Jumping translocations originate clonal rearrangements in SV40-transformed human fibroblasts

The Central Role of Cytogenetics in Radiation Biology

Radiation cytogenetics has a rich history seldom appreciated by those outside the field. Early radiobiology was dominated by physics and biophysical concepts that borrowed heavily from the study of radiation-induced chromosome aberrations. From such studies, quantitative relationships between biological effect and changes in absorbed dose, dose rate and ionization density were codified into key concepts of radiobiological theory that have persisted for nearly a century. This review aims to provide a historical perspective of some of these concepts, including evidence supporting the contention that chromosome aberrations underlie development of many, if not most, of the biological effects of concern for humans exposed to ionizing radiations including cancer induction, on the one hand, and tumor eradication on the other. The significance of discoveries originating from these studies has widened and extended far beyond their original scope. Chromosome structural rearrangements viewed in mitotic cells were first attributed to the production of breaks by the radiations during interphase, followed by the rejoining or mis-rejoining among ends of other nearby breaks. These relatively modest beginnings eventually led to the discovery and characterization of DNA repair of double-strand breaks by non-homologous end joining, whose importance to various biological processes is now widely appreciated. Two examples, among many, are V(D)J recombination and speciation. Rapid technological advancements in cytogenetics, the burgeoning fields of molecular radiobiology and third-generation sequencing served as a point of confluence between the old and new. As a result, the emergent field of "cytogenomics" now becomes uniquely positioned for the purpose of more fully understanding mechanisms underlying the biological effects of ionizing radiation exposure.

Jumping translocations of chromosome 1q occurring by a multi-stage process in an acute myeloid leukemia progressed from myelodysplastic syndrome with a TET2 mutation

Background

Jumping translocations (JTs) are rare chromosome rearrangements characterized by re-localization of one donor chromosome to multiple recipient chromosomes. Here, we describe an acute myeloid leukemia (AML) that progressed from myelodysplastic syndrome (MDS) in association with acquisition of 1q JTs. The sequence of molecular and cytogenetic changes in our patient may provide a mechanistic model for the generation of JTs in leukemia.

Case presentation

A 68-year-old man presented with pancytopenia. Bone marrow aspirate and biopsy showed a hypercellular marrow with multilineage dysplasia, consistent with MDS, with no increase in blasts. Karyotype and MDS fluorescence in situ hybridization (FISH) panel were normal. Repeat bone marrow aspirate and biopsy after 8 cycles of azacitidine, with persistent pancytopenia, showed no changes in morphology, and karyotype was again normal. Myeloid mutation panel showed mutations in RUNX1, SRSF2, ASXL1, and TET2. Three years after diagnosis, he developed AML with myelodysplasia-related changes. Karyotype was abnormal, with unbalanced 1q JTs to the short arms of acrocentric chromosomes 14 and 21, leading to gain of 1q.

Conclusions

Our patient had MDS with pathogenic mutations of the RUNX1, SRSF2, ASXL1, and TET2 genes and developed 1q JTs at the time of progression from MDS to AML. Our data suggest that the formation of 1q JTs involves multiple stages and may provide a mechanistic model for the generation of JTs in leukemia.

Establishment of an untransfected human corneal stromal cell line and its biocompatibility to acellular porcine corneal stroma

AIM

To establish an untransfected human corneal stromal (HCS) cell line and characterize its biocompatibility to acellular porcine corneal stroma (aPCS).

METHODS

Primary culture was initiated with a pure population of HCS cells in DMEM/F12 media (pH 7.2) containing 20% fetal bovine serum and various necessary growth factors. The established cell line was characterized by growth property, chromosome analysis, tumorigenicity assay, expression of marker proteins and functional proteins. Furthermore, the biocompatibility of HCS cells with aPCS was examined through histological and immunocytochemistry analyses and with light, electron microscopies.

RESULTS

HCS cells proliferated to confluence 2 weeks later in primary culture and have been subcultured to passage 140 so far. A continuous untransfected HCS cell line with a population doubling time of 41.44 hours at passage 80 has been determined. Results of chromosome analysis, morphology, combined with the results of expression of marker protein and functional proteins suggested that the cells retained HCS cell properties. Furthermore, HCS cells have no tumorigenicity, and with excellent biocompatibility to aPCS.

CONCLUSION

An untransfected and non-tumorigenic HCS cell line has been established, and the cells maintained positive expression of marker proteins and functional proteins. The cell line, with excellent biocompatibility to aPCS, might be used for in vitro reconstruction of tissue-engineered HCS.

The conundrum of a jumping translocation (JT) in CVS from twins and review of JTs

Jumping translocations (JTs) are rare constitutional or acquired rearrangements involving a donor and several receiver chromosomes. They may be inherited or de novo. JTs can be found as a cultural artifact, in normal individuals or in pathological conditions. The clinical consequences range from spontaneous abortion, loss of fetus, chromosome syndrome, congenital abnormalities, and infertility to malignancy. Considering the breakpoints of JTs, they are localized predominantly in repeat regions such as pericentromeric, centromeric, subtelomeric, telomeric, and occasionally interstitial regions that may be in a low copy repeats (LCR) or in a telomere like sequence. Differences between the constitutional and acquired JTs donor breakpoints suggest an independent mechanism in their formation. In this review, a new JT involving a donor chromosome 18p10qter and recipients 17q25qter or 1q25qter found by CVS of a twin pregnancy is described. This case illustrates the diagnostic challenges posed by JTs.In this study, our knowledge on JTs is consolidated to improve identification, management, and counseling.

Jumping translocations

Jumping translocations (JT) are uncommon constitutional or acquired chromosome rearrangements involving one donor and several recipient chromosomes. They occur in various pathologic conditions and the mechanism of their formation remains elusive. A review of the literature showed that the major localizations of the breakpoints of JTs in human samples are nonrandomly located in pericentromeric and telomeric regions of chromosomes. Interestingly, comparison of the localization of the chromosomal breakpoints and of presence of interstitial DNA repeats showed differences between constitutional and acquired JTs suggesting differences in the mechanisms for the genesis of JTs and their consequences.

Ring chromosome 18q and jumping translocation 18p in an adult male with hypergonadotrophic hypogonadism

Constitutional jumping translocations (JT) are rare, especially in phenotypically normal individuals. We report on an adult male with partial hypogonadism as the sole phenotypic abnormality with an unusual chromosome abnormality. In this patient, centric fission of chromosome 18 lead to formation of a ring 18q chromosome, while 18p formed a JT through centromere-telomere fusion with chromosome 8q (66%) or 20q (13%). In 21% of cells, the 18p fragment was missing. Fluorescent in situ hybridization revealed the presence of interstitial telomeres at the junction site of the fusion and unequal distribution of the alphoid sequences through the centric fission, leaving a small, yet functional centromere within the ring. We discuss the phenotype of the patient in light of this unusual karyotype.

A novel tumorigenic human prostate epithelial cell line (M2205): molecular cytogenetic characterization demonstrates C-MYC amplification and jumping translocations

The paucity of cell lines from early-stage prostate cancer tumors has hindered the recognition of genetic and cellular changes that are associated with the acquisition of tumorigenesis. We describe the chromosomal complement of a novel tumorigenic prostate epithelial cell subline, called M2205, that acquired only three new, consistent chromosomal changes (from those present in the SV40T antigen immortalized parental cell line, P69SV40TAg) when it attained tumor-forming potential. The consistent changes, which were fully characterized using GTG-banding, CBG-banding, silver staining, fluorescence in situ hybridization (FISH), comparative genomic hybridization (CGH), and spectral karyotyping (SKY), involved segmental jumping translocations and resulted in gains in the copy number of genes located on the distal long arm of chromosome 8 (8q22 to 8q24.3), including c-myc. Furthermore, the jumping translocations also resulted in ribosomal genes being present in multiple, tandem copies next to the chromatin from 8q. Given the relatively small number of cytogenetic changes present, this subline provides a means for better understanding the cellular changes associated with the acquired chromosomal imbalances. Further studies of this subline could also provide insight as to the mechanism or mechanisms leading to the formation of jumping translocations, as well as potential position effects resulting from the relocation of ribosomal genes next to other cellular genes or oncogenes.

Analyzing radiation-induced complex chromosome rearrangements by combinatorial painting

Cornforth, M. N. Analyzing Radiation-Induced Complex Chromosome Rearrangements by Combinatorial Painting. Radiat. Res. 155, 643-659 (2001). Prior to the advent of whole-chromosome painting, it was universally assumed that virtually all radiation-induced exchanges represented a simple rejoining between pairs of chromosome breaks. It is now known that a substantial proportion of such exchanges are actually complex, meaning that they involve the interaction of three (or more) breaks distributed among two (or more) chromosomes. The purpose of this review is to discuss some of the implications of aberration analysis using whole-chromosome painting, with emphasis given to newer combinatorial painting schemes that allow for the unambiguous identification of all homologous chromosome pairs. Such analysis requires reconsideration of how resulting information is to be handled for the purposes of tabulating and communicating raw data, quantifying aberration yields, and presenting experimental results in a cogent manner. Facilitating these objectives requires the introduction of certain concepts and terminologies that have no counterpart in conventional cytogenetic analyses.

Jumping translocations are common in solid tumor cell lines and result in recurrent fusions of whole chromosome arms

Jumping translocations (JTs) and segmental jumping translocations (SJTs) are unbalanced translocations involving a donor chromosome arm or chromosome segment that has fused to multiple recipient chromosomes. In leukemia, where JTs have been predominantly observed, the donor segment (usually 1q) preferentially fuses to the telomere regions of recipient chromosomes. In this study, spectral karyotyping (SKY) and FISH analysis revealed 188 JTs and SJTs in 10 cell lines derived from carcinomas of the bladder, prostate, breast, cervix, and pancreas. Multiple JTs and SJTs were detected in each cell line and contributed to recurrent unbalanced whole-arm translocations involving chromosome arms 5p, 14q, 15q, 20q, and 21q. Sixty percent (113/188) of JT breakpoints occurred within centromere or pericentromeric regions of the recipient chromosomes, whereas only 12% of the breakpoints were located in the telomere regions. JT breakpoints of both donor and recipient chromosomes coincided with numerous fragile sites as well as viral integration sites for human DNA viruses. The JTs within each tumor cell line promoted clonal progression, leading to the acquisition of extra copies of the donated chromosome segments that often contained oncogenes (MYC, ABL, HER2/NEU, etc.), consequently resulting in tumor-specific genomic imbalances. Published 2001 Wiley-Liss, Inc.

Jumping translocations of 11q in acute myeloid leukemia and 1q in follicular lymphoma

Jumping translocation is a rare cytogenetic aberration in leukemia and lymphoma, and its etiologic mechanisms are not clearly known. We report two cases with jumping translocations. One had follicular lymphoma and jumping translocations of 1q onto the telomeric regions of 5p, 9p, and 15q in three cell lines, co-existing with the specific translocation t(14;18)(q32;q21). The second case had acute myeloid leukemia (AML) and jumping translocations of 11q as the sole aberration, onto multiple derivative chromosomes in each of the abnormal cells. A total of 17 telomeric regions were seen as the recipients of 11q in this case, and 9q was always involved as one of the recipients in all abnormal cells. Fluorescence in situ hybridization (FISH) confirmed the identification of 11q material in the derivative chromosomes. While 1q has been the most common donor of acquired jumping translocations, this is the first report on jumping translocations of 11q. Different from all previously reported jumping translocations which involve only one recipient in each cell line and lead to a mosaic trisomy, multiple recipients in most of the abnormal cells in this case had led to a tetrasomy, or a pentasomy of 11q. The pattern of chromosome involvement as the recipients of 11q appears to show a continuing evolutionary process of jumping, stabilization, and spreading of the donor material into other chromosomes. Somatic recombinations between the interstitial telomeric or subtelomeric sequences of a derivative chromosome and the telomeric sequences of normal chromosomes are believed to be the underlying mechanism of jumping translocations and their clonal evolution.

Jumping translocations involving 11q in a non-Hodgkin lymphoma

This paper presents the results of a cytogenetic analysis in an 11-year-old boy with non-Hodgkin lymphoma. The investigation was performed on slides obtained from short-term culture of lymph node cells. The analyses revealed an abnormal clone with loss of Y, gain of an X chromosome, t(3;22), trisomy 11, and three cytogenetically-related subclones with jumping translocations involving 11q13 as the common breakpoint region. This region is an unusual site of chromosome breakage in jumping translocations, and has not been reported thus far. Contrary to most published reports, the jumping translocation in our patient is associated with long survival.

Jumping translocations involving chromosome 1q in a patient with Crohn disease and acute monocytic leukemia: a review of the literature on jumping translocations in hematological malignancies and Crohn disease

A 36-year-old man with a 10-year history of Crohn disease (CD) presented with gross hematuria and blasts in his peripheral blood. A chromosome analysis revealed one normal cell and 33 abnormal cells. The stem line was 47,XY,+8. The multiple side lines also had a jumping translocation between chromosome 1q31-32 and 4, 8, 10, 17, and 18 terminal regions. A cytogenetic, morphologic, and immunophenotypic analysis of a bone marrow aspirate and biopsy demonstrated acute myeloid leukemia of monocytic lineage, AML-M5b. In this paper are reviewed (a) the unusual and rare phenomenon of jumping translocations in hematological malignancies and (b) leukemia in CD.

Jumping translocations of 3q in acute promyelocytic leukemia

Jumping translocation is a rare phenomenon, seldom reported to occur in cancer. A complex four-way translocation involving chromosomes 3, 9, 15, and 17 was identified in the chromosome study on a patient with a history of an acute promyelocytic leukemia (APL). In the follow-up studies, the same complex rearrangement exhibited a jumping translocation between chromosomes 3 and 9 in one clone and 3 and 6 in another clone. This is the first reported case of jumping translocation in APL.

Jumping Translocations of Chromosome 1q in Multiple Myeloma: Evidence for a Mechanism Involving Decondensation of Pericentromeric Heterochromatin

Karyotypes in multiple myeloma (MM) are complex and exhibit numerous structural and numerical aberrations. The largest subset of structural chromosome anomalies in clinical specimens and cell lines involves aberrations of chromosome 1. Unbalanced translocations and duplications involving all or part of the whole long arm of chromosome 1 presumably occur as secondary aberrations and are associated with tumor progression and advanced disease. Unfortunately, cytogenetic evidence is scarce as to how these unstable whole-arm rearrangements may take place. We report nonrandom, unbalanced whole-arm translocations of 1q in the cytogenetic evolution of patients with aggressive MM. Whole-arm or “jumping translocations” of 1q were found in 36 of 158 successive patients with abnormal karyotypes. Recurring whole-arm translocations of 1q involved chromosomes 5,8,12,14,15,16,17,19,21, and 22. A newly delineated breakpoint present in three patients involved a whole-arm translocation of 1q to band 5q15. Three recurrent translocations of 1q10 to the short arms of different acrocentric chromosomes have also been identified, including three patients with der(15)t(1;15)(q10;p10) and two patients each with der(21)t(1;21)(q10;p13) and der(22)t(1;22) (q10;p10). Whole-arm translocations of 1q10 to telomeric regions of nonacrocentric chromosomes included der(12)t(1;12) (q10;q24.3) and der(19)t(1;19)(q10;q13.4) in three and two patients, respectively. Recurrent whole-arm translocations of 1q to centromeric regions included der(16)t(1;16)(q10;q10) and der(19)t(1;19)(q10;p10). The mechanisms involved in the 1q instability in MM may be associated with highly decondensed pericentromeric heterochromatin, which may permit recombination and formation of unstable translocations of chromosome 1q. The clonal evolution of cells with extra copies of 1q suggests that this aberration directly or indirectly provides a proliferative advantage.

Jumping Translocations of Chromosome 1q in Multiple Myeloma: Evidence for a Mechanism Involving Decondensation of Pericentromeric Heterochromatin

Karyotypes in multiple myeloma (MM) are complex and exhibit numerous structural and numerical aberrations. The largest subset of structural chromosome anomalies in clinical specimens and cell lines involves aberrations of chromosome 1. Unbalanced translocations and duplications involving all or part of the whole long arm of chromosome 1 presumably occur as secondary aberrations and are associated with tumor progression and advanced disease. Unfortunately, cytogenetic evidence is scarce as to how these unstable whole-arm rearrangements may take place. We report nonrandom, unbalanced whole-arm translocations of 1q in the cytogenetic evolution of patients with aggressive MM. Whole-arm or “jumping translocations” of 1q were found in 36 of 158 successive patients with abnormal karyotypes. Recurring whole-arm translocations of 1q involved chromosomes 5,8,12,14,15,16,17,19,21, and 22. A newly delineated breakpoint present in three patients involved a whole-arm translocation of 1q to band 5q15. Three recurrent translocations of 1q10 to the short arms of different acrocentric chromosomes have also been identified, including three patients with der(15)t(1;15)(q10;p10) and two patients each with der(21)t(1;21)(q10;p13) and der(22)t(1;22) (q10;p10). Whole-arm translocations of 1q10 to telomeric regions of nonacrocentric chromosomes included der(12)t(1;12) (q10;q24.3) and der(19)t(1;19)(q10;q13.4) in three and two patients, respectively. Recurrent whole-arm translocations of 1q to centromeric regions included der(16)t(1;16)(q10;q10) and der(19)t(1;19)(q10;p10). The mechanisms involved in the 1q instability in MM may be associated with highly decondensed pericentromeric heterochromatin, which may permit recombination and formation of unstable translocations of chromosome 1q. The clonal evolution of cells with extra copies of 1q suggests that this aberration directly or indirectly provides a proliferative advantage.

Clonal telomeric fusions and chromosome instability in a subcutaneous sacrococcygeal myxopapillary ependymoma

Subcutaneous sacrococcygeal myxopapillary ependymoma (SSME) is a very rare neurologic tumor with no demonstrable connection to the spinal column. Little is known of its etiology, clinical characteristics, or cytogenetics. Giemsa-band analysis revealed a stemline karyotype showing 62 chromosomes. Sidelines within the tumor showed clonal telomeric fusions resulting in dicentric chromosomes involving the fusion of numerous chromosomes. Recurrent telomeric fusions resulted in the progressive deletion of chromosome bands 11q25 and 11q23 and subsequently the entire long arm. This is the first case of a SSME to show clonal cytogenetic aberrations. However, of greater interest is the demonstration of the clonal progression of telomeric fusions resulting in dicentric chromosomes and the subsequent loss of chromosome arms. The observation of clonal telomeric breakage/fusion cycles as progenitor lesions to subsequent deletions provides evidence for telomeric association as an intermediate step in the progression of chromosomal instability.

Differential gene expression in SV40-mediated immortalization of human fibroblasts

Normal human diploid fibroblasts (HF) have a limited life span, undergo senescence, and rarely, if ever, spontaneously immortalize in culture. Introduction of the gene for T antigen encoded by the DNA virus SV40 extends the life span of HF and increases the frequency of immortalization; however, immortalization requires both T-dependent and T-independent functions. We previously generated independent SV40-transformed non-immortal (pre-immortal) HF cell lines from which we then obtained immortal sublines as part of a multifaceted approach to identify functions responsible for immortalization. In this study we undertook a search for cellular mRNAs which are differentially expressed upon immortalization. A lambda cDNA library was prepared from a pre-immortal SV40-transformed HF (HF-C). We screened the library with a subtracted probe enriched for sequences present in HF-C and reduced in immortal AR5 cells. A more limited screen was also employed for sequences overexpressed in AR5 using a different strategy. Alterations in the level of mRNAs in AR5 encoding functions relevant to signal transduction pathways were identified; however, most cDNAs encoded novel sequences. In an effort to clarify which of the altered mRNAs are most relevant to immortalization, we performed Northern analysis with RNA prepared from three paired sets of independent pre-immortal and immortal (4 cell lines) SV40-transformants using eight cloned cDNAs which show reduced expression in AR5. Three of these were reduced in additional immortal cell lines as well; one, J4-4 (unknown function) is reduced in all the immortal cell lines tested; a second, J4-3 (possible PP2C type phosphatase) is reduced in 2 of the 3 matched sets; and a third, J2-2 (unknown function) is reduced in 2 unrelated immortal cell lines. Although the roles of these genes are as yet unclear, their further analysis should extend our understanding of the molecular bases for immortalization. In particular, the patterns of expression of J4-4 and J4-3 strongly suggest that they are involved in the process of immortalization and/or can serve as target genes for assessing regulators of gene expression in this process.

Jumping translocation in a phenotypically normal female

"Jumping translocation" jt refers to a rare type of chromosome mosaic, in which the same portion of a (donor) chromosome is translocated to different (recipient) chromosome sites. Jt have mainly been observed in lymphocyte cultures of patients with hematologic malignancies. We report a phenotypically normal female carrying a mosaic of two cell lines with the Xq26-qter segment translocated to the short arm of chromosomes 15 or 21 in peripheral blood lymphocytes. In skin fibroblasts, only the X/21 translocation was detected. We speculate that recombination between homologous repetitive sequences on non-homologous human acrocentrics may be the cause of such chromosomal rearrangements.

Radiation-induced carcinogenesis: individual sensitivity and genomic instability

In spite of a well-known relationship between exposure to radiation and increased risk for cancer development, the biological mechanisms involved in radiation-induced carcinogenesis remain poorly documented. Various hypotheses are discussed in this paper. It appears that radiation cannot be directly responsible for the numerous genetic alterations of cancer cells. Most of them occur during tumor progression. Only one or a very limited number of them was induced by radiation many years before tumor growth. This long delay is a major difficulty for experimental research and raises many questions. Recently, it has been shown that a genomic instability occurs after many generations in cells descending from irradiated cells. This instability leads to multiple genetic alterations and, preferentially, affects some chromosome structures, particularly telomeres. This kind of telomeric instability - related to the shortening of telomeric DNA sequences - has also been observed in senescent cells as well as in non-senescent cells from patients predisposed to cancer, and this process may possibly also occur in the progeny of irradiated cells.

Centromeric instability of chromosome 1 resulting in multibranched chromosomes, telomeric fusions, and "jumping translocations" of 1q in a human immunodeficiency virus-related non-Hodgkin's lymphoma

BACKGROUND

Acquired immunodeficiency syndrome-related non-Hodgkin's lymphomas are associated with the B-cell chromosomal translocation t(8;14)(q24; q32). The most common secondary chromosome aberrations in these patients involve 1q and are believed to be associated with tumor progression. A mechanism for the origin of these 1q aberrations has not been demonstrated. To their knowledge, the authors report the first human immunodeficiency virus (HIV)-positive patient to have centromeric decondensation and multibranched chromosome aberrations of chromosomes 1 and 16 resulting in telomeric associations and "jumping translocations" of 1q.

METHODS

Tumor cells from peritoneal fluid of an HIV-positive patient were cultured for 24, 48, and 72 hours and analyzed by both conventional G-banding and fluorescence in situ hybridization.

RESULTS

G-band analysis showed a stemline with t(8;14)(q24;q32), but also showed the progression from centromeric decondensation to multibranched chromosome configurations of chromosomes 1 and 16. The interchange and duplications of chromosome arms resulted in the gain of extra copies of 1q material on a number of different chromosomes, but also the loss of 16q in at least one sideline and the formation of micronuclei. Fluorescence in situ hybridization analysis demonstrated that micronuclei predominantly involved chromosome 1 and, to a lesser extent, chromosome 16.

CONCLUSIONS

The cytogenetic findings in this unique case suggest that immunodeficiency may be a factor involved in centromeric instability, multibranching, and the progression to the subsequent formation of telomeric fusions and multiple unbalanced translocations of 1q (jumping translocations). The striking similarity of the centromeric instability in this patient to those with ICF syndrome (variable immunodeficiency, centromeric heterochromatin instability, and facial anomalies) suggests hypomethylation as the etiologic mechanism for the chromosome instability.

Recurrent cytogenetic alterations of prostate carcinoma and amplification of c-myc or epidermal growth factor receptor in subclones of immortalized PNT1 human prostate epithelial cell line

To develop an experimental prostate cancer model, we immortalized normal human prostate adult epithelial cells with SV40 large-T antigen. Two sublines were derived in culture, namely PNT1A and PNT1B. They retained the characteristics of prostate epithelial cells, but did not clone in soft agarose. PNT1A occasionally formed undifferentiated adenocarcinoma tumors in nude mice, but only in the presence of matrigel. PNT1A and PNT1B displayed common cytogenetic alterations: a 10q arm deletion, which is a recurrent alteration in prostate carcinoma, chromosome losses and a translocation involving chromosome 5. An extensive study of oncogenic alterations occurring in these cells showed that PNT1A displayed c-myc gene amplification, forming an hsr on chromosome 4, as well as gene amplification, forming an hsr on chromosome 4, as well as c-myc mRNA overexpression, with a faster doubling time (25 hr); moreover, it seemed less sensitive to EGF than PNT1B. PNT1B had a doubling time identical to that of normal cells (48 hr) but displayed EGF receptor gene amplification accompanied by an increased number of EGF binding sites and sensitivity to EGF. Because both cell lines displayed cytogenetic and oncogenic alterations found in prostate cancer, as well as differing malignant potentials, they represent an interesting model for studying the progression of prostate tumors.

Jumping translocation in a newborn boy with dup(4q) and severe hydrops fetalis

We report on the unusual cytogenetic findings in a newborn boy with severe hydrops fetalis. He has a mosaic for 2 unbalanced chromosome rearrangements: a der(18)-t(4;18)(q31;q23) and a der(18)t(4;18)(q31;p11). As a result, this patient had a duplication of 4q31-qter in all cells, and was possibly monosomic for the distal ends of 18p and 18q, respectively in the 2 cell lines. Since in both rearrangements the same chromosome 4 segment was translocated to 2 different chromosome regions, we consider the present finding as a peculiar type of jumping translocation.

Clonal rearrangements in human irradiated fibroblasts

The cytogenetic dose response following in vivo localized irradiation is difficult to establish because of the occurrence of clones defined by chromosome alterations, with various proliferative rates. The biological meaning of these clones is not well understood. Two sets of experiments were performed to follow their behavior. R-banded karyotypes were established on human fibroblasts irradiated either before or after initiation of the cultures. Clones were observed in cultures developed after irradiation of biopsies, whereas irradiated cultures exhibited karyotypes with multiple non-clonal rearrangements. This difference suggests that most radiation-induced chromosome anomalies do not confer a selective advantage on the carrier cells in vitro. The appearance of clonal anomalies following biopsy irradiation would rather be a consequence of a strong selection at the time of the growth of the cells out of the explants, which would give rise to the progeny of a limited number of progenitor cells.

Senescence of immortal human fibroblasts by the introduction of normal human chromosome 6

In these studies we show that introduction of a normal human chromosome 6 or 6q can suppress the immortal phenotype of simian virus 40-transformed human fibroblasts (SV/HF). Normal human fibroblasts have a limited life span in culture. Immortal clones of SV/HF displayed nonrandom rearrangements in chromosome 6. Single human chromosomes present in mouse/human monochromosomal hybrids were introduced into SV/HF via microcell fusion and maintained by selection for a dominant selectable marker gpt, previously integrated into the human chromosome. Clones of SV/HF cells bearing chromosome 6 displayed limited potential for cell division and morphological characteristics of senescent cells. The loss of chromosome 6 from the suppressed clones correlated with the reappearance of immortal clones. Introduced chromosome 6 in the senescing cells was distinguished from those of parental cells by the analysis for DNA sequences specific for the donor chromosome. Our results further show that suppression of immortal phenotype in SV/HF is specific to chromosome 6. Introduction of individual human chromosomes 2, 8, or 19 did not impart cellular senescence in SV/HF. In addition, introduction of chromosome 6 into human glioblastoma cells did not lead to senescence. Based upon these results we propose that at least one of the genes (SEN6) for cellular senescence in human fibroblasts is present on the long arm of chromosome 6.

Specific chromosome instability induced by heavy ions: a step towards transformation of human fibroblasts?

Cultures of human skin fibroblasts were exposed to heavy ions: neon (E = 10.74 MeV/u) and argon (E = 10.52 MeV/u) at fluences of 10(6), 2 x 10(6) and 4 x 10(6) and lead (E = 9.5 MeV/u) at a fluence of 2 x 10(6) particles/cm2. Cultures were further prolonged for up to 25 passages and karyotyping was performed at various times. Radiation-induced chromosome anomalies progressively decreased, became quite rare at passages 5-7 and increased at later passages. Around passages 20-25, most anomalies occurring were dicentrics, involving telomeric regions of 13p and q arms principally and to a lesser degree those of 1p, 16p and 16q arms. These non-random rearrangements paralleled the appearance of clones with unbalanced karyotypes. In particular, two independent proliferating clones were characterized by a monosomy 13. It is concluded that most chromosome lesions directly induced by heavy ions are hardly compatible with cell survival and thus disappear after a few cell generations. However, surviving cells acquire a de novo chromosome instability leading to the formation of clones with unbalanced karyotypes at late passages.