Homogeneously Staining Regions Research Articles

Zoogeography of the chromosome 1 HSR in natural populations of the house mouse (Mus musculus).

A polymorphism of the central part of chromosome 1 has been described from natural populations of the house mouse (Mus musculus). The region shows up as a C band-positive homogeneously staining region (HSR) under the light microscope. M. m. domesticus mice carry single band HSRs, whereas M. m. musculus animals have double band HSRs. HSR size variations have been described in both subspecies. The frequency of the HSR chromosome 1 in populations varies from 4% to 81%, but none of the large samples examined consisted only of homozygotes. In the subspecies M. m. domesticus, HSRs were found in North Africa and Western Europe, mainly in the hilly regions of Southern Germany and Switzerland. Localities with double HSRs are distributed all over the area of M. m. musculus. Based on the population data presented and DNA similarity of different HSRs, the origin and distribution of HSR chromosomes in the house mouse are discussed.

Colcemid resistance in murine SEWA cells: non-Pgy gene amplification at low levels of resistance and preferential Pgy2 gene amplification at high levels of resistance.

Mammalian cell lines often become multidrug-resistant to cytotoxic drugs by amplification and/or overexpression of the P-glycoprotein (Pgy) genes. However, several malignant cell lines seem to acquire low levels of drug resistance by non-P-glycoprotein mediated mechanisms. We report here on cytogenetical signs of non-Pgy gene amplification in murine SEWA cells during the early steps of selection in Colcemid (COL). In line TC13COL0.01, rare cells exhibited a homogeneously staining region (HSR) distally in chromosome 16. As the COL-concentration was raised the HSR-chromosome was retained and, in addition, the cells developed numerous double minutes (DMs). The DMs, but not the HSR, contained amplified Pgy genes. The HSR may correspond to amplified heat shock protein 70 (Hsp70) genes, detected by Southern analysis. A second low-level COL-resistant line, TC13D70.01, contained DMs but showed no amplification of Pgy, Hsp70, Hsp90, alpha- or beta-tubulin genes. In higher COL-concentration, P-glycoprotein mediated drug resistance was induced. In contrast to actinomycin D-resistant SEWA cells, in which higher amplification levels of Pgy1 than of Pgy2 are regularly present, the COL-resistant lines showed a preference for Pgy2 gene amplification. These results are in line with the suggestion that the murine Pgy1 and Pgy2 genes have overlapping but distinct drug specificities.

Sequential cytogenetic and molecular cytogenetic characterization of an SV40T-immortalized nasopharyngeal cell line transformed by Epstein-Barr virus latent membrane protein-1 gene

Cytogenetic and molecular cytogenetic analyses were performed on four sublines derived from a newly established, SV40T-immortalized nasopharyngeal (NP) cell line, NP69, with two of the sublines expressing LMP1, an Epstein-Barr virus–encoded gene. A total of seven cytogenetically related subclones were identified, all having highly complex karyotypes with massive numerical and structural rearrangements. Centromeric rearrangements in the form of isochromosomes and whole-arm translocations were prevalent. A cytogenetic sign of gene amplification [i.e., homogeneously staining region (HSR)] was detected at 1q25 in all metaphase cells analyzed. Multicolor combined binary ratio labeling fluorescence in situ hybridization (COBRA-FISH) was used to confirm the karyotypic interpretations. Furthermore, multicolor COBRA-FISH also showed that part of the HSR contained chromosome 20 material. Extensive clonal evolution could be observed by the assessment of karyotypic variation among different subclones and individual metaphase cells. The evaluation of clonal evolution enabled the identification of the temporal order of chromosome aberrations during cell immortalization and malignant transformation. A striking karyotypic similarity was found between sublines expressing LMP1 and an NP carcinoma cell line, with loss of genetic material from chromosome arm 3p being an important recurrent observation. More interestingly, the karyotypic features of NP69 were also similar to those of many epithelial malignancies. Our observations suggest that serial transformation of NP cell lines might provide a useful in vitro model for the study of the multistep neoplastic transformation of NP cells.

P9 Proband-mediated information dissemination does not meet the expressed wishes in families with a BRCA1/2 gene mutation

Ribosomal RNA gene amplification has been demonstrated in the rat XC sarcoma cell line. Cells of this rat line have a fairly stable karyotype with several unusual features, which have been clarified by in situ hybridization, silver staining, and binding of antibodies to 5-methylcytosine. There are one or two tiny acrocentric chromosomes containing transcriptionally active 18S and 28S ribosomal RNA (rRNA) genes. The short arm of one chromosome No. 12 has been replaced by a GC-rich, C-band negative, differentially staining region (DSR) containing an increased number of rRNA genes; most of these are transcriptionally inactive and located in regions containing highly methylated DNA. The short arm of a small chromosome, probably a No. 20, has been replaced by a GC-rich, C-band negative, homogeneously staining region (HSR) that presumably represents amplification of a DNA sequence other than the 18S and 28S rRNA coding sequences. The DNA in this HSR is not enriched in 5-methylcytosine and neither is that in the HSRs of methotrexate-resistant Syrian hamster cells.

Cytogenetic and fluorescence in situ hybridization characterization of clonal chromosomal aberrations and CCND1 amplification in esophageal carcinomas

Cytogenetic analyses of four squamous cell carcinomas (SCC) of the esophagus showed complex numerical and structural abnormalities. Chromosomal bands or regions preferentially involved were 11q13, 8q10, 21q10, 3p10∼p11, 1p11∼q11, 5p11∼q11, and 14p11∼q11. For the first time, to our knowledge, recurrent aberrations were identified in esophageal SCC, including homogenous staining region (hsr), isochromosomes i(3q) and i(21q), and ring chromosome. Losses of chromosomal material dominated over gains. Recurrent imbalances included under-representation of 4p13∼pter, 5q14∼qter, 9p22∼pter, 10p, 11p13∼pter, 12p13∼pter, 17p10∼pter, 18p11∼pter, 21p, and 22p, as well as over-representation of 1q25∼qter, 3q, 7q, and 8q. Interestingly, hsr at different chromosomal regions occurred in three of four cases. With the application of fluorescence in situ hybridization (FISH) and multicolor combined binary ratio labeling–FISH with specific DNA probes, it could be shown that in two cases the hsr was derived from chromosome 11 material and that the amplicon included CCND1. Our results, together with previous molecular genetic findings, indicate that CCND1might be a prime target in 11q13 amplification, and that amplification of this gene might be crucial in the tumorigenesis of esophageal SCC. These observed chromosomal aberrations and imbalances thus provide important information for further molecular genetic investigation of esophageal SCC.

CA125 and UQCRFS1 FISH studies of ovarian carcinoma

Objective With the gene CA125 having recently been cloned, we chose to investigate the gene copy number of various ovarian cancer samples by FISH. As a control we chose BACs close to the chromosome 19 centromere. One of these BACs carries the gene UQCRFS1. Methods We developed FISH probes for CA125 and the UQCRFS1 region. We studied 22 touch preparations and 14 paraffin-embedded samples of ovarian carcinomas with known CA125 serum levels, two ovarian cancer cell lines, and one ascites sample from an ovarian cancer patient. The average copy number per cell of both probes was calculated. Metaphase analyses were done on cell lines and ascites cells to localize the signals. Results The CA125 gene mapped to 19p13.2. Three of 22 (13.6%) touch preparations and 1 of 14 (7.1%) paraffin samples had amplified levels of CA125. The cell lines and ascites sample did not have amplified CA125. Unexpectedly, 3 of 22 (13.6%) touch preparations, 1 of 14 (7.1%) paraffin samples, one cell line, and the ascites sample had amplification of the UQCRFS1 region. The amplification of the UQCRFS1 region occurred in the form of homogeneously staining regions (HSRs). Only one sample had coamplification of CA125 and UQCRFS1. Conclusion CA125 was only sometimes modestly amplified in ovarian carcinoma, even when the serum CA125 level was highly elevated. Unexpectedly, the UQCRFS1 region was also sometimes amplified as HSRs. The UQCRFS1 protein is also known as complex III of the mitochondrial respiratory chain. This product may have an important role in malignant cells.

Chromosome 2 (2p16) abnormalities in Carney complex tumours

Carney complex (CNC) is an autosomal dominant multiple endocrine neoplasia and lentiginosis syndrome characterised by spotty skin pigmentation, cardiac, skin, and breast myxomas, and a variety of endocrine and other...

Cytogenetics and cytology of retinoblastomas.

Chromosomal aberrations and the nuclear topography of retinoblastoma tumour cells as well as lymphocytes of patients suffering from the familiar or sporadic form of retinoblastoma were studied. Fluorescence in situ hybridisation (FISH) on fresh, paraffin-embedded tumour tissues and on peripheral blood leukocytes was used for cytogenetic analysis. The cell cycle profile and induction of apoptosis was studied by flow cytometry and gene expression changes were detected by RT-PCR. Using the repeated FISH technique, the average distances between the nuclear membrane and the fluorescence gravity centre (FGC) of seven selected chromosomes were determined in the same tumour population and three other cell types. Chromosome order in positioning from the nuclear membrane was similar in all cell populations investigated. Our experimental studies were focused on specific genetic loci relevant for retinoblastoma tumour pathogenesis. We revealed a certain heterogeneity in the copy number of the Rb1, N-myc, and TP53 gene loci in tumour cells. In addition, in lymphocytes isolated from peripheral blood of the patients, a high degree of copy number heterogeneity was also detected. In 60% of analysed retinoblastomas we observed numerical aberration involving the centromeric region of chromosome 6. In these tumours, apoptotic bodies were found irrespective of clinical therapy. Chromosome instability seems to be a typical feature of primary retinoblastomas as well as of the human pseudodiploid cell line Y79. These cells, of a hereditary form of retinoblastoma (Y79), were irradiated by gamma rays and exposed to anti-tumour drugs such as etoposide, vincristine, and cisplatin. These treatments induced apoptosis, changes in the cell cycle profile, and specific modifications in the nuclear topography of selected loci. Treatment with a non-lethal concentration of hydroxyurea was shown to induce the loss of the amplified N-myc gene involved in the homogenously staining region (HSR) that was found to be associated with the nuclear membrane of retinoblastoma Y79 cells. We assume that not only cytological and cytogenetic parameters but also aberrant chromatin structures and their nuclear topography can be useful tools for optimal tumour marker specification.

Autoimmune regulator: from loss of function to autoimmunity.

The autoimmune regulator (AIRE) is a gene where mutations cause the recessively inherited disorder called autoimmune polyendocrinopathy-candidiasis-ectodermal dystrophy (APECED) or autoimmune polyendocrinopathy syndrome type 1 (APS1). Variable combinations of autoimmune endocrine diseases such as Addison's disease, hypoparathyroidism, and type 1 diabetes characterize APECED. The AIRE protein has several domains indicative of a transcriptional regulator. AIRE contains two PHD (plant homeodomain) type zinc fingers, four nuclear receptor binding LXXLL motifs, a putative DNA-binding domain named SAND and, in addition, a highly conserved N-terminal domain similar to the homogenously staining region domain of the Sp100 protein. At the subcellular level, AIRE is expressed in nuclear dots resembling promyelocytic leukemia nuclear bodies, which are associated with several transcriptionally active proteins. AIRE is primarily expressed in thymic medullary epithelial cells and monocyte-dendritic cells in the thymus but also in a rare subset of cells in the lymph nodes, spleen and fetal liver. The disease, caused by mutations in AIRE, its function as a protein involved in transcription, and its restricted expression in cells important in negative selection, all together suggest that AIRE is a central protein in the maintenance of immune tolerance. In this review of the recent literature we discuss the results of these studies with particular attention on the AIRE expression pattern and its function as a transcriptional regulator, as well as the effects of patient mutations on the molecular characteristics of the protein.

Systematic mutagenesis of the functional domains of AIRE reveals their role in intracellular targeting.

Mutations in the human autoimmune regulator (AIRE ) gene cause a multi-systemic autoimmune syndrome that is known as autoimmune polyendocrinopathy-candidiasis-ectodermal dystrophy (APECED). To date more than 39 different disease mutations have been identified. They span the entire region of the AIRE gene that encodes a polypeptide with multiple functional domains: an N-terminal homogeneously staining region (HSR), a bipartied nuclear localization signal (NLS), a SAND domain, two PHD fingers and four nuclear receptor targeting motifs. The APECED mutations include insertions, deletions, substitutions and introduction of premature termination codons, while most mutations disrupt one of the functional domains. We have constructed a series of deletion mutants systematically removing one or more functional domain(s) and investigated the stability and sub-cellular compartmentalization of the corresponding polypeptides. Here we show that the first 188 amino acids, containing the HSR domain and the NLS proved necessary for both cytoplasmic filament formation and nuclear targeting. Deletion of the SAND domain and even point mutations in the SAND domain, resulted in the aggregation of the polypeptides in the cytoplasm and interfered with the proper nuclear targeting. The PHD fingers seemed to be necessary for the formation of characteristic dot-like complexes in the nucleus, but their deletion did not interfere with nuclear entry.

Chromosome instability in human lung cancers: possible underlying mechanisms and potential consequences in the pathogenesis.

Chromosomal abnormality is one of the hallmarks of neoplastic cells, and the persistent presence of chromosome instability (CIN) has been demonstrated in human cancers, including lung cancer. Recent progress in molecular and cellular biology as well as cytogenetics has shed light on the underlying mechanisms and the biological and clinical significance of chromosome abnormalities and the CIN phenotype. Chromosome abnormalities can be classified broadly into numerical (i.e., aneuploidy) and structural alterations (e.g., deletion, translocation, homogenously staining region (HSR), double minutes (DMs)). However, both alterations usually occur in the same cells, suggesting some overlap in their underlying mechanisms. Missegregation of chromosomes may result from various causes, including defects of mitotic spindle checkpoint, abnormal centrosome formation and failure of cytokinesis, while structural alterations of chromosomes may be caused especially by failure in the repair of DNA double-strand breaks (DSBs) due to the impairment of DNA damage checkpoints and/or DSB repair systems. Recent studies also suggest that telomere erosion may be involved. The consequential acquisition of the CIN phenotype would give lung cancer cells an excellent opportunity to efficiently alter their characteristics so as to be more malignant and suitable to their microenvironment, thereby gaining a selective growth advantage.

Isodicentric/pseudoisodicentric chromosome 21 amplification in four cases of acute myelocytic leukemia or myelodysplasia

The bone marrow karyotypes of three patients with acute myelocytic leukemia (AML) or myelodysplastic syndrome (MDS) were studied at diagnosis and revealed, multiple copies of the same chromosomal anomaly, considered as psu idic(21)(q22) associated with other rearrangement(s). The karyotype of a fourth patient with MDS in transformation showed one copy of a dicentric marker presumably derived from a similar psu idic(21) by (tandem?) interstitial amplification of part of its structure, resembling a “homogeneous staining region”, and described as der(21)psu idic(21)(q22)hsr(21)(q22). This rearrangement, previously described in isolated cases only, might be considered as recurrent in AML/MDS and associated with an unfavorable prognosis. It is most probably a secondary change, because it was never observed as sole abnormality and the main association, as for trisomy 21, was with del(5q). In the four cases, the number of partial supernumerary segmental 21pter→21q22 copies, ranged from 2 to 10. The AML1 gene did not appear to be the common target of this amplification because this locus had been lost by the psu idic(21) in one patient

Novel targets for the 18p11.3 amplification frequently observed in esophageal squamous cell carcinomas.

Amplification of DNA in certain chromosomal regions, with consequent over-expression of specific genes within these amplicons, plays a crucial role in the development and progression of human cancer. Since our previous comparative genomic hybridization (CGH) study revealed frequent amplifications at 18p in esophageal squamous cell carcinomas (ESC) cell lines, we focused on the identification of genetic target(s) within the 18p amplicon. In four cell lines having remarkable copy-number amplification with homogeneously staining region (HSR) pattern by fluorescence in situ hybridization (FISH), the smallest common region of overlapping covered approximately 3.5 Mb at 18p11.3. We screened 29 ESC cell lines to discern amplifications and expression levels of 14 known genes and 21 uncharacterized transcripts within the amplicon. Only four known genes, YES1, TYMS, HEC and TGIF showed amplification and consequent over-expression. These genes were amplified in several of primary ESCs. Moreover, resistance to transforming growth factor beta (TGFbeta)-induced growth inhibition was enhanced in four cell lines with amplification and expression of TGIF, which encodes the repressor for TGFbeta-activated transcription, appears to be involved in the progression of ESC. Taken together, these results suggest that YES1, TYMS, HEC and TGIF are likely to be candidate targets for 18p11.3 amplification and be associated with esophageal tumorigenesis.

Loss of Irreversibility of Granulocytic Differentiation Induced by Dimethyl Sulfoxide in HL-60 Sublines with a Homogeneously Staining Region

The human HL-60 acute leukemia cell line harbors double minutes (dmins) during early passages. During its continuous culture for a long term, a single marker chromosome with a homogeneously staining region (HSR) replaces the dmins. The both structures harbor amplified c-MYC sequences. Here we ask how the cellular phenotype is altered by the c-MYC integration into a HSR. Treatment with dimethyl sulfoxide induces granulocytic differentiation in the both types of cells. In contrast to HL-60/dmin cells, however, no apoptosis followed differentiation and the differentiation phenotype was reverted upon withdrawal of the drug in HL-60/HSR cells. Terminal differentiation and loss of DNase I hypersensitivity sites at c-MYC P2 promoter appeared to be unlinked in the both types of cells. By comparison with HL-60/dmin cells, we conclude that the integration into a HSR of an extrachromosomal gene(s) but not c-MYC likely leads to the loss of irreversibility of the differentiation phenotype.

Replication Timing of Amplified Genetic Regions Relates to Intranuclear Localization but Not to Genetic Activity or G/R Band

Amplified genes in many human cancer cells usually localize at the extrachromosomal double minutes (DMs). In the present study, we show that multiple DMs in the human colorectal tumor COLO 320DM line replicated semisynchronously during the early S phase. On the other hand, during longer passage of the cells with DMs, cells with the amplified genes at the chromosomal homogeneously staining region (HSR) generally dominate the population. We currently report that HSR was composed of a tandem array of DM-derived sequences, which was shown using a unique DM-painting probe. Nevertheless, we found that HSR was replicated much later during the S phase, unless the amplified c-myc genes were expressed almost equally from DMs and HSR. Therefore, this provided a novel instance in which the cytogenetic localization affected replication timing without alteration of expression. Furthermore, we unexpectedly found that HSR had a distinctive band structure with respect to replication timing. The replication band structure was usually associated with the chromosomal G/R bands; however, HSR was homogeneous in the G/R band and in the distribution of highly repetitive sequences. We discuss the mechanism by which the replication band may arise, in relation to the folding of chromatin inside the nucleus.

DNA amplification associated with double minutes originating from chromosome 19 in mouse hepatocellular carcinoma

DNA amplification is associated with genomic instability, the main characteristic of cancer cells, and it frequently involves protooncogenes. Double minute chromosomes (DM) and homogeneously stained regions (HSR) are cytological manifestations of DNA amplification. Gain of chromosome 19 is a recurrent alteration in mouse hepatocellular carcinoma (HCC). In one tumor cell line established from HCC developed in myc transgenic mice, DM derived from chromosome 19 were identified by spectral karyotyping and confirmed by fluorescence in situ hybridization (FISH). A probe generated by PCR from microdissected DM was localized by FISH on normal and HCC-derived cell lines on DM and chromosome 19 at two sites separated by several medium size G-bands. This organization of DM containing amplified sequences from separate loci of the same chromosome, indicates a complex mechanism of DNA amplification, possibly involving more than one gene. DM or HSR were not previously identified in mouse HCC and adult human HCC. The recognition of these loci could lead to the cloning of new genes or identification of known genes important in development or progression of HCC.

Human ribonucleotide reductase M2 subunit gene amplification and transcriptional regulation in a homogeneous staining chromosome region responsible for the mechanism of drug resistance

In our previous publication it was shown that a Gemcitabine-resistant KBGem clone derived from step-wise exposure to Gemcitabine resulted in overexpression of the human Ribonucleotide Reductase M2 subunit (hRRM2) mRNA and protein (Goan et al., 1999). In this study we confirm these results and show that the hRRM2 gene amplification arises in a homogeneous staining region (hsr) derived from chromosome translocation. The hydroxyurea-resistant clone (KBHURs) was studied as a comparison. PCR analysis of the hRRM2 gene promoter confirmed the amplification. Northern and Western blots were further employed to confirm the gene amplification and hRRM2 mRNA and protein expression were compatible with the level of drug resistance. Cells synchronized by serum starvation and then returned to serum-containing growth conditions showed a rapid induction of high levels of transcription of the hRRM2 gene. To clarify whether expression of hRRM2 mRNA was regulated at a transcriptional level, several transcription factors, including AP-1, Sp1, AP-2, CREB, NF-ĸB, and OCT1, were examined by gel-shift assay. Interestingly, the KBGem clone was regulated by different transcription factors than the KBHURs clone. Compared to the wild-type KB cells (KBwt), the KBGem clone exhibited a different binding pattern for Sp1 and NF-ĸB. The KBHURs clone, however, demonstrated a unique binding pattern with AP-1 and CREB, different from the KBwt control as well as the KBGem clone. Therefore, we conclude that the drug-resistant phenotype is associated with human RRM2 gene amplification from a homogeneous staining chromosome region and altered transcription regulation. Each clone demonstrated a unique pattern of transcription factor binding that may play a vital role in the mechanism of drug resistance.

Oncogene Amplification Detection by Fluorescence In Situ Hybridization (FISH).

Fluorescence in situ hybridization (FISH) represents the newest methodological approach for testing for genetic alterations in individual cells. FISH can detect gene amplification both in metaphase chromosomes and in interphase nuclei. FISH allows the determination of the amplification levels and amplification patterns: clustered signals and multiple scattered signals found by FISH correspond respectively to amplicons in homogeneous staining regions and in double-minute chromosomes found in conventional cytogenetics. Using dual-colour FISH, differentiation of low level amplification from increased gene number by polysomy is also possible. FISH can detect gene amplification not only in isolated nuclei and imprinted cells, but also in formalin-fixed paraffin-embedded tissues, and is therefore a potent tool to detect gene amplification in archival solid tumor specimens. A direct correlation can be made with the morphology, so that tissue localization of such genetic events as tumor heterogeneity and tumor progression is feasible. Furthermore, in combination with immunohistochemistry, direct correlation with the oncogene amplification and the oncoprotein overexpression are possible. Although there have been numerous FISH studies examining oncogene amplifications using clinical materials, at the present time the most important clinical application of FISH is the identification of breast cancer patients eligible for the new adjuvant therapy by humanized monoclonal antibody to c-erbB-2 protein (trastuzumab).

Coamplification of 3-hydroxy-3-methylglutaryl coenzyme A reductase genes in methotrexate-resistant human leukemia cell lines.

Methotrexate (MTX)-resistant K562 human myelocytic leukemia sublines with 20- and 200-fold amplified dihydrofolate reductase (DHFR) genes localized to homogeneously staining regions (HSRs) on the long arms of chromosomes 5, 6, and 19 were used to examine whether other genes mapping close to the DHFR genes were coamplified. The gene for 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase, located on chromosome 5q13.3-14, was coamplified 4-14-fold, corresponding to the levels of resistance exhibited by these cells. Similar observations were made with a MTX-resistant subline of the promyelocytic leukemia cell line, HL-60R, with 200 gene copies of DHFR. These observations indicate a tight linkage of DHFR and HMG-CoA genes on chromosome 5q.

Genetic abnormalities detected by comparative genomic hybridization in a human endometriosis-derived cell line.

Comparative genomic hybridization (CGH) was used in parallel with fluorescence in-situ hybridization (FISH) and conventional karyotyping to perform a genome-wide survey of DNA gains and losses in the endometriosis-derived permanent cell line, FbEM-1. The cytogenetic analysis showed a complex karyotype with numerical changes and multiple chromosome aberrations, including the der(1) complement marker exhibiting a large homogenous staining region (HSR). The chromosomal rearrangement interpreted as der(5) t(5;6)(q34;p11) was found in the majority of the metaphases indicating a clonal abnormality. Repeated CGH experiments demonstrated over-representation of chromosomes 1, 2, 3, 5, 6p, 7, 16, 17q, 20, 21q and 22q, while chromosomes 6q, 9, 11p, 12, 13q, 18 and X were under-represented. Using DNA from the original endometriotic tissues, including a peritoneal implant and ovarian endometrioma, CGH analysis revealed loss of DNA copy number on 1p, 22q and chromosome X, while gain was found on chromosomal arms 6p and 17q. FISH analysis confirmed that the gain at 17q includes amplification of the proto-oncogene HER-2/neu in 16% of the FbEM-1 nuclei and in 12% of cells from the primary ovarian endometrioma tissue. These findings demonstrate that FbEM-1 cells share certain molecular cytogenetic features with the original tissue and suggest that chromosomal instability is important in the development of endometriosis.