Meiosis of trisomy 21 in the human pachytene oocyte

Association modalities of the three 21 chromosomes were studied during pachytene in three trisomy 21 fetuses whose chromosomal constitution was identified following amniocentesis. -- Three classes of images were observed: a trivalent, a trivalent presenting an important asynaptic region of the long arm, and a bivalent accompanied by a univalent. Such behaviour is analagous to that observed in all trisomic organisms. -- We have been able to establish the sequence of chromomeres, whose number varies from 9 to 14 according to the state of contraction in the 21 chromosome. Each band is thus subdivided into several sub-bands: at maximal elongation 2 sub-bands for band p11, 4 for q21 and 3 for q222. In addition, the interchromomeric clear bands q221 and q223 are also subdivided by the presence of a very small chromomere. In this way, the G-bands visible on mitotic metaphase chromosomes result from the compression together of several chromomeres whose individuality disappears as chromosomal condensation increases with progression of prophase.     

Location of genes coding for 18S and 28S ribosomal RNA within the genome of Mus musculus

Cytological detection of cistrons coding for 18S and 28S ribosomal RNA (rRNA) within the genome of Mus musculus inbred strain SEC/1ReJ was accomplished using the technique of in situ hybridization. Metaphase chromosome spreads prepared from cultured fetal mouse cells were stained with quinacrine-HCl and photographed. After destaining, they were hybridized to Xenopus laevis tritiated 18S and 28S rRNA, specific activity 7.5 X 10(6) dpm/mug. Silver grains clustered over specific chromosomes were readily apparent after 4 months of autoradiographic exposure. The identity of the labelled chromosomes was established by comparing the autoradiographs to quinacrine photographs showing characteristic fluorescent banding of the chromosomes in each metaphase spread. The 18S and 28S rRNA was found to hybridize to chromosomes 12, 18, and 16. Statistical analysis of the grain distribution over 26 spreads revealed that the three chromosomes were significantly labelled. Grains over these chromosomes were concentrated in an area immediately distal to the centromere, a region which in chromosomes 12 and 18 in this particular strain is the site of a secondary constriction. The relative size of the secondary constrictions, long and thus prominent on chromosome 12, obvious but shorter on 18, and indistinguishable on chromosome 16, correlated with the average number of grains observed over the centromeric region of these chromosomes, 2.5, 1.0, and 0.78, respectively.     

Meiosis in four trisomic and one double trisomic males of the newt Pleurodeles waltlii

In the newt Pleurodeles waltlii, meiosis was studied in four trisomic and one double trisomic males. Study of first prophase shows that trivalent frequencies and trivalent configurations are correlated with chromosome length; moreover, trivalent configurations indicate that long chromosomes have multiple points of initiation of synapsis whereas two points might be adequate to secure synapsis of short chromosomes. From the study of metaphase II it appears that the extra chromosomes segregate in half of the spermatocytes II. Some abnormal spermatocytes, resulting from nondisjunction of chromosomes at mitosis or at first division of meiosis, or from precocious division of chromosomes at first division of meiosis were observed. In the male double trisomic meiosis fails at anaphase of second division; this accounts for the sterility of the individual.     

Centric-fusion translocation and whole-arm heterochromatin in the karyotype of the blue fox (Alopex lagopus L.): synaptonemal complex analysis.

Conventional observations of mitotic chromosomes from two male blue foxes, revealing a centric-fusion translocation and whole-arm heterochromatin, were verified by synaptonemal complex analysis. This analysis revealed that the centric fusion had been preceded by a conspicuous loss of chromosome material in the two one-armed chromosomes involved, but the chromosomal origin of the centric-fusion kinetochore could not be established. The nontranslocated chromosomes of the trivalent, which in all cells but one were in cis configuration, had reached by early pachytene a stage in which almost complete homologous pairing and nonhomologous association or pairing of the free ends of the chromosomes could be observed. In later stages, complete pairing of the nontranslocated chromosomes with the corresponding arms of the centric-fusion translocation was seen occasionally. One to six autosomal bivalents demonstrated unpaired heterochromatic arms in early pachytene, and the heterochromatic chromosome arms were sometimes unpaired even in late pachytene. Some of them showed a distinct size heteromorphism in late zygotene and early pachytene. In most late-pachytene cells, however, the heteromorphic chromosomes were completely length-adjusted. Only a small fraction of the cells showed pairing interference between nonhomologous chromosomes.     

Male meiosis and behaviour of sex chromosomes in different populations of Rumex acetosa L. from the Western Himalayas, India

Detailed meiotic analysis in 28 North West Himalayan populations of dioecious plant Rumex acetosa L. was carried out. The species is generally discussed as an important plant having sex chromosomes. Male meiosis in all the studied populations clearly showed the formation of six bivalents and one trivalent during diakinesis and metaphase-I. The sex chromosomes in male plants exhibit a chain of trivalent (Y₁–X–Y₂). In addition, among the presently investigated populations ring-shaped trivalents were also observed for the first time in the species. Varied frequency of abnormal segregation of sex trivalent was also observed leading to XY:Y segregation instead of normal X:Y₁Y₂ segregation. A majority of the populations exhibit normal meiosis. Plants of six populations show meiotic abnormalities like cytomixis, laggards, bridges, chromatin stickiness, etc., leading to reduced pollen fertility. Translocation between an autosome and sex chromosomes was also observed in some of the populations. 0–1B chromosomes were noticed in one population. This is the first ever meiotic analysis of the species from India.     

Physical mapping of the 18S-25S and 5S ribosomal RNA genes in diploid bananas

Fluorescent in situ hybridisation (FISH) was used to determine the number and distribution of the 18S-25S and 5S rDNA sites on mitotic chromosomes of 6 wild and 2 edible diploid (2n=22) accessions belonging to the two banana species, Musa acuminata and M. balbisiana. FISH with the 18S-25S probe resulted in signals on one pair of chromosomes, the position of signals corresponded to the secondary constriction at the end of a short arm. The intensity of labelling was different between the homologues and the larger site corresponded to a larger secondary constriction. This labelling pattern was observed consistently in all genotypes. On the other hand, differences in the number of 5S sites were observed between the accessions. While in some of the wild seeded species, the 5S rDNA was localised on two pairs of chromosomes, hybridisation signals appeared on three pairs of chromosomes in other wild accessions. Quite unexpectedly, only five sites of 5S rDNA were reproducibly observed in the two vegetatively propagated diploid edible cultivars, Pisang Mas and Niyarma Yik, evidence for structural heterozygosity. A dual colour FISH showed that in all accessions, the satellite chromosomes carrying the 18S-25S loci did not carry the 5S loci. The results demonstrate that molecular cytogenetics can be applied to Musa and that physical cytogenetic maps can be generated. This revised version was published online in July 2006 with corrections to the Cover Date.     

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.     

Telomere lengths at birth in trisomies 18 and 21 measured by Q-FISH

Trisomies 18 and 21 are genetic disorders in which cells possess an extra copy of each of the relevant chromosomes. Individuals with these disorders who survive birth generally have a shortened life expectancy. As telomeres are known to play an important role in the maintenance of genomic integrity by protecting the chromosomal ends, we conducted a study to determine whether there are differences in telomere length at birth between individuals with trisomy and diploidy, and between trisomic chromosomes and normal chromosomes. We examined samples of peripheral blood lymphocytes (PBLs) from 31 live neonates (diploidy: 10, trisomy 18: 10, trisomy 21: 11) and estimated the telomere length of each chromosome arm using Q-FISH. We observed that the telomeres of trisomic chromosomes were neither shorter nor longer than the mean telomere length of chromosomes as a whole among subjects with trisomies 18 and 21 (intra-cell comparison), and we were unable to conclude that there were differences in telomere length between 18 trisomy and diploid subjects, or between 21 trisomy and diploid subjects (inter-individual comparison). Although it has been reported that telomeres are shorter in older individuals with trisomy 21 and show accelerated telomere shortening with age, our data suggest that patients with trisomies 18 and 21 may have comparably sized telomeres. Therefore, it would be advisable for them to avoid lifestyle habits and characteristics such as obesity, cigarette smoking, chronic stress, and alcohol intake, which lead to marked telomere shortening.     

Synaptonemal complex analysis of an autosomal trisomy in the horse.

Synaptonemal complex analysis by electron microscopy of a trisomy 28 in a male horse demonstrated a trivalent or a bivalent plus a univalent in primary spermatocytes. Two of the chromosomes making up the trivalent were, most often, completely paired with each other and only partially paired or associated with the third one. Half of the spermatocytes analysed demonstrated heterologous pairing or association between the free axis of the trivalent and the sex bivalent. The pairings remained, to a large extent, into diakinesis-metaphase I. In most pachytene cells one autosomal bivalent showed proximal asynapsis and paired often, heterologously, with the trivalent or the sex bivalent. The horse demonstrated azoospermy, which was due, at least in part, to degeneration at both the spermatocyte and spermatid levels.     

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.     

Impact of Robertsonian translocation on meiosis and reproduction: an impala (Aepyceros melampus) model

The captive bred animal populations showing centric fusion polymorphism can serve as a model for analysis of the impact of the rearrangement on meiosis and reproduction. The synapsis of homologous chromosomes and the frequency and distribution of meiotic recombination events were studied in pachytene spermatocytes of captive bred male impalas (Aepyceros melampus) polymorphic for der(14;20) by immunofluorescent analysis and fluorescence in situ hybridization. The chromosomes 14 and 20 involved in the centric fusion were significantly shorter due to the loss of sat I repeats indicating ancient origin of the rearrangement. The fused chromosome and the normal acrocentric chromosomes 14 and 20 formed trivalent in pachynema which showed either protruding proximal ends of the acrocentric chromosomes or single axis with synaptic adjustment in the pericentromeric region. There was no significant difference in the number of recombination events per cell between the group of translocation heterozygotes and the animals with normal karyotype. A significant reduction in the number of recombination events was observed in the trivalent chromosomes compared to the normal chromosomes 14 and 20. The level of the recombination reduction was related to the trivalent configuration. The centric fusion der(14;20) was not apparently demonstrated by any spermatogenic defects or reproductive impairment in heterozygous impalas. However, the high incidence of the chromosomal polymorphism within the captive bred population shows the importance of cytogenetic examinations in captive breeding and wildlife conservation programs, especially in the case of reintroduction of the endangered species.     

Consistent deficiencies of chromosome 18 and of the short arm of chromosome 17 in eleven cases of human large bowel cancer: a possible recessive determinism

Cytogenetic study of 11 cases of colorectal carcinoma was performed after R-banding. In all instances, there was a rearrangement involving chromosome 17 in its juxtacentromeric region, leading to the loss of its short arm. There was also a relative lack of chromosome 18, unrelated to a rearrangement of this chromosome in all but one case. Other anomalies, involving chromosomes 1 and 8 among others, were frequently but not systematically observed. The consistent lack of chromosome 18 and of the short arm of chromosome 17, leading to a complete or partial monosomy of these chromosomes in near diploid cells suggests that the passage to the hemizygous status of recessive genes carried by these chromosomes may play an important role in the development of colorectal carcinoma.     

The mitotic chromosomes of Notophthalmus (=Triturus) viridescens: Localization of C banding regions and DNA sequences complementary to 18S, 28S and 5S ribosomal RNA

The metaphase chromosomes of Notophthalmus (Triturus) viridescens have been studied by C-banding and in situ hybridization. The chromosomes show the pericentric C-banding seen in many organisms and in addition have interstitial C-bands located a short distance from the pericentric C-bands on each chromosome arm. A few C-bands are seen in telomeric regions. Regions which hybridize in situ with 18S and 28S ribosomal RNA were found on three chromosome pairs. The animals studied fell into three groups with respect to which of the six possible sites showed detectable hybridization with 18S and 28S RNA. Individual animals differed not only in the pattern of in situ hybridization of ribosomal RNA but also in the number of ribosomal RNA cistrons in the genome as measured by saturation hybridization on purified DNA. In situ hybridization showed five pairs of chromosomes which contained DNA complementary to 5S RNA. The four pairs of subtelocentric chromosomes in the N. viridescens karyotype all have 5S DNA in the pericentric regions. The fifth cluster of 5S DNA is in the middle of one arm of the chromosomes in one of the two smallest submetacentric pairs in the genome. The five sites of 5S DNA differ markedly in the level of in situ hybridization with 5S cRNA.     

Meiotic configurations in female trisomy 21 foetuses

Summary Analysis of the meiotic configurations formed by the three No 21 chromosomes in oocytes from two trisomy 21 foetuses was undertaken using a spreading technique. Light microscope analysis of the first gave limited resolving power, such that over half the oocytes could not be classified as to presence or absence of trivalent or bivalent plusunivalent. In the second, investigated at the electron microscope level, all 65 cells analysed were informative and precise detail of meiotic pairing in trivalents could be obtained. Two principal forms of trivalent occurred, one in which pairing was initiated at opposite ends of the three No 21's, each initiation point involving only two of the three homologous lateral elements; the other in which pairing was initiated by all three elements at the same end, a triple synaptonemal complex being formed. Only in one oocyte out of the 65 analysed at EM level, however, did triple pairing occur along the entire length of the No 21 trivalent. All others showed splitting into bivalent and univalent at some point along the structure. Unpaired regions within trivalents and all univalents were consistently seen to be thickened and dark staining with silver over the whole period from pachytene to diplotene. This contrasted with the desynapsing lateral elements of previously paired synaptonemal complexes which appeared thin by comparison at diplotene. The significance of the thickening remains, as yet, obscure.     

Priming of centromere for CENP-A recruitment by human hMis18alpha, hMis18beta, and M18BP1

The centromere is the chromosomal site that joins to microtubules during mitosis for proper segregation. Determining the location of a centromere-specific histone H3 called CENP-A at the centromere is vital for understanding centromere structure and function. Here, we report the identification of three human proteins essential for centromere/kinetochore structure and function, hMis18alpha, hMis18beta, and M18BP1, the complex of which is accumulated specifically at the telophase-G1 centromere. We provide evidence that such centromeric localization of hMis18 is essential for the subsequent recruitment of de novo-synthesized CENP-A. If any of the three is knocked down by RNAi, centromere recruitment of newly synthesized CENP-A is rapidly abolished, followed by defects such as misaligned chromosomes, anaphase missegregation, and interphase micronuclei. Tricostatin A, an inhibitor to histone deacetylase, suppresses the loss of CENP-A recruitment to centromeres in hMis18alpha RNAi cells. Telophase centromere chromatin may be primed or licensed by the hMis18 complex and RbAp46/48 to recruit CENP-A through regulating the acetylation status in the centromere.     

Localization of the human myelin basic protein gene (MBP) to region 18q22----qter by in situ hybridization

A restriction endonuclease fragment derived from a cloned portion of human genomic DNA corresponding to the myelin basic protein gene has been used to map the position of this gene by in situ hybridization to human metaphase chromosomes. Ten percent of the radioactively labeled sites observed were on chromosome 18. Eighty-four percent of the grains on chromosome 18 were located within the region corresponding to 18q22----qter. This represents a greater than 10-fold increase in labeling at this position over the background grain distribution found along all of the other chromosomes.     

TRANSMISSION AND SIGNIFICANCE OF B CHROMOSOMES IN ANTHURIUM WAROCQUEANUM

Somatic and meiotic chromosomes of one plant of Anthurium warocqueanum J. Moore and its selfed offspring were analyzed. The parent showed 2n = 30 + 3B in both somatic cells and pollen mother cells. The B chromosomes divided normally in somatic cells, but meiotic associations of Bs varied. Three configurations of three B chromosomes were observed at metaphase I of parent meiosis: one trivalent, one bivalent and one univalent, or three univalents. The number of B chromosomes in offspring ranged from 0 to 6, indicating their transmission from both male and female gametes. Offspring with two B chromosomes appeared in greatest frequency. It was hypothesized that both male and female gametes of the 3 B parent frequently contained one B chromosome through the normal distribution of the bivalent Bs at meiosis and the elimination of the univalent B chromosome due to lagging. Examination of pollen mother cells of offspring also revealed irregular behavior of B chromosomes. With a high number of B chromosomes, normal A chromosome bivalent formation seemed to be reduced. No phenotypic effects of B chromosomes were observed.     

Differential mechanisms governing segregation of a univalent in oocytes and spermatocytes of Drosophila melanogaster

In tricomplex heterozygotes in Drosophila melanogaster three metacentric autosomes (the TRI chromosomes) appear as a trivalent in meiosis while one autosome consisting of two homologous arms attached to the same centromere (a compound) behaves as an obligatory univalent. Cytological analysis of meiosis of tricomplex heterozygotes indicates that in oocytes the univalent compound behaves non-independently in relation to segregation of the trivalent. The compound is distributed preferentially to the same pole as one TRI chromosome. In spermatocytes the compound is distributed at random. In some oocytes the directed segregation is shown to be due to a disjunctional interaction between the compound and one partner of the trivalent at the same time as the other two chromosomes of the trivalent are separating from each other. The basic difference between the segregational mechanisms in the two sexes is discussed with a review of evidence indicating that in males segregation is determined by physical linkage that produces a stable orientation of the homologues at metaphase I. On the other hand, both genetic and cytological evidence indicate that in females a physical linkage (a chiasma) is non-essential for maintenance of co-orientation and stability after the onset of prometaphase. Genetic and cytological evidence support the hypothesis that disjunction is predetermined by non-random arrangement of the centromeric regions of chromosomes in the chromocentre — a suprachromosomal organization characteristic of maturing oocytes.by D. Schweizer     

The heteromorphic marker on chromosome 18 using restriction endonuclease AluI.

The staining property of pericentromeric heterochromatin of chromosome 18 is compared by C-banding and restriction endonuclease AluI digestion methods. Only a small distal fraction of C-band of chromosome 18 is observed to be resistant to AluI treatment, which positively stained with subsequent Giemsa staining. The resistant fraction is characteristic and usually located toward the short arm. The extensive heterogeneity of constitutive heterochromatin revealed by AluI treatment is useful in demonstrating the heterozygosity of homologous chromosomes. This, in turn, may provide frequent markers to identify the chromosomes 18's. This present approach can be utilized in evaluation of the families to describe the origin of the extra chromosome 18 in Edward syndrome. As an example, one such family has been investigated where the additional chromosome 18 originated due to paternal nondisjunction at meiosis I.     

Meiotic association between the XY chromosomes and unpaired autosomal elements as a cause of human male sterility

Intimate association between autosomal translocation trivalents and XY bivalents at pachytene was observed in a majority of cells of two men ascertained through primary sterility and found to be heterozygous for a 14;21 Robertsonian translocation. The association, studied by light and electron microscopy of spread first spermatocytes, was between the unpaired short arms of the normal chromosomes of the translocation trivalent and the differential axes of the XY chromosomes. In a minority of cells, this contact was not established, or not maintained, as alternative combinations between the elements available for non-homologous pairing were realized. Following a suggestion of Lifschytz and Lindsley (1972), sterility in these patients was attributed to spermatogenic arrest caused by physical contact of sex chromosomes with autosomal material and consequent interference with the normal metabolism of the sex chromosomes. Autosomal aberrations and polymorphisms, which lead to the presence of unpaired segments at meiosis, may thus play a critical role in a general mechanism of chromosomally-derived male sterility. It is proposed that such a mechanism may also be instrumental in the initiation of reproductive barriers in nature.