Electron microscopic studies on the macronuclear development in the ciliate Chilodonella uncinata.

The development of macronuclear anlage in the ciliate Chilodonella uncinata has been studied through electron microscopy. The ultrastructure of macro- and micronuclei is described for comparison. During the first stage of development, when the DNA content of the macronuclear anage increases from 2 C to 32 C, chromosomes are visible as distinct osmiophilic bodies inside the anlage. At the end of the initial polyploidization phase, the chromosomes despiralize, giving rise to long filamentous structures 25 to 50 nm in diameter. The latter show a singular banding pattern, with dense bands 12 to 25 nm thick alternating regularly with less dense interbands. Such an organization has not yet been observed in any other type of nucleus. These filamentous structures have been interpreted as highly despiralized oligotenic chromosomes. During the final stage of macronuclear development, these structures condense into thin chromatin strands and small dense granules; the number of granules increases progressively as the chromatin strands disappear. These small granules very likely fuse amongst themselves to form the chromatin granules of the vegetative macronucleus. No evidence has yet been found for a fragmentation of chromatin in this ciliate, but this problem needs further study. The old macronucleus maintains a normal ultrastructure until a late stage of development of the macronuclear anlage, becoming pycnotic only towards the very end of the latter process.     

LYSOSOME FUNCTION IN THE REGULATION OF THE SECRETORY PROCESS IN CELLS OF THE ANTERIOR PITUITARY GLAND

The nature and content of lytic bodies and the localization of acid phosphatase (AcPase) activity were investigated in mammotrophic hormone-producing cells (MT) from rat anterior pituitary glands. MT were examined from lactating rats in which secretion of MTH¹ was high and from postlactating rats in which MTH secretion was suppressed by removing the suckling young. MT from lactating animals contained abundant stacks of rough-surfaced ER, a large Golgi complex with many forming secretory granules, and a few lytic bodies, primarily multivesicular bodies and dense bodies. MT from postlactating animals, sacrificed at selected intervals up to 96 hr after separation from their suckling young, showed (a) progressive involution of the protein synthetic apparatus with sequestration of ER and ribosomes in autophagic vacuoles, and (b) incorporation of secretory granules into multivesicular and dense bodies. The content of mature granules typically was incorporated into dense bodies whereas that of immature granules found its way preferentially into multivesicular bodies. The secretory granules and cytoplasmic constituents segregated within lytic bodies were progressively degraded over a period of 24 to 72 hr to yield a common residual body, the vacuolated dense body. In MT from lactating animals, AcPase reaction product was found in lytic bodies, and in several other sites not usually considered to be lysosomal in nature, i.e., inner Golgi cisterna and associated vesicles, and around most of the immature, and some of the mature secretory granules. In MT from postlactating animals, AcPase was concentrated in lytic bodies; reaction product and incorporated secretory granules were frequently recognizable within the same multivesicular or dense body which could therefore be identified as "autolysosomes" connected with the digestion of endogenous materials. Several possible explanations for the occurrence of AcPase in nonlysosomal sites are discussed. From the findings it is concluded that, in secretory cells, lysosomes function in the regulation of the secretory process by providing a mechanism which takes care of overproduction of secretory products.     

Organization, Structure, and Assembly of α-Carboxysomes Determined by Electron Cryotomography of Intact Cells

Carboxysomes are polyhedral inclusion bodies that play a key role in autotrophic metabolism in many bacteria. Using electron cryotomography, we examined carboxysomes in their native states within intact cells of three chemolithoautotrophic bacteria. We found that carboxysomes generally cluster into distinct groups within the cytoplasm, often in the immediate vicinity of polyphosphate granules, and a regular lattice of density frequently connects granules to nearby carboxysomes. Small granular bodies were also seen within carboxysomes. These observations suggest a functional relationship between carboxysomes and polyphosphate granules. Carboxysomes exhibited greater size, shape, and compositional variability in cells than in purified preparations. Finally, we observed carboxysomes in various stages of assembly, as well as filamentous structures that we attribute to misassembled shell protein. Surprisingly, no more than one partial carboxysome was ever observed per cell. Based on these observations, we propose a model for carboxysome assembly in which the shell and the internal RuBisCO (ribulose-1,5-bisphosphate carboxylase/oxygenase) lattice form simultaneously, likely guided by specific interactions between shell proteins and RuBisCOs.     

Fine structure and immunocytochemistry of cells within the endocrine pancreas of larval and adult sea lampreys, Petromyzon marinus L

Immunocytochemistry with protein A-gold and routine electron microscopy were used to identify cell types within the endocrine pancreas of larvae, juvenile adults, and upstream-migrant adults of the sea lamprey, Petromyzon marinus. The larval pancreatic islets are composed only of insulin-immunoreactive B-cells, which are uniform in their fine structure. The cranial and caudal pancreatic tissue in both adult periods contains three cell types: B-cells, somatostatin-immunoreactive D-cells, and a third cell type of unknown content. No glucagon-immunoreactive cells are present in lampreys, but B- and D-cells exist in equal numbers in the pancreatic tissue of adults. The B-cells of adults have a fine structure similar to those in larvae. D-cells have secretory granules that are distinctly different from those both in B-cells and in the third cell type. Although B- and D-cells in lamprey pancreatic tissues have a basic morphological similarity to these cells in other vertebrates, their granules are generally of smaller dimensions. The inclusion of granules within large pleomorphic bodies in many D-cells indicates that granule turnover is common. Immunocytochemistry will be a useful tool for showing the relationship between the cells in the degenerating bile ducts and those of the developing adult pancreas.     

The cytomorphology of goblet cells of the fetal intestine. Studies of the large intestine of cattle (Bos primigenius taurus)

In the region of the base of the intestinal crypts undifferentiated goblet cells display a configuration and constellation of organelles and membrane structures that are indicative of their importance for function. These images at this stage of development deliver a scenario of the mechanism of secretory granule production: aggregates of protein vesicles from the "transitional elements" (PALADE) of the granular endoplasmic reticulum are, so to speak, rolled up on the trans side of the Golgi apparatus by inversion of peripheral membrane segments of the innermost Golgi lamellae, thereby forming corpuscles. The origin of the capsulated vacuoles, which contain vesicles as single elements or as conglomerates, is well established. Their capsule consists of a trilaminar external and external and internal membrane; between them lies condensed material of the Golgi apparatus. In the opinion of the present author, the development of the ensheathed vacuoles represents a basic, more general mechanism. In contrast, the further steps of synthesis, for the formation of secretory granules, are more heterogeneous. Condensation of the vesicles and the inner capsular membrane results in the formation of a prosecretory granule, which in the basic element in the process of secretory granule production. The prosecretory granules develop singly or by fusion with other granules to give primary secretory granules. The complexity of this mechanism of secretory granule formation, however, becomes evident when considering the apposition of capsulated vacuoles and prosecretory--primary--secondary secretory granules, of prosecretory and primary secretory granules as well as prosecretory granules and secondary secretory granules. Generally, primary granules show a tendency to become secondary secretory granules or to fuse with them. During maturation of the goblet cells the secretory granules fuse to form larger mucous bodies in the theca by fusion of the laminae of the membranes; a final product, there is a homogeneous mucous mass devoid of membranes.     

Fine Structure of the Macronuclear Anlage of the Hypotrichous Ciliate Keronopsis rubra

In exconjugants of the hypotrich Keronopsis a large, highly polyploid macronuclear anlage is formed from which condensed chromatin bodies are passed into the cytoplasm where they are thought to give rise to the numerous small macronuclei of the vegetative cell. Electron microscopy shows that the chromatin bodies within the macronuclear anlage are separated from each other by sheets of low contrast lamellar material. The anlage appears therefore as a composite nucleus containing prepacked units which are extruded into the cytoplasm following condensation.     

Histochemistry and electron microscopy of follicle lining reticular cells in the rat spleen

Summary In the rat spleen cells are found staining with aldehyde fuchsin (AF-cells). Most of these cells are localized at the periphery of the follicles, at the inner border of the marginal sinus. They probably develop in situ. Comparable cells occur in other lymphoid organs. They are able to phagocytize, and resemble also histochemically red pulp macrophages. The aldehydefuchsinophilic granules do not stain for mucopolysaccharides. On the ultrastructural level the aldehydefuchsinophilic granules are represented by cytoplasmic bodies with a faintly granulated matrix. Because of their single membrane and the varying positive reaction on acid phosphatase these bodies are considered to be secondary lysosomes or residual bodies. They contain different materials of unknown endogenous origin. In non-immunized animals the AF-cells fail to show the characteristic dendritic protrusions and infoldings of antigen trapping cells.The cells possess some characteristics of reticular cells e.g. association with reticulin, and electron dense patches on the innerside of the cell membrane at the contact areas. They can be classified among the phagocytic reticular cells forming part of the metalophilic cells in the spleen.     

ULTRASTRUCTURE OF CARPOSPOROGENESIS IN THE PARASITIC RED ALGA FAUCHEOCOLAX ATTENUATA SETCH. (RHODYMENIALES,RHODYMENIACEAE)

Carpospore differentiation in Faucheocolax attenuata Setch. can be separated into three developmental stages. Immediately after cleaving from the multinucleate gonimoblast cell, young carpospores are embedded within confluent mucilage produced by gonimoblast cells. These carpospores contain a large nucleus, few starch grains, concentric lamellae, as well as proplastids with a peripheral thylakoid and occasionally some internal (photosynthetic) thylakoids. Proplastids also contain concentric lamellar bodies. Mucilage with a reticulate fibrous substructure is formed within cytoplasmic concentric membranes, thus giving rise to mucilage sacs. Subsequently, these mucilage sacs release their contents, forming an initial reticulate deposition of carpospore wall material. Dictyosome vesicles with large, single dark-staining granules also contribute to wall formation and may create a separating layer between the mucilage and carpospore wall. During the latter stages of young carpospores, starch is polymerized in the perinuclear cytoplasmic area and is in close contact with endoplasmic reticulum. Intermediate-aged carpospores continue their starch polymerization. Dictyosomes deposit more wall material, in addition to forming fibrous vacuoles. Proplastids form thylakoids from concentric lamellar bodies. Mature carpospores are surrounded by a two-layered carpospore wall. Cytoplasmic constituents include large floridean starch granules, peripheral fibrous vacuoles, mature chloroplasts and curved dictyosomes that produce cored vesicles which in turn are transformed into adhesive vesicles. Pit connections remain intact between carpospores but begin to degenerate. This degeneration appears to be mediated by microtubules.     

Fine structure of the macronucleus during the cell division cycle of Euplotes eurystomus,a Ciliate Protozoon

This paper reports new observations obtained from a study of macronuclear fine structure throughout various stages of the cell division cycle of Euplotes. Study of the ultrastructural organization of the macronuclear chromatin indicates that much of the chromatin is organized into continuous masses, portions of which appear to be attached to the nuclear envelope. The macronuclear envelope appears unchanged in the region of a replication band, and apparent attachments of the chromatin to the inner membrane of the nuclear envelope are maintained in the reticular and diffuse zones. Intranuclear helices were never observed in the diffuse zone. During macronuclear division, linear elements (fibrils or microtubules) were observed in close association with both chromatin bodies and nucleoli. The ultrastructural data suggest that the intranuclear linear fibrils have two functions: elongation of the dividing nucleus, and attachment of chromatin bodies and nucleoli to the envelope. The significance of these observations for macronuclear division and chromatin segregation is considered.     

Fine structural localization of alkaline phosphatase in the granular pneumonocytes of hamster lung.

The fine structural localization of nonspecific alkaline phosphatase was studied in the granular pneumonocytes (type II alveolar epithelial cells) of hamster lung by incubating sections of glutaraldehyde-fixed tissues in a medium containing lead ions and sodium beta-glycerophosphate or alpha-naphthyl acid phosphate. The specificity of the reaction was tested by exposing the sections to inhibitors of alkaline phosphatase. The results showed that alkaline phosphatase activity was present in the inclusion bodies of granular pneumonocytes. The enzyme reaction was strong in the membrane lining the inclusion bodies and a weaker reaction was generally detectable in the inclusion contents. Although only a proportion of the inclusion bodies showed enzyme activity, there was no obvious correlation between the reactivity of the inclusions and their intracellular position or size. The other organelles were unreactive. The finding of alkaline phosphatase activity within the inclusion bodies of granular pneumonocytes is an enigma as these organelles are generally considered to be lyosomes.     

The ultrastructure of megathrombocytes in May-Hegglin's anomaly

A clinical and extensive electron microscopic study was made of the circulating granulocytes and thrombocytes from three female patients of a family with May-Hegglin anomaly. There have been observed inclusion bodies (D?hle-bodies) in a high proportion of polymorphonuclear leukocytes as well as a thrombocytopenia and giant platelets (so-called megathrombocytes). Other family members did not show hematologic abnormalities. The investigated giant platelets show ultrastructurally a different electron density of the alpha-granules, however, these structures present no typical formation of "bull's eye granules" which has been observed in other cases of May-Hegglin anomaly. Peripheral or central situated net-like structures of the endoplasmic reticulum have been found frequently. There were seen no microtubuli whereas glycogen particles were scattered within the peripheral cytoplasm.     

Morphology,ultrastructure, and development of the parasitic larva and its surrounding trophamnion of Polypodium hydriforme Ussov (Coelenterata)

Summary The larval stage of Polypodium hydriforme is planuliform and parasitic inside the growing oocytes of acipenserid fishes. The larva has inverted germ layers and a special envelope, the trophamnion, surrounding it within the host oocyte. The trophamnion is a giant unicellular provisory structure derived from the second polar body and performing both protective and digestive functions, clearly a result of adaptation to parasitism. The trophamnion displays microvilli on its inner surface, and irregular protrusions anchoring it to the yolk on its outer surface. Its cytoplasm contains long nuclear fragments, ribosomes, mitochondria, microtubules, microfilaments, prominent Golgi bodies, primary lysosomes, and secondary lysosomes with partially digested inclusions.The cells of the larva proper are poorly differentiated. No muscular, glandular, neural, interstitial, or nematocyst-forming cells have been found. The entodermal (outer layer) cells bear flagella and contain rough endoplasmic reticulum; the ectodermal (inner layer) cells lack cilia and contain an apical layer of acid mucopolysaccharid granules. The cells of both layers contain mitochondria, microtubules, and Golgi bodies; their nuclei display large nucleoli with nucleolonema-like structure, decondensed chromatin, and some perichromatin granules. At their apical rims, the ectodermal cells form septate junctions; laterally, the cells of both layers form simple contacts and occasional interdigitations. The lateral surfaces of entodermal cells are strengthened by microtubules.     

CYTOLOGY OF BLUE-GREEN ALGAE. I. THE CELLS OF SYMPLOCA MUSCORUM

Pankratz , H. S., and C. C. Bowen . (Iowa State U., Ames.) Cytology of blue-green algae. I. The cells of Symploca muscorum . Amer. Jour. Bot. 50(4): 387–399. Illus. 1963.—The cellular morphology of Symploca muscorum is described, based upon electron micrographs utilizing improved techniques of specimen preparation. Except for a limiting plasma membrane, ribosomes, and Feulgen-positive chromatin, the cells have little resemblance to those of higher organisms. The longitudinal components of the cellular envelope consist of a 200–300 mμ fibrous sheath and a complex inner investment about 35 mμ thick which includes at least 3 distinctly layered wall elements in addition to the typical 7-mμ unit membrane forming the plasma membrane. A row of very small elongate “pores” pierce the inner investment on each side of, and immediately adjacent to, the junction of the longitudinal walls and the crosswalls. Crosswalls vary in thickness from 3 to 20 mμ, depending upon their age, and arise as elaborations of the inner layers of the longitudinal inner investment. The photosynthetic lamellar component of the cytoplasm consists of flattened sacs formed from unit membranes. The lamellae are concentrated in the peripheral region of the cell and usually are parallel to the longitudinal wall. These often extend from one crosswall to the next but, except for a few cases, are not continuous with the plasma membrane at either end. The Feulgen-positive nucleoplasm appears as an anastomosing system of lightstaining regions containing fibrils 2–5 mμ in diameter. The morphology and interrelationship of a number of other cellular elements are described: (1) structured granules range up to 0.5μ in diameter and occur near crosswalls; (2) polyhedral bodies, 0.2–0.5μ in diameter, are closely associated with the nucleoplasm; (3) “cylindrical bodies” characteristically consist of 2 concentric cylinders, are about 13 mμ in diameter and up to lμ in length; (4) “α granules” are spherical or somewhat elongate elements about 30 mμ in diameter and characteristically associated with the photosynthetic lamellae and structured granules; (5) “β granules” are spherical, highly osmiophilic granules which range from 30 to 90 mμ in diameter; (6) ribosomes, 10–15 mμ, in diameter, are most numerous near the nucleoplasm; (7) plasmodesms penetrate the crosswalls between adjacent cells. The cells of this organism can best be described as being in a “steady state” of division, and there is no evidence of any kind of organized distribution of the nucleoplasm to daughter cells during the constant progress of cytokinesis.     

THE STRUCTURE AND FORMATION OF PROTEIN GRANULES IN THE FAT BODY OF AN INSECT

In the larva of the butterfly Calpodes ethlius, the fat body begins to store protein in the form of granules at about 30 to 35 hours before pupation, at a time when the endocuticle is being resorbed. At least two sorts of granule can be distinguished. The first granules to arise are those within vesicles of the Golgi complex. These may increase in size by incorporating material from microvesicles at their surface and by coalescence with one another. Later, at about 10 hours before pupation, another sort of granule arises by the isolation of regions of the endoplasmic reticulum (ER) within paired membranes derived from Golgi vesicles. Several of these ER isolation bodies coalesce, with fusion of their outer isolating membranes. The ribosomes and membranes may then disappear and the granules become indistinguishable from the protein granules formed from Golgi vesicles, or the ribosomes may remain and be embedded in dense crystalline protein, forming a storage body for both protein and RNA. Mitochondria are isolated within paired membranes in the same way as regions of the ER. The isolated mitochondria also coalesce in a similar manner. When the inner membranes are lost, the structure of a group of isolation bodies is indistinguishable from that of a cytolysome. Isolation within paired membranes, as described here, may be of general importance in segregating regions of massive lysis or massive sequestration.     

Distribution and ultrastructure of neurosecretory cells in the cerebral ganglion of the earthworm

Neurosecretory (Nsy) cells within the cerebral ganglion of Lumbricus terrestris were classified ultrastructurally. The Nsy cells within the subesophageal ganglion, nerve cord ganglion, and the peripheral nervous system were also examined. A comparative survey of Nsy cells of four other species of oligochaetes, Eisenia feotida, octolasion cyaneum, Dendrobeona subrubicunda, and Allolophora longa, was also carried out. Seven cell types (A1, A2, A3, A4, A5, C, and SEF), distinguished by special cytological and ultrastructural features, were found within the cerebral ganglion. Distribution of these cells inside and outside the cerebral ganglion was studied in detail by light and electron microscopy. The nerve terminals of each cell type were followed into the neuropile region. Exocytosis from cell bodies appears to be the main release mechanism for the Nsy granules, whereas small Nsy vesicles are released through synapses in the neuropile. Peripheral fibers of some cell types (A1, A2, and A3) extend through the capsule to the pericapsular epithelium. It is possible that Nsy cells secrete hormones from their cell bodies and peripheral processes and that their centrally directed axons release modulators/transmitters within the neuropile.     

Specialized formations of endoplasmic reticulum in parenchyma cells ofMimosa pudica L.

Summary Parenchyma cells ofMimosa pudica display close associations between two or more cisternae of the endoplasmic reticulum. These associations form simplified types of lamellar bodies in which inner paired lamellae have lost their ribonucleoprotein granules and are separated by a dense layer.     

AN ELECTRON MICROSCOPE STUDY OF THE CYTOLOGY OF THE PROTOZOAN EUPLOTES PATELLA

1. Structurally the "sensory bristles" in Euplotes patella are typical cilia, but no ciliary rootlets connect their bases. 2. The "neuromotor fibrils" are composed of filaments 21 mµ in diameter. At the point of junction of the filaments with the peripheral ciliary fibrils a granular structure 65 to 90 mµ in diameter is seen which has dense central and peripheral zones separated by a less dense layer. Information on the interconnection of organelles is expanded. 3. A system of subpellicular fibrils is described. The external fibrillar system described by others could not be found. 4. The motorium is shown to be a mass of intertwining rootlet filaments. 5. The micronucleus is shown to have a spongy, dense material in a less dense material, all of which is surrounded by a double-layered membrane. 6. The double-layered macronuclear membrane contains annuli whose outside diameter is 70 mµ; the macronuclear bodies are sometimes closely applied to the membrane. In the macronuclear reorganization bands, the solution plane is a fine network, while the reconstruction plane is devoid of structure at the level of resolution observed. 7. The mitochondria are composed of tubules, only occasionally oriented, usually embedded in a surrounding material of lower density. 8. Microbodies whose diameters are 250 to 350 mµ are frequently observed in close association with mitochondrial surfaces. 9. The food vacuoles, contractile vacuoles, and ciliary vacuoles are bounded by single-layered membranes. In the food vacuoles, the bacteria are surrounded by membranes individually or in small groups. 10. Cytoplasmic rods localized in the oral region, and cytoplasmic granules dispersed at random, are described. No typical ergastoplasm, endoplasmic reticulum, or Golgi material was observed.     

Shell formation and calcium transport in the barnacle Chthamalus fragilis

The mantle epithelium of the barnacle Chthamalus fragilis (Darwin) exhibits several ultrastructural features which may serve to regulate the calcification process. At the basis-mural plate and intermural plate junctions where rapid shell growth occurs, cells are characterized by long apical cytoplasmic projections and large intercellular spaces. These features may increase the functional surface area of the epithelium and enable more rapid deposition of calcium. The cells underlying the general shell surfaces contain numerous electron-dense inclusion bodies and show frequent cellular disintegration near the growing shell interface. Release of the granular contents of these inclusion bodies has been observed in both disintegrating and non-disintegrating cells. X-ray microanalysis revealed significantly higher calcium levels in the inclusion bodies than in the surrounding cytoplasm. This suggests a calcium transport role for these inclusion bodies. Cellular debris produced as a result of the disintegration of the mantle cells near the shell may play some role in the formation of the organic matrix of the shell. The presence of large numbers of mitochondria and well-developed apical microvilli in the cells of the inner mantle epithelium suggest that these cells serve to transport calcium into the mantle from the ambient sea water.     

Localization of acid phosphatase activity in collagen-secreting and collagen-resorbing fibroblasts

The ultrastructural localization of acid phosphatase (ACPase) activity was examined in cultured human gingival fibroblasts in the formative and resorptive phases. In the collagen-secreting fibroblasts, weak ACPase activity was demonstrated in the lysosomes, inner Golgi cisternae, and condensing vacuoles, and none was found in the Golgi-associated endoplasmic reticulum-lysosome system (GERL), presecretory granules, or secretory granules. On the contrary, collagen phagocytosis induced strong ACPase activity in the GERL, which was in addition to the weaker activity found in the same sites as those in the collagen-secreting cells. At the same time, collagen secretion was suppressed, and dense elongated secretory bodies associated with ACPase activity accumulated within the cells. When collagen fibrils had been interiorized in whole or in part within the phagosomes, primary lysosomes derived from the Golgi-GERL complex then fused with them to form phagolysosomes. Collagen degradation occurred within these bodies. The observations indicate significant differences in ACPase activity used as a marker for lysosomal enzyme activities in the different functional phases of fibroblasts. These results suggest that fibroblasts work only one way at a given time, viz., collagen synthesis or collagen degradation.     

Studies on secretory activity in the pars intermedia of Xenopus laevis 1: Fine structural changes related to the onset of secretory activity in vivo

Changes in the fine structural organization of the pars intermedia related to the onset of secretory activity within the gland have been studied. It is shown that during the first seven days, following the onset of secretory activity, there is an extensive membraneogenesis within the cytoplasm of the parenchymatous cells of the pars intermedia which results in the formation of a well-organized array of endoplasmic reticulum and an increased development of the Golgi complex. Simultaneously the large population of secretory granules present in the cells in the inactive condition is reduced, the granules fusing with the plasma membrane and releasing their contents into the extracellular space. During the process of intracellular reorganization, in addition to the elaboration of those components of the Golgi complex which are believed to be concerned with the formation of the secretory granules, a second distinctive cisternal element develops within the Golgi area. This component which remains confined to the Golgi area for only a short time (days 2-4) appears to be responsible for the production of membrane-bound dense bodies with a finely granular content. The dense bodies, in turn, become transformed into the larger heterogeneous structures which are a prominent feature of actively secreting pars intermedia cells.