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  • Articles  (4)
  • Springer  (4)
  • 1
    ISSN: 1432-0886
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract Using in situ nucleic acid hybridizations, the genes that code for 28, 18 and 5S rRNA have been localized in the polytene chromosomes of Drosophila tumiditarsus. The 5S genes are found at a single site near the centromere of the second chromosome, whereas the 28 and 18S genes are found at the nucleolar organizer region of the dot chromosome. The dot chromosome has been previously described as α-heterochromatic. However, our cytochemical and autoradiographic results do not support such a conclusion. The autoradiographic results reveal that the dot chromosome is transcriptionally active and is not late-replicating, as is expected of α-heterochromatin. Further, the dot chromosomes possess none of the usual staining characteristics of heterochromatin except for its lack of polytene bands. Using rRNA-DNA filter hybridizations, we find that the rDNA of D. tumiditarsus salivary glands is under-replicated. This is the first species of Drosophila where the rDNA in not found on the sex chromosomes, and is the first report of an under-replicated autosomal locus which is not located in heterochromatic blocks.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1432-0878
    Keywords: Oogenesis ; Drosophila ; Ultrastructure ; Nurse cells ; Follicle cells
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary During stages 11 and 12, follicle cells surrounding the nurse cells produce lysosomes which presumably aid in the breakdown of the nurse cells. Accompanying a DNA reduction in nurse cell nuclei are several characteristic morphological changes including the appearance of intranuclear rod-like structures and nuclear granules about 300 Å in diameter. Similarities between structures seen in Drosophila nurse cell nuclei and those seen in other organisms are discussed.
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  • 3
    ISSN: 1432-0878
    Keywords: Vitelline membrane ; Chorion ; Ephestia ; Follicle cell ; Ultrastructure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary Ultrastructural studies on developing egg chambers of the moth, Ephesita kühniella reveal that the precursors of the vitelline membrane are synthesized within follicle cells which are in contact with the oocyte. The vitelline membrane precursors appear to be synthesized by the rough-surfaced endoplasmic reticulum, and this material apparently moves to the Golgi cisternae where the definitive vitelline membrane precursor body is produced. The previtelline bodies are then secreted into the spaces between the oocyte and follicle cells, where they fuse to form a continuous membrane. Chorion formation begins with the deposition of a layer of tubules at the outer edge of the vitelline membrane which coalesce to form the inner edge of a thin, striated layer. In subsequent stages, several compartmented layers are rapidly secreted external to the striated layer, giving rise to the mature chorion.
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  • 4
    ISSN: 1432-0878
    Keywords: Oogenesis ; Drosophila melanogaster ; Follicle cell ; Membrane formation ; Vitelline membrane
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary Electron microscopic studies of oogenesis in Drosophila melanogaster suggest that the ovarian follicle cells alone are responsible for the secretion of the vitelline membrane and chorion. The synthesis and assembly of the vitelline membrane is a complex process involving several stages of development and different populations of follicle cells. This combined autoradiographic and ultrastructural investigation of vitelline membrane formation has led to the conclusion that the protein component of the vitelline membrane is synthesized in the follicle cells, and that these cells possess a mechanism which directs the polarized synthesis and deposition of vitelline membrane and chorion in response to contact by a specific cell, the oocyte. Under certain aberrant conditions, however, other cell types may serve to induce formation of these membranes. The concept of Drosophila egg coverings as maternal cuticle is also discussed, with regard to the embryonic origin of secreting cells, the requirement for adjacent cells as inducers, and the differences in ultrastructural mechanisms of formation.
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