The Fine Structure of the Epithelial Cells of the Mouse Prostate : I. Coagulating Gland Epithelium

The fine structure of the epithelial cells of the anterior lobe, or coagulating gland, of the mouse prostate has been investigated by electron microscopy. This organ is composed of small tubules, lined by tall, simple cuboidal epithelium surrounded by connective tissue and smooth muscle. The epithelial cells are limited by a distinct plasma membrane, which covers minute projections of the cytoplasm into the lumen. The cell membranes of adjacent cells are separated by a narrow layer of structureless material of low density. The cavities of the endoplasmic reticulum are greatly dilated, and the cytoplasmic matrix is reduced to narrow strands, in which the various organelles are visible. The content of the cavities of the endoplasmic reticulum appears as structureless material of lesser density than the cytoplasmic matrix. Material which may be interpreted as secretion products can be seen in the lumina of the tubules. The possible nature of the material inside the cisternal spaces and the secretory mechanisms in these cells is discussed.     

STUDIES WITH CYANIDIUM CALDARIUM : I. The Fine Structure and Systematic Position of the Organism

The fine structure of Cyanidium caldarium, as seen in thin sections of KMnO₄-fixed cells examined with the electron microscope, is described. This organism, whose taxonomic position among algae is undetermined, contains a single well defined chloroplast, a nucleus, and mitochondria. Studies, with the electron microscope, of Chlorella pyrenoidosa and Nostoc are also reported. Structural differences within cells of Cyanidium, chlorella, and Nostoc are discussed. It is concluded that if Nostoc can be taken as a typical Cyanophyte and Chlorella as a representative Chlorophyte and if the items of fine structure examined are diagnostic, then Cyanidium is certainly not a Cyanophyte and, while it has numerous features in common with Chlorella, is not a green alga similar to Chlorella. Comparisons are also made between Cyanidium and other algae whose fine structure has been described by others.     

STUDIES ON THE OXIDATIVE METABOLISM OF SACCHAROMYCES CEREVISIAE : I. Observations on the Fine Structure of the Yeast Cell

Vegetative cells of Saccharomyces cerevisiae were fixed with potassium permanganate followed by uranyl nitrate, embedded in methacrylate, and studied in electron micrographs of thin sections. Details of the structure of the cell wall, cytoplasmic membrane, nucleus, vacuole, and mitochondria are described. Cell membranes, about 70 to 80 A thick, have been resolved into two dense layers, 20 to 25 A thick, separated by a light layer of the same dimensions, which correspond in thickness and appearance to the components of the "unit membrane" as described by Robertson (15). The cell wall is made up of zones of different electron opacity. Underlying the cell wall is the cytoplasmic membrane, a sinuous structure with numerous invaginations. The nucleoplasm, often of uneven electron opacity, is enclosed in a pair of unit membranes in which nuclear pores are apparent. The vacuole, limited by a single unit membrane, is usually irregular in outline and contains some dense material. Rod-shaped mitochondria, 0.4 to 0.6 µ in length and 0.2 to 0.3 µ in diameter, are smaller in size, but similar in structure to some of those described in plant and animal cells. Attempts to use osmium tetroxide as fixative were unsuccessful, a result similar to that obtained by other workers. It is suggested that yeast cells are impermeable to osmium tetroxide, except when grown under specific conditions.     

CORRELATED MORPHOLOGICAL AND PHYSIOLOGICAL STUDIES ON ISOLATED SINGLE MUSCLE FIBERS : I. Fine Structure of the Crayfish Muscle Fiber

Single fibers isolated from walking leg muscles of crayfish have 8- to 10-µ sarcomeres which are divided into A, I, and Z bands. The H zone is poorly defined and no M band is distinguishable. Changes in the width of the I band, accompanied by change in the overlap between thick and thin myofilaments, occur when the length of the sarcomere is changed by stretching or by shortening the fiber. The thick myofilaments (ca. 200 A in diameter) are confined to the A band. The thin myofilaments (ca. 50 A in diameter) are difficult to resolve except in swollen fibers, when they clearly lie between the thick filaments and run to the Z disc. The sarcolemma invaginates at 50 to 200 sites in each sarcomere. The sarcolemmal invaginations (SI) form tubes about 0.2 µ in diameter which run radially into the fiber and have longitudinal side branches. Tubules about 150 A in diameter arise from the SI and from the sarcolemma. The invaginations and tubules are all derived from and are continuous with the plasma membrane, forming the transverse tubular system (TTS), which is analogous with the T system of vertebrate muscle. In the A band region each myofibril is enveloped by a fenestrated membranous covering of sarcoplasmic reticulum (SR). Sacculations of the SR extend over the A-I junctions of the myofibrils, where they make specialized contacts (diads) with the TTS. At the diads the opposing membranes of the TTS and SR are spaced 150 A apart, with a 35-A plate centrally located in the gap. It appears likely that the anion-permselective membrane of the TTS which was described previously is located at the diads, and that this property of the diadic structures therefore may function in excitation-contraction coupling.     

STUDIES ON THE ORGANIZATION OF THE BRUSH BORDER IN INTESTINAL EPITHELIAL CELLS : II. Fine Structure of Fractions of Tris-Disrupted Hamster Brush Borders

Two of the fractions obtained by density gradient centrifugation of Tris-disrupted brush borders from hamster intestinal mucosa have been identified as the microvillus cores and their surrounding membranous coats, respectively. This identification has the following morphological basis. In shadowed preparations one fraction (cores) appears as rounded, compact rods, and the other fraction (coats) appears as flattened sheets. Both rods and sheets have dimensions appropriate to the identities assigned to them. In addition, negative staining shows that the rods are composed of aligned particles of roughly 60 A, consistent with the appearance of the core in tissue section, where 60-A fibrils are characteristic. The sheets are covered by non-aligned particles of approximately the same size. Sectioned preparations show that the core fraction contains predominantly fibrous material with some membranous contamination and that the coat fraction is apparently composed exclusively of elongated sacs with a unit membrane structure. Some details of the structure of the core are evident in cases where the compact rod appears to be loosened, revealing a doubled strand. The strand is approximately 350 A wide; the compact rod is roughly twice this width. With negative staining the strand shows a dense central region. The morphological identification presented here is consistent with the distribution of enzymic activity among the density gradient fractions described in the preceding paper.     

MORPHOLOGICAL AND CHEMICAL STUDIES OF COLLAGEN FORMATION : I. The Fine Structure of Guinea Pig Granulomata

This paper describes electron microscopic studies of developing connective tissue in granulomata induced by the subcutaneous injection of carrageenin into guinea pigs. Seven days after injection the granulomata contained many fibroblasts and exhibited rapid production of collagen. The fibroblasts were characterised by an extensively developed endoplasmic reticulum and showed numbers of fine, unstriated filaments in the outer regions of the cytoplasm. The filaments, about 50 A in diameter, tended to lie parallel to and closely adjacent to the cell boundary. The cytoplasmic membrane was frequently ill defined or disrupted, particularly bordering regions in which filaments occurred. In longitudinal sections of extended cell processes, filaments were abundant and, in some instances, the cytoplasmic membrane was barely detectable. In the extracellular space striated collagen fibrils were usually accompanied by filaments, 50 to 100 A in diameter, and these often exhibited the characteristic periodicity of collagen, particularly after intense electron bombardment. Much cellular debris was present in the extracellular space. These observations have led to the suggestion that connective tissue precursors are released from fibroblasts by the disintegration or dissolution of the cytoplasmic membrane and the shedding of cytoplasmic material, as in the apocrine gland cells. In some instances this release may take the form of the elongation from the cell of extended processes; disintegration of the cytoplasmic membrane surrounding these processes then leaves the contents in the extracellular phase.     

The Fine Structure of the Epithelial Cells of the Mouse Prostate : II. Ventral Lobe Epithelium

The fine structure of the epithelial cells of one component of the prostatic complex of the mouse—the ventral lobe—has been investigated by electron microscopy. This organ is composed of small tubules, lined by tall simple cuboidal epithelium, surrounded by smooth muscle and connective tissue. Electron micrographs of the epithelial cells of the ventral lobe show these to be limited by a cell membrane, which appears as a continuous dense line. The nucleus occupies the basal portion of the cell and the nuclear envelope consists of two membranes. The cytoplasmic matrix is of moderately low density. The endoplasmic reticulum consists of elongated, circular, and oval profiles representing the cavities of this system bounded by rough surfaced membranes. The Golgi apparatus appears localized in a region between the apical border and the nucleus, and is composed of the usual elements found in secretory cells (3, 9). At the base of the cells, a basement membrane is visible in close contact with the outer aspect of the cell membrane. A space of varying width, which seems to be occupied by connective tissue, separates the epithelial cells from the surrounding smooth muscle fibers and the blood vessels. Bodies with the appearance of portions of the cytoplasm, mitochondria, or profiles of the endoplasmic reticulum can be seen in the lumina of the acini and on the bases of these pictures and others of the apical region the mechanism of secretion by these cells is discussed. The fine structural organization of these cells is compared with that of another component of the mouse prostate—the coagulating gland.     

ACTIVE TRANSPORT BY THE CECROPIA MIDGUT : II. Fine Structure of the Midgut Epithelium

A morphological basis for transcellular potassium transport in the midgut of the mature fifth instar larvae of Hyalophora cecropia has been established through studies with the light and electron microscopes. The single-layered epithelium consists of two distinct cell types, the columnar cell and the goblet cell. No regenerative cells are present. Both columnar and goblet cells rest on a well developed basement lamina. The basal portion of the columnar cell is incompletely divided into compartments by deep infoldings of the plasma membrane, whereas the apical end consists of numerous cytoplasmic projections, each of which is covered with a fine fuzzy or filamentous material. The cytoplasm of this cell contains large amounts of rough endoplasmic reticulum, microtubules, and mitochondria. In the basal region of the cell the mitochondria are oriented parallel to the long axes of the folded plasma-lemma, but in the intermediate and apical portions they are randomly scattered within the cytoplasmic matrix. Compared to the columnar cell, the goblet cell has relatively little endoplasmic reticulum. On the other hand, the plications of the plasma membrane of the goblet cell greatly exceed those of the columnar cell. One can distinguish at least four characteristic types of folding: (a) basal podocytelike extensions, (b) lateral evaginations, (c) apical microvilli, and (d) specialized cytoplasmic projections which line the goblet chamber. Apically, the projections are large and branch to form villus-like units, whereas in the major portion of the cavity each projection appears to contain an elongate mitochondrion. Junctional complexes of similar kind and position appear between neighboring columnar cells and between adjacent columnar and goblet cells as follows: a zonula adherens is found near the luminal surface and is followed by one or more zonulae occludentes. The morphological data obtained in this study and the physiological information on ion transport through the midgut epithelium have encouraged us to suggest that the goblet cell may be the principal unit of active potassium transport from the hemolymph to the lumen of the midgut. We have postulated that ion accumulation by mitochondria in close association with plicated plasma membranes may play a role in the active movement of potassium across the midgut.     

STUDIES ON THE CORNEA : I. The Fine Structure of the Rabbit Cornea and the Uptake and Transport of Colloidal Particles by the Cornea in Vivo

Physiological studies have demonstrated that ions, as well as large molecules such as hemoglobin or fluorescein, can diffuse across and within the cornea. Most of the substrates for corneal metabolism are obtained from aqueous humor filling the anterior chamber. In order to receive its nutrients and in order to maintain its normal conditions of hydration, the avascular cornea must transport relatively large amounts of solute and solvent across the cellular layers which cover this structure. It has been suggested in the past that there may be a morphological basis for the transport of large amounts of solvents and solutes by cells by the mechanism of pinocytosis. The use of electron-opaque markers to study fluid movements at the electron microscope magnification level was described by Wissig (29). The present study describes the fine structure of the normal rabbit cornea and the pathways of transport of colloidal particles by the cornea in vivo. Rabbit corneas were exposed in vivo to suspensions of saccharated iron oxide, thorium dioxide, or ferritin by injection of the material into the anterior chamber. In other experiments thorium dioxide or saccharated iron oxide was injected into the corneal stroma, producing a small bleb. Particles presented at the aqueous humor surface of the rabbit corneal endothelium are first attached to the cell surface and then pinocytosed. It appears that the particles are carried around the terminal bar by an intracellular pathway involving the pinocytosis of the particles and their subsequent transport in vesicles to the lateral cell margin basal to the terminal bar. Particles introduced at the basal surface of the endothelium (via blebs in the corneal stroma) are apparently carried through the endothelial cells in membrane-bounded vesicles without appearing in the intercellular space. There appears to be free diffusion of these particles through Descemet's membrane and the corneal stroma. The stromal cells take up large quantities of the particles when blebs are injected into the stroma.     

Fine Structure of Bacillus subtilis : I. Fixation

The fine structure of Bacillus subtilis has been studied by observing sections fixed in KMnO₄, OsO₄, or a combination of both. The majority of examinations were made in samples fixed in 2.0 per cent KMnO₄ in tap water. Samples were embedded in butyl methacrylate for sectioning. In general, KMnO₄ fixation appeared to provide much better definition of the boundaries of various structures than did OsO₄. With either type of fixation, however, the surface structure of the cell appeared to consist of two components: cell wall and cytoplasmic membrane. Each of these, in turn, was observed to have a double aspect. The cell wall appeared to be composed of an outer part, broad and light, and an inner part, thin and dense. The cytoplasmic membrane appeared (at times, under KMnO₄ fixation) as two thin lines. In cells fixed first with OsO₄ solution, and then refixed with a mixture of KMnO₄ and OsO₄ solutions, the features revealed were more or less a mixture of those revealed by each fixation alone. A homogeneous, smooth structure, lacking a vacuole-like space, was identified as the nuclear structure in a form relatively free of artifacts. Two unidentified structures were observed in the cytoplasm when B. subtilis was fixed with KMnO₄. One a tortuous, fine filamentous element associated with a narrow light space, was often found near the ends of cells, or attached to one end of the pre-spore. The other showed a special inner structure somewhat similar to cristae mitochondriales.     

The Fine Structure of Streptomyces coelicolor : I. The Cytoplasmic Membrane System

Colonies and spore suspensions of Streptomyces coelicolor were fixed by the method of Kellenberger, Ryter, and Séchaud (1958) and embedded in methacrylate or araldite. Thin sections were cut with an A. F. Huxley microtome and examined in a Siemens' Elmiskop I. At all stages of development the hyphae of Streptomyces coelicolor have an extensive membranous component in the cytoplasm. The membranes are continuous with the plasma membrane and have a variety of configurations at different places in the hyphae. Tubular structures, vesicles, and parallel stacks of membranes are seen. In some areas concentric layers of membranes form whorled structures which are particularly frequent in the region of developing cross-walls and within maturing spores. In the spores membranous structures often lie embedded in the nuclear material. In disintegrating hyphae the intracytoplasmic membranes round off into small vesicles and remain when the rest of the cytoplasmic structure has gone. In the absence of typical mitochondria and other cytoplasmic membranous structures it is possible that the membranous component of the cytoplasm of Streptomyces coelicolor may perform the functions of the endoplasmic reticulum and/or the mitochondria of higher cells.     

STUDIES ON SEEDS : I. Fixation of Seeds

Several fixation procedures were studied to determine those most suitable for preservation of seeds during late stages of development and early stages of germination. These are the periods when the tissues are partially dehydrated and are most difficult to fix for electron microscopy. It was found that a prefixation with a mixture of glutaraldehyde, reconstituted formaldehyde (i.e. paraformaldehyde), and acrolein, followed by a postfixation in OsO₄ or KMnO₄, gives very acceptable images. The results also indicate that glutaraldehyde is necessary for preservation of cell shape, paraformaldehyde for stabilization of reserve proteins, and acrolein for rapid penetration of tissues. Phosphate, cacodylate, and collidine are all acceptable buffers, although collidine gives the most consistent results.     

The Fine Structure of Bamboo Fibres: I. OPTICAL PROPERTIES AND X-RAY DATA

Following the recent work on wood tracheides and sisal fibres,a detailed investigation has been made of the fine structureof a wide variety of bamboo fibres. A combination of X-ray analysis,measurement of refractive indices in longitudinal view and ofphase differences in transverse section, has presented a completepicture of cellulose chain orientation. The wall of bamboo fibresis many layered. An outermost, thin layer is composed of cellulosechains making an angle of 35° to cell length and this isfollowed by other, inner layers where the angle steadily decreasesfrom outer to inner layers, first to about 20° and thento about 10°. These layers are separated by thicker layers,dark in transverse section between crossed nicols, in whichthe angle is seldom more than 5–6°. These are averagefigures. The results show most clearly that each angle, , varieswith the fibre length, L, in such a way that the longer cellshave steeper spirals in harmony with a relation of the typeL=A+Bcot already proposed for wood tracheides.     

ELECTRON MICROSCOPIC STUDIES ON THE INDIRECT FLIGHT MUSCLES OF DROSOPHILA MELANOGASTER : I. Structure of the Myofibrils

The myofibrils in Drosophila have thick and thin types of myofilaments arranged in the hexagonal pattern described for Calliphora by Huxley and Hanson (15). The thick filaments, along most of their length in the A band, seem to be binary in structure, consisting of a dense cortex and a lighter medulla. In the H zone, however, they show more uniform density; lateral projections (bridges) also appear to be absent in this region. The M band has a varying number of granules (probably of glycogen) distributed between the myofilaments. The myofilaments on reaching the Z region appear to change their hexagonal arrangement and become connected to one another by Z filaments. The regular arrangement of the filaments found in most regions of the fibrils is not seen in the terminal sarcomeres of some flight muscles; the two types of filaments appear to be intermingled in an irregular pattern in these parts of the fibrils. The attachment of myofibrils to the cuticle through the epidermal cells is described.     

STUDIES ON THE CORNEA : III. The Fine Structure of the Frog Cornea and the Uptake and Transport of Colloidal Particles by the Cornea in vivo

The fine structure of the frog cornea has been studied and compared with that of the rabbit cornea (1, 2) particularly in relation to the uptake and transport of colloidal particles. The frog corneal endothelium does not possess a terminal bar and the fluid space of the intercellular space is apparently continuous with that of the anterior chamber. Colloidal markers (ThO₂, Fe₂O₃) placed in the anterior chamber pass down the intercellular space into the cornea. Markers injected intrastromally diffuse freely in the stroma and Descemet's membrane but pass across the endothelium only via membrane-bounded vesicles. These results are compared with those of similar experiments in the rabbit and it is concluded that the primary pathway for the passage of materials into the cornea is intercellular and that the pinocytotic pathway of the rabbit corneal endothelium (Kaye and Pappas; Kaye et al.) is an adaptation to the presence of a terminal bar. The significance of the separation of inward and outward pathways in terms of corneal metabolism is considered.     

Fine Structure of the Endogenous Stages of Eimeria labbeana. I. The First Generation Merozoites

SYNOPSIS. The fine structure of the 1st generation merozoites of Eimeria labbeana from the ileal mucosa of artificially infected pigeons ( Columba livia ) was investigated and described. The 1st generation merozoites which appeared between 36-48 hr after infection averaged 4.4 × 2.1 μm in size. The 3-membraned pellicle was irregular in texture and harbored a single micropore, and many micropore-like invaginations. Closely apposed to the inner pellicular membrane were seen 22 microtubules, each 22–25 nm in diameter. An apical vesicle, 50 nm in diameter, seen at the anterior extremity, was connected with the common duct of the micronemes. The conoid consisted of 9 spiral elements, each 30 × 25 nm. The paired organelle (rhoptries) varied in length (1.4–2.2 μm), and the ductules (23 nm diameter) were composed of 2 inner tubules, each 6 nm in diameter. A unit membrane enveloped the partially alveolar and differentially osmiophilic interior of the bulbous regions of the rhoptries. The "rod-like structure"was found to be tubular and represented the common duct of the micronemes.     

STUDIES ON CELL DEFORMABILITY : I. Effect of Surface Charge

The deformability of the surface membranes of Sarcoma 37 and Ehrlich murine ascites tumor cells was assessed by the pressure required to suck a hemispherical bulge from these cells into a micropipette. It was shown that treatment with neuraminidase allowed the cells to be deformed with significantly less suction, and that enzymatic treatment also produced a significant reduction in surface charge as determined by measurement of cellular electrophoretic mobility. It is suggested that the increase in cellular deformability may be related to charge reduction, and that the charge at the cell periphery may affect not only the magnitude of the potential energy barriers hindering contact between cells, but also the ease with which cells can form low radius of curvature probes in order to help overcome these barriers.