The fine structure of the collar cells in the optic tentacles of Helix aspersa

Summary At the base of the optic tentacular ganglion there is a group of large monopolar cells containing numerous secretory inclusions. These are the collar cells. Secretory material can be seen accumulating in swollen portions of the granular endoplasmic reticulum. It is postulated that this material is transported to the Golgi bodies and thus the limiting membrane of the inclusions is derived from the Golgi membranes. The Golgi bodies appear to be polarized and small vesicles resembling secretory inclusions are associated with one face of these organelles. The secretory inclusions fuse together to form large membrane-bound secretory pools in the perikaryon. The collar-cell processes are packed with secretory inclusions. These processes traverse the digital extensions of the tentacular ganglion and pass into the epithelium covering the tip of the tentacle. The secretory inclusions do not resemble neurosecretory inclusions in other situations. The collar cell processes receive a nerve supply from single axons containing granular and agranular vesicles. The evidence that these cells may be modified neurons is only minimal.This work was supported by the Australian Research Grants Committee.     

Structure and development of the secretory cavities of Myrtus communis leaves

The structure and development of Myrtus communis L. secretory cavities has been studied in young and expanded leaves, using light and scanning electron microscope. Secretory cavities are continuously formed during leaf development, but in mature leaves the rhythm of their appearance shows steep decrease. Each secretory cavity is developed from a single epidermal cell, which undergoes a periclinal division followed by anticlinal and several oblique cell divisions. The lumen of the secretory cavity is initiated by cell wall separation, i.e., schizogenously. The secretory cells line the cavity, where the secreted material is collected. Secretory cavities are covered by modified epidermal cells, which do not seem to form any special aperture. Essential oils seem to be discharged after mechanical treatment of the leaf.     

Changes in the secretory activity of the Golgi apparatus during the cell cycle in root tips of maize (Zea Mays L.)

Epidermal cells of maize roots were studied to determine the distribution of Golgi apparatus-derived secretory vesicles in various stages of cell division. The following conclusions were reached: 1) The pattern of Golgi apparatus secretion varies with the cell cycle. 2) Large numbers of secretory vesicles are incorporated into the cell plate. 3) Secretory vesicles from the Golgi apparatus are incorporated primarily in walls undergoing expansion. 4) Secretory vesicles are smaller during mitosis and the first part of cytokinesis than they are during interphase. 5) Secretory vesicles account for at least 12–23% of cell-plate plasma membrane and an estimated 25% of cell-plate volume.     

The 1989 Upjohn Award lecture. Cellular and molecular mechanisms in hormone and neurotransmitter secretion

Studies on adrenal medulla have had an important influence on the development of a variety of biological concepts, not only within the area of endocrinology, but also in the areas of chemical neurotransmission and secretion in general. The adrenal medulla chromaffin cells are derived embryologically from the neural crest, sharing a common origin with sympathetic neurons and common subcellular features with many endocrine cells. One such feature is the storage of secretory products in membrane-bound organelles, the secretory granules. Secretory cells with these characteristics have been named paraneurons, a term that embraces cells generally and traditionally not considered as neurons, and yet should be regarded as relatives of neurons on the basis of their structure, function, and metabolism. Many of the studies carried out in the past to understand the secretory process have employed perfused adrenal glands. Although this technique has provided very useful information regarding secretion, it did not allow the study of the cellular events involved in the secretory process. To obtain further information on cell secretion, several laboratories including our own have published methods for the isolation and culture of chromaffin cells. The cultured chromaffin cells have shown themselves to be one of the most useful systems developed for the study of the neuroendocrine functions of paraneurons. Studies on cultured chromaffin cells have provided important information on secretory cell cytoskeleton: a group of proteins, some of them previously known from studies on muscle, which form a cytoplasmic network in all non-muscle cells including secretory cells. Immunohistochemical studies have shown at least three types of filament systems: microfilaments, microtubules, and intermediate filaments. In addition, a large variety of cytoskeleton-associated proteins have been characterized. Chromaffin cells are among those non-muscle cells from which cytoskeleton proteins have been isolated and characterized. Owing to similarities between "stimulus-secretion coupling" and "excitation-contraction coupling" in muscle, it has been proposed that the secretory process might be mediated by contractile elements either associated with secretory vesicles or present elsewhere in the secretory cell. Cytoskeletal proteins (actin, myosin, alpha-actinin, fodrin, tubulin, and neurofilament subunits) and their regulatory proteins (calmodulin, gelsolin) have been isolated from chromaffin cells and characterized. Their physiochemical proteins have been studied and their cellular localizations have been revealed by biochemical, immunocytochemical, and ultrastructural techniques. alpha-Actinin and fodrin are components of chromaffin granule membranes and some of the cell actin co-purified with secretory granules. Actin forms a network of microfilaments in the subplasmalemma region.(ABSTRACT TRUNCATED AT 400 WORDS)     

Postnatal development of the Mongolian gerbil uterine glands

The development of gerbil uterine glands has been described. Gland formation starts about day 6 postnatally (p.n.). At day 10 p.n. the glandular lumen contains already some fluid, and the glandular cells are in an activated state. The apical shape of the glandular cells depends mainly on the width of the lumen. Secretory vesicles in early developmental stages are electron-lucent. As sexual maturity is reached, secretory granules become electron-dense. This change in secretory granular structure indicates a change in the quality of uterine gland fluid.     

Scinderin and cortical F-actin are components of the secretory machinery

Secretory vesicle exocytosis is the mechanism of release of neurotransmitters and neuropeptides. Secretory vesicles are localized in at least two morphologically and functionally distinct compartments: the reserve pool and the release-ready pool. Filamentous actin networks play an important role in this compartmentalization and in the trafficking of vesicles between these compartments. The cortical F-actin network constitutes a barrier (negative clamp) to the movement of secretory vesicles to release sites, and it must be locally disassembled to allow translocation of secretory vesicles in preparation for exocytosis. The disassembly of the cortical F-actin network is controlled by scinderin (a Ca(2+)-dependent F-actin severing protein) upon activation by Ca2+ entering the cells during stimulation. There are several factors that regulate scinderin activation (i.e., Ca2+ levels, phosphatidylinositol 4,5-bisphosphate (PIP2), etc.). The results suggest that scinderin and the cortical F-actin network are components of the secretory machinery.     

The mouse vomeronasal glands: a light and electron microscopical study

The glands of adult mouse vomeronasal organ (VNO) were studiedwith light- and electro-microscopical techniques. The vomeronasalglands (VN-Gs) consist of several individual glandular complexesdistributed along the long axis of the VNO. The secretory productsreleased from VN-G cells enter into the lumen of the VNO inthe region of transition between the neuroepithelium and thereceptor-free epithelium. The acini show the typical morphologicalfeatures of serous glands. The secretory cells of these aciniare characterized by a round to oval nucleus and a well-developed,rough endoplasmic reticulum, both preferentially located inthe basal part of the cell. The supranuclear region is occupiedby the Golgi apparatus and secretory granules varying in sizeand electron density. They accumulate towards the apical partof the cell. Secretory cells are connected by tight junctions,desmosomes and membrane interdigitations, moreover, they arealso coupled by gap junctions. Axonal terminals containing clearvesicles and dense-cored vesicles are frequently seen betweenthe secretory cells. Secretory cells are directly related tothe thin basal lamina of the acinus; myoepithelial cells arenot present. In the lamina propria, numerous smooth muscle cells,blood vessels and nerve bundles containing both myelinated andunmyelinated axons can be observed. An automatic regulationof the activity of the VN-Gs is discussed in relation to thevomeronasal pump.     

The bHLH protein Dimmed controls neuroendocrine cell differentiation in Drosophila

Neuroendocrine cells are specialized to produce, maintain and release large stores of secretory peptides. We show that the Drosophila dimmed/Mist1 bHLH gene confers such a pro-secretory phenotype on neuroendocrine cells. dimmed is expressed selectively in central and peripheral neuroendocrine cells. In dimmed mutants, these cells survive, and adopt normal cell fates and morphology. However, they display greatly diminished levels of secretory peptide mRNAs, and of diverse peptides and proteins destined for regulated secretion. Secretory peptide levels are lowered even in the presence of artificially high secretory peptide mRNA levels. In addition, overexpression of dimmed in a wild-type background produces a complimentary phenotype: an increase in secretory peptide levels by neuroendocrine cells, and an increase in the number of cells displaying a neuroendocrine phenotype. We propose that dimmed encodes an integral component of a novel mechanism by which diverse neuroendocrine lineages differentiate and maintain the pro-secretory state.     

火炬树分泌道的发育解剖学研究

本文报道了火炬树分泌道的结构、分布和发育。火炬树的分泌道是由一层分泌细胞及其外侧1—5层薄壁组织细胞组成的鞘细胞所包围。分泌道主要分布于根、茎、叶、花和果实的维管束的韧皮部内,此外,在茎的髓部也存在散生的分泌道。各类器官中的分泌道都以裂生方式发育;营养器官中的分泌道先于维管分子分化,生殖器官中的则后于维管分子的分化。     

Morphology of the aedeagal gland of the male mealworm beetle (Tenebrio molitor L.)

The aedeagal gland of male Tenebrio molitor consists of numerous acini containing several secretory units (organules) of three epithelial cells in series. The distal cortical cell and intermediate cell are secretory cells. Secretory products are passed into microvilli-lined extracellular reservoirs. From these storage areas products flow through minute canaliculi and into the efferent ductule. Canaliculi, cuticular trabeculae, and fibrillar material are characteristic features of the efferent ductules within the extracellular reservoirs of secretory cells. After passing from the secretory cells, the efferent ductule penetrates the basal ductule cell. The thin epicuticle that comprises the wall of the ductule is confluent with the epicuticle of the cuticular sheath forming the wall of the genital pocket. Secretory products flow from the cortical cell ductule into the intermediate cell and eventually empty into the genital pocket. A chemical reaction apparently takes place in the intermediate cell ductule, resulting in a frothy secretion product. When released from the ductule, this frothy product forms a foam-like layer that coats the inner wall of the genital pocket. Ultrastructural and probable functional aspects of this gland are described and discussed.     

Messenger RNA Levels of Chromogranin B, Secretogranin II, and VGF in Rat Brain After AF64A-Induced Septohippocampal Cholinergic Lesions

Abstract— The mRNA levels of secretogranin II, chromo-granin B, and VGF were compared in brains of control and AF64A-treated rats. This toxin induces specific lesions of the septohippocampal cholinergic pathway. As a consequence of this treatment, the Chromogranin B message was elevated in the dentate gyrus granule cells of the hippocampus. In the paraventricular nucleus of the hypothalamus, a concomitant elevation of the messages of secretogranin II and corticotropin-releasing factor occurred in the parvocellular neurons, and an increase of those of secretogranin II and VGF occurred in a subgroup of magnocellular neurons. Further increases for secretogranin II were seen in the amygdaloid nuclei and the reticular thalamic nuclei and increases for Chromogranin B in the temporal cortex, substantia nigra compacta, and ventral tegmental area. These results indicate that the toxin-induced lesion of the cholinergic pathway innervating the hippocampus apparently leads to the stimulation of several defined groups of neurons that react with an increase in the mRNA levels of their secretory peptides. We suggest that changes in mRNA expression of these peptides are useful parameters for defining neurons under chronic stimulation. Key Words: Secretory peptides—Large dense core vesicles—Corticotropin releasing factor—Septohippocampal cholinergic system—Hippocampus—AF64A.     

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.     

Ultrastructural studies on the secretory cavities ofCitrus deliciosa ten. II. Development of the essential oil-accumulating central space of the gland and process of active secretion

Summary Oil glands ofCitrus deliciosa are multicellular secretory structures, globular to oval in shape, in the centre of which an essential oil-accumulating space is formed. Opening of this space begins from a single cell. It undergoes lysis which later extends to the neighbouring gland cells.Secretory material in form of droplets is produced in plastids, from where it is transported to the parietal cytoplasm of the secretory cells via numerous ER-elements. After fusion of the ER-membranes with the plasmalemma, the exudate reaches the apoplast, through which it is driven to the central cavity of the gland.Peripheral cells of the secretory complex are modified into a protective sheath with thick walls and large vacuoles, while their plastids are differentiated from leucoplasts into typical amyloplasts.     

Intravesicular calcium release mediates the motion and exocytosis of secretory organelles: a study with adrenal chromaffin cells

Secretory vesicles of sympathetic neurons and chromaffin granules maintain a pH gradient toward the cytosol (pH 5.5 versus 7.2) promoted by the V-ATPase activity. This gradient of pH is also responsible for the accumulation of amines and Ca2+ because their transporters use H+ as the counter ion. We have recently shown that alkalinization of secretory vesicles slowed down exocytosis, whereas acidification caused the opposite effect. In this paper, we measure the alkalinization of vesicular pH, caused by the V-ATPase inhibitor bafilomycin A1, by total internal reflection fluorescence microscopy in cells overexpressing the enhanced green fluorescent protein-labeled synaptobrevin (VAMP2-EGFP) protein. The disruption of the vesicular gradient of pH caused the leak of Ca2+, measured with fura-2. Fluorimetric measurements, using the dye Oregon green BAPTA-2, showed that bafilomycin directly released Ca2+ from freshly isolated vesicles. The Ca2+ released from vesicles to the cytosol dramatically increased the granule motion of chromaffin- or PC12-derived granules and triggered exocytosis (measured by amperometry). We conclude that the gradient of pH of secretory vesicles might be involved in the homeostatic regulation of cytosolic Ca2+ and in two of the major functions of secretory cells, vesicle motion and exocytosis.     

Electron Microscopic Evidence Suggesting Secretory Granule Formation within the Golgi Apparatus

Secretory granules have been seen within components of the Golgi bodies of rat pituitary acidophils and mouse pancreatic acinar cells. The fact that secretory granules are much more frequently encountered within Golgi components under conditions of increased secretory activity suggests that granule formation may occur within the Golgi apparatus in these two types of cells.     

Development,structure, and occurrence of secretory trichomes ofPharbitis

Summary Secretory trichomes develop from epidermal cells on the leaf primordia and stem ofPharbitis nil. Following an initial growth phase, trichomes begin active secretion of a protein-carbohydrate mucilage. This mucilage covers the shoot apex and developing leaves ofPharbitis.The secretory cells possess cellular organelles in forms usually associated with actively secreting cells: many mitochondria, an elaborate network of rough endoplasmic reticulum (RER), many free ribosomes, and numerous dictyosomes. The role of the dictyosomes is twofold: 1. dictyosome vesicles bud coated vesicles which transport materials from the cell and, 2. dictyosome vesicles coalesce, forming large storage vesicles. The storage vesicles are surrounded by, and often in contact with, poculiform RER. The RER forms an interconnected network throughout the cytoplasm, extending from the nuclear envelope to the plasmalemma. Distended profiles of RER are frequently in direct contact with the plasmalemma. Thus, inPharbitis secretory trichomes, it is the coated vesicles and RER which are active in secretion export. These findings imply a secretory pathway which deviates from the usual pattern in glandular cells.Predoctoral fellow of National Science Foundation during part of the investigation.     

Structure of the uterine luminal epithelium of the brush-tailed possum (Trichosurus vulpecula)

Morphology and morphometry of the luminal surface of the uterus of the brush-tailed possum were studied during the oestrous cycle, in anoestrous animals and after ovariectomy. At oestrus the secretory cells were small and the epithelium heavily ciliated. The relative surface area occupied by secretory cells reached a maximum on Day 13 when plasma progesterone concentrations are maximal. The mean apical surface area of the secretory cells also reached a maximum at this time. Both these measures decreased on Day 18 when involution of the epithelium was taking place. This process was essentially complete by Day 24 and was followed by extensive ciliogenesis. Secretory cells from anoestrous animals appeared to have an apical surface area similar to the minimum recorded during the oestrous cycle and extensive loss of cilia did not occur. Ovariectomy caused loss of ciliated cells and a reduction in the mean apical surface area to a dimension much smaller than that measured in intact animals.     

Ultrastructure of secretory cells in the gut of the cattle-tick Boophilus microplus

The ultrastructural study of the secretory cells type 1 and 2 confirmed the separate identities of two secretory cell types in the gut of female B. microplus. Secretory cell type 1 (s₁) synthesized and secreted large, spherical, uniformly electrondense granules. Secretory cell type 2 (s₂) synthesized smaller, irregularly shaped and more complex granules. Another cell type, the basophilic cell, was shown to be the reorganized basal remnant of secretory cell s₂. A few of the basophilic cells retained remnant s₂ granules within their cytoplasm. In these cells the reorganized cisternae of rough endoplasmic reticulum were arranged in whorls and parallel arrays. The cells synthesized granules with a different ultrastructure and position in the cell from the earlier granules. The new secretory material may be egg proteins which are released into the haemolymph, and transported to the ovary. Another secretory cell type with smaller spherical granules was seen in the gut caeca of only two female ticks and more evidence is needed to prove its separate identity.     

Ultrastructure of sperm storage and male genital ducts in a male holocephalan, the elephant fish, Callorhynchus milii.

In chondrichthyes, the process of spermatogenesis produces a spermatocyst composed of Sertoli cells and their cohort of associated spermatozoa linearly arrayed and embedded in the apical end of the Sertoli cell. The extratesticular ducts consist of paired epididymis, ductus deferens, isthmus, and seminal vesicles. In transit through the ducts, spermatozoa undergo modification by secretions of the extratesticular ducts and associated glands, i.e., Leydig gland. In mature animals, the anterior portion of the mesonephros is specialized as the Leydig gland that connects to both the epididymis and ductus deferens and elaborates seminal fluid and matrix that contribute to the spermatophore or spermatozeugmata, depending on the species. Leydig gland epithelium is simple columnar with secretory and ciliated cells. Secretory cells have periodic acid-Schiff positive (PAS+) apical secretory granules. In the holocephalan elephant fish, Callorhynchus milii, sperm and Sertoli cell fragments enter the first major extratesticular duct, the epididymis. In the epididymis, spermatozoa are initially present as individual sperm but soon begin to laterally associate so that they are aligned head-to-head. The epididymis is a highly convoluted tubule with a small bore lumen and an epithelium consisting of scant ciliated and relatively more secretory cells. Secretory activity of both the Leydig gland and epididymis contribute to the nascent spermatophores, which begin as gel-like aggregations of secretory product in which sperm are embedded. Fully formed spermatophores occur in the ductus. The simple columnar epithelium has both ciliated and secretory cells. The spermatophore is regionalized into a PAS+ and Alcian-blue-positive (AB+) cortex and a distinctively PAS+, and less AB+ medulla. Laterally aligned sperm occupy the medulla and are surrounded by a clear zone separate from the spermatophore matrix. Grossly, the seminal vesicles are characterized by spiral partitions of the epithelium that project into the lumen, much like a spiral staircase. Each partition is staggered with respect to adjacent partitions while the aperture is eccentric. The generally nonsecretory epithelium of the seminal vesicle is simple columnar with both microvillar and ciliated cells.