Ultrastructural and histochemical observations on the epidermis, presumptive tegument and glands of the miracidium of Gigantocotyle explanatum (Trematoda:Paramphistomidae)

Dunn T. S., Hanna R. E. B. and Nizami W. A. 1987. Ultrastructural and histochemical observations on the epidermis, presumptive tegument and glands of the miracidium of Gigantocotyle explanatum (Trematoda: Paramphistomidae). International Journal for Parasitology17: 885–895. The miracidium is invested with 20 ciliated epidermal cells arranged in four tiers (6: 8: 4: 2 = 20). Non-ciliated ridges of cytoplasm, located between the epidermal cells, are continuous with an extensive multivesiculate syncytium which underlies the body musculature and comprises the main bulk of the miracidium. It is suggested that the syncytium represents the presumptive sporocyst tegument. Two distinct types of glands are present in the anterior region of the miracidium, viz. a large, syncytial apical gland and a single pair of small, unicellular lateral glands. The apical papilla is formed by the bounding membrane of the apical gland, which is elevated into a complex network of anastomosing lamellae. The lateral glands terminate in discrete rosetteshaped areas on the apical papilla. The possible function of glands in digenetic miracidia and the nature of their secretions are discussed.     

Composition, secretion, and fate of the glands in the miracidium and sporocyst of Fasciola hepatica L

The anterior end of the miracidium of Fasciola hepatica contains a large flask-shaped apical gland and four unicellular lateral glands, all of which have ducts which pass to the tip of the apical papilla. These glands appear to be involved in penetration of the larva into the snail host. The apical gland secretes as the miracidium proves the epidermis of the host before attachment. It seems likely that its secretion is a chemical which lyses the epidermal cells. The lateral glands are PAS-positive and may contain a neutral mucopolysaccharide. They also secrete as the miracidium probes the snail and a layer of PAS-positive material may be seen at the leading edge of the apical papilla as the larva penetrates into the host. Both the apical gland and the lateral glands may be visible in the sporocyst for several days after penetration.     

Morphology of the granular secretory glands in skin of poison-dart frogs (Dendrobatidae)

The granular glands of nine species of dendrobatid frogs were examined using light and electron microscopy. The glands are surrounded by a discontinuous layer of smooth muscle cells. Within the glands proper the secretory cells form a true syncytium. Multiple flattened nuclei lie at the periphery of the gland. The peripheral cytoplasm also contains mitochondria, rough surfaced endoplasmic reticulum, the Golgi apparatus, and an abundance of smooth endoplasmic reticulum. Centrally, most of the gland is filled with membrane-bound granules surrounded by amorphous cytoplasm. Few other organelles are found in this region. Early in the secretory cycle, the central part of the gland is filled with flocculent material which appears to be progressively partitioned off by membranes to form the droplet anlage. As granules form, the structure of the contents becomes progressively more vesicular. Dense vesicles, which bud off from the Golgi apparatus, fuse with the granular membrane during the development of granules, and might contain enzymes involved in toxin synthesis. The granules at this point resemble multivesicular bodies. Their structure is similar in all species of dendrobatid frogs even though the different frogs secrete substances of different chemical structure and toxicity.     

Release of packets of acetylcholine and synaptic vesicles elicited by brown widow spider venom in frog motor nerve endings poisoned by botulinum toxin

Homogenates of venom glands of brown widow spiders caused the release of packets of acetylcholine, observed as miniature end-plate potentials (mepps), from nerve terminals in sartorius and cutaneous pectoris muscles of the frog, even though the appearance of mepps which is normally induced by depolarization of the presynaptic membrane had been completely blocked by prior treatment with type A botulinum toxin (BotTX). The distribution of the amplitudes of the recorded mepps resembled that of the mepps in normal muscle and was quite different from the heavily skewed (to the left) distribution of the mepps recorded from BotTX-treated muscles. This suggests that the mepps elicited by brown venom glands homogenates in muscles blocked by BotTX were due to the release of a population of vesicles which is unaffected by BotTX and which is also released on hyperpolarization of nerve terminals.     

The anatomy of the parotoid gland in Bufonidae with some histochemical findings. II. Bufo alvarius.

The gross and microscopic anatomy of the venom producing parotoid glands of Bufo alvarius has been studied by light and electron microscopy. Histochemical reactions for the presence of venom constituents and of components in biochemical pathways in the synthesis and release of venom were performed. The gland is composed of numerous lobules. Each lobule is an individual unit with a lumen surrounded by a double cell layer. Microvilli of the outer layer interdigitate with microvilli of the inner layer. Cells of the outer layer resemble smooth muscle cells, are rich in adenosine triphosphatase and glucose-6-phosphatase, and contain numerous pinocytotic vesicles, glycogen granules and various organelles. These organelles include "crystalloids" of what seem to be highly organized agranular reticulum. These outer layer cells probably function in some aspects of venom synthesis, active cellular transport and contraction in the discharge of the secretory product. The inner cell layer demonstrates a positive chromaffin reaction, contains steroid material, various organelles, some pinocytotic vesicles and glycogen granules, and appears devoid of a plasmalemma on its inner surface. This layer is probably involved in venom formation and release via an apocrine type of secretion. Bufo alvarius parotid gland shows significant morphological and histochemical differences from that of B. marinus and more nearly resembles a typical steroid producing organ.     

Venom and Dufour's glands of the emerald cockroach wasp Ampulex compressa (Insecta,Hymenoptera, Sphecidae): Structural and biochemical aspects

The digger wasp species Ampulex compressa produces its venom in two branched gland tubules. They terminate in a short common duct, which is bifurcated at its proximal end. One leg is linked with the venom reservoir, the other one extends to the ductus venatus. Each venom gland tubule possesses, over its entire length, a cuticle-lined central duct. Around this duct densely packed class 3 gland units each composed of a secretory cell and a canal cell are arranged. The position of their nuclei was demonstrated by DAPI staining. The brush border of the secretory cells surrounds the coiled end-apparatus. Venom is stored in a bladder like reservoir, which is surrounded by a thin reticulated layer of muscle fibres. The reservoir as a whole is lined with class 3 gland units. The tubiform Dufour's gland has a length of about 350 μm (∅ 125 μm) only and is surrounded by a network of pronounced striated muscle fibres. The glandular epithelium is mono-layered belonging to the class 1 type of insect epidermal glands. The gland cells are characterized by conspicuous lipid vesicles. Secretion of material via the gland cuticle into the gland lumen is apparent. Analysis of the polypeptide composition demonstrated that the free gland tubules and the venom reservoir contain numerous proteins ranging from 3.4 to 200 kDa. The polypeptide composition of the Dufour's gland is completely different and contains no lectin-binding glycoproteins, whereas a dominant component of the venom droplets is a glycoprotein of about 80 kDa. Comparison of the venom reservoir contents with the polypeptide pattern of venom droplets revealed that all of the major proteinaceous constituents are secreted. The secreted venom contains exclusively proteins present in the soluble contents of the venom gland. The most abundant compound class in the Dufour's gland consisted of n-alkanes followed by monomethyl-branched alkanes and alkadienes. Heptacosane was the most abundant n-alkane. Furthermore, a single volatile compound, 2-methylpentan-3-one, was identified in various concentrations in the lipid extract of the Dufour's gland.     

Morphology and ultrastructure of the venom glands of the northern pacific rattlesnake Crotalus viridis oreganus

The venom gland of Crotalus viridis oreganus is composed of two discrete secretory regions: a small anterior portion, the accessory gland, and a much larger main gland. These two glands are joined by a short primary duct consisting of simple columnar secretory cells and basal horizontal cells. The main gland has at least four morphologically distinct cell types: secretory cells, the dominant cell of the gland, mitochondria-rich cells, horizontal cells, and “dark” cells. Scanning electron microscopy shows that the mitochondria-rich cells are recessed into pits of varying depth; these cells do not secrete. Horizontal cells may serve as secretory stem cells, and “dark” cells may be myoepithelial cells. The accessory gland contains at least six distinct cell types: mucosecretory cells with large mucous granules, mitochondria-rich cells with apical vesicles, mitochondria-rich cells with electron-dense secretory granules, mitochondria-rich cells with numerous cilia, horizontal cells, and “dark” cells. Mitochondria-rich cells with apical vesicles or cilia cover much of the apical surface of mucosecretory cells and these three cell types are found in the anterior distal tubules of the accessory gland. The posterior regions of the accessory gland lack mucosecretory cells and do not appear to secrete. Ciliated cells have not been noted previously in snake venom glands. Release of secretory products (venom) into the lumen of the main gland is by exocytosis of granules and by release of intact membrane-bound vesicles. Following venom extraction, main gland secretory and mitochondria-rich cells increase in height, and protein synthesis (as suggested by rough endoplasmic reticulum proliferation) increases dramatically. No new cell types or alterations in morphology were noted among glands taken from either adult or juvenile snakes, even though the venom of each is quite distinct. In general, the glands of C. v. oreganus share structural similarities with those of crotalids and viperids previously described.     

Ultrastructure of the Male Accessory Glands and Sperm Ducts of Cylindrotaenia hickmani(Cestoda,Cyclophyllidea)

Abstract The ultrastructure of unicellular accessory glands (= prostate glands) and external male ducts of the cestode Cylindrotaenia hickmaniare described. Accessory glands open into the lumen of the external common sperm duct (= external vas deferens). The gland cells contain abundant endoplasmic reticulum, Golgi bodies and secretory bodies, and have elongate necks that pierce the apical cytoplasm of the duct. Cell contact with the apical cytoplasm of the sperm duct is mediated by septate desmosomes. Accessory glands secrete spherical particles, with a diameter of approximately 70 nm, that adhere to spermatozoa. The roles of these accessory glands may relate to activity of the sperm or development of the female system after insemination. Paired sperm ducts arise from testes, and unite to form a common sperm duct. Each duct consists of a tubular anucleate cytoplasmic region which is supported by nucleated cytons that lie sunken in the parenchyma. The apical cytoplasm of the paired sperm ducts (= vasa efferentia) possesses apical microvilli and abundant mitochondria, but few other cytoplasmic features. The apical cytoplasm of the common sperm duct possesses sparse apical microvilli and numerous electronlucent vesicles. The male gonoducts form an elongate syncytium which is markedly polarized along the length of the ducts. The ducts also display apical–basal polarity in that sunken nucleated cytons support the apical cytoplasm which in turn has distinct basal and apical domains.     

Immunocytochemical localization and secretion process of the toxin CSTX-1 in the venom gland of the wandering spider Cupiennius salei (Araneae: Ctenidae)

Fluorescein and horseradish peroxidase-labeled monoclonal antibodies were used to localize the predominant toxic peptide CSTX-1 in the venom gland of the spider Cupiennius salei. There was no polarity of CSTX-1 expression in repleted glands, whereas the glands of previously milked spiders showed a decreasing immunofluorescent response from the distal to the proximal portion. Detailed investigation revealed a new structure in the venom-secreting epithelium, which is postulated to be an evolutionary adaptation to increasing gland volume. CSTX-1 was found to be synthesized and stored as a fully active toxin within complex units, composed of long interdigitating cells running perpendicular to the muscular sheath and extending into the central lumen of the gland. These venom-producing units were found in all sectors of the gland, including the transitional region between the main gland and the venom duct. The venom is liberated from the venom-producing units into the glandular lumen following the contraction of the surrounding muscle layer. Free nuclei or other cellular fragments, which would have provided evidence for a holocrine secretion process, were not found in the glandular lumen or in the crude venom obtained by electrical stimulation. The fine regulation of the spider's venom injection process is postulated to be the function of the bulbous ampulla, situated in the anterior third of the venom duct.     

The Oral Gland Cells of Oikopleura dioica (Tunicata Appendicularia)

Light and electron microscopic studies showed that the oral gland cells have two quite different zones. Medially, the basal zone is in contact with body fluids and the endostyle. Its strongly pyroninophile cytoplasm contains the extremely digitated nucleus and numerous small mitochondria. Laterally, the apical zone contacts the epidermis and it may also send a process between epidermal cells and deliver cell fragments into the primordium of the new house. This cell zone contains numerous membranes. It is concluded that the oral gland cells are light producing glands and that the membrane-rich cell fragments which are incorporated into the house wall are the source of the bioluminiscence which has been reported from empty houses. The ontogenetically related subchordal cells have a similar structure and it is possible that also these cells are light producers.     

Schistosoma mansoni: penetration apparatus and epidermis of the miracidium

Free swimming miracidia of Schistosoma mansoni were studied with the electron microscope for the purpose of describing the penetration apparatus and the epidermis. The penetration apparatus was composed of 3 unicellular glands which contain membrane-bound vesicles containing macromolecular diglycols. Each gland contained a nucleus, rough endoplasmic reticulum, Golgi complexes, numerous mitochondria, and glycogen stores. Each gland cell opened to the exterior through the apical papilla.The surface of the miracidium, with the exception of the apical papilla, was covered with ciliated epidermal cells containing numerous mitochondria, membranous bodies, and glycogen. No nuclei were detected within these epidermal cells. Intercellular ridges connecting with subepidermal cytons interrupted the epidermal cells at numerous points. The ridges were joined to the epidermal cells by septate desmosomes. Beneath the epidermal cells were found circular and longitudinal muscle bundles.Sensory structures of various types were associated with the outer covering. These consisted of (1) numerous “knob-like” cytoplasmic projections associated with epidermal cells, (2) bulbous, lamelloid structures with external cytoplasmic projections, and (3) ciliated nerve endings with posterior epidermal tiers and ciliated nerve pits associated with apical papilla.     

Ultrastructural observations on rhabdite formation in the planarian, Artioposthia triangulata

The epidermis of the predatory terrestrial flatworm, Artioposthia triangulata has been examined by transmission electron microscopy for the presence of rhabdiform secretions. Two types of secretion are present: epidermal rhabdoids, produced by a special type of epidermal cell and true adenal rhabdites produced by gland cells beneath the epidermis. The epidermal rhabdoids are formed from Golgi-derived vesicles, which fuse together to form the developing rhabdoid. Within the latter is a filamentous network on which granular material is deposited and coalesces to form a rod-shaped inclusion. The rhabdoids accumulate in the apical region of the cell and release their contents from the apical surface. The adenal rhabdites are formed by Golgi-derived vesicles, which become more elongated and their contents more electron-dense as they mature. The vesicles fuse together to form the primordial rhabdite, which continues to lengthen with the addition of further vesicles. The neck of the rhabdite-forming cell passes between the muscle layers and through the basement membrane to open into the base of the epidermal cell. The rhabdites move from the cell body through the neck into the cytoplasm of the epidermal cell and make their way to the apical surface where they are released to the exterior.     

Morphology and ultrastructure of the dufour's and venom gland in the ant,Myrmica rubra (L.) (Hymenoptera : Formicidae)

The morphology and fine structure of the Dufour's and venom gland, as well as their entrance into the sting, are described in the myrmicine ant, Myrmica rubra (Hymenoptera : Formicidae). The epithelial cells that constitute the Dufour's gland wall, contain a well-developed smooth endoplasmic reticulum. Older workers, compared with younger ones, show an increasing number of multilamellar inclusions. The venom gland secretory cells are arranged in 2 free filaments that carry the secretion to the reservoir. Their cytoplasm shows an intracellular collecting ductule with surrounding microvillar sheath, and an abundance of free ribosomes. However, a well-organized granular endoplasmic reticulum, which is typical in species with a more powerful sting, does not occur. Both the Dufour's and venom gland ducts are characterized by the insertion of extensive muscle fibres, which act as a precise and mutually independent control mechanism for the discharging activities of the 2 glands.     

New ultrastructural data from the larva of Paragordius varius (Nematomorpha)

Larvae of Paragordius varius (Leidy, 1851) were investigated using transmission electron microscopy, providing new observations concerning the cuticular structures of the preseptum, the postseptal gland and the pseudointestine. The cuticle is three‐layered but the basal layer is variable in structure. The hooks possess long, intracuticular roots and the stylets have apical teeth. Both postseptal gland and pseudointestine are secretory in function. The postseptal gland is composed of eight cells, which are all connected by a duct leading through the septum into the preseptum. Inside the postseptal gland, the duct wall has numerous pores. The pseudointestine is composed of four cells surrounding a cavity with an amorphous content. A flattened duct within a syncytium with five nuclei leads to a ventral pore close to the posterior end.     

Morphologic analysis of the venom gland of Apis mellifera L. (Hymenoptera: Apidae) in populations of Mato Grosso do Sul, Brazil

In Apis mellifera L. the venom gland (also called acid gland) is composed of secretory cells that surround a channel that opens into a reservoir devoid of musculature. This gland can present apical branching. In this study the frequency of branched venom glands in Africanized honeybee workers (A. mellifera) from eleven localities in the state of Mato Grosso do Sul was recorded. The relations among the length of the main duct, the length of the duct from the reservoir to the beginning of branching, the length of the branched segment (when present) and the total length of the gland were also analyzed. The frequency of branched glands varied from 50% to 83% in the workers, indicating that this characteristic is primitive in those bees. The results of the Analysis of Discriminant Functions indicated significant differences in the morphometrical segments of the venom gland (Wilks Lambda = 0.092; F (40, 55) = 3.43; P < 0.001), and permitted a differentiation of the populations studied. Using the Mantel test we verified that there does not exist a significant correlation between the morphologic characteristics and the geographical distance between the localities evaluated (Mantel r = -0.006, P = 0.48). The high frequency of workers with large venom gland in all the apiaries considered makes viable the development of a selection program in order to obtain bees with longer venom glands, aimed at the commercial production of venom by the beekeepers of those localities of Mato Grosso do Sul.     

The mechanism of venom secretion from Duvernoy's gland of the snake Thamnophis sirtalis

The venom glands of snakes of the families Elapidae and Viperidae are thought to have evolved from Duvernoy's gland of colubrid ancestors. In highly venomous snakes elements of the external adductor musculature of the jaw insert fibers directly onto the capsule of the venom gland. These muscles, upon contraction, cause release of contents by increasing intraglandular pressure. In Thamnophis sirtalis, a colubrid, there is no direct connection between Duvernoy's gland and the adductor musculature. The anatomical arrangement of the gland, skull, adductor muscles, and the integument is such that contraction of the muscles may facilitate emptying of the gland. This hypothesis was tested by electrical stimulation of the muscles, which resulted in significantly greater release of secretion than elicited by controls. The results suggest a possible early step in the evolution of a more intimate association between venom glands and adductor musculature in highly venomous snakes.     

Cytodifferentiation in the accessory glands of Tenebrio molitor I. Ultrastructure of the tubular gland in the post-ecdysial adult male

The tubular accessory reproductive glands of the male mealworm beetle consist of a secretory epithelium surrounded by a thin muscular sheath. Each columnar secretory cell is divisible into three zones: basal which is adjacent to the muscle layer and contains rough endoplasmic reticulum and Golgi, intermediate, which contains endoplasmic reticulum and Golgi zones in the immature gland and is filled with secretory vesicles in the mature gland, and apical. Maturation also involves proliferation and organization of the rough endoplasmic reticulum in the basal and intermediate zone. The process appears to be complete at four days after ecdysis. Parallels with other insect glands and with the mammalian prostate are striking.     

Fine structure of the male accessory glands in Aedes triseriatus

The paired accessory glands of the male mosquito, Aedes triseriatus, consisted of a single layer of columnar epithelial cells enclosed by a richly-nucleated circular muscle layer. Each accessory gland is divided into an anterior gland (AG) with one type of secretory cell, and a posterior gland (PG) with two types. The cells of the AG and those of the anterior region of the PG showed macroapocrine secretion. The mucus secreting cells located at the posterior region of the PG, however, released their contents into the lumen of the gland by rupturing the apical membrane of the cell. The secretion from all cells was in the form of membrane-bound granules which had distinct electron-dense and electron-lucent areas.     

A developmental study of the epidermis of young roots ofZea mays L.

Summary In the apical meristems of main and young lateral roots of corn the uniseriate epidermis is clearly continuous with the most distal cell tier of the quiescent centre. These cells are characterized by the presence on their outer periclinal walls of material which forms the thin root cap junction layer over the apical pole and which thickens appreciably over the flanks of the meristem to form a distinctive extracellular deposit on the young epidermal cells. This material is polysaccharide in nature as indicated by strong periodic acid Schiff's positivity but its autofluorescence also suggests the presence of phenolic compounds.During their development the epidermal cells undergo marked shape change from periclinally flattened, polygonal at the root pole, through columnar on the meristem flank to tabular in the root hair zone. The mucigel thins markedly as cells become tabular but initiation of a root hair is characterized by deposition of polysaccharide on the inside of the periclinal wall where the hair will develop.     

The fine structure of muscle attachments in a spider (Latrodectus mactans, Fabr.)

The fine structure of a spider myo-apodeme junction is described, and discussed in terms of other arthropod muscle attachments. This is contrasted with the situation in the venom gland, equipped with muscle fibers that control expulsion of the secreted material. The latter involves a cell-free collagenous matrix, lying between the muscle cells and the sheath of the gland. As in other arthropods, skeletal fibers are attached to the apodeme cuticle via specialized epidermal cells, containing oriented microtubules. Interdigitations between these cells and muscle, basally, and cuticle, apically, are described. Extracellular tonofibrillae described elsewhere are inconspicuous in the apodeme cuticle.