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PubMed1998

Induced chromosomal exchange directs the segregation of recombinant chromatids in mitosis of Drosophila.

In meiosis, the segregation of chromosomes at the reductional division is accomplished by first linking homologs together. Genetic exchange generates the bivalents that direct regular chromosome segregation. We show that genetic exchange in mitosis also generates bivalents and that these bivalents direct mitotic chromosome segregation. After FLP-mediated homologous recombination in G2 of the cell cycle, recombinant chromatids consistently segregate away from each other (x segregation). This pattern of segregation also applies to exchange between heterologs. Most, or all, cases of non-x segregation are the result of exchange in G1. Cytological evidence is presented that confirms the existence of the bivalents that direct this pattern of segregation. Our results implicate sister chromatid cohesion in maintenance of the bivalent. The pattern of chromatid segregation can be altered by providing an additional FRT at a more proximal site on one chromosome. We propose that sister chromatid exchange occurs at the more proximal site, allowing the recombinant chromatids to segregate together. This also allowed the recovery of reciprocal translocations following FLP-mediated heterologous recombination. The observation that exchange can generate a bivalent in mitotic divisions provides support for a simple evolutionary relationship between mitosis and meiosis.

Animals↗
PubMed2001

Synapsis in Robertsonian heterozygotes and homozygotes of Dichroplus pratensis (Melanoplinae, Acrididae) and its relationship with chiasma patterns.

Dichroplus pratensis has a complex system of Robertsonian rearrangements with central-marginal distribution; marginal populations are standard telocentric. Standard bivalents show a proximal-distal chiasma pattern in both sexes. In Robertsonian individuals a redistribution of chiasmata occurs: proximal chiasmata are suppressed in fusion trivalents and bivalents which usually display a single distal chiasma per chromosome arm. In this paper we studied the synaptic patterns of homologous chromosomes at prophase I of different Robertsonian status in order to find a mechanistic explanation for the observed phenomenon of redistribution of chiasmata. Synaptonemal complexes of males with different karyotypes were analysed by transmission electron microscopy in surface-spread preparations. The study of zygotene and early pachytene nuclei revealed that in the former, pericentromeric regions are the last to synapse in Robertsonian trivalents and bivalents and normally remain asynaptic at pachytene in the case of trivalents, but complete pairing in bivalents. Telocentric (standard) bivalents usually show complete synapsis at pachytene, but different degrees of interstitial asynapsis during zygotene, suggesting that synapsis starts in opposite (centromeric and distal) ends. The sequential nature of synapsis in the three types of configuration is directly related to their patterns of chiasma localisation at diplotene-metaphase I, and strongly supports our previous idea that Rb fusions instantly produce a redistribution of chiasmata towards chromosome ends by reducing the early pairing regions (which pair first, remain paired longer and thus would have a higher probability of forming chiasmata) from four to two (independently of the heterozygous or homozygous status of the fusion). Pericentromeric regions would pair the last, thus chiasma formation is strongly reduced in these areas contrary to what occurs in telocentric bivalents.

Animals↗
PubMed1991

Meiotic chromosome structure. Kinetochores and chromatid cores in standard and B chromosomes of Arcyptera fusca (Orthoptera) revealed by silver staining.

The behaviour of two chromosome structures in silver-stained chromosomes was analyzed through the first meiotic division in spermatocytes of the acridoid species Arcyptera fusca. Results showed that at diakinesis kinetochores and chromatid cores are individualized while they associate in bivalents of metaphase I; only kinetochores and distal core spots associate in the sex chromosome. Metaphase I is characterized by morphological and localization changes of both kinetochores and cores which define the onset of anaphase I. These changes analyzed in both autosomes and in the sex chromosome allow us to distinguish among three different substages in metaphase I spermatocytes. B chromosomes may be present as univalents, bivalents, or trivalents. Metaphase I B univalents are characterized by separated cores except at their distal ends and individualized and flat sister kinetochores. At anaphase I sister kinetochores of lagging B chromatids remain connected through a silver-stained strand. The behaviour of cores and kinetochores of B bivalents is identical with that found in the autosomal bivalents. The differences in the morphology of kinetochores of every chromosome shown by B trivalents at metaphase I may be related to the balanced forces acting on the multivalent. The results show dramatic changes in chromosome organization of bivalents during metaphase I. These changes suggest that chromatid cores are not involved in the maintenance of bivalents. Moreover, the changes in morphology of kinetochores are independent of the stage of meiosis but correlate with the kind of division (amphitelic-syntelic) that chromosomes undergo.

Animals↗
PubMed1975

A light- and electron-microscope study of the oocyte nucleus during development of the antral follicle in the prepubertal mouse.

The ordered changes which occur in the structural organization of the mouse oocyte nucelus during the preparatory, the maturative and the preovulatory stages of antral follicle development, have been studied under both light and electron microscopy. All observations have been made on those antral follicles whose development is initiated on postnatal day 14 and completed by postnatal day 28 in prepubertal animals of the ICR albino mouse strain. The formed entities that can be recognized within the oocyte nucleus during that period are the condensing bivalents, the heterochromatic knobs, the nucleolus and the extranucleolar bodies. At the onset of antral follicle development, the highly unravelled dictyate bivalents are seen to take on a lampbrush-type configuration. Subsequent condensation of these lampbursh bivalents appears to be a very gradual and lengthy process that extends over almost the entire period of antral follicle development. The shortening and thickening of the lampbrush bivalents are best interpreted as resulting from the withdrawal of their lateral loop-like projections into the chromosome axes and from the focal aggregation of these axes into compact chromatin masses. Electron-opaque granules, which appear within the oocyte nucleus during the preparatory and maturative follicle stages, are seen to be intimately associated with these condensing bivalents. A number of Feulgen-positive heterochromatic knobs make their appearance in contact with certain bivalents during the preparatory follicle stage. These knobs are not reincorporated as such into the condensing chromatin masses and undergo disintegration and dissolution during the preovulatory follicle stage. The size, shape and ultrastructural features of the nucleolus remain unchanged thoughout the period of antral follicle development. Breakdown and dissolution of the nucleolar mass is a swift process that takes place only in the fully mature preovulatory follicle and more or less concomitantly with the dismantling of the nuclear envelope. The extranucleolar bodies increase noticeably in size during the preparatory and the maturative follicle stages; they shrink in size and undergo dissolution during the preovulatory stage of antral follicle development. An attempt is made to interpret these morphological changes in the light of current knowledge concerning the architectural and functional organization of the oocyte nucleus in general during meiotic prophase. The relevant observational evidence would be consistent with the view that, during antral follicle deveopment, the mouse oocyte nucleus is not, as too often assumed, in a period of arrested evolution; its formed components undergo structural, maturational and functional changes which are of significance not only for the resumption of the first meiotic prophase but also for the early development of the embryo.

Age Factors↗
PubMed2005

Imaging of infection and inflammation with an improved 99mTc-labeled LTB4 antagonist.

UNLABELLED: Studies have demonstrated that the bivalent (111)In-labeled leukotriene B4 (LTB4) antagonist DPC11870 reveals infectious and inflammatory lesions in various rabbit models. The radioactive tracer accumulates quickly at the site of infection and clears rapidly from the circulation, resulting in high-quality images. In this study, 2 new hydrazinonicotinamide (HYNIC)-conjugated compounds that are structurally related to DPC11870 were studied to further improve image quality. METHODS: A bivalent HYNIC-conjugated LTB4 antagonist (MB81) and a monovalent one (MB88) were labeled with (99m)Tc. The radiolabeled compounds were intravenously injected into New Zealand White rabbits with E. coli infection in the left thigh muscle. The imaging characteristics of both compounds were compared with those of the bivalent (111)In-labeled LTB4 antagonist. RESULTS: Both (99m)Tc-labeled LTB4 antagonists revealed the abscess from 2 h after injection onward. Abscess uptake at 8 h after injection was similar for both compounds (0.22 +/- 0.08 percentage injected dose per gram [%ID/g] and 0.36 +/- 0.13%ID/g for the bivalent and monovalent compounds, respectively). However, visualization of the abscess and the quality of the images were better after injection of MB88 than after injection of either of the bivalent LTB4 antagonists. The excellent delineation of the abscess by MB88 was mainly due to the more rapid clearance of this compound from nontarget organs. CONCLUSION: The (99m)Tc-labeled HYNIC conjugated LTB4 antagonists MB88 and MB81 revealed infectious foci in rabbits within a few hours after injection. Imaging characteristics of monovalent (99m)Tc-MB88 were superior to those of the bivalent LTB4 antagonists DPC11870 and MB81. Therefore, of the 3 LTB4 antagonists, the monovalent LTB4 antagonist MB88 is the most potent and promising agent for visualizing and evaluating infection and inflammation in patients.

Animals↗
PubMed1984

The control of chiasma distribution.

The question of recombination control has been the subject of intensive investigation over many years. This paper is restricted to an evaluation of the information obtainable from cytological studies of chiasmata, since other approaches are well represented in other papers in this volume. The advantages and disadvantages of chiasmata as means of studying recombination are discussed. Cytological observations reveal many constraints on the distribution of chiasmata, which are interpreted as outward expressions of controls operating at different levels, namely between cells, between bivalents and within bivalents. Detailed descriptions of these constraints are presented as a preliminary to discussing models and mechanisms of control. They include, at the between-bivalent level, over-dispersal of chiasma number per bivalent and the formation of an obligatory minimum of one chiasma per bivalent; and at the within-bivalent level, chiasma localization and chiasma interference. The genetical basis of these constraints is emphasized and evidence presented which suggests that chiasma distribution at different levels is subject to both separate and coordinate genetical controls. These observations lead to the consideration and evaluation of general stochastic models of chiasma control based on the modification of site probabilities for chiasma formation. While these models are a useful approach to thinking about the control of recombination, they do not give a fully satisfactory explanation of all aspects of chiasma control. Finally, specific mechanisms for chiasma distribution control are considered. In a few exceptional species, localized pairing and synaptonemal complexes lead to localized chiasma formation; details of two such cases are presented. In the majority of species, pairing is not localized or restricted and in these species the control of chiasma distribution is more conjectural. Arguments are presented which suggest that even in these cases of full pairing, the pattern of pairing initiation and progression and perhaps the timing of these events could be important factors controlling the distribution of chiasmata.

Animals↗
PubMed1980

Analysis of crossing over in mouse meiotic cells by BrdU labelling technique.

Differential staining of sister chromatids in male mouse meiotic cells was achieved by continuous infusion with BrdU from the tail vein followed by Giemsa staining (the FPG technique of Perry and Wolff, 1974). Analysis of 341 bivalents including XY, and 21 univalents reveals that: (1) visible crossing over coincided exactly with the site of chiasmata; (2) no evidence was obtained in support of chiasma terminalisation; (3) an anomalous type of crossing over was found in the monochiasmatic bivalents, which could not be explained by the conventional hypothesis for crossing over; (4) some of the terminally associated bivalents might be achiasmatic, and univalents might have originated from such bivalents; (5) in XY bivalents, sister chromatid association was between lightly and darkly stained chromatids, suggesting a lack of crossing over and the existence of other genetic controls for this association; (6) during meiosis sister chromatid exchanges (SCEs) might be less frequent than crossovers.

Animals↗
PubMed1976

Pachytene mapping in the female silkworm, Bombyx mori L. (Lepidoptera).

Pachytene preparations of the chromosome complement of female larvae of Bombyx mori were improved to give a distinct chromomere pattern of the bivalents suitable for chromosome mapping. Six of the 28 bivalents are described and can be identified regularly in the bivalent complements, among them the bivalent containing the nucleolus organizer. The relative lengths of these bivalents compared with one another change during development of pachytene. In contrast to other members of the Lepidoptera there is no conspicuous heterochromatic W-chromosome, which corresponds to the female-specific heterochromatin body present in the nuclei of somatic tissues. This tissue-specific heteropycnosis indicates a different functional state of the responsible chromosome or chromosomal segment in germ line and somatic cells.

Animals↗
PubMed1984

Pachytene chromosomes in male and female mice heterozygous for the Is(7;1)40H insertion.

Pairing of pachytene chromosomes was studied in oocytes and spermatocytes of mice heterozygous for the male-sterile Is(7;1)40H insertion using light and electron microscopy for synaptonemal complex analysis in surface-spread, silver-stained preparations. The data comprised four males and four female embryos. The insertion/deletion configurations appeared as either two bivalents or one quadrivalent in both sexes, but the proportion of bivalents was higher in oocytes. Some insertion and deletion bivalents showed synaptic adjustment. The insertion/deletion configurations were associated with, or adjacent to, the XY bivalent in the majority of spermatocytes. End-to-end association of different bivalents was more frequent in oocytes than in spermatocytes. It is suggested that physiological differences between male and female gametocytes may lead to the difference in their reproductive potential.

Animals↗
PubMed1989

Tension, microtubule rearrangements, and the proper distribution of chromosomes in mitosis.

The basis for stable versus unstable kinetochore orientation was investigated by a correlated living-cell/ultrastructural study of grasshopper spermatocytes. Mal-oriented bivalents having both kinetochores oriented to one spindle pole were induced by micromanipulation. Such mal-orientations are stable while the bivalent is subject to tension applied by micromanipulation but unstable after tension is released. Unstable bivalents always reorient with movement of one kinetochore toward the opposite pole. Microtubules associated with stably oriented bivalents, whether they are mal-oriented or in normal bipolar orientation, are arranged in orderly parallel bundles running from each kinetochore toward the pole. Similar orderly kinetochore microtubule arrangements characterized mal-oriented bivalents fixed just after release of tension. A significantly different microtubule arrangement is found only some time after tension release, when kinetochore movement is evident. The microtubules of a reorienting kinetochore always include a small number of microtubules running toward the pole toward which the kinetochore was moving at the time of fixation. All other microtubules associated with such a moving kinetochore appear to have lost their anchorage to the original pole and to be dragged passively as the kinetochore proceeds to the other pole. Thus, the stable anchorage of kinetochore microtubules to the spindle is associated with tension force and unstable anchorage with the absence of tension. The effect of tension is readily explained if force production and anchorage are both produced by mitotic motors, which link microtubules to the spindle as they generate tension forces.

Animals↗
PubMed1986

Loop formation and synaptic adjustment in a human male heterozygous for two pericentric inversions.

Pachytene analysis was undertaken in an infertile male heterozygous for two pericentric inversions of chromosomes 1 and 9. The synaptic behaviour of the bivalent 1 inversion was the most informative. Analysis of the chromomere pattern combined with centromeric heterochromatin staining allowed precise description of synaptic initiation and extension leading to the homosynapsed loop. These techniques also allowed demonstration of the existence of heterosynapsis following alignment of the inverted segments. Non-homologous synapsed bivalents had the morphological aspects of straight bivalents with two distant blocks of centromeric heterochromatin. The numbering of the autosomal bivalent chromomeres at various successive phases of the inversion loop behaviour of bivalent 1 permitted us an alternative approach to the timing of pachytene.

Adult↗
PubMed1976

Comparative chiasma analysis using a computerised optical digitiser.

A new computerised technique has been devised for measuring the distribution of chiasmata along diplotene bivalents. The method involves the introduction into the field of view of the microscope, of a fine light spot which can be accurately manipulated along the chromosomes of each bivalent. The data recorded include (a) the positions of the chiasmata along the bivalent in terms of their relative distances from the centromere and (b) the individual bivalent and cellular chiasma frequencies. -- The method has been applied to the analysis of chiasma distribution patterns in the two known species of the genus Caledia, C. species nova 1 and C. captiva and in two chromosomal races of the latter. Statistical tests indicate that within bivalents at least 40% of the comparative distribution patterns of chiasmata between races and species are significantly different. Similar comparisons between populations within races reveal only 18% significant differences. -- The observed distribution patterns of chiasmata in this genus suggest that chiasma formation is sequential from centromere to telomere. -- The variation in the frequency and distribution of chiasmata between races and species suggests that the interference distances between successive chiasmata are, at least partially, independent of chiasma frequency and position. -- The interracial and interspecific differences in chromosome structure are correlated with changes in chiasma pattern.

Analog-Digital Conversion↗
PubMed1982

Chromosome segregation in crane-fly spermatocytes: cold treatment and cold recovery induce anaphase lag.

Anaphase lagging of autosomes was observed in 6.1 +/- 5.4% of the primary spermatocytes in untreated larvae of the crane fly, Nephrotoma suturalis. Lagging was induced by exposure of larvae to 6 degrees C and during recovery at 22 degrees C from exposure to 0.2, 2, and 6 degrees C. The incidence of anaphase lag was maximal at 80 to 90 min of recovery. Induced lagging was observed at that recovery time after exposures of only 2.5 h to 2 or 0.2 degrees C, but its incidence increased with longer exposures. As many as 85% of the cells in anaphase contained autosomal laggards after 61 h at 2 degrees C and 80 to 90 min of recovery. At 2 degrees C, cells reached the prophase-prometaphase transition, but spindles did not appear to form. Those cells proceeded through prometaphase during recovery, reaching mid-anaphase after 80 to 90 min of recovery. Chromosomes that lagged at anaphase during recovery from 2 degrees C were observed in living cells to be half-bivalents derived from bivalents that congressed to the metaphase plate. One or both half-bivalents of any bivalent could lag. In some cells, one half-spindle had more half-bivalents than the other. Cells with autosomal laggards often did not cleave, and in uncleaved cells the second division employed spindles having two, three, or four poles. The basis of induced lagging might be a lapse in spindle attachment or motive force application at the start of anaphase or a failure of chromosomes to achieve proper orientation before the onset of anaphase.

Animals↗
PubMed1982

A pachytene analysis of two male-fertile paracentric inversions in chromosome 1 of the mouse and in the male-sterile double heterozygote.

Meiotic studies have been made at pachytene on two paracentric inversions in chromosome 1 of the mouse. Surface-spread preparations of primary spermatocytes have been analysed at the light microscope level in males heterozygous for the inversions In (1) 1 Rk and In (1) 12 Rk and in the double heterozygote In (1) 1 RK/In (1) 12 Rk. In singly heterozygous form, neither inversion produces any serious effect on male fertility. In the double heterozygote, spermatogenesis is arrested in the majority of cells at the spermatocyte stage and males are rendered totally sterile by azoospermia. In the double heterozygote, a complex loop, indicating the inversion bivalent, is found in 90% of pachytene cells analysed. In the In (1) Rk/+ heterozygote, a looped bivalent was seen in 47 per cent of pachytene cells but in In (1) 12 Rk/+ no cells containing loops could be found. -- 80% of pachytene spermatocytes from the In (1) 1 Rk/In (1) 12 Rk double heterozygote showed apposition of the inversion bivalent to the sex bivalent. Such an association was rarely seen in pachytene cells of either of the fertile single heterozygotes. Spermatogenic failure in the double heterozygote may be related to interference, by the inversion bivalent, with X chromosome inactivation at meiotic prophase.

Animals↗
PubMed1994

Biosystematic study of hexaploids Elymus tschimganicus and E. glaucissimus. I. Morphology and genomic constitution.

Elymus tschimganicus and E. glaucissimus are hexaploids (2n = 6x = 42) that inhabit stony slopes and swales in the middle and upper mountain belts of Central Asia. Chromosome pairing at metaphase I in E. tschimganicus and E. glaucissimus was typical of other Elymus hexaploids, averaging 20.94 and 20.98 bivalents per cell, respectively. Meiotic pairing of tetraploid hybrids derived by crossing E. tschimganicus and E. glaucissimus with P. spicata (2n = 2x = 14; genome = SS) averaged 4.97 and 4.90 bivalents per cell respectively, indicating the presence of the S genome in the target taxa. Pentaploid hybrids derived by crossing E. tschimganicus and E. glaucissimus with tetraploid analyzer species E. mutabilis and E. sibiricus (2n = 4x = 28; genome = SSHH) had mean bivalent frequencies of 5.61 and 4.64 respectively, suggesting the absence of the H genome in the target taxa. Mean bivalent associations were similar among hybrids derived by crossing the target taxa with E. nevski (2n = 4x = 28; genome = SSYY), which averaged 10.61 and 11.42 bivalents, respectively, suggesting the presence of the Y genome in E. tschimganicus and E. glaucissimus. Based on chromosome pairing in the hybrids, the genomic formula for both E. tschimganicus and E. glaucissimus should be SSSSYY.

Chimera↗
PubMed1989

Studies on the pathology of Marek's disease following challenge in chicks vaccinated with three different vaccines.

The pathology of Marek's disease (MD) was studied in chickens vaccinated separately with three different vaccines, namely herpesvirus of turkeys (HVT), inactivated Marek's disease virus (IMDV) and a bivalent vaccine. The MD-specific mortality following challenge was significantly lower (2.0 per cent) in bivalent vaccinated birds than in those vaccinated with either HVT (5.9 per cent) or IMDV (13.7 per cent) alone. The occurrence, extent and severity of gross lymphomas and lymphoproliferative lesions in visceral organs was lower in the bivalent-vaccinated birds than in other groups. Atrophy and degenerative changes were seen in unvaccinated and challenged birds but not in challenged and bivalent-vaccinated birds. Mild degenerative lesions and slight RE cell hyperplasia occurred in HVT- and IMDV-inoculated and challenged birds. The low intensity and frequency of gross and histological lesions in bivalent-vaccinated birds following challenge is highly suggestive of better vaccine-induced resistance.

Animals↗
PubMed1990

Ultracentrifugation study on interactions among calmodulin, cardiac troponin and tropomyosin-actin complex.

In an effort to clarify the regulation of contractions in cardiac muscle, we performed ultracentrifugation studies on the interactions between cardiac troponin and tropomyosin-actin complex in the presence of Ca2+ or Sr2+. When troponin C and troponin I were centrifuged with tropomyosin-actin complex, troponin I was not removed from tropomyosin-actin complex in the presence of bivalent-cation. Troponin C was observed to bind very weakly to troponin T-tropomyosin-actin complex in either the presence of absence of bivalent-cation. When troponin C was replaced by calmodulin, troponin I was not removed from tropomyosin-actin complex in the presence of bivalent-cation. Calmodulin bound to the troponin I-troponin T-tropomyosin-actin complex only in the presence of bivalent-cation. These results suggest that the inhibitory action of troponin I is neutralized by troponin C or calmodulin upon binding of bivalent-cation while troponin I binds to tropomyosin-actin complex in cardiac muscle. Therefore cardiac muscle seems to differ from skeletal muscle in regard to regulation of its contraction.

Actins↗
PubMed2004

Identification of meiotic anomalies with multiplex fluorescence in situ hybridization: Preliminary results.

OBJECTIVE: To characterize meiotic anomalies in infertile men by multiplex fluorescence in situ hybridization (M-FISH) and to determine whether synaptic problems affect specific bivalents or whether anomalies are random. DESIGN: Analysis of meiotic preparations with standard techniques and M-FISH. SETTING: Assisted reproduction centers and Universitat Autònoma de Barcelona. PATIENT(S): Three fertile men undergoing vasectomy, four sterile patients with oligoasthenoteratozoospermia, and one patient with a Robertsonian translocation t(13;14). INTERVENTION(S): Unilateral testicular biopsy in controls and patients with oligoasthenoteratozoospermia and collection of a semen sample from the translocation carrier. MAIN OUTCOME MEASURE(S): Identification of bivalents in metaphase I and chromosomes in metaphase II and characterization of chromosome abnormalities. RESULT(S): All bivalents in metaphase I and all chromosomes in metaphase II could be identified. In controls and in one patient with oligoasthenoteratozoospermia, meiosis was normal. Other patients with oligoasthenoteratozoospermia showed different types of anomaly: desynapsis, breaks, precocious XY separation, or cryptic reorganizations. The Robertsonian translocation t(13;14) was easily identified. CONCLUSION(S): Results confirm the high incidence of synaptic errors in oligoasthenoteratozoospermia patients. Bivalents in metaphase I and chromosomes in metaphase II were individually identifiable. Nondisjunctional errors or small reorganizations overlooked in classic meiotic preparations were identified. Synaptic anomalies seem to affect meiotic bivalents at random.

Chromosome Mapping↗