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.

Synaptonemal complex spreading in Allium cepa and Allium fistulosum. III. The F1 hybrid

Genome ◽  
1990 ◽  
Vol 33 (6) ◽  
pp. 854-866 ◽  
Author(s):  
S. M. Albini ◽  
G. H. Jones
Keyword(s):  
Synaptonemal Complex ◽  
Allium Cepa ◽  
Chiasma Frequency ◽  
Chiasma Formation ◽  
Allium Fistulosum ◽  
Closely Related Species ◽  
F1 Hybrid ◽  
Late Zygotene ◽  
Prophase I ◽  
Surface Spreading

Synaptonemal complexes (SCs) were analysed, by surface spreading, in the F1 hybrid between Allium cepa and Allium fistulosum. These closely related species have a similar karyomorphology, but the A. cepa genome has 27% more DNA than A. fistulosum. At metaphase I, in the hybrid, heteromorphic bivalents were observed, and the pollen mother cell chiasma frequency in the F1 hybrid was reduced when compared with the parents. Synapsis was incomplete and disturbed to some extent in all the prophase I nuclei observed. The reduced level of synapsis at late zygotene – mid pachytene in the hybrid (mean percent homoeologous synapsis is 60%) corresponds to the percent reduction in chiasma frequency. It is suggested that failure of synapsis is the main cause of reduction of chiasma frequency in the F1 hybrid. The chiasma distribution in the hybrid is most similar to that of the A. cepa parent. Although some proximal chiasmata were observed (10% of total), none of the bivalents observed had only proximally localised chiasmata as found in the A. fistulosum parent. In the F1 hybrid, synapsis of the centromeric regions of the bivalents was invariably disturbed throughout prophase I. It is suggested that there are major DNA differences in these regions preventing regular synapsis or progression of synapsis and possibly proximal chiasma formation. Nonhomoeologous synapsis occurred within axes, giving foldback SCs, and between axes, resulting in multivalent formation. It is proposed that disturbance of synapsis is due to DNA differences. There is no indication of any rearrangement or adjustment of synapsis during prophase I either to give perfectly synapsed bivalents or to resolve multivalents into bivalents.Key words: synaptonemal complex, Allium, incomplete pairing, chiasma, nonhomologous pairing, DNA content.

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.

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.

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.

Recombination nodule mapping and chiasma distribution in spermatocytes of the pigeon, Columba livia

Genome ◽  
1999 ◽  
Vol 42 (2) ◽  
pp. 308-314 ◽  
Author(s):  
M I Pigozzi ◽  
A J Solari
Keyword(s):  
Synaptonemal Complex ◽  
Random Distribution ◽  
Phosphotungstic Acid ◽  
Columba Livia ◽  
Complex Karyotype ◽  
Synaptonemal Complexes ◽  
Recombination Nodules ◽  
Chiasma Distribution ◽  
The Mean ◽  
Good Agreement

Pigeon spermatocytes were processed with a drying-down technique and their synaptonemal complex (SC) complements were analyzed by electron microscopy. The synaptonemal complex karyotype of the macrobivalents shows an excellent correspondence with the mitotic karyotype. The number and distribution of recombination nodules (RNs) were scored in complete nuclei stained with phosphotungstic acid. The average number of RNs per nucleus is 64.7. The number of nodules per bivalent shows a clear linear relationship with SC length in the 10 longest synaptonemal complexes, while the microbivalents usually bear a single RN. The location of RNs has a non-random distribution along the largest synaptonemal complexes, with lower frequencies near kinetochores and higher frequencies toward the telomeres. The ZZ bivalent is the fourth in size and shows free recombination, having on average 3.8 RNs. The mean number of nodules per cell and the mean number of nodules in the largest bivalents show very good agreement with the corresponding number of chiasmata scored in metaphase-I spermatocytes. It is concluded that the recombination nodules provide a good check for reciprocal exchanges in this and other species of birds. Additionally, a new morphology for the recombination nodules is presented, consisting of groups of electron-dense particles measuring 43 nm in diameter.Key words: meiosis, chiasmata, recombination nodules, pigeon spermatogenesis.

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.

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.

The synaptonemal complex karyotype from spread spermatocytes of a dipteran (Aedes aegypti)

1983 ◽  
Vol 25 (4) ◽  
pp. 361-369 ◽  
Author(s):  
Annelise Wandall ◽  
Allan Svendsen
Keyword(s):  
Electron Microscope ◽  
Aedes Aegypti ◽  
Light Microscopy ◽  
Synaptonemal Complex ◽  
Complex Karyotype ◽  
Synaptonemal Complexes ◽  
Recombination Nodules ◽  
The One ◽  
Mitotic Cells

Synaptonemal complexes (SCs) from the spermatocytes of the mosquito, Aedes aegypti, were spread on a 0.3 M sucrose hypophase and analyzed in the electron microscope. The SC karyotype was similar to the one known from light microscopy of mitotic cells in both relative lengths and in centromere positions. All pachytene nuclei retained their bouquet configuration during spreading; the telomeres were polarized and clustered, and the three centromeric regions were close together. The kinetochores differentiated during pachytene, those of bivalent No. 1 (the sex bivalent) before the others. Recombination nodules were preserved in some spreads; out of 35 nodules, whose distal or proximal location on the SC arms could be determined, 27 were located in the distal one-third of the arms. No SC arm had more than one nodule.

Synaptonemal complexes of triploid (ZZW) chickens: Z–Z pairing predominates over Z–W pairing

Genome ◽  
1991 ◽  
Vol 34 (5) ◽  
pp. 718-726 ◽  
Author(s):  
Alberto J. Solari ◽  
M. H. Thorne ◽  
B. L. Sheldon ◽  
C. B. Gillies
Keyword(s):  
Synaptonemal Complex ◽  
Central Region ◽  
Sex Chromosomes ◽  
W Chromosome ◽  
Synaptonemal Complexes ◽  
Early Pachytene ◽  
Recombination Nodule ◽  
Recombination Nodules ◽  
Central Regions ◽  
Partial Elimination

Twelve triploid, ZZW chickens of ages ranging from day 19 of incubation to 15 days after hatching were used for oocyte analysis. Oocytes show 117 axes per nucleus. At early pachytene, most axes form double synaptonemal complexes (triplets). An average of 27 triplets, 12 bivalents, and 12 univalents was observed. Later, a partial elimination of triplets occurs, as they are converted into typical trivalents or bivalents and univalents. The number of recombination nodules per nucleus (52.7) is similar to that of diploids. These nodules can occur in register in both central regions of a triplet (no lateral interference), and they probably stabilize the central region. Among 31 oocytes, 29 had a regular ZZ bivalent and a W univalent, and only 2 had triple pairing between a ZZ bivalent and a terminal region of the W axis (less than 1 μm in length and having a terminal recombination nodule). Competition for pairing between the gonosomes results in a large (93.5% of cases) predominance of Z–Z pairing, because of a relatively minor homology between the W and Z chromosomes. The prevailing pairing failure of the W chromosome may lead to early oocyte loss.Key words: sex chromosomes, triploids, synaptonemal complex, Z–W pairing, chicken, recombination nodules.

KARYOTYPE, SYNAPTONEMAL COMPLEXES AND POSSIBLE RECOMBINATION NODULES OF THE OOMYCETE FUNGUS SAPROLEGNIA

1982 ◽  
Vol 24 (4) ◽  
pp. 385-396 ◽  
Author(s):  
Kenji Tanaka ◽  
I. Brent Heath ◽  
Peter B. Moens
Keyword(s):  
Synaptonemal Complex ◽  
Nuclear Dna ◽  
Central Element ◽  
Nuclear Dna Content ◽  
Mean Value ◽  
Synaptonemal Complexes ◽  
Recombination Nodules ◽  
Section Electron ◽  
Serial Section Electron Microscopy ◽  
Complex Length

Pachytene nuclei of the fungus Saprolegnia ferax (Gruith.) Thuret were analyzed by serial section electron microscopy. These nuclei contained 21 synaptonemal complexes, all of which terminated at both ends on the nuclear envelope. These complexes range from 1.6 μm to 5.5 μm in length and are composed of two rather diffuse lateral elements, lack a continuous central element and contain discontinuous central nodes. These nodes occur at about 1 per μm of synaptonemal complex length, have a diameter of approximately 50 nm, are predominantly short (<200 nm) and appear to occur as multiples of a basic 50 nm length. These nodes are in many respects similar to previously reported recombination nodules. The complexes were not seen to form a bouquet stage. Based on nuclear DNA content and synaptonemal complex length, the chromosomes are calculated to contain 2C values of between 5.2 and 17.3 fg of DNA, with a mean value of 9.3 fg. Thus it seems that Saprolegnia has large chromosomes relative to other fungi and a haploid complement of 21.

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