Ciliary Rootlets Research Articles

Ultrastructure of three types of sense receptors of larval Austramphilina elongata (Amphilinidea)

Ultrastructure of three types of sense receptors of larval Austramphilina elongata (Amphilinidea). International Journal for Parasitology 16: 245–251. The ultrastructure of three sense receptors is described. The first is the ending of an anterior dendrite which penetrates deeply into the epidermis and is surrounded by an invagination into the epidermis of the tegument, basal lamina and a thick layer of underlying fibrous matrix, and contains electrondense collars, a basal body and a short ciliary rootlet; it does not reach the surface and is without a cilium. The second is a dendrite which penetrates through the tegument and epidermis and does not contain electron-dense collars, a basal body or a cilium; it forms a free ending on the surface. The third is a nerve ending in the epidermis without electron-dense collars or a basal body, with microvilli-like structures (rhabdomere) and flanked by a densely granular (pigment?) body on one side; it is interpreted as a simple photoreceptor. Diagrams of six sense receptors previously described are given, and the distribution of the receptors in the larva is discussed.

Ultrastructural studies of Austramphilina elongata (Cestoda, Amphilinidea)

The fine structure of larval Austramphilina elongata is described using serial semithin and ultrathin sections. Densely packed germ cells with many ribosomes and mitochondria and with large Golgi complexes fill the middle third of the body. Some necrotic nuclei were observed near the anterior end. The neodermis consists of a subepidermal syncytium connected to pericarya in the parenchyma by means of cytoplasmic processes containing peripheral microtubules; electron-dense ovoid bodies condense in these processes. Myoblasts are connected to muscle fibres by means of cytoplasmic connections rich in mitochondria. Twelve (exceptionally eleven) type I gland cells containing large secretory granules and extensive granular endoplasmic reticulum are located in the dorso-posterior part of the body; they open through 12 (or 11) discrete ducts into an anterior invagination of the tegument which is covered by epidermis and not connected to the outside. Ten type II gland cells containing elongate secretory granules with regularly arranged longitudinal microtubules are located ventral to the type I cell bodies; they open on a ventral papilla a short distance behind the anterior end. Ten type III gland cells containing irregularly round-oval secretory granules with coiled microtubules are located anterior and ventral to the type I gland cells; they open through five discrete ventro-anterior openings on each side of the body. Ducts of all gland cells have mitochondria and microtubules. The spermatozoon has a basic pattern of two axonemes, each with a single central filament, a mitochondrion (mitochondria), and a row of surface microtubules interrupted by the axonemes. In the tips of epidermal cilia, doublet 1 and doublets adjacent to it lose their microtubules B first and close in on the central pair of filaments in a spiral fashion, enclosing an electron-dense rod. Presence of a neodermis and ultrastructure of the spermatozoon support the validity of the taxa Neodermata Ehlers and Trepaxonemata Ehlers and are strong evidence against a phylogenetic relationship of the ‘cestodarians’ — cestodes with the Acoelomorpha; this is also indicated by the ultrastructure of sense receptors and epidermal ciliary rootlets.

The anterior medullary velum and its involvement during autoimmune demyelination.

The anterior medullary velum (AMV), a thin lamina of central white matter forming the roof of the IVth ventricle, has been analysed ultrastructurally in the normal guinea pig and in guinea pigs with chronic relapsing experimental allergic encephalomyelitis. In the latter condition, the AMV appeared to provide a route of access for haematogenous elements from the circulation into the ventricular space. The normal AMV consisted of fascicles of myelinated nerve fibres embedded in a layer of highly attenuated ependymal cells. Between the fascicles, the AMV was comprised merely of a layer of ependymal cytoplasm, in places about 0.5 micron thick. In contrast to ependymal cells from other levels of the neuraxis, in ependymal cells in the AMV, ciliary rootlets of the basal body apparatus were extraordinarily long, numerous and prominent. Their prominence might be related to a need for increased flexibility in this region of the ventricular system. Despite previous claims to the contrary, nerve cell bodies were present within the AMV as well as many synaptic complexes, unmyelinated axons, and supra- and subependymal axons believed to belong to the serotoninergic plexuses. During autoimmune demyelination, the meningeal space over the AMV became heavily infiltrated, inflammatory cells entered the nerve fibre bundles, myelin was destroyed and, perhaps related to disruption of the ependymal layer in places, haematogenous macrophages gained access to the ventricular surface of the AMV. Clinical relapses were accompanied by renewed inflammatory and demyelinative activity and further attenuation of the AMV with concomitant fibrous astrogliosis. Thus the AMV is described in detail for the first time at the ultrastructural level and is presented as a region vulnerable during periods of meningeal infiltration. The cytoarchitecture of the AMV might contribute to the genesis of demyelinated plaques around the IVth ventricle.

Is the Turbellaria polyphyletic?

Within the last two decades, syntheses of both light-microscopic and ultrastructural characters have shown that there are three well-defined monophyletic groups within the Platyhelminthes: 1) the Catenulidale, 2) the Nemertodermatida-Acoela, and 3) the Haplopharyngida-Macrostomida-Polycladida-Neoophora (+ parasitic platyhelminth classes). However, the relationships among these three groups are problematic. The possible apomorphies that would unite them are either not true homologues (i.e. frontal organ), are mutually conflicting (i.e. 9+1 axoneme in spermatozoa vs. biflagellate spermatozoa, epidermal ciliary rootlet structure, and protonephridia), or are unrooted with any outgroup and hence untestable or uncertain as apomorphies (protonephridia, mode of epidermal replacement, absence of accessory centrioles on cilia). The chief obstacle to deciphering the relationships of these groups is the lack of information on them; presently available information is insufficient to test potential synapomorphies and insufficient also to allow agreement upon a narrowly defined outgroup for the Turbellaria.

Frontal organs in the Acoelomorpha (Turbellaria): Ultrastructure and phylogenetic significance

Using characters discernible through electron microscopy, we redefine the organ traditionally identified as the frontal organ in acoelomorph turbellarians as being a collection of two to several large mucus-secreting glands whose necks emerge together through a frontal pore at the exact apical pole of the body, i.e. at the point where the pattern of epidermal ciliary rootlets converges. Representatives that we have studied of each of the acoel families Paratomellidae, Diopisthoporidae, Solenofilomorphidae, Convolutidae, Otocelidae, and Mecynostomidae, as well as a representative of the Nemertodermatida, have such glands. Up to five additional types of glands that open anteriorly outside of the frontal pore, some of which are indistinguishable from glands of the general body wall, could be seen in the nemertodermatid, in Hesiolicium inops (Paratomellidae), and in representatives of the latter four acoel families. In Paratomella, three different types of glands open in diffuse fashion in a frontal glandular complex reminiscent of that in the Macrostomida.

Fine structure of the statocyst sensilla of the mysid shrimp Neomysis integer (Leach, 1814) (Crustacea, Mysidacea).

The fine structure of the statocyst sensilla of Neomysis integer was investigated. The statocyst contains about 35 sensilla, which are composed of two bipolar sensory cells, nine enveloping cells, and a seta. The sensory cells consist of an axon, a perikaryon, and a dendrite. The dendrite contains a proximal segment with a ciliary rootlet and at least one basal body, and a distal segment with a ciliary axoneme (9 × 2 + 0) at its base. The distal segment extends along the peripheral wall of the seta and is in close contact with the wall of the hair shaft. The enveloping cells surround the proximal and distal segments of the dendrite. The innermost enveloping cell contains a scolopale rod. It surrounds the receptor lymph cavity and secretes flocculent material into this cavity. From the tip of the cell a dendritic sheath, which encloses the distal segment of the dendrite, emerges. A peculiar feature of the second enveloping cell is the presence of a scolopale-like rod, which is more slender and less pronounced than in the first enveloping cell. The seta consists of three parts: a socket, a tubular midpart, and a gutter-like apical part, the tip of which penetrates into the statolith. The seta shows over its full length a bilaterally symmetrical axis that is coplanar with the plane in which the seta is bent toward the statolith. The structure of the seta and the position of the distal segments provide morphological evidence for directional sensitivity of the sensilla and for the magnitude of shear on the setal wall being an adequate stimulus.

Ultrastructure of the posterior sense receptor of larval Austramphilina elongata (Amphilinidea)

Rohde K. and Garlick P. R. 1985. Ultrastructure of the posterior sense receptor of larval Austramphilina elongata (Amphilinidea). International Journal for Parasitology 15: 399–402. Eight large papillae arranged in a circle at the posterior end of the body each contain one non-ciliate receptor. The receptor is the terminal swelling of a thin dendrite; it has many large mitochondria, a basal body from which cross-striated ciliary rootlets diverge, and a bundle of long non-striated filaments. The electrondense collar is formed by several thin rings, and some desmosomes are found between the receptor and the adjacent epidermis in addition to the apical septate desmosomes.

Subsurface sense receptors in the larva of Austramphilina elongata Johnston, 1931 (Amphilinidea)

The ultrastructure of tegumental and subtegumental receptors in the larva of Austramphilina elongata is described. The receptors are terminal swellings of dendrites and contain numerous small vesicles and neurofilaments which are predominantly peripheral. Tegumental receptors, together with a sheath consisting of basal lamina and tegument, project into the epidermis, and cross-striated rootlets were sometimes found in them. Subtegumental receptors lie below the tegument and ciliary rootlets were never observed in them. Anterior dendrites contain single centrioles and clusters of centrioles. The possible function of receptors and centrioles is discussed.

Structure of the antennal chordotonal sensilla of the American cockroach

The structure of the chordotonal sensillum in the antennal pedicel of the American cockroach has been examined. The sensillum contains two receptor cells, the sensory dendrites of which give rise to a single sensory cilium. The dendrites are attached by extensive desmosomes to a surrounding scolopale cell. The desmosomes are connected to a ciliary rootlet by filaments. The dendritic membrane above the desmosomes is backed by a lattice-like structure. The dendrite appears to be flexible at this point. The sensory cilium possesses an axoneme with a 9+0 pattern throughout its length. It is dilated and possesses many collaterals at mid length. The two cilia are free within the lumen formed by the scolopale cell, and distally enter the cavity of a cap. The shorter cilium ends free within the narrow midcap cavity. The cavity expands distally, where the longer cilium ends with a swollen terminus. The terminus contains a dense spheroid, where axonemal microtubules attach. The scolopale cell is tightly encased by an attachment cell filled with axially oriented microtubules: extensive desmosomes associated with microtubules, and septate desmosomes occur between the two cells. These data are discussed in relation to the sensory mechanism of this sensillum, which is known to be sensitive to both vibration and tension.

Immuno-electron-microscopic localization of a centriole-related antigen in ciliated cells

An antigen common to purported centriolar and basal body regions of a variety of cell types was previously visualized by immuno-fluorescence microscopy. The present study demonstrates the localization of the antigen relative to the defined basal body structures of ciliated tracheal cells at the electron-microscopic level. After ethyldimethylaminopropyl carbodiimide-glutaraldehyde-saponin (EGS) fixation and permeabilization, immunoferritin labeling is consistently found associated with amorphous electron-opaque material in proximity to basal bodies and their ciliary rootlets, but not with basal body microtubules themselves. This distribution pattern is distinct from that of other proteins found in the apical region of ciliated cells, such as calmodulin. It is proposed that the dense material may be analogous to pericentriolar material of centrosomes.

Are the funnel-canal organs the 'campaniform sensilla' of the shore crab, Carcinus maenas (Decapoda, Crustacea)? II. Ultrastructure.

The funnel-canal organs on the dactyls of the shore crab, Carcinus maenas, are innervated by 3-24 sensory cells with unbranched dendrites, which attain a length of 500-1400 micron. The outer dendritic segments are enclosed in a dendritic sheath and pass through the cuticle within a canal. Two dendrite types can be distinguished according to ultrastructural criteria: Type I has a long ciliary segment, A-tubules with an osmiophilic core and arms, and a thick ciliary rootlet. Type II possesses only a short ciliary segment and a thin ciliary rootlet. Each funnel-canal organ contains two type-I dendrites. Their ciliary bases appear a few micron distal to those of the type-II dendrites (1 to 22 in number). Two inner and two to eight outer enveloping cells belong to a sensillum. The innermost enveloping cell contains a large scolopale. In the second enveloping cell single scolopale rods are present. Thus, the funnel-canal organs are characterized by structural features typical for mechanosensitive scolopidia, on the one hand, and for chemoreceptors, on the other. Therefore, the funnel-canal organs are very likely bimodal sensilla (contact chemoreceptors). A comparison with other arthropod sensilla shows that cuticular mechanoreceptors of aquatic crustaceans generally exhibit a 'scolopidial' organization.

Morphology and ultrastructure of the organ of Bellonci in the marine amphipod Gammarus setosus.

The three-dimensional structure of the organ of Bellonci in the marine amphipod Gammarus setosus and the relationship between its sensory cells and concretion are described using light, transmission, and scanning electron microscopy, with chemical treatment for cell lysis, calcium chelation, glycogen staining, and lanthanum labelling. The organ is encapsulated and has three units called fuselli. Each is enclosed by two fusellar cells which generate and release calcium granule strands into the cores of the fusellar concretions, which are united in the center of the organ. The surface of each fusellus is traversed by spiral dendrites entering dorsally and ending ventrally. The spiral dendrites arise from sensory neurons contained in a palm-shaped ganglion in the center of the capsule, beyond which they are twisted like a rope before reaching the concretion. The spiral dendrites are linked in pairs by gap and tight junctions and each gives origin to two pairs of 9+0 sensory cilia 30 μm apart. The ciliary distal segments give rise to long tubules which are in contact with the calcium granule strands. The ciliary proximal segments are expanded by many long mitochondria which interdigitate with the branched striated ciliary rootlets. The concretion is suspended in the capsule cavity by axons originating from four neurons of a remote mechanoreceptor. The structure of the organ suggests that it is a sensory organ involved in the reception and integration of a variety of stimuli.

Novel organelle associations in photoreceptors of a serpulid polychaete worm

Cerebral and branchial eyes of serpulid polychaetes have been studied by electron microscopy for the first time. In one species both eye types possess a novel ultrastructure. The receptor cells of the simple cerebral ocelli are rhabdomeric and display a close structural and functional relationship between ciliary rootlets and mitochondria. The receptors of the compound branchial eyes contain both a rhabdom and a stack of photosensitive ciliary membranes.

Asymmetrical microtubule capping structures in frog palate cilia

Capping structures at the distal tips of frog palate cilia are attached to the A- and central pair microtubules by electron-dense plug structures similar to those found in protozoan cilia and flagella and in epithelial cilia from invertebrates and vertebrates (W.L. Dentler, 1980, J. Cell Sci. 42, 207-220; W.L. Dentler and E.L. LeCluyse, 1982, Cell Motil. 2, 549-573). The caps in frog palate cilia are composed of a proximal shelf, to which doublets Nos. 1-3, 8, 9 and the central microtubules are attached and a larger distal cap to which doublets Nos. 4-7 are bound. The smaller proximal shelf is positioned to one side of the cilium and gives the cap an asymmetrical appearance. Striated ciliary rootlets attached to the basal bodies are also described. The smaller cap is placed on the same side of all cilia on the palate relative to both the direction of the effective stroke and the position of the rootlets. These results confirm that capping structures are common to most, if not all, cilia and provide direct evidence that they are precisely positioned on specific microtubules.

Internal proprioceptive organs of the distal antennal segments in Allacma fusca (L.) (Collembola : Sminthuridae): Proprioceptors phylogenetically derived from sensillum-bound exteroceptors

The internal proprioceptive organs of the distal antennal segments of Allacma fusca (Collembola : Sminthuridae) were examined with light, scanning, and transmission electron microscopy. There are 2 such organs, each belonging to the sensory equipment of a sensory peg. These pegs are part of the sensory organs of the 3rd antennal segment (SO - AIII), and show characteristics of both hair sensilla and chordotonal organs. They have 5 sensory cells of which 4 can be regarded as chemoreceptors, because the walls of the pegs are pierced by pores. The 5th cells are the proprioceptors. Their dendritic outer segments are connected to the base of the SO - AIII peg but show no specializations. Their dendritic inner segments are distally joined to a thecogen cell containing a scolopale. Proximally, they span the hemolymph space within the antenna. The perikaryon of one of the organs is located on a muscle that deflects the 3rd antennal segment (IP - AIII). The perikaryon of the other is attached to the antennal nerve near a point where it is connected to a muscle that deflects the 4th antennal segment (IP - AIV). There is a conspicuous membrane system, associated with microtubules and a prominent ciliary rootlet within the dendritic inner segment of the IP - AIII. The cytological features of the organs are discussed with reference to 2 problems, the phylogeny of chordotonal organs and the process of mechanosensory transduction.

Structural properties of bimodal chemo- and mechanosensitive setae on the pereiopod chelae of the crayfish, Austropotamobius torrentium.

The setae on the inner edges of the pereiopod chelae of Austropotamobius torrentium contain eight receptor-cell endings. Two units are mechanosensitive, four react only to amino acids, to amines, or to pyridines. The remaining two units are most probably also chemoreceptors. All sensory cells possess long dendritic outer segments that extend to the tip of the seta, where a small pore is found. Structurally, two units differ from the other six by having (1) densely packed microtubules in their dendritic outer segments, (2) dense A-tubules with arms in their ciliary segments, (3) a well-developed ciliary rootlet in their dendritic inner segments, and (4) desmosomal junctions between the dendritic inner segment and the inner enveloping cell, which contains a scolopale. These features are probably general characteristics of crustacean mechanoreceptors. The mechanoreceptors respond only to strong mechanical stimuli. This corresponds to the structural features of the setae, which lack specialized socket structures. Deflection of the setae may lead to longitudinal stress to the dendrites; the latter seem to be attached proximally to the inner enveloping cell and distally to the cuticle. Thus, the mechanoreceptor structure suggests a function analogous to scolopidial receptors. The chemoreceptors are accessible to chemical stimuli via the subterminal pore. The walls of the setae, however, may be permeable as well. It seems probable that action potentials were recorded also from the dendrites of the sensory cells.

Ultrastructure of copulatory organs in Turbellaria

The copulatory organs in Macrostomum sp. and Microstomum sp. contain simple tubular stylets which are intracellular specializations. The stylet in Macrostomum sp. is produced in a syncytium covering part of the prostatic vesicle. The proximal region of the stylet surrounds the vesicle which contains six prostatic gland ducts and six accessory (sensory) cells containing ciliary rootlets. The stylet in Microstomum sp. is produced in an extension of a syncytium which lines the combined seminal-prostatic vesicle. The stylet is connected to the combined vesicle by a narrow bridge of matrix syncytium through which sperm, prostatic gland products and sensory cilia pass from the vesicle to the stylet lumen. In both species the matrix syncytium can be interpreted as a specialized terminal end of the male canal epithelium. Stylets of Turbellaria and other lower Metazoa are discussed in regards to structure (one or several pieces) and location (in separate cells, in a syncytium, or extracellular).

The system of epidermal ciliary rootlets in Turbellaria

The system of epidermal ciliary rootlets in Turbellaria

Structure of the auditory system of the weta Hemideina crassidens (Blanchard, 1851) (Orthoptera, Ensifera, Gryllacridoidea, Stenopelmatidae)

This study of the ultrastructure of the auditory sensilla of the New Zealand weta, Hemideina crassidens, is the first such study on a member of the orthopteran Superfamily Gryllacridoidea. Ultrastructure of the auditory sensilla is similar in all of the tibial mechanosensory organs, here called subgenual organ, intermediate organ and crista acoustica by analogy with comparable structures in Tettigoniidae. Distal to each sensory soma is a dendrite containing multiple ciliary rootlets that fuse into a single ciliary root. This splits into nine root processes that pass around the outside of the proximal basal body and then rejoin at the level of the distal basal body, distal to which the dendrite has a modified ciliary structure with a circlet of nine peripheral paired tubes and rods as it passes through the proximal extracellular space. It is then enclosed by a zone of scolopale cell cytoplasm before expanding into a dilatation within the distal extracellular space. In some sensilla this space is partially occluded by electron dense material which is part of the scolopale cell. Distal to the dilatation the cilium shrinks and ends surrounded by the scolopale cap. Accessory cells consist of glia enwrapping the sensory neuron in the region of its soma, the scolopale cell surrouinding the ciliary portion of the dendrite, and the attachment cell surrounding the scolopale cell and scolopale cap and connected to them by desmosomes. The attachment cells are filled with microtubules in differing densities and orientations. Lamellae are present in the acellular matrix surrounding the attachment cells. Banded fibres, presumably of collagen, are also present in the matrix.

Comparative ultrastructure of the pharynx simplex in turbellaria

The simple pharynges in thirteen species of Turbellaria in the orders Macrostomida, Haplopharyngida, Catenulida, and Acoela have been studied by electron microscopy. After consideration of the functional aspects of the pharynx simplex, the relationship of the pharynx simplex ultrastructure to the phylogeny of the above mentioned groups is analyzed. The Haplopharyngida and Macrostomida are united as a group by the following characters: a pharynx transition zone of 1–5 circles of insunk cells with modified ciliary rootlets or no cilia, pharynx sensory cells without stereocilia collars and with a variable number of cilia, a prominent nerve ring with more than 30 axons circling the pharynx at the level of the beginning of the pharynx proper distal to the gland ring, 2 or more gland cell types in the pharynx, with at least two layers of muscle present and the longitudinal muscles derived from regular and special body wall circular muscles and a prominent post-oral nerve commissure. This specific arrangement can be distinguished from the other pharynx simplex types and is called the pharynx simplex coronatus. The catenulid pharynx simplex is characterized by the lack of a prominent nerve ring, no prominent post-oral commissure, a transition zone with epidermal type ciliary rootlets, recessed monociliated sensory cells, and one or no type of pharynx gland cell. The Acoela are specialized because of the epidermal type rootlets in the pharynx proper. They also lack a transition zone and a prominent nerve ring and have monociliated sensory cells different from the catenulid type. Ultrastructural characters of the pharynx simplex support the view that the Haplopharyngida-Macrostomida are monophyletic. The more primitive catenulid pharynx probably arose from a common ancestral pool with the Haplopharyngida and Macrostomida, although it does not appear possible presently to establish a clear monophyletic line for these forms. The various pharynx types within the Acoela appear to indicate independent origins with no clear link to the basic pharynx simplex type in the three other orders.