ELECTRON MICROSCOPIC STUDIES OF MITOSIS IN AMEBAE : I. Amoeba proteus

Individual organisms of Amoeba proteus have been fixed in buffered osmium tetroxide in either 0.9 per cent NaCl or 0.01 per cent CaCl₂, sectioned, and studied in the electron microscope in interphase and in several stages of mitosis. The helices typical of interphase nuclei do not coexist with condensed chromatin and thus either represent a DNA configuration unique to interphase or are not DNA at all. The membranes of the complex nuclear envelope are present in all stages observed but are discontinuous in metaphase. The inner, thick, honeycomb layer of the nuclear envelope disappears during prophase, reappearing after telophase when nuclear reconstruction is in progress. Nucleoli decrease in size and number during prophase and re-form during telophase in association with the chromatin network. In the early reconstruction nucleus, the nucleolar material forms into thin, sheet-like configurations which are closely associated with small amounts of chromatin and are closely applied to the inner, partially formed layer of the nuclear envelope. It is proposed that nucleolar material is implicated in the formation of the inner layer of the envelope and that there is a configuration of nucleolar material peculiar to this time. The plasmalemma is partially denuded of its fringe-like material during division.     

ELECTRON MICROSCOPIC STUDIES OF EXTRAPLASTIDIC ASTAXANTHIN IN HAEMATOCOCCUS12

The ketonic carotenoid astaxanthin accumulates in perinuclear cytoplasm characterized by a network of ribosome-coated endoplnsmic reticulum segments, free ribosomes, dictyosomes in active stages of vesicle formation, and mitochondria. The pigment granules form in the ground substance and not within any organelle or vesicle. Coalescence of the globular granules results from increasing quantities of astaxanthin formed as the cells age. The gross differences in fixation image following glzitaraldehyde-KMnO₄ and glutaraldehyde-O_sO₄ are illustrated, and the need for n variety of fixations upon which interpretations are bused is emphasized. The bright red coloration of akinetes is due to a masking of the chlorophyll by the massive astaxnnthin deposits rather than m y break-down of the chloroplast thylakoids.     

ELECTRON MICROSCOPIC STUDIES OF RENAL DISEASE

The nephrotic syndrome, glomerulonephritis, disseminated lupus erythematosus and the Fanconi syndrome show characteristic changes with electron microscopy.Experimental studies of animals were carried out to determine the significance of such changes by observing reactions that occur under carefully controlled conditions. A lesion with collagen deposition that was found in the centrolobular region of glomeruli sheds new light on the function of this region. This evidence must be considered in developing an understanding of how the production of urine is controlled. Fluid-filled compartments and various bodies associated with the ultrastructure of tubule cells can be produced under conditions which suggest that these structures play a role in tubular resorption.     

AN ELECTRON MICROSCOPIC STUDY OF PINOCYTOSIS IN AMEBA : II. The Cytoplasmic Uptake Phase

This report is devoted principally to a consideration of the fate of the pinocytotic vacuole and its content in the ameba Pelomyxa carolinensis (Chaos chaos). High resolution micrographs of the plasmalemma have shown it to consist of three layers, i.e., an outermost filamentiferous zone, a middle homogeneous zone, and an inner zone which appears to be a unit membrane. The three zones can be identified in the membranes lining the pinoyctotic tunnels and vacuoles of amebas fixed shortly after pinocytosis occurred. The first apparent change in the pinocytotic vacuole is an increase in the surface-to-volume ratio which occurs during the 1st hour of its existence. Within 24 hours the marker substance commonly collects in defecation vacuoles which can be identified by the profiles of bacteria usually found in the lumen. Occasionally, however, thorotrast can be seen in the lumen of the contractile vacuole. The thorotrast appears to enter the two excretory organelles by the coalescence of vesicular fragments of the pinocytotic vacuoles with the limiting membranes of the excretory organelles.     

ELECTRON MICROSCOPIC STUDIES ON THE DEVELOPMENT OF VESICULAR STOMATITIS VIRUS IN KB CELLS

The development of vesicular stomatitis virus in KB cells was studied by electron microscopy. Sections of infected cells were made 1, 4, 7, 10, and 20 hours after inoculation of the cell cultures, and at the same intervals the supernatant fluid was assayed for virus titer by the plaque test in chick embryo cells. At 10, 14, and 20 hours after inoculation, virus rods were observed attached to cytoplasmic membranes, inside cytoplasmic vacuoles, and attached to the membranes delimiting these vacuoles; they were also found on the surface membrane of the cells. Besides the rods, spherical particles of different sizes and shapes were seen. The possibility that these structures are related to the development of virus rods is discussed. A similarity was noted between the site of maturation of vesicular stomatitis virus rods and that of some other arbor viruses.     

ELECTRON MICROSCOPIC STUDIES OF INDUCED CARTILAGE DEVELOPMENT AND CALCIFICATION

Cultured, human, amniotic cells (FL strain) injected into the thigh muscles of cortisone-conditioned mice proliferated to form discrete colonies which, over a period of 5 days, became invested by numerous fibroblasts. Cartilage cells and matrix appeared within the fibroblastic zones during the succeeding 2–4 days. Cartilage matrix calcified within 12 days following FL-cell injection. Cartilage cells closely resembled fibroblasts from which they appeared to be derived, and were readily distinguished from FL cells by their prominent ergastoplasm and Golgi complexes. Cartilage matrix was composed of a distinctive feltwork of randomly arranged, collagen fibrils (~600 A axial period and ~250 A width) from which small electron-opaque, leaflike matrix particles extended. Matrix calcification occurred with the deposition of radially arranged needle-like structures resembling hydroxyapatite. Dense centers were often identified within these clusters. Examination of heavily calcified areas revealed confluent masses of apatite-like material. In general, the fine structure of induced cartilage formation and calcification resembled that of cartilage development and calcification as previously described in the normal epiphysis.     

ELECTRON MICROSCOPIC STUDIES ON THE INDIRECT FLIGHT MUSCLES OFDROSOPHILAMELANOGASTER : II. Differentiation of Myofibrils

The differentiation of the indirect flight muscles was studied in the various pupal stages of Drosophila. Fibrillar material originates in the young basophilic myoblasts in the form of short myofilamants distributed irregularly near the cell membranes. The filaments later become grouped into bundles (fibrils). Certain "Z bodies" appear to be important during this process. The "Z bodies" may possibly be centriolar derivatives and are the precursors of the Z bands. The first formed fibrils (having about 30 thick myofilaments) are already divided into sarcomeres by Z bands. These sarcomeres, however, seem to be shorter than those of the adult fibrils.The H band differentiates in fibrils having about 40 thick myofilaments; the fibrils constrict in the middle of each sarcomere during this process. The individual myofibrils increase from about 0.3 µ to 1.5 µ in diameter during development, apparently by addition of new filaments on the periphery of the fibrils. The ribosomes seem to be the only cytoplasmic inclusions which are closely associated with these growing myofibrils. Disintegration of the plasma membranes limiting individual myoblasts was commonly seen during development of flight muscles, supporting the view that the multinuclear condition of the fibers of these muscles is due to fusion of myoblasts.     

ELECTRON MICROSCOPY OF MITOSIS IN A RADIOSENSITIVE GIANT AMOEBA

Various aspects of the ultrastructure of the dividing nuclei in the large radiosensitive amoeba Pelomyxa illinoisensis are demonstrated. Evidence of nuclear envelope breakdown is presented, and membrane fragments are traced throughout metaphase to envelope reconstruction in anaphase and telophase. Annuli in the nuclear envelope and its fragments are shown throughout mitosis. During metaphase and anaphase some 15 to 20 mitochondria are aligned at each end of the spindle, and are called polar mitochondria. The radioresistant amoebae Pelomyxa carolinensis and Amoeba proteus do not have polar mitochondria, and Pelomyxa illinoisensis is unique in this regard. The shape of the P. illinoisensis interphase nucleoli differs from that in the two radioresistant species, and certain aspects of nucleolar dissolution in the prophase vary. Helical coils in the interphase nucleoplasm are similar to those in the radioresistant amoebae. A "blister" phase in the flatly shaped telophase nuclei of P. illinoisensis is described which is interpreted to be the result of a rapid nuclear expansion leading to the formation of the normal spherical interphase nuclei.     

ELECTRON MICROSCOPE STUDY OF MITOSIS IN SEA URCHIN BLASTOMERES

The fine structure of cells at different stages of the mitotic cycle was studied in the blastomeres of 6-hour-old embryos of the sea urchin Strongylocentrotus purpuratus. The material was fixed in 1 per cent osmium tetroxide in sea water, buffered with veronal-acetate to pH 7.5, embedded in Araldite, and sectioned with glass knives. The aster, as it forms around the centriole, has the appearance of the endoplastic reticulum, with elements oriented radially from the centrosphere to the periphery of the cell. Anaphase structures described include the kinetochores, with bundles of fine filaments extending toward the centrioles, as well as continuous filaments passing between the chromosomes. Two cylindrical centrioles composed of parallel rods are present in each of the anaphase asters. At late anaphase, elements of the endoplasmic reticulum condense on the surface of the chromosomes to form a double membrane which already at this stage possesses pores or annuli. At telophase bundles of continuous filaments can be seen in the interzonal region. These filaments, as well as those associated with the chromosomes, have a diameter of approximately 15 mµ, and appear physically different from the astral structure.     

Mitochondria : II. The Nuclear-Mitochondrial Relationship in Pelomyxa carolinensis Wilson (Chaos chaos L.)

This study has demonstrated that in the ameba, Pelomyxa carolinensis Wilson (Chaos chaos L.) the limiting membranes of mitochondria and postdivision nuclei are often continuous. The morphological relationship may be functional in that it permits an exchange of material resulting directly or indirectly in an increased enzyme content of the mitochondria. It is suggested that through a series of progressive foldings of its envelope, the nucleus may be a site of formation of mitochondria.     

Mitochondria. II. The nuclear-mitochondrial relationship in Pelomyxa carolinensis Wilson (Chaos chaos L.)

This study has demonstrated that in the ameba, Pelomyxa carolinensis Wilson (Chaos chaos L.) the limiting membranes of mitochondria and postdivision nuclei are often continuous. The morphological relationship may be functional in that it permits an exchange of material resulting directly or indirectly in an increased enzyme content of the mitochondria. It is suggested that through a series of progressive foldings of its envelope, the nucleus may be a site of formation of mitochondria.     

ELECTRON MICROSCOPIC STUDIES ON THE BEHAVIOR OF GLYCOGEN PARTICLES DURING OOGENESIS IN THE SEA URCHIN

The behavior of glycogen particles during oogenesis in the sea urchin was studied by electron microscopy. Before the beginning of oogenesis the nurse cells include many glycogen particles, which are spherical or multiangular in shape and about 600 A in diameter, lying within the vesicle of the large granules and also in the cytoplasm among the granules. There are few glycogen particles in the spaces among the oocytes and the nurse cells. At the early stage of oogenesis the limiting membrane of the large granule breaks locally and the glycogen particles in the vesicle are dispersed into the cytoplasm. The plasma membrane of the nurse cell also breaks in places and glycogen particles are spread throughout the intercellular space. At the beginning of vitellogenesis, β-pinosomes begin to be formed at the periphery of the oocyte; these take in glycogen particles from the outside which are progressively broken into smaller units.     

AN ELECTRON MICROSCOPIC STUDY OF PINOCYTOSIS IN AMEBA : I. The Surface Attachment Phase

The attachment to the surface of the ameba (Chaos chaos L. (Pelomyxa carolinensis, Wilson)) of two proteins, ribonuclease and ferritin, and two colloidal suspensions, thorium dioxide and gold, was studied in the electron microscope. The initial step in the pinocytosis of ferritin and thorium dioxide particles by amebas is shown to be the attachment of these substances to the "hairlike" extensions of the plasmalemma. Ribonuclease caused alterations in the structure of the plasmalemma, but on account of its relative lack of density, it could not be definitely localized. Colloidal gold did not appear to be active with respect to pinocytosis in amebas. Since molecules in solution and particles in suspension are taken up by the same mechanism, the first step of which is their attachment to the cell surface, it is suggested that a single mechanism underlies phagocytosis, pinocytosis, ropheocytosis, cytopempsis, and potocytosis.     

ISOLATION OF SYNAPTIC COMPLEXES IN A CAESIUM CHLORIDE DENSITY GRADIENT: ELECTRON MICROSCOPIC AND IMMUNOHISTOCHEMICAL STUDIES1

A technique is described for the improved isolation of synaptic complexes. Homogenates of guinea pig cerebellum and cerebral cortex were subjected to centrifugation, first in a discontinuous sucrose gradient, and secondly in a continuous caesium chloride gradient. Of the six bands that were obtained, band four contained a high proportion of synaptic complexes showing both pre- and postsynaptic elements attached to each other; myelin and free mitochondria were not contaminants of this fraction. Fluorescein-labelled γ-globulin prepared against band four reacted with synaptic regions of cerebellum and cerebral cortex, but not with cervical cord.     

革蜱未成熟期哈氏器的扫描电镜研究

用扫描电镜观察了革蜱属8种幼虫和若虫的哈氏器,并与其他属5种幼虫和4种若虫的哈氏器进行比较,以阐明其形态特征及其在分类中的意义。其中,9种幼虫和8种若虫哈氏器的结构是首次报道。革蜱属幼期哈氏器的囊孔形状、前窝感毛数目及其中孔毛的位置等与其他属不同。东洋区的金泽革蜱与古北区的革蜱种类之间,在孔毛形状、位置和幼虫近端缝孔的位置上有明显差别。而后者中,阿坝革蜱幼虫一般无近端缝孔;网纹革蜱幼虫和若虫的囊孔形状和幼虫的近端缝孔的位置与其他种类不同。但其余几种革蜱幼虫和若虫的哈氏器无显著差别。     

革蜱成虫哈氏器的扫描电镜观察

本文报道了用扫描电镜观察革蜱属8种成虫的哈氏器.其中三种成虫(阿坝革蜱D. ahaensis、金泽革蜱D. auratus和中华革蜱D. sinicus)的哈氏器结构是首次报道,并与其他属6种成虫的哈氏器进行了比较,以阐明其形态特征及其在分类中的意义.另外,还将这14种成虫哈氏器与各自未成熟期的哈氏器进行了比较.分析和讨论了同种不同时期哈氏器结构的异同.东洋区的金泽革蜱和古北区的革蜱种类间,在孔毛形状,位置及基盘数目上有明显差别,而后者中,边缘革蜱D. marginatus的孔毛位于近端外侧,草原革蜱D. nuttalli和网纹革蜱D. reticulatus的孔毛位于远瑞外侧,其余种类无明显差别.     

ELECTRON MICROSCOPIC STUDIES ON ACHROSOME FORMATION IN THE COCKROACH, BLATTELLA GERMANICA

The development of achrosomes in spermiogenesis of Blattella germanica was studied by electron microscopy. Achrosomes consist of an achrosomal vesicle originating from Golgi vesicles and an axial rod composed of fine fibrils.
The achrosomal vesicle, formed at the mature face of the Golgi body, migrates to the anterior of the nucleus, where it later becomes the front structures of sperm head. After attachment to the nucleus, the achrosomal vesicle changes from a round to a tapering shape, passing through a coneshape phase. During these changes, the axial rod develops in the hollow formed by indentations of adjacent parts of the achrosomal vesicle and the nucleus.
The cisternae of the Golgi body concerned with formation of the achrosomal vesicle, are made by pinching off small vesicles from both the ER and the nuclear envelope.