Alternate centromere inactivation in a pseudodicentric (15;20)(pter;pter) associated with a progressive neurological disorder

Mixed gonadal dysgenesis in a patient with de novo tas(Y;19)(p11.3;q13.4) and 45,X mosaicism

We report a patient with a de novo telomeric association between chromosomes 19 and Y in conjunction with mixed gonadal dysgenesis. The patient was first admitted to the clinic because of abnormal external genitalia. Laparoscopic evaluation revealed (1) a rudimentary uterus, one fallopian tube, and a small gonad resembling an ovary on the right side, and (2) an immature fallopian tube, a vas deferens, and a gonad resembling a testis on the left side. Conventional cytogenetic analysis performed on cultivated peripheral blood cells, and tissue obtained from the phallus and a gonadal structure which resembled a testis revealed two different cell lines with the 46,X,tas (Y;19)(p11.3;q13.4) and 45,X karyotype. Y chromosome microdeletion analysis showed that the patient did not have any genomic deletions in the AZFa, b, c, or SRY regions on the long arm of the Y chromosome. This is the first report of a patient with mixed gonadal dysgenesis that is accompanied by a telomeric association between chromosomes 19 and Y with 45,X mosaicism.

Centromere activity in dicentric small supernumerary marker chromosomes

Twenty-five dicentric small supernumerary marker chromosomes (sSMC) derived from #13/21, #14, #15, #18, and #22 were studied by immunohistochemistry for their centromeric activity. Centromere protein (CENP)-B was applied as marker for all centromeres and CENP-C to label the active ones. Three different 'predominant' activation patterns could be observed, i.e., centric fusion or either only one or all two centromeres were active. In one inherited case, the same activation pattern was found in mother and son. In acrocentric-derived sSMC, all three activation patterns could be present. In contrary, in chromosome 18-derived sSMC, only the fusion type was observed. In concordance with previous studies a certain centromeric plasticity was observed in up to 13% of the cells of an individual case. Surprisingly, the obtained data suggests a possible influence of the sSMC carrier's gender on the implementation of the predominant activation pattern; especially, only one active centromere was found more frequently in female than in male carriers. Also, it might be suggested that dicentric sSMC with one active centromere could be less stable than such with two active ones-centromeric plasticity might have an influence here, as well. Also, centromere activity in acrocentric-derived dicentrics could be influenced by heteromorphisms of the corresponding short arms. Finally, evidence is provided that the closer the centromeres of a dicentric are and if they are not fused, the more likely it was that both of them became active. In concordance and refinement with previous studies, a distance of 1.4 Mb up to about 13 Mb the two active centromere state was favored, while centromeric distance of over approximately 15 Mb lead to inactivation of one centromere. Overall, here, the first and largest ever undertaken study in dicentric sSMC is presented, providing evidence that the centromeric activation pattern is, and parental origin may be of interest for their biology. Influence of mechanisms similar or identical to meiotic imprinting in the centromeric regions of human chromosomes might be present. Furthermore, centromeric activation pattern could be at least in parts meaningful for the clinical outcome of dicentric sSMC, as sSMC stability and mosaicism can make the difference between clinically normal and abnormal phenotypes.

Phylogenomics of African guenons

The karyotypes of 28 specimens belonging to 26 species of Cercopithecinae have been compared with each other and with human karyotype by chromosome banding and, for some of them, by Zoo-FISH (human painting probes) techniques. The study includes the first description of the karyotypes of four species and a synonym of Cercopithecus nictitans. The chromosomal homologies obtained provide us with new data on a large number of rearrangements. This allows us to code chromosomal characters to draw Cercopithecini phylogenetic trees, which are compared to phylogenetic data based on DNA sequences. Our findings show that some of the superspecies proposed by Kingdon (1997 The Kingdon Field Guide to African Mammals, Academic Press.) and Groves (2001 Primates Taxonomy, Smithsonian Institution Press) do not form homogeneous groups and that the genus Cercopithecus is paraphyletic, in agreement with previous molecular analyses. The evolution of Cercopithecini karyotypes is mainly due to non-centromeric chromosome fissions and centromeric shifts or inversions. Non-Robertsonian translocations occurred in C. hamlyni and C. neglectus. The position of chromosomal rearrangements in the phylogenetic tree leads us to propose that the Cercopithecini evolution proceeded by either repeated fission events facilitated by peculiar genomic structures or successive reticulate phases, in which heterozygous populations for few rearranged chromosomes were present, allowing the spreading of chromosomal forms in various combinations, before the speciation process.

Mitotic and meiotic instability of a telomere association involving the Y chromosome

Constitutional telomere associations and jumping translocations (JTs) are rare events and usually occur post-zygotically. We report a telomere association involving the Y chromosome which "jumped" during meiosis. A 21-year-old woman was referred for amniocentesis due to non-immune hydrops seen in a previous pregnancy. Cytogenetic analysis of the amniocytes showed a 45,X,tas(Y;15)[4]/45,X[16] karyotype with the long arm of the Y chromosome attached to the end of the short arm of chromosome 15. Parental chromosome analyzes revealed a tas(Y;19)[63]/45,X[7] karyotype in the father with Yq attached to the end of the short arm of chromosome 19. A phenotypically normal male was born and blood chromosome analysis confirmed a 45,X,tas(Y;15)[39]/45,X[10]/46,XY[1] karyotype. Two other male children have 46,XY karyotypes, which further demonstrates the instability of the tas(Y;19) in meiosis. Fluorescence in situ hybridization (FISH) analysis with probes for theY-centromere, the Yqh region, the shared Xq/Yq telomere and SRY showed hybridization on the tas(Y;19) and tas(Y;15). A chromosome 19p specific subtelomeric probe showed hybridization to the tas(Y;19) in the father. In addition, a probe for the simple telomeric sequences TTAGGG showed positive hybridization to the junction of the associations. The presence of TTAGGG telomere repeats and unique telomere sequences indicate that the Y;15 and Y;19 associations occur with no detectable loss of any sequences. The interstitial telomere sequences at the junction of the telomere association may explain the mitotic and meiotic instability of the association.

Mosaic paternal uniparental (iso)disomy for chromosome 20 associated with multiple anomalies

Uniparental disomy for a number of human chromosomes is associated with clinical abnormalities. We report a child with a complex chromosomal rearrangement involving chromosome 20 (45,XY,psu dic (20;20)(p13;p13)) and paternal uniparental isodisomy for chromosome 20 in peripheral blood and bone marrow. This patient had multiple congenital abnormalities including microtia/anotia, micrencephaly, congenital heart disease, neuronal subependymal heterotopias, and colonic agangliosis. Molecular studies on DNA from peripheral blood demonstrated paternal uniparental inheritance of chromosome 20. However, fibroblasts demonstrated a mosaic karyotype, with one cell line having 45 chromosomes, including the pseudodicentric chromosome 20 (75% of cells), and a second cell line having 46 chromosomes, including the pseudodicentric chromosome 20, and a normal chromosome 20 (trisomy 20) (25% of cells). FISH experiments using a sub-telomeric probe that maps approximately 120 kb from the 20p telomere, showed that both copies of these sequences were present on the rearranged chromosome, consistent with deletion of a very small interval. This leads us to suggest that in addition to trisomy 20 mosaicism, paternal uniparental disomy for chromosome 20 could contribute to his clinical phenotype.

Molecular and cytogenetic characterization of an azoospermic male with a de-novo Y;14 translocation and alternate centromere inactivation

BACKGROUND

Y-autosome (Y/A) translocations have been reported in association with male infertility. Different hypotheses have been made as to correlations between Y/A translocations and spermatogenetic disturbances. We describe an azoospermic patient with a de-novo Y;14 translocation: 45,X,dic(Y;14)(q12;p11).

METHODS AND RESULTS

Cytogenetic, fluorescent in-situ hybridization (FISH) and molecular studies have been performed. A 14/22 (D14Z1/D22Z1) centromere and a Y centromere (DYZ1) probe both showed a signal on the translocation chromosome, confirming its dicentricity. Each copy of the translocation chromosome had only one primary constriction, with inactivation of the Y centromere in most (90%) of the cells. The 14 centromere was inactive in the remaining cells (10%). FISH and molecular deletion mapping analysis allowed acute assignment of the Yq breakpoint to the junction of euchromatin and heterochromatin (Yq12), distal to the AZF gene location (Yq11).

CONCLUSIONS

This study supports the hypothesis that in Y/A translocations infertility might be related to meiotic disturbances with spermatogenetic arrest. In addition, sex chromosome molecular investigations, performed on single spermatids, suggest a highly increased risk of producing chromosomally abnormal embryos.

Mosaic telomeric (2;14) association in a child with motor delay

In a 6-year-old girl referred because of mild motor delay and hyperextensible joints, chromosome analysis disclosed a derivative chromosome consisting of end-to-end fusion of chromosomes 2 and 14. Two cell lines existed in which this telomere association was present, one with a 45,XX,tas(2;14)(q37;p11) karyotype and one with a 45,XX,tas(2;14) (q37;q32) karyotype. The cell line with the telomeric fusion of 2q and 14p was present in 90% of the cells; a telomeric fusion of 2q and 14q was seen in the remaining 10% of the cells. In both association complexes, only the centromere of chromosome 14 was active. Fluorescence in situ hybridization with telomere and subtelomere probes disclosed no deletion of chromosomal material. Microsatellite analysis showed that the patient had a normal biparental contribution of chromosomes 14.

Complex chromosome 9, 20, and 22 rearrangements in acute lymphoblastic leukemia with duplication of BCR and ABL sequences

Cytogenetic analysis was performed on bone marrow cells from a 28-year-old woman who was diagnosed with acute lymphoblastic leukemia (ALL). Her karyotype was: 46,XX,t(9;22)(q34;q11)[6]/47, XX,+8,t(9;22)(q34;q11)[4]/47,XX,+8,t(9;22)(q34;q11),del(20)(q11)[2]/46, XX,t(9;22)(q34;q11),del[20](q11)[7]/45,XX,der(9)t(9;22)(q34;q11),-20,-22 , +mar1[8]/45,XX,der(9)t(9;22)(q34;q11),-20,-22,+mar2[3]. Both marker chromosomes are dicentric and have the same size and banding pattern but different primary constrictions. Fluorescence in situ hybridization (FISH) demonstrated that both markers were derived from chromosomes 9, 20, and 22. FISH with the bcr/abl probe showed fusion of the BCR gene with the ABL gene; however, this fusion signal was present in duplicate on both marker chromosomes. To our knowledge, duplication of the BCR/ABL fusion signal on a single chromosome arm has not been reported before, except for the extensive amplification of BCR/ABL fusion signals in the leukemic cell line K-562. These data demonstrate that the marker chromosomes are the result of complex genomic rearrangements. At the molecular level, the BCR/ABL fusion gene encodes the p190 fusion protein. Similar findings have never been observed in any case of ALL.

Chromosome stability is maintained by short intercentromeric distance in functionally dicentric human Robertsonian translocations

While the formation of a dicentric chromosome often leads to chromosome instability, human dicentric Robertsonian translocations usually remain stable. To investigate the basis for this stability, we have examined the centromeres of 15 structurally dicentric rob(13q14q) Robertsonian translocations using immunofluorescence and fluorescence in situ hybridization (FISH). The immunofluorescence detection of centromere protein C (CENP-C) was used as a marker for centromere function as CENP-C seems to play an essential role in kinetochore structure and stability and was previously shown to be absent from inactive centromeres. In all 15 translocation-containing cell lines, CENP-C was confined to only one of the centromeres of the translocation in a fraction of the cells analyzed. This suggests that centromere inactivation commonly occurs on dicentric Robertsonian translocations and may serve as one mechanism allowing for their stability. However, in the majority of the translocations (12 out of 15), a portion of the cells analyzed displayed CENP-C immunofluorescence at both centromeres, suggesting that both centromeres were active and that the translocation was functionally dicentric. The percentage of cells with CENP-C at both centromeres ranged from 2% to 82%. These results support the hypothesis that the close proximity of two functional centromeres on Robertsonian translocations allows them to remain stable.

Centromere DNA dynamics: latent centromeres and neocentromere formation

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A stable dicentric chromosome: both centromeres develop kinetochores and attach to the spindle in monocentric and dicentric configuration

A stable, dicentric human chromosome, which is known from light microscopy to show a 50:50 distribution between monocentric/dicentric appearance, was examined by conventional electron microscopy and after labelling the centromere with anticentromere antibodies from CREST serum. Both centromeres of the chromosome developed kinetochores whether in monocentric or dicentric configuration. The eight monocentrics observed had all developed kinetochores at the centromere outside the constriction; at least six of them also had kinetochores at the centromere in the constriction. The dicentrics from glutaraldehyde fixed cells had spindle microtubules attached to both kinetochore sets irrespective of monocentric/dicentric configuration. The chromosome thus appeared to use both centromeres, either equally or with one serving a chromatid adhesion function while the second was used for transport along the spindle.

Molecular characterization of the secondary constriction region (qh) of human chromosome 9 with pericentric inversion

Pericentric inversion of the secondary constriction region (qh) of human chromosome 9 is a frequent occurrence. This structural alteration is regarded as a normal familial variant, termed heteromorphism, and is inherited in a Mendelian fashion without any apparent phenotypic consequences. We characterized the qh region of chromosome 9 from five individuals using a series of molecular cytogenetic techniques. Four out of the five individuals have an additional area composed of alphoid DNA sequences on the inverted chromosome 9 while one case was found to have an apparently intact alphoid DNA sequence. Although the direct function(s) of alphoid DNA sequences remain unclear, the centromeric breakage involving these sequences in inverted chromosome 9 raises a series of questions pertaining to the monocentric, dicentric and pseudodicentric nature of pericentric inversions. Nevertheless, these findings have prompted us to suggest that the structural organization of alphoid DNA sequences of the centromeric region of chromosome 9 are apparently “breakage prone” and may be associated with a higher incidence of pericentric inversions. Furthermore, the hierarchical organization of various satellite DNA families (alpha-satellite, beta-satellite and satellite III) within the primary and secondary constriction regions of chromosomes 9 are elucidated here.

Y isochromosome associated with a mosaic karyotype and inactivation of the centromere

A patient with azoospermia and a Y isochromosome is described. The breakpoint producing this i(Y) was within the terminal short arm of the Y chromosome. Lymphocyte cultures from peripheral blood contained a high proportion of 45,X cells and cells with different Y-chromosome rearrangements. The i(Y) had either a monocentric or dicentric appearance. In dicentrics, anti-kinetochore immunofluorescence was present at both centromeres. However, this was also true for most of the functional monocentrics (pseudodicentrics). Kinetochore staining was generally positive at the site of the inactive centromeres; only a minority of the suppressed centromeres had lost their antigenic properties. Permanently growing lymphoblasts consistently showed a monocentric i(Y) with only one fluorescing kinetochore; the immunonegative Y centromere did not recover antigenicity.