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[
Worm Breeder's Gazette,
1998]
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[
Worm Breeder's Gazette,
1977]
Two young adult C. elegans have been serially sectioned and reconstructed from the tail tip forward through the anterior end of the pre-anal ganglion. Thirty-nine neurons can be identified in the tail, twelve cells in each lumbar ganglion, twelve cells in the pre- anal ganglion, and three cells in the dorso-rectal ganglion. Each cell in the tail can be reproducibly identified on the basis of a set of morphological features, including cell body position, fiber projections, fiber size, and cytoplasmic appearance. Eleven neurons in each lumbar ganglion are bilaterally homologous. Many lumbar cells have sensory dendrites in the tail. Two pairs of lumbar cells which lack sensory dendrites are prominent interneurons in the synaptic interactions of the tail. Virtually all synaptic contacts in the tail are found in the pre-anal ganglion. Most synapses involve lumbar fibers and fibers from cells whose cell bodies lie anterior to the reconstructed region. Pre-anal ganglion cells themselves are relatively minor participants in these synaptic interactions. A complete connectivity matrix has been constructed for both animals, involving about 150 synapses in each case. Certain ceIls make repeated contacts with one another (up to thirteen contacts) in both animals. Other instances of non-reproducible synapses are found, usually involving one contact in one animal and none in the other. No self-synapses are observed, but sensory cells frequently synapse onto their bilateral homologues. Homologously paired cells make similar sets of synaptic contacts. One class of reciprocal synapse formation is found. Eighty per cent of the contacts are dyadic, with one pre-synaptic cell and two post-synaptic ones. Ten per cent of the contacts are triadic; the remaining ten per cent are apparently conventional synapses with a single post-synaptic element. Each dyadic synapse generally involves three different types of neurons - none homologous to another - such that A- B/C. Each type of pre-synaptic neuron (A) contacts only a few preferred pairs of fibers (B, C). Most dyadic contacts are involved in multiple routes of information flow, such that A- B/C and, elsewhere B-C. The formation of dyadic synapses appears to follow strict rules which may reflect important factors in the development of the nervous system. Most synaptic Interactions can be included in a simple wiring diagram by which information flows from sensory cells through multiple routes to converge on a pair of interneurons which project forward into the ventral cord. Positional information is used to identify three pairs of interneurons which are important both in ventral cord synaptic patterns and in the synaptic interactions of the pre-anal ganglion.
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[
International C. elegans Meeting,
1997]
This method has been used to study the expression pattern of a protein at high resolution in identified cells. A post-embedding procedure was performed on LR Gold thin sections of lightly fixed animals, marking MH27 binding with a gold-linked anti-mouse IgG secondary antibody. Methods for fixation, embedding, sectioning and antibody procedures were modified from those of Selkirk et al. (1). We will discuss improvements to the procedure, particularly to label fragile tissues and embryos. Adherens junctions (AJs) were intensely labelled in intestine, pharynx, seam cells and hypodermis. In the intestine, a continuous narrow band of apical AJs link adjacent pairs of intestinal cells. Gap junctions are known to lie very near to the apical AJs in both intestine and hypodermis, but were not labelled by MH27. Smooth septate junctions were heavily labelled between epithelial cells in the spermatheca. Pleated septate junctions immediately adjacent in the same membranes showed no labelling. Negative staining with lanthanum was used to further characterize the septate junctions. The high antigenicity and ubiquitous nature of AJs in intestine and hypodermis along the length of the nematode make the MH27 antibody useful when testing immunochemical procedures in C. elegans. MH27 antibody was generously provided by Jim Waddle and Ross Francis (2). 1. M.E. Selkirk et al. (1990) Mol. & Biochem. Parasitol. 42: 31. 2. G.R.Francis & R.H.Waterston (1985) J. Cell Biol. 101: 1532.
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[
Dev Neurobiol,
2016]
The nematode Caenorhabditis elegans utilizes gap junctions in different fashions in virtually all of its cells. This model animal has a surprisingly large number of innexin genes within its genome, and many nematode cell types can express multiple innexins at once, leading to the formation of diverse junction types and enough redundancy to limit the effect of single gene knockdowns on animal development or behavioral phenotypes. Here we review the general properties of these junctions, their expression patterns, and their known roles in tissue development and in the animal's connectome. This article is protected by copyright. All rights reserved.
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[
International C. elegans Meeting,
1977]
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[
Worm Breeder's Gazette,
1975]
Two young adult animals have been serially sectioned from the tip of the tail forward through the anterior end of the preanal ganglion. The 9 cells of each lumbar ganglion and the 12 cells of the preanal ganglion can be reproducibly identified on the basis of a set of morphological features, including cell body position, direction and extent of fiber projection, fiber size, and cytoplasmic appearance. A total of at least 6 bilaterally homologous pairs can be identified among the lumbar cells. Virtually all the synaptic contacts occur in the preanal ganglion; very few are found in the lumbar ganglia. However, the most prominent participants in these synapses are lumbar cells and a few cells whose bodies lie anterior to the sectioned region; the preanal ganglion cells themselves are relatively minor participants. A complete connectivity matrix has been constructed for both animals, involving about 90 synapses in each case. Certain cells make repeated contacts with one another (up to 13 contacts) in both animals. Other instances of non-reproducible synapses are found, usually involving one contact in one animal and none in the other. Homologously paired cells make similar sets of synaptic contacts. Most (~85/90) of the contacts are diadic, with one presynaptic cell and two postsynaptic ones. Several instances of 'multiple routes of information flow' are found, in which cell A sends to cell C in two ways, both by direct synaptic contact and through an intervening cell, B. No self-synapses are observed, but sensory cells frequently synapse onto their bilateral homologs. One case of reciprocal synapse formation is found. Most of the contacts can be included in a simple wiring diagram by which information flows from sensory cells through multiple routes to converge on a pair of interneurons that apparently constitute one of the major outputs of the system.
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[
Worm Breeder's Gazette,
1996]
Immunofluorescence studies using MH27 antibody have shown a wide variety of tissues to be labelled in patterns which define apical cell borders in C. elegans. Disappearance of MH27 binding during development often marks cell fusions in hypodermis and in the male tail (Podbilewicz and White, 1994; Fitch and Emmons, 1995). We have used an immunoEM method to learn the nature of membrane structures marked by MH27. A post-embedding technique was used to apply MH27 Ab to thin sectioned worms, followed by a gold-linked secondary Ab (for methods, see Selkirk et al., 1991; Hall, 1995). Electron microscopy reveals that MH27 binds only to a few types of cell junctions. By immunoEM, MH27 can be seen to bind to zonula adherens junctions in intestine, at hypodermal/seam cell borders, and at pharyngeal muscle/support cell borders. In adult pharyngeal muscle, small longitudinal stripes of adherens "junction" are also retained on the apical surface where pairs of muscle cells had fused to become syncytial. Thus MH27 binding can sometimes mark the vestiges of an old cell border, long after cell fusion. Spermathecal cells are held closely together by two types of "septate" junction, which together cover almost all of their lateral borders. Extensive, dark-staining apical junctions, which look vaguely adherens-like, are not labelled by MH27. In more basal regions, MH27 binds heavily to another class of extensive sinuous junctions, which lack any dramatic staining characteristics. Neither class of junction has osmiophilic septa visible in ordinary sections. The apical junctions are rather closely apposed and show periodic striping of the thick cytoplasmic density bordering the junctions. The basal, sinuous junctions show an even, widened extracellular space between adjacent plasma membranes, with faint periodic striations crossing the extracellular space between the cells. There is no cytoplasmic density associated with the sinuous junctions. Lanthanum infiltration has been used to negatively stain extracellular septa in the spermathecal junctions. The apical junctions have long, wavy septa; they may comprise a novel class of septate junction, characterized by the thick densely-staining coat on the cytoplasmic face of each cell. The sinuous junctions have not been well infiltrated with lanthanum yet. In one instance we did observe short septa at regular intervals, spanning the extracellular space, similar to those expected in "smooth septate junctions" as described in other invertebrate species. These two classes of septate junction may resist the stresses which would otherwise tear apart the spermatheca during the passage of an oocyte. Our current technique does not permit resolution of the exact locus of MH27 antigen within the adherens junction or the smooth septate junction. It could be cytoplasmic, extracellular, or within the plasma membrane. In glancing sections of both types of junction, it is clear the antigen is found evenly along the entire face of the cell-cell appositions, possibly at a fixed distance in relation to the plasma membrane. High resolution studies would require a more direct labelling method, such as attaching a small gold tag directly to a Fab fragment of the MH27 antibody. This would bring the gold tag into closer proximity to the true antigenic site within a thin section. We thank Jim Waddle and Ross Francis (Washington U.) for generously supplying MH27 antibody. Fitch and Emmons (1995) Dev. Biol. 170: 564-582. Hall (1995) In C. elegans: Modern Biological Analysis of an Organism. H.F. Epstein and D.C. Shakes (eds.). Academic Press, New York, pp. 395-436. Podbilewicz and White (1994) Dev. Biol. 161: 408-424. Selkirk et al. (1991) J. Biol. Chem. 266: 11002-11008.
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[
International C. elegans Meeting,
1997]
In late oogenesis, oocytes undergo a physiological change, referred to as meiotic maturation, as they exit meiotic prophase and enter meiotic M-phase. These changes in the oocyte coincide with a stereotypic motor program, called the ovulation motor program, carried out by the sheath cells of the proximal gonad that contract to drive ovulation. Using electron microscopy and immunofluorescence, we found several key structural aspects that may relate to meiotic maturation and ovulation: sheath/oocyte gap junctions; sheath/sheath gap junctions; sheath actin/myosin bundles anchored to dense-body-like structures; and oocyte cytoplasmic changes. Where adjoining sheath cell processes overlap, prominent gap junctions often form between them. Such junctions may aid in coordinating the contractions of adjoining sheath cells. Large gap junctions were found between proximal sheath cells and oocytes in some locations. These large gap junctions must be evanescent in nature since the oocytes lose contact with sheath cells when they are ovulated. Communication through these junctions may modulate or coordinate oocyte maturation and sheath motility. The cytoplasm of proximal oocytes becomes progressively reorganized prior to maturation. The cytoplasm becomes lower in electron density and mitochondria, rough ER, and other organelles increase in number. Although sheath cells abut closely in most regions, small gaps occur between them and possibly local holes in single sheath cells as well. In most instances where gaps or holes occur, there was evidence for extracellular yolk granules penetrating the gonadal basal lamina to directly touch the underlying oocytes. This and related data suggests that the primary route of yolk transport proceeds from the intestine into the pseudocoelom, then through discrete gaps in the sheath cells to be endocytosed by oocytes.
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[
International C. elegans Meeting,
1997]
Previous studies in Ascaris showed that sublateral nerve cords contain many synapses to bodywall muscle, esp. in the head, at least some of which are excitatory, as well as nerve-nerve synapses between sublateral neurons and passing motorneuron commissures (1,2,3). New immuno-fluorescence studies in C. elegans and Ascaris using several antibodies against synaptic proteins (CHA-1, SNT-1, UNC-17) suggest that the sublateral cords in C. elegans might be involved in similar contacts not described in "The Mind of the Worm" (4). Serial section EM of C. elegans shows periodic swellings of four classes of sublateral neurites. Most swellings form putative synapses: a large cluster of synaptic vesicles and one presynaptic density. These synapses usually lie near the border of two bodywall muscles in the same quadrant, and we presume that they are motor synapses. SIA contacts dorsal muscles; SIB contacts ventral muscles. SMB contacts dorsal muscles more often than ventral; SMD has the opposite preference. PLN and SDQL are involved in few synapses along the sublateral cords. If mechanisms for transmitter degradation are low in this vicinity, even synapses "pointing" towards hypodermis or other neurites may really target muscle. Sublateral nerves could globally modulate muscle activity or muscle tone, perhaps in reciprocal fashion via opposing classes of neurites (dorsal vs. ventral; e.g. SIA vs. SIB, and SMB vs. SMD). Synapses also occur in C. elegans where a circumferential motor commissure crosses a sublateral nerve. Some involve sublateral neurites synapsing onto commissures; others involve commissures synapsing onto sublateral neurites. 1. A.O.W.Stretton (1976) J. exp. Biol. 64:773-88. 2. C.D. Johnson & A.O.W. Stretton (1987) J Neurosci 7:223. 3. Manney, Donmoyer, Angstadt and Stretton, , pers. comm. 4. J.G. White et al. (1986) Phil. Trans. R.Soc.Lond. 314:1-340.