Browsing by Subject "Nuclear matrix"

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    Localization and functions of steroid hormone receptors
    (Murcia : F. Hernández, 1998) Yamashita, S.
    This review focuses on the subcellular localization of steroid hormone receptors (SHRs), taking into account the technical problems of immunohistochemistry and the characteristics of nuclear localization signals (NLSs) of each receptor, on the interaction between SHKs and cellular components, and on the possible roles of sex SHRs in the reproductive organs. It is concluded that SHRs are basically localized in the nucleus, regardless of hormonal status, and that considerable amounts of unliganded SHRs may be present in the cytoplasm of target cells in exceptional cases. Most immunohistochemical results that demonstrate nuclear translocation of liganded SHRs seem to be responsible for insufficient fixation. Immunoelectron microscopy shows that SHRs associate with the chromatin in absence or presence of hormones and that intranuclear translocation of liganded SHRs from the condensed chromatin to euchromatin which observed in some cell types, may be a passive process caused by a consequence of conformational changes in the chromatin binding receptors. Histochemical data suggest that the nuclear matrix (NM) is not a main binding site of liganded SHRs in the nucleus. The artificial formation of intermolecular disulfide bonds during NM preparation presumably causes the entrapment of liganded SHRs into the fraction. It seems that heat shock protein 90 (hsp90) does not form stable complexes with unliganded receptors in vivo, and it interacts with SHRs transiently cooperating with other heat shock proteins as a chaperone that helps folding of newly synthesized and refolding of denatured receptors. Estrogens transiently induce a number of nuclear protooncogenes, such as c-fos and c-jun family proteins, which act as transcription factors through estrogen receptor (ER) system in the endometrial epithelium of mature and immature rodents. Therefore, it is suggested that the changes in concentrations of these gene products trigger the proliferation and differentiation of uterine epithelium. In addition, ER system, not only in stroma cells but in the epithelia1 cells appears to participate in the growth response and abnormalities of epithelium elicited by the exogenous estrogen treatment at the neonatal period.
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    The nuclear matrix: a critical appraisal
    (Murcia : F. Hernández, 1996) Martelli, A.M.; Cocco, L.; Riederer, B.M.; Neri, L.M.
    It is becoming increasingly clear that the cell nucleus is a highly structurized organelle. Because of its tight compartmentalization, it is generally believed that a framework must exist, responsible for maintaining such a spatial organization. Over the last twenty years many investigations have been devoted to identifying the nuclear framework. Structures isolated by different techniques have been obtained in vitro and are variously referred to as nuclear matrix, nucleoskeleton or nuclear scaffold. Many different functions, such as DNA replication and repair, mRNA transcription, processing and transport have been described to occur in close association with these structures. However, there is still much debate as to whether or not any of these preparations corresponds to a nuclear framework that exists in vivo. In this article we summarize the most commonly-used methods for obtaining preparations of nuclear frameworks and we also stress the possible artifacts that can be created in vitro during the isolation procedures. Emphasis is placed also on the protein composition of the frameworks as well as on some possible signalling functions that have been recently' described to occur in tight association with the nuclear matrix.