Nucleocytoplasmic Interaction During Maturation of the Egg of the Fern Histiopteris incisa (Thunb.) J. Smith

The maturing egg of Histiopteris incisa has many features incommon with that of Pteridium, with which the species may berelated. The nuclear evaginations are however conspicuous inrespect of the extensive development of internal membrane systems,involving dilatation of the perinuclear space. In some in stancesthe inner membrane of the nuclear envelope, the proliferationof which gives rise to the dilatations, was strikingly tenuous,possibly indicating an extensive interchange between the perinuclearspace and that part of the nucleoplasm sequestered in the evaginations.The evaginations frequently contain an aggregate of electron-opaquematerial resembling structurally and in staining propertiessimilar aggregates in Pteridium, but in contrast to Pteridiumthere was no evidence that these aggregates were organized inor near the nucleolus. Histiopteris inciso (Thunb.)J. Smith, Pteridophyta, egg maturation, nucleocytoplasmic interaction, ultrastructure     

Nuclear envelope-limited chromatin sheets (ELCS) and heterochromatin higher order structure

The interphase nucleus and nuclear envelope can acquire a myriad of shapes in normal or pathological cell states. There exist a wide variety of indentations and invaginations, of protrusions and evaginations. It has been difficult to classify and name all of these nuclear shapes and, consequently, a barrier to understanding the biochemical and biophysical causes. This review focuses upon one type of nuclear envelope shape change, named “nuclear envelope-limited chromatin sheets” (ELCS), which appears to involve exaggerated nuclear envelope growth, carrying with it one or more layers of ∼30 nm diameter heterochromatin. A hypothesis on the formation of ELCS is proposed, relating higher order heterochromatin structure in an interphase nucleus, nuclear envelope growth, and nuclear envelope-heterochromatin interactions.     

普通针毛蕨颈卵器和卵的发育

蕨类植物卵发生是有性生殖研究的重要内容。真水龙骨类II的卵发生尚无人研究, 本文对该类群中的普通针毛蕨(Macrothelypteris torresiana)卵发生过程进行了光镜和透射电镜研究。结果显示: 卵细胞刚形成时, 与腹沟细胞紧密相连, 随着卵进一步发育, 卵细胞和腹沟细胞之间逐渐形成分离腔, 但孔区处卵细胞和腹沟细胞始终相连。随后, 卵细胞上表面有不定型物质堆积在质膜外, 形成一层加厚的卵膜, 孔区处没有卵膜覆盖的位置最后形成受精孔。在卵发育后期, 卵细胞核变得不规则, 近成熟时卵核产生大量核外突。卵发育过程中卵膜的出现、受精孔的产生以及核外突等特征, 与进化的真水龙骨类中其他蕨类植物的卵发生研究结果相似, 与薄囊蕨类中原始基部类群的卵发生现象有显著差别。由此可见, 普通针毛蕨属于进化类型。依据卵发生中卵膜和受精孔等特征推测原始薄囊蕨类经过里白类、桫椤类, 最终演化为水龙骨类。     

The fine structure of basidiospores of Panaeolus campanulatus (L.) Fr. revealed by freeze-etching

Summary Freeze-etch replicas of basidiospores of Panaeolus campanulatus treated for 16 hours in glycerol showed that germination processes had been initiated. The plasmalemma bore evaginations, abstricting vesicles into the paramural space, and the nuclear envelope evaginated abstricting promitochondrial initials. The significance of these results is discussed in relation to previous work on chemically-fixed spores of various fungi.     

Ultrastructural analysis of the effects of dominant cataract-Fr gene in mouse embryos]

An electron microscope study of lenses in 11--15 and 17 days old embryos of mice homozygous by dominant cataract-Fr (CatFr) gene has shown that ultrastructural changes in the nuclear envelope are the earliest expression of the mutant gene. The primary lens fibers of 12 days old embryos CatFr/CatFr, unlike those of the normal ones, are characterized by the decrease in the number of nuclear pores, evagination of the outer nuclear membrane, marked and unequal extension of perinuclear space which connects itself with the endoplasmic reticulum cisternae. In 14 days old embryos breaks in the outer nuclear membrane and evaginations in the inner one, fusion of nuclear membranes and breaks of the nuclear envelope are observed and resulted in the release of the nuclear contents with the nucleolus in the cytoplasm. Similar ultrastructural changes are characteristic also of the nuclei of secondary lens fibers at a comparable stage of differentiation. The destructive changes of nuclei are accompanied by the degeneration and autophagocytosis of cellular organelles and matrix.     

The spatial association of the sperm cells and vegetative nucleus in the pollen grain ofBrassica

Summary In mature viable pollen ofBrassica oleracea, the pair of sperm cells and the nucleus of the vegetative cell are linked to form a structured unit we term the male germ unit. The sperm cells are held within a common periplasm and have no cell walls. Each sperm cell has a central globular body containing the nucleus surrounded by several evaginations which provide the means for linkage between them. One sperm cell, usually that closest to the nucleus of the vegetative cell contains most of mitochondria profiles (plastids are absent). This sperm cell appears to be linked by its protoplasmic evaginations to the envelope of the vegetative nucleus. The role of this unit in interactions with the female gametic complex is considered.     

华东安蕨卵发生的超微结构观察

核心薄囊蕨是蕨类植物中的进化类群,但对受精作用具有显著影响的卵发生研究仍较少,该文利用超微技术对其中蹄盖蕨科的华东安蕨卵发生过程进行了研究,以进一步完善薄囊蕨植物卵发生的科学资料,为理解蕨类植物的有性生殖及演化机制奠定基础。超微结构观察显示:华东安蕨的幼卵和沟细胞在颈卵器中紧密联接;随后,在卵细胞上方出现了分离腔和临时细胞壁,但在卵细胞中间孔区处卵细胞和腹沟细胞始终联接在一起;分离腔中的无定形物质沉积在卵细胞的质膜外形成了1层加厚的卵膜,而在孔区处没有形成卵膜,该位置最后形成了受精孔。在进一步的卵发生过程中,卵细胞核变得高度不规则,形成了大量的核外突和核褶皱。     

The relationship between nuclear envelope-derived annulate lamellae and the asymmetric division of primary spermatocytes in aphids

The structure of dividing primary spermatocytes of Amphorophora tuberculata (Aphididae, Hemiptera) as determined by electron microscopy and serial sectioning is described. The developmental stages examined extend from late prophase I to late telophase I. We looked for any asymmetric organization that could be causally linked to the differences in chromatin behaviour between the two daughter nuclei towards the end of meiosis I of this species. In late prophase I, evaginations of the nuclear envelope in the vicinity of two neigh-bouring centrosomes develop into closed cytoplasmic compartments with a dense content. The compartments open in prometaphase I and come to lie together with fragments of the nuclear envelope within the spindle area. Since nuclear pores are preserved in the membranes, intraspindle annulate lamellae have formed. These and material of presumed nuclear origin associated with them are asymmetrically distributed within the cell. Although dispersed at stages beyond prometaphase I, the material may be largely incorporated into one of the two daughter cells and thus be decisive for further development. Some annulate lamellae form a cap at the chromosome surface opposite to the neighbouring centrosomes in prometaphase I. These membranes may prevent interaction between spindle microtubules and chromosomes until a bipolar spindle forms in metaphase I. At this stage, both the banana-shaped autosomal bivalent and the X univalent occupy the equatorial plane. This is strange, because the X univalent has microtubular connections with one spindle pole and would be expected to migrate towards that pole. Possibly, the kinetochore of the X chromosome is inactive, and remains so in anaphase I, when the X univalent remains located between the two autosomal half-bivalents.M.F. Trendelenburg     

Electron microscopy of zygospore formation inChlamydomonas reinhardii

Summary After the disappearance of flagella and associated organelles, and nuclear fusion and chloroplast fusion, zygotes grow considerably. Growth is preceded by an extensive proliferation of rough endoplasmic reticulum from the outer membrane of the nuclear envelope. Nuclear fusion involves the fusion of the outer membranes (or of these endoplasmic reticulum evaginations), and then of the inner membranes. During zygospore formation on agar a complex 4–8 layered wall is formed. Precursors of two of the layers are detectable in the cytoplasm before secretion, one in the Golgi cisternae. Two types of storage granules are formed and fill much of the cytoplasm which undergoes extensive dedifferentiation. Endoplasmic reticulum and Golgi apparatus disappear. The chloroplast undergoes extensive dedifferentiation, losing its chlorophyll and most of its disc membranes. The resulting leucoplast retains its envelope, some starch grains and a tiny pyrenoid. In liquid culture developing zygospores become joined together in a multicellular mass. This disrupts wall formation, partially inhibits cytoplasmic and chloroplast dedifferentiation, and greatly reduces the zygospores' ability to germinate. The significance of these observations is discussed.     

Characterization of the NAD+ glycohydrolase associated with the rat liver nuclear envelope.

The localization of NAD+ glycohydrolase [EC 3.2.2.5] (NADase) in purified rat liver nuclei has been examined. Subnuclear fractionation revealed that at least 70% of the NADase in nuclei was associated with the nuclear envelope fraction. The nuclear envelope fraction was practically free of microsomal contamination as judged by electron microscopic morphometry and assays of microsomal marker enzymes. Therefore, NADase was found to be an integral component of the nuclear envelope. The enzymological properties of the nuclear envelope NADase were compared with those of the microsomal enzyme. The nuclear envelope NADase was identical to the microsomal enzyme in its Km for NAD+ (60 muM), pH optimum (pH 6.5), ratio of transglycosidase activity to NADase activity (about 0.5), thermal stability and sensitivity to various inhibitors. Thus, NADase is a common enzymic component of both the nuclear envelope and the endoplasmic reticulum.     

Virtual breakdown of the nuclear envelope in fission yeast meiosis

Asymmetric localization of Ran regulators (RanGAP1 and RanGEF/RCC1) produces a gradient of RanGTP across the nuclear envelope. In higher eukaryotes, the nuclear envelope breaks down as the cell enters mitosis (designated "open" mitosis). This nuclear envelope breakdown (NEBD) leads to collapse of the RanGTP gradient and the diffusion of nuclear and cytoplasmic macromolecules in the cell, resulting in irreversible progression of the cell cycle. On the other hand, in many fungi, chromosome segregation takes place without NEBD (designated "closed" mitosis). Here we report that in the fission yeast Schizosaccharomyces pombe, despite the nuclear envelope and the nuclear pore complex remaining intact throughout both the meiotic and mitotic cell cycles, nuclear proteins diffuse into the cytoplasm transiently for a few minutes at the onset of anaphase of meiosis II. We also found that nuclear protein diffusion into the cytoplasm occurred coincidently with nuclear localization of Rna1, an S. pombe RanGAP1 homolog that is usually localized in the cytoplasm. These results suggest that nuclear localization of RanGAP1 and depression of RanGTP activity in the nucleus may be mechanistically tied to meiosis-specific diffusion of nuclear proteins into the cytoplasm. This nucleocytoplasmic shuffling of RanGAP1 and nuclear proteins represents virtual breakdown of the nuclear envelope.     

Freeze-etching observations of trophozoites of pathogenic Entamoeba histolytica.

Pathogenic Entamoeba histolytica trophozoites were studied by the freeze-etching (FE) technique of electron microscopy. Surface replicas of intact cell membranes were highly convoluted with numerous invaginations, evaginations, and undulations. Sperical depressions and elevations varying from 0.5 mu to 1.0 mu in diameter were commonly present on the external cell membrane and appeared to represent an extracellular secretory mechanism of trophozoites. Cleaved surfaces of amebae exhibited a granular and lumpy cytoplasm in which there were many vesicles and vacuoles that ranged in diameter from 0.2 mu to 9.0 mu. Some vacuoles contained tightly enveloped bacteria, while others contained bacteria and host cytocomponents. Occasional vesicles and vacuoles appeared to be fused to each other. Replicas of FE nucleus were enclosed by double nuclear membranes which were fenestrated by numerous sperical pores measuring approximately 640 A in diameter and spaced at intervals of 650 A. Counts of nuclear pores were possible and indicated 35 pores per square micron on the nuclear envelope. Golgi apparatus, mitochondria and well formed endoplasmic reticulum were absent in FE replicas. This was in agreement with electron microscope observations on thin sections previously reported by other investigators.     

Ultrastructure of post-fertilization development in the red alga Scinaia articulata (Galaxauraceae,Nemaliales, Rhodophyta)

The ultrastructure of the carposporophyte and carposporogenesis is described for the red alga Scinaia articulata Setch. After fertilization, the trichogyne disappears, and the pericarp develops to form a thick protective tissue that surrounds the carposporophyte. The hypogynous cell cuts off both one-celled and two-celled sterile branches. Patches of chromatin are frequently observed in evaginations of the nuclear envelope, which appear to produce vesicles in the cytoplasm of the cell of the sterile branch. Large gonimoblast lobes extend from the carpogonium and cleave to form gonimoblast initials. Subsequently, a fusion cell is formed from fusions of the carpogonium, the hypogynous cell and the basal cell of the carpogonial branch. The mature carposporophyte comprises the fusion cell that is connected to the sterile branch cells, gonimoblast cells and carpospores and is surrounded by extensive mucilage. Young carpospores possess a large nucleus and proplastids with a peripheral thylakoid, but they have few dictyosomes and starch granules and are indistinguishable from gonimoblast cells. Subsequently, dictyosomes are formed, which produce vesicles with an electron-dense granule, which indicates an initiation of wall deposition. Thylakoid formation coincides with incipient starch granule deposition. The nuclear envelope produces fibrous vacuoles and concentric membrane bodies. Carpospores are interconnected by pit connections with two cap layers. Dictyosome activity increases, resulting in the production of vesicles, which either continue to deposit wall material or coalesce to form fibrous vacuoles. The final stage of carposporogenesis is characterized by the massive production of cored vesicles from curved dictyosomes. Mature carpospores are uninucleate and contain fully developed chloroplasts, numerous cored vesicles, numerous starch granules and fibrous vacuoles. The mature carpospore is surrounded by a wall layer and a separating layer, but a carposporangial wall is lacking.     

The Fine Structure of the Mature Gametes of Haemoproteus columbae Kruse*

SYNOPSIS. The filiform microgamete of Haemoproteus columbae consists of an elongate double-walled nucleus paralleled by 2 axonemes embedded in a homogeneous matrix. At one end of the gamete, the axonemes are sharply flexed back on themselves, but no conventional kinetosome has been recognized. No mitochondria have been seen. Single-walled vesicles occur in the matrix, and the entire gamete is surrounded by a single membrane. The large round macrogamete has a conspicuous central nucleus with its outer membrane drawn out into anastomosing evaginations which extend to the periphery of the cell. A moderately electron dense material fills the space between the 2 nuclear membranes and the lumina of the evaginations. Nucleolar material may occur in scattered masses within the nucleus. One or 2 axonemes appear to arise endogenously next to the nuclear membrane. The cytoplasm is filled with ribosomes and perhaps glycogen granules. Typical protozoan mitochondria and vesicles containing pigment retained from the erythrocytic stage are found in the peripheral cytoplasm. Accumulations of dense-walled vesicles occur in the cytoplasm in conjunction with evaginations of the nuclear membrane. Amid these vesicles triple-ringed discs resembling the cytostomes of merozoites are frequently seen. Several distinct layers of dense material surround the micro-gamete.     

Effects of brefeldin A on the Golgi apparatus, the nuclear envelope, and the endoplasmic reticulum in a green alga,Scenedesmus acutus

Summary The effects of brefeldin A (BFA) on the structure of the Golgi apparatus, the nuclear envelope, and the endoplasmic reticulum (ER), and on the thiamine pyrophosphatase (TPPase) activity in these organelles were examined in a green alga,Scenedesmus acutus, to obtain evidence for the existence of a retrograde transport from the Golgi apparatus to the ER via the nuclear envelope. InScenedesmus, Golgi bodies are situated close to the nuclear envelope throughout the cell cycle and receive the transition vesicles not directly from the ER, but from the nuclear envelope. BFA induced the disassembly of Golgi bodies and an increase in the ER cisternae at the trans-side of decomposed Golgi bodies in interphase cells and multinuclear cells before septum formation. The accumulated ER cisternae connected to the nuclear envelope at one part. TPPase activity was detected in all cisternae of Golgi bodies, but not in the nuclear envelope or the ER in nontreated cells. On the contrary, in BFA-treated cells, TPPase activity was detected in the nuclear envelope and the ER in addition to the decomposed Golgi bodies. When septum-forming cells were treated with BFA, the disassembly of Golgi bodies was less than that in interphase cells, and TPPase activity was detected in the Golgi cisternae but not in the nuclear envelope or the ER. These results suggest mat BFA blocks the anterograde transport from the nuclear envelope to the Golgi bodies but does not block the retrograde transport from the Golgi bodies to the nuclear envelope in interphase and multinuclear cells.Abbreviations BFA brefeldin A - ER endoplasmic reticulum - TPPase thiamine pyrophosphatase     

Demonstration of succinic dehydrogenase in mitochondria of fern egg cells at electron microscope level

The use of ferricyanide in the presence of Cu++ to capture the ferrocyanide generated proved a reliable method for the location of succinic dehydrogenase in fern egg cells. The response of mitochondria-like nuclear evaginations was largely negative, but small patches of apparently authentic reaction product, absent in the controls, were occasionally encountered in their envelopes. From the point of view of deciding the nature of the nuclear evaginations the results were therefore equivocal.     

Permeability and Structural Characteristics of Isolated Nuclei from Chaetopterus Eggs

The germinal vesicle of the mature Chaetopterus egg is invested by an envelope which can be seen in electron micrographs to contain "pores" in its bilaminar structure. While under continuous microscopic observation, individual germinal vesicles were isolated in various test solutions by an extremely gentle method. Repeated measurements of nuclear diameter and of optical path differences with an interference microscope provided data on changes in mass after isolation. It was found that bovine serum albumin can readily penetrate the nuclear envelope of the isolated nucleus and that there are soluble elements which rapidly diffuse out. A relatively non-diffusible mass is lost at a much slower rate, the proportion of soluble to non-diffusible mass being dependent on the ionic environment. Calcium and manganese increase the proportion of the non-diffusible mass at the expense of the soluble components, while potassium decreases it. The shape and size of the isolated nucleus is at least partially dependent on the non-diffusible mass of its interior. Digestion with trypsin causes a complete structural collapse and loss of the non-diffusible elements, along with disappearance of the nucleolus. The nucleus shrinks and becomes wrinkled. A small residual mass is left which is probably associated with the nuclear envelope. Digestion with RNase or DNase causes no detectable effect on the isolated nucleus. Micromanipulation of the isolated nucleus consistently indicates that there are strands emanating from the nucleus. They may be up to several hundred microns long, are structurally strong, and are not destroyed by trypsin, RNase, or DNase. Electron micrographs of thin sections of intact cells show that the germinal vesicle is highly irregular in outline with complex evaginations extending into the cytoplasm. With the light microscope the isolated nucleus looks spherical and smooth and no emanating strands can be seen. The nature of the strands is not known.     

Demonstration of succinic dehydrogenase in mitochondria of fern egg cells at electron microscope level

Summary The use of ferricyanide in the presence of Cu⁺⁺ to capture the ferrocyanide generated proved a reliable method for the location of succinic dehydrogenase in fern egg cells. The response of mitochondria-like nuclear evaginations was largely negative, but small patches of apparently authentic reaction product, absent in the controls, were occasionally encountered in their envelopes. From the point of view of deciding the nature of the nuclear evaginations the results were therefore equivocal.     

Phosphatidic acid is the prominent product of endogenous neuronal nuclear lipid phosphorylation, an activity enhanced by sphingosine, linked to phospholipase C and associated with the nuclear envelope.

Using endogenous lipid substrates, assays of lipid phosphorylation indicated that neuronal nuclei had a considerable superiority in phosphatidic acid (PA) formation when compared with homogenates and other subfractions of cerebral cortex. This predominance of neuronal nuclear PA labelling was linked to a sizable pool of nuclear diacylglycerols that expanded significantly with incubation. PA was also the dominant product of neuronal nuclear lipid phosphorylation reactions. Nuclear envelope preparations and the parent neuronal nuclei showed specific rates of PA formation that were comparable, based upon membrane phospholipid contents. As well, using an exogenous diacylglycerol substrate, the distribution of diacylglycerol kinase activities closely followed phospholipid contents of subfractions derived from the neuronal nucleus during envelope preparation. This evidence suggested an association between diacylglycerol kinase and the neuronal nuclear envelope. Nuclear PA formation increased in the presence of sphingosine, while sphingosine decreased PA formation in other subfractions. Likely sphingosine exerted its effect on nuclear diacylglycerol kinase, as sphingosine did not elevate levels of nuclear diacylglycerols. Phosphoinositidase C was present in the nuclei and inhibitors of this enzyme did decrease PA formation, indicating diacylglycerols from inositides as substrates for nuclear diacylglycerol kinase. The nuclear envelope fraction had a considerably lower specific phosphoinositidase C activity than the parent nuclei, and showed an activation of PA formation by sphingosine, but a less efficient handling of the exogenous diacylglycerol substrate. It is possible that phosphoinositidase C and diacylglycerol kinase are closely situated within the neuronal nuclei, and a loss of the former activity may compromise the latter.