An analysis of the role of actin during pollen activation leading to germination in pear (Pyrus communis L.): treatment with cytochalasin D

Summary Major stages of actin organization during activation leading to germination of pear (Pyrus communis L.) pollen were disrupted by treatment with 5 g/ml cytochalasin D (CD), and the effects of the drug were monitored with rhodamine-phalloidin staining. CD induced the formation of granules or short rods in the place of the filamentous arrays that occur in normally developing pollen. Filamentous arrays, however, returned upon removal of CD. Pollen incubated directly in CD showed a gradual disappearance of circular actin profiles and their replacement by either granules or, less frequently, short rods. These granules and rods initially had a random distribution in the cell, but with time in CD they became localized at one of the three germination apertures. Pollen was also allowed to reach three stages of microfilament (MF) organization (initial fibrillar arrays, interapertural MFs, and MFs confined beneath a single aperture) prior to being continously exposed to CD. After CD treatment, germination was blocked and the number of cells containing short rods increased, but movement of actin to a single aperture continued. Finally, when pollen at different stages of MF organization was treated with a CD pulse and then transferred to drug-free medium, germination was delayed regardless of the stage of MF organization at the time of treatment. The results indicate that an uninterrupted progression of actin organization is essential for pollen germination, but that movement of actin in the cell is CD-insensitive.     

Pigment epithelial ensheathment and phagocytosis of rod tips in the retina of Rana catesbeiana

Two modes of shedding of rod disc membranes were observed by electron microscopy in bullfrog retinas illuminated for various periods from 10 min to 2 hr. One mode is "autonomous shedding" whereby rods shed disc packets directly into the subretinal space. Most of the discarded disc packets are subsequently brought into contact with villous apical processes of pigment epithelial (PE) cells and are ultimately engulfed by these cells. When some of the shed disc membranes remain in the subretinal space, it appears that these remnants may be phagocytized by ameboid phagocytes. The other mode is "cooperative shedding" whereby rods shed disc packets with the participation of pigment epithelial ensheathment. Shedding of a disc packet from a rod tip, and enclosing of the rod tip by a broad, sleeve-like apical process of a PE cell, take place simultaneously. The separated disc packets may be immediately engulfed by the PE cells without risk of failure. Both villous and sleeve-like types of apical processes of PE cells in the bullfrog lack pigment granules, in contrast to the finger-like apical processes that do contain pigment granules. Villous and sleeve-like processes therefore probably belong to the same category as the leaf-like apical processes of PE cells in mammalian retinas.     

Release of chromaffin granular content from staphylococcal enterotoxin B (SEB)-treated and-untreated PC12 cells

Summary The release of chromaffin granular content from staphylococcal enterotoxin B (SEB)-treated and-untreated PC12 cells was studied by electron microscopy. The treatment of the cells with SEB at the concentration of 20 μg/ml caused marked increase of the chromaffin granules that either bound to the plasma membrane by the characteristic rods, measuring 15 to 20 nm in length and showing a tubular structure, or budded off at the free cell surface, surrounded by a layer of rod-containing cytoplasm and enclosed by the plasma membrane. The binding between the granular and plasma membranes by the rods did not lead to membrane fusion and exocytosis of the granular content. Many of the bound granules showed vesiculation with loss of the electron-dense core material; at the same time, some of the binding rods contained intraluminal electron-dense material similar to the granular core material. These findings suggested that the electron-dense material (i.e., norepinephrine) of the bound granules was released extracellularly through channels within the rods. Although the granules were bound to the plasma membrane with equal frequency at the free and contiguous cell surfaces, the granular budding occurred only at the free cell surface, indicating that it occurred incidentally to some granules bound at the free cell surfaces. On the basis of the morphological observations, it is postulated that the electron-dense material of the bound granule is selectively released extracellularly through the rods, leaving the vesiculated granules behind in the cytoplasm. The same mode of release of the granular content was observed, though less frequently, in the untreated control cells. No morphological evidence that indicated that the granular content was released extracellularly by exocytosis was found in the treated and control cells. The present observations indicated that the SEB treatment of PC12 cells stimulated the binding of chromaffin granules to the plasma membrane by the rods and the budding of the bound granules at the free cell surface.     

Immunofluorescent demonstration of myeloperoxidase of phi bodies and rods in leukaemic leucocytes

Summary Previous studies employing enzyme histocytochemical methods based on the catalysis of the peroxidation of 3,3-diaminobenzidine (DAB) demonstrated the presence of hydroperoxidase activity in phi bodies and rods of immature leucocytes of patients with active acute myelogenous leukaemia. It could not be determined from these studies whether the DAB oxidation product was demonstrating a single hydroperoxidase, catalase or myeloperoxidase, or both. In the present study, immunofluorescence techniques for the two hydroperoxidases were applied in an attempt to identify this activity specifically. The results obtained indicate that myeloperoxidase is present in the phi bodies and rods, and that this enzyme may be the major on the only hydroperoxidase present. Its activity could account for the peroxidation of DAB under conditions which are more favourable for the demonstration of catalase.     

Catalase in salivary gland striated and excretory duct cells. II. ? Body: an ellipsoidal peroxisomal organelle with crystalloid axial projections

Synopsis A new distinctive and unique peroxisomal organelle with a spindle shape has been observed in luminal epithelial cells of striated and excretory ducts of mouse salivary glands. Light microscopic studies indicate it has an ellipsoidal centre from which catalase-positive filamentous or rod-like processes protrude along its major axis; hence, it is called a body. A role for this specialized peroxisome in the formation of nearby free filaments and rods is suggested by the frequent observation of segmentation of its axial processes. Complementary ultrastructural studies of osmium-fixed preparations show that the deformation to an oval shape results from the pressure of the extruding crystalloid coincident with the major axis of the ellipsoidal body. The size range and conformation of body axial processes are comparable to those of free catalase-positive rods and filaments observed in the same cells. The periodic substructure of the crystalloid in the body core is identical with that of nearby cytoplasmic rods. These observations are consistent with the view that the rods and filaments observed free in the cytoplasm are formed by extrusion from the crystalloid core of the body. Bodies could also be responsible for the Aver rods of leukemic leukocytes.     

Electron microscopic observations on a new cell type in the fundus mucosa of the mouse stomach

Summary In the course of electron microscopic investigations of the fundus mucosa of the mouse stomach, a few cells of an unknown type were found by chance in the deep portions of the glands. These cells are characterized by two different kinds of specific granules in their cytoplasm, one of which being large and less dense, and the other one being small and dense. The large less dense granules resemble zymogen granules of the chief cell, which are formed by the rough endoplasmic reticulum and Golgi system. The small dense granules are quite similar to the secretory granules of the basal granulated cell, and are considered to be formed in the Golgi complex. Release figures of the small dense granule were not observed, numerous granules, however, were observed in close contact with the basal cell membrane. The occurrence of these two kinds of granules in one cell suggests that the basal granulated cell and the zymogenic cell originate from the same entodermal stem element.The author cordially thanks Professor Dr. Hisao Fujita, Department of Anatomy, Hiroshima University School of Medicine, for his kind advices and criticisms.     

Ultrastructure of the median eminence of the rat

Summary The ependymal cells bordering the median eminence to the third ventricle are characterised by many microvillus-like projections and bulbous cell processes of the luminal plasma membrane. The latter contain many vesicles 500–1,000 Å in diameter. Cilia with 9+2 fibrillar pattern are seen occasionally. Adhesive devices in the from of zonula adhaerens and zonula occludens are found in the apical part of the intercellular junction. Unmyelinated nerve fibres with a mean diameter of 1 and containing many electron dense granules of 830–1,330 Å are often seen between the ependymal cells.Two types of glial cells are found in the median eminence. One is characterised by a nucleus with dense blods of chromatin and dense cytoplasm, and it is associated chiefly with the nerve fibres in the region of the hypothalamo-hypophysial tract. The other type of glial cell is characterised by fine, uniformly distributed chromatin in the nucleus and a relatively pale cytoplasm and branched processes which terminate perivascularly in the base of the median eminence.Myelinated nerve fibres are seen only in the region of the hypothalamo-hypophysial tract. Only a part of them contain electron dense granules 1,330–2,330 Å in diameter.Three types of unmyelinated nerve fibres can be distinguished in the median eminence according to the size of the electron dense granules they contain: 1. Nerve fibres containing granules 1,330–2,330 Å in diameter. They are seen primarily in the hypothalamo-hypophysial tract, but also in the zona externa; 2. those containing granules with a mean diameter of 1,330 Å; and 3. those containing granules with a mean diameter of 1,000 Å. The last two types are both encountered in the hypothalamo-hypophysial tract, the zona externa and the perivascular region of the base of the median eminence. Under high magnification, the membrane of the granules show evidence of a trilaminar structure and the content of the granules with a low electron density appeares to consist of small microvesicles or globular components. Besides granules, these nerve fibres contain vesicles mostly 420 Å in diameter whose relative number increases towards the perivascular nerve endings. 53 per cent of the inclusions in the hypothalamo-hypophysial tract are granules and 47 per cent vesicles, while the corresponding percentages for the zona externa are 40 and 60 and for the perivascular nerve endings 20 and 80.The mean width of the pericapillary space is 1 , but it varies greatly. It containes many collagen fibrils and fibroblasts. The capillary endothelium is frequently fenestrated and contains many vesicles of various sizes.Two types of granules-containing cells are found in the pars tuberalis depending on the size of the electron dense granules: 1. cells containing granules with a mean diameter of 1,330 Å: and 2. cells containing granules with a mean diameter of 2,000 Å. In addition, there are occasional follicular cavities filled with amorphous material, microvilli and cilia of 9+2 fibrillar pattern.Aided by a grant from the Sigrid Jusélius Stifteise.     

Ultrastructure of human amnion and amniotic plaques of normal pregnancy

Summary The fine structure of amniotic and amniotic-plaque epithelia has been studied from normal term pregnancies. The columnar/cuboidal amniotic epithelial cells usually have apical or central nuclei, some free ribosomes, patches of granular endoplasmic reticulum, juxtanuclear Golgi complexes, rod-shaped mitochondria, lipid droplets and some glycogen granules. They have short, blunt microvilli which frequently branch and bathe in the amniotic fluid. The lateral plasma membranes enclose tortuous intercellular spaces which are always interrupted by variously folded processes and desmosomes. The epithelial cells rest on a basal lamina and exhibit highly folded basal processes. The amniotic epithelial cells are neither distinctly Golgi and fibrillar types nor light and dark in appearance.Amnion from near the umbilical cord contains many microscopic and several large plaques. Similar structures are not found on the reflected amnion. The microscopic plaques are whitish and translucent, whereas the large ones are opaque. The large plaques vary between 1–3 mm in diameter, and are over 15 cell layers thick. Each large plaque has a main central region and edges continuous with either the microscopic plaque or the simple amniotic epithelium. The main region shows four zones, namely, stratum basale, stratum spinosum, stratum granulosum and stratum corneum. Such zones are not distinct at the edges. The fine structure of basal cells compares with the amniotic epithelial cells, but the cells of spinosum and granulosum layers possess variable amounts of tonofibrils, keratohyalin granules, free ribosomes and other cytoplasmic organelles and inclusions. The corneum cells are keratinized and are frequently separated by intercellular spaces. They slough into the amniotic cavity singly or as a sheet, and contribute towards the composition of the amniotic fluid. The plaques are of amniotic origin, and are not formed by adhesion of either squamous cells or fetal skin cells (masses of keratinized squames). The present observations suggest that the occurrence of amniotic plaques is normal. The presence of plaques may not be necessarily associated with fetal abnormality. However, increase in numbers of plaques may be caused by conditions of fluid imbalance. The homology and significance of plaques in eutherian mammals have been discussed.This research was supported by USPHS Grant AM-11376 and NIH Grant 69-2136.     

Ultrastructure of an extreme thermophilic hydrogen-oxidizing bacterium Calderobacterium hydrogenophilum

Calderobacterium hydrogenophilum is an extreme thermophilic, obligately chemoautotrophic, hydrogen-oxidizing bacterium. The cells were shown to be nonmotile straight rods of average size 0.4x2.5 m. After negative-staining of the whole cells, no flagella were observed. The multilayered cell wall was of type 1 and possessed a crystalline proteinaceous surface layer exhibiting p4 symmetry. The square unit cells had a lattice constant of approximately 11 nm. Cell division occurred by a constriction mechanism. C. hydrogenophilum differred from a similar hydrogen-oxidizing eubacterium, Hydrogenobacter thermophilus, by the absence of intracytoplasmic membrane structures in chemically fixed cells. However, an electron-dense intracytoplasmic hemispherical structure adhering to the inner membrane was frequently observed.     

Unique features of secretory granules observed in the pituitary growth hormone-secreting (GH) cells of the musk shrew (Suncus murinus L.)

Summary Unique rod-shaped secretory granules were observed among oval or spherical secretory granules in GH cells of the anterior pituitary gland of musk shrew using the protein A-gold procedure combined with electron microscopy. The rod-shaped and spherical secretory granules were both immunoreactive by the immuno-gold method using antiserum to sheep GH. The rod-shaped secretory granules, which seem to be formed directly from the Golgi vesicles, extend from several hundred to several thousand nm in length. They often touch each other and fuse. The spherical secretory granules are also unique in that they may also fuse with loss of dense contents to leave empty circular membrane profiles in the cytoplasm. Both the rodshaped and spherical secretory granules are secreted from the cell by exocytosis.     

Presence of cells combining features of two different cell types in the colonic crypts and pyloric glands of the mouse.

A small number of epithelial cells which combine features of two cell types were observed in the descending colon and pyloric stomach of the mouse. In the descending colon, where the base of the crypts is mainly composed of poorly differentiated "vacuolated" cells, a few of these cells contain, besides the characteristic "vacuoles," mucous globules identical to those in mucous cells or, less frequently, dense granules such as are found in entero-endocrine cells. Because there is evidence that the poorly differentiated vacuolated cells give rise to the other cells of the epithelium, those which also contain mucous globules or dense granules are likely to be differentiating into mucous cells or entero-endocrine cells respectively. In the pyloric stomach, where the glands are mainly composed of mucous cells, some of which are poorly differentiated, a few of the latter exhibit, besides the mucous globules, entero-endocrine type granules or features of caveolated cells. It is likely that the poorly differentiated mucous cells give rise to the other gland cells; and, therefore, those mucous-containing cells which also display dense granules or caveolated cell features are taken to be differentiating into entero-endocrine or caveolated cells respectively. Most of the cells containing two kinds of secretory materials are believed to be stem cells which initially contain a few vacuoles (colon) or mucous globules (pylorus) but are differentiating into a cell containing a different type of secretion. Rare observations of two kinds of secretory materials in a mature cell suggest that the transitional period may be prolonged, perhaps indefinitely.     

Isolation and Characterization of Cytoplasmic Cofilin-Actin Rods

Cofilin-actin bundles (rods), which form in axons and dendrites of stressed neurons, lead to synaptic dysfunction and may mediate cognitive deficits in dementias. Rods form abundantly in the cytoplasm of non-neuronal cells in response to many treatments that induce rods in neurons. Rods in cell lysates are not stable in detergents or with added calcium. Rods induced by ATP-depletion and released from cells by mechanical lysis were first isolated from two cell lines expressing chimeric actin-depolymerizing factor (ADF)/cofilin fluorescent proteins by differential and equilibrium sedimentation on OptiPrep gradients and then from neuronal and non-neuronal cells expressing only endogenous proteins. Rods contain ADF/cofilin and actin in a 1:1 ratio. Isolated rods are stable in dithiothreitol, EGTA, Ca²⁺, and ATP. Cofilin-GFP-containing rods are stable in 500 mm NaCl, whereas rods formed from endogenous proteins are significantly less stable in high salt. Proteomic analysis of rods formed from endogenous proteins identified other potential components whose presence in rods was examined by immunofluorescence staining of cells. Only actin and ADF/cofilin are in rods during all phases of their formation; furthermore, the rapid assembly of rods in vitro from these purified proteins at physiological concentration shows that they are the only proteins necessary for rod formation. Cytoplasmic rod formation is inhibited by cytochalasin D and jasplakinolide. Time lapse imaging of rod formation shows abundant small needle-shaped rods that coalesce over time. Rod filament lengths measured by ultrastructural tomography ranged from 22 to 1480 nm. These results suggest rods form by assembly of cofilin-actin subunits, followed by self-association of ADF/cofilin-saturated F-actin.     

Mast cells in human bile duct obstruction

Surgical biopsy specimens obtained from 50 patients with secondary cholangitis caused by obstruction of the common bile duct were studied immunohistochemically. Data on the number and ultrastructural appearances of mast cells positive for tryptase, chymase, vasointestinal polypeptide (VIP), and substance P (SP) were obtained. The bile ducts from patients presenting combined chronic exacerbated cholangitis and chronic sclerotic cholangitis showed significantly higher numbers of mast cell types compared to the controls (P < 0.0001). Cases with sclerotic cholangitis alone had significantly lower number of cells than patients with chronic exacerbated cholangitis alone (P 0.0001). Morphometric measurements of electron micrographs showed that mast cell granules containing VIP, SP and chymase were commensurable in size. Electron-lucent granules without reaction product (altered granules) and granules with focal distribution of the reaction product were observed in all types of mast cells. Furthermore, some nerve fibers positive for SP and VIP and serotonin-positive endocrine cells were observed in close proximity to the mast cells. In conclusion, the results of our study demonstrate the existence of different populations of mast cells, nerve structures and endocrine cells in the lower part of the human large bile duct, and suggest their participation in the development of pathological processes.     

Temporally and spatially restricted expression of a gland cell gene during regeneration and in vitro transdifferentiation in the hydrozoan Podocoryne carnea

An antiserum to transdifferentiated striated muscle cells from the medusa of Podocoryne carnea was prepared and used to screen a gt11-expression library prepared from gonozoids of P. carnea. We isolated a cDNA clone termed Pod-EPPT with at least 63 tandem repeats of the tetrapeptide-motive glu-pro-pro-thr, named Pod-EPPT. Using Pod-EPPT as a molecular marker for head quality the morphological relationship between the two metagenic life stages of this hydroid, the polyp and the medusa, was studied. In situ hybridization demonstrated that expression of the gene corresponding is restricted to secretory cells in the endoderm of the oral hypostome region of polyps and medusae and, presumably, to progenitor cells of this type. Cells expressing Pod-EPPT could not be observed in the larval stage. During head regeneration in polyps, Pod-EPPT expression is upregulated soon after head removal in previously non-expressing cells and in newly differentiating secretory cells. This activation of a head-specific gene precedes the morphologically obvious events of head regeneration. Pod-EPPT is one of the genes that are activated during manubrium (mouth) regeneration from experimentally combined subumbrellar plate endoderm and striated muscle of the medusa.     

An histochemical approach to characterization of anionic constituents in mast cell secretory granules

We used cationized colloidal gold in order to investigate the distribution of anionic sites in different secretory granules of rat and mouse mast cells. The localization of the anionic sites was performed by post-embedding labeling of thin sections of rat peritoneal cells or mouse skin tissue, fixed in Karnovsky's fixative and OsO₄ and embedded in Araldite or LR white, respectively. In all cases anionic sites were demonstrated with a high density variation depending on cell type. In all mast cell secretory granules we have observed the highest density (ca. 500–900 gold particles/m²), while in other peritoneal cell granules it was about 10 times less (ca. 40–80 gold particles/m²). Pretreatment of the LR white sections with heparinase I and III resulted in a reduction of 97% and 72%, respectively, in the binding of the gold particles to the granules, indicating that the majority of the gold binding reactivity is due to heparin. Correlation of section profile area with labeling density revealed that the smaller granules were significantly more labeled when compared to the larger profiles. On the basis of these observations it seems that a post-translational change (mainly sulfation of heparin) of secretory content influences the granule anionic charge and thus may affect the intragranule buffer capacity.     

Über den Bau und die Hell-Dunkel-Adaptation der Augen des Polychäten Platynereis dumerilii

Summary The eye of Platynereis dumerilii consists of three components: a short optic nerve, a cup-shaped retina, and a vitreous body within the cup. The opening of the retinal cup is called pupil. The retina is composed of supporting cells and visual cells. The supporting cells are stuffed with dark blue violet pigment granules. The visual cells have orange pigment granules which are only found in the narrow middle piece of the cells. The supporting cell pigment may be lacking in abnormally pigmented eyes. The jellylike matter of the vitreous body apparently is produced by the supporting cells. It is of high protein contents and does not seem to be derived from the cuticle which consists of polysaccharides.The ultrastructure of the photoreceptor region shows club-shaped processes of visual cells. Each club is of low electron density and contains elongate membranous structures. It is surrounded by many microvilli. The clubs correspond to the rods in light microscopy.The eye of Platynereis dumerilii adapts to changes in light intensity by movements of the retina and the rods. The cup-shaped retina spreads towards its pupillar opening thus adapting the pupil area to light intensity. The length of the rods in darkfixed immature specimens is about 20, in light-fixed ones about 7 . In mature specimens (Heteronereis) the length is 46 or 19 respectively.During metamorphosis the eyes enlarge to about three times their original volume. This enlargement is due to an increase in volume of the retina and the vitreous body, not to cell divisions.

---

---

Durchgeführt mit Unterstützung durch ein Stipendium aus Mitteln der Fritz-Thyssen-Stiftung, ferner mit Hilfe der Deutschen Forschungsgemeinschaft.

---

Die Anregung zu dieser Arbeit und das Platynereis-Zuchtmaterial verdanke ich Herrn Prof. Dr. C. Hauenschild. Für Hilfe bei der Herstellung des Bildmaterials danke ich Frl. U. Poltz (Freiburg).     

Sulla organizzazione dello strato granulare esterno e della membrana limitante esterna nella retina di coniglio

Summary The organisation of the outer nuclear layer and the structure of the outer limiting membrane of rabbit retina have been studied. In specimens stained by the Golgi method it was observed that in the outer nuclear layer each Müller cell envelops with its thin lamellar expansions ten to fifteen rod and cone cell bodies.The only cytoplasmic organelles in rod and cone cell bodies are a few free ribosomes and smooth surfaced vesicles. Neurotubules are prominent in the outer and inner fibres of the rods and cones.The processes of the Müller cells are distinctive because of the presence of many glycogen granules and glial filaments. Also present but only found near the outer limiting membrane are mitochondria, occasional centrioles and cilia that lack inner fibres. Long microvilli originate from the Müller cell processes on the scleral side of the outer limiting membrane.The photoreceptor cells on the vitreal side of the outer limiting membrane are completely isolated from each other by glial processes. On the scleral side of the membrane, the inner segments of the photoreceptor cells are not completely isolated by glial processes and so are frequently found in mutual contact. In the outer nuclear layer the granule of each photoreceptor is surrounded by more than one glial process while the fibres are often deeply embedded in a single glial process and provided with a mesofibre.At the level of the outer limiting membrane the visual cells and the glial expansions enveloping them are joined together by a junctional complex formed by a zonula adhaerens interposed between two very short zonulae occludentes. The same junctional complex joins to each other the contiguous expansions of the Müller cells and the mesofibres of the visual elements.     

Studies on the gastrulation of amphibian embryos: Ultrastructure of the migrating cells of anurans

Summary In order to investigate the ultrastructure of the migrating cells in anuran gastrulae, three anurans, which belong to three different genera, were observed with transmission electron microscopy supported by light microscopy of the 1 m sections and scanning electron microscopy. Fine filopodial cell processes, as well as cell processes probably flattened against the inner surface of the blastocoel wall, were formed by the migrating cells. Blebs and lobopodial cell processes were frequently observed inBufo, sometimes inXenopus, but not observed inRana. Microfilaments were observed in the cell processes. Focal close contacts, probably having adhesive properties, were made between the migrating cells and the inner surface of the blastocoel wall. These observations suggest that the cells migrate along the inner surface of the blastocoel wall by forming filopodia and pseudopodia flattened against the wall. The role of the blebs and lobopodial cell processes requires more investigation.     

The fine structure of Gnathostomulid reproductive organs

Summary The male copulatory organs of five species of Gnathostomulida Scleroperalia have been studied by TEM techniques. These observations provide a more solid basis for classification in the light microscope: inLabidognathia longicollis (fam. Mesognathariidae) the stylet is composed of eight, and inSemaeognathia sterreri, Gnathostomula jenneri, Gnathostomula mediterranea andGnathostomula microstyla (Gnathostomulidae) of ten stylet rods. Each rod consists of a microtubule-filled inner rod, and of an outer rod, filled with crystallized inclusions. The inner rods are continuous with eight — or ten — rod formation cells which are located in the proximal stylet sack. Bipartition of rods occurs by a longitudinal invagination of the basement lamina, underlying the rod cells and the gland cells and continuous with that of the body wall epithelium. InLabidognathia, the outer rods are interlocked, in Gnathostomulidae, the stylet rods are surrounded by an extracellular (cuticular) tube-like stylet sheath of variable fine structure, which is believed to provide extra rigidity. In the species investigated, one single stylet gland, consisting of a monolayered epithelium showing different gland cell types, surrounds the stylet. In the apical gland cell portions, medially and distally membrane-bound secretory granules lie adjacent to the stylet sheath. In Gnathostomulidae, two anterior gland cells are seen in connection with the formation of the stylet sheath. In the muscular sheath the cross-striated fibers, basically derived from the longitudinal body wall musculature, show a tendency towards helical and circumferential arrangement. Musculature is especially prominent in the proximal stylet sack, which is rather a propulsive element than a sperm-storing vesicle, and lacks glands. InGnathostomula species, atrial cells underlie the distal tip of the stylet. The entrance into the male opening is lined with ciliary receptor cells and specialized gland cells.Stylet evolution in Scleroperalia is characterized by progressive differentiation of the muscular sheath, in particular of the proximal stylet sack, and of the stylet — the occurrence of a stylet sheath is seen in connection with increasing diversity of stylet shape.Abbreviations ac atrial cell(s) - ag anterior gland cell(s) - b bursa - bl basal lamina - c rod-crystal in outer rod - cj cuticle of jaw - d desmosome - di dictyosome - e body wall epithelium - ej pharyngeal epithelium - g stylet gland (cell) - gm median gland cell - i gut (cell) - ir inner rod - jc junctional complex - m muscular layer - mo male opening - mv microvillar protrusions - nu nucleus - o ovary - or outer rod - po proximal opening of the proximal stylet sack - ps proximal stylet sack - r stylet rod - rc rod cell - sg secretory granule - sj septate junction - sp sperm - ss stylet sheath - st stylet - te testes - v ventral - z centriole     

Ultrastructural and immunohistochemical study of endocrine cells in the midgut of the cockroach Blaberus craniifer (Insecta,Dictyoptera)

Summary The midgut of Blaberus craniifer is principally made up of columnar epithelial cells which are derived from small regenerative cells found grouped in nidi. Between them, small sparsely granulated cells with clear cytoplasm can be observed lying on the basal lamina. Mainly based on the size, shape and texture of their secretory granules, at least ten types of such endocrine cells have been identified. Five cell types contain a uniform population of dense granules: (1) medium-sized, round to oval granules; (2) small elongated granules; (3) large irregular granules; (4) oval granules with a highly osmiophilic core; (5) oval, haloed granules. Five others are characterized by a heterogeneous population of granules: (6) small, round to oval, variably electron-dense granules; (7) oval medium-sized granules of variable electron density; (8) large irregular granules of variable electron density; (9) small dense granules and large vesicles with filamentous material; (10) small dense granules and very large pale vesicles.In addition, near the regenerative cells, large cells characterized by very large, irregular, dense granules (up to 4 m), lack contact with the lumen, and reach the basal lamina only by slender cytoplasmic processes.Several antisera raised against mammalian peptides and amine were used to reveal axonal fibers and endocrine cells. Serotonin-like immunoreactivity is localized in a profuse innervation of the muscle layers that surround the epithelium, whereas cholecystokinin and methionine-enkephalin antisera stain a more moderate number of axonal fibers. Cholecystokinin-, methionine-enkephalin-, substance P-, vasoactive intestinal peptide-, somatoliberin-, and gonadoliberin-like immunoreactivities were detected in endocrine cells of the epithelium. While most of the cells appear pyramidal, oval, fusiform or bowl-shaped, and seem to lack contact with the lumen, cells reaching it have been detected reacting with antisera to cholecystokinin, substance P, vasoactive intestinal peptide, somatoliberin and gonadoliberin.