Genomic Instability in Wheat Induced by Chromosome 6b(s) of Triticum Speltoides

A massive restructuring of chromosomes was observed during the production of a substitution of chromosome 6B(s) from Triticum speltoides (Tausch) Gren. ex Richter for chromosome 6B of Chinese Spring wheat (Triticum aestivum L.). Deletions, translocations, ring chromosomes, dicentric chromosomes and a paracentric inversion were observed. Chromosome rearrangements occurred in both euchromatic and heterochromatic regions. Chromosome rearrangements were not observed either in the amphiploid between Chinese Spring and T. speltoides or in Chinese Spring. No chromosome rearrangements were observed in the backcross derivatives; however, after self-pollination of a monosomic substitution (2n = 41) of chromosome 6B(s) for wheat chromosome 6B, 49 of the 138 plants carried chromosome aberrations. Chromosome rearrangements were observed in both wheat and T. speltoides chromosomes. The frequency of chromosome rearrangements was high among the B-genome chromosomes, moderate among the A-genome chromosomes, and low among the D-genome chromosomes. In the B genome, the rearrangements were nonrandom, occurring most frequently in chromosomes 1B and 5B. Chromosome rearrangements were also frequent for the 6B(s) chromosome of T. speltoides. An intriguing aspect of these observations is that they indicate that wheat genomes can be subject to uneven rates of structural chromosome differentiation in spite of being in the same nucleus.     

del(X)(p22.1)/r(X)(p22.1q28) Dynamic mosaicism in a Turner syndrome patient

We report on a 16-year-old patient with Turner syndrome who presented a mos 46,X,del(X)(p22.1)[35]/45,X [19]/46,X,r(X)(p22.1q28)[6]GTG-band karyotype. The R-banding showed that the abnormal X-chromosome was inactive in all 61 cells analyzed. Fluorescence in situ hybridization with a Xp/Yp subtelomeric probe revealed that both abnormal chromosomes lacked the complementary sequences, a fact consistent with a terminal deletion. Besides, the molecular analysis of the human androgen receptor gene showed that the rearranged chromosome was paternal in origin. Since the deleted and the ring chromosomes had the same size and banding pattern, and because the former was the predominant cell line, it was inferred that the Xp- formed a ring in some cells apparently without further loss of genetic material. However, the reverse sequence and even a simultaneous origin due to a complex intrachromosomal exchange are also conceivable. The mild Turner syndrome phenotype is explained by the mosaicism and by the size of the deleted segment.     

Proof of partial imbalances 6q and 11q due to maternal complex balanced translocation analyzed by microdissection of multicolor labeled chromosomes (FISH-MD) in a patient with Dandy-Walker variant

We report on a family in which a daughter is described with mental retardation, as well as malformations of the heart, and of the brain (Dandy-Walker variant). The patient's phenotype suggests a chromosomal rearrangement. However, her karyotype was unremarkable by conventional cytogenetic analysis. In order to detect chromosome rearrangements overseen by this method, the subtelomere regions of suspicious chromosomes were verified by fluorescence in situ hybridization (FISH). A rearranged derivative chromosome 6 was identified. Further examinations by FISH-microdissection (FISH-MD) revealed a maternal complex balanced translocation. The patient inherited the derivative chromosome 6 from her mother and therefore carries a partial monosomy 6q26-->qter and a partial trisomy 11q23.3-->qter.     

A reciprocal whole-arm translocation, rcp(1;6)(1p6p;1q6q) in a boar, localization of the breakpoints, and reassignment of the genes for glucose phosphate isomerase (GPI) and calcium release channel (CRC).

A reciprocal whole-arm translocation between chromosomes 1 and 6 in a Swiss Large White boar with reduced fertility was identified by the use of different staining techniques in mitotic metaphase cells, synaptonemal complex analyses, and meiotic chromosome preparations. The karyotype of this boar was demonstrated to be 38,XY,rcp(1;6)(1p6p;1q6q). To further localize the breakpoints more precisely and determine the precise gene locations, several in situ hybridization experiments were performed with a chromosome 1 centromere-specific probe and two other gene probes. The breakage and reunion points of both chromosomes were located in the centromeric regions. The genes for glucose phosphate isomerase and calcium release channel were mapped to 6cen----q12.     

Molecular cytogenetic characterization of 17 rob(13q14q) Robertsonian translocations by FISH, narrowing the region containing the breakpoints.

We have characterized 17 rob(13q14q) Robertsonian translocations, using six molecular probes that hybridize to the repetitive sequences of the centromeric and shortarm regions of the five acrocentric chromosomes by FISH. The rearrangements include six de novo rearrangements and the chromosomally normal parents, five maternally and three paternally inherited translocations, and three translocations of unknown origin. The D21Z1/D13Z1 and D14Z1/D22Z1 centromeric alpha-satellite DNA probes showed all rob(13q14q) chromosomes to be dicentric. The rDNA probes did not show hybridization on any of the 17 cases studied. The pTRS-47 satellite III DNA probe specific for chromosomes 14 and 22 was retained around the breakpoints in all cases. However, the pTRS-63 satellite III DNA probe specific for chromosome 14 did not show any signals on the translocation chromosomes examined. In 16 of 17 translocations studied, strong hybridization signals on the translocations were detected with the pTRI-6 satellite I DNA probe specific for chromosome 13. All parents of the six de novo rob(13q14q), including one whose pTRI-6 sequence was lost, showed strong positive hybridization signals on each pair of chromosomes 14 and 13, with pTRS-47, pTRS-63, and pTRI-6. Therefore, the translocation breakpoints in the majority of rob(13q14q) are between the pTRS-47 and pTRS-63 sequences in the p11 region of chromosome 14 and between the pTRI-6 and rDNA sequences within the p11 region of chromosome 13.     

Localization of the human gene for 230-kDal bullous pemphigoid autoantigen (BPAG1) to chromosome 6pter----q15.

Chromosome mapping of the human gene encoding the 230-kDal autoantigen of an autoimmune skin disease, bullous pemphigoid, was performed using flow-sorted human chromosomes of cells of normal karyotype and cells carrying a reciprocal translocation t(6;16)(q15;q24). The cDNA of the autoantigen hybridized with intact chromosome 6 and translocation chromosome 6p- (6pter----q15::16q24----qter). The gene (BPA230) was located to the chromosome region 6pter----q15.     

Cytogenetic analysis of sperm from a man heterozygous for a pericentric inversion, inv (3) (p25q21).

Human sperm chromosomes were studied in a man heterozygous for a pericentric inversion of chromosome 3(p25q21). The pronuclear chromosomes were analyzed after in vitro penetration of golden hamster eggs. A total of 144 sperm were examined: 69.2% were chromosomally balanced and 30.8% were recombinant. Of the balanced complements, the proportion with a normal chromosome 3 (37.6%) was approximately equal to the proportion with an inverted 3 (31.6%). Of the recombinant complements, the proportion of sperm with a duplication q/deletion p (17.3%) was approximately equal to the reciprocal event of duplication p/deletion q (13.5%). The recombinant chromosome 3 with a duplication q and deletion p has been observed in several abnormal children, but the duplication p/deletion q has never been reported. My results demonstrate that both recombinant chromosomes are produced as expected from an unequal number of crossovers within an inversion loop. In all likelihood the duplication p/deletion q chromosome is an early embryonic lethal because of the amount of genetic material deleted. The proportions of X-bearing (48.9%) and Y-bearing sperm (51.1%) were not significantly different from the expected 1:1 ratio. There was no evidence for an interchromosomal effect. Of the three inversions studied by human sperm chromosome analysis, recombinant chromosomes have been observed only in this case.     

Genome-wide association study of white blood cell count in 16,388 African Americans: the continental origins and genetic epidemiology network (COGENT)

Total white blood cell (WBC) and neutrophil counts are lower among individuals of African descent due to the common African-derived "null" variant of the Duffy Antigen Receptor for Chemokines (DARC) gene. Additional common genetic polymorphisms were recently associated with total WBC and WBC sub-type levels in European and Japanese populations. No additional loci that account for WBC variability have been identified in African Americans. In order to address this, we performed a large genome-wide association study (GWAS) of total WBC and cell subtype counts in 16,388 African-American participants from 7 population-based cohorts available in the Continental Origins and Genetic Epidemiology Network. In addition to the DARC locus on chromosome 1q23, we identified two other regions (chromosomes 4q13 and 16q22) associated with WBC in African Americans (P<2.5×10(-8)). The lead SNP (rs9131) on chromosome 4q13 is located in the CXCL2 gene, which encodes a chemotactic cytokine for polymorphonuclear leukocytes. Independent evidence of the novel CXCL2 association with WBC was present in 3,551 Hispanic Americans, 14,767 Japanese, and 19,509 European Americans. The index SNP (rs12149261) on chromosome 16q22 associated with WBC count is located in a large inter-chromosomal segmental duplication encompassing part of the hydrocephalus inducing homolog (HYDIN) gene. We demonstrate that the chromosome 16q22 association finding is most likely due to a genotyping artifact as a consequence of sequence similarity between duplicated regions on chromosomes 16q22 and 1q21. Among the WBC loci recently identified in European or Japanese populations, replication was observed in our African-American meta-analysis for rs445 of CDK6 on chromosome 7q21 and rs4065321 of PSMD3-CSF3 region on chromosome 17q21. In summary, the CXCL2, CDK6, and PSMD3-CSF3 regions are associated with WBC count in African American and other populations. We also demonstrate that large inter-chromosomal duplications can result in false positive associations in GWAS.     

Sperm chromosome analysis in a man heterozygous for a paracentric inversion of chromosome 7 (q11q22)

Summary Human sperm chromosomes were studied in a man heterozygous for a paracentric inversion of chromosome 7 (q11q22). The pronuclear chromosomes were analysed after in vitro penetration of golden hamster (Mesocricetus auratus) eggs. Ninety-four sperm chromosome spreads were examined, of which 34 contained the normal number 7 chromosome and 59 the inverted 6. This segregation was significantly different from the expected 1:1 ratio. The number of X- to Y-bearing sperm was 48 and 46 respectively. No sperm contained a recombinant chromosome caused by a crossover within the inversion. The frequency of chromosomal abnormalities in other chromosomes was 9.6%, which is not significantly different from the frequency observed in normal donors (8.9%) in our laboratory. These result suggest that the risk of chromosomally unbalanced sperm is not high for this paracentric inversion.     

Meiotic recombination and spatial proximity in the etiology of the recurrent t(11;22)

Although balanced translocations are among the most common human chromosomal aberrations, the constitutional t(11;22)(q23;q11) is the only known recurrent non-Robertsonian translocation. Evidence indicates that de novo formation of the t(11;22) occurs during meiosis. To test the hypothesis that spatial proximity of chromosomes 11 and 22 in meiotic prophase oocytes and spermatocytes plays a role in the rearrangement, the positions of the 11q23 and 22q11 translocation breakpoints were examined. Fluorescence in situ hybridization with use of DNA probes for these sites demonstrates that 11q23 is closer to 22q11 in meiosis than to a control at 6q26. Although chromosome 21p11, another control, often lies as close to 11q23 as does 22q11 during meiosis, chromosome 21 rarely rearranges with 11q23, and the DNA sequence of chromosome 21 appears to be less susceptible than 22q11 to double-strand breaks (DSBs). It has been suggested that the rearrangement recurs as a result of the palindromic AT-rich repeats at both 11q23 and 22q11, which extrude hairpin structures that are susceptible to DSBs. To determine whether the DSBs at these sites coincide with normal hotspots of meiotic recombination, immunocytochemical mapping of MLH1, a protein involved in crossing over, was employed. The results indicate that the translocation breakpoints do not coincide with recombination hotspots and therefore are unlikely to be the result of meiotic programmed DSBs, although MRE11 is likely to be involved. Previous analysis indicated that the DSBs appear to be repaired by a mechanism similar to nonhomologous end joining (NHEJ), although NHEJ is normally suppressed during meiosis. Taken together, these studies support the hypothesis that physical proximity between 11q23 and 22q11--but not typical meiotic recombinational activity in meiotic prophase--plays an important role in the generation of the constitutional t(11;22) rearrangement.     

Partial trisomy 13 as a result of de novo (6p;13q) translocation

Summary A newborn infant with the clinical features of the Patau syndrome was found to have excess chromosome 13 material present as a tandem translocation involving the short arm of chromosome 6 and the long arm of an extra chromosome 13: 46,XY,t(6;13)(p24;q12). The major part of the long arm of the extra chromosome 13 was attached linearly (tandem translocation) to the short arm of chromosome 6. Both parents were phenotypically and karyotypically normal.     

Single-copy flanking sequences in human histone gene clusters map to chromosomes 1 and 6

Two single-copy sequences flanking two different human histone gene clusters were used as probes to map these clusters by in situ hybridization. pFF435B, a unique sequence subclone derived from a lambda genomic clone (lambda HHG55) containing H2A, H2B, H3, and H4 genes, mapped to chromosome 1q21 (chi 2 = 120.99, P less than 0.001). pST519E, a single-copy sequence derived from a lambda genomic clone (lambda HHG17) containing only H3 and H4 genes, mapped to chromosome 6p21 (chi 2 = 112.62, P less than 0.001). These findings agree with previous assignments of human histone genes to chromosomes 1 and 6 and demonstrate that the single-copy flanking sequences in different human histone gene clusters are unique for different chromosomes.     

SV40-transformed human fibroblasts exhibit a characteristic chromosomal pattern

A karyotype study of seven SV40-transformed human fibroblast cell lines was performed using R-banding. Although large variations existed from line to line and, to a lesser degree, from cell to cell in a given line, many common features were found. The most characteristic were chromosome imbalances. Some of the chromosomes or chromosome segments present in excess were, in decreasing order of frequency, the early replicating X, 12q, 3q, 12p, 19, 1p, and 6p. Losses of other chromosomes and chromosome segments were also frequent and involved 11p, 2p, 6q, 10p, 18, 4q, 8p, 4p, 10q, and 16. These imbalances seemed to correlate with metabolic characteristics, previously described, such as low activities of catalase (11p), superoxide dismutase 2 (6q), and acid phosphatase (2p, 11p) and a high ratio of lactate dehydrogenase B (LDHB, 12p) activity to LDHA (11p) activity.     

Replication timing in a single human chromosome 11 transferred into the Chinese hamster ovary (CHO) cell line

DNA replication in eukaryotes initiates from discrete genomic regions, termed origins, according to a strict and often tissue-specific temporal program. However, the genetic program that controls activation of replication origins has still not been fully elucidated in mammalian cells. Previously, we measured replication timing at the sequence level along human chromosomes 11q and 21q. In the present study, we sought to obtain a greater understanding of the relationship between replication timing programs and human chromosomes by analysis of the timing of replication of a single human chromosome 11 that had been transferred into the Chinese hamster ovary (CHO) cell line by chromosome engineering. Timing of replication was compared for three 11q chromosomal regions in the transformed CHO cell line (CHO(h11)) and the original human fibroblast cell line, namely, the R/G-band boundary at 11q13.5/q14.1, the centromere and the distal telomere. We found that the pattern of replication timing in and around the R/G band boundary at 11q13.5/q14.1 was similar in CHO(h11) cells and fibroblasts. The 11q centromeric region, which replicates late in human fibroblasts, replicated in the second half of S phase in CHO(h11) cells. By contrast, however, the telomeric region at 11q25, which is late replicating in fibroblasts (and in several other human cell lines), replicated in the first half of S phase or in very early S phase in CHO(h11) cells. Our observations suggest that the replication timing programs of the R/G-band boundary and the centromeric region of human chromosome 11q are maintained in CHO(h11) cells, whereas that for the telomeric region is altered. The replication timing program of telomeric regions on human chromosomes might be regulated by specific mechanisms that differ from those for other chromosomal regions.     

fra(1) (p11), fra(1) (q22) and r(1) (p11q22) in a retarded girl.

A mentally retarded girl with a 46,XX/47, XX+r(1) (p11q22q22p11)/47, XX+r(1) (p11q22) fra(1) (p31) fra(1) (p11) fra(1) (q22) karyotype who inherited the fragile sites from the normal mother was studied. The conicidence of fra(1) (p11) and fra(1) (q22) with the ring chromosome breakpoints strongly suggests a cause-effect relationship. This finding agrees with other reported associations between fragile sites and structural chromosome abnormalities and constitutes the fourth reported of a de novo structurally abnormal chromosome as a consequence of presumed in vivo fragile sites instability. Although risk figures for chromosome anomalies and cancer associated with fragile sites are lacking, carriers of fra (1) (p11) may have a higher risk for abnormalities of chromosome 1 in somatic and gonadal cells than the general population.     

Identification of DNA sequences flanking the breakpoint of human t(14q21q) Robertsonian translocations.

We have employed molecular probes and in situ hybridization to investigate the DNA sequences flanking the breakpoint of a group of t(14q21q) Robertsonian translocations. In all the families studied, the probands were patients with Down syndrome who carried a de novo t(14q21q) translocation. The DNA probes used were two alphoid sequences, alphaRI and alphaXT, which are specific for the centromeres of chromosomes 13 and 21 and of chromosomes 14 and 22, respectively; a satellite III sequence, pTRS-47, which is specific for the proximal p11 region of chromosomes 14 and 22; and a newly defined satellite III DNA, pTRS-63, which is specific for the distal p11 region of chromosome 14. The two alphoid probes detected approximately the same amount of autoradiographic signal on the translocated chromosomes as was expected for chromosomes 14 and 21 of the originating parent, suggesting that there has been no loss of these centromeric sequences during the translocation events. Results with the two satellite III probes indicated that the domain corresponding to pTRS-47 was retained in the translocated chromosomes, whereas the domain for pTRS-63 was lost. These results have allowed us to place the translocation breakpoint between the pTRS-47 and pTRS-63 domains within the p11 region of chromosome 14.     

Distal monosomy of the long arm of chromosome 6 (6q25----6qter) inherited by maternal translocation t(6q;17q)

Two half-sisters with distal monosomy of the long arm of chromosome 6 (q25----qter) inherited by maternal translocation t(6q;17q) were investigated. The clinical manifestations of these patients are compared with eight cases reported in the literature for further characterization of the 6q-syndrome. The cytogenetic diagnosis of alterations involving small chromosome fragments and the different origins of this type of deletion are also discussed.     

兴义维蚋多线染色体研究（英文）

首次在国内对兴义维蚋Simulium (Wilhelmia) xingyiense的多线染色体进行研究, 并提供其多线染色体标准图。选取兴义维蚋的成熟幼虫, 用改良苯酚品红染色法进行唾腺多线染色体制备, 并进行测量、 描述及分析。结果表明： 兴义维蚋多线染色体数目为3对（2n=6）。Ⅰ号染色体具中央着丝粒, Ⅱ和Ⅲ号染色体均为亚中央着丝粒染色体。核仁组织者区位于Ⅰ号染色体短臂近着丝粒端。巴尔比尼氏环和双泡位于Ⅱ号染色体短臂近中央位置。3对染色体的着丝粒区可形成明显的染色中心。兴义维蚋多线染色体具有多态性的倒位, 倒位频率为0.64。兴义维蚋多线染色体的着丝粒、 核仁组织区、 巴氏环、 双泡等主要特征性结构的位置及形态恒定一致,可作为该种的重要鉴别特征。其多态性的倒位可为该蚋种在细胞水平上进行蚋类分类鉴别和系统发育等研究提供基础资料。