Cytodifferentiation in the accessory glands of Tenebrio molitor. III. Fine structure of the spermathecal accessory gland in the pupa

To establish indices for studying the hormonal control of differentiation of the accessory reproductive glands of insects, the ultrastructural development of the spermathecal accessory gland (SAG) of female mealworm beetles has been analyzed. Over the 9 days between adult and pupal ecdysis, the SAG transforms from a stubby sac of columnar epithelium into an elongate cylindrical gland, lined with cuticle, and containing several distinct types of differentiated cells. The first phase of pupal differentiation is one of cell division and overall gland morphogenesis which lasts 3--4 days; at its close, two populations of cells can be distinguished. One of these populations will produce the cuticular ductules while the other will yield the three-cell secretory units or organules. In the second phase which lasts 2 days, the three cells of each organule become wrapped around one another and then the innermost puts out a pseudocilium and retracts within the next ensheathing cell. In the third phase which lasts 4 days, the cuticles of the axial duct, of the efferent ductule, of the vestibule upon which the ductules converge, and of the end apparatus, are deposited. The ciliary process degenerates, and after ecdysis, the secretory cells undergo peak differentiation.     

Morphology of defense glands of the opilionids (daddy longlegs) Leiobunum vittatum and L. flavum (Arachnida: Opiliones: Palpatores: Phalangiidae)

Opilionid defense glands consist of 0.5 × 0.9-mm sacs attached to the underside of low tubercles located on the dorsal side of the cephalothorax, posterior to the first pair of legs. Each gland opens via an elongated slit, located in the posterior floor of a crater that is situated at the summit of the tubercle. The center of the sac, called the reservoir, is lined by a cuticle consisting of epicuticle and endocuticle which is continuous through the slit with the exoskeleton. The layers of cuticle vary in thickness with different locations in the gland. A hemocoelomic (basement) membrane, 0.5–1, μ thick, forms the boundary between glandular cells and hemocoel. The gland has a nonsecretory portion consisting only of cuticle-supporting cells and a secretory portion consisting of secretory and cuticle-supporting cells. The cuticle lining the reservoir in the secretory area is broached by many cuticle-lined ductules, each of which drains an isolated intercellular space called the intercalated cistern. This in turn drains microvilli-lined canaliculi located between and extending into secretory cells. The cisterns are devoid of microvilli. Secretory cell cytoplasm contains a Golgi apparatus, many free ribosomes, rough endoplasmic reticulum (RER), two types of granules (speckled and dense), and mitochondria. Speckled granules are partially filled with fairly large particles and are found in association with the Golgi apparatus. They also surround canaliculi into which they empty. Dense granules are packed with very small particles, have a gray homogeneous appearance, and are scattered throughout the cytoplasm. Mitochondria containing matrix granules tend to scatter throughout the cytoplasm but are concentrated around canaliculi.     

黑胸散白蚁腹腺的形态学与细微构造

对黑胸散白蚁(Reticulitermes chinensis Snyder)腹腺整体装片和切片进行了描述.腹腺分前、后两部分.“腹腺前部”有两类分泌细胞和一个中央腔.两类分泌细胞中,一类是圆形,个体较大;另一类细胞突起很长,具扁平的核.复盖于腹腺前部的体壁上有许多小管和一些感器,表明腹腺前部的分泌细胞产物可能是经体壁上的小管或者先贮存于中央腔中,再经体壁小管逸出体外.“腹腺后部”由大的椭圆形分泌细胞组成.根据腹腺前部紧贴于第Ⅴ腹节表皮层,而腹腺后部是可动的,并且复盖于腹腺后部的体壁上无排出小管,作者认为这些细胞的分泌物可能是释放入血淋巴中.腹腺前部及腹腺后部分泌细胞的分泌物可能有不同的机能,有待于进一步研究.     

Identification of Cell Types in the Developing Goat Mammary Gland

The goat was chosen as the model system for investigating mammary gland development in the ruminant. Histological and immunocytochemical staining of goat mammary tissue at key stages of development was performed to characterize the histogenesis of the ruminant mammary gland. The mammary gland of the virgin adult goat consisted of a ductal system terminating in lobules of ductules. Lobuloalveolar development of ductules occurred during pregnancy and lactation which was followed by the regression of secretory alveoli at involution. The ductal system was separated from the surrounding stroma by a basement membrane which was defined by antisera raised against laminin and Type IV collagen. Vimentin, smooth-muscle actin and myosin monoclonal antisera as well as antisera to cytokeratin 18 and multiple cytokeratins stained a layer of myoepithelial cells which surround the ductal epithelium. Staining of luminal epithelial cells by monoclonal antibodies to cytokeratins was dependent on their location along the ductal system, from intense staining in ducts to variable staining in ductules. The staining of epithelial cells by monoclonals to cytokeratins also varied according to the developmental status of the goat, being maximal in virgin and involuting glands, lowest at lactation and intermediate during gestation. In addition, cuboidal cells, situated perpendicular to myoepithelial cells and adjacent to alveolar cells in secretory alveoli, were also stained by cytokeratin monoclonal antibodies and antisera to the receptor protein, erbB-2, in similar fashion to luminal epithelial cells. These results demonstrate that caprine mammary epithelial cell differentiation along the alveolar pathway is associated with the loss of certain types of cytokeratins and that undifferentiated and secretory alveolar epithelial cells are present within lactating goat mammary alveoli.     

The ultrastructure of the female accessory gland,the cement gland,in the insect Rhodnius prolixus

The cement gland of Rhodnius prolixus is an epidermally derived tubular gland consisting of a distal synthetic region and a proximal muscular duct region. The synthetic region consists of numerous secretory units joined to a central chitinous duct via cuticular ductules. Proteinaceous secretion, synthesized by the goblet-shaped secretory cell, passes through the delicate cuticular lattice of a ductule-end apparatus and out through fine ductules to the central duct. Secretory cells are rich in rough endoplasmic reticulum and mitochondria. Light microscopy, SEM and TEM reveal the delicate lattice-like end apparatus structure, its formation and relationship to the secretory cell. The secretory cell associates via septate junctions with a tubular ductule cell that encloses a cuticle-lined ductule by forming an elaborate septate junction with itself. The ductules are continuous with the cuticle lining of the large central duct that conveys secretion to the proximal area. The proximal muscular duct has a corrugated cuticular lining, a thin epithelium rich in microtubules and thick longitudinal, striated muscles which contract during oviposition, forcing the secretion out. Histochemistry and electrophoresis reveal the secretion as proteinaceous.     

黄花补血草叶片盐腺的发育解剖学研究

利用扫描电镜和石蜡切片法对黄花补血草叶片进行解剖学研究,观察叶片营养器官中盐腺的分布、密度、结构及发育过程。结果表明:黄花补血草叶片上、下表皮有大量的盐腺分布,且下表皮的盐腺密度比上表皮的多,盐腺周围有7～9个表皮细胞呈辐射状排列;盐腺的成熟结构由12个细胞构成,中央有4个分泌细胞,每个分泌细胞都有一个明显的分泌孔,是盐分泌出的通道;分泌细胞外侧伴有4个弧形的毗邻细胞围成一圈;盐腺内部靠近叶肉细胞处有4个收集细胞。研究认为,黄花补血草盐腺由一个表皮原始细胞发育而成,分别经历单细胞时期、2细胞时期、4细胞时期、8细胞时期和12细胞时期的不同发育阶段。     

The development of amphids and amphidial glands in adult Syngamus trachea (Nematoda: Syngamidae)

Nematode amphids are a pair of lateral cephalic sense organs, each comprising a group of sensory endings terminating in a cuticle-lined pit. In Syngamus trachea, a parasite of birds, each amphid is surrounded by two non-nervous supporting elements, a large gland cell basally and a smaller supporting cell anteriorly. The amphidial glands display high levels of secretory activity from five to six days postinfection. Secretory material is discharged through the lumen of the sense organ onto host tissue. The ultrastructure of amphids and amphidial glands has been investigated in newly moulted, immature and mature adults to trace the development of glandular activity and its effect on amphid-amphidial gland relationships. In newly moulted adults, the glands have very low levels of secretory activity and appear to act only as supporting cells to the amphids. As secretory activity increases, the gland cell membrane surrounding the sensory endings is elaborated into a reticulum which probably forms the secretory surface. In mature adults the amphid pit is swollen and filled with secretion; the sensory endings are relegated to the periphery of the lumen. It is suggested that amphidial glands develop from typical supporting cells, but acquire a new role possibly associated with parasite attachment.     

Fine structure of the Nassonow's gland in the neotenic endoparasitic of female Xenos vesparum (Rossi) (Strepsiptera, Insecta)

Nassonow's gland consists of a number of cells with ducts that open on to the ventral surface of the brood canal in the cephalothoracic region of a neotenic female strepsipteran. The structural organization of the gland is reminiscent of the class 3 of the epidermal gland cells as defined by Noirot and Quennedey [Ann. Rev. Entomol. 19 (1974) 61], which consists of secretory and duct forming cells. The ultrastructure of the Nassonow's gland is described in female Xenos vesparum (Rossi) parasitic in the social wasp Polistes dominulus Christ. The large secretory cells are clustered in groups of three to four, rich in smooth endoplasmic reticulum and produce a secretion made up of lipids. In young females, just before mating, the ultrastructure of the cells and their inclusions indicate that they are active. In old-mated females the Nassonow's gland degenerates. Microvilli line an extracellular cavity and there are pores present in the irregularly thick cuticle of the efferent duct. The small duct forming cells, intermingle with epidermal cells, overlap secretory cells and produce a long efferent duct, the cuticle of which becomes thick close to its opening in the brood canal. Nassonow's gland could be the source of a sex pheromone, which might be capable of attracting the free-living male to a permanently endoparasitic female.     

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.     

Development of the prepupal Verson's gland of the tobacco hornworm, Manduca sexta, and its hormonal control

The segmentally arranged Verson's glands are epidermal derivatives comprised of three cells: the duct, saccule, and secretory cells. The development of these glands was followed through the 5th instar and larval-pupal transition of Manduca sexta. The glands are relatively small during the feeding stage, begin to grow at wandering, and undergo about a 50-fold increase in size during the prepupal period. The increase in size is due mainly to the hypertrophy of the secretory cell which synthesizes a heterogeneous set of proteinaceous secretory products. Three prominent 11 to 12 kiloDalton (kD) polypeptides are made by the pharate fifth larval gland, whereas the pupal gland produces polypeptides ranging from 14 to 75 kD with a major complex at 30 to 34 kD. The secretory product is poured out onto the surface of the new cuticle at the time of ecdysis and contains all of the major proteins detected in extracts of the whole gland. The accumulation of secretory products by the gland occurs during the prepupal peak of ecdysteroid and is blocked if this rise is prevented by abdominal isolation. Infusion of 30 micrograms 20-hydroxyecdysone (20-HE) into such isolated abdomens caused synthesis of the pupal products. Treatment with the juvenile hormone mimic, methoprene, during the fifth instar showed that the commitment of the glands to produce the pupal proteins is independent of and occurs before the overlying epidermis becomes committed to make pupal cuticle.     

Development of the labial gland of the ponerine ant Pachycondyla obscuricornis (Hymenoptera, Formicidae) during the pupal stage

The labial gland of adult workers of the ant Pachycondyla obscuricornis is made up of many acini, each consisting of one central cell surrounded by approximately 10 parietal cells. Both cell types are associated with a system of ramified canaliculi that remove the secretion towards a ductule outside the acinus. These ductules, each associated with one acinus, fuse together and form a ramified system of ducts, ending in two paired ducts. These paired ducts widen to form a reservoir and anteriorly join into a common unpaired duct, which ends at the base of the labium. During development in the pupal stage, epithelial acini are formed first, consisting of a monolayered epithelium lining a central lumen. In these acini, one cell grows out to become the central cell, while the others will re-arrange around it to form the parietal cells. At the end of the pupal stage, the canaliculi are formed inside the acini by the central and parietal cells that secrete a lipidic substance and a cuticle. This gland type, which also occurs in some other Hymenoptera, is structurally different from the epithelial glands and the glands consisting of bicellular units, that have been traditionally distinguished until now.     

Ultrastructural investigation of a salivary gland in a centipede: structure and origin of the maxilla I-gland of Scutigera coleoptrata (Chilopoda, Notostigmophora)

The maxilla I-gland of Scutigera coleoptrata was investigated using light and electron microscopy methods. This is the first ultrastructural investigation of a salivary gland in Chilopoda. The paired gland opens via the hypopharynx into the foregut and extends up to the third trunk segment. The gland is of irregular shape and consists of numerous acini consisting of several gland units. The secretion is released into an arborescent duct system. Each acinus consists of multiple of glandular units. The units are composed of three cell types: secretory cells, a single intermediary cell, and canal cells. The pear-shaped secretory cell is invaginated distally, forming an extracellular reservoir lined with microvilli, into which the secretion is released. The intermediary cell forms a conducting canal and connects the secretory cell with the canal cell. Proximally, the intermediary cell bears microvilli, whereas the distal part is covered with a distinct cuticle. The cuticle is a continuation of the cuticle of the canal cells. This investigation shows that the structure of the glandular units of the salivary maxilla I-gland is comparable to that of the glandular units of epidermal glands. Thus, it is likely that in Chilopoda salivary glands and epidermal glands share the same ground pattern. It is likely that in compound acinar glands a multiplication of secretory and duct cells has taken place, whereas the number of intermediary cells remains constant. The increase in the number of salivary acini leads to a shifting of the secretory elements away from the epidermis, deep into the head. Comparative investigations of the different head glands provide important characters for the reconstruction of myriapod phylogeny and the relationships of Myriapoda and Hexapoda.     

The development of the female accessory gland in the insect Rhodnius prolixus

The specialized cell types and two distinct regions of the adult Rhodnius prolixus cement gland develop from a simple pseudostratified epithelial tube during the 20–22 days of the fifth stadium. Feeding initiates the first phase, proliferation. Cells round up and divide tangentially to the lumen. Following the proliferation phase, differentiative mitoses occur and differentiation, resulting in secretory units (consisting of a ductule, gland cell and cuticular lining), ensues in the distal region. Ductule morphogenesis occurs without pseudocilia, thus differing from other insect glands. The complex changes in cell shape and interaction occur during development of the secretory unit. The secretory cell and end-apparatus develop from a double cell unit at the base of elongating ductules. The inner cell produces a complex end-apparatus of epicuticle that mirrors the microvillar pattern and then it degenerates. The ductules are lined by cuticulin and inner epicuticle while the central gland lumen has a layer of endocuticle as well. The epithelium of the proximal region remains simple producing the thick corrugated cuticle characteristic of the adult secretory duct. The mesodermal covering forms a thick longitudinal striated muscle layer that adheres to the epithelium via desmosomes.     

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.     

Immunocytochemical identification of cell types in human mammary gland: variations in cellular markers are dependent on glandular topography and differentiation

Antiserum to epithelial membrane antigen and three monoclonal antibodies (MAb) to milk-fat globule membranes immunocytochemically stain only epithelial cells, whereas a fourth reacts also with myoepithelial cells in inter- and intralobular ducts of human breast. Staining with peanut lectin shows a gradual increase for epithelial cells, from little or no staining in ducts through variable staining in ductules to intense staining in secretory alveoli. Antisera and MAb to vimentin, smooth-muscle actin, MAb to the common acute lymphoblastic leukemia antigen and to a glycoprotein of 135 KD stain myoepithelial cells in main ducts, but this staining is reduced in inter- and intralobular ducts and ductules. MAb to epithelial-specific keratin 18 stain a minor population of ductal epithelial cells, the major population of epithelial cells in interlobular (ILD) and extralobular terminal ducts (ETD), and epithelial cells in a minority of ductules. In lactating glands most epithelial cells in ductules are stained, but the alveolar and myoepithelial cells are unstained. Keratin MAb PKK2 and LP34 strongly stain myoepithelial cells, but only a minor population of epithelial cells in main ducts. However, these MAb stain principally the epithelial cells in ILD, ETD, and a minority of ductules. In lactating glands most epithelial cells are stained in ductules, but the myoepithelial and not the alveolar cells are stained intensely in secretory lobules. It is suggested that the unusual staining pattern of cells found principally in the ILD, ETD, and some ductules may represent regions of growth and/or subpopulation(s) of cells intermediate between epithelial and myoepithelial cells.     

The structure of the salt gland of Aegiceras corniculatum

Summary The salt glands of Aegiceras corniculatum have been examined by light- and electron-microscope techniques. A gland consists of a large number of abutting secretory cells and a single, large basal cell. The secretory cells and basal cell are joined by well defined plasmodesmata. The glandular cuticle shows differences between the top and sides of the gland, which may indicate a variation in the nature or quality of wax deposited. These variations may be significant in the secretion process, in view of the lack of evidence for the presence of pores. In ultrastructure, the secretory cells are generally similar to others that have been described, though there is no evidence of any particular association of vacuoles within these cells.     

The development, structure and function of the mandibular glands of Blaberus craniifer burm. (Dictyoptera Blaberidae)]

The mandibular glands of Blaberus craniifer are examined by histochemical, electrophoretic, thin-layer chromatography and electron microscopical techniques. These glands are known to secrete a volatile aggregative pheromone. The gregarious behaviour increases during insect development and is maximal in imagos. Each gland is composed of a bundle of secretory cells with efferent ductules which arise in a common duct. Secretory cells contain a myeloid secretion more abundant in imagos than in larval stages. Histochemical and electrophoretic criteria show that the myeloid product is made up of a mixture of glycoproteins. A lipidic component is also present in the secretion; its ultrastructural localization remains to be elucidated. Cytological features are in agreement with the gregarious behaviour of cockroaches. Detailed structure and functional interpretation are also discussed.     

An electron microscopic study of the spermathecal complex of virgin Aedes aegypti mosquitoes

Virgin mosquitoes were studied with the electron microscope. Spermathecal duct walls contain cuticle, epithelium, and a richly innervated spiral muscle; myocytes are linked by desmosome-like attachment plaques to the underlying epithelium. Periductal cells along upper portions of the ducts have a large secretory droplet within a highly irregular extracellular lacuna and are attached to a long secretory ductule through which finely granular material is delivered to the duct lumen and this enters the spermathecae. Basal gland cells of spermathecae have short ductules containing secretion in virgins. Secretory material in spermathecae of virgins does not form a complete internal membrane.     

Studies on the host/parasite interface during the development of a pentastomid arthropod parasite in rodent intermediate hosts, with observations on protective surface membranes

The changing structure of the cuticle of the arthropod pentastomid parasite Porocephalus crotali, during growth to the infective stage in mouse and rattlesnake hosts, is described. The outermost cuticulin layer of the cuticle in instars II-VI is elevated to form a dense mat of epicuticular hairs. Since the VI larval cuticle is retained by the infective (VII) nymph as a protective sheath, effectively all stages in mice present a hairy surface to the host and this may constitute a physical barrier to inflammatory cells. The entire surface is overlain by a triple-track 'unit' membrane whose biophysical properties resemble those of a conventional plasma membrane, and there is evidence to suggest that this membrane is susceptible to immune attack. Under natural circumstances, epicuticular hairs entrap secretion, delivered to the cuticle via innumerable minute ducts which communicate with tegumental secretory cells termed subparietal cells (SPC). SPC synthesize lamellate droplets which unfold on the cuticle to constitute a layer of protective polymorphic vesicles. By contrast, infective nymphs in snakes possess a smooth cuticle and SPC membranous secretion is stacked over the entire surface, in sheets up to 20 deep. The function of the lipid and protein components of SPC secretion is discussed.     

Morphology of the salivary glands of Mastotermes darwiniensis Froggatt (Isoptera : Mastotermitidae)

The salivary glands of Mastotermes darwiniensis (Isoptera : Mastotermitidae) workers consist of acini made up of peripherally and centrally placed cells with storage cells. A network of small efferent ductules is associated with each acinus. Intracellular ductules of the central and peripheral cells are filled with protruding microvilli. Central cells contain an abundance of rough endoplasmic reticulum and vacuoles. Continua of rough endoplasmic reticulum and vacuoles are present. Pinocytosis does not appear to be involved in secretion by the central cells. Peripheral cells are compartmental, having electron-lucent vesicle accumulations away from intracellular ductules and the basal plasmalemma invaginations. Peripheral cell morphology is similar to cells which are associated with fluid movement. Storage cells contain a large vacuole and exhibit micropinocytosis. Two axon profile types are present near and on the acini and salivary ducts, one of which appears associated with neuronal end plates.