The development and fine structure of ultimobranchial glands in larval anurans

A comparative optical microscopic and ultrastructural study on the ultimobranchial (UB) glands of three common species of Israeli anurans: Bufo viridis, Hyla arborea, and Rana ridibunda during metamorphosis is presented. The UB glands typically consist of a single follicle with a central lumen, though occasionally secondary follicles are present in Hyla and Rana. A single UB cell type is found which appears either in a very electron-dense "dark" form or as a less dense "light" form, though the ratio of dark: light cells from gland to gland at any one stage of metamorphic development is quite variable. By the end of metamorphosis in Bufo and Hyla all the UB cells are usually of the light variety, whereas in Rana the dark cells persist. The organelles of these secretory cells including secretory granules, granular endoplasmic reticulum, free ribosomes, tonofilaments, microtubules, Golgi bodies, and lipid droplets, their distribution, abundance, and possible functions in relation to metamorphosis are described. Apocrine secretion into the central lumen of the gland is also described and discussed.     

Fine structure of the corpuscles of stannius in the toadfish.

The micro-anatomy of the corpuscles of Stannius of the toadfish, Opsanus tau, an aglomerular marine teleost, has been studied by light and electron microscopy. The corpuscles are composed of extensively anastomosed cords of epithelial cells which maintain intimate contact with blood capillaries. Most of the epithelial cells contain acidophilic granules which also show a positive reaction with the periodic acid-Schiff technique and aldehyde fuchsin. On the basis of fine structural criteria, three cell types can be recognized. The granular cells contain abundant quantities of granular endoplasmic reticulum, ribosomes, Golgi apparatus with prosecretory granules, coated vesicles, polymorphic mitochondria with lamellar cristae, filaments, microtubules, a cilium, a variety of lysosome-like dense bodies, glycogen particles, lipid droplets, secretory granules and intranuclear lipid-like inclusions. One variety of agranular cell (type I) is characterized by the total absence of secretory granules, but it contains large amounts of granular endoplasmic reticulum and ribosomes, conspicuous profiles of Golgi apparatus, coated vesicles and sometimes an abundance of glycogen. Another variety of agranular cell (type II) has poorly developed cytoplasmic organelles. The perivascular space between the capillary and parenchyma contains connective tissue cells and abundant nerve fibers. The different types of epithelial cells observed in the corpuscles of Stannius of this fish may represent functional stages of the secretory cycle in a single cell type.     

Ultrastructure of palatal taste buds in the perihatching chick.

Palatal taste buds of perihatching chicks were examined by electron microscopy. Four intragemmal cell types were characterized. 1) Light: with voluminous, electron-lucent cytoplasm containing scattered free ribosomes, rough and smooth endoplasmic reticulum, plump mitochondria, sparse perinuclear filaments, occasional Golgi bodies, and numerous clear and dense-cored vesicles. Clear vesicles sometimes aggregate in a presynaptic-like configuration apposed to an axonal profile. These cells contained large, spherical, uniformly granular nuclei with one nucleolus. 2) Dark: with dense cytoplasm containing filamentous bundles surrounding the nucleus, occasional clear vesicles, centrioles, rough endoplasmic reticulum, and compact mitochrondria. The apical cytoplasm noticeably lacks dense secretory granules. Irregular to lobulated nuclei are densely granular, and contain scattered clumps of chromatin, adhering especially to the inner leaflet of the nuclear membrane, and at least one nucleolus. Cytoplasmic extensions of dark cells envelop other intragemmal cell types and nerve fibers. Light and dark cells project microvilli into the taste pore. 3) Intermediate: contain gradations of features of light and dark cells. 4) Basal: darker than the other intragemmal cell types and confined to the ventral bud region. Putative afferent synapses in relation to light cells, and axo-axonal contacts are described. While the appearance of axo-axonal contacts may be a transient developmental event, other bud features are consonant with observations in adult chickens and suggest that the peripheral gustatory apparatus is mature at hatching in this precocial avian species.     

The ultrastructure of the Sertoli cell of the vervet monkey, Chlorocebus aethiops

The ultrastructure of the Sertoli cell of the vervet monkey was studied using both scanning and transmission electron microscopic techniques. SEM micrographs revealed perforated sleeve-like processes which encased mature elongated spermatids which are ready for spermiation. TEM micrographs showed a large Sertoli cell nucleus characterized by many lobes (4–5) and consisting of a homogenous nucleoplasm and a distinctive nucleolus. The nucleus occupies a significant portion of the basal region of the cell. The distribution of chromatin clearly shows high activity of these cells. Lipid droplets and free ribosomes are also found scattered throughout the cytoplasm. Well-developed Golgi apparatus is found in the basal region of the cell. There is phagocytic activity in the Sertoli cells as revealed by the presence of numerous phagosomes. Numerous mitochondria with well-developed tubular cristae are found on the basal side of the nucleus, whereas few mitochondria are located on the apical side of the nucleus. Distinct desmosomes are located between cells. A well-developed smooth endoplasmic reticulum and granular endoplasmic reticulum are frequently found in the cytoplasm of the Sertoli cells. The results of this investigation showed that Sertoli cells of the vervet monkey are almost similar to those of humans and show many similarities with other mammalian species.     

Fine structure of the midgut epithelium in the developing brown shrimp,Penaeus aztecus

The midgut epithelium of larval and early postlarval brown shrimp has been studied with light and electron microscopy. Ultrastructurally the features of the midgut do not change during these stages of development. On the basis of electron density, two epithelial cell types can be distinguished, and these are referred to as light and dark cells. The dark cells contain more rough endoplasmic reticulum and more free ribosomes than the light cells. Mitochondria in the dark cells have a matrix which is less electron dense than the mitochondrial matrix of the light cells. Both cell types have a microvillous border with a surface coat. The microvilli lack microfilaments within their core, and a terminal web is not differentiated in the stages examined. Tubular smooth endoplasmic reticulum is abundant in the basal portions of the cells. Electron dense, membrane bound vesicles are consistently seen in association with the Golgi apparatus, apical cell surface, and gut lumen and therefore are believed to be secretory granules. Cells in the anterior portion of the midgut often contain very large lipid droplets in the cytoplasm.     

LYSOSOMES AND GERL IN NORMAL AND CHROMATOLYTIC NEURONS OF THE RAT GANGLION NODOSUM

The rat ganglion nodosum was used to study chromatolysis following axon section. After fixation by aldehyde perfusion, frozen sections were incubated for enzyme activities used as markers for cytoplasmic organelles as follows: acid phosphatase for lysosomes and GERL (a Golgi-related region of smooth endoplasmic reticulum from which lysosomes appear to develop) (31–33); inosine diphosphatase for endoplasmic reticulum and Golgi apparatus; thiamine pyrophosphatase for Golgi apparatus; acetycholinesterase for Nissl substance (endoplasmic reticulum); NADH-tetra-Nitro BT reductase for mitochondria. All but the mitochondrial enzyme were studied by electron microscopy as well as light microscopy. In chromatolytic perikarya there occur disruption of the rough endoplasmic reticulum in the center of the cell and segregation of the remainder to the cell periphery. Golgi apparatus, GERL, mitochondria and lysosomes accumulate in the central region of the cell. GERL is prominent in both normal and operated perikarya. Electron microscopic images suggest that its smooth endoplasmic reticulum produces a variety of lysosomes in several ways: (a) coated vesicles that separate from the reticulum; (b) dense bodies that arise from focal areas dilated with granular or membranous material; (c) "multivesicular bodies" in which vesicles and other material are sequestered; (d) autophagic vacuoles containing endoplasmic reticulum and ribosomes, presumably derived from the Nissl material, and mitochondria. The number of autophagic vacuoles increases following operation.     

Ultrastructure of the indifferent gonad in male and female pig embryos.

Pig embryos aged 24 days were obtained from artifically inseminated sows for ultrastructural study of the indifferent gonads. Sex was identified by chromosome analysis. The gonads are composed in both sexes of three different tissues: the surface epithelium, the gonadal blastema and the mesenchyme. The surface epithelial cells contained elongate mitochondria, granular endoplasmic reticulum, free polysomes, the Golgi complex, fine filaments and coated vesicles. The primitive cords were continuous with the surface epithelium and the interior of the gonad was occupied by blastema cells. They had prominent nucleoli, elongate mitochondria, granular endoplasmic reticulum, the Golgi complex, free polysomes, some lipid droplets and occasionally circular smooth membrane profiles resembling the agranular endoplasmic reticulum. Individual primordial germ cells were seen in all parts of the gonad. They were roundish with prominent nucleoli, globular mitochondria, granular endoplasmic reticulum, free polysomes, the Golgi complex, coated vesicles, lipid droplets and dense bodies. Degenerating cells and cells having pseudopods were also encountered. In comparison to the gonad at the age of 22 days, the primordium had grown into a longitudinal roundish protrusion and the number of primoridal germ cells had increased. Histological and ultrastructural observations showed that the pig gonads at the age of 24 days were similar in both sexes.     

Ultrastructural evidence for the presence of secretory cells in the pineal parenchyma ofHeteropneustes fossilis

There is an extensive literature dealing with the study of indoles, especially serotonin and melatonin, but with considerably less emphasis on the cells and cell types involved in the synthetic process. In the present electron microscopical investigation of the pineal end vesicle ofHeteropneustes fossilis, pinealocytes have been revealed in the pineal parenchyma characterized with extensive synthetic apparatus viz., rough endoplasmic reticulum, free ribosomes, lipid droplets, mitochondria and Golgi bodies. Two sub-populations of the pinealocytes are easily distinguishable on the basis of electron opacity and the preponderance of one or other morphological profile: light cells and dark cells. Light cells represent the active phase of secretion while dark cells represent the storage and release phase of secretion. A neuroendocrine role for the pineal body inHeteropneustes fossilis is suggested which may be significant in view of the nocturnal habit of the fish. Dedicated to my father, Prof. C B L Srivastava     

Adaptation of a non-radioactive in situ hybridization method to electron microscopy: detection of tenascin mRNAs in mouse cerebellum with digoxigenin-labelled probes and gold-labelled antibodies

In this study we describe a method for the detection of mRNAs at the ultrastructural level using a non-radioactive in situ hybridization method based on digoxigenin-labelled cRNA probes and gold-labelled digoxigenin-specific antibodies. We applied this protocol to an analysis of the expression of the extracellular matrix protein tenascin in the developing cerebellar cortex of the mouse. To gain an impression of the sensitivity attainable with digoxigenin-labelled probes, we first established at the light microscopic level that the hybridization signal obtained with the non-radioactive probe is as sensitive as that obtained with a ³⁵S-labelled probe. The non-radioactive hybridization protocol was then combined with electron microscopic post-embedding and immunogold detection techniques. Tenascinspecific, digoxigenin-labelled cRNA probes were hybridized to ultrathin sections of Lowicryl K4M-embedded tissue and the probe/target mRNA hybrids were detected using gold-labelled antibodies to digoxigenin. In agreement with the observations from in situ hybridization at the light microscopic level, specific labelling was observed in Golgi epithelial cells in the region of the Purkinje cell layer and cells in the internal granular layer, which could be identified as astrocytes by ultrastructural criteria. Labelling was detectable in association with free ribosomes and ribosomes of the rough endoplasmic reticulum. In addition, focal hybridization signals were occasionally found in the nucleus. No signal was observed in Golgi epithelial cells or astrocytes using sense or in any other cerebellar cell type using either sense or anti-sense probes. The described in situ hybridization technique uses ultrastructural criteria to associate the presence of a given mRNA species with a particular cell type. Additionally, it provides information about the target mRNA's subcellular distribution, thus offering the possibility to study intracellular transport of particular mRNAs.     

ELECTRON MICROSCOPIC AUTORADIOGRAPHY OF GERMINAL CENTER CELLS IN MOUSE SPLEEN

The fine structure of tritiated thymidine-labeled cells in antigen-stimulated mouse spleen germinal centers is described. In studies on the ultrastructural level, two labeled cell types found in germinal centers are observed. Large lymphocytes are characterized by their very numerous free ribosomes, a paucity of endoplasmic reticulum, relatively few mitochondria, and a poorly developed Golgi region. The nuclei are large and vesicular, and large nucleoli are present. A second labeled cell type appears to contain more mitochondria and has a higher development of the Golgi area. The nucleus contains large, numerous blocks of chromatin, indicative of a more differentiated cell type. Reticular cells, both phagocytic and non-phagocytic, were not observed to be labeled in the germinal centers.     

Ultrastructure of the haemocytes of Tetrodontophora bielanensis Waga (Collembola)

Five types of haemocytes: prohaemocytes, plasmatocytes, granular haemocytes, spherule cells and phagocytes, have been distinguished on the basis of ultrastructural studies. Prohaemocytes are ovoid cells with a simple structural organization. Plasmatocytes are larger; their cytoplasm contains well-developed rough endoplasmic reticulum, numerous mitochondria and free ribosomes. Granular haemocytes are the most numerous of the blood cells, characterized by the presence of electron-dense granules. The cytoplasm of spherule cells contains many spherules made up of filamentous material of medium electron density. Rough endoplasmic reticulum, free ribosomes and mitochondria are also found in the cytoplasm. Phagocytes are the largest haemocytes. Their cytoplasm contains an abundance of lysosomes and myelin structures. In addition to haemocytes, cells intermediate between plasmatocytes and granular haemocytes have been observed, which indicates that the granular haemocytes are derived from plasmatocytes.     

A comparative study of the ultrastructure of resting and active cambium of Salix fragilis,L.

Summary Cells of the resting cambium contain vesiculate smooth endoplasmic reticulum, free ribosomes, oil droplets, and protein bodies. There are comparatively few vacuoles, and these are small. The nucleus is fairly central within the cell and is surrounded by a cluster of plastids and mitochondria. Active cambial cells and young differentiating xylem elements are highly vacuolate, contain rough endoplasmic reticulum and polyribosomes, the Golgi apparatus is active in the production of vesicles, and the distribution of organelles is a function of the vacuolation of the cell.It is suggested that the lipid droplets and protein bodies are storage materials which are required during the first stages of differentiation at the beginning of the growing period.     

Ultrastructural pathology of the epidermis of molting elaterid larvae (Coleoptera) with a fungus and a bacterium in the ecdysial space

Toxins produced by the fungus Metarrhizium anisopliae and the bacterium Pseudomonas aeruginosa in the ecdysial space of a molting wireworm are absorbed through the thin new cuticle and ultrastructurally change the epidermal cells into two distinct types. One is a rounded, degenerative type characterized by a “light” cytoplasm with vesiculated rough endoplasmic reticulum, rounded mitochondria with degenerated cristae, little ground plasm, and a rounded nucleus with little nucleoplasm and large globules of condensed chromatin from which chromatin fibrils separate in loose folds or granulelike tight folds. The other type has very irregular outlines and is characterized by a “dark” cytoplasm with abundant, whorled laminae of rough endoplasmic reticulum and abundant free ribosomes in a dense ground plasm, large rounded clear vacuoles, and apparently normal mitochondria and nuclei. The fungal toxins are believed to be primarily responsible for the formation of the light cells, and the bacterial toxins, for the separation of the chromatin into fibrils in the light cells, the fusion of their nuclei into large nuclear bodies, and the changes in the cytoplasmic contents of the dark cells. The dark cells, although abnormal, appear to retain a limited secretory activity.     

Fine structure of the nemertean worm Lineus lacteus red blood corpuscles

In the blood of Lineus lacteus, haemoglobin-containing cells measuring 6-7 micrometer in diameter were seen. Using electron microscopy different cellular components were identified, including a nucleus which contains a nucleolus, mitochondria, rough and smooth endoplasmic reticulum, free ribosomes, osmiophilic deposits, and Golgi apparatus. The morphological appearance of the Lineus lacteus erythrocyte was found to resemble an immature mammalian red cell.     

Regional differences in the ultrastructure of Purkinje cells of the rat

Summary In the albino rat, perikaryal diameter, volume density of the granular endoplasmic reticulum and Golgi apparatus, and lumenal diameter of cisternae of the granular endoplasmic reticulum are larger in Purkinje cells of lobule Via (neocerebellum) than in those of lobule X (archicerebellum). In contrast, only the surface density of cisternae of the granular endoplasmic reticulum is larger in Purkinje cells of lobule X. The cisternae of granular endoplasmic reticulum are arranged into conspicuous Nissl bodies parallel to the nuclear membrane, but the content of ribosomes and polysemes is markedly less in lobule-X cells than in cells from lobule VI a. These results indicate qualitative and quantitative differences between the metabolically important organelles in Purkinje cells of the neo- and archicerebellum (cf. Larsell 1952).Supported by a grant from the Deutsche Forschungsgemeinschaft (La 184/7)     

LIVER PARENCHYMAL CELL INJURY : I. Initial Alterations of the Cell Following Poisoning with Carbon Tetrachloride

The structure of the endoplasmic reticulum, plasma membrane, mitochondria, and Golgi apparatus of the liver parenchymal cell is strikingly altered within 1 hour following the administration of a single oral dose of carbon tetrachloride to rats. Progressive loss of glucose-6-phosphatase activity accompanies dispersal of the ergastoplasm. Electron microscopy reveals that these changes are associated with vacuolization of the cisternae of the granular endoplasmic reticulum, degranulation of its membranes, and the appearance of increased number of free ribosomes in the adjacent cytoplasmic matrix. Concomitantly, calcium enters the liver parenchymal cell and is sequestered by mitochondria. First increased at 30 minutes, calcium content is maximal at 1 hour and returns to normal at 2 hours. Although succinic and glutamic dehydrogenase activity patterns within the liver lobule are unaffected, liver cell mitochondria enlarge and some appear to fuse or assume cup-like configurations. Microvilli lining the space of Disse become irregularly indistinct and increasingly pleomorphic by 30 minutes when the plasma membrane becomes increasingly permeable to calcium. Golgi vesicles swell and discharge their granules during the period of poisoning studied. Although all the changes observed may be the result of direct interaction of carbon tetrachloride with the membranes of the cytoplasmic constituents of the liver parenchymal cell, the possibility that the irreversible changes observed in the granular endoplasmic reticulum may be due to the chemical interaction between the poison and this system is discussed.     

Ultrastructure of the pineal organ of the killifish,Fundulus heteroclitus,with special reference to the secretory function

Summary The pineal organ of the killifish, Fundulus heteroclitus, was investigated by electron microscopy under experimental conditions; its general and characteristic features are discussed with respect to the photosensory and secretory function. The strongly convoluted pineal epithelium is usually composed of photoreceptor, ganglion and supporting cells. In addition to the well-differentiated photosensory apparatus, the photoreceptor cell contains presumably immature dense-cored vesicles (140–220 nm in diameter) associated with a well-developed granular endoplasmic reticulum in the perinuclear region and the basal process. These dense-cored vesicles appear rather prominent in fish subjected to darkness. The ganglion cell shows the typical features of a nerve cell; granular endoplasmic reticulum, polysomes, mitochondria and Golgi apparatus are scattered in the electron-lucent cytoplasm around the spherical or oval nucleus. The dendrites of these cells divide into smaller branches and form many sensory synapses with the photoreceptor basal processes. Lipid droplets appear exclusively in the supporting cell, which also contains well-developed granular endoplasmic reticulum and Golgi apparatus. Cytoplasmic protrusions filled with compact dense-cored vesicles (90–220 nm in diameter) are found in dark-adapted fish. The origin of these cytoplasmic protrusions, however, remains unresolved. Thus, the pineal organ of the killifish contains two types of dense-cored vesicles which appear predominantly in darkness. The ultrastructural results suggest that the pineal organ of fish functions not only as a photoreceptor but also as a secretory organ.We thank Dr. Grace Pickford for the fishes.     

Ultrastructure of the sexual segments of the kidney in male and female lizards,Cnemidophorus l. lemniscatus (L.)

Summary Kidneys of adult male and female lizards were studied by electron microscopy, in order to understand the ultrastructure of the collecting duct and a differentiated part thereof, the sexual segment, which is an important accessory sexual organ. First portion of sexual segment in males: The cells are filled with large secretory granules of a wide range of opacities. The granular endoplasmic reticulum is abundant; basal formations of superimposed flat cisternae are frequent. Distended vesicles and microvesicles prevail in the supranuclear, well developed Golgi apparatus. Evidences indicate that secretion of these cells is holocrine. Second portion of sexual segment in males: All of the secretory granules are apical in location and relatively electron-opaque; they show a denser core. This core is formed by a substance which, after lying in contact with ribosomes, enters the secretory vesicles of the highly developed Golgi apparatus. A lighter substance is then condensed around it. The secretion of the granules is merocrine. The granular endoplasmic reticulum is very abundant in these cells, but basal ergastoplasmic formations are lacking. Sexual segment in females: The cells show features similar to those of the male first portion, but they are smaller. Undifferentiated collecting duct: Most of the cells are mucigenic. They have small ovoid, apical secretory granules. The density of the granules varies from cell to cell; when they are electron-lucent, they exhibit laminar or dotted opaque figures. Moderately developed Golgi apparatus and granular endoplasmic reticulum, as well as elongated mitochondria, occur in mucigenic cells. Intercalated among the latter are non-secretory cells. They have very abundant mitochondria, numerous microvilli, many pinocytic and smooth-membrane vesicles, whereas the organelles participating in synthetic processes are poorly developed; their function is most likely related to active solute transport.     

Enzyme synthesis and potential during induction synchrony in the fission yeast Schizosaccharomyces pombe

The fine structure of L cells is described at 30 min and 24 h after enucleation by centrifugation in cytochalasin B. The morphology of the 30-min enucleates is the same as that of the cytoplasm of nucleated cells. Centrioles, a normal Golgi apparatus, endoplasmic reticulum, mitochondria, microtubules, and some microfilaments, are present in enucleates. At 24 h after enucleation, the enucleates are extensively vacuolated. The cisternae of the Golgi apparatus are extremely dilated, and the granular ER is sometimes dilated. Microtubules, and, in particular, microfilaments, are still abundant. Nuclei removed from cells by enucleation in cytochalasin B are surrounded by a thin shell of cytoplasm containing numerous ribosomes, an occasional mitochondrion, a few pieces of endoplasmic reticulum, and an enclosing plasma membrane. Continuities between the nuclear envelope and the ER are particularly frequent. These nuclei possesses a normal fine structure.     

Ultrastructure of the cell types of the anterior hypophysis in a lizard. I. Corticotrophs

Corticotrophs of the teiid lizard Cnemidophorus lemniscatus are situated in the rostral zone of the pars distalis. In normal animals, they are usually rounded cells with slightly eccentric vesicular nuclei, especially characterized by a lucent hyaloplasm and medium-sized secretory granules of uniform high density. Granules are almost spherical, with small angular deformations, and closely bounded by a fuzzy membrane. Many cells have only a few or a moderate number of granules, with large areas of cytoplasm devoid of them; in others, granules fill the supranuclear region. The cytoplasm exhibits numerous ribosomes, often in rosettes and mostly free, a series of loosely superimposed cisternae of rough endoplasmic reticulum, small dictyosomes, and elongate mitochondria of light matrix. Metyrapone administration during 2-8 days causes dramatic alterations in corticotrophs; they become hypertrophic and extensively degranulated, with a great development of the endoplasmic reticulum and Golgi apparatus, eventually showing a row of large peripheral granules of uneven structure, enclosed in ample vesicles studded with ribosomes. A lesser degree of hypertrophy and degranulation of corticotrophs appears during the first two weeks after thyroidectomy or gonadectomy, and may be partially attributed to surgical stress. Well granulated enlarged corticotrophs, with hypertrophic endoplasmic reticulum and Golgi apparatus, are probably a result of hormonal imbalance in lizards of both sexes gonadectomized for one or two months.