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  • 1
    Electronic Resource
    Electronic Resource
    Immunoelectron microscope localization of snRNPs in the polytene nucleus of salivary glands ofChironomus thummi (1990)
    Springer
    Chromosoma 99 (1990), S. 44-51 
    Details
    ISSN: 1432-0886
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract The ultrastructural distribution of small nuclear ribonucleoproteins (U1-snRNP and Sm antigen) in the nucleus ofChironomus salivary gland cells was investigated by means of specific antibodies and immunocytochemistry using colloidal gold complexes as markers. Particular attention was paid to the structural relationships of snRNPs with transcriptionally active areas in polytene chromosomes and with Balbiani ring granules. Our results demonstrate strong binding of anti-snRNP antibodies to RNP fibrils or the fibrillar network occurring within nuclear regions active in transcription (Balbiani rings or minor puffs). This confirms data reported previously on mammalian cells showing early association of snRNPs with nuclear fibrillar constituents containing newly synthesized pre-mRNA. In addition, Balbiani ring granules in the process of formation at the transcriptionally active sites were sometimes labeled on their periphery or on the transitory part between the granule and its precursor RNP fibril, while free granules observed in the nucleoplasm were virtually devoid of label. These findings suggest that mRNA processing, including splicing, takes place prior to the formation of mature Balbiani ring granules.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01737288
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  • 2
    Electronic Resource
    Electronic Resource
    Immunoelectron microscope localization of Mr 90000 heat shock protein and Mr 70000 heat shock cognate protein in the salivary glands of Chironomus thummi (1992)
    Springer
    Chromosoma 102 (1992), S. 50-59 
    Details
    ISSN: 1432-0886
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract The Mr 90000 heat shock protein (hsp 90) and one of the Mr 70000 heat shock cognate proteins (hsc 70) were localized by immunoelectron microscopy in salavary gland cells of normal and heat-shocked larvae of Chironomus thummi using polyclonal antibodies raised against Drosophila proteins. Immunoblotting after separation of proteins by gel electrophoresis shows that these antibodies cross-react with the corresponding proteins of Chironomus. Hsp 90 was localized both in the cytoplasm and in the nucleus, where it is associated with intrachromosomal and extrachromosomal ribonucleoprotein (RNP) fibrils, as well as with the peripheral region of compact chromatin. After heat shock the concentration of hsp 90 increases in the nucleus. This increase is prevented by actinomycin D administration during the heat shock. Hsp 90 is associated with the chromatin of puffs repressed by heat shock and with the RNP fibrils of actively transcribing heat shock puffs. Hsc 70 is mainly found in RNP fibrils and in the periphery of compact chromatin. During heat shock the concentration of hsc 70 decreases in the cytoplasm while it becomes more abundant in association with chromatin and intrachromosomal and extrachromosomal RNP fibrils. These results suggest a translocation of the existing protein from the cytoplasm toward the nucleus. They are supported by observations of the effect of heat shock carried out in the presence of actinomycin D.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00352290
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  • 3
    Electronic Resource
    Electronic Resource
    A new type of ribonucleoprotein constituent of the polytene nucleus of the salivary glands ofChironomus thummi andCh. tentans (1993)
    Springer
    Chromosoma 102 (1993), S. 693-699 
    Details
    ISSN: 1432-0886
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract Using electron spectroscopic imaging, a new type of small granular structural constituent has been observed in the extrachromosomal zone of the polytene nucleus of the salivary gland cells ofChironomus thummi andChironomus tentans. These granules appear isolated or in small clumps and are often seen to be connected with surrounding thin fibrils. They are stained by the EDTA procedure, which is preferential for nuclear ribonucleoprotein (RNP) constituents, and by the bismuth oxynitrate method for visualizing phosphorylated compounds. The granules are 15–23 nm in diameter and are digested by prolonged post-embedding RNAse hydrolysis. These structural elements contain the highest concentration of phosphorus in the interchromosomal space as revealed by electron energy loss spectroscopy. The small granules exhibit several morphological and cytochemical features in common with interchromatin granules, but they are not labeled with antibodies directed against extranucleolar small nuclear RNPs (snRNPs), as are interchromatin granules.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00650895
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  • 4
    Electronic Resource
    Electronic Resource
    Fine structural organization of a non-reticulate plant cell nucleus (1992)
    Springer
    Chromosoma 101 (1992), S. 311-321 
    Details
    ISSN: 1432-0886
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract We studied the fine structural organization of the meristematic nucleus in roots of Lycopesicon esculentum (tomato) using ultracytochemical and immunocytochemical approaches. The nucleus has a non-reticulate (i.e. low DNA content) structure whose supramolecular organization differs in some respects from that in reticulate nuclei, principally in the organization of the chromocentres associated with the nuclear envelope, with which centromeric structures appear to be associated. The main difference at the nucleolar level is found in the fibrillar centres, which have a low amount of DNA labelling and in which inclusions of condensed chromatin are present only very rarely. The distribution of nucleolar DNA amongst the nucleolar compartments is similar to that in reticulate nucleoli as demonstrated using an anti-DNA monoclonal antibody. Tomato nuclei have nucleolus-associated bodies or karyosomes, like other plant species with a low DNA content and non-reticulate nuclear organization. The nuclear ribonucleoprotein structures in the inter- and perichromatin regions, namely inter- and perichromatin fibrils and granules, show similar ultrastructural and cytochemical characteristics in both types of nuclei.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00346010
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  • 5
    Electronic Resource
    Electronic Resource
    Electron spectroscopic imaging analyses of the distribution of phosphorus in Balbiani ring granules and in the surrounding nucleoplasm (1997)
    Springer
    Chromosoma 105 (1997), S. 360-368 
    Details
    ISSN: 1432-0886
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract. The in situ distribution of phosphorus was studied in unstained ultrathin sections of salivary glands of Chironomus tentans and Ch. thummi larvae using elemental mapping by means of an energy-filtering transmission electron microscope. This distribution was related to the structures observed using contrast enhancement with inelastically scattered electrons at 250 eV. This procedure demonstrated that a phosphorus-containing fibril about 2 nm thick is the common substructure of the following nuclear ribonucleoprotein structural constituents: the Balbiani ring granules, their precursor fibrils seen at the sites of transcription, especially at the Balbiani rings, and the fibres traversing the pore of the nuclear envelope. These phosphorus-containing thin fibrils are sensitive to RNase. Thicker substructural features of the Balbiani ring granules, occurring as a curved ribbon on a dense particle, appear to be formed by the dense packing of the fine fibrils. The Balbiani ring granules located near the nuclear envelope are often linked to it by fine filaments.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004120050195
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  • 6
    Electronic Resource
    Electronic Resource
    Electron microscope study of the atretic oocytes of the rat (1967)
    Springer
    Cell & tissue research 80 (1967), S. 518-533 
    Details
    ISSN: 1432-0878
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary The ultrastructural aspect of ovular and follicular atresia were studied in 6–60 days old white rats. In pre-antrum folliculi two types of follicular cells were encountered, one, the more numerous, is a round clear cell, the other is dark and elongated. In antrum folliculi, vacuolization of the cytoplasm and nuclear pyknosis are seen. The disappearance of the prolongations of the follicular cells and ovular microvilli occur in all ages. The oocytes of atretic follicles may present the following changes: 1. lamellar alteration of the cytoplasmic matrix. It consists of clear zones devoid of cytoplasmic organelles (initial aspect) in which the disordered fibrous matrix organizes gradually in parallel lamella. Each lamella shows a regularly spaced longitudinal striation. 2. Changes in the distribution of the oocyte organelles; mitochondria, Golgi bodies, multivesicular bodies and clumps of vesicles which in the normal growing oocytes form a cortical and perinuclear layers are distributed at random in the cytoplasm like it occur in fertilized eggs. 3. Anomalous segmentation. Many oocytes undergo a process of segmentation. The segments are of unequal size, some of them are nucleated, others are devoid of a nucleus, Nuclei in an apparent process of amitotic division are frequently found, mitotic divisions are rare. Final stages of atresia are characterized by loss of contact of the oocytes with the corona cells, increase of the density of the cytoplasm in some cases or decrease in others. In the oocyte cytoplasm vacuolization and increase in density of the mitochondria are very intense. The oocyte outline changes as a consequence of a general shrinking of the oocyte. The last remnant of the follicle and oocyte within the ovary is the zona pellucida.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00330720
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  • 7
    Electronic Resource
    Electronic Resource
    Evidence for estrogen receptor expression in germ cell and somatic cell subpopulations in the ovary of the newly hatched chicken (1999)
    Springer
    Cell & tissue research 298 (1999), S. 145-152 
    Details
    ISSN: 1432-0878
    Keywords: Estrogen receptor Ovary Somatic cells Steroid receptors 17ß-Estradiol Chicken (White Leghorn)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract. Estrogens are involved in the gonadal morphogenesis of vertebrates, and almost all hormonal effects of 17ß-estradiol are mediated through specific receptors. At the time of sexual differentiation in the chicken, or even before, there is evidence of the presence of estrogen receptors and the secretion of 17ß-estradiol. However, no information is available regarding the cellular types that express the estrogen receptor in the immature chick ovary. The present study analyzes estrogen receptor expression in germ and somatic cells of the ovary in the newly hatched chicken. Highly purified cell subpopulations of germ and somatic cells were evaluated for specific 17ß-estradiol nuclear binding. In addition, the estrogen receptor was localized at the ultrastructural level by the immunogold technique. Finally, reverse transcription and polymerase chain reaction procedures detected a steady-state level of mRNA for the estrogen receptor. Somatic cells including typical steroidogenic cells showed specific 17ß-estradiol nuclear binding, displayed the estrogen receptor, and possessed estrogen receptor transcripts. The same result was observed in primary oocytes, together with the ultrastructural localization of estrogen receptor in extended chromatin filaments. Our experimental data support the hypothesis that estrogens are involved in the function of somatic and germ cells subpopulations in the immature chicken ovary.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004419900088
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  • 8
    Electronic Resource
    Electronic Resource
    Electron microscope study of the developing nerve terminals in the acoustic organs of the chick embryo (1968)
    Springer
    Cell & tissue research 92 (1968), S. 325-338 
    Details
    ISSN: 1432-0878
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary The stages of growth of the acoustic pathway (peripheral branch) were studied with the electron microscope in serial sections of the acoustic organs of 3 to 7 day chick embryos. Migration of cells from the acoustic epithelium was found at three days of incubation. These cells are presumably the futur ganglion cells. Fascicles of nerve fibers penetrate the epithelium through gaps of the basement membrane at 4–5 days of incubation. A dilatation develops in the intraepithelial fibers at about six days and thin and long prolongations grow from these dilatations and distribute among the cells. In the course of the next day the fibers embrace the foot of the sensory cell and the prolongations become shortened. Many of these extensions are charged with vesicles. At this stage (seven days) specialized structures (synaptic bars) differentiate in the region of the sensory cell contacting the large nerve ending (calix) or its short extensions. Each cell may show several synaptic bars, and each prolongation may contact with more than one cell.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00455590
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