1,721,013 research outputs found
Reconstitution of gametes for assisted reproduction
No full textEichenlaub-Ritter U. Reconstitution of gametes for assisted reproduction. HUMAN REPRODUCTION. 2003;18(3):473-475.There are basically two major problems in the genesis of 'cloned' gametes in mammals, which have not been addressed in the original debate article. There is no adequate discussion on the mechanisms providing for high fidelity of chromosome segregation in mitosis and meiosis, and for proper imprinting in construction of 'reconstituted gametes'. The original debate article is uncritical with respect to the currently insufficient database and the incomplete documentation of results
Development of female germcells
No full textEichenlaub-Ritter U. Development of female germcells. Gynäkologische Endokrinologie . 2018;16(4):220-229
Expression in in-vivo and in-vitro growing and maturing oocytes: focus on regulation of expression at the translational level
No full textEichenlaub-Ritter U, Peschke M. Expression in in-vivo and in-vitro growing and maturing oocytes: focus on regulation of expression at the translational level. HUMAN REPRODUCTION UPDATE. 2002;8(1):21-41.Studies of expression in in-vivo and in-vitro maturing oocytes have the potential to elucidate signalling pathways involved in the intricate crosstalk between the oocyte and its somatic compartment during differentiation and morphogenetic processes, and the origin of disturbances in oocyte maturation possibly involved in reduced fertility. This review summarizes data on expression studies with focus on regulation of expression at the translational level in the maturing oocyte. The regulation of gene expression at the translational level as analysed in in-vitro maturing oocytes is complex and highly conserved between different species. It is characterized by differential degradation, and by storage and recruitment of distinct maternal mRNAs involving conserved consensus sequences in the 5' or 3' untranslated regions (UTRs) of mRNAs. Proteins interacting with such sequences affect the temporal 3' polyadenylation, and bring the 5' and, 3' UTRs of mRNAs into close proximity for efficient initiation of translation. Post-translational modifications of mRNA-associated proteins contribute to maturation- and developmentally controlled and to cell cycle-dependent expression. New methodologies for analysis of ovary-specific gene expression and function of genes in oogenesis,are also reviewed, e.g. RT-PCR, SAGE-PCR, real-time rapid cycle fluorescence monitored RT-PCR, differential display techniques, and microinjection of anti-sense RNA, double-stranded RNAs or mRNAs expressing green fluorescent protein-tagged proteins into maturing oocytes
Preantral follicle culture and oocyte quality
No full textHeiligentag M, Eichenlaub-Ritter U. Preantral follicle culture and oocyte quality. REPRODUCTION FERTILITY AND DEVELOPMENT. 2017;30(1):18-43.The formation of high-quality oocytes depends on complex stage-specific interactions between the germ cell and the somatic compartment involving endocrine, paracrine, and autocrine regulation. Cooperativity in bidirectional signalling and metabolism in response to factors in the microenvironment drive growth, proliferation, cell cycle regulation, spindle formation and the establishment of epigenetic marks in oocytes. This is essential to ensure faithful chromosome segregation and to achieve high oocyte quality, with far-reaching consequences for embryo survival, development and the health of offspring. Oocytes reach developmental capacity throughout early meiotic stages up to full growth and acquisition of nuclear and cytoplasmic maturational competence during folliculogenesis. Improved preantral follicle culture in which ideally intimate contacts between oocyte and somatic cells are retained provides unique opportunities to assess the effects of microenvironment, growth factors, hormones, cryopreservation and environmental exposure on folliculogenesis and oocyte quality. An optimised follicle culture can contribute to the generation of highquality oocytes for use in fertility preservation in cancer patients, animal breeding and the preservation of endangered species. The past decade has brought about major advances in follicle culture from different species. Recent advances in preantral follicle culture are discussed to assess the effects of environment, adverse exposure, cryopreservation and age on oocyte quality
Nondisjunction, disturbances in spindle structure, and characteristics of chromosome alignment in maturing oocytes of mice heterozygous for Robertsonian translocations
No full textEichenlaub-Ritter U, Winking H. Nondisjunction, disturbances in spindle structure, and characteristics of chromosome alignment in maturing oocytes of mice heterozygous for Robertsonian translocations. Cytogenetic and Genome Research. 1990;54(1-2):47-54
Aurora kinase B, epigenetic state of centromeric heterochromatin and chiasma resolution in oocytes
No full textVogt E, Kipp A, Eichenlaub-Ritter U. Aurora kinase B, epigenetic state of centromeric heterochromatin and chiasma resolution in oocytes. REPRODUCTIVE BIOMEDICINE ONLINE. 2009;19(3):352-368.Aurora kinases comprise a family of phosphoproteins performing multiple functions in mitosis and meiosis. Because Aurora kinase B (AURKB) expression is altered in aged oocytes and there is only limited information on its function in meiosis, it was decided to study the spatial distribution and co-localization of AURKB with other regulatory proteins at centromeres during mouse oocyte maturation. AURKB associates with chromosomes after germinal vesicle breakdown, is enriched at centromeres from prometaphase I and transits to the spindle midzone at late anaphase I. Preferential inhibition of AURKB by low concentrations of ZM 447439 inhibitor prevents polar body formation and affects spindle formation and chromosome congression at meiosis I, associated with expression of BubR1 checkpoint protein at kinetochores. Release of cohesion between sister chromatids appears inhibited resulting in failure of chiasma resolution in oocytes progressing to anaphase I. Concomitantly, the inhibitor reduces histone H3 lysine 9 trimethylation at centromeric heterochromatin and affects chromosome condensation. The cytokinesis arrest protects young, healthy oocytes from errors in chromosome segregation although increasing polyploidy. This study shows that changes in activity of AURKB may increase risks for chromosome non-disjunction and aneuploidy in mammalian oocytes, irrespective of age
Differential chromosome behaviour in mammalian oocytes exposed to the tranquilizer diazepam in vitro
No full textSun FY, Yin H, Eichenlaub-Ritter U. Differential chromosome behaviour in mammalian oocytes exposed to the tranquilizer diazepam in vitro. MUTAGENESIS. 2001;16(5):407-417.There are several reports demonstrating that aneugens may preferentially affect segregation of particular chromosomes in somatic cells. Much less is known on specific susceptibility of individual chromosomes to non-disjunction in mammalian meiosis in response to chemical exposures. To explore possible chromosome-specific behaviour and susceptibility to errors in chromosome segregation in mammalian oogenesis we employed spindle immunofluoresecence in combination with FISH with chromosome-specific probes to analyse congression of chromosomes X, 8 and 16 in diazepam (DZ)-treated, meiotically delayed meiosis I oocytes of the mouse. Concomitantly, we assessed the susceptibility of homologues to precociously segregate prior to anaphase I during DZ-induced meiotic arrest. About 50% of all oocytes exposed to 25 mug/ml DZ became meiotically delayed. Chromosomes failed to congress at the spindle equator in one-third of these meiosis I oocytes. The X chromosome was significantly more often located away from the spindle equator as compared with the expected random behaviour. Concomitantly, DZ exposure induced untimely segregation of homologous chromosomes of the gonosome and the autosomes in meiosis I. This occurred with similar frequencies. The observations confirm that DZ perturbs cell cycle progression, interferes with chromosome alignment, causes predivision and thus may predispose mammalian oocytes to errors in chromosome segregation. For the first time, chromosome-specific behaviour is reported in female meiosis in response to exposure to an aneugenic chemical
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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