Meiotic chromosome behaviour in male triploid transparent coloured crucian carp, Carassius auratus L.

Meiotic chromosome behaviour was investigated by surface-spreading, air-drying and thin sectioning testes for light and electron microscope examination in artificial triploid transparent coloured crucian carp ( Carassius auratus L.) produced by hydrostatic pressure shock. Unsynapsed univalents, synapsed bivalents and partially synapsed trivalents could be observed and distinguished from each other in the surface-spread spermatocytes. The pairing of the partially paired trivalents mainly occurred in the telomeric regions. Similarly, lateral elements of unsynapsed univalents, typical synapsed bivalents and triple pairing configurations having three lateral elements and two central elements in the trivalents were also observed in the thin sectioned pachytene spermatocytes. The metaphase I cells were mainly composed of univalents, bivalents and trivalents, but a few tetravalents, pentavalents and hexavalents were also found. The relationship between disturbed chromosome pairing and abnormal spermatogenesis is briefly discussed.     

Unpaired chromosomes at meiosis: cause or effect of gametogenic insufficiency?

Pairing failure at meiosis has been postulated as a cause of gametogenic arrest in both heterozygous translocation carriers and males whose spermatocytes exhibit univalent X and Y chromosomes. The present investigation is a survey of pachytene translocation configurations, at the electron microscopic level, in six stocks of mice, comprising a total of 464 spermatocytes and 343 oocytes. Univalence of the X and Y chromosomes was studied in the same stocks, as well as in three additional homozygous translocation stocks. Fully paired as well as asynaptic configurations were found in all translocation stocks, and the proportions of each configuration differed considerably between spermatocytes and oocytes of mice carrying the same translocation. In both spermatocytes and oocytes, other pairing anomalies were more frequent in cells with asynapsed than with fully synapsed configurations, and spermatocytes with univalent sex chromosomes had a higher proportion of autosomal anomalies than did spermatocytes with XY bivalents. It is concluded that pairing failure at meiosis is primarily a symptom, rather than a cause, of gametogenic arrest, and that chromosome rearrangements, even if they appear to be balanced, may affect the rate of atresia by interfering with the normal rate of meiotic progression. Once pairing failure is established, it could secondarily increase the probability of gametogenic failure.     

Synaptonemal complex analysis in spermatocytes and oocytes of tertiary trisomic Ts(512)31H mice with male sterility

Whole-mount preparations of silver-stained spermatocytes and oocytes from Ts(512)31H mice were examined in the electron microscope. The 5(12) chromosome was associated with the XY bivalent in the large majority of spermatocytes, whereas in about one-half of the oocytes, the 5(12) was associated with either unpaired chromosomes or heterochromatic parts of chromosomes or showed self-synapsis. There was a tendency for 5(12) chromosomes to be more fully heterochromatic in oocytes than in spermatocytes. A large proportion of oocytes (50%) and a much smaller proportion of spermatocytes exhibited various errors of chromosome pairing, but these proportions were only marginally greater than in control gametocytes from mice with normal karyotypes. It is concluded that the observed errors of pairing bear no simple relation to the almost complete breakdown of spermatogenesis and the marked impairment of oogenesis that occur in tertiary trisomic Ts(5(12))31H mice.     

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.     

The effect of multiple simple Robertsonian heterozygosity on chromosome pairing and fertility of wild-stock house mice (Mus musculus domesticus)

The influence of Robertsonian (Rb) heterozygosity on fertility has been the subject of much study in the house mouse. However, these studies have been largely directed at single simple heterozygotes (heterozygous for a single Rb metacentric) or complex heterozygotes (heterozygous for several to many metacentrics which share common chromosome arms). In this paper we describe studies on male multiple simple heterozygotes, specifically the F(1) products of crosses between wild-stock mice homozygous for four or seven metacentrics and wild-stock mice with a standard all-acrocentric karyotype; these F(1) products were characterized by four and seven trivalents at meiosis I, respectively. Mice with the same karyotype, but two different genetic backgrounds were examined. Although a range of meiotic and fertility studies were conducted, particular emphasis was paid to analysis of chromosome pairing, previously not well-described in multiple simple heterozygous mice. The progression of spermatocytes through prophase I was followed by electron microscopy of surface spread material. As previously shown for single simple Rb heterozygotes, the trivalents that characterize multiple simple heterozygotes initially showed delayed pairing of the centromeric region and later showed side arm formation, resulting from non-homologous pairing by the centromeric ends of the acrocentric chromosomes. In the four trivalent groups of mice, 15 and 32% of trivalents showed unpairing in the centromeric region at mid pachytene; equivalent values were 29 and 39% for the seven trivalent groups. Pairing abnormalities (largely attachments and interlocks between trivalents and between a trivalent and the XY configuration) were observed in 18 and 23% of mid pachytene cells in the four trivalent groups and 36 and 49% of cells in the seven trivalent groups. The greater level of pachytene irregularity (unpairing and pairing abnormalities) in seven versus four trivalent heterozygotes was mirrored in terms of higher anaphase I nondisjunction frequency and lower germ cell counts. However, while pachytene irregularities appear to contribute to germ cell death, examples of male sterility in our material undoubtedly also involve genic incompatibilities.     

Sex-dependent synaptic behaviour in triploid turbot,Scophthalmus maximus (Pisces,Scophthalmidae)

A surface-spreading synaptonemal complex (SC) technique was used to analyse spermatocytes and oocytes of triploid turbot (Scophthalmus maximus) in order to visualise the process of chromosome synapsis. The most conspicuous characteristic of triploid oocytes is that, in the trivalents, the lateral elements of the SC were frequently associated in threes, either completely along the length of the trivalent, or partially, forming a variety of forked structures. In these nuclei, synapsis usually occurred among homologous chromosomes and the number of bivalents observed was significantly higher than that expected under the assumption of random chromosome association among all partners. However, the frequency of trivalents was very low in triploid spermatocytes, triple synapsis being also scarce. In these nuclei chromosomes that were excluded from homologous synapsis become engaged in random SC formation, and, therefore a considerable number of non-homologous associations are produced. The causes of the synaptic differences observed in triploid males and females of turbot and their possible relation to the sterility displayed by these animals are discussed.     

Further insights on chromosomal pairing of autopolyploids: a triploid and tetraploids of rye

Chromosomal pairing of one triploid and three tetraploid plants of rye, Secale cereale, was analyzed by electron microscopy in surface-spread prophase I nuclei and compared with light microscopic observations of metaphase I cells. Prophase I is characterized by: (i) the weak alignment showed by the three or four unsynapsed or partially homologous synapsed axes; (ii) the low number ber of pairing partner switches (PPSs) displayed by both trivalents and quadrivalents; and (iii) the existence of complex multivalents in which up to 13 chromosomes in the triploid and 22 chromosomes in the tetraploids were involved. However, only few heterologous chromosomal associations were maintained at metaphase I. The results obtained are discussed under the assumptions of the random end pairing model with some modifications.     

Sex-dependent frequency and type of autosomal univalency at the first meiotic metaphase in mouse germ cells

Univalents at the first meiotic metaphase in mouse spermatocytes occur mainly in the XY pair, making it difficult to compare the amounts of univalency in males and females. In this study, the amounts of autosomal univalency in male and female meiosis were compared using the model strain CBA-T6, in which univalency of the small marker autosome pair T6 has been shown to occur very frequently in spermatocytes. Mice from inbred CBA and DBA strains were also analysed. The total frequencies of univalency (sex chromosomes plus autosomes) in metaphase I spermatocytes were 45.6% in CBA, 36.9% in CBA-T6, and 37.3% in DBA males. The aneuploidy in metaphase II spermatocytes ranged from 1.4 to 3% in these strains, which was in agreement with previous findings that most primary spermatocytes with abnormal chromosome configurations are arrested in their development before metaphase II. In the CBA-T6 strain, autosomal univalency at metaphase I mostly involved chromosome pair T6; however, its frequency differed significantly between the sexes, amounting to 18.9% in spermatocytes and 4.3% in oocytes. In the CBA strain, autosomal univalents at metaphase I were seen in 7.7% of the spermatocytes and 1.4% of the oocytes and, in DBA mice, in 4.9% of the spermatocytes and 3.8% of the oocytes. However, in DBA oocytes, when univalency occurred it usually concerned a greater number of bivalents in one cell (range: 2-19 disjoined bivalents), a phenomenon very rare in males of this strain. This study shows that univalent formation differs between the male and female types of meiosis.     

Electron microscopic investigations of synaptonemal complexes in an infertile human male carrier of a pericentric inversion inv(1)(p32q42)

Summary Electron microscopic investigations of surface spread synaptonemal complexes in spermatocytes from a 37-year-old man ascertained for infertility detected a pericentric inv(1), and subsequent lymphocyte analysis placed the break-points at p32 and q42. Most spermatocytes showed a maturation arrest at mid-pachytene explaining the azoospermia. As in two other comparatively large loop-forming pericentric inversions, initiation of synapsis took place in the middle of the inverted segment. Thus there is no indication of interstitial synaptic initiation being restricted to special pairing sites along the length of the chromosome. All spermatocytes investigated at mid-pachytene showed inversion loops, none of which was fully synapsed with a specific delay in pairing of the heterochromatic block 1qh and adjacent segments. The loops were of similar size in all the cells examined and synaptic adjustment had not taken place. There was no indication of a preferential association between the inv(1) bivalent and the XY configuration, and a functional disturbance of the X seems an unlikely reason for the meiotic maturation arrest. The most likely cause may be the failure of adequate synapsis of the inverted segment and the possibly associated pairing abnormalities of other homologues, including asynapsis and/or precocious desynapsis.     

卵巢发育阻滞的人工三倍体鱼减数分裂染色体配对的光镜观察

采用界面铺张制片和硝酸银一步染色的方法,对人工三倍体水晶彩鲫卵巢发育阻滞型个体的减数分裂染色体配对进行了光镜观察。在分化有初级卵母细胞的卵巢发育阻滞型的三倍体鱼中,减数分裂粗线期细胞主要的由二价体和单价体组成,也见有少量三价体和其它多价体,其染色体成员数大多在９０左右;在不同细胞间,染色体的大小变化较大;配对联会过程中形成的配对叉和产生的特异蛋白在一些细胞中明显可见。文中讨论了三倍体染色体配对紊乱     

男性育性障碍与联会复合体异常的关系

据有关资料统计,男人中大约有11%育性有障碍,其中由遗传因素引起的男性不育占居首位,包括染色体异常、微小缺失和基因突变等3类。研究表明,男性染色体畸变与精子发生失败或受孕浪费现象密切相关。联会复合体（synaptonemal complex SC）分析为揭示二者之间的关系提供了证据。本文结合近年来SC在男性不育症诊断中的应用和我们在这方面的研究结果,对男性育性障碍与SC异常的关系进行了以下5个方面的评述和讨论。1.XY-二价体与重排染色体联合,干扰或影响X染色体的正常功能,从而干扰精子发生。2. 重排染色体在断裂点处广泛的不配对,引起精子发生失败。3. SC粉碎化、侧生组分膨化、配对紊乱导致精子发生失败。 4. 重排染色体直接的异源配对导致不平衡配子的产生而出现受孕浪费。5.SC蛋白基因的突变引起SC超微结构的变化导致男性不育。     

Inter-sex variation in synaptonemal complex lengths largely determine the different recombination rates in male and female germ cells

Meiotic chromosomes in human oocytes are packaged differently than in spermatocytes at the pachytene stage of meiosis I, when crossing-over takes place. Thus the meiosis-specific pairing structure, the synaptonemal complex (SC), is considerably longer in oocytes in comparison to spermatocytes. The aim of the present study was to examine the influence of this length factor on meiotic recombination in male and female human germ cells. The positions of crossovers were identified by the DNA mismatch repair protein MLH1. Spermatocytes have approximately 50 crossovers per cell in comparison to more than 70 in oocytes. Analyses of inter-crossover distances (and presumptively crossover interference) along SCs suggested that while there might be inter-individual variation, there was no consistent difference between sexes. Thus the higher rate of recombination in human oocytes is not a consequence of more closely spaced crossovers along the SCs. The rate of recombination per unit length of SC is higher in spermatocytes than oocytes. However, when the so-called obligate chiasma is excluded from the analysis, then the rates of recombination per unit length of SC are essentially identical in the two sexes. Our analyses indicate that the inter-sex difference in recombination is largely a consequence of the difference in meiotic chromosome architecture in the two sexes. We propose that SC length per se, and therefore the size of the physical platform for crossing-over (and not the DNA content) is the principal factor determining the difference in rate of recombination in male and female germ cells. A preliminary investigation of SC loop size by fluorescence in situ hybridization (FISH) indicated loops may be shorter in oocytes than in spermatocytes.     

The influence of the Robertsonian translocation Rb(X.2)2Ad on anaphase I non-disjunction in male laboratory mice

A Robertsonian translocation in the mouse between the X chromosome and chromosome 2 is described. The male and female carriers of the Rb(X.2)2Ad were fertile. A homozygous/hemizygous line was maintained. The influence of the X-autosomal Robertsonian translocation on anaphase I non-disjunction in male mice was studied by chromosome counts in cells at metaphase II of meiosis and by assessment of aneuploid progeny. The results conclusively show that the inclusion of Rb2Ad in the male genome induces non-disjunction at the first meoitic division. In second metaphase cells the frequency of sex-chromosomal aneuploidy was 10.8%, and secondary spermatocytes containing two or no sex chromosome were equally frequent. The Rb2Ad males sired 3.9% sex-chromosome aneuploid progeny. The difference in aneuploidy frequencies in the germ cells and among the progeny suggests that the viability of XO and XXY individuals is reduced. The pairing configurations of chromosomes 2, Rb2Ad and Y were studied during meiotic prophase by light and electron microscopy. Trivalent pairing was seen in all well spread nuclei. Complete pairing of the acrocentric autosome 2 with the corresponding segment of the Rb2Ad chromosome was only seen in 3.2% of the cells analysed in the electron microscope. The pairing between the X and Y chromosome in the Rb2Ad males corresponded to that in males with normal karyotype. Reasons for sex-chromosomal non-disjunction despite the normal pairing pattern between the sex chromosomes may be seen in the terminal chiasma location coupled with the asynchronous separation of the sex chromosomes and the autosomes.(ABSTRACT TRUNCATED AT 250 WORDS)     

Chromosome pairing in triploid intergeneric hybrids ofFestuca pratensis withLolium multiflorum, revealed by GISH

Genomic in situ hybridisation (GISH) was used to reveal chromosome pairing in two partly fertile, triploid (2n = 3x = 21) hybrids obtained by crossing the diploid (2n = 2x = 14) Festuca pratensis Huds. (designated FpFp), used as a female parent, with the autotetraploid (2n = 4x = 28) Lolium multiflorum Lam. (designated LmLmLmLm), used as a male parent. The pattern of chromosome pairing calculated on the basis of the mean values of chromosome configurations identified in all 100 PMCs analysed, was: 0.71I Lm + 2.24I Fp + 2.18II Lm/Lm + 0.54II Lm/Fp + 4.18III Lm/Lm/Fp. A relatively high number of Lm/Lm bivalents and Fp univalents, and a low number of Lm/Fp bivalents and Lm univalents indicated that the pairing was preferential between L. multiflorum chromosomes. Other observations regarding chromosome pairing within the Lm/Lm/Fp trivalents also confirmed this preferential pairing in the analysed triploids, as the Fp chromosome was not randomly located in the chain- and frying-pan-shaped trivalents. The similarities and differences in chromosome pairing at metaphase I and the level of preferential pairing between Lolium chromosomes in the different triploid Lolium-Festuca hybrids are discussed.     

家鸡联会复合体的亚显微结构分析

本文以表面铺展——硝酸银染色技术,对家鸡的联会复合体(Syneptonemal Complex,SC)作亚显微结构分析。根据对10个精母细胞和10个卵母细胞SC的测量结果,绘制组型图。发现雌雄家鸡的常染色体的SC组型相同。在精母细胞中,性染色体(ZZ)的行为与常染色体相似。在卵母细胞中,性染色体ZW的长度不同,长轴为Z,短轴为W,两者之间只有部分配对,形成SC。从早粗线期到晚粗线期,由同源配对调整为非同源配对。另外,在一只雌鸡中,第一次观察到,有些细胞的常染色体能正常配对,而性染色体完全不配对的现象。     

Presence of an extra chromosome alters meiotic double-stranded break repair dynamics and MLH1 foci distribution in human oocytes

Studies performed on human trisomic 21 oocytes have revealed that during meiosis, the three homologues 21 synapse and, in some cases, achieve what looks like a trivalent. This implies that meiotic recombination takes place among the three homologous chromosomes 21, and to some extent, crossovers form between them. To see how meiotic recombination is in the presence of an extra chromosome 21, we analyzed the distribution of three recombination markers (γH2AX, RPA, and MLH1) on trisomic 21 oocytes at pachynema and, in particular, on chromosomes 21. Results clearly show how the presence of an extra chromosome 21 alters meiotic recombination progression, leading to the presence of a higher number of early recombination markers at pachynema. Moreover, the distribution on these chromosomes 21 of some of these markers is different in aneuploid oocytes. Finally, there is a substantial increase in the number of MLH1 foci, a marker of most crossovers in mammals, which is related to the number of synapsed chromosomes in pachynema. Thus, bivalents 21 had fewer MLH1 foci than partial or total trivalents, suggesting a close relationship between synapsis and crossover designation. All of the data presented suggest that the presence of an extra chromosome alters meiotic recombination globally in aneuploid human oocytes.     

Synaptic adjustment,non-homologous pairing,and non-pairing of homologous segments in sex chromosome mutants of Ephestia kuehniella (Insecta,Lepidoptera)

Microspread pachytene nuclei of wild-type and W chromosome mutants of the mealmoth Ephestia kuehniella were used to study synaptonemal complex (SC) formation. In structurally heterozygous bivalents, axial elements of considerable length differences were brought to the same length by synaptic adjustment. The adjustment length was a compromise between the mutant and the wildtype homologue length in a structural heterozygote of a W chromosome-autosome translocation, T(A; W). The translocated non-homologous W segment really participated in SC formation as could be seen from the W chromosomal heterochromatin, used as a cytogenetic marker. Pachytene pairing of the wild-type W-Z bivalent extended from about two-thirds to the full length of the W chromosome, though from cytogenetic and genetic evidence W and Z are largely — if not completely — non-homologous. Nonhomologous pairing was even more conspicuous in sex chromosome bivalents containing a deleted W chromosome, Df(W). In one of the pairing configurations the halves of the Z chromosome were synapsed to either side of the Df(W). Thus, one side was pairing with the Df(W) in reversed order. The pairing behavior of the W with homologous chromosome segments was tested by introducing supernumerary W segments via the T(A; W) translocation. Pairing between the W and the translocated homologous W segment never occurred, whereas the Z frequently synapsed with it. Even in T(A; W) homozygotes, pairing between the two translocated W segments was not regularly found while the autosomal parts of the translocation chromosomes were always completely paired. Homologous chromosomes and the ability to form an SC are not sufficient for pairing initiation. Specific loci or sequences are postulated for this function. They are either absent from the W chromosome or are present in only low concentrations.     

All paired up with no place to go: pairing, synapsis, and DSB formation in a balancer heterozygote

The multiply inverted X chromosome balancer FM7 strongly suppresses, or eliminates, the occurrence of crossing over when heterozygous with a normal sequence homolog. We have utilized the LacI-GFP: lacO system to visualize the effects of FM7 on meiotic pairing, synapsis, and double-strand break formation in Drosophila oocytes. Surprisingly, the analysis of meiotic pairing and synapsis for three lacO reporter couplets in FM7/X heterozygotes revealed they are paired and synapsed during zygotene/pachytene in 70%–80% of oocytes. Moreover, the regions defined by these lacO couplets undergo double-strand break formation at normal frequency. Thus, even complex aberration heterozygotes usually allow high frequencies of meiotic pairing, synapsis, and double-strand break formation in Drosophila oocytes. However, the frequencies of failed pairing and synapsis were still 1.5- to 2-fold higher than were observed for corresponding regions in oocytes with two normal sequence X chromosomes, and this effect was greatest near a breakpoint. We propose that heterozygosity for breakpoints creates a local alteration in synaptonemal complex structure that is propagated across long regions of the bivalent in a fashion analogous to chiasma interference, which also acts to suppress crossing over.     

Synaptonemal complex analysis in spermatocytes of diploid and triploid Chinese shrimp Fenneropenaeus chinensis

A modified surface spreading technique for synaptonemal complex (SC) analysis was tested to assess the process of chromosome synapsis in spermatocytes of diploid and induced triploid Fenneropenaeus chinensis. Spermatocytes of diploid shrimp showed typical morphological characteristics of eukaryote SC, with complete synapsis of bivalents. No recognizable bivalent associated with sex chromosomes was observed in spermatocytes of diploid shrimp. However, differences in morphology of SC, including unsynapsed univalents, bivalents, totally paired trivalents with non-homologous synapsis, partner switches and triple synapsis were identified at early pachytene stage of triploid spermatocytes. Triple synapsis was especially common at late pachytene stage in spermatocytes of triploid shrimp. The observed abnormal synapsis behavior of chromosomes in spermatocytes indicated that triploid male shrimp may find it difficult to develop normal haploid sperm.     

Pachytene pairing in relation to sperm and oocyte numbers in a male-fertile reciprocal translocation in the mouse

In adult males carrying the male-fertile reciprocal translocation T(2;4)13H, body weights, testis weights, and sperm counts were higher in heterozygotes than in homozygotes. Heterozygotes whose mothers were C3H/He exceeded their reciprocal counterparts in the same criteria. At 3-4 days of age, no significant differences between homozygous and heterozygous females were found in body weight, ovarian volume, or oocyte numbers, although mean oocyte volumes were somewhat larger in heterozygotes than in homozygotes. In homozygous males and females the synaptonemal complexes of rearranged chromosomes appeared as bivalents that were indistinguishable from normal bivalents. In most gametocytes of heterozygotes, the translocation was present in the form of a quadrivalent. The degree of pairing failure was greater in oocytes than in spermatocytes. Terminal asynapsis of quadrivalents was very rare in spermatocytes, but it affected one quarter of the oocytes. Only very few translocation configurations were associated with the XY bivalent. It is concluded that the number of sperm produced in male heterozygotes can match the general increase in vigor by the formation of a high level of fully paired quadrivalents, whereas a greater degree of terminal asynapsis in the quadrivalents of oocytes may indicate a slightly more deleterious effect of this translocation on oogenesis.