Prenatal detection of an unstable ring 21 chromosome

Summary An unstable ring chromosome 21 detected through prenatal studies was associated at birth with an apparently normal male phenotype. At 14 months of age, examination indicated only minor developmental delay. The majority of cells examined from amniocyte, fibroblast, and lymphocyte cultures contained an asymmetrical dicentric ring 21 chromosome which was larger than a normal chromosome 21. This ring is presumed to be a duplication for most of chromosome 21 and a deletion of part of the terminal regions. The karyotype is described as mos45, XY,-21/46,XY,r(21)(p13q22.3). The child is monosomic for part of the sub-band 21q22.3 in every cell and trisomic for the remainder of the chromosome in most of his cells. The terminal deletion does not appear to have been severely detrimental to the phenotype and the effective trisomy present in many cells studies was insufficient to cause the Down syndrome.     

Meiosis in a sterile male mouse with an isoYq marker chromosome

A male mouse with a metacentric Y chromosome of twice the normal size has been studied chromosomally in bone marrow mitoses, spermatogonial mitoses, and diakinesis-metaphase I primary spermatocytes. A low frequency of nondisjunction for this chromosome (2%) was noted in both bone marrow and spermatogonial mitoses. In spermatogonial mitoses, loss of the Y chromosome had occurred to the extent that 12% of spermatogonia were XO, resulting in 17% XO primary spermatocytes. Hardly any stages beyond the primary spermatocyte stage were encountered, which agrees with testis weights of approximately 30% of normal. Surface-spread pachytene spermatocytes yielded few cells that were analyzable for their total complement of synaptonemal complexes. The Y chromosome showed complete fold-back pairing and was located far away from the X chromosome. X and Y chromosomes were paired in 14.5% of the diakinesis-MI spermatocytes that contained a Y chromosome. The origin of this chromosome is discussed against the background of localization of the gene for the testis-determining factor on the short arm of the mouse Y chromosome.     

Human gene mapping using an X/autosome translocation.

Human fibroblasts containing a translocation between the X chromosome and chromosome 15 were fused with the 6-thioguanine-resistant mouse cell line, IR. Resulting hybrids, selected in HAT medium, retained the X/15 chromosome. Hybrids which were counterselected in 6-thioguanine lost this chromosome. The X-linked markers glucose-6-phosphate dehydrogenase (G6PD), phosphoglycerate kinase (PGK), and hypoxanthine phosphoribosyl transferase (HPRT), and the non-X-linked markers pyruvate kinase (PKM2) mannose phosphate isomerase (MPI), N-acetyl hexosaminidase A (HEXA) and beta2-microglubulin (beta2-m) all segregated in concordance with the X/15 translocation chromosome. The latter markers have been assigned to chromosome 15. Selection against the X/15 chromosome was done using antihuman beta2-m serum. Electrophoretic and immunochemical analyses of the N-acetyl hexosaminidases A and B in these hybrids were performed.     

The trisomy 18 syndrome with an E/G translocation

Summary An infant with a typical Edwards syndrome and a modal chromosome number of 46 is reported. In all cells analyzed one chromosome G was missing and an additional chromosome similar to a pair No. 16 was present. The phenotype of the child indicates that the extra element is a translocation between G and 18 chromosomes as in one case described previously.     

Prader-Willi syndrome with an unusually large 15q deletion due to an unbalanced translocation t(4;15)

Prader-Willi syndrome (PWS) is a neurobehavioral disorder caused by deletions in the 15q11-q13 region, by maternal uniparental disomy of chromosome 15 or by imprinting defects. Structural rearrangements of chromosome 15 have been described in about 5% of the patients with typical or atypical PWS phenotype. An 8-year-old boy with a clinical diagnosis of PWS, severe neurodevelopmental delay, absence of speech and mental retardation was studied by cytogenetic and molecular techniques, and an unbalanced de novo karyotype 45,XY,der(4)t(4;15)(q35;q14),-15 was detected after GTG-banding. The patient was diagnosed by SNURF-SNRPN exon 1 methylation assay, and the extent of the deletions on chromosomes 4 and 15 was investigated by microsatellite analysis of markers located in 4qter and 15q13-q14 regions. The deletion of chromosome 4q was distal to D4S1652, and that of chromosome 15 was located between D15S1043 and D15S1010. Our patient's severely affected phenotype could be due to the extent of the deletion, larger than usually seen in PWS patients, although the unbalance of the derivative chromosome 4 cannot be ruled out as another possible cause. The breakpoint was located in the subtelomeric region, very close to the telomere, a region that has been described as having the lowest gene concentrations in the human genome.     

A dicentric iso (Y) chromosome in an infertile male

A dicentric Y chromosome was detected in a 30-year-old azoospermic male patient who was found to be mosaic for 45,X/46,X,dic Y(qter----p11::p11----qter). The dicentric iso (Y) chromosome was identified conclusively with C-banding, G-banding and Q-banding techniques. The relationship of structural abnormalities of the Y chromosome and azoospermia is discussed.     

Lactococcal plasmid pWV01 as an integration vector for lactococci.

A Bacillus subtilis strain was constructed that contained the repA gene of the lactococcal plasmid pWVO1 in its chromosome. This strain was used to construct the pWVO1-based integration vector pINT1, which lacked the repA gene. The 3.6-kb plasmid pINT1 was not able to replicate in Lactococcus lactis MG1363 but integrated into the chromosome via a Campbell-like mechanism when a lactococcal chromosomal DNA fragment was incorporated in the plasmid. Transformants were obtained that carried between one and four plasmid copies, in stable tandem arrangement on the chromosome. The results indicate that pWVO1 can be used for the development of a Campbell-like integration system fully derived of lactococcal DNA, with which stable multiple copies of any gene of interest can be generated in the lactococcal chromosome.     

Cytological identification of an isotetrasomic in rice and its application to centromere mapping

The aneuploid with isochromosome or telochromosome is ideal material for exploring the position of centromere in lingkage map.For obtaining these aneuploids in rice,the primary trisomics from triplo-1 to triplo-12 and the aneuploids derived from a triploid of indica rice variety Zhongxiao 3037 were carefully investigated.From the offsprings of triplo-10,a primary trisomic of chromosome 10 of the variety,an isotetrasomic “triplo-10-1” was obtained.Cytological investigation revealed that a pair of extra isochromosomes of triplo-10-1 were come from the short arm of chromosome 10.In the offsprings of the isotetrasomic,a secondary trisomic “triplo-10-2”,in which the extra-chromosome was an isochromosome derived from the short arm of chromosome 10,was identified.With the isotetrasomic,secondary trisomic,primary trisomic and diploid of variety Zhongxiao 3037,different molecular markers were used for exploring the position of the centromere of chromosome 10.Based on the DNA dosage effect,it was verified that the molecular markers G1125,G333 and L169 were Located on the short arm,G1084 and other 16 available molecular markers were on the long arm of chromosome 10.So the centromere of chromosome 10 was located somewhere between G1125 and G1084 according to the RFLP linkage map given by Kurata et al[1].The distance from G1125 to G1084 was about 3.2cM.     

Lactococcal plasmid pWV01 as an integration vector for lactococci.

A Bacillus subtilis strain was constructed that contained the repA gene of the lactococcal plasmid pWVO1 in its chromosome. This strain was used to construct the pWVO1-based integration vector pINT1, which lacked the repA gene. The 3.6-kb plasmid pINT1 was not able to replicate in Lactococcus lactis MG1363 but integrated into the chromosome via a Campbell-like mechanism when a lactococcal chromosomal DNA fragment was incorporated in the plasmid. Transformants were obtained that carried between one and four plasmid copies, in stable tandem arrangement on the chromosome. The results indicate that pWVO1 can be used for the development of a Campbell-like integration system fully derived of lactococcal DNA, with which stable multiple copies of any gene of interest can be generated in the lactococcal chromosome.     

RB1 deletion in gonadoblastoma in an XY female

Cytogenetic studies of normal and tumor cells in a patient with gonadal dysgenesis and bilateral gonadoblastoma were performed. The karyotype was 46,XY in peripheral blood lymphocytes and skin fibroblasts. The conserved region of the SRY gene was detected by polymerase chain reaction amplification. Sequencing of this region did not reveal any alterations. A 46,XY chromosome constitution was observed in the right gonadoblastoma, but a partial deletion of chromosome 13 was present in the left tumor. This deletion included band 13q14, where the retinoblastoma gene is mapped. The study of the polymorphism of the variable number of tandem repeats region in intron 17 of the RB1 locus disclosed loss of heterozygosity in both the left tumor, which showed the deletion of chromosome 13, and in the right tumor, where no chromosome alterations of chromosome 13 were detected. In situ hybridization covering 130 kb of RB1 showed that a partial deletion of one of the RB1 alleles had occurred in the right tumor. Since the deletions affected different alleles in each tumor, independent events must have been involved in the development of the tumors. These findings point toward a significant role of RB1 in the development of gonadoblastoma. Received: 17 October 1995 / Accepted: 14 July 1997     

Bcl-2 is an integral component of mitotic chromosomes

We previously demonstrated that phospho-Thr56 Bcl-2 colocalizes with Ki-67 and nucleolin in nuclear structures in prophase cells and is detected on mitotic chromosomes in later mitotic phases. To gain insight into the fine localization of Bcl-2 on mitotic chromosomes, we further investigated Bcl-2 localization by immunostaining of Bcl-2 with known components of metaphase chromosomes and electron microscopic immunocytochemistry. Immunofluorescence analysis on HeLa mitotic cells together with chromatin immunoprecipitation assays showed that Bcl-2 is associated with the condensed chromatin. Co-immunostaining experiments performed on mitotic chromosome spreads demonstrated that Bcl-2 is not localized on the longitudinal axis of chromatids with the condensin complex, but partially colocalizes with histone H3 on some regions of the mitotic chromosome. Finally, most of the Bcl-2 staining overlaps with Ki-67 staining at the chromosome periphery. Bcl-2 localization at the periphery and over the mitotic chromosome was confirmed by immunoelectron microscopy on mitotic cells.Our results indicate that Bcl-2 is an integral component of the mitotic chromosome.     

Flow cytometric sorting of maize chromosome 9 from an oat-maize chromosome addition line

Large numbers of maize chromosome 9 can be collected with high purity by flow cytometric sorting of chromosomes isolated from a disomic maize chromosome addition line of oat. Metaphase chromosome suspensions were prepared from highly synchronized seedling root-tips of an oat-maize chromosome-9 addition line (OM9) and its parental oat and maize lines. Chromosomes were stained with propidium iodide for flow cytometric analysis and sorting. Flow-karyotypes of the oat-maize addition line showed an extra peak not present in the parental oat line. This peak is due to the presence of a maize chromosome-9 pair within the genome of OM9. Separation of maize chromosome 9 by flow cytometric sorting of a chromosome preparation from a normal maize line was not possible because of its size similarity (DNA content) to maize chromosomes 6, 7 and 8. However, it is possible to separate maize chromosome 9 from oat chromosomes and chromatids. An average of about 6×10³ chromosomes of maize chromosome 9 can be collected by flow-sorting from chromosomes isolated from 30 root tips (ten seedlings) of the oat-maize addition line. Purity of the maize chromosome 9, sorted from the oat-maize chromosome addition line, was estimated to be more than 90% based on genomic in situ hybridization analysis. Sorting of individual chromosomes provides valuable genomic tools for physical mapping, library construction, and gene isolation. Received: 28 February 2000 / Accepted: 14 July 2000     

The Meiotic Behavior of an Inversion in Caenorhabditis Elegans

The rearrangement hIn1(I) was isolated as a crossover suppressor for the right end of linkage group (LG) I. By inducing genetic markers on this crossover suppressor and establishing the gene order in the homozygote, hIn1(I) was demonstrated to be the first genetically proven inversion in Caenorhabditis elegans. hIn1(I) extensively suppresses recombination in heterozygotes in the right arm of chromosome I from unc-75 to unc-54. This suppression is associated with enhancement of recombination in other regions of the chromosome. The enhancement observed maintains the normal distribution of events but does not extend to other chromosomes. The genetic distance of chromosome I in inversion heterozygotes approaches 50 map units (m.u.), approximately equal to one chiasma per meiosis. This value is maintained in hIn1(I)/szT1(I;X) heterozygotes indicating that small homologous regions can pair and recombine efficiently. hIn1(I)/hT2(I;III) heterozygotes share no uninverted homologous regions and segregate randomly, suggesting the importance of chiasma formation in proper segregation of chromosomes. The genetic distance of chromosome I in these heterozygotes is less that 1 m.u., indicating that crossing over can be suppressed along an entire chromosome. Since one of our goals was to develop an efficient balancer for the right end of LGI, the effectiveness of hIn1(I) as a balancer was tested by isolating and maintaining lethal mutations. The meiotic behaviour of hIn1(I) is consistent with other genetic and cytogenetic data suggesting the meiotic chromosomes are monocentric. Rare recombinants bearing duplications and deficiencies of chromosome I were recovered from hIn1(I) heterozygotes, leading to the proposal the inversion was paracentric.     

Cytogenetics of an unstable trisomie in barley (Hordeum vulgare).

The origin, identification, meiotic chromosome behavior, and breeding behavior of an unstable trisomic barley were studied. The extra chromosome originated by breakage and fusion of an acrocentric chromosome 3 in a plant from an F2 population of a cross between acrotrisomic 3L3S (2n = 14 + 1 acro3L3S) and a balanced lethal stock, xc. (xantha) ac (albino). The F2 population segregated only for the albino trait. The genotypic constitution of the trisomic plant was ac ac (for both normal chromosome 3) and Ac (for the unstable metacentric chromosome). The unstable extra metacentric chromosome was designated as metacentric 3B (abbreviated as meta3B). Meiotic chromosome behavior in plants with 2n = 14 + 1 meta3B differed from plant to plant and within spikes. Some plants showed only trisomic cells with a chromosome configuration of 1 III + 6 II and 7 II + 1 I at metaphase I, whereas other plants showed both trisomie and disomic cells (7 II) that resulted from the elimination of the extra meta3B. The frequency of ring trivalents was low (6.8%). An average transmission rate of unstable meta3B ranged from 4.3 to 12.9%. The elimination of meta3B, and hence loss of the dominant Ac allele, resulted in albino seedlings as well as white stripes on plants, leaves, and spikes. Chromosome numbers of albino seedlings in the progeny of 2n = 14 + 1 meta3B were all diploid (2n = 14), while green seedlings contained 2n = 14 + 1 meta3B. However, progenies of some spikes of one trisomic plant showed a low frequency of green diploids and metatrisomics (2n = 14 + 1 meta3B), which was attributed to crossing-over.     

Cytogenetic study of an interspecific cross of Nicotiana debneyi X N. umbratica

Summary Interspecific F₁ hybrids of Nicotiana debneyi Domin (2n=48) and N. umbratica Burbidge (2n=46), both belonging to the section Suaveolentes, showed a high degree of meiotic chromosome pairing. Two of the five F₂ plants obtained exhibited chromosome mosaicism. The first colchiploid generation (C₁) had the expected chromosome number of 2n=94 while C₂ showed 2n=88, a loss of three pairs of chromosomes. This same chromosome number continued in further colchiploid generations, followed up to C₅, except for a few plants in C₃ which showed chromosome mosaicism. The F₁ phenotype was stable through C₁ to C₅ and fertility was normal in colchiploids through all generations in spite of the loss of three pairs of chromosomes and chromosome mosaicism. This stability and fertility apparently reflect the tolerance of the genomes to the genetic adjustment of chromosome complements which is believed to be associated with the originally polyploid nature of the parental species and the chromosome doubling brought about in the amphidiploids.     

Chromosome rearrangement patterns of an SD chromosome (SDKona-2) in Drosophila melanogaster caused by hybrid dysgenesis.

The types and frequencies of spontaneous chromosome rearrangements caused by hybrid dysgenesis were studied in a second chromosome autosome of Drosophila melanogaster. This second chromosome, being an SD chromosome, had two important advantages over other autosomes for this study: (i) it had the two inversions characteristic of a standard SD-72 chromosome type, which distinguished it from its homolog in polytene chromosome spreads, and (ii) because of the meiotic drive associated with the segregation distorter system, it was preferentially transmitted to the next generation. The chromosome mutation frequency of this chromosome (given the name SDKona-2) was 8.3 and 11.7% in the F2 and F3 generations, respectively. The types of new chromosome rearrangements observed in the first four generations included paracentric inversions, pericentric inversions, duplications, deletions, reciprocal translocations (involving the third chromosome), and transpositions. Small paracentric inversions were the most common type of new rearrangement. Later, over 35 generations, some of these new rearrangements changed, either by becoming more complex or by being replaced with yet another new chromosome rearrangement. Duplications were unstable and were replaced by paracentric inversions whose breakpoints were on either side of the duplication. Transpositions arose both from a single multibreak event and from a series of two-break events.     

Amplification of satellite III DNA in an unusually large chromosome 14p+ variant

Summary A phenotypically normal male (WSm) was found to have an unusually large short arm of chromosome 14. Increase in the size of this variant chromosome [Wsm-var(14)] was estimated to be approximately 30% that of a normal chromosome 14 by G-banding using trypsin and staining with Leishman. The extra chromosomal material was positive in CBG staining (C-banding using BaOH and staining with Giemsa), suggesting the presence of repetitive DNA. In situ hybridisation using repetitive probes demonstrated this material to be strongly positive for satellite III DNA, and negative for Y-specific heterochromatic DNA. Hybridisation with an alpha DNA probe specific for human acrocentric chromosomes indicated the retention of the centromere, and the absence of alpha DNA in the extra chromosomal material. We propose the origin of the extra chromosomal material in WSm-var(14) to be a result of amplification of contiguous satellite III DNA that is normally present in the short arm of chromosome 14. This variant chromosome does not appear to be associated with the abnormal phenotype in WSm's daughter who is mentally retarded and carries a t(1;?)(q41;?) translocation of chromosome 1.     

Equine half sibs with an unbalanced X;15 translocation or trisomy 28

Two unrelated chromosome abnormalities were found in equine half sibs. The proposita, Case 1, which was short in stature and infertile, had a de novo unbalanced X;15 translocation involving loss of Xp. Replication studies indicated that the translocated X was preferentially late replicating and that this late replication spread variably into the autosomal segment. Case 2, a half brother of the proposita, was short in stature, had cryptorchidism, and was trisomic for chromosome 28. Cytogenetic analysis of the dam, the sire of Case 1, and two other phenotypically normal half sibs revealed normal chromosome complements. Five further normal pregnancies were reported. The finding of two unrelated chromosome abnormalities is therefore probably fortuitous in this family. This is the first case of an unbalanced X-autosome translocation and the first case of an autosome trisomy to be reported in the horse.     

Molecular and cytological characterization of an extra acrocentric chromosome that restores male fertility of wheat in the msH1 CMS system

A new CMS system designated as ‘msH1’ has been reported in bread wheat using the cytoplasm of H. chilense. While testing this system in different wheat backgrounds, a highly fertile line with chromosome number 42 plus an extra acrocentric chromosome was obtained. The extra chromosome did not pair with any wheat chromosome at meiosis, and progeny from this line which lack the acrocentric chromosome showed pollen abortion and male sterility. In order to establish the origin of this chromosome, FISH using H. chilense genomic DNA as probe was used and showed that it had originated from H. chilense chromosome(s). The novel chromosome did not possess sequences similar to wheat rDNA; however, the probe pSc119.2 from S. cereale containing the 120 bp family was found to occur at the end of its long arm. Data obtained from FISH and EST molecular markers confirm that the long arm of the acrocentric chromosome is indeed, the short arm of chromosome 1H^ch from H. chilense. We suggest that the novel chromosome originated from a deletion of the distal part of the long arm of chromosome 1H^ch. Neither the 1H^chS short arm, nor the whole chromosome 1H^ch restores pollen fertility of the alloplasmic wheat. Therefore, the restorer gene on the acrocentric chromosome must be located on the retained segment from the hypothetical 1H^chL, while some pollen fertility inhibitor could be present on the deleted 1H^chL distal segment. Disomic addition of the acrocentric chromosome was obtained and this line resulted fully stable and fertile.     

Physical mapping of sequences homologous to an endogenous retrovirus LTR on human chromosome 19

The human genome contains multiple copies of sequences related to the HERV-K family of endogenous retroviruses, homologous to the B-type mouse mammary tumour virus. A DNA fragment closely resembling an HERV-K long tandem repeat (LTR) was detected in a library of hncDNA clones enriched for sequences from human chromosome 19. Sites showing homology to the sequence of this fragment have been identified on human chromosome 19 by hybridization to previously mapped chromosome 19 cosmids. Thus the distribution of LTR sequences on a specific human chromosome has been mapped for the first time. We estimate the total number of such sites on human chromosome 19 to be at least 110. Many of these sites are located in the vicinity of known genes. The precise localizations (to specific cosmids) of LTR-homologous sequences on chromosome 19 can serve as a reference source and will automatically provide further insight into LTR-gene relationships as new genes are mapped onto the chromosome.