Chromosome 18 replaced by two ring chromosomes of chromosome 18 origin

We here describe the first example of the replacement of an autosome by two ring chromosomes originating from the missing chromosome, presented in a patient with a single chromosome 18 and two additional ring chromosomes. Detailed fluorescence in situ hybridization (FISH) analysis revealed the chromosome 18 origin of both ring chromosomes and characterized the small and the large ring chromosome as derivatives of the short and long arm of chromosome 18, respectively. The loss of subtelomeric regions of the short and the long arm of chromosome 18 in the ring chromosomes was confirmed by FISH studies. Molecular studies showed the exclusive presence of the paternal alleles for microsatellite markers located distal to the short and long arm loci D18S843 and D18S474, respectively. This indicates the maternal origin of both rings and provides evidence for substantial deletions of the distal parts of both arms of chromosome 18 in the ring chromosomes. The dysmorphic features of the patient can be explained by these deletions in both chromosome arms, as the clinical findings partly overlap with observations in 18p- and 18q-syndrome and are similar to some cases of ring chromosome 18. Centromere misdivision is suggested as one mechanism involved in the formation of the ring chromosomes.     

Amplification of portions of the genome in mammalian somatic cells resistant to colchicine. II. Marker chromosomes with long homogeneously staining regions in colchicine-resistant cells of the Djungarian hamster

The series of sublines 170-750 times more resistant to colchicine were obtained from 10 independent clones of Djungarian hamster cells possessing 16-22-fold resistance to the drug. From each clone, several sublines with different levels of colchicine-resistance were developed. The drug resistance was unstable. 2,7-4,0% of cells per population doubling lost resistance to selective dosages of colchicine. The loss of resistance was stepwise. The chromosomes stained by trypsin G-banding technique were studied in 17 sublines. 15 sublines derived from 9 independent clones contained chromosomes with long homogeneously staining regions (HSRs). These were, as a rule, primarily localized in the long arm of chromosome 4. During cultivation, HSRs were transferred from chromosome 4 into other chromosomes. Evidently, transposition of HSRs was due to translocations of different chromosomes of HSRs in the chromosome 4 and to subsequent breakages of the resulting dicentrics within HSRs. A great number of different chromosomal rearrangements was also found in the cells containing HSRs. Possibly, formation of HSR leads to destabilization of the karyotype and to the variability of the genome. The length of HSRs varied in different cells of each subline. The levels of colchicine-resistance in different sublines did not correlate with the average length of HSRs in their cells. The lack of connection between the lengths of HSRs and the levels of drug resistance as well as the existence of highly resistant sublines with gene amplification, but without HSRs, suggest that amplified genes are localized in Djungarian hamster colchicine-resistant cells both in chromosomes and extrachromosomally.     

The causes of appearance of a double insertion of homogeneously staining regions in the chromosome 1 of house mouse (Mus musculus musculus)]

A high resolution analysis of G-band pattern of normal and aberrant chromosome 1 bearing two linked insertions of homogeneously staining regions (HSRs) in the house mouse (Mus musculus musculus) reveals an inverted pattern of the euchromatic region between the HSRs. On the basis of this analysis, a hypothesis on the causes for appearance of the aberrant chromosome was put forward: the double insertion is a result of inversion of the chromosome 1 of Mus musculus domesticus bearing a single long insertion. The proximal breakpoint is localized inside the HSR and the distal one--between subbands E3 and E4. From the point of view of these data, new symbols for the aberrations are proposed: Ls (HSR, 1C5) 1Icg--for the proximal insertion, Is(HSR, 1D)21cg--for the distal one, In (1) 1Icg--for the inverted region, including the bands D, E1-E3 and the insertion Is(HSR 1D)21cg.     

Unusual chromosome architecture and behaviour at an HSR

Amplification of sequences within mammalian chromosomes is often accompanied by the formation of homogeneously staining regions (HSRs). The arrangement of DNA sequences within such amplicons has been investigated, but little is known about the chromosome structure or behaviour of these unusual regions. We have analysed the metaphase chromosome structure of the dihydrofolate reductase (DHFR) amplicon of CHOC400 cells. The chromatin in this region contains hyperacetylated nucleosomes yet, at the same time, appears to be densely packed like heterochromatin. The region does not bind heterochromatin proteins. We show that the dense packing of the region is restricted to DNA located close to the chromosome core/scaffold. In contrast, levels of the chromosome scaffold protein topoisomerase II at HSRs are the same as those found at other euchromatic locations. Metaphase chromosome condensation of the HSR is shown to be sensitive to topoisomerase II inhibitors, and sister chromatids often appear to remain attached within the HSRs at metaphase. We suggest that these features underlie anaphase bridging and the aberrant interphase structure of the HSR. The DHFR amplicon is widely used as a model system to study mammalian DNA replication. We conclude that the higher-order chromosome structure of this amplicon is unusual and suggest that caution needs to be exercised in extrapolating data from HSRs to normal chromosomal loci. Received: 19 October 1999; in revised form: 13 December 1999 / Accepted: 27 December 1999     

Extensive DNA sequence homologies between the human Y and the long arm of the X chromosome.

It has been proposed that sequence homology should exist between the short arms of the human sex chromosomes, in the regions pairing at meiosis. Out of 40 clones picked at random from a collection of non-repetitive DNA sequences derived from the human Y chromosome, we have found nine sequences which show very high homology with sequences located on the X chromosome. All nine probes originate from the euchromatic part of the Y chromosome. All the homologous sequences are located within the Xq12-Xq22-24 region. None of them map to the short arm of the X chromosome. We conclude that an important part of the euchromatic region of the Y chromosome is homologous to the middle of the X chromosome long arm, possibly as a result of recent translation event(s).     

Polymorphic HSRs in chromosome 1 of the two semispecies Mus musculus musculus and M. m. domesticus have a common origin in an ancestral population

HSRs (homogeneously staining regions) are the cytological correlates of DNA amplification. In the house mouse, Mus musculus, many populations are polymorphic for the presence or absence of HSRs on chromosome 1. In the semispecies M. m. domesticus the amplified DNA is present within one HSR, whereas in M. m. musculus chromosomes 1 with two HSRs are found. Hybridization of HSR-specific probes to Southern blots of HSR-carrying genomic DNAs from different localities and semispecies revealed similar complex band patterns. the remaining variation is restricted to sequences with a low degree of amplification. Variation is higher between semispecies than within one semispecies. It is assumed that HSRs are derived from one original amplification event and that unequal recombination is the mechanism underlying the length variation of HSRs present today in both semispecies. Evidence from G-banding and in situ hybridization shows that the two HSRs of M. m. musculus originated from a single HSR by means of a paracentric inversion, where one break-point was located within the single HSR and the second outside the HSR. As a consequence of the paracentric inversion the two HSRs of M. m. musculus are permanently linked together. Since exchange of genes between the two semispecies is restricted to a narrow hybrid zone the amplification that gave rise to the HSR most probably occurred prior to the divergence into the semispecies M. m. domesticus and M. m. musculus about 1 million years ago.by D. Schweizer     

Chiasma formation in the short arm of the nucleolar chromosome of the tomato

Summary A translocation heterozygote in tomato (Lycopersicon esculentum) is shown to have a cyclical type of interchange between the long arms of chromosomes 1, 2 (nucleolar) and 3. A study of chromosome association in this plant at metaphase I has indicated that in 21% of the cells a ring of six chromosomes is present. Since an open ring hexavalent can occur only if there is chiasma formation in all the translocated segments and in all the short arms of the three chromosomes, it is concluded that there is considerable frequency of chiasma formation in the short arm of the nucleolar chromosome. This conclusion contradicts the previous observations that chiasma formation is either absent or very rare in the entirely dark staining chromatic, sometimes referred to as heterochromatic, short arm of the nucleolar chromosome.Part of this investigation was carried out at the Department of Genetics, Agricultural University, Wageningen, when the author was serving a contract between the EURATOM-I.T.A.L. and the Agricultural University.     

Chromosome 1 in human colorectal tumors

Summary The significance of short and long arm anomalies of chromosome 1 was investigated in 55 colorectal tumors comprising 41 carcinomas and 14 adenomas. The tumors were at various stages of transformation from adenoma to carcinoma. Our investigation was prompted by the observation of a p32-pter deletion on the short arm of chromosome 1 in a case of benign tubulovillous adenoma with mild dysplasia, as well as by frequent reports that chromosome 1 is involved in many neoplastic processes. Long arm anomalies were found in seven of the 41 carcinomas, six of which were in stage B2, and short arm anomalies in ten carcinomas at various stages. Three of the adenomas exhibited chromosome 1 anomalies, which in one case comprised a 1p32-pter deletion only. Overall, short arm anomalies especially concerned the p32–36 region. These results suggest that the cytogenetic anomalies respectively located on the short and long arms of chromosome 1 should be considered separately. Damage to the long arm might constitute a late non-specific event, whereas damage to the p32-pter region of the short arm might be involved in triggering colorectal tumor development.     

Double insertion of homogeneously staining regions in chromosome 1 of wild Mus musculus musculus: effects on chromosome pairing and recombination

An examination of the meiotic pattern of chromosome 1 isolated from a feral mouse population and containing a double insertion (Is) of homogeneously staining regions (HSRs) was carried out. The region delineated by the proximal breakpoint of Is(HSR;1C5) 1Icg and the distal breakpoint of Is(HSR;1E3)2Icg is desynapsed during the early pachytene stage and heterosynapsed at the midpachytene, as shown by electron microscopic analysis of synaptonemal complexes. The HSRs have no effect on the segregation of chromosome 1 in heterozygous mice. The lack of homosynapsis in the region under study causes chiasmata redistribution in heteromorphic bivalents. In normal males, single chiasmata are located in the medial part of the chromosome. In heterozygotes, this segment is heterosynapsed and unavailable for recombination. This leads to a significant decrease in the frequency of bivalents bearing single chiasmata. The total number of chiasmata per bivalent is much higher in heterozygous males than in normal ones. The recombination frequency between proximal markers fz and In also is higher in heterozygous animals. The increase in the total chiasma number in the heteromorphic bivalent is due to the addition of double chiasmata located mostly at precentromeric and pretelomeric regions of the chromosome.     

Meiotic behaviour of single-arm tetrasomic combinations of isochromosomes,telocentrics and normal chromosomes in rye (Secale cereale L.)

The isochromosome studied was derived from the short arm of the satellite chromosome of rye (Secale cereale, 2n=14); the telocentrics represent both the short and long arms of the same chromosome. Three different combinations, tetrasomic for the short arm, have been composed and studied: I: 2 isochromosomes (short arm) + 2 telocentrics (long arm) + 6 normal pairs. II: 1 isochromosome + 2 telocentrics (short arm) + 2 telocentrics (long arm) + 6 normal pairs. III: 1 isochromosome + 1 telocentric (short arm) + 1 normal satellite chromosome + 1 telocentric (long arm) + 6 normal pairs. — Over 20,000 cells were analysed. Simple mathematical models describing the frequencies of the different types of MI configurations in terms of frequency of chiasmata in the different pairing combinations of the polysomic arms, and of the frequency of multivalent pairing of this arm, were developed. They were used to derive estimates for chiasma frequencies and multivalent pairing frequencies in the different chromosome constitutions from the observations on configuration frequencies. Variation between plants and within plants was studied, and it was concluded that much of the within plant heterogeneity was due to regulatory variation expressed independently in different chromosomal segments. There was also a significant genetic component. Analysis of the reasons for the models to fail under certain conditions led to suggestions for extension of the models.     

Molecular cytogenetic mapping of Humulus lupulus sex chromosomes

Dioecy is relatively rare in plants and sex determination systems vary among such species. A good example of a plant with heteromorphic sex chromosomes is hop (Humulus lupulus). The genotypes carrying XX or XY chromosomes correspond to female and male plants, respectively. Until now no clear cytogenetic markers for the sex chromosomes of hop have been established. Here, for the first time the sex chromosomes of hop are clearly identified and characterized. The high copy sequence of hop (HSR1) has been cloned and localized on chromosomes by fluorescence in situ hybridization. The HSR1 repeat has shown subtelomeric location on autosomes with the same intensity of the signal. The signal has been present in the subtelomeric region of the long arm and in the near-centromeric region but absent in the telomeric region of the short arm of the X chromosome. At the same time the signal has been found in the telomeric region only of the long arm of the Y chromosome. This finding indicates that the sex chromosomes of hop have evolved from a pair of autosomes via ancient translocation or inversion. The observation of the meiotic configuration of the sex bivalents shows the location of a pseudoautosomal region on the long arms of X and Y chromosomes.     

Mammalian sex chromosomes. II. Pairing and alignment of the X and Y chromosomes of the pygmy mouse, Mus dunni

In the pygmy mouse, Mus dunni, the entire Y chromosome and the short arm of the X and distal region of its long arm are constitutively heterochromatic. Different banding studies on somatic chromosomes revealed the GC nature of the distally located heterochromatin of the long arms of both the X and Y chromosomes. The short arm of the X and the rest of the Y are AT-rich. During meiosis, the long arms of the X and Y paired extensively, sometimes more than half of the Y pairing with the X. This observation is in disagreement with that of Pathak and Hsu (1976) who reported end-to-end pairing between the long arm of the X and the short arm of the Y. The orientation observed by us is favourable to a successful meiotic recombination but whether this takes place remains to be demonstrated.     

Cytogenetic Analysis and Chromosomal Characteristics of the Polymorphic 18S rDNA of Haliotis discus hannai from Fujian,China

We report on novel chromosomal characteristics of Haliotis discus hannai from a breeding population at Fujian, China. The karyotypes of H. discus hannai we obtained from an abalone farm include a common type 2n = 36 = 10M + 8SM (82%) and two rare types 2n = 36 = 11M + 7SM (14%) and 2n = 36 = 10M + 7SM + 1ST (4%). The results of silver staining showed that the NORs of H. discus hannai were usually located terminally on the long arms of chromosome pairs 14 and 17, NORs were also sometimes located terminally on the short arms of other chromosomes, either metacentric or submetacentric pairs. The number of Ag-nucleoli ranged from 2 to 8, and the mean number was 3.61 ± 0.93. Among the scored interphase cells, 41% had 3 detectable nucleoli and 37% had 4 nucleoli. The 18S rDNA FISH result is the first report of the location of 18S rDNA genes in H. discus hannai. The 18S rDNA locations were highly polymorphic in this species. Copies of the gene were observed in the terminal of long or/and short arms of submetacentric or/and metacentric chromosomes. Using FISH with probe for vertebrate-like telomeric sequences (CCCTAA)₃ displayed positive green FITC signals at telomere regions of all analyzed chromosome types. We found about 7% of chromosomes had breaks in prophase. A special form of nucleolus not previously described from H. discus hannai was observed in some interphase cells. It consists of many small silver-stained nucleoli gathered together to form a larger nucleolus and may correspond to prenucleolar bodies.     

The origin of tertiary monosomics in the tomato

Six aneuploid tomato plants with 2n–1=23 chromosomes were observed in populations grown from the seedlings treated with thermal neutrons and from seeds treated with X-rays. Four of the aneuploids were tertiary monosomics in which, as a result of centromeric interchanges between two different chromosomes, two whole arms were missing from the complement and two arms connected at the centromere. In one aneuploid, as a result of centromeric breakage, the two short arms of a homologous pair were missing from the complement and the two long arms connected to the long arm and the short arm respectively of another chromosome in which breakage had occurred also at the centromere. In one aneuploid, the interchange has occurred in the arms, and not in the centromere. Here the aneuploid condition is due to the loss of an arm with a centromere and a short piece of the other arm.In most of the tertiary monosomics the missing arms were either the short arms of sub-metacentric chromosomes or any of the arms of metacentric chromosomes. However, in one case the long arms of two submetacentric chromosomes were lost from the complement. That in spite of such large chromosomal deletions the sporophyte can survive, may be due to the fact that the aberrant plants are mostly chimeras.This study was part of a project resulting from a contract between the Association Euratom-I.T.A.L., and the Agricultural University of Wageningen.     

Light and electron microscopy of Ag-NORs in domestic horse chromosomes identified after R-banding

Silver staining shows the presence in the domestic horse of six NORs located on chromosomes 1, 26 and 31 as identified after R-banding. Following electron microscopy, the argyrophilic material was observed outside the terminal secondary constrictions (satellite stalks) on the terminal portion of the short arm of chromosome 1, outside the secondary constrictions on the proximal region of the long arms of chromosome 31, and beside the proximal region of the long arms of chromosome 26. Satellite staining applied to these chromosomes appears to reveal only the active NORs.     

Multiple reconstruction of barley karyotype resulting in complete cytological marking of the chromosome complement

Summary A new reconstructed barley karyotype, PK88, which is a quadruple homozygote for three unequal translocations, 1–2, 3–4, 5–7, and one pericentric inversion in chromosome 6, was studied. As a result of these chromosome rearrangements, a complete cytological marking of the complement has been achieved. Due to the specific intra or interchromosomal transfer of particular bands, Giemsa staining of somatic chromosomes provided clear-cut indications about the localization of translocation and inversion breakpoints. It was established that the long arms of chromosomes 1, 2, 4, 5 and 7 and the short arm of chromosome 3 have been involved in interchanges 1–2, 3–4, and 5–7. The breakpoints of pericentric inversion proved to be located proximally to the short (satellite) arm and distally in the long arm of chromosome 6. PK-88 offers an essential gain in resolution power and extension of the areas of application in cytogenetics over other reconstructed karyotypes produced so far in barley.     

Characterization of a rare short arm heteromorphism of chromosome 22 in a girl with down-syndrome like facies

Chromosomal heteromorphisms are described as interindividual variation of chromosomes without phenotypic consequence. Chromosomal polymorphisms detected include most regions of heterochromatin of chromosomes 1, 9, 16 and Y and the short arms of all acrocentric chromosomes. Here, we report a girl with Down-syndrome such as facies and tremendously enlarged short arm of a chromosome 22. Fluorescence in situ hybridization (FISH) with a probe specific for all acrocentric short arms revealed that the enlargement p arms of the chromosome 22 in question contained exclusively heterochromatic material derived from an acrocentric short arm. Parental studies identified a maternal origin of this heteromorphism. Cryptic trisomy 21 of the Down-syndrome critical region was excluded by a corresponding FISH-probe. Here, we report, to the best of our knowledge, largest ever seen chromosome 22 short arm, being ~×1.5 larger than the normal long arm.     

Localization of 5S RNA genes on chromosomes of plethodontid salamanders

Ribosomal 5S RNA, labelled with 125 I, was annealled to denatured spermatocyte chromosomes of salamanders from 11 different genera of the family Plethodontidae. The salamanders studied have genomes with 1, 2 or 3 gene clusters. Eleven sites are located interstitially on short chromosome arms; 3 are found interstitially on long arms; 5 sites are at centromeric regions and one is telomeric. — Salamanders from five genera of Neotropical plethodontids carry a 5S gene cluster on the short arm of a large asymmetric chromosome, presumably a linkage group that has remained stable since the divergence of these genera in Tertiary time. In Lineatriton lineola this short arm is heterochromatic during pachytene and it shows a high incidence of chiasma failure at the first meiotic metaphase, contrasting with the situation found in two other species. The localization and number of 5S gene sites is consistent with the proposed phylogeny of these Neotropical genera by Wake and Lynch (1976).     

Identification and designation of telocentric chromosomes in barley by means of Giemsa N-banding technique

Summary Seven complete chromosomes and nine telocentric chromosomes in telotrisomics of barley (Hordeum vulgare L.) were identified and designated by an improved Giemsa N-banding technique. Karyotype analysis and Giemsa N-banding patterns of complete and telocentric chromosomes at somatic late prophase, prometaphase and metaphase have shown the following results: Chromosome 1 is a median chromosome with a long arm (Telo 1L) carrying a centromeric band, while short arm (Telo 1S) has a centromeric band and two intercalary bands. Chromosome 2 is the longest in the barley chromosome complement. Both arms show a centromeric band, an intercalary band and two faint dots on each chromatid at middle to distal regions. The banding pattern of Telo 2L (a centromeric and an intercalary band) and Telo 2S (a centromeric, two intercalary and a terminal band) corresponded to the banding pattern of the long and short arm of chromosome 2. Chromosome 3 is a submedian chromosome and its long arm is the second longest in the barley chromosome complement. Telo 3L has a centromeric (fainter than Telo 3S) and an intercalary band. It also shows a faint dot on each chromatid at distal region. Telo 3S shows a dark centromeric band only. Chromosome 4 is the most heavily banded one in barley chromosome complement. Both arms showed a dark centromeric band. Three dark intercalary bands and faint telomeric dot were observed in the long arm (4L), while two dark intercalary bands in the short arm (4S) were arranged very close to each other and appeared as a single large band in metaphase chromosomes. A faint dot was observed in each chromatid at the distal region in the 4S. Chromosome 5 is the smallest chromosome, which carries a centromeric band and an intercalary band on the long arm. Telo 5L, with a faint centromeric band and an intercalary band, is similar to the long arm. Chromosomes 6 and 7 are satellited chromosomes showing mainly centromeric bands. Telo 6S is identical to the short arm of chromosome 6 with a centromeric band. Telo 3L and Telo 4L were previously designated as Telo 3S and Telo 4S based on the genetic/linkage analysis. However, from the Giemsa banding pattern it is evident that these telocentric chromosomes are not correctly identified and the linkage map for chromosome 3 and 4 should be reversed. One out of ten triple 2S plants studied showed about 50% deficiency in the distal portion of the short arm. Telo 4L also showed a deletion of the distal euchromatic region of the long arm. This deletion (32%) may complicate genetic analysis, as genes located on the deficient segment would show a disomic ratio. It has been clearly demonstrated that the telocentric chromosomes of barley carry half of the centromere. Banding pattern polymorphism was attributed, at least partly, to the mitotic stages and differences in techniques.Contribution from the Department of Agronomy and published with the approval of the Director of the Colorado State University Experiment Station as Scientific Series Paper No. 2730. This research was supported in part by the USDA/SEA Competitive Research Grant 5901-0410-9-0334-0, USDA/ SEA-CSU Cooperative Research Grant 12-14-5001-265 and Colorado State University Hatch Project. This paper was presented partly at the Fourth International Barley Genetics Symposium, Edinburgh, Scotland, July 22–29, 1981     

Regular pattern of karyotypic alterations accompanying gene amplification in Djungarian hamster cells: study of colchicine,adriablastin, and methotrexate resistance

Chromosomal analysis of 26 Djungarian hamster cell lines obtained from 11 independent clones and possessing different levels of resistance to colchicine or adriablastin as a consequence of gene amplification revealed regular patterns in the karyotypic changes that accompanied the development of drug resistance. Usually the sequence of karyotypic changes was as follows: first an additional chromosome 4 appeared; then single unpaired small chromatin bodies (SCBs) arose; later in the middle part of the long arm of one of three chromosomes 4 long homogeneously staining regions (HSRs) and double minute chromosomes (DMs) were formed; and finally in the most resistant variants large clusters of SCBs appeared. The emergence of the clusters of the SCBs correlated well with the occurrence of autonomously replicating, amplified DNA sequences. In contrast to DNA of the HSRs the DNA of the SCBs could replicate outside the S-phase of the cell cycle. When kept in a non-selective medium, the cells gradually lost their resistance to colchicine: 1%–4% of the cells lost the capacity to form colonies in the selective medium independently of the pattern of location in them of amplified genes (in chromosomal HSRs, SCBs, or DMs). Loss of drug resistance was accompanied by disappearance of the chromosomal HSRs, SCBs, and DMs. Chromosomal analysis of the set of methotrexate-resistant Djungarian hamster cell lines indicated the following karyotypic evolution: first the additional material on the distal part of one of two chromosomes 3 appeared; then the light HSRs were formed on the distal part of one of two chromosomes 4; later clusters of SCBs and HSRs arose on the distal part of the short arm of chromosome 3. Probably the amplification of different genes is characterized by specific patterns of karyotypic alterations.