Ultrastructure of the epidermis of Meara stichopi (Platyhelminthes,Nemertodermatida) and associated extra-epidermal bacteria

This preliminary mechanistic model of normal swimming and phototactic behaviour in individual Daphnia was constructed using data and assumptions based on experiments and observations. Swimming under constant light intensity is characterized by short periods of upward movements alternating with equal periods of downward movements. Two oscillators are proposed that generate these phases in swimming. Unexpected shifts in depth, as observed in D. magna and D. longispina, are also present in the swimming of the computer daphnid and thus seem to be inherent to the underlying mechanism. As in real daphnids, during relative decreases in light intensity of low velocity, positive phototactic upward swimming is stepwise. With increasing velocity in the change in light, these steps disappear. When the model is triggered by a natural increase in light at dawn, a small downward movement results. Migration distance can be increased to commonly found depths of migrating Daphnia by the introduction of a fish exudate factor into the model, which enhances the phototactic response. Since attenuation of light in the water affects the phototactic swimming response, it also influences migration distance. The results of model calculations agree quite well with an empirical relationship between Secchi disc depth and amplitude of diel vertical migration in a number of lakes.     

Ultrastructural studies of epidermis, sense receptors and sperm of Craspedella sp. and Didymorchis sp. (Platyhelminthes, Rhabdocoela)

Craspedella has a non-ciliated epidermis with nuclei located in the epidermis and with short microvilli. There is a thin basal lamina and thick underlying fibrous matrix. Rhabdites are secreted through ducts lined by microtubules. Multiciliate sense receptors consist of bundles of dendrites in a depression of the epidermis. Each dendrite has a cilium with a cross-striated rootlet; there are no electron-dense collars. Spermatozoa have peripheral microtubules which in cross-section are arranged in a ring-like or spiral fashion, numerous electron-dense granules, mitochondria and a nucleus; axonemes of the 9 +'1'type are free for most of their length. Centrioles occur in some nerve fibres. In Didymorchis parts of the epidermis are ciliated and epidermal perikarya are 'insunk', connected to the surface part of the epidermis by a single cytoplasmic process. Epidermal cilia have cross-striated vertical and horizontal rootlets. In the ciliary tips a short electron-dense rod along the central pair of tubules extends to the tip, where it widens to become a terminal plate; peripheral doublets gradually disappear by losing their microtubules. Receptors observed are uniciliate. Spermatozoa are as in Craspedella . Ultrastructural evidence indicates that Craspedella and Didymorchis arc closely related and belong to the Rhabdocoela.     

An ultrastructural analysis of the cuticle,epidermis and esophageal epithelium of Eisenia foetida (Oligochaeta)

The epidermis of Eisenia is covered by a cuticle and rests on a basement lamella. The cuticle, which is resistant to a variety of enzymes, is composed of non-striated, bundles of probable collagen fibers that are orthogonally oriented and are embedded in a proteoglycan matrix. The basement lamella consists of striated collagen fibers with a 560 Å major periodicity. Proximity and morphology suggest that the epidermis may contribute to both the cuticle and the basement lamella — that is, the single tissue may synthesize at least two types of collagen. The epidermis is a pseudostratified epithelium containing three major cell types (columnar, basal and gland) and a rare fourth type with apical cilia. The esophagus is lined by a simple cuticulated epithelium composed predominantly of a single cell type, which resembles the epidermal columnar cell. Rare gland cells occur in the esophageal epithelium, but basal cells are lacking.     

Molecular and ultrastructural studies of the sperm chromatin from Triturus cristatus

The study of nuclear molecular architecture during gametogenesis represents one approach towards the deciphering of the molecular organization of eukaryotic chromatin. During spermatogenesis, chromatin undergoes several dynamic transitions, which are often associated with important changes not only in its physical conformation but even in its composition and structure. Dynamic alterations in chromatin structure mediated by postsynthetic histone modification and DNA methylation constitute a major regulatory mechanism of gene function of eukaryotes. Using transmission electron microscopy and molecular investigations, some peculiar aspects of chromatin organization and evolution in spermatogenesis of the crested newt Triturus cristatus were investigated. We focused our investigations on the dynamics of chromatin structure after treatment with TSA (a histone deacetylase inhibitor).     

Comparative ultrastructural studies of spermiogenesis and spermatozoa in some species of Polyplacophora (Mollusca)

Summary

Comparative data on the ultrastructure of spermiogenesis and spermatozoa of the Polyplacophora Acanthochitona crinita, Chaetopleura angulata and Callochiton septemvalvis are presented in this study. In contrast to what has been described for this and other classes of Mollusca, no acrosome is present in the spermatozoa of these Polyplacophora. The nucleus is extended by a long, thin apical point. In A. crinita and C. angulata the mitochondria are situated at the basal and lateral regions of the nucleus. They do not present a typical middle piece. These species present a pericentriolar process. In C. septemvalvis the mitochondria are situated at the base of the nucleus, surrounding the centrioles, which are orthogonally positioned in all species. The ultrastructural development during spermiogenesis is similar. In middle spermatids of A. crinita, the chromatin is arranged in fine filaments. In C. septemvalvis and C. angulata the chromatin filaments are thicker, forming coarse bands. In late spermatids elongation of the nucleus continues, it becomes rather electron-dense and the chromatin filaments are more condensed. Finally, the nucleus has a uniformly electron-dense appearance, with no signs of filamentous organization. Considering the ultrastructural modifications observed, the Polyplacophora spermatozoa could be included in a modified type.     

Comparative structure of the epidermis in polychaetes (Annelida)

The polychaete epidermis generally consists of a single layer of supportive cells, gland cells and sensory cells. Except for the latter, this paper reviews the recent literature on the annelid epidermis, focussing on the mentioned cell types and the cuticle. The annelid epidermis is compared to that of Sipuncula, Echiura and Myzostomida. Supportive cells predominate in the polychaete epidermis. They show a high structural diversity even within single specimens. Ciliated cells are usually multiciliary and only two cases of monociliary epidermis cells are known. Unambigous epithilio-muscle cells are only described in feeding palps of a Magelona species. Secretory cells release a large number of gland products and some of them are essential for tube secretion. Rather pecularities of the cells and its arrangement within glands than the ultrastructure of the secretions is useful for phylogenetic considerations. One of the main components of the cuticle is collagen. Recent studies indicate that annelid cuticular collagen differs in several aspects from collagen of the connective tissue and might be of interest for systematics.     

The muscular system of Nemertoderma westbladi and Meara stichopi (Nemertodermatida, Acoelomorpha)

Nemertodermatida is a small taxon of marine worm-like animals; its position in the tree of life is highly contested. The musculature of Nemertoderma westbladi and Meara stichopi is studied here in detail using fluorescent phalloidin and confocal microscopy. In both species, the musculature is composed of an outer layer of circular and an inner layer of longitudinal musculature, diagonal muscles form a distinct layer in N. westbladi, but in M. stichopi these fibres connect to both other layers. The supraterminally opening male pore and antrum are formed by invagination of the whole body-wall in both species, and the seminal vesicle is lined by a thin net of musculature only in full male maturity. Modifications of the ventral body-wall adjacent to the mouth are small and transient in N. westbladi including no extra musculature, whereas it consists of additional strong U-shaped musculature in M. stichopi. Myogenesis in N. westbladi is not finished in hatchlings and will be completed dorsally in juvenile specimens and ventrally in male mature ones, after the loss of the mouth. Musculature between the two species differs considerably and might give insights into the internal relationships of Nemertodermatida and might prove to be useful in studies investigating their phylogenetic position. More data of other species and developmental changes are needed.     

A comparative scanning electron-microscopical study of endoneurial collagen around normal mouse nerve fibres,nerve fibres following crush injury and nerve fibres of the dystonic mouse mutant (dt/dt)

Summary The endoneurial collagen sheath around teased nerve fibres following crush injury was studied by scanning electron microscopy and compared with uninjured sciatic nerve fibres and with fibres from the dystonic mutant mouse. Following crush injury the endoneurial collagen became more abundant than seen in untreated nerve fibres and formed large, separate and longitudinally oriented bundles. However, by four weeks post injury the sheath regained a normal external appearance. Mutant nerve fibres were also associated with more than the usual amount of collagen, but the sheaths were more disorganised, with a marked disorientation and irregular aggregation of collagen, and these abnormalities were not confined to obviously degenerating or demyelinated regions of the fibres. The dystonic abnormalities of the endoneurial sheath may be important in the mechanism of the neuropathy.Medical Research Council, Radiobiology Unit, Harwell, Didcot, Oxon, OX11 ORD     

Spermiogenesis and sperm in Mesostoma viaregginum (Plathelminthes, Rhabdocoela): an ultrastructural study to infer sperm orientation

Spermiogenesis in Mesostoma viaregginum begins with the formation of a zone of differentiation containing striated rootlets, two centrioles, and an intercentriolar body in-between. These centrioles generate two parallel free-flagella with the 9+“1” pattern of the Trepaxonemata growing out in opposite directions. Spermatid differentiation is characterised by a 90° latero-ventral rotation of flagella and a subsequent disto-proximal centriolar rotation, with a distal cytoplasmic projection. The former rotation involves the compression of a row of cortical microtubules and allows recognising a flagellar side and an aflagellar side in the late spermatid and in the mature spermatozoon. At the end of the differentiation, centrioles and microtubules lie parallel to the spermatid axis. The disto-proximal centriolar rotation is proposed as a synapomorphy for the Rhabdocoela. The modifications of the intercentriolar body during spermiogenesis and the migration of the nucleus and the centrioles towards the cytoplasmic distal projection are also described. The mature spermatozoon of M. viaregginum is filiform and tapered at both ends and presents many features found in the Rhabdocoela gametes. The nucleus disappears before the flagellar insertion and a density gradient of mitochondria is observed along the sperm axis. The anterior end of the spermatozoon of M. viaregginum is characterised by a tapering capped by a membrane expansion. This study has enabled us to describe precisely the orientation of spermatozoa in the Rhabdocoela in general: the centriolar extremity is proposed as the anterior one for the Rhabdocoela.     

The skin of Osedax (Siboglinidae,Annelida): An ultrastructural investigation of its epidermis

The symbiotic polychaetes of the genus Osedax living on the bones of whale carcasses have become known as bone‐eating worms. It is believed that whale bones are the source of nutrition for those gutless worms and that fatty acids are produced by their symbionts and transferred to the host. However, the symbionts are of the heterotrophic group Oceanospirillales and as such are not able to synthesize organic carbon de novo. Also, they are not housed in close contact to the bone material. We studied the ultrastructure of the integument overlying the symbiont housing trophosome in the ovisac region and the roots region and of the symbiont‐free trunk region of Osedax to investigate the host's possible contribution in feeding for the whole symbiosis. The epidermis differs conspicuously between the three regions investigated and clearly points to being correlated with different functions carried out by those regions. The ultrastructure of the integument of the root region changed towards the ovisac region and corresponds with the change of the ultrastructure observed in the Osedax trophosome. We suggest that the epidermis in the root region is tightly linked to bone degradation and nutrient uptake. The trunk region possess two types of unicellular gland cells, at least one of which seems to be involved in secretion of the gelatinous tube of adult Osedax females. J. Morphol., 2010. © 2010 Wiley‐Liss, Inc.     

Comparative histochemical distribution of nerve fibres storing noradrenaline and neuropeptide Y (NPY) in human ovary, fallopian tube, and uterus

Nerves containing noradrenaline were studied by formaldehyde-induced fluorescence and neuropeptide Y (NPY) was visualised by immunohistochemistry in the human ovary, Fallopian tube and uterus. All structures were richly supplied with noradrenergic fibres closely associated with the vascular and non-vascular smooth musculature. NPY-containing nerve terminals were consistently fewer, particularly in the ovary. The best developed nerve supply was found in the tubal isthmus and uterine cervix. Vessels were usually innervated by plexuses of nerves, containing NPY as well as noradrenaline. The discrepancy between the number of the two types of histochemically distinguishable nerves suggests that, if noradrenaline and NPY are co-localised in one and the same nerve, this is not a constant phenomenon in the human female reproductive tract.     

The epidermis of Timarete filigera (Polychaeta, Cirratulidae): histochemical and ultrastructural analysis of the gland cells

The aim of this study was to verify whether different living conditions of Polychaeta are correlated with morphological and functional differences in the organization of the integument. For this purpose, we decided to study the epidermis of Timarete filigera, a non-tubicolous polychaete. With this objective in mind, we have identified the various cellular types responsible for mucous secretion in the epidermis of this species and defined the histochemical composition of the mucus produced by different types of gland cells. Three types of gland cells have been identified by histochemical and ultrastructural studies in the epidermis of this polychaete. The histochemistry was carried out using standard techniques and peroxidase-labelled lectins. In type 1 cells, the secretory granules contain neutral glycoproteins with glucosidic residues of GalNAc, Galbeta 1,3 GalNAc, glucosidic and/or mannosidic residues. In type 2 cells, the secretory granules contain acid glycoproteins mainly sulphated with glucosidic residues of GalNAc, Galbeta 1,3 GalNAc, glucosidic and/or mannosidic residues, and some terminal sialic acid. In type 3 cells, the residual granules have the same chemical composition as that of granules present in type 2 cells. The secretion of these glandular mucous cells consists of mainly sulphated acidic glycoproteins and GAG resistant to testis jaluronidase. In these cells, the residual granules have the same chemical composition as that of their secretion. The heterogeneity of mucus composition may be correlated with its different functions.     

Comparative morphology of the leaf epidermis in Schisandra (Schisandraceae)

The leaf epidermis of 127 samples representing ten species within Schisandra Michaux. and one species of the related genus, Kadsura Kaempf. ex Juss., was investigated using light and scanning electron microscopy. Many characters of the leaf epidermis in Schisandra , such as pattern of epidermal cells, type of stomata, shape of guard cell pairs and cuticular ornamentation, are usually constant within species and thus make good characters for studying the relationship between and within genera. A new character, rim number, of the outer stomatal rim in the genus is introduced. It is shown that double outer stomatal rims occur only in evergreen Schisandra species, whereas a single rim occurs in deciduous species. This character supports the classification of Schisandra into two subgenera based on habit and androecial organs. This classification is also supported by additional morphological and molecular taxonomic characters. Kadsura coccinea (Lem.) Smith A. C. is the most primitive taxon in the related genus Kadsura . The outer stomatal rim of this species also has double rims. Combined with morphological and molecular evidence, this suggests that Schisandra and Kadsura are closely related and may share a recent common ancestor.  © 2005 The Linnean Society of London, Botanical Journal of the Linnean Society , 2005, 148 , 39–56.     

Comparative observations on inclusions in nerve fibres of the mammalian neurohypophysis

Summary A comparative study has been made of the inclusions within neurohypophysial nerve fibres of eight species of mammals.Four classes of small inclusions have been found in each of these species, namely small and large membranous vesicles, and small and large osmiophilic membrane-bound granules. No inclusions resembling the rod-shaped inclusions in the hedgehog's neurohypophysis have been found. It seems probable that more than one type of neurosecretory fibre occurs in the infundibular process of all these species.Large lamellated structures were found in some species, and these possibly give rise to membranous vesicles.     

A study of pre- and postganglionic fibres in the intestinal nerve (Remak's nerve) of the chicken

Summary The mean peak CV's of two electrophysiologically defined groups of fibres in the intestinal nerve of the chicken have been determined.One group of fibres is constituted by the processes of enteric cholinergic neurones which project along the side branches of the intestinal nerve and synapse within the nerve trunk. These preganglionic fibres have a mean peak CV (at 40 °C) of 0.31 m·s^–1.The other group is made up of fibres of postganglionic neurones which project orally along the nerve trunk. The results suggest that some postganglionic neurones project only as far as the next ganglion whilst others project beyond the next two ganglia for distances greater than 5 mm. The postganglionic fibres have a mean peak CV (at 40 °C) of 0.71 m·s^–1.These figures demonstrate that both pre- and postganglionic fibres are unmyelinated. The temperature coefficient (Q₁₀) for the CV of unmyelinated fibres in the intestinal nerve was 1.57.Abbreviations CAP compound action potential - CV conduction velocity - Q ₁₀ temperature coefficient     

Dynorphin-A (1-8) is contained within perikarya, nerve fibres and nerve terminals of rat duodenum

By the use of well-characterized antibodies against porcine dynorphin-A(1-8), an endogenous opioid peptide, and the use of a modified immunofluorescence microscopic technique, dynorphin-A(1-8) stained perikarya, nerve fibres, and nerve terminals were visualized in the rat duodenum. Dynorphin-A(1-8) immunoreactive perikarya were revealed with certainty only in the myenteric plexus, while dynorphinergic nerve fibres could bee seen in the myenteric plexus and circular muscle layer, but not in the longitudinal muscle layer and submucous plexus. Dynorphin-A(1-8) immunofluorescent nerve endings were in close contacts with submucosal blood vessels, probably arterioles, and Brunner's gland cells. These findings suggest that the opioid peptide dynorphin-A(1-8) might be synthetized within myenteric plexus perikarya of the rat duodenum and that it might modulate the peristaltic activity, intestinal blood pressure, and production of mucopeptides synthetized within Brunner's gland cells.