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  • Polymer and Materials Science  (37)
  • Molecular Sequence Data  (23)
  • Cell & Developmental Biology
  • Engineering General
  • Organic Chemistry
  • 2010-2014  (13)
  • 1990-1994  (77)
  • 1935-1939  (4)
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  • 1
    Publication Date: 2010-03-09
    Description: The tumour suppressor ARF is specifically required for p53 activation under oncogenic stress. Recent studies showed that p53 activation mediated by ARF, but not that induced by DNA damage, acts as a major protection against tumorigenesis in vivo under certain biological settings, suggesting that the ARF-p53 axis has more fundamental functions in tumour suppression than originally thought. Because ARF is a very stable protein in most human cell lines, it has been widely assumed that ARF induction is mediated mainly at the transcriptional level and that activation of the ARF-p53 pathway by oncogenes is a much slower and largely irreversible process by comparison with p53 activation after DNA damage. Here we report that ARF is very unstable in normal human cells but that its degradation is inhibited in cancerous cells. Through biochemical purification, we identified a specific ubiquitin ligase for ARF and named it ULF. ULF interacts with ARF both in vitro and in vivo and promotes the lysine-independent ubiquitylation and degradation of ARF. ULF knockdown stabilizes ARF in normal human cells, triggering ARF-dependent, p53-mediated growth arrest. Moreover, nucleophosmin (NPM) and c-Myc, both of which are commonly overexpressed in cancer cells, are capable of abrogating ULF-mediated ARF ubiquitylation through distinct mechanisms, and thereby promote ARF stabilization in cancer cells. These findings reveal the dynamic feature of the ARF-p53 pathway and suggest that transcription-independent mechanisms are critically involved in ARF regulation during responses to oncogenic stress.〈br /〉〈br /〉〈a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3737736/" target="_blank"〉〈img src="https://static.pubmed.gov/portal/portal3rc.fcgi/4089621/img/3977009" border="0"〉〈/a〉   〈a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3737736/" target="_blank"〉This paper as free author manuscript - peer-reviewed and accepted for publication〈/a〉〈br /〉〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Chen, Delin -- Shan, Jing -- Zhu, Wei-Guo -- Qin, Jun -- Gu, Wei -- P01 CA080058/CA/NCI NIH HHS/ -- P01 CA097403/CA/NCI NIH HHS/ -- R01 CA085533/CA/NCI NIH HHS/ -- R01 CA118561/CA/NCI NIH HHS/ -- R01 CA129627/CA/NCI NIH HHS/ -- R01 CA131439/CA/NCI NIH HHS/ -- England -- Nature. 2010 Mar 25;464(7288):624-7. doi: 10.1038/nature08820. Epub 2010 Mar 7.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Institute for Cancer Genetics, and Department of Pathology and Cell Biology College of Physicians & Surgeons, Columbia University, 1130 St Nicholas Avenue, New York, New York 10032, USA.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/20208519" target="_blank"〉PubMed〈/a〉
    Keywords: ADP-Ribosylation Factors/*metabolism ; Cell Line ; Fibroblasts/metabolism ; *Gene Expression Regulation ; Humans ; Molecular Sequence Data ; Nuclear Proteins/metabolism ; Proto-Oncogene Proteins c-myc/metabolism ; Stress, Physiological/*physiology ; Tumor Suppressor Protein p53/*metabolism ; U937 Cells ; Ubiquitin-Protein Ligases/metabolism ; Ubiquitination
    Print ISSN: 0028-0836
    Electronic ISSN: 1476-4687
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
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  • 2
    Publication Date: 1991-12-09
    Description: The three-dimensional structure of an active, disulfide cross-linked dimer of the ligand-binding domain of the Salmonella typhimurium aspartate receptor and that of an aspartate complex have been determined by x-ray crystallographic methods at 2.4 and 2.0 angstrom (A) resolution, respectively. A single subunit is a four-alpha-helix bundle with two long amino-terminal and carboxyl-terminal helices and two shorter helices that form a cylinder 20 A in diameter and more than 70 A long. The two subunits in the disulfide-bonded dimer are related by a crystallographic twofold axis in the apo structure, but by a noncrystallographic twofold axis in the aspartate complex structure. The latter structure reveals that the ligand binding site is located more than 60 A from the presumed membrane surface and is at the interface of the two subunits. Aspartate binds between two alpha helices from one subunit and one alpha helix from the other in a highly charged pocket formed by three arginines. The comparison of the apo and aspartate complex structures shows only small structural changes in the individual subunits, except for one loop region that is disordered, but the subunits appear to change orientation relative to each other. The structures of the two forms of this protein provide a step toward understanding the mechanisms of transmembrane signaling.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Milburn, M V -- Prive, G G -- Milligan, D L -- Scott, W G -- Yeh, J -- Jancarik, J -- Koshland, D E Jr -- Kim, S H -- AI 30725/AI/NIAID NIH HHS/ -- DK09765/DK/NIDDK NIH HHS/ -- New York, N.Y. -- Science. 1991 Nov 29;254(5036):1342-7.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Department of Chemistry, University of California, Berkeley 94720.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/1660187" target="_blank"〉PubMed〈/a〉
    Keywords: Amino Acid Sequence ; Aspartic Acid/metabolism ; Binding Sites ; Disulfides/analysis ; Hydrogen Bonding ; Models, Molecular ; Molecular Sequence Data ; Protein Conformation ; *Receptors, Amino Acid ; Receptors, Cell Surface/*chemistry/metabolism ; Salmonella typhimurium/metabolism ; X-Ray Diffraction
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 3
    Publication Date: 1990-01-26
    Description: A synthetic peptidemimetic substrate of the human immunodeficiency virus 1 (HIV-1) protease with a nonhydrolyzable pseudodipeptidyl insert at the protease cleavage site was prepared. The peptide U-81749 inhibited recombinant HIV-1 protease in vitro (inhibition constant Ki of 70 nanomolar) and HIV-1 replication in human peripheral blood lymphocytes (inhibitory concentration IC50 of 0.1 to 1 micromolar). Moreover, 10 micromolar concentrations of U-81749 significantly inhibited proteolysis of the HIV-1 gag polyprotein (p55) to the mature viral structural proteins p24 and p17 in cells infected with a recombinant vaccinia virus expressing the HIV-1 gag-pol genes. The HIV-1 like particles released from inhibitor-treated cells contained almost exclusively p55 and other gag precursors, but not p24. Incubation of HIV-like particles recovered from drug-treated cultures in drug-free medium indicated that inhibition of p55 proteolysis was at least partially reversible, suggesting that U-81749 was present within the particles.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉McQuade, T J -- Tomasselli, A G -- Liu, L -- Karacostas, V -- Moss, B -- Sawyer, T K -- Heinrikson, R L -- Tarpley, W G -- New York, N.Y. -- Science. 1990 Jan 26;247(4941):454-6.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Infectious Disease Research Unit, Upjohn Company, Kalamazoo, MI 49001.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/2405486" target="_blank"〉PubMed〈/a〉
    Keywords: Amino Acid Sequence ; Antiviral Agents/*pharmacology ; DNA, Viral/genetics ; Endopeptidases/*metabolism ; Fusion Proteins, gag-pol/genetics/metabolism ; Gene Products, gag/metabolism ; HIV Protease ; HIV-1/*drug effects/genetics/physiology ; Humans ; Lymphocytes/microbiology ; Molecular Sequence Data ; Molecular Structure ; Oligopeptides/*pharmacology ; Protease Inhibitors/*pharmacology ; Protein Precursors/metabolism ; RNA, Viral/metabolism ; Transfection ; Virus Replication/drug effects
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 4
    Publication Date: 1992-03-20
    Description: The highly symmetric pyruvate dehydrogenase multienzyme complexes have molecular masses ranging from 5 to 10 million daltons. They consist of numerous copies of three different enzymes: pyruvate dehydrogenase, dihydrolipoyl transacetylase, and lipoamide dehydrogenase. The three-dimensional crystal structure of the catalytic domain of Azotobacter vinelandii dihydrolipoyl transacetylase has been determined at 2.6 angstrom (A) resolution. Eight trimers assemble as a hollow truncated cube with an edge of 125 A, forming the core of the multienzyme complex. Coenzyme A must enter the 29 A long active site channel from the inside of the cube, and lipoamide must enter from the outside. The trimer of the catalytic domain of dihydrolipoyl transacetylase has a topology identical to chloramphenicol acetyl transferase. The atomic structure of the 24-subunit cube core provides a framework for understanding all pyruvate dehydrogenase and related multienzyme complexes.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Mattevi, A -- Obmolova, G -- Schulze, E -- Kalk, K H -- Westphal, A H -- de Kok, A -- Hol, W G -- New York, N.Y. -- Science. 1992 Mar 20;255(5051):1544-50.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Department of Chemistry, University of Groningen, The Netherlands.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/1549782" target="_blank"〉PubMed〈/a〉
    Keywords: Amino Acid Sequence ; Animals ; Azotobacter vinelandii/enzymology ; Chloramphenicol O-Acetyltransferase/genetics ; Humans ; Models, Molecular ; Molecular Sequence Data ; Molecular Structure ; Pyruvate Dehydrogenase Complex/*chemistry/genetics ; Sequence Homology, Nucleic Acid
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 5
    Publication Date: 1990-04-06
    Description: The epidermal growth factor (EGF) receptor (EGFR) can efficiently couple with mitogenic signaling pathways when it is transfected into interleukin-3 (IL-3)-dependent 32D hematopoietic cells. When expression vectors for erbB-2, which is structurally related to EGFR, or its truncated counterpart, delta NerbB-2, were introduced into 32D cells, neither was capable of inducing proliferation. This was despite overexpression and constitutive tyrosine kinase activity of their products at levels associated with potent transformation of fibroblast target cells. Thus, EGFR and erbB-2 couple with distinct mitogenic signaling pathways. The region responsible for the specificity of intracellular signal transduction was localized to a 270-amino acid stretch encompassing their respective tyrosine kinase domains. Thus, tissue- or cell-specific regulation of growth factor receptor signaling can occur at a point after the initial interaction of growth factor with receptor. Such specificity in signal transduction may account for the selection of certain oncogenes in some malignancies.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Di Fiore, P P -- Segatto, O -- Taylor, W G -- Aaronson, S A -- Pierce, J H -- New York, N.Y. -- Science. 1990 Apr 6;248(4951):79-83.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Laboratory of Cellular and Molecular Biology, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/2181668" target="_blank"〉PubMed〈/a〉
    Keywords: Animals ; Base Sequence ; Cell Division ; Cell Line ; DNA/genetics ; DNA, Recombinant ; Fibroblasts/cytology/metabolism ; Gene Expression ; Genetic Vectors ; Hematopoietic Stem Cells/cytology/metabolism ; Immunoblotting ; Mice ; *Mitogens ; Molecular Sequence Data ; Protein-Tyrosine Kinases/genetics/*physiology ; Proto-Oncogene Proteins/genetics/*physiology ; Receptor, Epidermal Growth Factor/genetics/*physiology ; Sequence Homology, Nucleic Acid ; Signal Transduction ; Transfection
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 6
    Publication Date: 2011-02-08
    Description: Geographic atrophy (GA), an untreatable advanced form of age-related macular degeneration, results from retinal pigmented epithelium (RPE) cell degeneration. Here we show that the microRNA (miRNA)-processing enzyme DICER1 is reduced in the RPE of humans with GA, and that conditional ablation of Dicer1, but not seven other miRNA-processing enzymes, induces RPE degeneration in mice. DICER1 knockdown induces accumulation of Alu RNA in human RPE cells and Alu-like B1 and B2 RNAs in mouse RPE. Alu RNA is increased in the RPE of humans with GA, and this pathogenic RNA induces human RPE cytotoxicity and RPE degeneration in mice. Antisense oligonucleotides targeting Alu/B1/B2 RNAs prevent DICER1 depletion-induced RPE degeneration despite global miRNA downregulation. DICER1 degrades Alu RNA, and this digested Alu RNA cannot induce RPE degeneration in mice. These findings reveal a miRNA-independent cell survival function for DICER1 involving retrotransposon transcript degradation, show that Alu RNA can directly cause human pathology, and identify new targets for a major cause of blindness.〈br /〉〈br /〉〈a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3077055/" target="_blank"〉〈img src="https://static.pubmed.gov/portal/portal3rc.fcgi/4089621/img/3977009" border="0"〉〈/a〉   〈a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3077055/" target="_blank"〉This paper as free author manuscript - peer-reviewed and accepted for publication〈/a〉〈br /〉〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Kaneko, Hiroki -- Dridi, Sami -- Tarallo, Valeria -- Gelfand, Bradley D -- Fowler, Benjamin J -- Cho, Won Gil -- Kleinman, Mark E -- Ponicsan, Steven L -- Hauswirth, William W -- Chiodo, Vince A -- Kariko, Katalin -- Yoo, Jae Wook -- Lee, Dong-ki -- Hadziahmetovic, Majda -- Song, Ying -- Misra, Smita -- Chaudhuri, Gautam -- Buaas, Frank W -- Braun, Robert E -- Hinton, David R -- Zhang, Qing -- Grossniklaus, Hans E -- Provis, Jan M -- Madigan, Michele C -- Milam, Ann H -- Justice, Nikki L -- Albuquerque, Romulo J C -- Blandford, Alexander D -- Bogdanovich, Sasha -- Hirano, Yoshio -- Witta, Jassir -- Fuchs, Elaine -- Littman, Dan R -- Ambati, Balamurali K -- Rudin, Charles M -- Chong, Mark M W -- Provost, Patrick -- Kugel, Jennifer F -- Goodrich, James A -- Dunaief, Joshua L -- Baffi, Judit Z -- Ambati, Jayakrishna -- NIHU10EY013729/EY/NEI NIH HHS/ -- P30 EY006360/EY/NEI NIH HHS/ -- P30 EY014800/EY/NEI NIH HHS/ -- P30 EY014800-07/EY/NEI NIH HHS/ -- P30 EY021721/EY/NEI NIH HHS/ -- P30EY003040/EY/NEI NIH HHS/ -- P30EY008571/EY/NEI NIH HHS/ -- P30EY06360/EY/NEI NIH HHS/ -- R01 EY018350/EY/NEI NIH HHS/ -- R01 EY018350-05/EY/NEI NIH HHS/ -- R01 EY018836/EY/NEI NIH HHS/ -- R01 EY018836-04/EY/NEI NIH HHS/ -- R01 EY020672/EY/NEI NIH HHS/ -- R01 EY020672-02/EY/NEI NIH HHS/ -- R01 GM068414/GM/NIGMS NIH HHS/ -- R01EY001545/EY/NEI NIH HHS/ -- R01EY011123/EY/NEI NIH HHS/ -- R01EY015240/EY/NEI NIH HHS/ -- R01EY015422/EY/NEI NIH HHS/ -- R01EY017182/EY/NEI NIH HHS/ -- R01EY017950/EY/NEI NIH HHS/ -- R01EY018350/EY/NEI NIH HHS/ -- R01EY018836/EY/NEI NIH HHS/ -- R01EY020672/EY/NEI NIH HHS/ -- R01GM068414/GM/NIGMS NIH HHS/ -- R01HD027215/HD/NICHD NIH HHS/ -- R21 EY019778/EY/NEI NIH HHS/ -- R21 EY019778-02/EY/NEI NIH HHS/ -- R21AI076757/AI/NIAID NIH HHS/ -- R21EY019778/EY/NEI NIH HHS/ -- RC1 EY020442/EY/NEI NIH HHS/ -- RC1 EY020442-02/EY/NEI NIH HHS/ -- RC1EY020442/EY/NEI NIH HHS/ -- T32HL091812/HL/NHLBI NIH HHS/ -- Howard Hughes Medical Institute/ -- England -- Nature. 2011 Mar 17;471(7338):325-30. doi: 10.1038/nature09830. Epub 2011 Feb 6.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Department of Ophthalmology & Visual Sciences, University of Kentucky, Lexington, Kentucky 40506, USA.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/21297615" target="_blank"〉PubMed〈/a〉
    Keywords: Alu Elements/*genetics ; Animals ; Cell Death ; Cell Survival ; Cells, Cultured ; DEAD-box RNA Helicases/*deficiency/genetics/metabolism ; Gene Knockdown Techniques ; Humans ; Macular Degeneration/*genetics/*pathology ; Mice ; MicroRNAs/metabolism ; Molecular Sequence Data ; Oligonucleotides, Antisense ; Phenotype ; RNA/*genetics/*metabolism ; Retinal Pigment Epithelium/enzymology/metabolism/pathology ; Ribonuclease III/*deficiency/genetics/metabolism
    Print ISSN: 0028-0836
    Electronic ISSN: 1476-4687
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  • 7
    Publication Date: 1994-05-20
    Description: 〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Broder, C C -- Nussbaum, O -- Gutheil, W G -- Bachovchin, W W -- Berger, E A -- New York, N.Y. -- Science. 1994 May 20;264(5162):1156-9; author reply 1162-5.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/7909959" target="_blank"〉PubMed〈/a〉
    Keywords: Animals ; Antigens, CD4/*physiology ; Antigens, Differentiation, T-Lymphocyte/*physiology ; Base Sequence ; *Cell Fusion ; Cell Line ; Dipeptidyl Peptidase 4 ; Gene Products, env/*physiology ; Giant Cells/physiology ; HIV-1/*physiology ; Humans ; Hybrid Cells ; Molecular Sequence Data
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 8
    Publication Date: 1993-05-28
    Description: The retinoblastoma gene product (Rb) is a nuclear phosphoprotein that regulates cell cycle progression. Elf-1 is a lymphoid-specific Ets transcription factor that regulates inducible gene expression during T cell activation. In this report, it is demonstrated that Elf-1 contains a sequence motif that is highly related to the Rb binding sites of several viral oncoproteins and binds to the pocket region of Rb both in vitro and in vivo. Elf-1 binds exclusively to the underphosphorylated form of Rb and fails to bind to Rb mutants derived from patients with retinoblastoma. Co-immunoprecipitation experiments demonstrated an association between Elf-1 and Rb in resting normal human T cells. After T cell activation, the phosphorylation of Rb results in the release of Elf-1, which is correlated temporally with the activation of Elf-1-mediated transcription. Overexpression of a phosphorylation-defective form of Rb inhibited Elf-1-dependent transcription during T cell activation. These results demonstrate that Rb interacts specifically with a lineage-restricted Ets transcription factor. This regulated interaction may be important for the coordination of lineage-specific effector functions such as lymphokine production with cell cycle progression in activated T cells.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Wang, C Y -- Petryniak, B -- Thompson, C B -- Kaelin, W G -- Leiden, J M -- R01 AI29673-01/AI/NIAID NIH HHS/ -- New York, N.Y. -- Science. 1993 May 28;260(5112):1330-5.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Department of Medicine, University of Chicago, IL 60637.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/8493578" target="_blank"〉PubMed〈/a〉
    Keywords: Amino Acid Sequence ; Animals ; Base Sequence ; Binding Sites ; Cell Cycle ; Cell Line ; DNA-Binding Proteins/chemistry/*metabolism ; Eye Neoplasms/genetics ; Humans ; Lymphocyte Activation ; Molecular Sequence Data ; Mutation ; Oligodeoxyribonucleotides ; Phosphorylation ; Recombinant Fusion Proteins/metabolism ; Retinoblastoma/genetics ; Retinoblastoma Protein/*metabolism ; T-Lymphocytes/immunology/*metabolism ; Transcription Factors/chemistry/*metabolism ; Transcription, Genetic
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  • 9
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 20 (1937), S. 1059-1077 
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 1. Azoprotein (sowohl in vitro hergestelltes als in vivo entstehendes) enthält entsprechend der Annahme von Pauly die Azo-gruppierung —N=N—.
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  • 10
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Journal of Morphology 204 (1990), S. 177-196 
    ISSN: 0362-2525
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: This light and transmission electron microscopical study shows that the first polar body is given off before ovulation and that part of its cell membrane and that of the surrounding oocyte have long microvilli at the time of its ejection. Several layers of cumulus cells initially surround the secondary oocyte and first polar body, but the ovulated oocytes in the oviducts in the process of being fertilized do not have cumulus cells around them. Partly expelled second polar bodies occur in the oviduct; they are elongated structures that lack organelles and have electron-dense nuclei. A small fertilization cone appears to form around the sperm tail at the time of sperm entry into the egg and an incorporation cone develops around the sperm head in the egg cytoplasm. In three fertilized eggs a small hole was seen in the zona, which was presumably formed by the spermatozoon during penetration. Cortical granules, present in ovarian oocytes, are not seen in fertilized tubal or uterine eggs; release of their contents probably reduces the chances of polyspermy, although at least one polyspermic fertilized egg was seen and several other fertilized eggs had spermatozoa within the zona pellucida. In the zygote the pronuclei come to lie close together, but there was no evidence of fusion. A “yolk mass,” which becomes eccentric before ovulation, is extruded by the time the two-cell embryos are formed, but many vacuoles remain in the non-yolky pole of the egg. A shell membrane of variable thickness is present around all uterine eggs but its origin remains undetermined.
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