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[
Reproduction,
2003]
Gametogenesis is a key developmental process that involves complex transcriptional regulation of numerous genes including many that are conserved between unicellular eukaryotes and mammals. Recent expression-profiling experiments using microarrays have provided insight into the co-ordinated transcription of several hundred genes during mitotic growth and meiotic development in budding and fission yeast. Furthermore, microarray-based studies have identified numerous loci that are regulated during the cell cycle or expressed in a germ-cell specific manner in eukaryotic model systems like Caenorhabditis elegans, Mus musculus as well as Homo sapiens. The unprecedented amount of information produced by post-genome biology has spawned novel approaches to organizing biological knowledge using currently available information technology. This review outlines experiments that contribute to an emerging comprehensive picture of the molecular machinery governing sexual reproduction in eukaryotes.
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[
Proc Natl Acad Sci U S A,
2021]
Electrical synapses are specialized structures that mediate the flow of electrical currents between neurons and have well known roles in synchronizing the activities of neuronal populations, both by mediating the current transfer from more active to less active neurons and by shunting currents from active neurons to their less active neighbors. However, how these positive and negative functions of electrical synapses are coordinated to shape rhythmic synaptic outputs and behavior is not well understood. Here, using a combination of genetics, behavioral analysis, and live calcium imaging in <i>Caenorhabditis elegans</i>, we show that electrical synapses formed by the gap junction protein INX-1/innexin couple the presynaptic terminals of a pair of motor neurons (AVL and DVB) to synchronize their activation in response to a pacemaker signal. Live calcium imaging reveals that <i>
inx-1</i>/innexin mutations lead to asynchronous activation of AVL and DVB, due, in part, to loss of AVL-mediated activation of DVB by the pacemaker. In addition, loss of <i>
inx-1</i> leads to the ectopic activation of DVB at inappropriate times during the cycle through the activation of the L-type voltage-gated calcium channel EGL-19. We propose that electrical synapses between AVL and DVB presynaptic terminals function to ensure the precise and robust execution of a specific step in a rhythmic behavior by both synchronizing the activities of presynaptic terminals in response to pacemaker signaling and by inhibiting their activation in between cycles when pacemaker signaling is low.
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[
East Asia C. elegans Meeting,
2006]
Mitochondria are specialized organelles that are intimately responsible for three important processes: i) ATP production, ii) generation of reactive oxygen species (ROS), and iii) regulation of programmed cell death, or apoptosis. In these processes, it is believed that cellular damage caused by ROS leads to aging. Electrons are transferred ultimately to oxygen after their passage through four complexes that are anchored to the mitochondrial inner membrane. It is known that, in addition to its role as a terminal electron acceptor, oxygen can be converted to superoxide (O<SUB>2</SUB><SUP>-</SUP>) by electrons leaked from complexes I and mainly complex III. Such endogenously generated ROS can readily attack a wide variety of cellular entities, resulting in damage that compromises cell integrity and function. To explore the role that mitochrondrial energetics and superoxide anion production play in the aging, we assessed change of mitochondrial structure and function of wild-type <U>C. elegans</U>. Ultrastructural analyses reveal the presence of enlarged mitochondria, presumably produced by fusion events. Two key mitochondrial functions--the activity of electron transport chain complexes I and II; oxygen consumption--decreased as animals aged. Carbonylated proteins, one byproduct of oxidative stress, accumulated in mitochondria much more than in the cytoplasm, which is consistent with the notion that mitochondria are the primary source of endogenous free radicals. In contrast to these anticipated events, the level of mitochondrially generated superoxide anion did not change significantly during aging, suggested that superoxide anion generated constantly accumulates oxidative damages chronologically. In concert, these data support the notion that the mitochondrial function is an important aging determinant.