Electron microscope study on human ceruloplasmin.

Electron microscopy of human ceruloplasmin (CP) molecules revealed a few distinctive types of particle images. Analysis of these images allows to propose a tentative model for CP: six "subunits" (which we call domains) not much different in size are arranged with 32 point group pseudosymmetry. The determination of the number of polypeptides arising at the spontaneous specific proteolytic fragmentation of CP and their molecular weights conform with this assumption. The electrophoretic studies of the CP samples prepared both with and without potent proteolytic inhibitor, PMSF, revealed that CP is a single-chain protein with molecular weight of 130 000. Isolated and stored without PMSF the polypeptide chain of CP undergoes specific proteolytic cleavage which results in the appearance of polypeptides with molecular weights of 16 000, 48 000, and 64 000. The latter two polypeptides degradate to about two- and three-fold decreased molecular weights fragments, respectively. Therefore, the single polypeptide chain of CP contains at least five peptide bonds which are particularly susceptible to proteolytic attack and which connect six principal segments of the chain. The hydrolysis of these bonds results in liberation of the six fragments which were integrated in the enzymatically active globule of CP.     

Electron microscope study ofLeptospira

A leptospira consists of the cytoplasmic cylinder (contained within its own wall) which winds helically anticlockwise around the axistyle; both these components are enclosed by the outer covering membrane enveloping the whole organism.     

Electron cytochemistry of acetylcholinesterase in the neuromuscular junction during ontogenesis.

Electron histochemical studies were performed on neuromuscular junctions of the diaphragm in early postnatal states of development in rat by means of the acetylthiocholine technique. Presynaptic AChE appears to be derived from perikaryal sources, carried along by means of axonal transport mechanisms. Postsynaptic AChE is synthesized in the sarcotubular system of the underlying muscle fiber and within the perinuclear and endoplasmic reticulum of fundamental cells. Distribution of AChE synthesizing loci parallels with that of acetylcholine sensitive areas.     

Electron microscope study on spermatogenesis

Summary The morphogenesis of chromosomes at early prophase of spermatocytes I is studied in three ortoptherian species: Grillus argentinus (Grillidae), Laplatacris dispar (Acrididae) and Blaptica dubia (Blaptidae).The first chromosome component appearing at the beginning of meiosis is a thread (single elementary thread; S.E.T.) of low electron density measuring about 700 Å to 0.1 width. A group having the same width and integrated by three helically twisted ribbon-like components develops from S.E.T. and is called primary tripartite group, P.T.G. The three components are at first of the same width (about 200 Å) but the lateral arms progressively increase in thickness and in that way the group becomes coated by a layer of dense microfibrils supposed to be chromatin.Late stages of prophase were not thoroughly investigated in this study, but many evidences were however found helping to identify synaptene stage. In accordance with these evidences each homologous chromosome is integrated by an axial component (tripartite groups) coated by chromatin.The medial component of tripartite groups of Blaptica dubia is double and also shows multistranded regions which are called puffy regions.A comparative optical and electron microscope study was made in order to better understand the above described process. This study includes the comparison of the thickness of chromosomes as measured in light and electron micrographs.On the other hand, rubber models were made to illustrate the same process and pohotographs of these models are exhibited in the text.The nuclear structure of early spermatids of the same species is also studied in this paper. It was found that Blaptica and Grillus early spermatids nuclei contain groups similar to those found at the beginning of prophase of spermatocyte I, with the only difference that in many cases composite groups, formed by fusion of the lateral arms of two or more than two single groups, were found.The nuclear structure of late spermatids was also considered in this paper. Notwithstanding the study only aimed to point out that the pattern of organization of the spermatozoon chromatin greatly differs in the species examined.     

Electron microscope study on meiosis

Summary The cycle of the nucleolus and sex chromosome was studied with the electron microscope during the following stages of spermatogenesis and spermiogenesis of Gryllus argentinus: (1) spermatogonia; (2) prophase cyte I, leptotene, part of pachytene, and end of diplotene till breakdown of the nuclear envelope; (3) division I, metaphase and anaphase; (4) cyte II, prometaphase; (5) division II, metaphase, anaphase and telophase; (6) early and late spermatids. Some observations were also carried out in the primary oocyte until beginning of the growth period.It was found that nucleolus and sex chromosome are associated, at first without mixture of their components (leptotene) and afterwards interchanging components (pachytene). The interchange takes place by the passage from one element to another of filamentous units ot low electron density, similar in appearance to those existing in the medial plane of tripartite groups (synaptinemal complexes).At pachytene the primary results of interchange are: (1) the nucleolus contains filaments of chromosomal nature; (2) the nucleolus emits a long rod-like prolongation containing a cylindrical bundle of filaments, and an axial unit of the same nature; two equidistant clear spaces separate the axial unit from the cylindrical bundle and the latter from the dark wall of nucleolar material. At the end of diplotene these components are found organized in two bodies and a prolongation. One of the bodies is formed by a number of alternatively dark and light bands, the other by a pack of tubular units each showing the structure of the former nucleolar prolongation. The prolongation is either formed as in the preceding stage or it is composed of five ribbons, two dark ones outside and three light ones between them. It is supposed that both bodies are united by the prolongation but no definite proof was obtained. It is assumed that the complex thus constituted represents the sex chromosome.The sex chromosome was found at any phase of both divisions as well as at the intermediate stages between them; at the division phase the chromosome is separated from the autosomes and moves independently of them.The element could not be traced at telophase II but it reappears within the reorganized nuclei of spermatids. Amorphous nucleolar-like material and chromosome-like material are found associated at this stage with banded complexes like those seen at the end of prophase I. All these components undergo involution during spermatid maturation. At the final step of maturation no traces of them are found.A similar association of nucleolus and chromosome was found at prophase of primary oocytes of the same species. The associated body is of the same structure as that described for primary spermatocytes. The structures existing in the primary oocytes disorganize at the beginning of growth. At this time the nucleolus has developed into a large body containing masses of chromatin-like material.This investigation was supported in part by U.S. Public Health Service, Research Grant No. GM-08337 from the National Institute of General Medical Sciences.     

Electron microscope study of Cryptostroma corticale

An ultrastructural study of Cryptostroma corticale has been carried out with scanning and transmission electron microscopes. The usual features in fungi, as well as features characteristic of the family, were shown. It was noted that lomasomes and myelin-type structures were demonstrated by the two fixatives used. Their significance is discussed.     

Electron microscope study of lens fibers

The in vitro swelling action of L-thyroxine on rat liver mitochondria as examined photometrically represents an acceleration of a process which the mitochondria are already inherently capable of undergoing spontaneously, as indicated by the identical kinetic characteristics and the extent of thyroxine-induced and spontaneous swelling, the nearly identical pH dependence, and the fact that sucrose has a specific inhibitory action on both types of swelling. However, thyroxine does not appear to be a "catalyst" or coenzyme since it does not decrease the temperature coefficient of spontaneous swelling. The temperature coefficient is very high, approximately 6.0 near 20 degrees . Aging of mitochondria at 0 degrees causes loss of thyroxine sensitivity which correlates closely with the loss of bound DPN from the mitochondria, but not with loss of activity of the respiratory chain or with the efficiency of oxidative phosphorylation. Tests with various respiratory chain inhibitors showed that the oxidation state of bound DPN may be a major determinant of thyroxine sensitivity; the oxidation state of the other respiratory carriers does not appear to influence sensitivity to thyroxine. These facts and other considerations suggest that a bound form of mitochondrial DPN is the "target" of the action of thyroxine. The thyroxine-induced swelling is not reversed by increasing the osmolar concentration of external sucrose, but can be "passively" or osmotically reversed by adding the high-particle weight solute polyvinylpyrrolidone. The mitochondrial membrane becomes more permeable to sucrose during the swelling reaction. On the other hand, thyroxine-induced swelling can be "actively" reversed by ATP in a medium of 0.15 M KCl or NaCl but not in a 0.30 M sucrose medium. The action of ATP is specific; ADP, Mn(++), and ethylenediaminetetraacetate are not active. It is concluded that sucrose is an inhibitor of the enzymatic relationship between oxidative phosphorylation and the contractility and permeability properties of the mitochondrial membrane. Occurrence of different types of mitochondrial swelling, the intracellular factors affecting the swelling and shrinking of mitochondria, as well as the physiological significance of thyroxine-induced swelling are discussed.     

Electron microscope studies of human spermatozoa.

Semen of 40 healthy fertile men aged between 22--44 years was investigated. A triple morphological investigation of the semen was performed in each person. For the ultramicroscopic evaluation the semen specimens were selected according to the quantative criterion of normospermic. The ultrastructure of spermatozoon was described in comphiance with its division into head, neck and tail. The substructure of the axial fibre was separately analyzed. The physiological role of individual organelles of normal spermatozoon in fertilization was discussed.     

Watching the neuromuscular junction

To understand how synapses form, it is important to be able to watch them as they form. Transgenic mice in which motor axons are indelibly labeled with the Green Fluorescent Protein (GFP) or one of its spectral variants (XFPs) provide a new way to image motor nerve terminals; when combined with contrasting stains for the postsynaptic membrane, both pre- and postsynaptic elements can be viewed in live animals. The development, maturation, stability, remodeling and regeneration of neuromuscular junctions and motor units can then be assessed over intervals ranging from seconds to months.     

Glycobiology of the neuromuscular junction

Most molecules that are present at synapses are glycosylated with carbohydrates, and some carbohydrate structures are themselves uniquely synaptic in their localization. Thus, proteins or lipids at the synapse may bear distinct carbohydrates that alter their localization or function. Here, I will review the evidence that there are unique synaptic carbohydrates at the neuromuscular junction. Then, I will review the evidence that such carbohydrates can affect the function of synaptic proteins, with particular attention to agrin, dystroglycan, and the neural cell adhesion molecule (NCAM). Finally, I will review recent data that demonstrates a role for one carbohydrate structure, the cytotoxic T cell (CT) antigen, in neuromuscular development. These studies suggest that glycosylation is an important modification to consider in studies of synapse formation and function.     

Electron microscope observations of the melanocyte of the human epidermis

Proteins and colloidal materials, administered orally to suckling rats and mice, were ingested by columnar absorptive cells of the jejunum and ileum, but not of the duodenum. Bovine gamma globulin and ovalbumin were identified in the apical cytoplasm by staining with fluorescent antibody; trypan blue, Evans blue, saccharated iron oxide, and colloidal gold were detected intracellularly by their color, specific staining, and appearance in the electron microscope. Each substance was segregated in membrane-enclosed vacuoles, apparently part of a system of potentially interconnecting vacuoles and tubules in the apical cytoplasm which is continuous in places with the apical cell membrane. We postulate that ingestion of foreign materials was accomplished by pinocytosis, that is, by invagination of the apical cell membrane to form vacuoles containing material from the intestinal lumen. Approximately 18 days after birth columnar absorptive cells lost the ability to ingest proteins and colloids, and no longer contained large vacuoles and numerous tubules. At this age rats and mice lose the ability to absorb antibodies from the intestine in an immunologically intact form, and we conclude that cellular ingestion is part of the mechanism of absorption of intact proteins in suckling animals. Particulate fat apparently is absorbed in both newborn and adult animals by micropinocytosis. Thus adult animals may not have lost the capacity for pinocytosis, but rather have become selective as to what substances provoke it. Cortisone acetate, administered subcutaneously to rats 8 to 10 days old alters the columnar absorptive cells within 72 hours so that they resemble the cells in adult animals and no longer ingest proteins.     

Electron microscope study of the structure of Holospora caryophila

The ultrastructure of the symbiont Holospora caryophila found in the macronucleus of Paramecium biaurelia has been studied in the electron microscope following preparation by thin sections, negative staining and shadow-casting techniques. Holospora were identified by their characteristic morphology of slender elongated cells when seen in whole mounts in negative stain or contrasted with shadowing. The long forms were seen to possess a helical configuration, also an asymmetrical shape.Thin sections of Holospora revealed the cell envelope structure consistent with a Gram-negative organism. A complex network of internal membranes, together with a relatively electron transparent region at one end of the cytoplasm, was frequently observed.     

Electron microscope study of the developing chick embryo heart

Summary Myofibrillar differentiation in heart myocells of the chick embryo was studied with aid of the electronmicroscope. At early stages (29 hrs.) thin myofibrillar bundles are seen already differentiated in the cytoplasm of the myoblast and a few hours later cross striation can be depicted as ill-defined densities regularly spaced along the myofilaments.At later stages it was seen that some myofibrillar bundles seem to arise from a Z-band belonging to a thicker bundle. This disposition was frequently seen but the number of bundles observed arising from a single Z-band is varied. Cases were found in which two or three bundles were interconnected by myofibrillar bridges. The disposition was nominated Z center and it is interpreted as favouring spreading of the contractil wave from bundle to bundle. Conduction of the contractil wave from cell to cell is insured through intercalated discs.Desmosomes and intercalated discs were observed during the course of this study, but no relationship between both components of the cell membranes nor between desmosomes and myofilaments were found.Fellow working under a local fellowship program supported by Grant No. 56030 of The Rockefeller Foundation.