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  • 1
    Digitale Medien
    Digitale Medien
    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
    Schlagwort(e): Oogenesis ; Accessory nuclei ; Developmental gradients ; Ultrastructure
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: 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.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01705853
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  • 2
    Digitale Medien
    Digitale Medien
    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
    Schlagwort(e): Oogenesis ; Cytoskeleton ; Accessory nuclei ; Ultrastructure
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: 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.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00188843
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  • 3
    Digitale Medien
    Digitale Medien
    Ultrastructural studies on the vitellogenesis of Tetrodontophora bielanensis (Waga) (Collembola) (1976)
    Springer
    Cell & tissue research 168 (1976), S. 399-410 
    Details
    ISSN: 1432-0878
    Schlagwort(e): Vitellogenesis ; Dictyosomes ; Micropinocytosis ; Ultrastructure ; Collembola
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Medizin
    Notizen: Summary Vitellogenesis in Tetrodontophora bielanensis (Waga) is of the “mixed” type. Part of the yolk material is produced inside the oocyte (auto-synthesis), while part is absorbed by micropinocytosis. During autosynthesis polyribosomes, rough endoplasmic reticulum and dictyosomes take part. Regardless of their origin, mature yolk spheres are constructed identically and are composed of three elements: cortex layer, matrix and crystals. Histochemical tests show that polysaccharides are present in the yolk spheres. Lipid droplets have been observed in the ooplasm; they develop without visible contact with any of the organelles. Among the reserve materials the following have been found: rough endoplasmic reticulum, dictyosomes, polyribosomes, mitochondria and a few microtubules.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00215316
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  • 4
    Digitale Medien
    Digitale Medien
    Oogenesis in Campodea sp. (Diplura) (1979)
    Springer
    Cell & tissue research 202 (1979), S. 133-143 
    Details
    ISSN: 1432-0878
    Schlagwort(e): Oogenesis ; Yolk formation ; Nurse cells ; Ultrastructure ; Diplura
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Medizin
    Notizen: Summary The egg chamber of Campodea consists of a group of nurse cells and an oocyte, and is surrounded by a simple, markedly flattened follicular epithelium. Three types of yolk occur in the oocytes: type I appears within elements of the rough endoplasmic reticulum; type II is produced by specific complexes of endoplasmic reticulum and dictyosomes; type III is incorporated by micropinocytosis. Histochemical tests show that mature yolk spheres contain proteins and polysaccharides. The main function of the nurse cells is to synthesize RNA, but they also produce small amounts of type I yolk. Phylogenetic conclusions are drawn from this and other studies of oogenesis in apterygote insects.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00239226
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  • 5
    Digitale Medien
    Digitale Medien
    Ultrastructural studies on oogenesis in Symphyla (1979)
    Springer
    Cell & tissue research 202 (1979), S. 145-153 
    Details
    ISSN: 1432-0878
    Schlagwort(e): Oogenesis ; Yolk formation ; Ultrastructure ; Symphyla
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Medizin
    Notizen: Summary The paired ovaries of Symphyla are sac-shaped. Their interior is filled with synchronously developing oocytes surrounded by a simple follicular epithelium. Previtellogenic oocytes have spherical or oval nuclei, the latter containing a large number of small nucleoli. Part of the nuclear surface is covered by a thick “coat” made up of a granular substance of medium electron density. The “coat” is penetrated by cisternae of the smooth endoplasmic reticulum. Micropinocytosis is the principal source of yolk in Symphyla; a small amount of yolk material arises within the mitochondrial cristae. Vitellogenic oocytes are characterized by a highly active rough endoplasmic reticulum synthesizing a material, probably lipoprotein in nature, which is incorporated into lipid droplets.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00239227
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  • 6
    Digitale Medien
    Digitale Medien
    Oogenesis in Acerentomon gallicum Jonescu (Protura) (1977)
    Springer
    Cell & tissue research 179 (1977), S. 401-412 
    Details
    ISSN: 1432-0878
    Schlagwort(e): Oogenesis ; Yolk formation ; Follicle cells ; Ultrastructure ; Protura
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Medizin
    Notizen: Summary Late stages of oogenesis in Acerentomon gallicum Jonescu have been studied by means of light and electron microscopy. Each of the two ovaries of this species consists of a single panoistic ovariole. Late previtellogenic and early vitellogenic oocytes are enclosed in an electron opaque layer, the so-called primary sheath. The precursors for this sheath are most likely synthesized by follicle cells. The yolk develops through autosynthesis, with free ribosomes, dictyosomes and lamellar bodies being involved in the process. Mature yolk spheres contain proteins and polysaccharides. Besides the organelles that take part in vitellogenesis, mitochondria and cisternal stacks of the rough endoplasmic reticulum occur in the ooplasm.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00221110
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  • 7
    Digitale Medien
    Digitale Medien
    Ultrastructural studies on oogenesis in symphyla (1981)
    Springer
    Cell & tissue research 215 (1981), S. 431-436 
    Details
    ISSN: 1432-0878
    Schlagwort(e): Oogenesis ; Cortical granules ; Chorion ; Ultrastructure
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Medizin
    Notizen: Summary In the oocytes of Hanseniella nivea, cortical granules are formed in the peripheral ooplasm during late stages of oogenesis. Single Golgi elements are involved in the process. Concurrent with the formation of cortical granules is the appearance of a chorion on the oocyte surface. Precursors of this envelope are most likely synthesized by follicle cells.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00239126
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