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PubMed1987

The human inactivated X chromosome folds in early metaphase, prometaphase, and prophase.

The inactivated X chromosome has a site of unusually frequent folding in region Xq1, whereas a fold in Xq1 is uncommon on the active X. We investigated the pattern of X chromosome folding in high-resolution GTG- and RBG-stained preparations from four women. In early metaphase cells, slightly more than 50% of late-replicating Xs folded at Xq1----Xq21, compared with about 6% of early replicating Xs. The late-replicating X folded in about 80% of prometaphase cells; the early, in only about 14% of these cells. and the late-replicating X folded in 19 of 20 prophase cells. Occasionally, one X had an omega-shaped loop or apparent physical connection between Xq13 and Xq21.1. It is possible that a segment of Xq1 never completely uncoils and may help to provide continuity for the Barr body from one interphase to the next.

Chromosome Banding↗
PubMed1983

A light- and electron microscopic analysis of meiotic prophase in female mice.

In the paper we describe meiotic prophase of female mice on successive days of embryonic and early postnatal development. For this purpose we used three different techniques on ovarian material, i.e., Giemsa staining for the light microscopic study of chromatin, silver staining for the light microscopic study of the synaptonemal complex (SC), and agar filtration followed by uranyl acetate staining for the electron microscopic study of the SC. In all types of preparation it was impossible to distinguish leptotene stages, and we conclude that if leptotene really exists, it is of very short duration.--Two types of zygotene stages were found: the "normal" one, resembling zygotene stages in male mice, and a second type that has never been described in males and is characterized by, probably stable, unpaired regions together with totally unpaired axial elements of the SC.--The duration of pachytene was found to be 3-4 days, which is considerably shorter than in males. During early diplotene despiralization of the chromatin and disintegration of the axes of the SC were usually found together with desynapsis.--A considerable variation in distribution of meiotic stages was found between different litters in the same day of gestation. Fetuses in the same litter showed no significant variation. However, the oocytes in an ovary did not pass through meiosis synchronously, with differences up several days. The appearance of chromosomes in a highly contracted state could not be interpreted as a preleptotene condensation stage but probably is a mitotic phenomenon.

Animals↗
PubMed1988

Two major components of synaptonemal complexes are specific for meiotic prophase nuclei.

Monoclonal antibody II52F10 was elicited against purified synaptonemal complexes (SCs); it recognizes two major components of the lateral elements of SCs, namely an Mr = 30,000 and an Mr = 33,000 protein. We studied the distribution of the antigens of II52F10 within tissues and cells of the male rat by immunoblot analysis and immunocytochemical techniques. Nuclear proteins from various cell types, including spermatogonia and spermatids, did not react with antibody II52F10 on immunoblots; the same holds for proteins from isolated mitotic chromosomes. As expected, an Mr = 30,000 and an Mr = 33,000 protein from spermatocyte nuclei did react with the antibody. In cryostat sections of liver, brain, muscle and gut we could not detect any reaction with II52F10. In the testis the reaction was confined to SCs or SC fragments. Partly on the basis of indirect evidence we identified the antigen-containing cells as zygotene up to and including post-diffuse diplotene spermatocytes. The persistence of some antigen-containing fragments in the earliest stages of spermatids could not be excluded. We conclude that the lateral elements (LEs) of SCs are not assembled by rearrangement of pre-existing components of the nucleus: at least two of their major components are newly synthesized, presumably during zygotene. Furthermore we conclude partly from indirect evidence that the major components of the LEs of SCs are not involved in the chromosome condensation processes that take place during the earliest stages of meiotic prophase.

Animals↗
PubMed1979

Light microscope analysis of meiotic prophase chromosomes by silver staining.

A method is described for the silver staining of the synaptonemal complex in surface-spread mammalian spermatocytes for light microscope examination. The method is quick, reliable, of broad applicability, and provides a means of making karyotype analysis at meiotic prophase. Many hundreds of suitable cells can be examined in an average preparation in a relatively short space of time. It has so far been applied only to mammalian spermatocytes, but could be used for karyotype analysis in oocytes of mammals and also applied to gonocytes of non-mammalian species.

Animals↗
PubMed1985

The prophase stages in human foetal oocytes studied by light and electron microscopy.

The progression of the prophase stages of meiosis in human foetal ovaries is reported from a series of aborted foetuses spanning the first two trimesters of gestation. A surface-spreading technique allowed cells to be examined at both light and electron microscope levels. The pachytene stage was specifically examined for evidence of synaptic or other abnormalities. Two observations of interest are the relatively high incidence with which errors of pairing occur and second the state of thickening observed when such unpaired axes are stained with silver.

Cells, Cultured↗
PubMed1990

Telomere and centromere DNA are associated with the cores of meiotic prophase chromosomes.

Mouse (Mus musculus) whole-mount, surface-spread, meiotic prophase chromosomes have an axial core structure, the synaptonemal complex, SC, from which extend chromatin loops. This arrangement permits a novel approach to the analysis of chromosome structure. Using in situ hybridization, the types of DNA sequences preferentially associated with the SC and the types located primarily in the chromatin loops can be determined. With biotinylated probes, detected by avidin conjugated to FITC, we present evidence for differential chromatin-SC interaction. The telomere sequence (TTAGGG)n is associated exclusively with the two ends of each autosomal SC rather than with the chromatin loops. The minor satellite DNA sequences are predominantly localized to the centromeric region of the SC, as defined by CREST serum anti-centromere antibodies. In contrast, the major satellite DNA probe hybridizes to the chromatin loops of the centromeric heterochromatin, and a probe containing a LINE sequence hybridizes to chromatin loops in general with no obvious preference for the SC. These observations demonstrate that, depending on the type of DNA sequence, the chromatin has different properties in regard to its association with the SC.

Animals↗
PubMed1995

Identification of functional domains in the Sep1 protein (= Kem1, Xrn1), which is required for transition through meiotic prophase in Saccharomyces cerevisiae.

The Sep1 (also known as Kem1, Xrn1, Rar5, DST2/Stpbeta) protein of Saccharomyces cerevisiae is an Mr 175,000 multifunctional exonuclease with suspected roles in RNA turnover and in the microtubular cytoskeleton as well as in DNA recombination and DNA replication. The most striking phenotype of SEP1 null mutations is quantitative arrest during meiotic prophase at the pachytene stage. We have constructed a set of N- and C-terminal as well as internal deletions of the large SEP1 gene. Analysis of these deletion mutations on plasmids in a host carrying a null allele (sep1 ) revealed that at least 270 amino acids from the C-terminus of the wild-type protein were dispensable for complementing the slow growth and benomyl hypersensitivity of a null mutant. In contrast, any deletion at the N-terminus abrogated complementing activity for these phenotypes. The sequences essential for function correspond remarkably well with the regions of Sep1 that are homologous to its Schizosaccharomyces pombe counterpart Exo2. In addition, these experiments showed that, despite the high intracellular levels of Sep1, over-expression of this protein above these levels is detrimental to the cell. We discuss the potential cellular roles of the Sep1 protein as a microtubule-nucleic acid interface protein linking its suspected function in the microtubular cytoskeleton with its role as a nucleic acid binding protein.

Alleles↗
PubMed1977

Effect of actinomycin D on the quail oocyte nucleolus during meiotic prophase I.

Actinomycine D alters profoundly the distribution of the nucleolar constituents in the quail oocyte at prophase I of meiosis. As a consequence of nucleolar segregation, the normally existing relations between the nucleolus fibrillar centers and the microchromosomes are ruptured. The relations between the fibrillar center and the dense fibrills which surround it remain intact, suggesting that they constitute together a functional unit.

Animals↗
PubMed1998

The hBUB1 and hBUBR1 kinases sequentially assemble onto kinetochores during prophase with hBUBR1 concentrating at the kinetochore plates in mitosis.

The kinetochore binds an evolutionarily conserved set of checkpoint proteins that function to monitor whether chromosomes have aligned properly at the spindle equator. Human cells contain two related protein kinases, hBUB1 and hBUBR1, that appear to have evolved from a single ancestral BUB1 gene. We generated hBUB1- and hBUBR1-specific antibodies so that the localization patterns of these kinases could be directly compared. In the human U2OS osteosarcoma cell line, hBUB1 first appeared at kinetochores during early prophase before all kinetochores were occupied by hBUBR1 or CENP-F. Both proteins remained at kinetochores throughout mitosis but their staining intensity was reduced from anaphase onward. Kinetochores of unaligned chromosomes exhibited stronger hBUB1 and hBUBR1 staining. Immunoelectron microscopy showed that hBUBR1 appeared to be concentrated in the outer kinetochore plate and in some instances the inner plate as well. When chromosome spreads were examined by light microscopy, hBUB1 and hBUBR1 were coincident with CENP-E. This suggests that both kinases are concentrated near the surface of the kinetochore where they can monitor kinetochore-microtubule interactions.

Cell Cycle Proteins↗
PubMed2000

Characterization of fission yeast meiotic mutants based on live observation of meiotic prophase nuclear movement.

We characterized four meiotic mutants of the fission yeast Schizosaccharomyces pombe by live observation of nuclear movement. Nuclei were stained with either the DNA-specific fluorescent dye Hoechst 33342 or jellyfish green fluorescent protein (GFP) fused with the N-terminal portion of DNA polymerase alpha. We first followed nuclear dynamics in wild-type cells to determine the temporal sequence of meiotic events: nuclear fusion in the conjugated zygote is immediately followed by oscillatory nuclear movements that continue for 146 min; then, after coming to rest, the nucleus remains in the center of the cell for 26 min before the first meiotic division. Next we examined nuclear dynamics in four meiotic mutants: mei1 (also called mat2), mei4, dhc1, and taz1. Mei1 and mei4 both arrest during meiotic prophase; our observations, however, show that the timing of mei1 arrest is quite different from that of mei4: the mei1 mutant arrests after nuclear fusion but before starting the oscillatory nuclear movements, while the mei4 mutant arrests after the nucleus has completed the oscillatory movements but before the first meiotic division. We also show examples of the dynamic phenotypes of dhc1 and taz1, both of which complete meiosis but exhibit impaired nuclear movement and reduced frequencies of homologous recombination: the dhc1 mutant exhibits no nuclear movement after nuclear fusion, while the taz1 mutant exhibits severely impaired nuclear movement after nuclear fusion.

Bacterial Outer Membrane Proteins↗
PubMed1984

Identification and immunochemical characterization of spermatogenic cell surface antigens that appear during early meiotic prophase.

Three spermatogenic cell populations isolated from prepuberal mice--type B spermatogonia, preleptotene spermatocytes, and leptotene/zygotene spermatocytes--were used to elicit distinct polyclonal antisera. Surface binding specificities were determined for purified IgGs by indirect immunofluorescence and rosette assays on live cells. Binding activities were assayed both before and after absorptions with a variety of somatic and spermatogenic cells. Each of these antisera binds to surface antigens that are present on germ cells throughout spermatogenesis and are not shared by splenocytes, thymocytes, and erythrocytes. Only the antiserum raised against leptotene and zygotene spermatocytes (ALZ) recognizes a stage-specific subset of surface determinants. After appropriate absorptions, ALZ binds to the surface of early pachytene spermatocytes and germ cells at subsequent stages of differentiation, including vas deferens spermatozoa. Antigens which react with this absorbed IgG are not detected on the surface of spermatogonia or meiotic cells prior to pachynema, including leptotene and zygotene spermatocytes. The observed binding specificities may result from the synthesis of one or more surface molecules during the early meiotic stages, followed by delayed insertion into the plasma membrane during the pachytene stage of meiotic prophase. Stage-specific antigens recognized by ALZ, including both protein and probably lipid, have been localized immunochemically on nitrocellulose blots from one-dimensional SDS gels. A dithiothreitol-sensitive constituent (Mr approximately 39,000) recognized by ALZ has been identified as the major protein determinant present in early meiotic cells but absent in 8-day-old seminiferous cell suspensions containing spermatogonia and Sertoli cells. This determinant is present in populations of preleptotene, leptotene/zygotene, and early pachytene spermatocytes isolated from 17-day-old animals, an observation consistent with the hypothesis of delayed insertion into the plasma membrane.

Animals↗
PubMed1991

Induction of M-phase entry of prophase-blocked mouse oocytes through microinjection of okadaic acid, a specific phosphatase inhibitor.

We report that a specific inhibitor of types 1 and 2A phosphatases, okadaic acid (OA), induces germinal vesicle break down (GVBD) and chromosome condensation when microinjected into denuded mouse oocytes maintained in prophase block by analogs of cAMP, inhibitors of phosphodiesterase, or a tumor-promoting phorbol ester. GVBD and chromosome condensation are also observed when incompetent oocytes are similarly injected with OA, this effect being dependent on the oocyte diameter. Marked changes in cell shape, cytoskeletal organization, and chromosome condensation with abnormal or abortive spindle formation are associated with such injections. The polar body is not formed. These results led to the conclusions that in mouse oocytes, OA acts distal to both the cAMP-modulated pathway involved in meiotic arrest and the inhibitory action exerted by tumor-promoting phorbol esters.

1-Methyl-3-isobutylxanthine↗
PubMed1991

Dislocation of chromatin elements in prophase induced by diethylstilbestrol: a novel mechanism by which micronuclei can arise.

The in vitro micronucleus test with Syrian hamster embryo (SHE) cells assays the induction of micronuclei by chemical agents. Both chromosome fragments and lagging chromosomes can give rise to micronuclei. Nevertheless, only limited information is available on the ultrastructure of micronuclei and the mechanisms of their formation. Diethylstilbestrol (DES), a non-mutagenic carcinogen, as well as its analogue 3.3'-DES induce micronuclei in SHE cells. A comparison of the dose response of DES-induced micronucleus formation with the previously published ones for aneuploidy and transformation shows that all 3 run in parallel. Thus, a functional relationship between these endpoints, in the SHE system, may be implied. The present study is designed to address the formation of micronuclei using supravital UV microscopy, to test for the presence of defined chromosome domains within micronuclei using immunocytochemistry, and to define aspects of their ultrastructure by electron microscopy. Supravital UV microscopy showed that 3.3'-DES induces displacement of chromosomes/chromatids during prophase/anaphase and formation of micronuclei during cytokinesis. Immunocytochemistry revealed that micronuclei contain, at high frequencies, CREST antibody-reactive kinetochores, indicating the presence of whole chromosomes or centric fragments in these structures. Moreover, transmission electron microscopy showed that micronuclei exhibit ultrastructural details typical of interphase nuclei. Specifically, micronuclei exhibited morphological evidence of a nuclear lamina and segregation of karyoplasm into euchromatic and heterochromatic regions. All micronuclei examined were enclosed by a nuclear envelope of normal morphology and showed nuclear pore complexes. Together the findings provide evidence that DES interferes with the mitotic apparatus as early as prophase, resulting in the formation of micronuclei and, as a consequence, in the loss of chromatids or chromosomes.

4-Nitroquinoline-1-oxide↗
PubMed1987

Sodium-dependent and sodium-independent phosphate uptake by full-grown, prophase-arrested oocytes of Xenopus laevis before and after progesterone-induced maturation.

The uptake of inorganic phosphate by full-grown, prophase-arrested oocytes occurs by two essentially independent transport systems, which accomplish the delivery of extracellular phosphate into two different cellular compartments. One transport system is sodium-dependent, the other is sodium-independent. Both systems can be inhibited by sulfhydryl reagents and the sodium-dependent system becomes inhibited during progesterone-induced oocyte maturation.

4-Chloromercuribenzenesulfonate↗
PubMed2005

Coordinating the events of the meiotic prophase.

Meiosis is a specialized type of cell division leading to the production of gametes. During meiotic prophase I, homologous chromosomes interact with each other and form bivalents (pairs of homologous chromosomes). Three major meiotic processes--chromosome pairing, synapsis and recombination--are involved in the formation of bivalents. Many recent reports have uncovered complex networks of interactions between these processes. Chromosome pairing is largely dependent on the initiation and progression of recombination in fungi, mammals and plants, but not in Caenorhabditis elegans or Drosophila. Synapsis and recombination are also tightly linked. Understanding the coordination between chromosome pairing, synapsis and recombination lends insight into many poorly explained aspects of meiosis, such as the nature of chromosome homology recognition.

Animals↗
PubMed1997

X-ray-induced synaptonemal complex damage during meiotic prophase in female fetuses of Rattus norvegicus.

The different types of damage (synaptic anomalies, chromosome reorganizations and nucleolar fragmentation) observed in oocytes from female rat fetuses irradiated at 14, 16 and 18 days of gestation (d.g.), respectively, indicates the existence of a special sensitivity at the different stages of prophase to X-rays. At the highest dose (5 Gy), we observed a decrease in some of the synaptonemal complex indicators of chromosomal damage, probably reflecting a selection against cells with the highest degree of chromosome anomalies.

Animals↗
PubMed1998

Chromosome cores and chromatin at meiotic prophase.

We review the synaptonemal complex, SC, of the synapsed homologous chromosomes at meiotic prophase in insects and mammals in terms of its formation, and the association of specific chromatin elements with the synaptonemal complexes. The focus is: (1) The SC as visualized with a variety of techniques; (2) The nature of the chromatin loops where they are associated with the SCs--the bases of the loops may be instrumental in recombinant events judging from the presence of Rad51 protein and late recombination nodules at the SCs; (3) Differences in DNA content of similarly sized loops; (4) Requirements for chromatin attachment to the chromosome cores, requirements that are apparently lacking in foreign DNA inserts; (5) Regulation of loop size by the position along the chromosome; (6) The structural correlates of recombination at the SCs--these comments are based on studies of SC structure, DNA-core protein associations, fluorescent in situ hybridization to visualize specific DNA segments, and fluorescent immunocytology to visualize the chromosome core proteins.

Animals↗
PubMed2000

Two distinct pathways remove mammalian cohesin from chromosome arms in prophase and from centromeres in anaphase.

In yeast, anaphase depends on cohesin cleavage. How anaphase is controlled in vertebrates is unknown because their cohesins dissociate from chromosomes before anaphase. We show that residual amounts of the cohesin SCC1 remain associated with human centromeres until the onset of anaphase when a similarly small amount of SCC1 is cleaved. In Xenopus extracts, SCC1 cleavage depends on the anaphase-promoting complex and separin. Separin immunoprecipitates are sufficient to cleave SCC1, indicating that separin is associated with a protease activity. Separin activation coincides with securin destruction and partial separin cleavage, suggesting that several mechanisms regulate separin activity. We propose that in vertebrates, a cleavage-independent pathway removes cohesin from chromosome arms during prophase, whereas a separin-dependent pathway cleaves centromeric cohesin at the metaphase-anaphase transition.

Anaphase↗