Browsing by Subject "Meiosis"

Now showing 1 - 7 of 7
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    Cytogenetic analysis and morphology of malignant nuclear vlimata. The life cycle of malignant cells
    (Murcia : F. Hernández, 1994) Logothetou-Rella, H.
    The karyotype of malignant nuclear vlimata (NVs) was investigated with the in situ and chromosomal spreading techniques. NV metaphases were recognised by the head with tail morphology, kept in situ and evaluated by the chromosomal spreading technique. It was shown that malignant NVs were produced by random, uncontrolled meiosis. NVs contain and carry single, hypodiploid, haploid, hypohaploid, hyperdiploid and atypical sets of chromosomes. NVs are unstable parasitic cellular elements, invading the cytoplasm or the nucleus of host cells, extruding and implanting their chromosomes in the host cell upon contact. Within a malignant cell culture, NVs play the role of chromosomal donors and host cells of chromosomal recipients. NVs were identified as episomatic on host cell nuclei or incorporated into host cell metaphases. The observations are discusssed in terms of fertilization, vira1 infection and apoptosis. Comparison of malignant NVs with phytohaemagglutinin (PHA)-activated lymphocytic NVs is provided, as well as the life cycle of the malignant cells as follows: meiosis invasion Malignant cell - NVs - recipient host cell - hybrid cells NVs formation
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    Germ cell sex and cell cycle
    (F. Hernández y Juan F. Madrid. Universidad de Murcia: Departamento de Biología Celular e Histología, 2012) Miles, Denise C.; Western, Patrick S.
    Germ cells are the only cells in the body capable of transferring an individual’s genetic and epigenetic information to the next generation. However, the developmental processes that provide the foundation for male and female germ line development and later gamete production are complex and poorly understood. In mice the primordial germ cells enter the bipotential gonad at E10.5 and, in response to the testicular or ovarian micro-environment, commit to spermatogenesis or oogenesis. This paper reviews progress in understanding the molecular processes underlying the early stages of male and female germ line development.
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    Mammalian spermatogenesis investigated by genetic engineering
    (Murcia : F. Hernández, 1999) Escalier, D.
    Genes involved in mammal spermatogenesis can now be identified through mutants created by genetic engineering. Information has been obtained on male meiosis, but also on the factors regulating the proliferation, maintenance and differentiation of male germ cells. Its has also increased our knowledge of the germ cell phenotype emerging from an altered germ cell genotype. This review is focused on data from genes expressed in male germ cells and on the question of how germ cells and Sertoli cells cope with the molecular lesions induced. The conservation of a wild-type phenotype of male germ cells in mutant mice is discussed, and how the mouse genetic background can lead to different germ cell phenotypes for a given gene mutation.
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    Nuclear vlimata and aneuploidy in embryonic cells is caused by meiosis. Behaviour and properties of meiotic cells
    (Murcia : F. Hernández, 1995) Logothetou-Rella, H.
    This study demonstrates that human embryonic cells divide by meiosis. The use of trophoblastic tissue cells (early embryo) and amniotic cells (late embryo) exhibited the following characteristic events of meiosis: nuclear (NVs) and nucleolar (NuVs) vlimata formation; NV invasion in host cells; extrusion of chromosomes; nuclear fusion; metaphase fusion; hybrid cell formation; nuclear, nucleolar and cytoplasmic bridges, chromosomal transfer, variablesized nuclei; nuclear fragmentation; condensed meiotic chromosomes; "0" chromosome; and aneuploidy. Two types of nuclear bridges (NBs) were identified and defined as communicative tubules through which chromosomal transfer among cells is achieved. The wall of NBs is an extension of the nuclear membrane and the lumen contained chromosomal fusion substance (CFS). Embryonic cells formed glycosaminoglycan-sacs (GSGsacs) and rivulets, forming a cytoplasmic communicative system. The extracellular matrix (ECM), GSG-sacs and CFS were composed of glycosaminoglycan-bound protease. The protease which immuno-crossreacted with the al-chymotrypsin antiserum was the meiotic calciumactivated neutral proteinase (CANP). Cytogenetic analysis of early embryonic cells showed higher ratio of aneup1oidy:diploidy than late embryonic cells. The results are discussed in terms of differentiation-mitosis and undifferentiation-meiosis. These observations lead to an embryonic cell life cycle identical to that of malignant cells as follows: meiosis invasion Zygote & NVs and NuVs - recipient host nuclear fusion cells - hybrid cells-w organogenesis metaphase fusion + mitosis
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    Steroid receptors in the testis: implications in the physiology of prenatal and postnatal development and translation to clinical application
    (Universidad de Murcia. Departamento de Biología Celular e Histología, 2023) Rey, Rodolfo A.
    The testes are the main source of sex steroids in the male, especially androgens and to a lesser extent estrogens. In target cells, steroid hormones typically signal after binding to intracellular receptors, which act as transcription factors. Androgens and estrogens have ubiquitous functions in peripheral organs, but also have paracrine actions within the gonads where they are far more concentrated. The levels of steroid production by the testes vary throughout fetal and postnatal development: they are high in intrauterine life and in the first months after birth, then they decline and are almost undetectable in childhood and increase again during puberty to attain adult levels. The expression of the androgen and estrogen receptors also depict specific ontogenies in the various testicular cell types. The combination of intratesticular steroid concentration with the pattern of expression of the steroid hormone receptors defines androgen and estrogen action on Sertoli, germ and Leydig cells. Here, we review the ontogeny of expression of the androgen and estrogen receptors in the testis, its impact on testicular physiology during prenatal and postnatal development, as well as its implication on the pathophysiology of different disorders affecting gonadal function throughout life.
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    Synaptic behaviour of some structural and numerical chromosome anomalies in female and male rats (Rattus norvegicus)
    (Murcia : F. Hernández, 2001) Martínez Flores, I.; Egozcue, J.; Cabero, Ll.; García, M.
    The processes of synapsis and synaptic adjustment have been detected in some structural and numerical anomalies in two female rat foetuses and in one male rat in the course of a stu.dy on X-ray genotoxicity. The synaptic characteristics and adjustment of one pericentric inversion and a deletion have been analysed by electron microscopy in synaptonemal complex spreads from two female foetuses, and the synaptic behaviour of a trisomy has been studied in a testicular biopsy from an adult male. In a large proportion (frorn 50% to 90%) of the analysed cells, the abnormal meiotic configuration could not be detected either because the anomaly was present in mosaic from trisomy or because synaptic adjustment had already taken place (inversion) or as result of a combination of two of the above (deletion).
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    What are the germ cell phenotypes from infertile men telling us about spermatogenesis?
    (Murcia : F. Hernández, 1999) Escalier, D.
    Drosophila mutants for known genes and those obtained following germline genetic engineering in mice have led to the identification of genes involved in the initiation and the maintenance of spermatogenesis and in the different steps of meiosis. Mutants allow the definition of meiosis-specific checkpoint controls that ensure the transmission of complete and undamaged genetic information. They reveal what spermatogenesis events are interdependent. In the light of these data, an attempt is made to define which events of spermatogenesis could be defective in some well-defined human spermatogenesis failures. They appear to be good models to study the decouplages of spermatogenesis events, the morphogenetic relationships between germ cell structures and the occurrence of pleiotropic sperm phenotypes. It is discussed whether a germ cell with a normal phenotype can transmit a non-functional gene involved in spermatogenesis and how homologous genes can lead to different germ cell phenotypes depending on the species.