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Showing papers on "Metaphase published in 1985"


Journal ArticleDOI
01 May 1985-Nature
TL;DR: In addition to the known transient rise of [Ca2+]i at fertilization, further peaks are now revealed during pronuclear migration, nuclear envelope breakdown, the metaphase/anaphase transition and cleavage.
Abstract: Although the regulation of events in the cell division cycle by calcium or other cations has been the subject of much interest and speculation, experimental studies have been hampered by the difficulty of measuring submicromolar intracellular free calcium concentrations ([Ca2+]i) over an entire cell cycle. We now describe experiments using a new fluorescent calcium chelator, fura-2 (see Fig. 1c for structure), for continuous measurement of [Ca2+]i from fertilization through the first cleavage of individual eggs of the sea urchin Lytechinus pictus. We also show for comparison the results of parthenogenetic activation by ammonia. In addition to the known transient rise of [Ca2+]i at fertilization, further peaks are now revealed during pronuclear migration, nuclear envelope breakdown, the metaphase/anaphase transition and cleavage. Parthenogenetic activation by ammonia also elicits a sustained rise starting at nuclear envelope breakdown.

572 citations


Journal ArticleDOI
TL;DR: Results indicate that microtubules forming within fertilized mouse oocytes are required for the union of the sperm and egg nuclei and raise questions about the paternal inheritance of centrioles in mammals.
Abstract: Microtubules forming within the mouse egg during fertilization are required for the movements leading to the union of the sperm and egg nuclei (male and female pronuclei, respectively). In the unfertilized oocyte, microtubules are predominantly found in the arrested meiotic spindle. At the time for sperm incorporation, a dozen cytoplasmic asters assemble, often associated with the pronuclei. As the pronuclei move to the egg center, these asters enlarge into a dense array. At the end of first interphase, the dense array disassembles and is replaced by sheaths of microtubules surrounding the adjacent pronuclei. Syngamy (pronuclear fusion) is not observed; rather the adjacent paternal and maternal chromosome sets first meet at metaphase. The mitotic apparatus emerges from these perinuclear microtubules and is barrel-shaped and anastral, reminiscent of plant cell spindles; the sperm centriole does not nucleate mitotic microtubules. After cleavage, monasters extend from each blastomere nucleus. The second division mitotic spindles also have broad poles, though by third and later divisions the spindles are typical for higher animals, with narrow mitotic poles and fusiform shapes. Colcemid, griseofulvin, and nocodazole inhibit the microtubule formation and prevent the movements leading to pronuclear union; the meiotic spindle is disassembled, and the maternal chromosomes are scattered throughout the oocyte cortex. These results indicate that microtubules forming within fertilized mouse oocytes are required for the union of the sperm and egg nuclei and raise questions about the paternal inheritance of centrioles in mammals.

358 citations


Journal ArticleDOI
01 Dec 1985-Cell
TL;DR: The results suggest that not all, if any, of the effects of H-rasval12 protein in this system are mediated by adenylate cyclase.

289 citations


Journal ArticleDOI
01 Mar 1985-Science
TL;DR: The locus for the alpha-chain T-cells receptor may participate in oncogene activation in T-cell tumors through translocations and inversions detectable in human T- cell leukemias and lymphomas.
Abstract: A human complementary DNA clone specific for the alpha-chain of the T-cell receptor and a panel of rodent X human somatic cell hybrids were used to map the alpha-chain gene to human chromosome 14 in a region proximal to the immunoglobulin heavy chain locus. Analysis by means of in situ hybridization of human metaphase chromosomes served to further localize the alpha-chain gene to region 14q11q12, which is consistently involved in translocations and inversions detectable in human T-cell leukemias and lymphomas. Thus, the locus for the alpha-chain T-cell receptor may participate in oncogene activation in T-cell tumors.

280 citations


Journal ArticleDOI
TL;DR: A human autoantiserum directed against pericentriolar material (PCM) was used to study the distribution of microtubule-organizing centers (MTOCs) in the oocyte and during the first cell cycle of mouse development.
Abstract: A human autoantiserum (5051) directed against pericentriolar material (PCM) was used to study the distribution of microtubule-organizing centers (MTOCs) in the oocyte and during the first cell cycle of mouse development. In oocytes, the PCM was found not only at the poles of the barrel-shaped metaphase II spindle but also at many discrete loci around the cytoplasm near the cell cortex. The spindle poles were also composed of several PCM foci. In metaphase-arrested eggs only the PCM foci located near the chromosomes acted as MTOCs. However, after reduction of the critical concentration for tubulin polymerization by taxol, the cytoplasmic PCM foci were also found to be associated with nucleation of microtubules. After fertilization the cortical PCM foci remained in a peripheral position until the end of the S phase, when they appeared to migrate centrally towards the pronuclei. At prometaphase of the first mitotic division, numerous MTOCs were found around the two sets of chromosomes; these MTOCs then aligned to form two bands on either side of the metaphase plate of the first mitosis.

257 citations


Journal ArticleDOI
TL;DR: Biotin labeling was found to be a rapid, consistent, and reliable technique to detect repeated DNA sequences by in situ hybridization in wheat and should be a useful technique for the physical mapping of DNA sequences on plant chromo- somes.
Abstract: A biotin-labeling technique was used to map a 120 bp rye DNA probe by in situ hybridization to somatic metaphase chromosomes of common wheat. Twenty-four hybrid- Ization sites were revealed on 11 chromosomes including 4A, 2D, 3D, 5D, and the seven B-genome chromosomes. The observed results were similar to those of previous studies that used isotope labeling. Biotin labeling was found to be a rapid, consistent, and reliable technique to detect repeated DNA sequences by in situ hybridization in wheat and should be a useful technique for the physical mapping of DNA sequences on plant chromo- somes.

238 citations


Journal ArticleDOI
TL;DR: The results confirm the predictions of the model in that when the inactivation centre is deleted from one of the X-chromosomes neither X present in a diploid cell can be inactivated, and in addition considerably further localize the position of the in activation centre on theX- chromosome.
Abstract: The predictions of a model for the initiation of X-chromosome inactivation based on a single inactivation centre were tested in a cytogenetic study using six different embryo-derived (EK) stem cell lines, each with a different-sized deletion of the distal part of one of the X-chromosomes. Metaphase chromosomes were prepared by the Kanda method from each cell line in the undifferentiated state and after induction of differentiation, and cytogenetic evidence sought for a dark-staining inactive X-chromosome. The results confirm the predictions of the model in that when the inactivation centre is deleted from one of the X-chromosomes neither X present in a diploid cell can be inactivated, and in addition considerably further localize the position of the inactivation centre on the X-chromosome.

213 citations


Journal ArticleDOI
01 Aug 1985-Cell
TL;DR: This work has obtained preparations that allow the visualization of several levels of chromosome structure that suggest that metaphase packing is achieved by the compaction through helical coiling of a 200-300 nm fiber that is in turn composed of radial loops.

204 citations


Journal ArticleDOI
TL;DR: Detailed studies of mitosis in Physarum polycephalum macroplasmodia suggest that cleavage of ubiquitin from the uH 2As and uH2B is a very late, possibly final event in chromosome condensation to metaphase chromosomes and that ubiquitination is an early event in their decondensation.

130 citations


Journal ArticleDOI
TL;DR: It is suggested that a flux of calcium, derived from the extracellular compartment, may cause the final splitting of sister chromosomes and trigger the onset of anaphase, however, once anaphases has begun, chromosome motion and cell plate initiation proceed normally even under conditions of extrace cellular calcium restriction.
Abstract: Agents that lower extracellular calcium concentration (EGTA) or modulate calcium transport (lanthanum or D600) have been applied to dividing stamen hair cells of Tradescantia and analyzed for their ability to change the following: (a) the time required to progress from nuclear envelope breakdown to the onset of anaphase (metaphase transit time), (b) the time required to progress from anaphase to the initiation of the cell plate, and (c) the rate of chromosome motion in anaphase Control cells complete metaphase in 32 min, initiate a cell plate in 19 min, and display a chromosome motion rate of 145 micron/min If cells are treated with a calcium-EGTA buffer (pCa 8) for 4 h, the metaphase transit time is increased to 53 min without any change in the time of cell plate formation or the rate of chromosome motion Lanthanum and D600, under conditions in which their access to the plasmalemma has been facilitated by pretreating the cells with cutinase, also markedly extend metaphase and in several instances permanently arrest cells Lanthanum, however, produce little or no change in cell plate initiation or the rate of chromosome motion Microscopic observations of the mitotic apparatus in calcium-stressed cells reveal normal chromatin condensation and metaphase progression Chromosomes partly untwine but remain attached at their kinetochores It is suggested that a flux of calcium, derived from the extracellular compartment, may cause the final splitting of sister chromosomes and trigger the onset of anaphase However, once anaphase has begun, chromosome motion and cell plate initiation proceed normally even under conditions of extracellular calcium restriction

103 citations


Journal ArticleDOI
TL;DR: The random association of Epstein-Barr virus DNA with host cell metaphase chromosomes of all sizes in Burkitt's lymphoma-derived cell lines was demonstrated by two substantially different techniques, namely fluorescence-activated chromosome sorting and in situ hybridization.
Abstract: The random association of Epstein-Barr virus DNA with host cell metaphase chromosomes of all sizes in Burkitt's lymphoma-derived cell lines was demonstrated by two substantially different techniques, namely fluorescence-activated chromosome sorting and in situ hybridization. The nature and potential importance of this association are discussed.

Journal ArticleDOI
01 Jul 1985-Cell
TL;DR: The results suggest that the mutant phenotype of Drosophila melanogaster is due to an altered structural component of the spindle other than tubulins.

Journal ArticleDOI
TL;DR: Zygotes of Plasmodium berghei were cultured 15-25 h in vitro to yield mature infective ookinetes and observations are consistent with a haploid genome of 8-10 chromosomes.
Abstract: Zygotes of Plasmodium berghei were cultured 15–25 h in vitro to yield mature infective ookinetes. Samples taken in the first 5 h of culture were examined by electron microscopy. Meiotic figures were detected in the nuclei of the zygotes. Threadlike leptotene chromatids (chromosomes) condensed from attachment plaques on the nuclear envelope; chromatid pairing followed (zygotene), with synaptonemal complexes subsequently appearing (pachytene). These complexes persisted into metaphase but dissociated when the chromatids rapidly decondensed during anaphase. At telophase of the first meiotic division the kinetochores were retracted toward two small spindle complexes, which were found at widely separated poles in the nuclear envelope. The observations are consistent with a haploid genome of 8–10 chromosomes.

Journal ArticleDOI
TL;DR: The kinetochore fraction is seen to contain numerous small immunoperoxidase-positive masses which are morphologically similar to the centromere/kinetochores region of intact metaphase chromosomes.
Abstract: We have partially isolated the kinetochore and associated centromeric structures from mammalian metaphase chromosomes. Human autoantibodies from scleroderma CREST (calcinosis, Raynaud's phenomenon, esophageal dysmotility, sclerodactyly, telangiectasia) patients were used as immunofluorescent probes to monitor fractionation. The procedure includes digestion of total chromosomal DNA with micrococcal nuclease, dehistonization with heparin, and dissociation of the remaining material with detergent and urea. We used a density gradient (metrizamide) to obtain an enriched fraction of stained material (kinetochore). When examined by electron microscopy, the kinetochore fraction is seen to contain numerous small immunoperoxidase-positive masses which are morphologically similar to the centromere/kinetochore region of intact metaphase chromosomes. The particulate fraction that contains kinetochore components represents less than 5% of total chromosomal proteins and contains less than 1% of total DNA. Two polypeptides of 18 and 80 kD were identified as kinetochore antigens by immunoblotting with CREST antiserum. In this paper we discuss the distribution of these kinetochore polypeptides with the associated centromeric chromatin.

Journal ArticleDOI
Laura Manuelidis1
TL;DR: Mouse and human DNA sequences from centromeric and ribosomal domains were labeled with biotinylated deoxynucleotides and hybridized in situ to paraformaldehyde-fixed tissue culture cells, indicating a relative "movement" of centromeres, away from the nuclear membrane and toward the central nucleolar region.
Abstract: Mouse and human DNA sequences from centromeric and ribosomal domains were labeled with biotinylated deoxynucleotides and hybridized in situ to paraformaldehyde-fixed tissue culture cells. Centromeres were widely dispersed in most of these interphase nuclei. At late G2 phases of the cell cycle, centromeres appeared to coalesce and then to align in an orderly pattern, with discrete positional assignments for individuals chromosomes in metaphase and anaphase. Ribosomal cistrons were also organized in an orderly and defined fashion during mitosis. As soon as the nuclear membrane forms in early G1, centromeres rapidly disperse throughout the nucleus. Centromere patterns during G1 and S were indistinguishable in cultured cells, as determined by double-labeling experiments. Antibodies that bind to centric chromosomal proteins revealed the same patterns in cultured cells as those obtained with DNA sequence-specific probes. Large differentiated neurons display reproducible collections of centromeres in interphase that are very different from those seen in cultured cells. Neurons in widely divergent mammalian species, despite large differences in centromeric DNA sequences, maintain similar nuclear positions for these chromosomal segments. Similarly, ribosomal cistrons are positioned in comparable nuclear locales in neurons of divergent species. It is suggested that such arrangements reflect, or are necessary for, the function of a given cell type. Studies of large cerebellar neurons at critical times in development indicated a relative "movement" of centromeric domains, away from the nuclear membrane and toward the central nucleolar region. It is possible that the orderly and temporal positioning of centromeric, as well as of other chromosomal regions, is based on protein-nucleic acid interactions. Implications for trisomy 21 and other disorders involving chromosomal rearrangements, such as transposition, are considered from this perspective.

Journal Article
TL;DR: Application of a modified immunofluorescence technique using an anti-kinetochore serum enables cytogeneticists to obtain quality metaphase spreads and to localize kinetochores in patients with a 45, XX, -9, -11, tdic constitution.
Abstract: Application of a modified immunofluorescence technique using an anti-kinetochore serum enables cytogeneticists to obtain quality metaphase spreads and to localize kinetochores. In a patient with a 45, XX, -9, -11, tdic (9p;11p) constitution, we found that the dicentric marker chromosome has an intensely fluorescent kinetochore (no. 11), the functional centromere, and a less intensely fluorescent kinetochore (no. 9), the inactive centromere. The data suggest that in the process of tandem fusion (telomere-telomere between 11p and 9p), the centromere of chromosome 9 was not deleted, but, rather, inactivated.

Journal ArticleDOI
TL;DR: The Miller spreading procedure was applied to mouse metaphase spreads of methotrexate-resistant 3T3 cells that contain large numbers of minute chromosomes and dihydrofolate reductase genes, finding no evidence that the DNA in minutes is linear.
Abstract: The Miller spreading procedure was applied to mouse metaphase spreads of methotrexate-resistant 3T3 cells that contain large numbers of minute chromosomes and dihydrofolate reductase genes. There is substantial variation in both size and numbers of minutes in individual cells, the smallest of which (estimated as 5 × 103 kilobase pairs) would be undetected by standard light microscopic analyses. Minute chromosomes are composed of nucleosomal chromatin, which is organized into typical higher order fibers that are folded to form rosette-like structures characteristic of normal chromosome organization. There is no evidence that the DNA in minutes is linear. Minutes exist singly and in pairs, and members of a pair are connected by higher order chromatin fibers, suggesting that they are topologically interlocked. They are often closely apposed to chromosomal telomeres or arms, a configuration that may be involved in their distribution at mitosis. In addition to typical minutes, which do not possess kinetochores, a small marker chromosome possessing all of the features of a centromere region is present in parental and resistant cells. An unusual feature of this cell line is the retention of resistance, minute chromosomes, and amplified dihydrofolate reductase genes; most methotrexate-resistant mouse cell lines with minute chromosomes lose these properties when grown in the absence of methotrexate.

Journal Article
TL;DR: In situ hybridization of a recombinant cDNA probe containing the human alpha 1-antitrypsin gene to metaphase chromosomes demonstrated significant hybridization to chromosomal segment 14q31-32.
Abstract: In situ hybridization of a recombinant cDNA probe containing the human alpha 1-antitrypsin gene to metaphase chromosomes demonstrated significant hybridization to chromosomal segment 14q31-32. A high percentage of cells analyzed (31%) displayed labeling on chromosome 14. Of all labeled sites on chromosome 14, 60% were found on segment 14q31-32. These results refine the previous assignment of the human alpha 1-antitrypsin gene to segment 14q24.1-32.1.

Journal ArticleDOI
01 Feb 1985-Heredity
TL;DR: Although total nucleolar volume differs between cells at different stages of development, the genetic variation influencing volume appears to have similar effects in root tip, premeiotic and young pollen cells.
Abstract: The major nucleoli in the wheat variety Chinese Spring are formed at the nucleolus organisers (NORs) on chromosomes 1B and 6B. Minor nucleoli are formed from the NORs on chromosomes 5D and 1A. Nucleolar volume is poorly correlated with the number of ribosomal RNA genes in the NOR region. The nucleolus on chromosome 1B is twice the volume of that on chromosome 6B even though only half as many ribosomal RNA genes reside at the 1B locus compared with the number at the 6B locus. Nucleolus size is correlated with the size of the NOR constriction seen in metaphase chromosomes. When major NORs are deleted, the volumes of the remaining nucleoli increase to compensate for the deletions. Varying the dosage of many of the chromosomes in the total complement influences the volume of the minor nucleoli. Chromosomes 1D and 6B have been shown to carry genes regulating total nucleolar volume. Although total nucleolar volume differs between cells at different stages of development, the genetic variation influencing volume appears to have similar effects in root tip, premeiotic and young pollen cells.

Journal ArticleDOI
TL;DR: It is concluded that the assembly of a certain, large fraction of microtubule subunits into stable microtubules is dependent on the presence of chromosomes, and Chromosome-dependent regulation of micro Tubule length may account for some features of normal mitosis.
Abstract: We extracted chromosomes by micromanipulation from Melanoplus differentialis spermatocytes, producing metaphase spindles with only one or a few chromosomes instead of the usual complement of 23. Cells with various numbers of chromosomes were prepared for electron microscopy, and spindle microtubule length was measured. A constant increment of microtubule length was lost upon the removal of each chromosome; we estimate that only approximately 40% of the original length would remain in the total absence of chromosomes. Unexpectedly, kinetochore microtubules were not the only ones affected when chromosomes were removed: nonkinetochore microtubules accounted for a substantial fraction of the total length lost. No compensatory increase in microtubule length outside the spindle was found. Studies by others show that the kinetochore microtubules of extracted chromosomes are left behind in the cell and dissassemble. The resulting increase in subunit concentration would be expected from in vitro studies to drive microtubule assembly until the original total microtubule length was restored, but that did not happen in these living cells. We conclude that the assembly of a certain, large fraction of microtubule subunits into stable microtubules is dependent on the presence of chromosomes. Possible explanations include (a) limits on microtubule length that prevent any net assembly of the subunits released after chromosomes are removed or (b) a promotion of microtubule assembly by chromosomes, which therefore is reduced in their absence. Chromosome-dependent regulation of microtubule length may account for some features of normal mitosis.

Journal ArticleDOI
TL;DR: Prometaphase I chromosome behavior was examined in wild-type Drosophila melanogaster primary spermatocytes and results suggest that most chromosome motions can be explained by poleward forces acting on or through kinetochore microtubules that span the distance between the kinetchore and the vicinity of a pole.
Abstract: Prometaphase I chromosome behavior was examined in wild-type Drosophila melanogaster primary spermatocytes. Cine analysis of live cells reveals that bivalents exhibit complex motions that include (1) transient bipolar orientations, (2) simultaneous reorientation of homologous kinetochores, (3) movements not parallel to the spindle axis, and (4) movement along the nuclear membrane. --Kinetochores and kinetochore microtubule have been analyzed for bivalents previously studied in life. The results suggest that most chromosome motions (complex though they may be) can be explained by poleward forces acting on or through kinetochore microtubules that span the distance between the kinetochore and the vicinity of a pole. The results also suggest that the majority of short kinetochore microtubules may be remnants of previous microtubule-mediated associations between a kinetochore and a pole.

Journal ArticleDOI
TL;DR: Results are taken to imply that individual nuclei in these polykaryons can control cyclin distribution and DNA synthesis in spite of the fact that they share a common cytoplasm.
Abstract: Nuclear patterns of cyclin (PCNA) distribution that subdivide S-phase (determined using PCNA autoantibodies specific for this protein) as well as [3H]thymidine incorporation followed by autoradiography have been used to determine the S-phase synchrony of homophasic polykaryons produced by polyethylene glycol (PEG)-induced fusion of populations of mitotic transformed human amnion cells (AMA) exhibiting the following average distribution of phases: prophase, 9%, metaphase, 60% (including early and late prometaphase), anaphase, 3.8%, telophase, 26.2% and interphase, 1%. Both synchronous and asynchronous polykaryons were generated from these fusions; the latter being frequently observed only amongst populations of multinucleated cells having three or more nuclei. These results are taken to imply that individual nuclei in these polykaryons can control cyclin distribution and DNA synthesis in spite of the fact that they share a common cytoplasm.

Journal ArticleDOI
TL;DR: Although meiotic maturation was induced in both animals by specific hormones which have been previously shown to release Ca2+ within cytoplasm, InsP3 microinjection into prophasearrested oocytes did not release them from prophase block.

Journal ArticleDOI
TL;DR: It is suggested that chromosomes in lymphocytes from old donors express more damage after exposure to [3H]Tdr or BrdU than do chromosomes inymphocytes from young donors.
Abstract: Lymphocytes from young and old donors were incubated with PHA for 96 h and exposed to [3H]Tdr during the last 24 h of culture. Comparable amounts of [3H]Tdr were incorporated into chromosomes of old and young lymphocytes as measured by autoradiography of metaphase chromosomes. However, chromosomal damage and cell-cycle arrest were far greater in lymphocytes from old as compared to young humans. The frequency of chromosome breaks, fragments, exchange figures and dicentric chromosomes induced by [3H]Tdr was greater in cultures from old than in cultures from young humans. Lymphocytes from old donors exposed to 20 μM BrdU during the last 24 h of culture showed significantly more sister-chromatid exchanges than did lymphocytes from young donors. These data suggest that chromosomes in lymphocytes from old donors express more damage after exposure to [3H]Tdr or BrdU than do chromosomes in lymphocytes from young donors.

Journal ArticleDOI
TL;DR: The internal distribution revealed by this study is compared with the data in the literature, especially with the conflicting data obtained by other methods used to determine the interphase arrangement of chromosomes.
Abstract: The in situ spatial distribution of nucleolus-organizing-region (NOR) bearing chromosomes in relation to the inactive X chromosome was studied during interphase in human fibroblasts. The respective positions of these chromosomes were examined in 30 growing and 32 resting fibroblasts from reconstructed nuclei, using nucleoli and the Barr body as ultrastructural markers. Experimental values for the distance between the nucleoli and the Barr body were estimated by their coefficient of closeness and compared to the uniform distribution. The following results were obtained: the distribution patterns for the two populations of nuclei were similar, the distribution of the NOR-bearing chromosomes in relation to the inactive X chromosome varied and differed significantly from a uniform distribution, and in many cases the Barr body was observed to be in a juxta-nucleolar position. The internal distribution revealed by this study is compared with the data in the literature, especially with the conflicting data obtained by other methods used to determine the interphase arrangement of chromosomes. The relationship between interphase and metaphase arrangements such as can be deduced with these methods, is discussed in relation to the mechanisms of the formation of metaphase plates or chromatid translocations.

Journal ArticleDOI
TL;DR: A restriction endonuclease fragment derived from a cloned portion of human genomic DNA corresponding to the myelin basic protein gene has been used to map the position of this gene by in situ hybridization to human metaphase chromosomes.
Abstract: A restriction endonuclease fragment derived from a cloned portion of human genomic DNA corresponding to the myelin basic protein gene has been used to map the position of this gene by in situ hybridization to human metaphase chromosomes. Ten percent of the radioactively labeled sites observed were on chromosome 18. Eighty-four percent of the grains on chromosome 18 were located within the region corresponding to 18q22→qter. This represents a greater than 10-fold increase in labeling at this position over the background grain distribution found along all of the other chromosomes.

Journal ArticleDOI
TL;DR: Chromosomal mapping of the Thy-1 gene by hybridization to metaphase chromosomes and Southern blots of DNA from hybrid cells indicate that the Thy -1 gene is located on the long arm of chromosome 11.
Abstract: We have isolated the gene coding for human Thy-1. Introduction of this gene into HeLa cells by DNA-mediated transfer results in the expression of Thy-1 antigen on the cell surface. Chromosomal mapping of the Thy-1 gene by hybridization to metaphase chromosomes and Southern blots of DNA from hybrid cells indicate that the Thy-1 gene is located on the long arm of chromosome 11.

Journal Article
TL;DR: The possibility is raised that TGF-alpha might contribute to tumor progression in these cases of Burkitt's lymphoma, because of the variant Burkitt lymphoma translocation t(2;8) occur within these bands.
Abstract: Transforming growth factors (TGFs) are defined as biologically active polypeptides which reversibly confer the transformed phenotype onto untransformed cultured cells TGF-alpha shows sequence homology with epidermal growth factor and competes with epidermal growth factor for binding to the epidermal growth factor receptor, stimulating the phosphorylation of the receptor TGF-alpha is secreted by many transformed cells and may be involved in embryonic development A cloned human TGF-alpha gene was used to map the locus for the TGF-alpha precursor to the short arm of human chromosome 2, region 2p11----2p13, by Southern blotting techniques with DNA prepared from rodent X human somatic cell hybrids These hybrids contained different subsets of human chromosomes and included a set with a translocation between human chromosomes 1 and 2 [t(1;2) (q32;q13)] In situ hybridization of the TGF-alpha probe to normal human metaphase spreads confirmed these data and localized TGF-alpha more precisely to bands 2p11----2p13 Breakpoints in the variant Burkitt lymphoma translocation t(2;8) occur within these bands Such a t(2;8) translocation could place TGF-alpha next to c-myc in band 8q24 The possibility is raised that TGF-alpha might contribute to tumor progression in these cases of Burkitt's lymphoma

Journal ArticleDOI
TL;DR: The distribution of U snRNAs during mitosis was studied by indirect immunofluorescence microscopy with snRNA cap-specific anti-m3G antibodies as mentioned in this paper, which showed that most of the snRNPs present in sonicates of mitotic cells do not sediment as free RNP particles, but remain associated with high molecular weight (HMW) structures other than chromatin.

Journal ArticleDOI
TL;DR: Evidence was obtained to suggest that procentrioles elongate progressively during the subsequent stages of the cell cycle, and that they start to separate from their parents during mitosis.
Abstract: An investigation of the centriole cycle was based on serial-section electron microscopy of the centrioles of 790 3T3 cells and 40 CHO cells (incomplete sets of sections were excluded from the analysis). Time-course studies indicated that procentrioles first appear 4 h after the start of S-phase; evidence was obtained to suggest that they elongate progressively during the subsequent stages of the cell cycle, and that they start to separate from their parents during mitosis. An association of the structural features of the centriole cycle with the Two-transition Model of the Cell Cycle was ruled out by the finding of two centrioles in most quiescent cells, and the appearance of procentrioles in S-phase in transiently stimulated cells.