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  • 1
    Electronic Resource
    Electronic Resource
    Are accessory nuclei involved in the establishment of developmental gradients in hymenopteran oocytes? (1991)
    Springer
    Development genes and evolution 199 (1991), S. 423-426 
    Details
    ISSN: 1432-041X
    Keywords: Oogenesis ; Accessory nuclei ; Developmental gradients ; Ultrastructure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary In the oocytes ofTenthredo olivacea, accessory nuclei (AN) are formed by budding from the nuclear envelope of the oocyte nucleus. Newly formed AN contain electron-dense material of nuclear origin and are surrounded by a double envelope devoid of pores. Such structures are subsequently transported to the peripheral ooplasm (periplasm), where they grow to reach a final diameter of 5 µm. In the envelopes of advanced AN nuclear pores arise. Through these pores “nuage” material is extruded into the surrounding periplasm. These findings are discussed with respect to a possible involvement of AN in the establishment of developmental gradients in hymenopteran oocytes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01705853
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  • 2
    Electronic Resource
    Electronic Resource
    Morphogenesis of accessory nuclei during final stages of oogenesis in Cosmoconus meridionator (Hymenoptera: Ichneumonidae) (1993)
    Springer
    Development genes and evolution 203 (1993), S. 100-103 
    Details
    ISSN: 1432-041X
    Keywords: Oogenesis ; Accessory nuclei ; Morphogenetic signals ; Hymenoptera
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Morphogenesis of accessory nuclei (AN) in chorionated oocytes of Cosmoconus meridionator is described. Initially, each AN contains two dense, morphologically distinct inclusions. During the final stages of postvitellogenesis, these inclusions undergo characteristic transformation that is followed by the extrusion of some substances from AN to the surrounding periplasm. Histo- and cytochemical tests indicate that both inclusions contain RNA, although their precise composition is different. Our results support previous suggestions on the involvement of AN in the distribution of morphogenetic signals.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00539895
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  • 3
    Electronic Resource
    Electronic Resource
    Subcortical microtubule network separates the periplasm from the endoplasm and is responsible for maintaining the position of accessory nuclei in hymenopteran oocytes (1995)
    Springer
    Development genes and evolution 205 (1995), S. 54-61 
    Details
    ISSN: 1432-041X
    Keywords: Oogenesis ; Cytoskeleton ; Accessory nuclei ; Ultrastructure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Oocytes of hymenopterans are equipped with peculiar organelles termed accessory nuclei. These organelles originate from the germinal vesicle (oocyte nucleus) and gather preferentially at the anterior pole. To gain insight into the mechanism of uneven (asymmetrical) distribution of accessory nuclei, the organization of the microtubule cytoskeleton in the oocytes of two hymenopterans Chrysis ignita and Cosmoconus meridionator has been studied. It is shown that during late previtellogenesis two networks of microtubules are present along the contact zone between the oocyte and enveloping follicular epithelium. The external one is associated with belt desmosomes connecting neighbouring follicular cells. The internal network is composed of randomly orientated microtubules and separates transparent, organelle-free periplasm from the endoplasm. All cellular organelles and the germinal vesicle are localized in the endoplasm. Accessory nuclei are accumulated in the anterior endoplasm; they always lie in direct contact with the subcortical network. Treatment with colchicine results in the disappearance of the periplasm as well as in the redistribution of cellular organelles including accessory nuclei. Presented findings suggest that subcortical microtubules play an important role in the positioning of accessory nuclei throughout the ooplasm.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00188843
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  • 4
    Electronic Resource
    Electronic Resource
    Subcortical microtubule network separates the peripiasm from the endoplasm and is responsible for maintaining the position of accessory nuclei in hymenopteran oocytes (1996)
    Springer
    Development genes and evolution 205 (1996), S. 319-319 
    Details
    ISSN: 1432-041X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00365810
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  • 5
    Electronic Resource
    Electronic Resource
    Extrachromosomal amplification of rDNA in oocytes of Hemerobius spp. (Insecta, Neuroptera) (1995)
    Springer
    Chromosoma 103 (1995), S. 606-612 
    Details
    ISSN: 1432-0886
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract In previtellogenic oocytes of the neuropteran, Hemerobius spp., two distinct, DNA-positive intranuclear structures have been observed. Chromosomes of meiotic prophase assemble in the center of the oocyte nucleus forming a highly polymorphic karyosphere, which persists in this position until the very late stages of vitellogenesis. The extrachromosomal DNA body, containing amplified ribosomal genes, undergoes fragmentation and dispersion in the nucleoplasm. At the onset of previtellogenic growth, transcription of extra rDNA starts, which is accompanied by the appearance of dense, granular material (multiple nucleoli). Arising nucleoli gradually fill the nucleoplasm. At the electron microscopic (EM) level two electron dense structural forms of the granular material have been described. Together with general histological and ultrastructural analysis the amplification of rDNA genes in Hemerobius spp. oocytes has been demonstrated by means of the spreading technique, which has shown that extra rDNA is organized in rings containing various numbers of active ribosomal genes. The transcription activity of amplified genes is manifested in the form of typical “Christmas tree” structures.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00357687
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  • 6
    Electronic Resource
    Electronic Resource
    Formation and function of accessory nuclei in the oocytes of the bird louse, Eomenacanthus stramineus (Insecta, Mallophaga) (1989)
    Springer
    Chromosoma 97 (1989), S. 321-326 
    Details
    ISSN: 1432-0886
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract In the oocytes of Eomenacanthus stramineus accessory nuclei arise by budding from the nuclear envelope. It is suggested that microtubules and the thick layer of the nuclear lamina are involved in this process. Newly formed accessory nuclei contain aggregations of fibrillogranular material. These aggregations are slightly Feulgen positive, RNA negative and stain positively with the AgNOR method. During later developmental stages one dense, RNA-positive inclusion appears in each accessory nucleus. These inclusions consist of on Ag-NOR-positive cortical layer and an Ag-NOR-negative core. The function of accessory nuclei in the species investigated is discussed in the light of these results.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00371973
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  • 7
    Electronic Resource
    Electronic Resource
    The ovary ofCatajapyx aquilonaris (Insecta, Entognatha): ultrastructure of germarium and terminal filament (1992)
    Springer
    Zoomorphology 112 (1992), S. 247-251 
    Details
    ISSN: 1432-234X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Each of the two ovaries ofCatajapyx aquilonaris is composed of seven segmentally (metamerically) arranged ovarioles. The two lateral oviducts that join and bear ovarioles extend throughout the abdomen. In the ovariole three regions can be recognized: the terminal filament, the germarium and the vitellarium. The terminal filaments do not fuse with each other but attach separately (by means of muscle fibres) to the closest lobes of the fat body. Germ cells in the germarium are not joined by intercellular bridges and do not form clusters. Thus the ovarioles ofC. aquilonaris are interpreted as being primarily panoistic. The results obtained support the hypothesis that both dipluran subgroups (Campodeina and Japygina) do not form a monophyletic unit.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01632822
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  • 8
    Electronic Resource
    Electronic Resource
    Ultrastructural modifications of the follicular epithelium accompanying the onset of vitellogenesis in the whirligig beetle, Gyrinus natator (1987)
    Springer
    Cell & tissue research 249 (1987), S. 209-214 
    Details
    ISSN: 1432-0878
    Keywords: Oocyte ; Follicle cells ; Gap junctions ; Cytoskeleton ; Gyrinus natator
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary The ultrastructure of the follicle cells during previtellogenesis and early vitellogenesis have been studied. In previtellogenesis follicle cells are columnar with numerous bundles of microtubules located along the lateral plasma membranes. Oocyte-follicle cell gap junctions are not found in this stage. At the onset of vitellogenesis, the bundles of microtubules disappear and are replaced by an apically located ring of microtubules. The modification of microtubular cytoskeleton is not followed by the development of intercellular spaces between the follicle cells. Concurrently, numerous gap junctions are formed between specialized follicle cell processes and oocyte microvilli, which are arranged in characteristic cone-shaped aggregations. It is suggested that cytoskeletal changes and formation of heterologous gap junctions, occurring at the onset of vitellogenesis, are induced by juvenile hormone.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00215435
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  • 9
    Electronic Resource
    Electronic Resource
    A new version of the Ag−NOR technique. A combination with DAPI staining (1996)
    Springer
    Journal of molecular histology 28 (1996), S. 651-656 
    Details
    ISSN: 1573-6865
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary The Ag−NOR staining technique is widely used for visualizing nucleolar organizer regions (NORs) in various plant and animal tissues. We describe a simple and time-saving combination of Ag−NOR staining with DNA detection by fluorescence microscopy. This modification was tested on cultured cells and semi-thin sections of plastic-embedded tissues. Of the different fixatives and embedding media used in our studies, the best results (i.e., high selectivity of staining, and lack of or very low background precipitation) were obtained with fixation in methanol-acetone at −20°C for cultured cells, and fixation in 4% formaldehyde followed by embedding in Histocryl resin for tissue sections. The optimal time of Ag−NOR staining was determind experimentally for all materials tested. The specificity of the staining was checked at the electron microscopical level. Especially good results were obtained by mixing epifluorescence with standard bright-field illumination. In such a combination, Ag−NOR-positive nucleoli, or their fibrillar centres and dense fibrillar components, were clearly visible against a bright background of nuclear DNA.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02331386
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  • 10
    Electronic Resource
    Electronic Resource
    Structure of ovaries in ensign scale insects, the most primitive representatives of Coccomorpha (Insecta, Hemiptera) (1995)
    New York, NY : Wiley-Blackwell
    Journal of Morphology 224 (1995), S. 23-29 
    Details
    ISSN: 0362-2525
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: The ovaries of Orthezia urticae and Newsteadia floccosa are paired and composed of numerous short ovarioles. Each ovariole consists of an anterior trophic chamber and a posterior vitellarium that contains one developing oocyte. The trophic chamber contains large nurse cells (trophocytes) and arrested oocytes. The total number of germ cells per ovariole (i.e., cluster) is variable, but it is always higher than 32 and less than 64. This suggests that five successive mitotic cycles of a cystoblast plus additional divisions of individual cells are responsible for the generation of the cluster. Cells of the trophic chamber maintain contact with the oocyte via a relatively broad nutritive cord. The trophic chamber and oocyte are surrounded by somatic cells that constitute the inner epithelial sheath around the former and the follicular epithelium around the latter. Anagenesis of hemipteran ovarioles is discussed in relation to the findings presented. © 1995 Wiley-Liss, Inc.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jmor.1052240104
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