Abundant Agranular Endoplasmic Reticulum Research Articles

Characterization of the Cytochrome P-450 Monooxygenase System in Nonciliated Bronchiolar Epithelial (Clara) Cells Isolated from Mouse Lung

The nonciliated bronchiolar epithelial (Clara) cell of the mouse is highly susceptible to toxicants that undergo metabolic activation, presumably because this cell type has high levels of cytochrome P-450 monooxygenases. As a first step in further defining the role of Clara cells in pulmonary xenobiotic activation and detoxication, we have isolated Clara cells (75 to 80% purity) and characterized them morphologically and biochemically. The identity of Clara cells, confirmed by transmission electron microscopy, was based on several features, including abundant agranular endoplasmic reticulum, large mitochondria, and dense secretory granules. Immunocytochemistry of isolated mouse cells showed that the majority were positive with antibodies against three major components of the pulmonary cytochrome P-450 monooxygenase system, cytochrome P-450 isozymes 2 (IIB), 5 (IVB), and NADPH cytochrome P-450 reductase, purified from rabbit lung. The isolated cells also showed a positive reaction with an antibody against the cytochrome P-450 isozyme that is active in the stereoselective metabolism of naphthalene, cytochrome P-450 mN (mN). Immunocytochemistry using the antibody against cytochrome P-450 isozyme 6 (IA1), purified from rabbit lung, showed no reaction in the isolated cells. The presence of intact cytochrome P-450 protein was confirmed by sodium dodecyl sulfate polyacrylamide gel electrophoresis and Western blots of homogenates of isolated cell preparations. The N-demethylation of benzphetamine and epoxidation of naphthalene occurred at easily measurable rates in incubations of isolated Clara cells. In contrast, diols, quinones, and monohydroxylated benzo(a)pyrene metabolites, analyzed by high performance liquid chromatography, were undetectable in extracts of Clara cells incubated with 3H-labeled substrate.(ABSTRACT TRUNCATED AT 250 WORDS)

Root phloem ultrastructure of the saprophytic orchid neottia nidus-avis

The ultrastructure of the mature sieve-tube element (SE) of Neottia nidus-avis shows no distinctive features. Conversely, companion cells (CC) possess a number of structural features, so far detected in this species, exclusively. One of these is the presence of leucoplasts with thylakoids as long lamellae located peripherally. The leucoplasts are invariably surrounded by the cisternae of endoplasmic reticulum, almost lacking ribosomes. Another feature is the presence of abundant agranular endoplasmic reticulum appearing as flat cisternae and tubules. The above ultrastructural features of companion cells are viewed in terms of possible involvement of these cells in hormonally regulated phloem transport in the mycorrhizal orchid.

Ultrastructural features of the ventral prostate epithelial cells in the Australian plains rat, Pseudomys australis.

The fine structure of epithelial cells of the small ventral prostate of Pseudomys australis males was studied. The cells were sometimes binucleated, exhibited relatively little granular endoplasmic reticulum, generally few secretory granules (probably reflecting a low proteinaceous secretory activity), but had abundant agranular endoplasmic reticulum (AER), similar to that in steroidogenic cells. Some of the mitochondria also showed tubular cristae. Furthermore, most cells had some irregular dense bodies in the cytoplasm which may have developed, by a gradual transformation process, from the membranes of AER, mitochondria and other organelles; they could be the product of degenerative changes in these organelles. These findings indicate a significant difference in the structure of these cells from those present in the ventral prostate of the hopping mouse, Notomys alexis. It is speculated that this gland secretes relatively little protein but perhaps more lipid or cholesterol-derived substance.

Cytodifferentiation of the nonciliated bronchiolar epithelial (Clara) cell during rabbit lung maturation: an ultrastructural and morphometric study.

The nonciliated bronchiolar epithelial (Clara) cell of adult lung is commonly defined by two cellular components: abundant agranular endoplasmic reticulum (AER) and electron-dense ovoid secretory granules. These reflect the Clara cell's proposed functions as the source of bronchiolar surface secretions and the site of xenobiotic metabolism via the cytochrome P-450 monooxygenase system. Since previous studies have indicated that Clara cells may not attain a fully functional state until some weeks after birth, the present study was undertaken to characterize systematically the differentiation of this cell type during lung maturation. Lungs were fixed by airway infusion with glutaraldehyde/paraformaldehyde (550 mOsm, pH 7.4) from at least three male rabbits at each of the following ages: 24, 27, and 30 days fetal, and 0-1 day, 3-4 days, 1, 2, 3, 4, 5, 8, 12, 15, 17, and 25 weeks postnatal; and pieces were processed for transmission electron microscopy by a selective embedding procedure. Quantitation was performed on electron micrographs (at 15,750 X) of cell profiles, which included the base, apex, and nucleus. Volume fractions of constituents of a minimum of 30 cells per animal (8 weeks and younger) and 10 per animal in older groups, were estimated by point counting with a Weibel 168-point test grid. Cell and nuclear size were estimated with a computerized digitizer (Zeiss Videoplan). Nonciliated cells of prenatal animals had large amounts of cytoplasmic glycogen (over 60% of the cell cytoplasm), few mitochondria (less than 15%), little granular endoplasmic reticulum (GER) (20%), minimal AER (less than 5%), and no granules. Postnatal animals 2 weeks of age and younger were similar, except for the presence of secretory granules and slightly more abundant AER (5 to 20%). By 4 weeks postnatal age, nonciliated cells resembled that of older animals with abundant apical AER (over 40%), secretory granules, little glycogen (11%), and GER (10%). We concluded that (1) the Clara cell is immature at birth; (2) differentiation occurs primarily during weeks 3 and 4 of postnatal life; (3) vast amounts of cytoplasmic glycogen are characteristic of the undifferentiated cell; and (4) four cellular constituents, AER, glycogen, mitochondria, and GER, undergo significant shifts in abundance during differentiation. These shifts appear to be in the sequence expected of a cell type undergoing the initiation of biosynthesis of secretory products and biogenesis of agranular endoplasmic reticulum.

Studies on zonation in the epididymis of the guinea pig. I. Ultrastructural and biochemical analysis of the zone rich in large lipid droplets (zone II).

In the epididymis of the guinea pig, zone II exhibits striking histological features that distinguish it readily from the other six regions of the epididymis. At the light microscope level, the pseudostratified epithelium of zone II is characterized by tall principal cells that are densely packed with large, intensely staining granules or droplets ranging up to 8 mu in diameter. At the electron microscope level, the principal cells exhibit numerous large lipid droplets and abundant agranular endoplasmic reticulum, which is frequently arranged in concentric whorls around one or more of the droplets. Quantitative biochemical studies comparing zone II with zones I and III show that zone II contains 2.5 - 3-fold more cholesterol and a significantly greater amount of cholesterol ester than the other two zones. These data indicate that the epididymal duct of the guinea pig includes a clearly defined region of epithelial cells possessing ultrastructural and biochemical characteristics consistent with steroidogenic activity. The potential significance of these observations to the epididymal physiology of the guinea pig and epididymal physiology in general is discussed.

Fine structure of taste buds in the barbel of the catfish, Ictalurus punctatus

Taste buds occur in the epithelium of the catfish barbel along its entire length. Two major cell types, light and dark cells, occupy the upper two-thirds of the taste bud. A third cell type, the basal cell, lies on the basal lamina and is essentially separated from the light and dark cells by a plexus of unmyelinated nerve fibers. The dark cells have branching processes, both apically and basally whereas the light cells have a single apical process and many basal processes. The apical processes of dark cells contain secretory granules, while the apical processes of light cells contain an abundant agranular endoplasmic reticulum. Light cell nuclei contain bundles of 10 nm filaments, often arranged in the shape of a cup or ring, but nucleoli are rarely seen. It is suggested that this morphology indicates a low degree of RNA synthesis by light cells. The basal cells contain large numbers of vesicles, about 60 nm in diameter, which are sometimes seen in clumps in relation to an adjacent nerve fiber in a configuration resembling a synapse. Curiously, although basal cells present a large surface to the basal lamina, there are no hemidesmosomes. This suggests that the basal cell does not originate from the epidermis.

Fine structure of the gular gland of the free-tailed bat Tadarida brasiliensis.

AbstractThe gular gland of the bat Tadarida brasiliensis is a specialized sebaceous gland located in the skin of the suprasternal region of adult males. It consists of an aggregation of simple branched tubulo‐acinar gland units, the number of which varies seasonally. Each acinus is composed of densely packed sebaceous cells at various stages of differentiation. Acinar basal cells and cells of the epithelium of the ducts can differentiate into sebaceous cells. Two main changes appear in the cytoplasm concurrent with the sebaceous transformation: the differentiation of cytoplasmic organelles and the deposition of lipid material. The appearance of a different type of mitochondrion and the development of large numbers of ribosomes and polyribosomes can be recognized in the cytoplasm at an early stage of differentiation. Concomitant with the deposition of significant numbers of lipid droplets, the cells develop abundant agranular endoplasmic reticulum occurring mainly as scattered tubular cisternae. These at times form whorls surrounding lipid droplets. At later stages, the cisternae of the agranular endoplasmic reticulum often occur in crystalline arrays between secretory oil droplets. The roles of the different cytoplasmic organelles, especially in relation to the production of sebum, are discussed.

Comparative ultrastructural and histochemical studies of the interstitial cells of the rat testis during fetal and postnatal development.

Summary. The interstitial cells of the albino rat testis were studied in animals ranging from the 15th day of fetal life until adulthood. The interstitial cells developed in two phases, a fetal phase from the 17th fetal day to the 2nd postnatal week and an adult phase from the 3rd week onwards. Lipid histochemical and ultrastructural techniques demonstrated the abundance of lipid droplets in the fetal interstitial cells and the paucity of lipid in the adult interstitial cells. The enzyme Δ5-3β-hydroxysteroid dehydrogenase (HSD) was studied in the interstitial cells throughout development using dehydroepiandrosterone (DHEA), pregnenolone and 17α-hydroxy pregnenolone as substrates. The enzyme activity was found with all substrates in both types of interstitial cells, DHEA producing the greatest reaction. The activity of HSD using pregnenolone on substrates was greater in the fetal interstitial cells. The ultrastructural studies demonstrated the presence of abundant agranular endoplasmic reticulum in both the fetal and adult interstitial cells. The prominent cup-shaped mitochondria and lipid droplets present in the fetal cells were not present in the adult interstitial cells. The differences in the histochemical and ultrastructural features of the cells of each phase suggests that they represent separate generations of interstitial cells.

Ultrastructure of the corpus luteum of the white-tailed deer during pregnancy.

AbstractThe fine structure of corpora lutea from 14 white‐tailed deer was studied from early through near‐term pregnancy. The corpora contained both thecal and granulosal lutein cells. The small, elongate and cylindrical thecal lutein cells contained many lipid droplets, juxtanuclear Golgi elements, abundant agranular endoplasmic reticulum, and other cytoplasmic organelles. These cells were observed throughout pregnancy. Some of the thecal lutein cells became modified during early to midpregnancy. The modified thecal lutein cells possessed many lipid droplets, several lysosomes, packets of PAS‐positive glycogen granules, and numerous small membranous whorls of agranular endoplasmic reticulum. The granulosal lutein cells had highly folded and/or ruffled plasma membranes, abundant tortuous tubular and cisternal agranular endoplasmic reticulum, numerous rod‐shaped to round mitochondria with tubular and lamellar cristae, Golgi elements, and a few packets of granular endoplasmic reticulum. Many granulosal lutein cells became modified during mid‐ to near‐term pregnancy by the addition of numerous small membrane‐bound osmiophilic droplets and variable numbers of large nonmembrane‐bound lipid droplets. The granulosal and thecal lutein cells appeared more active in steroid biosynthesis than the modified granulosal and thecal lutein cells.

Fine structure of the interstitial cells of Leydig in the squirrel monkey during seasonal regression.

AbstractThe fine structure of the interstitial cells of Leydig has been examined in the squirrel monkey, Saimiri sciureus, during the non breeding portion of the year when the testes are essentially azoospermic. Interstitial cells are present in abundance as a layer, several cells thick, on the inner aspect of the tunica albuginea. Cytologically, the cells possess the characteristics usually associated with cells which synthesize and secrete steroid hormones: an abundant agranular endoplasmic reticulum in the form of anastomotic tubules; mitochon‐chondria with both lamellar and tubular cristae; only a few strands of granular endoplasmic reticulum; a Golgi apparatus and associated vesicles, some of which are of the coated variety; a varying population of lipid droplets and dense bodies. Some of the dense bodies appeared to be lipofuscin pigment. A previously undescribed inclusion was frequently encountered which consisted of arrays of a honeycomb like structure. Most frequently these structures were present near the cell periphery or in blunt protrusions of the cytoplasm.

On the histogenesis of the ovarian interstitial gland in rabbits. I. Primary interstitial gland

AbstractOvaries from rabbits one to three months old were examined to demonstrate the histogenesis of ovarian interstitial cells.Electron micrographs showed that “primary interstitial gland cells” with abundant agranular endoplasmic reticulum were present prior to appearance of follicular atresia and that extensive development of the agranular endoplasmic reticulum and accumulation of lipid droplets occurred in the epithelial cells of medullary cords and granulosal cell nests. Therefore, it was concluded that the “primary interstitial gland” of juvenile rabbit ovaries is of epithelial origin, derived from the medullary cords and the granulosal nests, although the “secondary interstitial gland” is considered to arise from the theca interna of atretic follicles.This conclusion was confirmed by biochemical and histochemical demonstration of 3β‐hydroxysteroid dehydrogenase, an enzyme system necessary for steroid biosynthesis. The activity of 3β‐hydroxysteroid dehydrogenase increased significantly at two months when the agranular reticulum began to devlop in epithelial cells. Histochemical findings showed that the cells having the enzyme activity were consistent with the cells containing a large quantity of lipid.

The postnatal development of the Sertoli cells of the mouse.

The development of the Sertoli cells of the testis of the white mouse was studied with the electron microscope at weekly intervals from birth to sexual maturity, utilizing fixation in a glutaraldehyde-formaldehyde mixture followed by OsO4. The Sertoli cells underwent a rapid structural differentiation between 1–2 and 4–5 weeks postnatally. Large increases were noted in cell size, in the extent of cell processes extending between germinal cells, and in the abundance of certain cytoplasmic organelles, particularly the agranular endoplasmic reticulum and Golgi apparatus. The apparent sequences of development of the characteristic junctional complexes and tri-partite nucleoli of Sertoli cells were observed. The development of structural specializations is discussed in terms of established and proposed functions of the Sertoli cells, and the demonstration of abundant agranular endoplasmic reticulum is considered in relation to the possibility of steroid hormone production by Sertoli cells.

The fine structure of testicular interstitial cells in mice.

AbstractThe testicular interstitial cells of mice contain an abundant agranular endoplasmic reticulum occurring as a network of interconnected tubules. Unusual features of the reticulum are occasional extensive whorls of concentric membranes and the occurrence of bundles of parallel double‐walled tubules. The mitochondria have tubular cristae and are occasionally very large.In contrast to the interstitial cells of other species that have been described, the mouse interstitial cells show a segregation of the cytoplasm into areas of dense agranular reticulum and other areas where the agranular reticulum is relatively sparse. The latter areas contain scattered cistenae of granular reticulum, many free ribosomes in clusters, mitochondria, lipid droplets and small granules. The mitochondria and lipid droplets are often encircled by cisternae of the reticulum.Biochemical evidence from other laboratories, taken with the present results, indicates that the membranes of the endoplasmic reticulum in mouse interstitial cells are the site of the enzymes that mediate the synthesis of testosterone from progesterone. There is also an indication that cholesterol biosynthesis is associated with the agranular reticulum. The membranes of the agranular reticulum may also serve as a reservoir for the storage of cholesterol.

THE FINE STRUCTURE OF TESTICULAR INTERSTITIAL CELLS IN GUINEA PIGS

In guinea pig testes perfused with either glutaraldehyde or osmium tetroxide fixative, the cytoplasm of the interstitial cells contains an exceptionally abundant agranular endoplasmic reticulum. The reticulum in central regions of the cell is a network of interconnected tubules, but in extensive peripheral areas the reticulum is commonly organized into closely packed, flattened cisternae which are fenestrated. Occasional small patches of the granular reticulum occur in the cytoplasm and connect freely with the agranular reticulum. The mitochondria have a dense matrix and contain cristae and some tubules. The Golgi complex is disperse and shows no evidence of secretory material. The cytoplasm also contains lipid droplets. Lipofuscin pigment granules are probably polymorphic residual bodies and contain three components: (1) a dense material which at high magnification shows a 75-A periodicity; (2) a medium-sized lipid droplet; and (3) a cap-like structure. In glutaraldehyde-perfused testis the interstitial cell cytoplasm appears to have the same density from cell to cell, and the agranular reticulum is tubular or cisternal but not in the form of empty vesicles. Thus the "dark" and "light" cells and the vesicular agranular reticulum sometimes encountered in other fixations may be artifacts. Biochemical results from other laboratories, correlated with the present findings, indicate that the membranes of the agranular endoplasmic reticulum in guinea pig interstitial cells are the site of at least two enzymes of androgen biosynthesis, the 17-hydroxylase and the 17-desmolase.

The normal fine structure of opossum testicular interstitial cells.

The interstitial tissue of the opossum testis includes interstitial or Leydig cells, macrophages, and small cells which morphologically resemble mesenchymal cells. The latter are thought to give rise to mature interstitial cells. The most prominent feature of the interstitial cell cytoplasm is an exceedingly abundant agranular endoplasmic reticulum. This reticulum is generally in the form of a meshwork of interconnected tubules about 300 to 450 A in diameter, but occasionally it assumes the form of flattened, fenestrated cisternae resembling those of pancreatic acinar cells, except for the lack of ribonucleoprotein particles on the surface of the membranes. The interstitial cells vary considerably in their cytoplasmic density. The majority are quite light, but some appear extremely dense, and in addition usually have a more irregular cell surface, with numerous small pseudopodia. These differences may well reflect variations in physiological state. Cytoplasmic structures previously interpreted as "crystalloids" consist of long bundles of minute parallel tubules, each about 180 A in diameter, which seem to be local differentiations of the endoplasmic reticulum. The mitochondria are rod-shaped, and contain a moderately complex internal membrane structure, and also occasional large inclusions that are spherical and homogeneous. The prominent juxtanuclear Golgi complex contains closely packed flattened sacs and small vesicles. The results of the present study, coupled with biochemical evidence from other laboratories, make it seem highly probable that the agranular endoplasmic reticulum is involved in the synthesis of the steroid hormones produced by the interstitial cell. This finding therefore constitutes one of the first functions of the agranular reticulum for which there is good morphological and biochemical evidence.