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  • 1
    Electronic Resource
    Electronic Resource
    Evolution of sea urchin non-repetitive DNA (1980)
    Springer
    Journal of molecular evolution 16 (1980), S. 95-110 
    Details
    ISSN: 1432-1432
    Keywords: Evolutionary Divergence ; DNA ; Single copy ; Thermal Stability ; S1 Nuclease ; Hydroxyapatite
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary New methods have been applied to the determination of single copy DNA sequence differences between the sea urchin speciesStrongylocentrotus purpuratus, S. franciscanus, S. drobachiensis, andLytechinus pictus. The thermal stability of interspecies DNA duplexes was measured in a solvent (2.4 M tetraethylammonium chloride) that suppresses the effect of base composition on melting temperature. The lengths of duplexes were measured after digestion with S1 nuclease and correction made for the effect of length on thermal stability. The degree of base substitution that has occurred in the single copy DNA during sea urchin evolution is significantly larger than indicated by earlier measurements. We estimate that 19% of the nucleotides of the single copy DNA are different in the genomes of the two sea urchin congeners,S. purpuratus, andS. franciscanus, which apparently diverged only 15 to 20 million years ago.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01731580
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  • 2
    Electronic Resource
    Electronic Resource
    Insertion of a short repetitive sequence (D881) in a sea urchin gene: A typical interspersed repeat? (1984)
    Springer
    Journal of molecular evolution 20 (1984), S. 195-201 
    Details
    ISSN: 1432-1432
    Keywords: DNA ; Mobile genetic element ; Enhancer ; Rare maternal transcript
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary A comparison has been made between the Sp88 gene regions of the DNAs of the sea urchinsStrongylocentrotus purpuratus (Sp.) andStrongylocentrotus drobachiensis (Sd.). Examination of the 3′ terminal part of the transcribed region revealed a short repetitive sequence present in Sd. but absent from Sp. A 12-nucleotide sequence present once in Sp. is almost perfectly duplicated at both ends of the repeat in Sd., suggesting that a mobile repeat was inserted in the Sd. genome. Other members of this family of repeated sequences occur in many interspersed locations in the genomes of both species. Except for the insertion duplication, the inserted sequence lacks direct or reverse repeats.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02104726
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  • 3
    Electronic Resource
    Electronic Resource
    Freeze-fracture studies on the cockroach hemocyte membrane complex: Symmetric and asymmetric membrane particle distributions (1974)
    Springer
    Cell & tissue research 151 (1974), S. 385-394 
    Details
    ISSN: 1432-0878
    Keywords: Membrane particles ; Cockroach hemocytes ; Freeze-fracture ; Electron microscopy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary Freeze-fracture studies were conducted on the membranes of normal cockroach hemocytes. The plasmalemma is asymmetric with the A fracture face containing 80–100 Å membrane intercalated particles at a concentration of ∼2500/μ2. The B fracture face contains 120–150 Å particles with a relatively low density (∼800/μ2). The nuclear envelope displays an asymmetry with the A fracture face containing ∼1500 particles/μ2 and the B face containing ∼300/μ 2. No significant particle size differences were observed in nuclear envelope fracture faces. Two types of symmetric membranes were also found in these cells. Both A and B fracture faces of the membrane surrounding the numerous cytoplasmic inclusion bodies contain particle sizes and concentrations similar to the B face of the plasmalemma. A second type of symmetry was observed in cells apparently engaged in “exocytosis”. Vesicles (∼0.1 μD) from this process were completely particle free on both fracture faces. Such particle free vesicles could be found in the cytoplasm, attached to the plasmalemma, or completely separated from the cell.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00224548
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  • 4
    Electronic Resource
    Electronic Resource
    Double membrane-bounded intestinal microvilli in Oncopeltus fasciatus (1983)
    Springer
    Cell & tissue research 232 (1983), S. 593-600 
    Details
    ISSN: 1432-0878
    Keywords: Peritrophic membrane ; Insect ; Microvilli ; Electron microscopy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary A double plasma membrane (DPM) surrounding intestinal microvilli of the migratory milkweed bug, Oncopeltus fasciatus, is described. Mutant and wild types of the phytophagous insect have been studied by conventional SEM and TEM procedures with the use of membrane-enhancing staining methods. Longitudinal and transverse sections revealed a DPM surrounding microvilli and continuing over the apical portions of the intestinal cell. The outer membrane of the DPM contributes to an intestinal lining or peritrophic membrane (PTM), which apparently accumulates in layers. SEM studies reveal a rugose intestinal surface and complete PTM in both starved and fed insects. Only rarely are exposed microvilli seen by SEM. SEM examinations also enable the observation of numerous blebs on the luminal side of the PTM apparently held in position by a neck-like attachment and apparently derived from the outer membrane of the DPM. Preliminary TEM studies of microvilli revealed unique microvesicle-like structures, lying just inside the inner membrane of the DPM, which may be of membrane origin based on their typical trilaminar appearance after en bloc staining with uranyl acetate. Highly ordered microfilaments were observed to occupy the most central aspect of the microvilli.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00216431
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