bluuebunny/crossref_metadata_2025 huggingface dataset:
The Two-Wavelength Method of Microspectrophotometry
Authors: Mendelsohn Mortimer L.
Published: May 2004

In spite of a number of examples of the apparently successful application of the two-wavelength method of microspectrophotometry to biological materials, a demonstration of the effective transition from the theoretical to the practical aspects of the method has never been given. The following tests were carried out on model systems in order to confirm the practical validity of the method:

(1) Spherical droplets of Sudan blue or Sudan IV (varying in volume by as much as 400 times) were measured with the surrounding blank field included and were found to have amounts of chromophore which conformed to the estimated droplet volume to within 3 to 6 per cent.

(2) Repeated determinations on the same isolated nucleus gave results which did not vary in spite of wide variations in the area of the photometric field.

(3) The results of repeated determinations on the same droplet of dye were unaffected by gross changes in the focus of the objective.

The microspectrophotometer on which these measurements were made has been briefly described; it was designed specifically for the two-wavelength method. Some of the details of instrumentation have been discussed, in particular, the effects of non-uniform illumination and the contrasting demands of the two integral parts of this type of photometry. Although it has certain limitations, the two-wavelength method conforms to its theoretical promise and is a practical method of measuring light absorption in complex objects.
Metachromasy: An Experimental and Theoretical Reevaluation
Authors: Bergeron John A. , Singer Marcus
Published: May 2004

Non-chromotropic substances such as fibrin and gelatin and most tissue and cellular structures stain orthochromatically with internal dye concentrations of such metachromatic dyes as methylene blue and toluidine blue which, if in solution, would be metachromatic. Therefore, at ordinary levels of staining these substances depress the natural tendency of these dyes to change color. However, at elevated levels of dye-binding metachromasy eventually occurs. This phenomenon is explained on the basis of the distribution of dye-binding sites. In these substrates, by contrast with chromotropic substances, many binding sites are too far removed for dye interaction, consequently the interaction frequency can become high enough to produce a color change only as saturation of the available sites is approached.

It is also shown that the destruction of color is a characteristic of metachromasy and that water molecules intercalated between approximated dye ions are responsible for the loss and change of color. A concept of metachromasy is proposed in which the interaction between water molecules and suitably approximated dye ions plays an essential role.

The experimental studies are described against a background of the history and evolution of ideas on metachromasy. The literature is reviewed and reassessed particularly from the physicochemical viewpoint.
The Fine Structure of the Rod-Bipolar Cell Synapse in the Retina of the Albino Rat
Authors: Ladman Aaron J.
Published: May 2004

The fine structure of the rod-bipolar synapse is described and illustrated. Each rod spherule possesses a large, single, oval or elongate mitochondrion approximately 0.5 x 2.0 microns. Surrounding the mitochondrion are elements of agranular endoplasmic reticulum. The bipolar dendrite projects into the lower pole of the spherule and usually terminates in two lobes separated by a cleft. The plasma membranes appear dense and thicker in the region of the synapse. In the rod spherule cytoplasm, contiguous with the plasma membrane is a dense, slightly concave arciform structure, the rod arciform density, extending from the base of the bipolar bifid process through the cleft to an equivalent point on the opposite side. Also within the spherule, and external (towards the sclera) to the rod arciform density, is a parallel, dense, thin lamella, the rod synaptic lamella. This is approximately 25 mµ in thickness and 400 mµ in width at its widest extent. This halfmoon-shaped plate straddles the cleft between the two lobes of the bipolar process. The lamella appears to consist of short regular rodlets or cylinders 5 to 7 mµ in diameter, oriented with their long axes perpendicular to the plane of the lamella. Minute cytoplasmic vesicles found in the cytoplasm of both the rod spherule and the bipolar terminal are most abundant near the rod synaptic lamella.
The Histochemical Localization of Triphosphopyridine Nucleotide Diaphorase
Authors: Nachlas Marvin M. , Walker Donald G. , Seligman Arnold M.
Published: May 2004

A histochemical method is described for the localization of triphosphopyridine nucleotide diaphorase using a recently synthesized tetrazolium salt (Nitro-BT). By virtue of the favorable histochemical properties of this reagent, it has been possible to demonstrate that whereas DPN diaphorase is usually restricted to the mitochondria, the TPN diaphorase activity of corresponding cells was distributed throughout the cytoplasm in granules too fine to be considered mitochondria. Furthermore, although the diaphorase alone is responsible for the passage of electrons from TPNH to the tetrazole, it has been found that sites of activity of different TPN-linked dehydrogenases can be visualized in tissue sections, and characteristic loci for each enzyme may be observed. For example, whereas TPN diaphorase and isocitric dehydrogenase have an extensive distribution in the kidney cortex, 6-phosphogluconic dehydrogenase is limited to the cells of the macula densa.
The Spermatid Nucleus in Two Species of Grasshopper
Authors: Gall Joseph G. , Bjork Lois B.
Published: May 2004

The nuclear changes accompanying spermatid elongation have been studied in two species of grasshopper, Dissosteira carolina and Melanoplus femur-rubrum. Testes were fixed in 1 per cent buffered OsO4, imbedded in butyl methacrylate, and examined as thin sections in the electron microscope.

In both species nuclear changes during spermatid development involve (1) an early period, during which the nuclear contents are predominately fibrous; (2) a middle period, characterized by the lateral association of the nuclear fibers to form plates or lamellae which are oriented longitudinally in the major axis of the elongated nucleus; and (3) a late period, involving coalescence of the lamellae into a crystalline body which eventually becomes so dense that all resolvable detail is lost.

The fibers seen in the early spermatid nucleus are about 150 A in diameter and so are similar to fibers described from other types of nuclei. The thickness of the lamellae varies from about 150 A when first formed to 70 A during the later stages. The lack of evident chromosomal boundaries in the spermatid nucleus makes it difficult to relate either the fibers or lamellae to more familiar aspects of chromosome structure. We see no apparent reason to consider that the fiber alignment described here is related to conventional chromosome pairing.
Serial Observations on Patterns of Growth, Myelin Formation, Maintenance and Degeneration in Cultures of New-Born Rat and Kitten Cerebellum
Authors: Bornstein Murray B. , Murray Margaret R.
Published: May 2004

New-born rat and kitten cerebellum may be maintained for prolonged periods (over 5 months) in the Maximow assembly if explanted on to a coverslip previously coated with a thin gel of reconstituted rat tail collagen and fed a glucose-enriched "natural" medium.

After a 2 week period of adjustment and early outgrowth, most cultures exhibit myelin formation. Axons located within the surrounding neuroglial sheet of the explant area myelinate. The sheaths are first evident as long, unsegmented, smooth, parallel, refractile lines. Simultaneously, neuronal nuclei tend to assume central positions and powdery granules of Nissl substance and lipoid materials begin to accumulate within the cytoplasm.

During prolonged maintenance, axons may increase in width and the myelin may thicken. Some exhibit transient irregularities and swellings. Degeneration of some axons occurs manifested either by (a) progressive swellings and distortions of the myelin sheath and thinning of intervening portions of the axons which finally yield, leaving the swellings as myelin bodies, or by (b) small aneurysm-like distortions of myelin sheaths on thinning axons which become dull, irregular, and thread-like filaments beaded by the former herniations.

The observations are compared with previous studies of in vitro and in vivo myelin formation with particular reference to neuronal-neuroglial relationships.
The Fine Structure of the Interrelationship of Cells in the Human Epidermis
Authors: Obland George F.
Published: May 2004

In the present investigation an analysis has been made of the fine structure of the interrelationships of cells in human forearm epidermis by means of the electron microscope.

The "intercellular bridges," here called attachment zones, are more complex than has previously been recognized. It is shown that dense oval thickenings, called attachment plaques, appear in apposed areas of adjacent epidermal cell membranes. The tonofibrils terminate at the internal face of the attachment plaque and do not traverse the 300 A distance between apposed plaques. Seven intervening layers of unidentified substance occupy the space between attachment plaques. The attachment zones appear in all of the classical histological layers of the epidermis.

The portions of epidermal cell membrane not involved in intercellular attachments have extensive surface area resulting from plication of the membrane, and its further modification to form microvilli. The possible functional significance of these observations is discussed. Prior observations concerning the basement membrane of epidermis are confirmed.

Identification of epidermal melanocytes is achieved, the finer morphology of their dendritic processes is described, and their relationship to epidermal cells is discussed.
The Early Changes in the Axoplasm during Wallerian Degeneration
Authors: Vial Juan D.
Published: May 2004

Axoplasmic changes were studied in the saphenous nerve of the albino rat during the early stages of Wallerian degeneration. The axons were examined at 0, 24, and 48 hours after the surgical transection of the nerve. The material was fixed in 2 per cent OsO4 in phosphate buffer (pH 7.2–7.5) with sucrose (added to a final osmolar concentration of ∼0.37 M).

The earliest changes were seen in the endoplasmic reticulum which became fragmented into rows of small vesicles. Then, between 24 and 48 hours, the neurofilaments underwent complete disintegration and the axoplasm became filled with finely granular material which later formed irregular clumps surrounded by a structureless matrix, probably fluid in vivo.

The fragmentation of the neurofilaments was accompanied by pronounced swelling of the mitochondria.
Cytochemical Localisations and Ultrastructure in the Fertilized Unsegmented Egg of Paracentrotus lividus
Authors: Pasteels J. J. , Castiaux P. , Vandermeerssche G.
Published: May 2004

Fertilized, but still unsegmented, eggs of the sea urchin Paracentrotus lividus have been centrifugated at 30,000 gravity. A comparison has been made between the cytochemical reactions of the different layers (RNA, polysaccharides, acid phosphatase) and the fine structure as shown in thin sections studied with the electron microscope.
Methods and Principles of Fixation by Freeze-Substitution
Authors: Feder Ned , Sidman Richard L.
Published: May 2004

Freeze-substitution is based on rapid freezing of tissues followed by solution ("substitution") of ice at temperatures well below O°C. A 1 to 3 mm. specimen was thrown into 3:1 propane-isopentane cooled by liquid nitrogen to -175°C. (with precautions). The frozen tissue was placed in substituting fluid at -70°C. for 1 week to dissolve ice slowly without distorting tissue structure. Excess substituting agent was washed out, and the specimen was embedded, sectioned, and stained conventionally.

For best morphological and histochemical preservation, substituting fluids should in general contain both chemical fixing agent and solvent for ice, e.g., 1 per cent solutions of osmium tetroxide in acetone, mercuric chloride in ethanol, and picric acid in ethanol. Preservation of structure was poorer after substitution in solvent alone. Evidence was obtained that the chemical agent fixes tissue at low temperatures. The chemical mechanisms of fixation are probably similar to those operating at room temperature: new chemical cross-linkages, which contain the fixing agent, join tissue constituents together. This process is distinguished from denaturation by pure solvents.

Freeze-substitution has many advantages, particularly the preservation of structure to the limit of resolution with the light microscope, and the accurate localization of many soluble and labile substances.
A Cytochemical Study of the Sulfhydryl Groups of Sea Urchin Eggs during the First Cleavage
Authors: Kawamura Naoko , Dan Katsuma
Published: May 2004

In the eggs of four species of echinoderms, Mespilia globulus, Pseudocentrotus depressus, Hemicentrotus pulcherrimus and Clypeaster japonicus, changes in the distribution of protein-bound SH groups from fertilization to the 2 cell stage have been studied cytochemically by use of a mercaptide-forming azo dye.

In the eggs of these species, the color intensity in the cytoplasm increased upon fertilization. The astral centers and spindle during mitosis were stained deeply. When the aster formation was suppressed by ether, hyaline spots appeared in the egg cytoplasm instead of well formed astral centers and these spots were stained by the SH-specific dye. Upon recovery of such eggs in pure sea water, and when cleavage ensued, such spots disappeared and two new astral centers were reorganized.

The SH-protein occurring in the centrosphere is considered to be the precursor material for the asters and spindle, and this material is apparently derived from the cytoplasm.
Morphological and Chemical Studies of the Spores and Parasporal Bodies of Bacillus laterosporus
Authors: Fitz-James Philip C. , Young I. Elizabeth
Published: May 2004

Spores of Bacillus laterosporus were studied to determine the chemical and morphological nature of their basophilic canoe-shaped parasporal bodies. An unusually high phosphorus content of these spores compared to other Bacillus species appeared to be associated with the parasporal body. Preparations of these "canoes" still attached to the spore coats were indeed high in phosphorus, but also in nitrogen. They were free of lipide-soluble and nucleic acid phosphorus and stained for protein. Some 50 per cent of the total nitrogen, but only 6 to 10 per cent of the total P were liberated by extraction with alkali-thioglycollate (pH 11.5) or alkali alone (pH 12.2–12.5). Proteinaceous material was recovered from these alkaline extracts and electron microscopy indicated that there had been a marked loss of "canoe" substance. Extraction with acid, removed some 80 per cent of the phosphorus associated with the "canoes" as orthophosphate. Chromatographic analyses for amino acids indicated some 14 ninhydrin-positive spots in the canoe-coat preparations whereas the whole spores contained at least 16.
The Fine Structure of Brown Adipose Tissue in the Newborn Mouse and Rat
Authors: Napolitano Leonard , Fawcett Don
Published: May 2004

Interscapular fat from newborn rats and mice was fixed in buffered 1 per cent osmium tetroxide and thin sections of the methacrylate-embedded tissue were studied with the electron microscope. The findings have reaffirmed the epithelioid character of brown adipose tissue, and have provided additional information on the relation of its cells to each other and to the rich capillary bed. For the most part, the earlier description of the fine structure of brown adipose cells by Lever, has been confirmed, but our observations on the mitochondria and their relation to fat droplets have led us to different conclusions concerning the role of these organelles in lipogenesis. Mitochondria were often found to be very closely associated with lipide inclusions, but no actual communication between the two was observed and no evidence was found to support the hypothesis that mitochondria are transformed into lipide droplets. Large dense bodies which showed a highly ordered fine structure suggesting a crystalline protein were seen in the matrix of some mitochondria. The cytoplasm of the adipose cells contained fine granules that seemed to be of two kinds: particles of uniform size (∼150 A) and appreciable density that are believed to be ribonucleoprotein, and granules of lower density and more variable size that are tentatively interpreted as a form of glycogen. The Golgi complex of the adipose cells was small and the endoplasmic reticulum almost entirely absent. The significance of the poor development of these organelles is discussed in relation to current concepts of their function.
The Effect of HCl Hydrolysis on the Retention of Thymidine in DNA
Authors: Savage R. E. , Plaut Walter
Published: May 2004

Allium roots grown in C14-thymidine and H3-thymidine media were treated with N hydrochloric acid at 60°C. as in standard Feulgen hydrolysis. The retention of the radioactive thymidine in DNA as a function of hydrolysis time was studied autoradiographically. No significant loss of label was detected until hydrolysis was extended beyond the optimal time for Feulgen staining. The data are consistent with the assumption that there is no significant loss of DNA during normal Feulgen hydrolysis in the material used.
Adenosinetriphosphatase and 5-Nucleotidase Activities in the Plasma Membrane of Liver Cells as Revealed by Electron Microscopy
Authors: Essner Edward , Novikoff Alex B. , Masek Bertha
Published: May 2004

The sites of reaction product resulting from ATPase and 5-nucleotidase activities remaining in parenchymatous cells of osmium-fixed rat liver were studied by electron microscopy of thin sections. These indicate that both ATPase and 5-nucleotidase activities are localized in the plasma membrane where it folds to form the microvilli of the bile canaliculus, and that 5-nucleotidase activity is also present in the microvilli at the sinusoidal aspects of the cells.

It is suggested that these enzymes, particularly ATPase, may play a role in molecular transport or in some kind of membrane activity at the cell surface. Of special interest is the apparent differential localization of these enzymes at the absorptive and secretory regions of the plasma membrane of the cell. It may be of interest to study changes in these enzyme localizations in pathologic states, as a sign of changed cell function.

Some of the difficulties in the interpretation of enzyme reaction products seen in electron micrographs are discussed.
The Fine Structure of Nerve Cells and Fibers, Neuroglia, and Sheaths of the Ganglion Chain in the Cockroach (Periplaneta americana)
Authors: Hess Arthur
Published: May 2004

The abdominal nerve cord of Periplaneta americana was studied utilizing light and electron microscopes. In the nerve cells, delicate granules, similar to those probably responsible for cytoplasmic basophilia, are evenly distributed in "dark" cells and clumped in "light" cells. Neuroglial cells are stained metachromatically by cresyl violet. The neuroglial cells have many processes which ramify extensively and are enmeshed to form overlapping layers. These imbricated processes ensheath the nerve cells; the inner layer of the sheath penetrates into the neuron and is responsible for the appearance of the trophospongium of Holmgren. Nerve fibers are embedded within glial cells and surrounded by extensions of the plasma membrane similar to mesaxons. Depending on their size, two or several nerve fibers may share a single glial cell. Nerve fibers near their terminations on other nerve fibers contain particles and numerous, large mitochondria. The ganglion is ensheathed by a thick feltwork of connective tissue and perilemmal cells. The abdominal connective has a thinner connective tissue sheath which is without perilemmal cells. The nerve fibers and sheaths in the connective become thinner as they pass through ganglia.
An Autoradiographic Study of Nucleic Acid and Protein Turnover in the Mammalian Neuraxis
Authors: Koenig Harold
Published: May 2004

The turnover of nucleic acids and proteins in the central nervous system has been explored by autoradiography following the subarachnoid injection of tagged precursors. Nuclear PNA of neurons and oligodendrocytes becomes radioactive earlier than cytoplasmic PNA after injection of adenine-C14 and orotic-C14 acid. By 24 hours following injection, cytoplasmic PNA is radioactive. Radioactivity persists with little decrease for as long as 51 days after an injection of adenine-C14. The cells of the ependymal lining, choroidal plexus, leptomeninges, blood vessel walls, and Schwann cells also exhibit radioactivity in PNA as judged by the loss of radioactivity following ribonuclease digestion. From the 3rd day on, increasing numbers of the aforementioned cells, with the exception of nerve cells, exhibit ribonuclease-resistant nuclear radioactivity which is abolished by deoxyribonuclease. This radioactivity indicates labelling of nuclear DNA.

Following the intrathecal injection of methionine-S35 and glycine-2-H3, nerve cells, oligodendrocytes, cells of ependymal lining, choroidal plexus, leptomeninges, blood vessels, and Schwann cells become radioactive. Nerve cells lose most of their radioactivity within a few hours, first from the cytoplasm and later from the nucleus. Other cell types retain their radioactivity for considerable periods of time.

Although astrocytes, microglia, and satellite cells of sensory ganglia do not appear to incorporate labelled precursors into nucleic acids or proteins, reacting phagocytic microglia actively take up labelled amino acids.

These results are discussed with particular reference to PNA and protein turnover in nerve cells, oligodendrocytes, and Schwann cells. It is believed that these metabolic activities in neurons are concerned in part with the elaboration of axoplasmic proteins. The nucleoprotein metabolism of oligodendrocytes and Schwann cells may be related to myelin biosynthesis both in the immature and the mature nervous system.
LASER MICROSCOPE IRRADIATION OF PHYSARUM POLYCEPHALUM: DYNAMIC AND ULTRASTRUCTURAL EFFECTS
Authors: Griffin Joe L. , Stein Marvin N. , Stowell Robert E.
Published: May 2004

Streaming plasmodia of Physarum polycephalum were irradiated with a microscope-mounted ruby laser and the resulting changes were recorded by cinemicrography or streak photographs. Some lesions were processed for electron microscopy. By varying the incident energy, three levels of response were detected. Two transient responses, a gelation briefly blocking streams and a more severe gelation with contraction, changed movement patterns but not organelle ultrastructure. At higher energies, a permanently coagulated lesion was rapidly segregated from normal and transiently altered cytoplasm by formation of new membranes. Within the coagulum, pigment granules were destroyed, membranes were disrupted, and cytoplasm was flocculent. Nuclei and mitochondria were compact in the center and swollen in a peripheral space left by contraction of the coagulum.

These changes are probably caused by heat produced by the interaction between the laser beam and the pigment granules of the plasmodium. Many of the changes seem to be secondary responses that follow the primary capture of energy during irradiation.
CORTICAL CELL DEATH DURING LATERAL ROOT FORMATION
Authors: Bonnett Howard T.
Published: May 2004

Root segments of Convolvulus arvensis, the field bindweed, were examined with the electron microscope to make possible a description of the fine structural correlates of lateral root protrusion through cortical parenchyma. Particular attention was directed to the outermost primordium cells, derived by meristematic activity from the endodermis, and to the contiguous cortical parenchyma cells. By following the fate of the Casparian strip through numerous divisions of the endodermal cell, information has been obtained relating to the minimum contribution of the endodermis to the root primordium structure. Cortical parenchyma cells during lateral root growth are specifically degraded so that only the cell wall remains. A layer of cell wall material, representing numerous cortical parenchyma cells, accrues at the tip of the advancing root primordium. It is suggested that the intensive coated-vesicle activity along the plasmalemma of the outermost primordium cell and the appearance of the vesicle contents in the outer wall of this cell are indicative of the secretion of hydrolases which move through the wall and attack the adjacent cortical parenchyma cells.
MEASUREMENT OF RATES OF PHAGOCYTOSIS
Authors: Michell Robert H. , Pancake Samuel J. , Noseworthy John , Karnovsky Manfred L.
Published: May 2004

A method has been developed for measuring the rate of phagocytosis rather than the quantity of particles ingested per cell when the process is virtually complete. The method, which is simpler and more rapid than those described previously, utilizes cellular monolayers, radioactive particles, and short incubation times. Under the conditions described, the rate of uptake of particles by either guinea-pig peritoneal or human blood leukocytes was proportional to both cell concentration and the time of incubation, and was independent of changes in the concentration of particles during the measurement. The particles were retained by the cells for at least 90 min. The most suitable particles so far used have been 32P-labeled Salmonella typhimurium, and acetyl-14C- or methyl-14C-labeled starch particles. The oxidation of 14C-labeled glucose has been studied under the same conditions that were used for the assays of phagocytosis: the greatest increase in formation of 14CO2 from glucose-1-14C occurred a few minutes after the most rapid period of phagocytosis.
AN ULTRASTRUCTURAL AND BIOCHEMICAL STUDY OF THE EFFECTS OF THREE INHIBITORS OF CHOLESTEROL BIOSYNTHESIS UPON MURINE ADRENAL GLAND AND TESTIS
Authors: Dietert Scott E. , Scallen Terence J.
Published: May 2004

Triparanol and 20,25-diazacholesterol inhibit cholesterol biosynthesis and result in the accumulation of desmosterol. AY-9944, another inhibitor, produces an accumulation of 7-dehydrocholesterol. Adult male C3H mice receive one of these drugs intraperitoneally. Livers, adrenal glands, and testes from each drug group are excised, and portions of each are analyzed by a modified Liebermann-Burchard reaction for quantitation of sterols. Adrenals and testes are examined also by electron microscopy. Fine-structural localization of acid phosphatase has been studied in triparanol-treated adrenal glands. Biochemical analysis reveals that 14–64% of the sterols occurs as desmosterol or 7-dehydrocholesterol. Fine-structural alterations in the adrenal glands and testes from each drug group are essentially identical. The predominant cytological feature is the occurrence of increased numbers of pleomorphic, unit-membrane-limited, electron-opaque, cytoplasmic inclusions. Hence, the cellular modifications following triparanol administration are not unique, as has been suggested. They represent a generalized phenomenon, probably related to inhibition of cholesterol biosynthesis, which is an effect common to each drug. Lead phosphate reaction product (indicating acid phosphatase activity) is demonstrable within these membrane-limited cytoplasmic bodies, identifying them as morphological lysosomes. The utilization of a lysosomal mechanism in sterol-synthesizing cells, which are accumulating cholesterol intermediates, is discussed.
ESTROGEN-INDUCED CYTODIFFERENTIATION OF THE OVALBUMIN-SECRETING GLANDS OF THE CHICK OVIDUCT
Authors: Kohler Peter O. , Grimley Philip M. , O'malley Bert W.
Published: May 2004

The histological, ultrastructural, and biochemical changes occurring during hormone-induced cytodifferentiation of the ovalbumin-secreting glands in the chick oviduct have been studied. Marked perivascular edema is an initial response of the immature oviduct stroma to diethylstilbestrol administration and is accompanied by an interstitial migration of mononuclear cells. Mitotic activity in the immature mucosal epithelium increases within 24 hr, and glands begin to develop on days 2–4 as budlike invaginations into the subepithelial stroma. An immediate intracellular effect of the hormone is aggregation of previously dispersed ribosomes. Ribosomal zones in the nucleolus gain prominence, and there is a progressive development of rough endoplasmic reticulum in the epithelial cells. Extensive profiles of endoplasmic reticulum are present in the gland cells by day 6. Fine apical progranules appear in the epithelial cells on day 2, and ovalbumin can be measured immunochemically by day 3 at about the same time that new species of nuclear RNA have been identified. Ovalbumin granules form within condensing vacuoles in the Golgi zone and begin to be released into the lumina of the gland acini at about day 6 of the treatment.
CELL CYCLE EVENTS IN THE HYDROCORTISONE REGULATION OF ALKALINE PHOSPHATASE IN HELA S3 CELLS
Authors: Griffin M. J. , Ber R.
Published: May 2004

The increase in alkaline phosphatase in asynchronous cultures of HeLa S3 cells grown in medium supplemented with hydrocortisone is characterized by a lag period of 10–12 hr. Present studies utilizing synchronous cell populations indicate: (a) a minimum of 8–10 hr of incubation with hydrocortisone is necessary for maximum induction of alkaline phosphatase; (b) the increase in enzyme activity produced by hydrocortisone is initiated exclusively in the synthetic phase of the cell cycle; (c) alkaline phosphatase activity does not vary appreciably over a normal control cell cycle. Radioactive hydrocortisone is rapidly distributed into HeLa cells irrespective of their position in the cell cycle, indicating that inductive effects are not governed by selective permeability during the cell cycle. Hydrocortisone-1,2-[3H] diffuses back from the cell into the medium when the cells are incubated in fresh medium containing no hydrocortisone, and the alkaline phosphatase induction, under these conditions, is completely reversible.
AN ULTRASTRUCTURAL STUDY OF EARLY MORPHOGENETIC EVENTS DURING THE ESTABLISHMENT OF FETAL HEPATIC ERYTHROPOIESIS
Authors: Rifkind Richard A. , Chui David , Epler Hazel
Published: May 2004

Morphogenetic events are described which characterize early stages of the interaction between mesenchyme and expanding epithelial cell cords derived from the hepatic endodermal diverticulum in the C57BL/6J mouse. This interaction culminates in the differentiation of hepatic epithelial and hematopoietic tissues. No basement membrane separates the presumptive hepatic epithelial cells from the adjacent mesenchyme, while intercellular attachments, both adherent junctions and desmosomes, are established transiently between heterologous cell types across this epithelio-mesenchymal interface. Yolk sac-derived erythroblasts found in the primitive liver are distinguished morphologically from endogenous hepatic erythroid cells; they are confined to the vascular compartment and are not, apparently, precursors for hepatic erythropoiesis. The earliest recognizable endogenous hepatic hematopoietic cells appear, extravascularly, among those mesenchymal cells in intimate contact with the endodermal epithelium between the 10¼ and 10½ gestational day. Definitive erythropoiesis commences between the 10½ and 11th fetal days. The ultrastructure of these primitive hepatic erythroid cells (proerythroblasts) and their transition to more mature forms (basophilic and polychromatophilic erythroblasts) are described.
THE ELASTIC FIBER
Authors: Ross Russell , Bornstein Paul
Published: May 2004

The two morphologically different constituents of the mature elastic fiber, the central amorphous and the peripheral microfibrillar components, have been separated and partially characterized. A pure preparation of elastic fibers was obtained from fetal bovine ligamentum nuchae by extraction of the homogenized ligament with 5 M guanidine followed by digestion with collagenase. The resultant preparation consisted of elastic fibers which were morphologically identical with those seen in vivo. The microfibrillar components of these elastic fibers were removed either by proteolytic enzymes or by reduction of disulfide bonds with dithioerythritol in 5 M guanidine. The microfibrils solubilized by both methods were rich in polar, hydroxy, and sulfur-containing amino acids and contained less glycine, valine, and proline than the amorphous component of the elastic fiber. In contrast, the amino acid composition of the amorphous component was identical with that previously described for elastin. This component demonstrated selective susceptibility to elastase digestion, but was relatively resistant to the action of other proteolytic enzymes and to reduction. These observations establish that the microfibrils consist of a different connective tissue protein (or proteins) that is neither collagen nor elastin. During embryologic development the microfibrils form an aggregate structure before the amorphous component is secreted. These microfibrils may therefore play a primary role in the morphogenesis of the elastic fiber.
A DIFFUSIBLE FACTOR WHICH SUSTAINS CONTACT INHIBITION OF REPLICATION
Authors: Yeh Jen , Fisher Harold W.
Published: May 2004

Confluent 3T3 cultures make and release into the medium a diffusible factor which sustains the state of contact inhibition of replication. Evidence is given that the factor is a specific and reversible inhibitor of the RNA synthesis which precedes cellular replication.
UNUSUAL MICROTUBULAR PATTERNS AND THREE-DIMENSIONAL MOVEMENT OF MEALYBUG SPERM AND SPERM BUNDLES
Authors: Ross Jean , Robison W. Gerald
Published: May 2004

The spermatozoon of the mealybug Pseudococcus obscurus Essig is a filamentous cell (0.25 µ by 300 µ) which exhibits three-dimensional flagellations throughout most of its length. It has microtubules (200 A diameter) and a threadlike nuclear core (0.07–0.09 µ diameter) which extend almost its entire length, but apparently it has no mitochondria, centrioles, typical flagellum, or acrosome. The microtubules are arranged in two and a half concentric rings and total 56 in the most actively motile region but form two or three concentric rings with totals of 28 or 56 tubules, respectively, in less active regions. The relation of unusual microtubular patterns to the 9 + 2 complex and to flagellar motion is discussed. Mealybug spermatozoa are transmitted to the female in motile bundles which are approximately 1.3 µ by 750 µ and have four regions: (1) an anterior corkscrew region; (2) a region which contains approximately 16 spermatozoa; (3) a region of amorphous content; and (4) an endpiece. Bundle motility originates from the synchronous movements of its spermatozoa which appear to be arranged in two concentric multistranded helices. The spermatozoa provide both forward and gyratory motions of the bundle, and the corkscrew complements bundle propulsion by converting part of the rotation into forward movement.
EXTRACELLULAR MICROTUBULES
Authors: Bouck G. Benjamin
Published: May 2004

Mastigonemes (Flimmer) from the sperm of Ascophyllum and Fucus were found to consist of a tripartite structure—a ca. 2000-A tapered basal region, a closed microtubular shaft, and a group of terminal filaments. Each of these regions appears to be constructed of globular subunits with a center-to-center distance of about 45 A. The mastigoneme microtubule is of smaller diameter (170–190 A) than cytoplasmic microtubules in these or other plant cells. During the initial stages of flagellar ontogeny, structures similar to mastigonemes (presumptive mastigonemes) are found within membrane-limited sacs in the cytoplasm or within the perinuclear space. Mastigonemes at this time are generally not found on the flagellar surface. Later, when the anterior flagellum acquires mastigonemes, the presumptive mastigonemes are absent from the cytoplasm. The regularity of attachment of mastigonemes to the flagellar surface suggests that specific attachment sites are constructed on the plasma membrane during flagellar ontogeny. No evidence for penetration of the mastigoneme through the plasma membrane was obtained. The origin and structure of mastigonemes are discussed in relation to reports of the origin and structure of other microtubular systems.
PERSISTENCE OF MESSENGER RNA THROUGH MITOSIS IN HELA CELLS
Authors: Hodge L. D. , Robbins E. , Scharff M. D.
Published: May 2004

The decrease in protein synthesis which occurs in mammalian cells during cell division is associated with significant disaggregation of polyribosomes. For determining whether messenger RNA survives this disaggregation, the reformation of polyribosomes was investigated in synchronized HeLa cells as they progressed from metaphase into interphase in the presence of 2 µg/ml Actinomycin D. The persistence of messenger during cell division was evidenced by: (1) a progressive increase in the rate of protein synthesis in both treated and untreated cells for 45 min after metaphase; (2) reformation of polyribosomes, as determined by both sucrose gradients and electron microscopy, within 30 min after the addition of Actinomycin D to metaphase cells; (3) the persistence of approximately 50% of the rapidly labeled nonribosomal RNA which had associated with polyribosomes just before metaphase; (4) the resumption of synthesis, following cell division, of 6 selected peptides in Actinomycin-treated cells.
THE MORPHOGENESIS OF BASAL BODIES AND ACCESSORY STRUCTURES OF THE CORTEX OF THE CILIATED PROTOZOAN TETRAHYMENA PYRIFORMIS
Authors: Allen Richard D.
Published: May 2004

Dividing cells of Tetrahymena pyriformis were observed by transmission electron microscopy for signs of morphogenesis of cortical structures. The earliest stage of basal body development observed was of a short cylinder of nine single tubules connected by an internal cartwheel structure. This is set perpendicular to the mature basal body at its anterior proximal surface under the transverse microtubules and next to the basal microtubules. Sequential stages show that the single tubules become triplet tubules and that the "probasal bodies" then elongate and tilt toward the organism's surface while maintaining a constant distance of 75–100 mµ with the "parent." The new basal body after it is fully extended contacts the pellicle, and then assumes a parallel orientation with and moves anterior to the parent basal body. The electron-opaque core in the lumen of the basal body and accessory structures around its outer proximal surface appear after the developing basal body has elongated. These accessory structures associating with their counterparts from other basal bodies and with the longitudinal microtubules may play a role in the final positioning of basal bodies and thus in the maintenance of cortical patterns. Observations on a second sequence of basal body formation suggest that the oral anlage arises by multiple duplication of somatic basal bodies.
UPTAKE OF COLLOIDAL THORIUM DIOXIDE BY MAST CELLS
Authors: Padawer Jacques
Published: May 2004

Mast cells from the peritoneal cavity of the rat were obtained at various times following in situ injection of a colloidal thorium dioxide preparation (Thorotrast). They were prepared for electron microscopy by aldehyde fixation, osmium tetroxide postfixation, and embedding in Epon. Thorotrast was rapidly taken up by mast cells through enhanced or newly elicited surface specializations. It was confined at first to large vesicles which moved to the Golgi area. Subsequently, in a matter of a few hours only, it became associated with progressively more mature granules, including "fully" mature ones. In addition to demonstrating a further phagocytic or pinocytotic activity of mast cells, the findings suggest that mast cell granules share a common membranous investment, and that substances from the tissue environment may theoretically percolate over and interact with the granules. Mast cell function could thus be served primarily by absorptive rather than secretory processes.
THE REACTIVITY AND STAINING OF TISSUE PROTEINS WITH PHOSPHOTUNGSTIC ACID
Authors: Silverman Lloyd , Glick David
Published: May 2004

After aldehyde-fixation, treatment with phosphotungstic acid (PTA) in aqueous acidic medium was shown to produce an intense electron-opaque stain with minimal distortion of organelles. Mitochondrial matrix, cisternae of the endoplasmic reticulum, and the Z-band of muscle were densely stained, whereas membranes stood out in negative contrast. Staining of glycogen or lipid was not apparent. Under certain conditions the stain density reflected the concentration of protein based on the quantitative reaction of PTA with the positively charged groups, although the stoichiometry of the reaction between PTA and protein varied with the kind of protein. The staining conditions established should provide a base for the use of the method in quantitative electron microscopy, particularly on thin sections.
CORTICAL ULTRASTRUCTURE OF PARAMECIUM AURELIA
Authors: Hufnagel Linda A.
Published: May 2004

Two methods have been devised for the isolation of large quantities of purified pellicles (cortical layers) of Paramecium aurelia. Pellicles isolated by both procedures, when examined by electron microscopy, were found to contain ciliary basal bodies, two types of cortical membranes, ribbons of microtubules, kinetodesmal fibers, and elements of the infraciliary lattice system. By electron microscopy, the extent of preservation of the various cortical structures when pellicles are isolated by each method has been characterized.

Pellicles isolated in both ways have been utilized to investigate cortical morphology of Paramecium. Both phase-contrast and electron microscopic observations have been made. Many new ultrastructural features were observed and are reported herein.

An interesting result of this study is the discovery in stock CD that the structure of cortical territories (the territory is the functional unit of cortical morphogenesis and physiology) may vary within a single organism. Features which show variation include number of parasomal sacs, microtubular ribbons, and basal bodies (and therefore cilia) per territory, number of microtubules per ribbon, and length of kinetodesmal fibers. The possible significance of these variations, with respect to territory replication, is discussed.

In addition, preliminary observations on the solubility of various cortical organelles in the presence of a number of protein-denaturing agents are reported.
A COMPARATIVE STUDY OF THE ISOLATION OF THE CORTEX AND THE ROLE OF THE CALCIUM-INSOLUBLE PROTEIN IN SEVERAL SPECIES OF SEA URCHIN EGG
Authors: Kane R. E. , Stephens R. E.
Published: May 2004

A comparative study was made of the isolation of the cortex in the eggs of several sea urchin species. Since the isolation method developed by Sakai depends on the presence of magnesium in the medium, the protein composition of the cortex was investigated to determine whether the protein component of the egg described by Kane and Hersh which is gelled by divalent ions, is present in these cortices. Isolation of the cortex was found to require the same divalent ions at the same concentrations as protein gelation, and in the eggs of some species much of the gel protein of the cell was found in the isolated cortical material. In the eggs of other species a smaller fraction of this protein was found in the isolated cortex, although it was more concentrated there than in the endoplasm, and in one species this protein appeared to be uniformly distributed throughout the cell. These results indicate that this protein is localized in the cortical region of the eggs of some species of sea urchin, possibly in the cortical granules, but also point up the fact that results from one species cannot be uncritically extrapolated to others.
ISOLATION AND PROPERTIES OF SECRETORY GRANULES FROM RAT ISLETS OF LANGERHANS
Authors: Greider Marie H. , Howell S. L. , Lacy P. E.
Published: May 2004

Beta granules isolated from rat islets of Langerhans and subjected only to phosphotungstic acid had, in negatively stained images, a 50-A periodicity. This periodicity was also observed in thin-section profiles of beta granules in intact cells. In shadowed preparations, the granules were spherical in shape and had irregular edges and surface structure. The presence of such a periodicity in the beta granule indicates that its matrix may be composed of a crystalline material.
MITOSIS AND THE PROCESSES OF DIFFERENTIATION OF MYOGENIC CELLS IN VITRO
Authors: Bischoff Richard , Holtzer Howard
Published: May 2004

The relation between the mitotic cycle and myoblast fusion has been studied in chick skeletal muscle in vitro. The duration of the cell cycle phases was the same in both early and late cultures. By tracing a cohort of pulse-labeled cells, it was found that myoblast fusion does not occur in S, G2, or M. Cell surface alterations required for fusion are dependent upon the position of the cell in the division cycle. In early cultures, fusion takes place only after a minimum delay of 5 hr from the time the cell has entered G1. The mitosis preceding fusion may condition the cell for the abrupt shift in synthetic activity that occurs in the subsequent G1. In older cultures fusion of labeled cells is diminished. Two factors account for the cessation of fusion in older cultures. First, the number of myogenic stem cells declines, but these cells do not disappear as the cultures mature. Their persistence was demonstrated by labeling dividing mononucleated cells in older cultures and challenging them with nascent myotubes. Some of these labeled cells were incorporated into the forming myotubes. Second, a block to fusion develops during myotube maturation. Well developed myotubes challenged with labeled competent myogenic cells failed to incorporate the labeled nuclei.
MICROTUBULES IN THE FORMATION AND DEVELOPMENT OF THE PRIMARY MESENCHYME IN ARBACIA PUNCTULATA
Authors: Gibbins John R. , Tilney Lewis G. , Porter Keith R.
Published: May 2004

Prior to gastrulation, the microtubules in the presumptive primary mesenchyme cells appear to diverge from points (satellites) in close association with the basal body of the cilium; from here most of the microtubules extend basally down the lateral margins of the cell. As these cells begin their migration into the blastocoel, they lose their cilia and adopt a spherical form. At the center of these newly formed mesenchyme cells is a centriole on which the microtubules directly converge and from which they radiate in all directions. Later these same cells develop slender pseudopodia containing large numbers of microtubules; the pseudopodia come into contact and fuse to form a "cable" of cytoplasm. Microtubules are now distributed parallel to the long axis of the cable and parallel to the stalks which connect the cell bodies of the mesenchyme cells to the cable. Microtubules are no longer connected to the centrioles in the cell bodies. On the basis of these observations we suggest that microtubules are a morphological expression of a framework which opeartes to shape cells. Since at each stage in the developmental sequence microtubules appear to originate (or insert) on different sites in the cytoplasm, the possibility is discussed that these sites may ultimately control the distribution of the microtubules and thus the developmental sequence of form changes.