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.     

Synaptonemal complex analysis in spermatocytes and oocytes of turbot, Scophthalmus maximus (Pisces, Scophthalmidae).

A surface-spreading synaptonemal complex (SC) technique was used to analyze spermatocytes and oocytes of turbot (Scophthalmus maximus) to visualize the process of chromosome synapsis. The total SC length was 205 +/- 12 microm in males and 172 +/- 29 microm in the only female analyzed. A representative SC karyotype of turbot was obtained. Each SC showed lateral elements of equal length. No bivalent exhibiting atypical synaptic behaviour that could be associated with heteromorphic sex chromosomes was observed, either in males or in the female. The DNA content of turbot was evaluated in eight individuals of both sexes by flow cytometry analysis. The 2C mean DNA content of turbot (1.308 +/- 0.009 pg/cell) was among the lowest observed within fishes. No statistical differences in DNA content were revealed between the sexes [Wilcoxon/Mann-Whitney test; P(W(x) = 0.243)]. The SC/DNA content ratio observed in turbot was the highest reported to date in bony fishes (Osteichthyes).     

Immunocytogenetics. III. Analysis of trivalent and multivalent configurations in mouse pachytene spermatocytes by human autoantibodies to synaptonemal complexes and kinetochores

Mice heterozygous for one or more Robertsonian (Rb) translocation chromosomes have been used to analyze synaptonemal complex (SC) configurations and kinetochore arrangements in trivalents and multivalents. Rb heterozygosity without arm homologies leads to the formation of heteromorphic trivalents in meiosis I; alternating homology of the chromosome arms produces ringlike or chainlike multivalents. Immunofluorescence double-labeling with human antibodies to SCs and kinetochores was performed on surface-spread pachytene spermatocytes. Both Rb bivalents and Rb trivalents clearly showed that metacentrics possess only one centromere. In heteromorphic trivalent SCs, the nonhomologous kinetochores of the two acrocentrics were closely paired in a cis-configuration and juxtaposed opposite the kinetochore of the metacentric; the latter appeared to be an integral part of the longitudinal SC axis. Meiotic multivalents of interpopulation hybrids included up to 36 chromosome arms. In multivalent SCs, the kinetochores always lay together, with the SC arms arranged away from the central centromere cluster. The paracentromeric regions of the Rb chromosomes appeared to remain unsynapsed on both sides of the centromeres. The SC arms were often linked by end-to-end associations. Following desynapsis of the multivalent SC, the kinetochores of the Rb metacentrics showed a highly nonrandom topologic distribution within the nucleus, reminiscent of their arrangement during synapsis.     

A comparative analysis of the mole vole sibling species Ellobius tancrei and E. talpinus (Cricetidae, Rodentia) through chromosome painting and examination of synaptonemal complex structures in hybrids

A comparative genomic analysis was carried out in the mole vole sibling species Ellobius tancrei and E. talpinus. Performing fluorescent in situ hybridisation (Zoo-FISH) using chromosome paints from the field vole Microtus agrestis showed no differences in the allocation of syntenic groups in the karyotypes of these sibling species. The only difference between their karyotypes was the position of the centromere in one pair of chromosomes, which is assumed to be the result of an inversion. To verify this hypothesis, we analysed chromosome synapsis in prophase I of meiosis. We utilised a synaptonemal complex (SC) surface-spreading technique to visualise the process of chromosome synapsis in the spermatocytes and oocytes of first-generation hybrids and back-crosses of these sibling species. In prophase I of meiosis, immunocytochemical and electron microscopy analyses revealed that all bivalents had been fully adjusted. Even in the case of a submetacentric-acrocentric bivalent with different centromere locations, synapsis of SC lateral elements was fulfilled along the entire length of the chromosomes and the formation of an inversion loop was not observed. We hypothesise that a possible mechanism leading to the change in centromere position is the repositioning and/or generation of a neocentromere. Despite the great similarity in the karyotypes of these sibling species, they exhibited significant genomic diversification, which manifested as hybrid sterility and parous female death.     

Meiosis and pollen mitosis in diploid and triploid Colocasia antiquorum Schott.

The relationship between diploid and triploid forms of Colocasia antiquorum Schott. was assessed through comparative meiotic and pollen mitotic studies. Owing to poor spreading of the chromosomes of both materials, karyological observations on pachytene nuclei were limited to a few chromosomes. Among the two nucleolar chromosomes and a metacentric, telochromomere-bearing chromosome of the diploid, the latter and one of the nucleolar chromosomes characterized by a heteropycnotic short arm were identified in both bivalent and trivalent associations in the triploid. The homologues in these cases were homomorphic and intimately paired. Two types of heteromorphic bivalents exhibiting partial pairing of homomorphic segments were also recorded in the triploid. Among the 14 bivalents of the diploid at diakinesis, two were nucleolus-associated. In the triploid, chromosomal associations at diakinesis included trivalents (2 to 9), bivalents and univalents, and the chiasma frequency per paired chromosome was lower than in the diploids. In 21.6 percent of the PMCs at this stage intragenomic pairing of one or two chromosomes was observed. Post-diakinesis stages in the diploid were regular while in the triploid they were marked by various irregularities in a majority of the cells. However, fertility (stainability), size and divisional frequency of pollen in both materials were remarkably similar. Chromosome numbers in pollen nuclei in the triploid ranged from 8 to 25. Based on these data an autopolyploid origin for the triploid Colocasia and a lower base number than the gametic chromosome number for this genus are advanced.     

Polyploidy and reproductive patterns in the root-knot nematode Meloidogyne hapla

A total of 32 populations and egg mass isolates of Meloidogyne hapla obtained from various geographical areas were studied cytologically and with respect to their mode of reproduction. In 29, maturation of oocytes is by regular meiosis. The reduced chromosome number at metaphase I is 17 in 18 populations, 16 in 8, and 15 in 3 populations. Reproduction in all these populations is by cross-fertilization, although nonfertilized eggs can develop by parthenogenesis. In the latter case, the two groups of telophase chromosomes of the second maturation division become enclosed in the same pronucleus, thus reestablishing the somatic chromosome number. Maturation of spermatocytes in three populations studied is by regular meiosis and the reduced chromosome number appears to be equal to that of the oocytes. In the remaining three populations, no synapsis takes place and the somatic number of 45 chromosomes is observed at metaphase of the single maturation division of both oocytes and spermatocytes. Reproduction is by obligatory mitotic parthenogensis. It is postulated that the basic chromosome number for the genus is nine and that the facultatively parthenogenetic populations are tetraploid, whereas, the obligatorily parthenogenetic populations are pentaploid. A preliminary scheme of the phylogeny in the family Heteroderidae is given.     

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.     

Chromosome pairing and germ cell loss in male and female mice carrying a reciprocal translocation

Female carriers of the T(5;12)31H reciprocal translocation had an average reduction of 73% in oocyte numbers compared with normal litter mates, which was of a magnitude similar to the reduction in sperm counts of male carriers. Analysis of synaptonemal complexes showed that the translocated chromosomes appeared as quadrivalents, or trivalents and univalents, or bivalents in both sexes. Quadrivalents were of three types: fully synapsed, with asynapsis confined to breakpoints, and with unsynapsed ends. There was more pairing in spermatocytes than in oocytes: 37% of spermatocytes, but only 14% of oocytes, contained a fully synapsed quadrivalent, and trivalents were also more frequently fully synapsed in spermatocytes. When these results are compared with those previously obtained for other chromosome anomalies, it becomes evident that there are considerable differences in chromosome pairing between males and females, and that different chromosome rearrangements differ in the relative amount of pairing failure occurring in male and female carriers.     

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.     

Meiotic chromosome pairing in fetal oocytes of trisomy 21 human females

The influence of trisomy on meiotic chromosome association and synapsis was studied in oocytes of two trisomy 21 fetuses. The patterns of association of the three chromosomes 21 were determined by analysis of late zygotene to early diplotene fetal oocytes after immunofluorescent staining of synaptonemal complexes. The identity of chromosome 21 was confirmed using FISH with either a whole chromosome 21 paint or an alpha-satellite DNA repeat probe. In both fetuses, a wide variety of configurations was present at pachytene. The most common configurations were a trivalent (35.5% and 51.6% of analyzable cells) and a bivalent plus univalent (62.9% and 45.2%). These different frequencies between the fetuses were not significant. Trivalents showed either triple synapsis or double synapsis with pairing-partner switches. The extent of triple synapsis varied from a short segment, either terminal or interstitial, to the whole chromosome length. Through use of immunofluorescent staining of the centromeres, we identified novel types of abnormal chromosome behavior in trisomy 21 fetal oocytes. Thus, we found that 6/41 trivalents had one of the chromosomes associated "out of register," i.e., in a nonhomologous fashion, with its two homologs. Likewise, we found three cells with bivalent plus univalent configurations, in which the univalent showed self-synapsis. The presence of three copies of chromosome 21 therefore results not only in the formation of complex and highly variable synaptic associations but also causes a significant increase in the occurrence of nonhomologous synapsis in human fetal oocytes.     

Robertsonian chromosomes and the nuclear architecture of mouse meiotic prophase spermatocytes

Background

The nuclear architecture of meiotic prophase spermatocytes is based on higher-order patterns of spatial associations among chromosomal domains from different bivalents. The meiotic nuclear architecture depends on the chromosome characteristics and consequently is prone to modification by chromosomal rearrangements. In this work, we consider Mus domesticus spermatocytes with diploid chromosome number 2n = 40, all telocentric, and investigate a possible modification of the ancestral nuclear architecture due to the emergence of derived Rb chromosomes, which may be present in the homozygous or heterozygous condition.

Results

In the 2n = 40 spermatocyte nuclei random associations mediated by pericentromeric heterochromatin among the 19 telocentric bivalents ocurr at the nuclear periphery. The observed frequency of associations among them, made distinguishable by specific probes and FISH, seems to be the same for pairs that may or may not form Rb chromosomes. In the homozygote Rb 2n = 24 spermatocytes, associations also mediated by pericentromeric heterochromatin occur mainly between the three telocentric or the eight metacentric bivalents themselves. In heterozygote Rb 2n = 32 spermatocytes all heterochromatin is localized at the nuclear periphery, yet associations are mainly observed among the three telocentric bivalents and between the asynaptic axes of the trivalents.

Conclusions

The Rb chromosomes pose sharp restrictions for interactions in the 2n = 24 and 2n = 32 spermatocytes, as compared to the ample possibilities for interactions between bivalents in the 2n = 40 spermatocytes. Undoubtedly the emergence of Rb chromosomes changes the ancestral nuclear architecture of 2n = 40 spermatocytes since they establish new types of interactions among chromosomal domains, particularly through centromeric and heterochromatic regions at the nuclear periphery among telocentric and at the nuclear center among Rb metacentric ones.     

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     

Cytogenetics of collared lemmings (Dicrostonyx groenlandicus). II. Meiotic behavior of B chromosomes suggests a Y-chromosome origin of supernumerary chromosomes

The patterns of synapsis and chiasma formation of the B chromosomes of male collared lemmings (Dicrostonyx groenlandicus) were analyzed by light and electron microscopy and compared to expectations for various hypotheses for the intragenomic origin of supernumerary chromosomes. Pachytene analysis revealed a variety of synaptic configurations including B-chromosome univalents, bivalents and trivalents. In approximately one-half of the pachytene nuclei examined, B chromosomes were in synaptic associations with the normally unpaired portion of the Y chromosome. The B-chromosome configurations at pachynema, including those involving the Y chromosome, were maintained into diakinesis and metaphase I. The meiotic behavior of the B chromosomes was inconsistent with their derivation from centric-fusion products, isochromosome formation, small-autosome polysomy, or the X chromosome. However, the frequent synapsis and apparent recombination between B chromosomes and the Y chromosome implicate this sex chromosome as a possible source of the B chromosomes in collared lemmings.     

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.     

Live cell analyses of synaptonemal complex dynamics and chromosome movements in cultured mouse testis tubules and embryonic ovaries

During mammalian meiotic prophase, homologous chromosomes connect through the formation of the synaptonemal complex (SC). SYCP3 is a component of the lateral elements of the SC. We have generated transgenic mice expressing N- or C-terminal fluorescent-tagged SYCP3 (mCherry-SYCP3 (CSYCP) and SYCP3-mCherry (SYCPC)) to study SC dynamics and chromosome movements in vivo. Neither transgene rescued meiotic aberrations in Sycp3 knockouts, but CSYCP could form short axial element-like structures in the absence of endogenous SYCP3. On the wild-type background, both fusion proteins localized to the axes of the SC together with endogenous SYCP3, albeit with delayed initiation (from pachytene) in spermatocytes. Around 40% of CSYCP and SYCPC that accumulated on the SC was rapidly exchanging with other tagged proteins, as analyzed by fluorescent recovery after photobleaching (FRAP) assay. We used the CSYCP transgenic mice for further live cell analyses and observed synchronized bouquet configurations in living cysts of two or three zygotene oocyte nuclei expressing CSYCP, which presented cycles of telomere clustering and dissolution. Rapid chromosome movements were observed in both zygotene oocytes and pachytene spermatocytes, but rotational movements of the nucleus were more clear in oocytes. In diplotene spermatocytes, desynapsis was found to proceed in a discontinuous manner, whereby even brief chromosome re-association events were observed. Thus, this live imaging approach can be used to follow changes in the dynamic behavior of the nucleus and chromatin, in normal mice and different infertile mouse models.     

Differential distribution and association of repeat DNA sequences in the lateral element of the synaptonemal complex in rat spermatocytes

The synaptonemal complex (SC) is an evolutionarily conserved structure that mediates synapsis of homologous chromosomes during meiotic prophase I. Previous studies have established that the chromatin of homologous chromosomes is organized in loops that are attached to the lateral elements (LEs) of the SC. The characterization of the genomic sequences associated with LEs of the SC represents an important step toward understanding meiotic chromosome organization and function. To isolate these genomic sequences, we performed chromatin immunoprecipitation assays in rat spermatocytes using an antibody against SYCP3, a major structural component of the LEs of the SC. Our results demonstrated the reproducible and exclusive isolation of repeat deoxyribonucleic acid (DNA) sequences, in particular long interspersed elements, short interspersed elements, long terminal direct repeats, satellite, and simple repeats. The association of these repeat sequences to the LEs of the SC was confirmed by in situ hybridization of meiotic nuclei shown by both light and electron microscopy. Signals were also detected over the chromatin surrounding SCs and in small loops protruding from the lateral elements into the SC central region. We propose that genomic repeat DNA sequences play a key role in anchoring the chromosome to the protein scaffold of the SC. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Meiotic chromosome missegregation during apyrene meiosis in the gypsy moth,Lymantria dispar,is preceded by an aberrant prophase I

The gypsy moth, Lymantria dispar, produces two structurally and genetically distinct types of spermatozoa. The eupyrene spermatozoa are genetically haploid and structurally typical. The apyrene spermatozoa are anucleate and structurally different from eupyrene spermatozoa. To understand further the events contributing to meiotic chromosome missegregation in apyrene spermatocytes, we examined the progression of meiosis in these cells with respect to their eupyrene counterparts. Chromosomal bouquet formation and fusion of nucleolar organizing regions are disrupted in apyrene nuclei. In addition, the chromatin of apyrene nuclei is prematurely and extremely condensed compared with that of eupyrene nuclei. An antibody to the conserved synaptonemal complex protein 3 (SCP3) labeled eupyrene pachytene chromosomes, but not apyrene pachytene chromosomes. In addition, apyrene meiotic spindles are missing a subset of microtubules, which likely include kinetochore microtubules. Because the condensation behavior of meiotic chromatin in apyrene spermatocytes deviates from that of eupyrene spermatocytes, we examined the appearance and distribution of the phosphorylated form of histone H3, but no significant differences in histone H3 phosphorylation were found between apyrene and eupyrene spermatocytes. We argue that because a pachytene checkpoint is not initiated in apyrene spermatocytes, this system may provide a way to understand better the underlying biochemical connections between pairing, recombination, synapsis, kinetochore assembly and segregation of chromosomes during meiosis in a higher eukaryote.     

Chromosome banding and genome compartmentalization in fishes

The diploid chromosome number of the Chinese raccoon dog varies from 54 (no B chromosomes) to 58 (4 B chromosomes). The B chromosomes are totally heterochromatic. An electron microscopic study was made of the synaptonemal complexes (SC) in spermatocytes of these animals. The SC karyotype consists of 27 regular chromosome pairs (autosomes and the sex chromosomes) plus the B chromosomes. The Bs pair effectively with one another at pachytene, but the SC axes of the B chromosomes are much denser than those of the A chromosomes. Depending on the number of Bs, both bivalents and multivalents have been observed. When three B chromosomes are present in a cell, parallel alignment of all three SCs can be seen. Formation of multivalents indicates high homology among these supernumerary heterochromatic chromosomes. Fusiform bulges are found along unpaired regions of all chromosomes which are particularly pronounced in diplotene.     

The synaptic behaviour of the wild forms of Triticum turgidum and T. timopheevii.

Different wild allopolyploid species of Triticeae show extensive bivalent formation at zygotene while a considerable number of multivalents is present in cultivated polyploid wheats. To study the chromosome behaviour at early meiotic stages in wild forms of tetraploid wheats Triticum turgidum and T timopheevii (2n = 4x = 28) we have analysed the synaptic pattern in fully traced spread nuclei at mid- and late zygotene and at pachytene of wild accessions of these species. The mean number of synaptonemal complex (SC) bivalents at mid-zygotene ranged from 12.22 to 13.14 among the accessions studied indicating a strong restriction of synapsis initiation to homologous chromosomes. The mean of bivalents increased at pachytene because of the transformation of multivalents into bivalents. Ring bivalents observed at metaphase I support that SC bivalents were formed by homologous chromosomes. The average values of SC bivalents at mid-zygotene in the wild forms are much higher than the average values observed in the cultivated tetraploid wheats but similar to that of a mutant line of T turgidum with a duplication that includes Ph1, the major homoeologous pairing suppressor locus. These results suggest that the efficiency of the mechanism operating in the homologous recognition for synapsis is higher in wild wheat populations than in cultivated varieties. Apparently, a relatively detrimental modification of the pairing regulating genetic system accompanied the domestication of the wild wheat forms.     

Meiotic synapsis proceeds from a limited number of subtelomeric sites in the human male

The formation of the synaptonemal complex (SC) is a crucial early step in the meiotic process, but relatively little is known about the establishment of the human SC. Accordingly, we recently initiated a study of synapsis in the human male, combining immunofluorescence and fluorescence in situ hybridization methodologies to analyze prophase spermatocytes from a series of control individuals. Our results indicate that synapsis is a tightly regulated process, with relatively little variation among individuals. On nonacrocentric chromosomes, there are two synaptic initiation sites, one on the distal short arm and one on the distal long arm, whereas acrocentric chromosomes exhibit a single site on the distal long arm. For both types of chromosomes, synapsis then proceeds toward the centromere, with little evidence that specific p- or q-arm sequences affect the process. However, the centromere appears to have an inhibitory effect on synapsis--that is, when one arm of a nonacrocentric chromosome is "zippered up" before the other, the centromere acts as a barrier to further movement from that arm.