Three autosomal chromosome translocations associated with repeated early embryonic loss (REEL) in the domestic horse (Equus caballus)

Repeated early embryonic loss (REEL) represents a considerable economic loss to the horse industry. Mares that experience REEL may be overlooked as potential carriers of a chromosome abnormality. Here we report three different autosomal translocations in Thoroughbred mares presented for chromosome analysis because of REEL. The karyotypes were 64,XX,t(1;21), 64,XX,t(16;22), and 64,XX,t(4;13), respectively. In order to confirm the chromosomes involved in the translocations, to map the breakpoints, and to determine if the translocations were reciprocal, genes surrounding the breakpoints were identified using existing maps and from the newly assembled horse genome sequence. Bacterial artificial chromosomes containing the genes of interest were identified and mapped to the translocation chromosomes by fluorescence in situ hybridization (FISH). FISH confirmed that the t(16;22) and t(4;13) translocations were reciprocal, while the t(1;21) was not. The breakpoints on horse chromosomes 1 and 16 appear to be the same or near breakpoints previously identified in translocations. These breakpoints are at the fusion boundary of human chromosomes 10 and 15 on horse chromosome 1 and at human chromosome 3p and 3q on horse chromosome 16. These sites may represent ancient breakpoints reused during equid evolution. Overall, chromosome abnormalities may have a greater influence on mare fertility than previously known. Thus, it is important to karyotype subfertile mares exhibiting REEL.     

Chromosomal rearrangements in wheat: their types and distribution.

Four hundred and sixty polyploid wheat accessions and 39 triticale forms from 37 countries of Europe, Asia, and USA were scored by C-banding for the presence of translocations. Chromosomal rearrangements were detected in 70 of 208 accessions of tetraploid wheat, 69 of 252 accessions of hexaploid wheat, and 3 of 39 triticale forms. Altogether, 58 types of major chromosomal rearrangements were identified in the studied material; they are discussed relative to 11 additional translocation types described by other authors. Six chromosome modifications of unknown origin were also observed. Among all chromosomal aberrations identified in wheat, single translocations were the most frequent type (39), followed by multiple rearrangements (9 types), pericentric inversions (9 types), and paracentric inversions (3 types). According to C-banding analyses, the breakpoints were located at or near the centromere in 60 rearranged chromosomes, while in 52 cases they were in interstitial chromosome regions. In the latter case, translocation breakpoints were often located at the border of C-bands and the euchromatin region or between two adjacent C-bands; some of these regions seem to be translocation "hotspots". Our results and data published by other authors indicate that the B-genome chromosomes are involved in translocations most frequently, followed by the A- and D-genome chromosomes; individual chromosomes also differ in the frequencies of translocations. Most translocations were detected in 1 or 2 accessions, and only 11 variants showed relatively high frequencies or were detected in wheat varieties of different origins or from different species. High frequencies of some translocations with a very restricted distribution could be due to a "bottleneck effect". Other types seem to occur independently and their broad distribution can result from selective advantages of rearranged genotypes in diverse environmental conditions. We found significant geographic variation in the spectra and frequencies of translocation in wheat: the highest proportions of rearranged genotypes were found in Central Asia, the Middle East, Northern Africa, and France. A low proportion of aberrant genotypes was characteristic of tetraploid wheat from Transcaucasia and hexaploid wheat from Middle Asia and Eastern Europe.     

Mapping RFLP Loci in Maize Using B-a Translocations

Plants hypoploid for specific segments of each of the maize (Zea mays L.) chromosomes were generated using 24 different B-A translocations. Plants carrying each of the B-A translocations were crossed as male parents to inbreds, and sibling progeny hypoploid or not hypoploid for specific chromosomal segments were recovered. Genomic DNAs from the parents, hypoploid progeny, and nonhypoploid (euploid or hyperploid) progeny for each of these B-A translocations were digested with restriction enzymes, electrophoresed in agarose gels, blotted onto reusable nylon membranes, and probed with nick-translated, cloned DNA fragments which had been mapped previously by restriction fragment length polymorphism (RFLP) analysis to the chromosome involved in the B-A translocation. The chromosomal segment on our RFLP map which was uncovered by each of the B-A translocations was determined. This work unequivocally identified the short and long arms of each chromosome on this map, and it also identified the region on each chromosome which contains the centromere. Because the breakpoints of the B-a translocations were previously known on the cytological and the conventional genetic maps, this study also allowed this RFLP map to be more highly correlated with these maps.     

Altered chromatin modifications in AML1/RUNX1 breakpoint regions involved in (8;21) translocation

The RUNX1/AML1 gene is the most frequent target for chromosomal translocation, and often identified as a site for reciprocal rearrangement of chromosomes 8 and 21 in patients with acute myelogenous leukemia. Virtually all chromosome translocations in leukemia show no consistent homologous sequences at the breakpoint regions. However, specific chromatin elements (DNase I and topoisomerase II cleavage) have been found at the breakpoints of some genes suggesting that structural motifs are determinant for the double strand DNA-breaks. We analyzed the chromatin organization at intron 5 of the RUNX1 gene where all the sequenced breakpoints involved in t(8;21) have been mapped. Using chromatin immunoprecipitation assays we show that chromatin organization at intron 5 of the RUNX1 gene is different in HL-60 and HeLa cells. Two distinct features mark the intron 5 in cells expressing RUNX1: a complete lack or significantly reduced levels of Histone H1 and enrichment of hyperacetylated histone H3. Strikingly, induction of DNA damage resulted in formation of t(8;21) in HL-60 but not in HeLa cells. Taken together, our results suggest that H1 depletion and/or histone H3 hyperacetylation may have a linkage with an increase susceptibility of specific chromosomal regions to undergo translocations.     

Cartographic study: Breakpoints in 1574 families carrying human reciprocal translocations

Reciprocal translocations (rcp) are among the most common constitutional chromosomal aberrations in man. Using a European database of 1574 families carrying autosomal rcp, a cartographic study was done on the breakpoints involved. The breakpoints are non-randomly distributed along the different chromosomes, indicating “hot spots”. Breakpoints of rcp that result in descendants that are unbalanced chromosomally at birth are more frequent in a distal position on chromosomal arms, and 65% of them are localised in R-bands. Among the R-bands, bands rich in GC islands and poor in Alu repetitive sequences are more frequently the site of breakpoints, as well as bands that include a fragile site. This result suggests that the variation in degree of methylation in GC islands could be involved in chromosomal breakage and hence in chromosomal rearrangements. Received: 10 April 1995 / Revised: 1 July 1995     

Structural analysis of aberrant chromosomes that occur spontaneously in diploid Saccharomyces cerevisiae: retrotransposon Ty1 plays a crucial role in chromosomal rearrangements.

The structural analysis of aberrant chromosomes is important for our understanding of the molecular mechanisms underlying chromosomal rearrangements. We have identified a number of diploid Saccharomyces cerevisiae clones that have undergone loss of heterozygosity (LOH) leading to functional inactivation of the hemizygous URA3 marker placed on the right arm of chromosome III. Aberrant-sized chromosomes derived from chromosome III were detected in approximately 8% of LOH clones. Here, we have analyzed the structure of the aberrant chromosomes in 45 LOH clones with a PCR-based method that determines the ploidy of a series of loci on chromosome III. The alterations included various deletions and amplifications. Sequencing of the junctions revealed that all the breakpoints had been made within repeat sequences in the yeast genome, namely, MAT-HMR, which resulted in intrachromosomal deletion, and retrotransposon Ty1 elements, which were involved in various translocations. Although the translocations involved different breakpoints on different chromosomes, all breakpoints were exclusively within Ty1 elements. Some of the resulting Ty1 elements left at the breakpoints had a complex construction that indicated the involvement of other Ty1 elements not present at the parental breakpoints. These indicate that Ty1 elements are crucially involved in the generation of chromosomal rearrangements in diploid yeast cells.     

Chromosomal breakpoints in a cohort of head and neck squamous cell carcinoma patients

Head and neck squamous cell carcinoma (HNSCC) presents complex chromosomal rearrangements, however, the molecular mechanisms behind HNSCC development remain elusive. The identification of the recurrent chromosomal breakpoints could help to understand these mechanisms. Array-CGH was performed in HNSCC patients and the chromosomal breakpoints involved in gene amplification/loss were analyzed. Frequent breakpoints were clustered in chromosomes 12p, 8p, 3q, 14q, 6p, 4q, Xq and 8q. Chromosomes 6, 14, 3, 8 and X exhibited higher susceptibility to have breaks than other chromosomes. We observed that low copy repeat DNA sequences are localized at or flanking breakpoint sites, ranging from 0 to 200 bp. LINES, SINES and Simple Repeats were the most frequent repeat elements identified in these regions. We conclude that in our cohort specific peri-centromeric and telomeric regions were frequently involved in breakpoints, being the presence of low copy repeats elements one of the explanations for the common rearrangement events observed.     

The t(4;8) is mediated by homologous recombination between olfactory receptor gene clusters, but other 4p16 translocations occur at random

The t(4;8)(p16;p23) is the second most common constitutional chromosomal translocation and is caused by an ectopic meiotic recombination between the olfactory receptor gene clusters (ORGC), located on chromosome 4p and 8p. Given that ORGCs are scattered across the genome and make-up about 0.1% of the human genome we reasoned that translocations between 4p16 and other chromosomes might be mediated by ectopic recombination between different ORGC. In 13 patients, we mapped the breakpoints of either a balanced or unbalanced translocation between chromosome 4p16 and different chromosomes. For all four t(4;8) cases, the breakpoints fall within the 4p and 8pter ORGC, confirming that non-allelic homologous recombination (NAHR) between the ORGC is the main mechanism of the t(4;8) formation. For the nine other translocations, the breakpoints on chromosome 4 mapped to different loci, one of them within the ORGC and in two flanking the ORGC. In these three cases, the translocation breakpoint at the reciprocal chromosome did not contain ORGC sequences. We conclude that only the t(4;8) is mediated by NAHR between ORGC.     

Diagrammatic representation for chromosomal mutagenesis studies. II. Radiation-induced rearrangements in Macaca fascicularis

A qualitative study is presented of chromosomal rearrangements induced in peripheral blood lymphocytes of Macaca fascicularis, after exposure to gamma-irradiation at 2 Gy and 3 Gy. The use of a new diagrammatic representation allowed us to compare, for each type of rearrangement, the distribution of the observed break-points with the theoretical random distribution. It was concluded that chromosomal mutagenesis does not occur at random: an excess of involvement of small chromosomes is found for dicentrics and reciprocal translocations; an excess of telomeric breaks exists in dicentrics and paracentric inversions. In our sample of 27 pericentric inversions, the larger chromosomes are too frequently involved, 2 different inversions are observed at least twice and 7 (or 8) reproduce chromosomes of other primates.     

Localization of translocation breakpoints in somatic metaphase chromosomes of barley

Karyotype analyses based on staining by acetocarmine followed by Giemsa N-banding of somatic metaphase chromosomes of Hordeum vulgare L. were carried out on 61 reciprocal translocations induced by X-irradiation. By means of computer-based karyotype analyses all of the 122 breakpoints could be localized to defined sites or segments distributed over the seven barley chromosomes. The pre-definition of translocations with respect to their rearranged chromosome arms from other studies rendered it possible to define the break positions even in translocations having exchanged segments equal in size and the breakpoints located distally to any Giemsa band or other cytological marker. The breakpoints were found to be non-randomly spaced along the chromosomes and their arms. All breaks but one occurred in interband regions of the chromosomes, and none of the breaks was located directly within a centromere. However, short and long chromosome arms recombined at random. An improved tester set of translocations depicting the known break positions of most distal location is presented.     

Precise location of breakpoints in a frequent reciprocal translocation between chromosomes 11 and 22

One of the most frequent chromosomal translocations in human beings is 11q/22q, which results in the "partial trisomy of 22q syndrome." However, the breakpoint on the long arms of chromosomes 11 and 22 is still a matter of controversy. In the present study, we have used chromosomes from lymphocytes of a neonate who happened to have this classical abnormality, and by R-banding prometaphase chromosomes with acridine orange it has been possible to establish that the translocation between chromosomes 11 and 22 resulted from 3:1 meiotic maternal nondisjunction. A detailed analysis of the chromosome regions involved in this translocation revealed that the breakpoints on chromosomes 11 and 22 were at 11q23.3 and 22q11.1, respectively.     

The chromosomal location of T-cell receptor genes and a T cell rearranging gene: possible correlation with specific translocations in human T cell leukaemia.

We have examined the chromosomal location of human T cell-specific genes which are involved in antigen recognition and of a gene which specifically rearranges in T cells. The genes encoding both the variable and constant region segments of the T cell receptor alpha chain are found on chromosome 14 while the delta chain gene of the T cell receptor-associated T3 complex is localised to chromosome 11. Further, the two tandemly arranged T cell-specific rearranging genes, designated gamma, were mapped to chromosome 7, but apparently not closely linked to the previously mapped T cell receptor beta-chain gene. The locations of the three different genes, which undergo rearrangement in T cells, may correlate with the chromosomal breakpoints known to be involved in translocations within abnormal human T cells.     

Molecular analysis of X-autosome translocations in females with Duchenne muscular dystrophy.

To further an understanding of the mechanism of constitutional chromosomal rearrangement, the translocation breakpoints of two X-autosome translocations carried by females with Duchenne or Becker muscular dystrophy have been mapped, cloned and sequenced. Breakpoints were mapped to specific introns within the dystrophin gene and intron sequences spanning the two breakpoints were cloned and used as probes to identify DNA fragments containing the translocation junctions. The junction-containing fragments were cloned after amplification by inverse PCR or single-specific-primer PCR. Sequence through the junctions and the autosomal regions spanning the breakpoints identified the mechanism of rearrangement as non-homologous exchange with minor additions or deletions (0-8 nucleotides) at the breakpoints. Paternal origin of these X-autosome translocations, coupled with evidence for non-transmission of X-autosome translocations through male meiosis suggested that the translocations were the result of a post-meiotic rearrangement in spermiogenesis.     

Nonrandom chromosomal distribution of spontaneous breakpoints and satellite DNA clusters in two geographically distant populations of Chironomus riparius (Diptera: Chironomidae)

Two geographically distant populations of Chironomus riparius (syn. C. thummi) from two environmentally polluted sites (Santena, Italy and Varna, Bulgaria) show numerous somatic and inherited chromosomal aberrations (inversions, deletions and deficiencies). Fifty-five percent of the observed breakpoints occurred in at least two larvae from both populations. Breakpoints occurring twice or more were considered as common structural chromosomal breakpoints. We tested whether such common breakpoints in larvae of the two polluted populations had a random chromosomal distribution or occurred preferentially in specific heterochromatic regions. Distribution of common breakpoints was not random, and proximal regions of first and third chromosome had significantly more common breakpoints than distal ones. By FISH we identified and mapped 56 chromosomal sections containing clusters of two tandem-repetitive satellite DNA families called Hinf and Alu elements. Like the common breakpoints, these repetitive DNA clusters appeared to be significantly more abundant in regions of constitutive heterochromatin such as the pericentromeric regions, while in distal sections of chromosomal arms they were rare or absent. Twenty-four out of 45 common breakpoints (i.e., 53.3%) occurred in cytogenetic sections where Alu and Hinf satellite DNA probes hybridized. The frequency of co-localization between common breakpoints and repetitive DNA hybridization signals was significantly higher than expected by chance. We hypothesize that spontaneous or induced breaks occur more frequently in sections containing blocks of repetitive DNA.     

Nineteen of 26 cellular oncogenes precisely localized in the human genome map to one of the 83 bands involved in primary cancer-specific rearrangements

Summary A total of 83 bands have been found to be specifically involved in primary structural chromosome rearrangements in human cancer. We have compared the distribution of these cancer-specific breakpoints with the chromosomal sites of the 26 cellular oncogenes currently mapped to individual bands within the human genome. Nineteen of the 26 oncogenes are localized in cancer-associated bands. This clustering of oncogene sites and cancer breakpoints is statistically highly significant (P=0.0000012).     

Jumping translocations in spontaneous abortions

Chromosome translocations involving one donor chromosome and multiple recipient chromosomes have been referred to as jumping translocations (JTs). Acquired JTs are commonly observed in cancer patients, mainly involving chromosome 1. Constitutional forms of JTs mostly involve the acrocentric chromosomes and their satellites and have been reported in patients with clinical abnormalities. Recognizable phenotypes resulting from these events have included Down, Prader-Willi, and DiGeorge syndromes. The presence of JTs in spontaneous abortions has not been previously described. The breakpoints of all JTs occur in areas rich in repetitive DNA (telomeric, centromeric, and nucleolus organizing regions). We report two different unstable chromosome rearrangements in samples derived from spontaneous abortions. The first case involved a chromosome 15 donor. The recipient chromosomes were 1, 9, 15, and 21, and the respective breakpoints were in either the heterochromatic regions or the centromeres. FISH studies confirmed that the breakpoints of the jumping 15 rearrangement did not involve the Prader-Willi region but originated at the centromere or in the proximal short arm. A second case of instability was observed with a rearrangement resulting from a presumed de novo 8;21 translocation. Three JT cell lines were observed. They consisted of a deleted 8p chromosome, a dicentric 8;21 translocation, and an 8q isochromosome. The instability regions appeared to be at the pericentromeric region of chromosome 8 and the satellite region of chromosome 21. Both cases proved to be de novo events. The unstable nature of the JT resulting in chromosomal imbalance most likely contributed to the fetal loss. It appears that JT events may predispose to chromosomal imbalance via nondisjunction and chromosomal rearrangement and, therefore, may be an unrecognized cause of fetal loss.     

Die Speicheldrüsenchromosomen der StechmückeCulex pipiens L. III. Induzierte Chromosomale Aberrationen

Fifteen X-ray induced chromosomal aberrations in twelve autogenous lines of the mosquitoCulex pipiens were analysed: eight simple reciprocal translocations, one double reciprocal translocation, one translocation combined with an intrachromosomal transposition and a small deficiency, one simple transposition, and one pericentric inversion. The breakpoints were located on the morphological map of the salivary gland chromosomes. Their distribution seems to be random. A consideration of distances between breakpoints argues against the assumption of a linear order of chromosomes in the elongated sperm head. The extent of sterility in the heterozygote was recorded for 12 of the aberrations. Translocation heterozygotes, carrying the genetic pool of the lines here analysed, produced about 50% aneuploid gametes, independently of the length of the interstitiell segments.     

Molecular definition of high-resolution multicolor banding probes: first within the human DNA sequence anchored FISH banding probe set.

Fluorescence in situ hybridization (FISH) banding approaches are standard for the exact characterization of simple, complex, and even cryptic chromosomal aberrations within the human genome. The most frequently applied FISH banding technique is the multicolor banding approach, also abbreviated as m-band, MCB, or in its whole genomic variant multitude MCB (mMCB). MCB allows the differentiation of chromosome region-specific areas at the GTG band and sub-band level and is based on region-specific microdissection libraries, producing changing fluorescence intensity ratios along the chromosomes. The latter are used to assign different pseudocolors to specific chromosomal regions. Here we present the first bacterial artificial chromosome (BAC) array comparative genomic hybridization (aCGH) mapped, comprehensive, genome-wide human MCB probe set. All 169 region-specific microdissection libraries were characterized in detail for their size and the regions of overlap. In summary, the unique possibilities of the MCB technique to characterize chromosomal breakpoints in one FISH experiment are now complemented by the feature of being anchored within the human DNA sequence at the BAC level.     

Chromosome breakage and recombination at fragile sites.

Chromosomal fragile sites are points on chromosomes that usually appear as nonstaining chromosome or chromatid gaps. It has frequently been suggested that fragile sites may be involved in chromosome breakage and recombination events. We and others have previously shown that fragile sites predispose to intrachromosomal recombination as measured by sister-chromatid exchanges. These findings suggested that fragile site expression often, if not always, is accompanied by DNA strand breakage. In the present report, fragile sites are shown to predispose to deletions and interchromosomal recombination. By use of somatic cell hybrids containing either human chromosome 3 or the fragile X chromosome, deletions and translocations were induced by FUdR or aphidicolin with breakpoints at the fragile sites Xq27 or 3p14.2 (FRA3B) or at points so close to the fragile sites as to be cytogenetically indistinguishable. Southern blot analysis of DNA from a panel of chromosome 3 deletion and translocation hybrids was then utilized to detect loss or retention of markers flanking FRA3B and to corroborate the cytogenetic evidence that the breakpoints were at this fragile site. One cell line with a reciprocal translocation between human chromosome 3 (with breakpoint at 3p14.2) and a hamster chromosome showed cytogenetically that the fragile site was expressed on both derivative chromosomes, supporting the hypothesis that the fragile site represents a repeated sequence. The approach described provides a means of generating specific rearrangements in somatic cell hybrids with a breakpoint at a fragile site.(ABSTRACT TRUNCATED AT 250 WORDS)