Indiscriminate synapsis in achiasmate Allium fistulosum L. (Liliaceae)

1992 ◽  
Vol 103 (2) ◽  
pp. 415-422
Author(s):  
G. Jenkins ◽  
A. Okumus
Keyword(s):  
Synaptonemal Complex ◽  
Allium Fistulosum ◽  
Cell Nuclei ◽  
Male Sterile ◽  
Allium Species ◽  
Lateral Element ◽  
Synaptonemal Complexes ◽  
Independent Process ◽  
Surface Spread ◽  
Metaphase I

Seedlings of Allium fistulosum (2n=2x=16) were treated with aqueous colchicine with the intention of inducing tetraploidy. One treated, but undoubled, diploid mutant is described which consistently fails to form any chiasmata at diakinesis and metaphase I of meiosis. Electron microscopy of whole-mount surface-spread synaptonemal complex complements of pollen mother cell nuclei revealed that the achiasmate condition is probably due not only to the failure to complete synapsis, but also to the indiscriminate way in which the chromosomes form synaptonemal complexes during meiotic prophase. Synapsis begins and progresses with complete disregard to homology, with frequent exchanges of pairing partners resulting in the formation of multiple associations comprising heterologous chromosomes. Intrachromosomal synapsis is also evident as fold-back loops. Up to 78% of lateral element length is incorporated into synaptonemal complex, the morphology of which is not unlike that of normal A. fistulosum and other Allium species described previously. However, all the synaptonemal complexes are ineffective in terms of supporting chiasmata, since 16 univalents enter metaphase I and disjoin irregularly at anaphase I. The mutant is as a consequence completely male sterile. The synaptic behaviour observed confirms that the recognition of homology is an independent process and not a prerequisite for synaptonemal complex formation. It is hoped this mutant will be a valuable tool for probing the molecular basis of homology.

Synaptonemal complex spreading in Allium cepa and Allium fistulosum. II. Pachytene observations: the SC karyotype and the correspondence of late recombination nodules and chiasmata

Genome ◽  
1988 ◽  
Vol 30 (3) ◽  
pp. 399-410 ◽  
Author(s):  
S. M. Albini ◽  
G. H. Jones
Keyword(s):  
Synaptonemal Complex ◽  
Allium Cepa ◽  
Positional Distribution ◽  
Allium Fistulosum ◽  
Dna Amount ◽  
Closely Related Species ◽  
Synaptonemal Complexes ◽  
Recombination Nodules ◽  
Surface Spreading ◽  
Metaphase I

Pachytene synaptonemal complexes and recombination nodules were analysed, by surface spreading, in the closely related species Allium fistulosum and Allium cepa (both 2n = 16), which show highly contrasting patterns of chiasma distribution. Pachytene observations show that all eight pairs of homologues are fully paired in both species, despite the pronounced localisation of chiasmata in A. fistulosum. Synaptonemal complex karyotype analysis reveals similar marker complexes in both species. These are presumed homoeologues, which, possibly due to the uneven distribution of the higher DNA amount found in A. cepa, rank in slightly different positions in the two karyotypes. Darkly staining ellipsoidal late recombination nodules were observed associated with PTA stained pachytene synaptonemal complexes. The positional distribution of late recombination nodules along synaptonemal complexes corresponds almost exactly to the distribution of chiasmata along metaphase I bivalents in the two species. These observations strongly support the proposal that late recombination nodules are involved in reciprocal meiotic recombination. The frequencies of late recombination nodules at pachytene showed deficits (30% in A. fistulosum, 70% in A. cepa) compared to metaphase I chiasma frequencies. It is suggested that the greater deficit of late recombination nodules in A. fistulosum could be related to a longer duration of meiosis in this species resulting from its greater genomic DNA content.Key words: synaptonemal complex, recombination nodules, Allium.

scholarly journals Meiotic cohesin REC8 marks the axial elements of rat synaptonemal complexes before cohesins SMC1β and SMC3

2003 ◽  
Vol 160 (5) ◽  
pp. 657-670 ◽  
Author(s):  
Maureen Eijpe ◽  
Hildo Offenberg ◽  
Rolf Jessberger ◽  
Ekaterina Revenkova ◽  
Christa Heyting
Keyword(s):  
Synaptonemal Complex ◽  
Sister Chromatid ◽  
Meiotic Prophase ◽  
S Phase ◽  
Synaptonemal Complexes ◽  
Sister Chromatids ◽  
Chromatid Cohesion ◽  
Axial Element ◽  
Striking Contrast ◽  
Metaphase I

In meiotic prophase, the sister chromatids of each chromosome develop a common axial element (AE) that is integrated into the synaptonemal complex (SC). We analyzed the incorporation of sister chromatid cohesion proteins (cohesins) and other AE components into AEs. Meiotic cohesin REC8 appeared shortly before premeiotic S phase in the nucleus and formed AE-like structures (REC8-AEs) from premeiotic S phase on. Subsequently, meiotic cohesin SMC1β, cohesin SMC3, and AE proteins SCP2 and SCP3 formed dots along REC8-AEs, which extended and fused until they lined REC8-AEs along their length. In metaphase I, SMC1β, SMC3, SCP2, and SCP3 disappeared from the chromosome arms and accumulated around the centromeres, where they stayed until anaphase II. In striking contrast, REC8 persisted along the chromosome arms until anaphase I and near the centromeres until anaphase II. We propose that REC8 provides a basis for AE formation and that the first steps in AE assembly do not require SMC1β, SMC3, SCP2, and SCP3. Furthermore, SMC1β, SMC3, SCP2, and SCP3 cannot provide arm cohesion during metaphase I. We propose that REC8 then provides cohesion. RAD51 and/or DMC1 coimmunoprecipitates with REC8, suggesting that REC8 may also provide a basis for assembly of recombination complexes.

Genetic and cytogenetic analyses of the A genome of Triticum monococcum. IV. Synaptonemal complex formation in autotetraploids

Genome ◽  
1987 ◽  
Vol 29 (2) ◽  
pp. 309-318 ◽  
Author(s):  
C. B. Gillies ◽  
J. Kuspira ◽  
R. N. Bhambhani
Keyword(s):  
Synaptonemal Complex ◽  
Theoretical Models ◽  
Triticum Monococcum ◽  
Pachytene Nucleus ◽  
Lateral Element ◽  
A Genome ◽  
Cytogenetic Analyses ◽  
The Difference ◽  
Quadrivalent Frequency ◽  
Metaphase I

Electron microscopy of synaptonemal complex spreads from autotetraploid Triticum monococcum (2n = 4x = 28) revealed a minimum mean of 3.59 multivalents per zygotene–pachytene nucleus. The range of values was from 1 to 6 multivalents per nucleus. Most of the multivalents were quadrivalents with single, medially located pairing partner switch points. Lateral element pairing switches, particularly the few multiple switches, were often accompanied by extensive asynapsis around the switch point. The synaptonemal complex multivalent frequency is considerably higher than the metaphase I quadrivalent frequency previously reported for the same material. Calculations of expected pachytene quadrivalent frequency from metaphase I data, using several published theoretical models, gave values that did not agree with the results obtained here. The difference between the multivalent frequencies at pachytene and metaphase I does not appear to be the result of a correction process. Instead, it could be caused by a combination of preferential pairing or crossing-over and the effects of the position of partner switches and asynapsis associated with switches. Key words: autotetraploid, multivalents, synaptonemal complex, pairing effects.

Meiosis in triploid Lolium. I. Synaptonemal complex formation and chromosome configurations at metaphase I in aneuploid autotriploid L. multiflorum

Genome ◽  
1994 ◽  
Vol 37 (2) ◽  
pp. 181-189 ◽  
Author(s):  
Huw M. Thomas ◽  
Barry J. Thomas
Keyword(s):  
Complex Formation ◽  
Synaptonemal Complex ◽  
Lolium Multiflorum ◽  
Synaptonemal Complexes ◽  
Pollen Mother Cells ◽  
Partner Exchange ◽  
Synaptonemal Complex Formation ◽  
Mother Cells ◽  
Axial Element ◽  
Metaphase I

A spreading technique for synaptonemal complexes (SCs) was applied to pollen mother cells of two aneuploid genotypes of autotriploid Lolium multiflorum (2n = 3x + 1 = 22). In the earliest nuclei analyzed the axial elements are in six groups of 3 and one group of 4. Most groups have formed multivalents with from one to five pairing partner exchanges, but there are also groups that have formed bivalents and univalents. Some axial elements have formed triple associations, in one case for the length of the trivalent. Unsynapsed axial elements remain aligned with their homologous SCs into pachytene, but this alignment is abolished as these axes pair heterologously among themselves until the entire axial element complement is synapsed. At metaphase I most chromosomes are associated as trivalents and quadrivalents.Key words: Lolium, triploid, pairing partner exchange, chiasma, multivalent.

scholarly journals The rad9 Gene of Coprinus cinereus Encodes a Proline-Rich Protein Required for Meiotic Chromosome Condensation and Synapsis

Genetics ◽  
1996 ◽  
Vol 142 (4) ◽  
pp. 1105-1117
Author(s):  
Lisa C Seitz ◽  
Keliang Tang ◽  
W Jason Cummings ◽  
Miriam E Zolan
Keyword(s):  
Synaptonemal Complex ◽  
Meiotic Chromosome ◽  
Chromatin Condensation ◽  
Complex Form ◽  
Coprinus Cinereus ◽  
Wild Type ◽  
Normal Completion ◽  
Type C ◽  
Surface Spread ◽  
Metaphase I

Abstract The rad9 gene of Coprinus cinereus is essential for the normal completion of meiosis. We examined surface-spread preparations of wild-type and rad9-1 nuclei from the meiotic stages of karyogamy through metaphase I, and we determined the primary sequence, structure, and meiotic expression of the rad9 gene. In wild-type C. cinereus, karyogamy is followed by condensation and alignment of homologous chromosomes. Condensation and axial core development largely precede synapsis, which often initiates at telomeres. A diffuse diplotene phase coincides with dissolution of the synaptonemal complex, and subsequently chromosomes further condense as the cells progress into metaphase I. In contrast, although karyogamy and nucleolar fusion are apparently normal in rad91 basidia, only short stretches of synaptonemal complex form. These correlate with stretches of condensed chromatin, mostly at apparent chromosome ends, and regions of presumptive triple synapsis are numerous. rad9-1 basidia enter the diffuse stage of early diplotene, and then 50% of these cells enter metaphase I by the criteria of nucleolar elimination and at least some chromatin condensation. rad9 gene expression is induced after gamma irradiation and during meiosis. The gene has 27 exons and encodes a predicted protein of 2157 amino acids, with a proline-rich amino terminus.

Localized chiasmata and meiotic nodules in the tetraploid onion Allium porrum

Genome ◽  
1996 ◽  
Vol 39 (4) ◽  
pp. 770-783 ◽  
Author(s):  
Stephen M. Stack ◽  
Dick Roelofs
Keyword(s):  
Key Words ◽  
Synaptonemal Complex ◽  
Allium Porrum ◽  
Crossing Over ◽  
High Fertility ◽  
Unusual Behavior ◽  
Synaptonemal Complexes ◽  
Recombination Nodules ◽  
Metaphase I

Allium porrum L. (cultivated leek) (2n = 4x = 32) is a fertile tetraploid that forms bivalents with pericentric chiasmata at metaphase I. To investigate the basis of this unusual behavior for a tetraploid, we describe the karyotype, axial cores, synaptonemal complexes (SCs), and meiotic nodules of A. porrum. The karyotype appears to be autotetraploid. This conclusion is also supported by presynaptic alignment of axial cores in groups of four and partner trades between pairs of SCs. Numerous early nodules are distributed all along axial cores and SCs during zygonema, but they are lost by late zygonema – early pachynema. Late (recombination) nodules (RNs) are present on SCs near kinetochores throughout the remainder of pachynema. This pattern of RNs corresponds to the pattern of pericentric chiasmata. Pachytene quadrivalents usually are resolved into bivalents because partner trades between SC lateral elements rarely occur between RNs on the same segment of SC. Thus, the patterns of crossing-over and partner trades promote balanced disjunction and high fertility in autotetraploid A. porrum. Rare quadrivalents observed at metaphase I must be due to infrequent partner trades between RNs. Polycomplexes, unusual in their number and size, were observed during zygonema. Key words : synaptonemal complex, recombination nodules, localized chiasmata, polycomplex, Allium porrum.

Synaptonemal complex formation and metaphase I configuration patterns in a translocation heterozygote of rye (Secale cereale)

Genome ◽  
1989 ◽  
Vol 32 (1) ◽  
pp. 72-81 ◽  
Author(s):  
J. H. de Jong ◽  
J. van Eden ◽  
J. Sybenga
Keyword(s):  
Complex Formation ◽  
Synaptonemal Complex ◽  
Secale Cereale ◽  
Chiasma Formation ◽  
Terminal Segment ◽  
Pachytene Nucleus ◽  
Synaptonemal Complexes ◽  
Synaptonemal Complex Formation ◽  
Chromosome 1R ◽  
Metaphase I

Four rye plants heterozygous for translocation 248, involving chromosomes 1R and 6R, were used for a comparative study of synaptonemal complex formation at midprophase I and chromosome configurations at metaphase I. Synaptonemal complexes were obtained with a cell-spreading technique and studied with electron microscopy. The total length of the synaptonemal complexes in the 28 analyzable pachytene nuclei varied considerably, both within and among plants. The variation of synaptonemal complex lengths of the bivalents in a nucleus was partly stage dependent; i.e., it was greater at early than at late pachytene. In all but one pachytene nucleus, pairing in the quadrivalent was regular, and the four pairing arms were usually easy to identify. Most noticeable was the variation of pairing saturation at the breakpoint of the quadrivalent. Pairing in the breakpoint region was delayed with respect to the pairing in the bivalents. Variation in the arm lengths of the quadrivalent was the result of incomplete and nonhomologous pairing at the breakpoint as well as differential contraction rates among chromosome segments. It was shown that the completion of delayed pairing throughout pachytene is mainly long-arm pairing. The actual breakpoint was therefore not in the middle of the unpaired segments, but more distal. The analysis of metaphase I nuclei revealed that chiasma frequency in this material was higher than in similar material used in former studies. When one of the translocation segments lacked a chiasma, this was in most cases the short translocated segment 1RS, the terminal segment of the satellite of chromosome 1R. Positive chiasma interference was demonstrated between the interstitial and exchanged segment in 1RS. This agreed with the observation of a negative correlation in extent of pairing between these two segments. Other interference phenomena, which have been described for this translocation in other material, remained undetected because of lack of variation in chiasma formation owing to high chiasma frequency.Key words: Secale cereale, meiosis, translocation, synaptonemal complex, metaphase I.

Spreading synaptonemal complexes of B isochromosomes in the grasshopper Omocestus burri

Genome ◽  
1994 ◽  
Vol 37 (6) ◽  
pp. 1035-1040 ◽  
Author(s):  
A. L. del Cerro ◽  
A. Fernández ◽  
J. L. Santos
Keyword(s):  
Electron Microscopy ◽  
Meiotic Pairing ◽  
Synaptonemal Complexes ◽  
Peripheral Location ◽  
Hairpin Loops ◽  
Pairing Model ◽  
Similarities And Differences ◽  
Surface Spread ◽  
Pairing Behaviour ◽  
Metaphase I

Meiotic pairing behaviour of one and two B isochromosomes (iso-Bs) in the grasshopper Omocestus burri was analysed by electron microscopy in surface-spread prophase I nuclei and compared with light microscopic observations of metaphase I. Iso-Bs display a peripheral location in the surface-spread nuclei and early pairing relative to that of the long members of the A set. Single iso-Bs undergo foldback pairing to give symmetrical hairpin loops. Two iso-Bs may show interarm pairing, mterchromosome pairing, or combinations of the two. Pericentromeric interarm pairing can be delayed in one or both Bs and this delay is mostly observed in bivalents with pairing partner switches. The iso-B bivalent frequencies observed in the three males analysed were 64, 44, and 41%, respectively; the two latter values were significantly lower than the 66% predicted by the random-end-pairing model. There is a reduction in the frequencies of iso-ring univalents (in 1B males) and bivalents (in 2B males) from pachytene to metaphase I. Similarities and differences between the pairing behaviour of iso-Bs from different species are also discussed.Key words: B isochromosomes, meiosis, grasshopper, synaptonemal complexes, pairing partner switches.

Differences in the synaptic pattern in two autotetraploid cultivars of rye with different quadrivalent frequencies at metaphase I

Genome ◽  
1999 ◽  
Vol 42 (4) ◽  
pp. 662-667
Author(s):  
M Martínez ◽  
C Cuadrado ◽  
J Sybenga ◽  
C Romero
Keyword(s):  
Electron Microscopy ◽  
Synaptonemal Complex ◽  
Prophase I ◽  
Quadrivalent Frequency ◽  
Surface Spread ◽  
Metaphase I

Synaptic behaviour of the two tetraploids rye cultivars Gigantón (G) and Tetrapico (T) displaying significant differences in their quadrivalent frequencies at metaphase I was analyzed by electron microscopy in surface-spread prophase I nuclei. A different behaviour was observed between the two cultivars; the synaptonemal complex (SC) quadrivalents frequency being significantly higher in G than in T at prophase I. Moreover, the G SC quadrivalents had more synaptic partner exchanges (SPEs) and their location was more distal than the T SC quadrivalents. However, inverse findings were found at metaphase I, the quadrivalent frequency was higher in T than in G. The role that different factors, mainly the number and location of the SPEs and the frequency and distribution of chiasmata, could play in the evolution from prophase I to metaphase I in both cultivars is discussed.Key words: autotetraploid rye, synaptonemal complex, spreading.

Chromosome pairing in the allotetraploid Aegilops biuncialis and a triploid intergeneric hybrid

Genome ◽  
1996 ◽  
Vol 39 (4) ◽  
pp. 664-670 ◽  
Author(s):  
N. Cuñado ◽  
S. Callejas ◽  
M. J. García ◽  
J. L Santos ◽  
A. Fernández
Keyword(s):  
Synaptonemal Complex ◽  
Chromosome Pairing ◽  
Complex Analysis ◽  
Intergeneric Hybrid ◽  
Chiasma Formation ◽  
Triploid Hybrid ◽  
Homologous Chromosomes ◽  
Prophase I ◽  
Surface Spread ◽  
Metaphase I

Chromosome pairing behaviour of the natural allotetraploid Aegilops biuncialis (genome UUMM) and a triploid hybrid Ae. biuncialis × Secale cereale (genome UMR) was analyzed by electron microscopy in surface-spread prophase I nuclei. Synaptonemal-complex analysis at zygotene and pachytene revealed that synapsis in the allotetraploid was mostly between homologous chromosomes, although a few quadrivalents were also formed. Only homologous bivalents were observed at metaphase I. In contrast, homoeologous and heterologous chromosome associations were common at prophase I and metaphase I of the triploid hybrid. It is concluded that the mechanism controlling bivalent formation in Ae. biuncialis acts mainly at zygotene by restricting pairing to homologous chromosomes, but also acts at pachytene by preventing chiasma formation in the homoeologous associations. In the hybrid the mechanism fails at both stages. Key words : Aegilops biuncialis, allotetraploid, intergeneric hybrid, pairing control, synaptonemal complex.

Sign in / Sign up

Export Citation Format

Share Document