A comparative ultrastructural study of ‘glue’ production and secretion of the salivary glands in different species of theDrosophila melanogaster group

Summary Salivary gland cells of members of theDrosophila melanogaster group (from four different subgroups) were examined electron microscopically and histochemically during the late larval period of development. The secretory product, which is supposed to be utilized as glue at the time of puparium formation, appears, by analogy to Palade and Jamieson's results, to be synthesized partially in the rough endoplasmic reticulum (RER) and partially in the Golgi complex. The latter is also the usual site of the packaging of the product into secretory granules, except in the case of one of the secretory granule components ofD. lucipennis. The phylogenetic relationships among the subgroups, implied by the morphological appearance of the secretory granules, fit well with the existing phylogenetic relationships within the group. The secretory granules of each species have their own morphological features; granules of species of the same subgroup share some of these features. Secretion occurs from the cells via exocytosis during which the morphology of the secretory granules changes. Light microscope examination of PAS (Periodic Acid-Schiff reaction) stained glands shows a strong positive reaction in most species, with the exception of the species of thesuzukii subgroup which show a weak, or a negative reaction (D. rajasekari). Electron histochemical localization of polysaccharides in the secretory granules was possible inD. melanogaster and the species of theananassae subgroup.     

Ultrastructure of the tubular accessory gland in Haemaphysalis longicornis (Acari: Ixodidae)

The paired tubular accessory glands in Haemaphysalis longicornis open at the junction of the cervical and the vestibular parts of vagina via short and narrow ducts. The pseudostratified columnar glandular epithelium covered by the muscle layer consists of both secretory and supporting cells. As feeding proceeds, the secretory cells increase in volume. In ovipositing females, well-developed rough endoplasmic reticulum, the Golgi complex, and membranebound granules that are undergoing exocytosis suggest that the secretory cells are involved in protein synthesis. However, in virgin females that fed 10 days, only small dense granules and no secretion activity were observed. The secretions from the tubular accessory gland may be released into the genital tract during the egg passage through the vagina. However, the supporting cells located between the secretory cells become slender during feeding, cohere to each other at the luminal side, and have a very narrow attachment at the basement membrane. Supporting cells probably help maintain secretory cell shape especially during granular discharge into the lumen. © 1994 Wiley-Liss, Inc.     

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.     

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.     

Immunocytochemical and morphometrical study of thyrotropic cells of Rana ridibunda

Summary Indirect immunoflorescence and PAP techniques for light microscopy as well as the immunogold complex technique for electron microscopy were used to localize and identify thyrotropic (TSH) producing cells in the pars distalis of Rana ridibunda. A double immunostaining procedure was used to distinguish TSH cells from other glycoprotein hormone producing cells. Rabbit anti-human--TSH was used as the primary antiserum and revealed a basophil, PAS and alcian blue positive cell type in the ventro-central zone of the gland. Under the electron microscope, TSH cells show irregular morphology, polymorphic secretory granules with diameters ranging between 120 and 375 nm and poor development of the endoplasmic reticulum and Golgi complex; they are usually polarized towards capillaries. Ultrastructural morphometry (point-counting method) was used to evaluate stereological parameters of rough endoplasmic reticulum, Golgi complex, secretory granules and mitochondria.This work has been supported by grant 2184-83 from the Comisión Asesora (CAICYT) of Spain     

On the fine structure of corpuscles of Stannius of the eel,Anguilla japonica

Summary The Stannius corpuscle of the eel (Anguilla japonica) consists of numerous ovoid or polymorphic lobules separated by loose connective tissue containing blood capillaries. Each lobule is composed of a number of columnar secretory cells, containing numerous secretory granules, and arranged more or less radially. Each secretory granule, spherical, 0.5–1.0 in diameter, and osmiophilic, is surrounded by a limiting membrane derived from the Golgi membrane. The well developed rough-surfaced endoplasmic reticulum is closely associated with the Golgi field. Some Golgi elements might also be intimately associated with the outer nuclear membrane. Numerous glycogen particles are distributed throughout the cytoplasm. The secretory granules which tend to accumulate near the basal part of the cell might be released into the loose connective tissue. From these facts, the corpuscles of Stannius are considered to be protein-secretory endocrine glands without any similarity to the adrenal gland.     

The ultrastructure of the male accessory reproductive glands of the colorado beetle

Summary The accessory reproductive glands of Leptinotarsa decemlineata males are simple epithelial tubular glands. They are surrounded by a network of slow acting muscle cells. All the gland cells have a very extensive granular endoplasmic reticulum, a prominent Golgi apparatus, but few secretory granules. The secretory product in the lumen, which is a neutral mucopolysaccharide-protein complex, appears as a granular material in which fibrillar structures occur. Neither in the gland cells nor in the lumen were regional differences observed. After allatectomy the gland cells degenerate in a remarkable way. A zone containing microvillous structures appears between the outer and inner cells. While the inner cells degenerate completely, the outer ones do not but become organised for minimal consumption of energy, necessary to survive diapause.Grateful acknowledgment is made for a mandate as Aangesteld Navorser of the National Foundation of Scientific Research in Belgium.We wish to thank Ing. W. Bohijn for operating the EM and Mr. G. Maes for photography.     

Ultrastructure of epidermal glands in neotenic reproductives of the termite Prorhinotermes simplex (Isoptera: Rhinotermitidae)

The ultrastructure of epidermal glands in neotenic reproductives of Prorhinotermes simplex is described and their development is compared among young and old neotenics of both sexes. Secretory cells forming the epidermal gland are attached to the cuticle all over the body. The glands are formed by class 1 and class 3 secretory cells and corresponding canal cells with secretory function. Class 1 cells are sandglass-like and class 3 secretory units are located among them. Class 1 cells contain predominantly tubular endoplasmic reticulum, the major part represents the smooth and the minor the rough form. Numerous electron dense granules occur in the cytoplasm, they are always disintegrated prior to be released. Class 3 secretory cells contain a large amount of vacuoles, which are always lucent in males while newly produced vacuoles are dense in females. Dense vacuoles are frequently transformed into lucent ones before being released. Canal cells are locally equipped with microvilli. The conducting canal is surrounded by an electron dense secretion of regular inner structure. The cytoplasm of the canal cell contains numerous mitochondria, rough endoplasmic reticulum and a large proportion of microtubules. The young neotenic reproductives differ from the old ones by a lower amount of secretory products. Epidermal glands probably produce substances inhibiting the occurrence of superfluous reproductives.     

Light and electron microscopy study of the salivary glands of the carnivorous opisthobranch Philinopsis depicta (Mollusca, Gastropoda)

Cephalaspideans are a group of opisthobranch gastropods that comprises carnivorous and herbivorous species, allowing an investigation of the relationship between these diets and the morphofunctional features of the salivary glands. In this study, the salivary glands of the carnivorous cephalaspidean Philinopsis depicta were observed by light and electron microscopy. The secretory epithelium of these ribbon-shaped glands is formed by ciliated cells, granular cells and cells with apical vacuole. In ciliated cells the nucleus and most cytoplasmic organelles are located in the wider apical region and a very thin stalk reaches the base of the epithelium. These cells possess significant amounts of glycogen. Granular cells are packed with electron-dense secretory granules and also contain several cisternae of rough endoplasmic reticulum and Golgi stacks. The other type of secretory cell is mainly characterized by the presence of a large apical vacuole containing secretion. These cells possess high amounts of rough endoplasmic reticulum cisternae and several Golgi stacks. Vesicles with peripheral electron-dense material are also abundant, and seem to fuse to form the apical vacuole. The available data point out to a significant difference between the salivary glands of carnivorous and herbivorous cephalaspidean opisthobranchs, with an intensification of protein secretion in carnivorous species.     

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.     

Development of secretory activity in the long hyaline gland of the male migratory grasshopper,Melanoplus sanguinipes (Fabr.) (Orthoptera : Acrididae)

Changes in the ultrastructure of epithelial cells from long hyaline glands of male Melanoplus sanguinipes (Fabr.) (Orthoptera : Acrididae) have been examined during sexual maturation and after allatectomy. In newly emerged males, the long hyaline gland epithelium is composed of 1–3 cell layers. The cells contain almost no rough endoplasmic reticulum, inconspicuous Golgi complexes, and large numbers of free ribosomes and polysomes. Within 24 hr, the cells undergo considerable reorganization to form a 1-cell-thick layer. Changes in cytostructure include proliferation of the rough endoplasmic reticulum and the development of several elaborate Golgi complexes. The developing lumen contains a coarse fibrous material. By 3 days postemergence, columnar epithelial cells are clearly capable of considerable synthesis and export of secretory protein. Rough endoplasmic reticulum, and large, elaborate Golgi complexes are the major structural features of the cytoplasm. From day 3 to sexual maturity (day 7), no major ultrastructural changes occur, although massive accumulation of secretion in the lumen causes the epithelium to become cuboidal or flattened. Isoelectric focusing of soluble proteins from long hyaline gland secretions shows that maturing glands contain increasing numbers and quantities of secretory proteins.Allatectomy has minor effects on long hyaline gland ultrastructure. A reduction in the density of rough endoplasmic reticulum and ribosomes suggests that glands from operated males are metabolically less active. This is confirmed by qualitative and quantitative changes in the amount of secretion as revealed by isoelectric focusing. The observations are discussed in terms of the juvenile hormone control of long hyaline gland maturation.     

Ultrastructure of the parathyroid gland of the japanese lizard in the spring and summer season

The ultrastructure of the parathyroid glands of adult Japanese lizards (Takydromus tachydromoides) in the spring and summer season was examined. The parenchyma of the gland consists of chief cells arranged in cords or solid masses. Many chief cells contain numerous free ribosomes and mitochondria, well-developed Golgi complexes, a few lysosome-like bodies, some multivesicular bodies and relatively numerous lipid droplets. The endoplasmic reticulum is mainly smooth-surfaced. Cisternae of the rough endoplasmic reticulum are distributed randomly in the cytoplasm. Small coated vesicles of 700-800 Å in diameter are found occasionally in the cytoplasm, especially in the Golgi region. The chief cells contain occasional secretory granules of 150-300 nm in diameter that are distributed randomly in the cytoplasm and lie close to the plasma membrane. Electron dense material similar to the contents of the secretory granules is observed in the enlarged intercellular space. These findings suggest that the secretory granules may be discharged into the intercellular space by an eruptocrine type of secretion. Coated vesicles (invaginations) connected to the plasma membrane and smooth vesicles arranged in a row near the plasma membrane are observed. It is suggested that such coated vesicles may take up extracellular proteins. The accumulation of microfilaments is sometimes recognized. Morphological evidence of synthetic and secretory activities in the chief cells suggests active parathyroid function in the Japanese lizard during the spring and summer season.     

Anatomy and ultrastructure of the salivary gland in the thorax of the honeybee worker,Apis mellifera (Insecta,Hymenoptera)

Summary The thoracic salivary gland of the worker honeybee was investigated by dissection, light microscopy, scanning electron microscopy, and transmission electron microscopy. The glands are paired and each lateral half consists of two parts, a smaller external and a larger internal lobe. The lobes are composed of densely packed secretory tubes and ducts, the tubes of which often show ramifications. A reservoir is packed within the anterior medial part of the gland. The secretory tubes are composed of two types of cells, secretory cells, which are most frequent, and parietal cells. Secretory cells are characterized by a basal labyrinth, abundant rough endoplasmic reticulum, dark secretory vesicles, light vesicles of different sizes, and apical microvilli. Parietal cells are smaller and have a characteristically lobed nucleus and no secretory vesicles. Between the cells there are intercellular canaliculi. In the center of each tube there is an extracellular space with a central cuticular channel. The abundance of rough endoplasmic reticulum and the rare occurrence of smooth endoplasmic reticulum implies a saliva with proteins but rarely with pheromones. Between the secretory tubes there are frequently neuronal profiles which are partly in contact with the secretory cells. Thus a nervous control of this gland is, in contrast to previous investigations, clearly demonstrated. The axonal endings contain dark neurosecretory vesicles as well as light synaptic vesicles. Large parts of the glands are surrounded by a thin tissue sheath which has a smooth surface towards the secretory tubes and shows irregular protrusions towards the outer side. This sheath is considered to be a tracheal air sac, and due to its large extension is probably of importance for the hemolymph flow in the thorax.     

Effects of isoproterenol on the fine structure of the hamster parathyroid gland

Ultrastructural changes of the parathyroid glands of isoproterenol-treated golden hamsters were investigated. Many chief cells in the parathyroid glands after 5 and 10 minutes of administration of isoproterenol contain well-developed Golgi complexes and granular endoplasmic reticulum, numerous prosecretory granules, and many secretory granules in the peripheral cytoplasm as compared with the control animals. Many chief cells in the parathyroid glands after 1, 3, 6 and 12 hours of administration have poorly-developed Golgi complexes, granular endoplasmic reticulum, many secretory granules and numerous lipid droplets as compared with the control animals. The morphology of the parathyroid gland after 30 minutes and 24 hours of administration resembles that of the control animals. It is considered that isoproterenol affects the secretory activity of the parathyroid gland.     

Schistosoma mansoni: Development of acetabular glands of cercaria at ultrastructural level

Cercariae of Schistosoma mansoni in daughter sporocysts in Biomphalaria glabrata were studied with the electron microscope to observe the maturing process of their acetabular glands. The undifferentiated acetabular gland displays its enlarged basal area (fundus) and extended narrow process (duct) before other organ systems are recognized. Its fundus contains a prominent nucleus and subcellular organelles typical of active secretory cells.The secretory granules of the postacetabular glands are formed in a milieu of dilated rough endoplasmic reticulum and Golgi. Two morphologically different secretory granules are produced: (1) homogeneously granular ones, and (2) other granular ones with electron dense bodies in their matrices. Mostly, the homogeneously granular ones are produced first in the fundus and are forced into the ducts as the other type is formed.The secretory granules of preacetabular glands are formed from translucent vacuoles which arise from an environment of endoplasmic reticulum and Golgi. Two morphologically different secretory granules are produced: (1) one type has a homogeneous dense matrix, and (2) the other type has a less dense matrix containing electron-lucid bodies.The duct of an undifferentiated acetabular gland has either filamentous material or microtubules dispersed in its cytoplasm. Once microtubules are formed, they persist during the life of the cercaria. The microtubules are believed to have possibly two functions: (1) to support the long duct, and (2) to assist the movement of the secretory granules into the channels of the ducts where they remain until released during host penetration.Few of the subcellular organelles associated with secretory granules formation are seen in the duct except the area in close proximity to the fundus; thus, the few secretory granules produced in the duct are in this region.     

The relationship between the morphology of cell organelles and kinetics of the secretory process in male sex accessory glands of mice

Summary Two male sex accessory glands of the mouse, seminal vesicle and coagulating gland, were compared with the aim of relating differences in the morphology of organelles to the kinetics of the secretory process. The epithelial cells of the two glands were assessed by morphometric analysis, cytochemical staining, and electron-microscopic autoradiography after administration of a labeled amino acid. The rough endoplasmic reticulum of the seminal vesicle comprised narrow parallel cisternae, while that of the coagulating gland was greatly distended and occupied a much larger percentage of the cytoplasmic volume. Radioactively labeled products were secreted much more rapidly in the seminal vesicle than in the coagulating gland. The primary point of difference in kinetics of intracellular transport between the two glands was in exit of material from the rough endoplasmic reticulum. The more rapid drainage of the rough endoplasmic reticulum may be related to its relatively greater membrane surface density and lesser internal volume. In contrast, similarities in size and cytochemical staining in the Golgi apparatus of the two glands were accompanied by similar kinetics of intracellular transport of secretory protein through this organelle.     

Microtubules in some unicellular glands of two leeches

Summary What appear to be two types of unicellular glands are found in the integument of the leech, Helobdella stagnalis. Type I cells are characterized by a peripheral, subplasmalemmal sack of rough endoplasmic reticulum and accumulations of secretory product in the form of small membrane bound droplets. Type II cells are characterized by large numbers of closely opposed sacks of rough endoplasmic reticulum and secretory product in the form of large, evidently amorphous accumulations of secretory product.Both cell types attenuate into long, slender processes through which the secretory product passes to the surface of the leech. Each process is characterized by a subplasmalemmal sack of ER which runs the entire length of the process and is continuous, at the proximal end of the process, with sacks of rough ER. Associated with the inner member of the ER membrane pair are microtubules with a diameter of approximately 240 Å.A similar arrangement of a subplasmalemmal ER sack associated with microtubules also is found in secretory processes of the leech, Macrobdella decora.The possible source and functions of these microtubules are discussed.This investigation was supported by Public Health Service grant number GM 723-04 of the National Institutes of Health.The author is greatly indebted to Dr. David B. Slautterback for his advice and encouragement during the course of this investigation.     

The localization of endogenous peroxidase in the lacrimal gland of the rat during postnatal development. Electron microscope cytochemical and biochemical studies

The distribution of endogenous peroxidase activity in the lacrimal gland of the rat during postnatal development was investigated by electron microscope cytochemistry Peroxidase activity is first found 6 hr after birth in only a few acinar cells At this stage, reaction product fills only localized segments of the scant rough endoplasmic reticulum and of the perinuclear cisternae. Peroxidase activity thus develops asynchronously in a given cell as well as in the secretory cell population as a whole 2 days after birth, all cisternae of the rough endoplasmic reticulum of a peroxidase-positive cell contain reaction product, but the majority of the acinar cells is still negative During the next days, the number of peroxidase-positive cells and the amount of the rough endoplasmic reticulum increase rapidly. By 15 days postparturition, all secretory cells are peroxidase-positive. Reaction product is then found in all cisternae of the rough endoplasmic reticulum including the perinuclear cisternae, in smooth surface vesicles located mainly between the rough endoplasmic reticulum and the Golgi stacks, in condensing vacuoles, and in all secretory granules The Golgi cisternae rarely contain reaction product In total homogenates and in fractions of glandular tissue of adult rats, peroxidatic and catalatic activities are demonstrable. The microsomal fractions and the postmicrosomal supernatants were used to separate peroxidase from catalase by precipitation with ammonium sulfate, and the following parameters were determined: substrate (H₂O_2-) optimum (∼ 2.0 x 10^-4 M), pH-optimum (pH 6 5), temperature-optimum (42°C), and the absorption maximum (415 nm before and 425 nm after addition of H₂O₂) The same parameters were obtained from lacrimal fluid peroxidase. Both peroxidase from lacrimal gland and that from lacrimal fluid are almost completely inhibited by 10^-3 M aminotriazole and are possibly identical enzymes. Peroxidase is secreted into lacrimal fluid, which does not contain catalase.     

Possible relationship between the activity of the adrenal gland and the subcommissural organ in the lizard Lacerta s. sicula raf.

Summary In order to study the possible functional relationship between the adrenal gland and the subcommissural organ (SCO) in the lizard Lacerta s. sicula Raf., ACTH was administered to some specimens of this species in January when both the adrenal gland and the subcommissural organ have a very low activity. In comparison to untreated controls, the adrenals of animals treated with ACTH showed clear signs of stimulation, presenting enlarged blood vessels, very few lipid droplets, numerous polymorphic mitochondria and abundant tubular smooth endoplasmic reticulum. In addition, a distinct increase in secretory material was observed in the subcommissural cells of specimens treated with ACTH. These cells showed large cisternae of the rough endoplasmic reticulum filled with granular material in the basal region, numerous secretory granules of two types in the apical region and a reduced number of microvilli on the free cell surface. These findings, together with the results of preceding studies, lead the authors to the consideration that steroid hormones might play a role in the regulation of the secretory activity of the SCO.     

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.