Ciliary Rootlets Research Articles

Ultrastructure of pigmented photoreceptors of larvalMulticotyle purvisi (Trematoda, Aspidogastrea)

The two eyespots of larvalMulticotyle purvisi lie on the posterior of the brain dorsal to the pharynx. Each ocellus consists of one pigment cell and two rhabdomeres, one in the antero-lateral and one in the postero-lateral part of the pigment cup. Each rhabdomere comprises two bundles of microvilli diverging from a central dendritic mass that is connected by a narrow connection lined by dense material along the cell membrane to a perikaryon outside the ocellus. Many cross-striated microfibrils (possibly ciliary rootlets) are scattered at the bases of the rhabdomeres. Microvilli of the rhabdomeres consist of a central tubular zone lined by dense granules and an outer light, homogeneous zone. Phylogenetic implications and possible functions of the photoreceptors are discussed.

Cytoskeletal elements in insect sensilla

Abstract Insect sensilla have evolved prominent cytoskeletal elements as part of their functional specialization. The cytoskeleton present in sensory cells as well as in auxiliary cells may play an important role in sensilla function. The scolopale, the characteristic cytoskeletal component in the innermost auxiliary cell of mechanosensitive scolopidia and thermo-/hygrosensitive sensilla, is mainly composed of bundles of 10 nm filaments. Cytochemical approaches for light and electron microscopy identified these structures as actin filaments that exhibited a unique filament orientation and uniform filament polarity. None of these approaches has provided evidence for the presence of myosins in the scolopale. In contrast, tropomyosin and the microtubule-associated protein 2 are associated with the actin filament bundles in the scolopale of scolopidia. All data taken together suggest that the actin filaments of scolopale have a stabilizing rather than a contractile function. In scolopidia, in addition to cellular stabilization, filament elasticity would appear to be important during stimulation. Owing to the high number of microtubules, the scolopale in thermo-/hygrosensitive sensilla seems more rigid than in scolopidia and may protect sensory dendrites from mechanical forces. In sensory cells of scolopidia, regularly cross-striated ciliary rootlets are additional prominent cytoskeletal structures. Immunohistochemistry reveals that these rootlets contain the Ca 2+ -binding protein centrin, which forms contractile filaments in other systems, e.g., unicellular green algae. Accordingly, contractions of ciliary rootlets may also be part of the filament function in insect sensilla.

Domain-specific changes of ciliary striated rootlets during the cell cycle in the hypotrich ciliate Paraurostyla weissei

ABSTRACT The dynamics of striated ciliary rootlets (cr) during development of ciliary structures in cells of the hypotrich ciliate Paraurostyla weissei was studied by immunostaining with polyclonal antibody raised against isolated cr of Paramecium tetraurelia. Wildtype cells and two mutants: mlm showing multiple left marginal cirri and mlm/pl showing in addition a certain degree of pattern lability were used to study the boundaries of particular cortex domains. In interphase cells, cr are attached to all left marginal and caudal cirri and to only the posterior third of the right marginal cirri, cr appear in all nonoral primordia during the first wave of basal body proliferation. After nucleation and early elongation of cr, some cr undergo site-specific regression or stabilization. The spatial deployment of these different modes of development corresponds to specific cortical domains. In mlm/pl mutants, where specific cortical domains are broadened, changes in the cr system are characteristic for a given domain, regardless of its broadening, but boundaries between adjacent domains are weakened.

Ultrastructure of the sense receptors of adult Multicotyle purvisi (Trematoda, Aspidogastrea)

The following presumptive sense receptors of adult Multicotyle purvisi from the intestine of freshwater turtles in Malaya are described by transmission electron microscopy: disc‐like receptor with many electron‐dense collars and modified ciliary rootlet forming a ‘disc’; non‐ciliate receptor with long rootlet; non‐ciliate receptor with branching rootlet and dense mass of irregularly arranged microtubules; non‐ciliate receptor with rootlet fanning out from basal body, cross‐striated in its upper and with electron‐dense structures in its lower part; uniciliate receptor with thick layer of cytoplasm around axoneme; receptor with short cilium, at base of deep invagination of tegument; receptor with short cilium terminating in an electron‐dense apical cap; and uniciliate receptor with long cilium. In addition, there may be a small non‐ciliate receptor with a long ciliary rootlet at the base of the thick dorsal tegument, and uniciliate receptors differing from the uniciliate receptor with long cilium in the number of electron‐dense collars and the length of the cilium and ciliary rootlet. Implications of the findings for the phylogeny of the parasitic Platyhelminthes and for evolutionary trends within that group arc discussed. The considerable degree of divergence of receptor types between the species of one family is attributed to the archaic nature of the group.

Ultrastructure of a possible new type of crustacean cuticular strain receptor in Carcinus maenas (crustacea, decapoda).

A hitherto unknown sensillum type, the "intracuticular sensillum" was identified on the dactyls of the walking legs of the shore crab, Carcinus maenas. Each sensillum is innervated by two sensory cells with dendrites of "scolopidial" (type I) organization. The ciliary segment of the dendrite is 5-6 μm long and contains A-tubules with an electron-dense core and dynein arm-like protuberances; the terminal segment is characterized by densely packed microtubules. The outer dendritic segments pass through the endo- and exocuticle enclosed in a dendritic sheath and a cuticulax tube (canal), which is suspended inside a slit-shaped cavity by cuticular lamellae. The dendrites and the cavity terminate in a cupola-shaped invagination of the epicuticle. External cuticular structures are lacking. Three inner and four to six outer enveloping cells are associated with each intracuticular sensillum. The innermost enveloping cell contains a large scolopale that is connected to the ciliary rootlets inside the inner dendritic segments by desmosomes. Scolopale rods are present in enveloping cell 2. Since type I dendrites and a scolopale are regarded as modality-specific structures of mechanoreceptors, and since no supracuticular endorgan is present, the intracuticular sensilla likely are sensitive to cuticular strains. The intracuticular sensilla should be regarded as analogous to insect campaniform sensilla and arachnid slit sense organs.

Paired multiciliate receptor complexes in larvalMulticotyle purvisi (Trematoda, Aspidogastrea)

An anterior pair of receptor complexes dorsal to the mouth cavity of larvalMulticotyle purvisi (Trematoda, Aspidogastrea) is described by transmission electronmicroscopy. Each complex consists of two dendrites. One dendrite forms a large terminal swelling, approx. 7.5×3 μm in diameter, that contains a liquid-filled cavity. At least ten short cilia with basal bodies but without ciliary rootlets project from the dendrite into the cavity, most of them into the median and anterior parts. Lamellate extensions of the ciliary membrane, of irregular shape and with many cavities, extend along and beyond many of the cilia. A second narrow dendrite penetrates the anterior wall of the cavity; it has an apical septate junction and a single cilium that forms several projections, giving it a star-like appearance. Possible functions of the complexes are discussed.

Non-ciliate sensory receptors of larvalMulticotyle purvisi (Trematoda, Aspidogastrea)

Four types of presumptive non-ciliate sensory receptors of larvalMulticotyle purvisi (Trematoda, Aspidogastrea) are described by transmission electronmicroscopy. One pair of receptors in the mouth cavity has two to several electron-dense collars and a long crossstriated rootlet with some fibres fanning out from the basal body. Four pairs in the ventral wall of the posterior sucker and in the tegument ventral to the sucker contain numerous electron-dense collars and, diverging from the basal body, a large, round-ovoid ciliary rootlet that is cross-striated in its proximal and has numerous dense structures in its distal part. Two large bulbous receptors with much dense material in their apical parts and some desmosome-like structures occur in the lateral surface tegument at the level anterior to the posterior sucker, and similar smaller ones occur at the anterior end. A receptor with both a bulbous projection containing numerous vesicles with dense inclusions and some long cytoplasmic processes occurs at the posterior end.

Uniciliate sensory receptors of larvalMulticotyle purvisi (Trematoda, Aspidogastrea)

Seven types of presumptive ciliate sensory receptors of larvalMulticotyle purvisi (Trematoda, Aspidogastrea) are described by transmission electronmicroscopy. The type 1 receptor has one electron-dense collar and a short (approx. 0.6 μm long) cilium. The type 2 receptor contains two electron-dense collars and a cilium with much dense cytoplasm around the ring of doublets of nicrotubules. In the type 3 receptor, two electrondense collars with large reticulate extensions into the receptor are present. The type 4 receptor has two electron-dense collars and a long, cross-striated ciliary rootlet. The cilium of the type 5 receptor contains a large number of single microtubules and doublets. The type 6 receptor has two electron-dense collars and a cilium at least 6 μm in length, and the type 7 receptor is characterized by two electron-dense collars and a cilium that is approx. 1.3 μm long.

The hair-peg organs of the shore crab, Carcinus maenas (Crustacea, Decapoda): Ultrastructure and functional properties of sensilla sensitive to changes in seawater concentration

The hair-peg organs of the shore crab, Carcinus maenas, are modified hair-sensilla. A small hair shaft (peg) is surrounded by a tuft of solid cuticular bristles (hairs). Each hair-peg organ is innervated by 6 sensory neurons, 2 of which have “scolopidial” (type-I) dendrites. The outer segments of all dendrites pass through a cuticular canal extending to the articulated hair base in which the 2 type-I dendrites terminate. The other 4 (type-II) dendrites reach the clavate tip of the hair shaft and have access to a terminal pore and a large sickle-shaped aperture. Three inner and 8–12 outer enveloping cells belong to a hair-peg organ. The innermost enveloping cell contains a scolopale, which has desmosomal connections to the ciliary rootlets of the type-I dendrites. An inner and an outer sensillum lymph space are present. The ultrastructural features of the dendrites and the cuticular apparatus indicate that the hair-peg organs are bimodal sensilla, comprising 2 mechano- and 4 chemosensitive sensory neurons. Extracellular recordings from the leg nerve indicate that the chemosensitive neurons of the hair-peg organs respond to changes in seawater concentration in the physiological range of Carcinus maenas.

Ultrastructural Observations on the Epidermis of Xenoturbella bocki Westblad, 1949; With a Discussion of Epidermal Cytoplasmic Filament Systems of Invertebrates

AbstractThe highly complex epidermis of Xenoturbella bocki has been studied, mainly employing transmission electron microscopical and histochemical methods. The epidermal organization is described to best advantage in terms of the various cell types present, their intricate interrelationships and their interaction with the highly developed subepidermal membrane complex (SMC). The epidermis is composed mainly of ciliated epidermal supporting cells, at least two types of gland cells (one dominant mucous type with basophilic, alcian blue‐positive granules; another possessing acidophilic, PAS‐positive granules), several types of nerve cells present in the intraepidermal nerve layer and, finally, some peculiar basally arranged ‘pillow cells’. Junctional structures are sparsely developed. The epidermal supporting cell is provided with a distinct cell web, but diagnostic for this cell type is the presence of a very prominent single supporting fibre (SF) composed of supporting filaments. Distally some of these filaments may terminate on the tapering proximal ends of ciliary rootlets, a highly unusual phenomenon. Basally the SF is attached to the SMC in a complex arrangement. The possible relationship of the supporting filaments to cytoskeletal intermediate filaments is discussed. The SF is compared to other cytoplasmic filament systems in mammals and various invertebrates. The ultrastructural organization of Xenoturbella is now fairly well understood, nevertheless, our conclusion must be that it is still not possible to assign an appropriate place for this animal in the systematic‐phylogenetic system.

Characterization of ependymal cells in hypothalamic and choroidal primary cultures

Long-term primary cultures derived from fetal mouse or rat hypothalamus and choroid plexus were obtained in serum-supplemented and chemically defined media. In order to identify and characterize cell types growing in our cultures, we used morphological features provided by phase-contrast, scanning and transmission electron microscopy. Immunological criteria were recognized, using antibodies against intermediate filament proteins (vimentin, gliofibrillar acid protein, cytokeratin, desmin, neurofilament proteins), actin, myosin, ciliary rootlets, laminin and fibronectin in single or double immunostaining, and monoclonal antibodies known to detect epitopes of ependymal or endothelial cells. Minor cell types such as astrocytes, fibroblasts and endothelial cells were distinguished. Ependymal cells, which exceeded 75% of the cultured cells, were identified by their cell shape and epithelial organization revealed by phase-contrast and transmission electron microscopy, by their apical differentiation evidenced by scanning and transmission electron microscopy, and by certain molecular markers ( e.g. gliofibrillar acid or ciliary rootlet proteins) detected by immunofluorescence. Four ependymal cell types were recognized: choroidal ependymocytes, ciliated and unciliated ependymal cells, and tanycytes. All these cultured ependymal cell types showed a remarkable resemblance to in vivo ependymocytes, in terms of marker expression and ultrastructural features.

Fine Structure and Function of Pharynx Cilia in Glossobalanus minutus Kowalewsky (Enteropneusta)

AbstractTwo kinds of cilia have been observed in the pharynx of Glossobalanus minutus Kowalewsky. From the present study, a ciliary specialization can be found in order to move a determinate substance, i.e. mucus or water. Mucus‐moving cilia (type I cilia) have a single basal centriole and poorly developed ciliary rootlets. Their tips are rounded, bearing an inner, asymmetrical cap attached to some tubules. Water‐moving cilia (type II cilia) are exclusively located at lateral epithelia of branchial bars, giving rise to the water current through the gills. They have two basal centrioles, proximal and distal, and a complex system of ciliary rootlets made up of a principal rootlet, a secondary or accessory rootlet and a ‘fan’ rootlet. The tips of type II cilia have a long process with some tubules inside. All basal structures are precisely orientated in order to assure a good coordination of ciliary beat. The possible functional significance of ciliary substructure is also discussed. From these observations a model for mucus and water currents through gill slits is postulated.

Different functions of tight junctions in the ascidian branchial basket

The stigmatal cells in the branchial basket of ascidians from a number of genera have been examined as to the nature and distribution of their intercellular junctions. The branchial wall consists of ciliated and parietal cells; the ciliated cells are arranged in seven rows and are associated by junctions with other cells in the same row as well as with those in adjacent rows. They are also associated by junctions with peripheral parietal cells. Junctions between adjacent ciliated cells in all cases exhibit tight junctions or zonulae occludentes. However, these cell borders also possess fasciae or zonulae adhaerentes if they are in the same row and the ciliary rootlets insert-into these junctions. If the cells are in adjacent rows they exhibit adhaerentes junctions only in species belonging to the orders Phlebobranchiata and Aplousobranchiata. In contrast, if the cells in adjacent rows belong to the order Stolidobranchiata. they never exhibit any adhaerentes junctions and the ciliary rootlets of the basal bodies from the cilia insert instead into the tight junctions and the non-junctional membrane below them. At the homologous junctional borders between adjacent parietal cells and also at heterologous junctional borders between parietal and ciliated cells, tight junctions alone occur, with no co-existing adhaerentes junctions along their lateral borders. Again, fibrils from ciliary rootlets insert into zonulae occludentes. This shows that tight junctions are capable both of forming permeability barriers, in that they can be seen to prevent the entry of exogenous tracers such as lanthanum, and of acting as adhesive devices.

Types of sensory cells in Notocotylus attenuates (Rud., 1809) rediae (Digenea, Notocotylidae)

Three types of sensory cells were shown to occur in the tegument of Notocotylus attenuatus (Rud., 1809) rediae, using electron microscopy. The morphology of the receptive parts were distinguished as follows: cells containing a single cilium and a single basal body without a ciliary rootlet (type 1 A); cells possessing two axonemes, covered by a common membrane, and two separate basal bodies (type 1B); cells having one cilium and a basal body with a long rootlet (type 2); and cells containing a single cilium and a basal body, and only one electron-dense ring adjacent to the tegument (type 3). A description is given of the ultrastructure as well as the morphological and functional similarity of the cells in question.

Fine structure and absorption of ferritin in the digestive organs of Loligo vulgaris and L. Forbesi (Cephalopoda, Teuthoidea)

AbstractThe digestive organs possibly involved in food absorption in Loligo vulgaris and L. forbesi are the caecum, the intestine, the digestive gland, and the digestive duct appendages. The histology and the fine structure showed that the ciliated organ, the caecal sac, and the intestine are lined with a ciliated epithelium. The ciliary rootlets are particularly well developed in the ciliated organ, apparently in relation to its function of particle collection. Mucous cells are present in the ciliated organ and the intestine. Histologically, the digestive gland appears rather different from that of other cephalopods. However, the fine structure of individual types of squid digestive cell is actually similar to that of comparable organs in other species, and the squid cells undergo the same stages of activity. Digestive cells have a brush border of microvilli, and numerous vacuoles, which sometimes contain “brown bodies.” However, no “boules” (conspicuous protein inclusions of digestive cells in other species) could be identified in their cytoplasm; instead only secretory granules are present. In the digestive duct appendages, numerous membrane infoldings associated with mitochondria are characteristic features of the epithelial cells in all cephalopods. Two unusual features were observed in Loligo: first, the large size of the lipid inclusions in the digestive gland, in the caecal sac, and in the digestive duct appendages; and second, the large number of conspicuous mitochondria with well‐developed tubular cristae. When injected into the caecal sac, ferritin molecules can reach the digestive gland and the digestive duct appendages via the digestive ducts, and they are taken up by endocytosis in the digestive cells. Thus, it appears that the digestive gland of Loligo can act as an absorptive organ as it does in other cephalopods.

Archenteron elongation in the sea urchin embryo is a microtubule-independent process

Earlier studies using colchicine ( L. G. Tilney and J. R. Gibbins, 1969, J. Cell Sci. 5, 195–210 ) had suggested that intact microtubules (MTs) are necessary for archenteron elongation during the second phase of sea urchin gastrulation (secondary invagination), presumably by allowing secondary mesenchyme cells (SMCs) to extend their long filopodial processes. In light of subsequently discovered effects of colchicine on other cellular processes, the role of MTs in archenteron elongation in the sea urchin, Lytechinus pictus, has been reexamined. Immunofluorescent staining of ectodermal fragments and isolated archenterons reveals a characteristic pattern of MTs in the ectoderm and endoderm during gastrulation. Ectodermal cells exhibit arrays of MTs radiating away from the region of the basal body/ciliary rootlet and extending along the periphery of the cell, whereas endodermal cells exhibit a similar array of peripheral MTs emanating from the region of the apical ciliary rootlet facing the lumen of the archenteron. MTs are found primarily at the bases of the filopodia of normal SMCs. β-Lumicolchicine (0.1 m M), an analog of colchicine which does not bind tubulin, inhibits secondary invagination, indicating that the effects previously ascribed to the disruption of MTs are probably due to the effects of colchicine on other cellular processes. The MT inhibitor nocodazole (5–10 μg/ml) added prior to secondary invagination does not prevent gastrulation or spontaneous exogastrulation, even though indirect immunofluorescence indicates that cytoplasmic MTs are completely disrupted in drug-treated embryos. Transverse tissue sections indicate that a comparable amount of cell rearrangement occurs in nocodazole-treated and control embryos. Significantly, SMCs in nocodazole-treated embryos often detach prematurely from the tip of the gut rudiment and extend abnormally large broad lamellipodial protrusions but are also capable of extending long slender filopodia comparable in length to those of control embryos. These results indicate that cytoplasmic MTs are not essential for either filopodial extension by SMCs or for the active epithelial cell rearrangement which accompanies archenteron elongation during sea urchin gastrulation.

Ultrastructure of flame cells and protonephridial capillaries of Craspedella and Didymorchis (Plathelminthes, Rhabdocoela)

The ultrastructure of the flame cells and protonephridial capillaries of the Rhabdocoela Craspedella sp. and Didymorchis sp., ectocommensals on the freshwater crayfish Cherax destructor in eastern Australia is described. The flame cells of both species have variable numbers of cilia without distinct rootlets and with decreasing numbers of axonemal tubules towards the ciliary tips. Bundles of microtubules extend from the cytoplasm adjacent to the ciliary rootlets through the ribs of the weir apparatus into the distal cytoplasmic tube, where the numbers of microtubules gradually decrease. The weir apparatus is formed by a single row of longitudinal ribs connected by a membrane. In Craspedella, but not in Didymorchis, the ribs have external branched leptotriches. Mitochondria are common in the wall of the flame cell of both species. The protonephridial capillary just above the end of the ciliary tuft narrows in both species and bends sharply in Craspedella. The lumen of the flame cell and the capillary is lined by a dark layer of cytoplasm; there is no enlargement of the surface area by microvilli or lamellae. Centrioles were seen in the capillary wall of Craspedella, and in Didymorchis the cytoplasm around the capillaries has a very loose and light appearance. The ultrastructure of the flame cells and capillaries of both species corresponds closely to that of Temnocephala sp.

The ciliated epidermis of Xenoturbella bocki (Platyhelminthes, Xenoturbellida) with some phylogenetic considerations

The epidermis of Xenoturbella bocki Westblad was studied by scanning and transmission electron microscopy. Two cell types predominate in the epidermis: multiciliated epidermal cells and non‐ciliated or monociliated gland cells. A conspicuous feature is the dense ciliary coverage and the numerous gland cell openings. Xenoturbella has a characteristic pattern of axonemal filament termination in the distal tips of their cilia. Each epidermal cilium has the typical 9 + 2 patten through the major part of its shaft. Near the tip there is a shelf at which doublets 4–7 terminate. Doublets 1, 2, 3, 8 and 9 continue into the thinner distal part of the cilium. A similar shelf in cilia is known only from the turbellarian orders Nemertodermatida and Acoela, and hence may be an apomorphic feature which indicates a close relationship between Xenoturbellida, Nemertoder‐matida and Acoela. The basal body is provided with a so‐called basal foot which has a cross‐striated appearance and an expanded distal plate that seems to act as a microtubule organizing center. Approximately 15–25 microtubuli radiate from the endplate of the basal foot to the basal bodies caudally. The arrangement of basal foot and ciliary rootlets in Xenoturbella differs from that of Acoela and related orders in that there are two striated rootlets only (an anterior and a posterior one), rather than one main rootlet and two lateral rootlets.

Ultrastructural analysis of primary cilium in the embryonic nervous tissue of mouse

In the embryonic nervous system, the morphology and spatial organization of the ciliary apparatus in the primordial cells, the neuroepithelial bipolar cells, has been analysed from frontal and horizontal ultrathin sections. Projecting into the ventricular fluid, the primary cilium is located just at the interface between the ventricular fluid and the cytoplasm of these cells. Always associated with a basal body and a centriole, their structural components are nine microtubule doublets equally spaced around the luminal cylinder without central doublet. The cilium is short with a thick base displaying a reduced ciliary necklace and a 9 + 0 pattern. In its tip, the pattern decreases from 7 + 0 to 2 + 0. The basal body differs from the basal body of the motil cilium by internal and external sheets interconnecting triplets from base to apex, the constant existence of an accessory basal foot and the scarcity of a ciliary rootlet. All these characteristics suggest that in the neuroepithelial bipolar cells the ciliary apparatus is a rigid, polarized and transient structure probably important in the possible exchange between the ventricular fluid and the developing nervous system.

Structural and functional properties of the mechanoreceptors and chemoreceptors in the anterior oesophageal sensilla of the crayfish, Astacus astacus

The anterior oesophageal sensilla (AOS) of Astacus astacus are short cuticular cylinders with a terminal pore. Three sensory cells belong to each AOS, two of them having a dendritic ciliary segment of about 2 μm length (A-cells), the third having this segment about 12 μm long (B-cell). The ciliary A-tubules in the B-cells only possess arms and an electron-dense core. The dendritic inner segments of the A-cells terminate 3–6 μm distal of the B-cells. The dendritic tips of most A-cells are connected by desmosomes. All dendritic inner segments contain a ciliary rootlet and are accompanied by a scolopale within the innermost enveloping cell. There are four enveloping cells, three of which form thin subepithelial columns together with the enclosed sensory cells. Recordings from the posterior branch of the anterior oesophageal nerve containing the axons of the AOS revealed the presence of three types of sensory cells, two being chemosensitive and one mechanosensitive. One chemoreceptor is specifically sensitive to nicotinamide, but responded also to β-NAD, 6-aminonicotinamide, nicotinamide methyl esther and nicotin. It was blocked by p(4)-acetylpyridine. The second chemoreceptor responded only to crayfish gastric fluid. The mechanoreceptors reacted to stretch of the oesophageal wall adapting only slowly to maintained stimuli. It is assumed that the A-cells are the chemosensitive cells and the B-cells the mechanosensitive ones. The latter show only a small number of modality-specific characteristics. Several structural features appear to be correlated with the location of the AOS within a flexible surface, which undergoes considerable dilation.