Extensive nonhomologous meiotic synapsis between normal chromosome axes of an rcp(3;6)(p14;q21) translocation in a hairless Mexican boar

Due to its low fertility, expressed as small litter size, a Mexican hairless boar was subjected to cytogenetic investigation. Analysis of G-banded mitotic chromosomes revealed a reciprocal chromosome translocation, rcp(3;6) (p14;q21). Synaptonemal complex analysis showed a regular pairing behavior of the translocation chromosome axes, always resulting in a quadrivalent configuration. However, due to extensive nonhomologous pairing between the axes of nonderivative chromosomes 3 and 6, the quadrivalent mostly had an asymmetrical cross-shaped morphology. The nonhomologous pairing occurred not only at mid and late pachytene, but also at the earliest stage of pachytene. It seems that early pachytene heterosynapsis is a common phenomenon in the pairing behavior of pig reciprocal translocations. Therefore, heterosynapsis may reduce apoptosis of germ cells due to partial absence of homologous synapsis during the pairing phase of meiosis. The frequency of spermatocytes showing quadrivalent configurations with unpaired axial segments apparently did not affect germ cell progression in the boar, since fairly normal testicular histology was noticed.     

Heterosynapsis in a heterozygous fertile boar carrier of a 3;7 translocation

Silver-stained synaptonemal complexes (SCs) in surface-spread pachytene nuclei from a boar, heterozygous for a reciprocal translocation, were analysed by electron microscopy. In such heterozygotes, cross-shaped quadrivalent configurations are expected to form in order to maximize homologous pairing. Contrary to the classical, expected cross-shaped configuration, heterosynapsis was often observed, with asymmetrical association in the lateral elements of the non-homologous partners of the quadrivalents. This heterosynapsis is assumed to be a mechanism preventing spermatocyte loss, but inducing a secondary segregational type of impairment of fertility due to foetal wastage leading to reduced prolificacy.     

Pachytene analysis in a 17;21 reciprocal translocation carrier: role of the acrocentric chromosomes in male sterility

Summary Pachytene analysis was undertaken in an infertile male, heterozygous for a 17;21 reciprocal translocation. The quadrivalent was identified by its configuration and chromomere pattern. A non-random association was found between the quadrivalent and the sex vesicle in 77% of the pachytene nuclei analysed. In 13.1% of the cells the contact with the sex vesicle was established by the terminal chromomere of the two chromosomes 21; in 63.9% of the cells, the entire region of the breakpoints was completely hidden by the sex vesicle. In some nuclei asynapsis was found in the region of the breakpoints. The nature of the contact between the quadrivalent and the sex vesicle is discussed in this paper. It is proposed that the acrocentric chromosome favours the contact between the quadrivalent and the sex vesicle, and increases the risk of sterility in male carriers of Robertsonian translocations and of reciprocal translocations involving one acrocentric chromosome.     

Analysis of synaptonemal complexes in a heterozygous human male carrier of a reciprocal translocation involving an acrocentric chromosome: heterosynapsis without previous homosynapsis

Summary Silver-stained synaptonemal complexes in surface-spread pachytene nuclei from an oligospermic man, heterozygous for a reciprocal translocation involving an acrocentric chromosome, were analyzed by electron microscopy. Contrary to the classically expected configuration, nonhomologous pairing was observed with asymetrical association of the lateral elements of the nonhomologous arms of the quadrivalents. A possible role of heterosynapsis in germ cell conservation is discussed.     

Two different XY-quadrivalent associations and impairment of fertility in men

One sterile and one subfertile man with balanced reciprocal autosomal translocations, a t(9;15), and a t(14;21), were analyzed using whole mount pachytene spreads, histology, and semen analyses. In both probands with different types of quadrivalent complexes lack of pairing near the translocation breakpoints and significant associations with XY bivalents were found. Variability in the frequency of XY-quadrivalent contacts and an increase in late pachytene to 52% in t(9;15) and 90% in t(14;21) could be observed. The lower rate was associated with reduced postmeiotic spermatogenesis and the higher rate with complete spermatogenic arrest. In both translocation carriers the XY-quadrivalent association is considered to be the main cause for testicular malfunction rather than nonpaired segments in the multivalent complexes.     

Karyotyping of Neurospora crassa using synaptonemal complex spreads of translocation quadrivalents.

The purposes of the present research are (i) to establish the karyotype of Neursopora crassa using visualization of kinetochores in the synaptonemal complex (SC) spreads, (ii) to assign each chromosome to a linkage group, and (iii) to examine chromosome pairing and recombination nodules in quadrivalents. Two strains containing reciprocal translocations were used: T(I;II)4637, which involves linkage groups I and II, and alcoy, which contains 3 independent translocations involving I and II, IV and V, and III and VI. Visualization of kinetochores in the spreads requires the use of freshly prepared fixatives. Kinetochore locations and arm ratios were documented in all 7 N. crassa chromosomes. This new information, based on kinetochore position, arm ratios, chromosome length, and quadrivalent analyses, enabled unequivocal confirmation of chromosome assignments to genetic linkage groups. Chromosome pairing in a translocation quadrivalent starts at the 4 terminal regions, and proceeds right up to the translocation break point. Recombination nodules are found in all 4 arms of quadrivalents. The ability to identify a specific chromosome to a genetic linkage group together with the ability to visualize recombination nodules and their locations will allow future cytological analysis of recombination events.     

Chromosomal abnormalities in hypoprolific boars

Four new chromosomal rearrangements are reported in the domestic pig: 3 reciprocal translocations, rcp(4;12)(p13;q13) in a crossbred boar, rcp(1;7)(q17;q26) in a Large White purebred boar, rcp(1;6)(q17;q35) in a purebred synthetic paternal line boar, and a pericentric inversion inv(2)(p13q11) in a crossbred boar. The 1/7 reciprocal translocation and the pericentric inversion were detected in animals that had sired small litters. The effect of the 1/7 translocation was accurately determined: -4.5 piglets born per litter, i.e. -36%. Both the 1/6 and 1/7 reciprocal translocations were of maternal origin. All the chromosomal rearrangements were highlighted using GTG and/or RBG banding techniques. Chromosome painting experiments were also carried out to confirm the proposed hypotheses for the three reciprocal translocations.     

Two novel reciprocal translocations involving chromosome 6 in the domestic pig]

In the present study 2 new reciprocal translocations are described in two hypoprolific boars. The first one, a Gascon/Meishan boar, has produced a mean value of 7.37 +/- 0.69 piglets, vs 12.41 +/- 0.22 piglets per litter in contemporaries. The second one, a Pietrain/Large-White boar, has produced a mean of 5.42 +/- 0.69 vs 12.41 +/- 0.22 piglets per litter in contemporaries. Each of these animals carries a new chromosome translocation involving chromosomes 6, 8 and 15, respectively. The first translocation seems to be a de novo occurring abnormality. The economic consequences of these abnormalities are discussed. Carrier of the gene HAL, the abnormal chromosomes 6 involved in these translocations are important, and could useful markers in gene mapping and flow cytometry studies in pigs.     

Meiotic behaviour of chromosomes 1R, 2R and 5R in autotetraploid rye

The meiotic behaviour of chromosomes 1R, 2R and 5R was studied in C-banded preparations of autotetraploid rye. Analysis of pairing and chiasma formation was based on metaphase I configurations, using the model designed by Sybenga, with slight modifications. Frequencies of two modes of pairing (one quadrivalent or two bivalents) differed from those expected for random pairing. Although preferential pairing for some arm pairs of chromosome 2R was detected, this did not seem to be the cause of the increased bivalent pairing. This increase was attributed to either the spatial separation of the four homologous chromosomes in some premeiotic cells into two groups of two, or a correction of the synaptonemal complex, or both. The number of chiasmate associations showed variation between chromosomes and between arms within the same chromosome. It was closely related to arm length, but different after quadrivalent and bivalent pairing. This is suggested to be a consequence of partner exchange interfering with pairing and, consequently, with chiasma formation, and a different chiasma distribution after quadrivalent pairing. Variation between chromosomes in the frequencies of alternate and adjacent co-orientation in metaphase I quadrivalents without interstitial chiasmata suggests that the relative positions of the centromeres in the quadrivalent influence their co-orientation.     

Meiotic analysis of two human reciprocal X-autosome translocations

Two cases of human reciprocal X-autosome translocation, t(X;12) and t(X;2), are described in sterile males, along with meiotic findings. Each carrier had inherited the translocation from his mother. Both showed azoospermia and germ-cell maturation arrest at the primary spermatocyte level, with most cells being arrested at the pachytene stage. A few metaphase I (MI) divisions were found, with occasional metaphase II cells being seen in the t(X;2) carrier. MI air-dried preparations gave clear evidence of chain quadrivalent formation. In the t(X;2) heterozygote, the pairing characteristics of the quadrivalent at pachytene were also analyzed in electron microscopic spreads. Disturbance of pairing around the breakpoints characterized most quadrivalents, and there was evidence in about 20% of the cells that nonhomologous pairing had taken place between the translocated chromosomes and the normal chromosome 2. Comparisons are made with similar nonhomologous pairing configurations seen at pachytene in quadrivalents of male reciprocal X-autosome translocations of the mouse.     

Most Uv-Induced Reciprocal Translocations in SORDARIA MACROSPORA Occur in or near Centromere Regions

In fungi, translocations can be identified and classified by the patterns of ascospore abortion in asci from crosses of rearrangement x normal sequence. Previous studies of UV-induced rearrangements in Sordaria macrospora revealed that a major class (called type III) appeared to be reciprocal translocations that were anomalous in producing an unexpected class of asci with four aborted ascospores in bbbbaaaa linear sequence (b = black; a = abortive). The present study shows that the anomalous type III rearrangements are, in fact, reciprocal translocations having both breakpoints within or adjacent to centromeres and that bbbbaaaa asci result from 3:1 disjunction from the translocation quadrivalent.-Electron microscopic observations of synaptonemal complexes enable centromeres to be visualized. Lengths of synaptonemal complexes lateral elements in translocation quadrivalents accurately reflect chromosome arm lengths, enabling breakpoints to be located reliably in centromere regions. All genetic data are consistent with the behavior expected of translocations with breakpoints at centromeres.-Two-thirds of the UV-induced reciprocal translocations are of this type. Certain centromere regions are involved preferentially. Among 73 type-III translocations, there were but 13 of the 21 possible chromosome combinations and 20 of the 42 possible combinations of chromosome arms.     

Meiotic studies in two infertile males with autosomal translocations

Summary Meiotic studies were performed in two infertile male carriers of balanced reciprocal translocations between chromosomes 3;5 and 6;10. The first patient had severe oligozoospermia with all stages of meiosis present. The other patient was azzospermic with meiotic breakdown after the first meiotic division. A ring quadrivalent configuration was found in diakinesis in both cases.     

Pachytene pairing and oocyte numbers in mice with two single Robertsonian translocations and the male-sterile compound with monobrachial homology

Oocyte numbers and synaptonemal complexes were studied in two Robertsonian translocations, Rb(6.15)1Ald and Rb(4.6)2Bnr, and their male-sterile compound. Oocyte numbers in the compound were lower than those of either parent, and there was a marked difference between reciprocal crosses. Synaptonemal complexes of homozygous females appeared as 19 bivalents, those of single heterozygotes as 18 bivalents and a trivalent, and those of compound heterozygotes as 17 bivalents and a quadrivalent. Most trivalents were fully paired, whereas the majority of quadrivalents exhibited terminal asynapsis. About one-half of all oocytes had other pairing abnormalities, probably reflecting reduced survivability. Whereas all fully paired quadrivalents were present in cells not showing any pairing anomalies, one-half of the quadrivalents with terminal asynapsis were seen in oocytes with other anomalies. It is suggested that in oocytes destined for atresia, there is a predisposition to synaptic failure of translocation configurations. Additional oocytes are likely to break down because of the deleterious effect of the compound translocation on gametogenesis. This effect seems to be more pronounced in Rb1Ald/Rb2Bnr spermatocytes than in oocytes.     

Meiotic studies in an azoospermic boar carrying a Y;14 translocation

A reciprocal translocation between the q arm of the Y chromosome and the q arm of chromosome 14 was identified in a young, phenotypically normal boar presenting azoospermia. Testicular biopsies were analyzed by classical histological and immunolocalization techniques, and by fluorescence in situ hybridization. Meiotic pairing analysis of 85 pachytene spreads showed the presence of an open structure corresponding to a quadrivalent formed by chromosomes 14, X, and the derivative chromosomes 14 and Y in 84.7% of the cases. In the remaining cases (15.3%), a 'trivalent plus univalent' configuration was observed. Immunolocalization of gammaH2AX revealed the presence of this modified histone in the chromatin domains of unsynapsed segments (centromeric region of chromosome 14) and spreading of the gammaH2AX signal from the XY body throughout chromosome 14 in 7.05% of the cells analyzed. The potential causes of the observed infertility, i.e. activation of meiotic checkpoints and/or silencing of genes necessary for the progression of meiosis, are discussed.     

Pairing of ZW gonosomes and the localized recombination nodule in two Z-autosome translocations in Gallus domesticus

Electron microscopic observations of synaptonemal complexes of oocytes from chickens heterozygous for two Z-autosome translocations have been used to identify and study the pairing region of the Z and W chromosomes. The two translocations, MN t(Z;1) and t(OH 10), have breakpoints in opposite arms of the Z, and the arm having the breakpoint of MN t(Z;1) is marked by the terminal C+ band. In both translocations the short arm of the W was specifically paired with the euchromatic short arm of the Z. In MN t(Z;1) only open quadrivalents (74%) and trivalents plus W univalents (26%) were observed, whereas t(OH 10) exhibited, in addition to the prevalent quadrivalents (62%), III + I (19%) and II + II (19%) configurations. The extent of W pairing was slightly decreased in MN t(Z;1) (68.4% of the W chromosomes paired) and considerably decreased in t(OH 10) (25.3% of the W chromosomes paired). Nonhomologous synapsis occurred regularly at the quadrivalent crosspoint in MN t(Z;1) and also in bivalents from t(OH 10). The recombination nodule normally located in the terminus of the pairing region in normal ZW pairs is present in both translocations without any alteration of its frequency or its strict terminal position. Based on these data and previous observations (Rahn and Solari, 1986), it is proposed that an obligatory recombination event occurs at a locus between 0.7 microns and 0.15 microns of the paired ZW telomeres, establishing a recombinational region and a pseudoautosomal region which determine partial sex-linkage and no sex-linkage, respectively. Most of the pairing region of the ZW pair is nonhomologously paired.     

Male pachytene pairing in single and double translocation heterozygotes and spermatogenic impairment in the mouse

In order to clarify the relationship between meiotic pairing and progress of spermatogenesis, an analysis of male meiotic pairing was carried out in four reciprocal translocation heterozygotes and two double heterozygotes for two semi-identical reciprocal translocations. The reciprocal translocations were chosen to range from fertility (T70H/+) through almost complete sterility (T31H/+) to complete sterility (T32H/+, T42/H+). If meiotic pairing in the translocation multivalent was incomplete, it concerned terminal or probably more often proximal chromosome segments (Chain IV). If both segments failed to pair the multivalent symbol is Chain III+I. Complete pairing is symbolized by Ring IV. To contrast and complement observations of this type, the double heterozygotes were introduced. Males of this type in theory possess two heteromorphic bivalents with a central area of incomplete meiotic pairing (loop formation). Of the T70H/T1Wa double heterozygotes, 36% of the males are capable of inducing at least one decidual reaction in two females whereas for T26H/T2Wa, 79% of the males can do so. For the reciprocal translocations, it was found that proximity of the multivalent to the sex bivalent during pachytene increased in the order Ring IV, Chain IV, Chain III+I. The degree of spermatogenic impairment as measured from cell counts in histological sections and tubular whole mounts, is positively related to the frequency of proximity between the sex chromosomes and the translocation multivalent and thus to lack of meiotic pairing within the multivalent. The meiotic pairing analysis of the double heterozygotes yielded the following findings. For the long heteromorphic bivalents a true loop was never seen in T70H/T1Wa and only rarely observed in T26H/T2Wa. Small marker bivalents of both types were usually recognizable by the following criteria: (i) pairing confined to distal or proximal segments, (ii) both distal and proximal segments pairing and loop formation and (iii) pairing covering the entire length of both homologues but the longer one often with a thickened lateral element. The same positive correlation between the absence of pairing (proximal, distal or central) and the proximity of the small marker bivalent synaptonemal complex to the sex bivalent has been found as for unpaired segments within reciprocal translocation multivalents. One unexpected finding was the occurrence of diploid spermatids and spermatozoa especially in T32H/+ males (70–91%) but also in T31H/+ (3–39%).     

Meiotic Recombination Analyses in Pigs Carrying Different Balanced Structural Chromosomal Rearrangements

Correct pairing, synapsis and recombination between homologous chromosomes are essential for normal meiosis. All these events are strongly regulated, and our knowledge of the mechanisms involved in this regulation is increasing rapidly. Chromosomal rearrangements are known to disturb these processes. In the present paper, synapsis and recombination (number and distribution of MLH1 foci) were studied in three boars (Sus scrofa domestica) carrying different chromosomal rearrangements. One (T34he) was heterozygote for the t(3;4)(p1.3;q1.5) reciprocal translocation, one (T34ho) was homozygote for that translocation, while the third (T34Inv) was heterozygote for both the translocation and a pericentric inversion inv(4)(p1.4;q2.3). All three boars were normal for synapsis and sperm production. This particular situation allowed us to rigorously study the impact of rearrangements on recombination. Overall, the rearrangements induced only minor modifications of the number of MLH1 foci (per spermatocyte or per chromosome) and of the length of synaptonemal complexes for chromosomes 3 and 4. The distribution of MLH1 foci in T34he was comparable to that of the controls. Conversely, the distributions of MLH1 foci on chromosome 4 were strongly modified in boar T34Inv (lack of crossover in the heterosynaptic region of the quadrivalent, and crossover displaced to the chromosome extremities), and also in boar T34ho (two recombination peaks on the q-arms compared with one of higher magnitude in the controls). Analyses of boars T34he and T34Inv showed that the interference was propagated through the breakpoints. A different result was obtained for boar T34ho, in which the breakpoints (transition between SSC3 and SSC4 chromatin on the bivalents) seemed to alter the transmission of the interference signal. Our results suggest that the number of crossovers and crossover interference could be regulated by partially different mechanisms.     

Studies on chiasma frequency and distribution in two fertile men carrying reciprocal translocations; one with a t(9;10) karyotype and one with a t(Y;10) karyotype

Summary The frequency and distribution of chiasmata was investigated in two fertile carriers of reciprocal translocations, one with a 46,XY,t(9;10)(p22;q24) karyotype and one with a 46,X,-Y,+der(Y),t(Y;10)(q12;q24) karyotype. In both cases the chromosomes involved in the translocation showed an increase in chiasma frequency in comparison to karyotypically normal controls and in both cases this increase was localised, affecting only one interstitial segment of each translocation quadrivalent. In the t(9;10) case chiasmata appeared in substantial numbers in a novel location, the proximal two thirds of 9p, while in the t(Y;10) case chiasmata appeared in a conventional location, the medial region of 10q, but at an increased frequency. Furthermore there was evidence for inter-chromosomal effects in the t(9;10) case.     

Effect of the quinolone coccidiostat decoquinate on the rearrangement of chromosomes of Eimeria tenella

The present report concerns our attempts to further study the effect of quinolone coccidiostats on the sporulation of Eimeria tenella oocysts by analyzing the meiotic behaviour of the chromosomes. To that end, synaptonemal complexes were analyzed by TEM applied to intact meiotic chromosomes. These were isolated after disruption of oocysts, which were harvested from decoquinate-medicated and non-medicated (control) birds. In oocysts from control birds, synaptonemal complexes appeared as the 14 bivalents of the normal karyotype. However, in oocysts from medicated birds, our synaptonemal complex analysis revealed a reciprocal translocation, which was observed as an irregular pairing of chromosome axes 5 and 12 resulting in quadrivalent and trivalent configurations. This finding suggests breakage points in chromosomes 5 and 12 and exchange of chromosomal segments. Furthermore, breakpoints in chromosome 12 resulted in telomere deletion. The chromosomal aberrations described in the present study may result in reduced sporulation since chromosomes involved in translocations segregate abnormally during meiosis. In addition, the results reported provide new evidence of the inhibitory effect of quinolones on the sporulation of E. tenella oocysts, since sporocysts were not formed.     

Strukturheterozygotie beiVicia faba

Summary The karyotypes and the meiotic behaviour of two spontaneous reciprocal translocations and one pericentric inversion are described. One of these translocations was characterized by chiasma-formation in the interstitial-segments, the other was not. The types of orientation and distribution of the chromosomes from the chain-configurations in meta-anaphase I are specified, compared mutually and with those of translocation rings and chains in maize and the similarities and differences are pointed out. In the range of the heterozygous pericentric inversion there was no pairing in meiotic prophase and therefore no chiasma formation and sterility. It will be tried to cross especially one of the translocations with the inversion-type in order to rebuild the karyotype ofVicia faba. In this case it would be possible to distinguish between all five pairs of small chromosomes according to their morphological structure, a possibility very important in localizing chromosome aberrations on the chromosomes ofVicia faba.

---

---

Mit 15 Abbildungen