Cytogenetic evidence for the absence of an inactivated X chromosome in a human female (XX) breast carcinoma cell line

An extra-genital cell population contributes to urethra closure during mouse penis development

Hypospadias, or incomplete closure of the urethra along the penis, is the second most common birth defect in the United States. We discovered a population of extra-genital mesenchymal cells that are essential for proper penile urethra closure in mouse embryos. This extra-genital population first appeared in the mesenchyme posterior to the hindlimb of the fetus after the onset of penis formation. These extra-genital cells, which transiently express a lineage marker Nr5a1, migrated centrally and colonized the penis bilateral to the urethra epithelium. Removal of the Nr5a1+ extra-genital cells, using a cell-type specific ablation model, resulted in severe hypospadias. The absence of extra-genital cells had the most significant impacts on another mesenchymal cells, the peri-urethra that were immediately adjacent to the Nr5a1+ extra-genital cells. Single cell mRNA sequencing revealed that the extra-genital cells extensively interact with the peri-urethra, particularly through Neuregulin 1, an epidermal Growth Factor (EGF) ligand. Disruption of Neuregulin 1 signaling in the ex-vivo slice culture system led to failure of urethra closure, recapitulating the phenotypes of extra-genital cell ablation. These results demonstrate that the Nr5a1+ extra-genital mesenchymal cells from outside of the fetal penis are indispensable for urethra closure through their interaction with the peri-urethra mesenchymal cells. This discovery provides a new entry point to understand the biology of penis formation and potential causes of hypospadias in humans.

Sex determination efficacy of Papanicolaou and acriflavine Schiff stains in buccal smears

BACKGROUND

Barr body is formed from random inactivation and condensation of one of the two female chromosomes in virtually all the somatic cells of female mammals. Buccal smears have been reported to be potential sources of Barr bodies.

AIM

This study was done to assess the efficacy of acriflavine (AF) Schiff and Papanicolaou (PAP) stains in sex determination by identifying Barr bodies in buccal smears of both sexes.

MATERIALS AND METHODS

Two samples of buccal smears, collected from thirty males and thirty females in the age group of 16-60 years were used to demonstrate Barr bodies using AF Schiff and PAP stains, respectively. Hundred cells were examined for Barr body positive nucleus, and its mean percentage was calculated and statistically analyzed.

RESULTS

In females, AF Schiff stained positive cells ranged from 16% to 53% and PAP stained positive cells ranged from 9% to 38%. In males, 0-9% AF positive Barr bodies and 0-5% PAP stained Barr bodies were identified.

CONCLUSION

Sex determination using buccal smear is a simple and reliable method. AF Schiff stain is better both qualitatively and quantitatively when compared to PAP stain, thus aids in more accurate sex determination.

Potential mechanisms of aberrant DNA hypomethylation on the x chromosome in uterine leiomyomas

We recently found that aberrant DNA hypomethylation is more common on the X chromosome than on other chromosomes in uterine leiomyomas by genome-wide DNA methylation profiling. To investigate the mechanism of aberrant hypomethylation on the X chromosome in uterine leiomyomas, we analyzed methylome and transcriptome data from three cases of leiomyomas and the adjacent myometrium. We found that eleven of the aberrantly hypomethylated genes on the X chromosome were common to the three cases. None of these 11 genes were transcriptionally upregulated in the leiomyoma. However, one of them, TSPYL2, was hypomethylated in 68% of multiple leiomyoma specimens. The incidence of aberrant hypomethylation of TSPYL2 was comparable to that of the MED12 mutation (68%), which is known to be detected at a high frequency in uterine leiomyomas. We also analyzed the aberration of the X chromosome inactivation (XCI) mechanism in uterine leiomyomas. Hypomethylation was not enriched in the imprinted genes, suggesting that dysfunction of polycomb repressive complexes is not involved in the aberrant hypomethylation on the X chromosome. The expression analysis of XCI-related genes revealed that the XIST and SATB1 expression was downregulated in 36% and 46% of 11 leiomyoma specimens, respectively, while the HNRNPU and SMCHD1 expression was not altered. In conclusion, the aberration of XCI-related genes such as SATB1 or XIST may be involved in aberrant hypomethylation on the X chromosome in a certain population of the patients with uterine leiomyomas. TSPYL2 of the aberrantly hypomethylated genes on the X chromosome can be used as a biomarker of uterine leiomyomas.

Multicentric breast cancer: clonality and prognostic studies

Clonality of multicentric breast cancer has traditionally been difficult to assess. We aimed to assess this using analysis of TP53 status (expression and mutation status). These results were then incorporated into an analysis of prognostic factors in multicentric tumours in a 10-year follow up study. Clonal status of multicentric breast cancer foci (n = 88 foci) was determined by immunohistochemical and molecular studies of TP53 in a total of 40 patients. Prognostic factors from these patients were also compared with 80 age- and stage-matched controls with unicentric breast cancer from the Royal Marsden NHS Foundation Trust Breast Cancer Database. Our results indicate that multicentric breast cancer foci were polyclonal within an individual patient in at least 10 patients (25%) with respect to immunohistochemical staining and in four patients (10%) with respect to abnormal band shifts on single strand conformational polymorphism (SSCP) molecular analysis. No individual variable was predictive of multicentric or unicentric disease. However, there was a worse overall survival in the multicentric breast cancer patients in whom at least two cancer foci stained positively on TP53 immunohistochemistry compared with the matched control group (P = 0.04). In conclusion, these results suggest that a proportion of multicentric breast cancer foci are polyclonal with respect to TP53 status and that TP53 over-expression predicts for a poorer prognosis in multicentric breast cancer.

Misbehaviour of XIST RNA in breast cancer cells

A role of X chromosome inactivation process in the development of breast cancer have been suggested. In particular, the relationship between the breast cancer predisposing gene BRCA1 and XIST, the main mediator of X chromosome inactivation, has been intensely investigated, but still remains controversial. We investigated this topic by assessing XIST behaviour in different groups of breast carcinomas and in a panel of breast cancer cell lines both BRCA1 mutant and wild type. In addition, we evaluated the occurrence of broader defects of heterochromatin in relation to BRCA1 status in breast cancer cells. We provide evidence that in breast cancer cells BRCA1 is involved in XIST regulation on the active X chromosome, but not in its localization as previously suggested, and that XIST can be unusually expressed by an active X and can decorate it. This indicates that the detection of XIST cloud in cancer cell is not synonymous of the presence of an inactive X chromosome. Moreover, we show that global heterochromatin defects observed in breast tumor cells are independent of BRCA1 status. Our observations sheds light on a possible previously uncharacterized mechanism of breast carcinogenesis mediated by XIST misbehaviour, particularly in BRCA1-related cancers. Moreover, the significant higher levels of XIST-RNA detected in BRCA1-associated respect to sporadic basal-like cancers, opens the possibility to use XIST expression as a marker to discriminate between the two groups of tumors.

Reactivation of inactive X chromosome in buccal smear of carcinoma of breast

Buccal mucosal smears of 100 female patients of carcinoma of breast were compared with 100 controls matched accordingly. The frequency of Barr bodies was significantly lower in carcinoma of breast patients (menstruating and menopausal women) P < 0.001 when compared with controls indicating reactivation of the inactive X chromosome.

Aberrant expression of X-linked genes RbAp46, Rsk4, and Cldn2 in breast cancer

The consequence of activation status or gain/loss of an X-chromosome in terms of the expression of tumor suppressor genes or oncogenes in breast cancer has not been clearly addressed. In this study, we investigated the activation status of the X-chromosomes in a panel of human breast cancer cell lines, human breast carcinoma, and adjacent mammary tissues and a panel of murine mammary epithelial sublines ranging from low to high invasive potentials. Results show that most human breast cancer cell lines were homozygous, but both benign cell lines were heterozygous for highly polymorphic X-loci (IDS and G6PD). On the other hand, 60% of human breast carcinoma cases were heterozygous for either IDS or G6PD markers. Investigation of the activation status of heterozygous cell lines revealed the presence of only one active X-chromosome, whereas most heterozygous human breast carcinoma cases had two active X-chromosomes. Furthermore, we determined whether or not an additional active X-chromosome affects expression levels of tumor suppressor genes and oncogenes. Reverse transcription-PCR data show high expression of putative tumor suppressor genes Rsk4 and RbAp46 in 47% and 79% of breast carcinoma cases, respectively, whereas Cldn2 was down-regulated in 52% of breast cancer cases compared with normal adjacent tissues. Consistent with mRNA expression, immunostaining for these proteins also showed a similar pattern. In conclusion, our data suggest that high expression of RbAp46 is likely to have a role in the development or progression of human breast cancer. The activation status of the X-chromosome may influence the expression levels of X-linked oncogenes or tumor suppressor genes.

Loss of the Inactive X Chromosome and Replication of the Active X in BRCA1-Defective and Wild-type Breast Cancer Cells

In females, X chromosome inactivation (XCI) begins with the expression of the XIST gene from the X chromosome destined to be inactivated (Xi) and the coating of XIST RNA in cis. It has recently been reported that this process is supported by the product of the BRCA1 tumor suppressor gene and that BRCA1-/- cancers show Xi chromatin structure defects, thus suggesting a role of XCI perturbation in BRCA1-mediated tumorigenesis. Using a combined genetic and epigenetic approach, we verified the occurrence of XCI in BRCA1-/- and BRCA1wt breast cancer cell lines. It was ascertained that the Xi was lost in all cancer cell lines, irrespective of the BRCA1 status and that more than one active X (Xa) was present. In addition, no epigenetic silencing of genes normally subjected to XCI was observed. We also evaluated XIST expression and found that XIST may be occasionally transcribed also from Xa. Moreover, in one of the BRCA1wt cell line the restoring of XIST expression using a histone deacetylase inhibitor, did not lead to XCI. To verify these findings in primary tumors, chromosome X behavior was investigated in a few BRCA1-associated and BRCA1-not associated primary noncultured breast carcinomas and the results mirrored those obtained in cancer cell lines. Our findings indicate that the lack of XCI may be a frequent phenomenon in breast tumorigenesis, which occurs independently of BRCA1 status and XIST expression and is due to the loss of Xi and replication of Xa and not to the reactivation of the native Xi.

Chromosome banding analysis of gynecomastias and breast carcinomas in men

Male breast cancer is 100 times less frequent than its female counterpart and accounts for less than 1% of all cancers in men. Although men with breast cancer also often have gynecomastia, it is still unknown whether gynecomastia per se predisposes the male breast to malignant disease. We describe the cytogenetic analysis of three gynecomastias and four breast cancers in men. No chromosome abnormalities were detected in two cases of gynecomastia, with no other concomitant breast disease. The third gynecomastia sample, taken from a site where a breast carcinoma had previously been removed, had a t(2;11)(p24;p13) as the sole chromosome change; this is the first time that an abnormal karyotype has been described in gynecomastia. All four cancers had clonal chromosome abnormalities. Several cytogenetically unrelated clones were found in the breast tumor and in a metastasis from case 1. In the carcinoma of case 2, a single abnormal clone was found, characterized by loss of the Y chromosome, monosomy 17, and a deletion of the long arm of chromosome 18. In the carcinoma of case 3, a clone with loss of the Y chromosome as the sole change dominated, accompanied by the gain of an X chromosome in a subclone. In the lymph node metastasis examined from case 4, a single clone carrying trisomies for chromosomes 5 and 16 was detected. Our findings, especially when collated with data on the six karyotypically abnormal breast carcinomas in men described previously, indicate that gain of the X chromosome, gain of chromosome 5, loss of the Y chromosome, loss of chromosome 17, and del(18)(q21) are nonrandom abnormalities in male breast carcinomas.

Karyotypic evolution of cells in culture: a new concept

The Chapter summarizes peculiarities of karyotypic variability during establishment and long-term cultivation of permanent cell lines. A new concept on pathways of karyotypic evolution of cells in culture is put forward. A detailed description is presented of the author's original approach of cytogenetic analysis of cell lines provided for a principally new characteristic of the cell line: its generalized reconstructed karyotype (GRK). Its use as a criterion to evaluate authenticity, purity, and stability of cell lines is discussed. Based on analysis of the GRK, two stages of karyotype evolution of cell lines are revealed: establishment and stabilization, different in karyotypic variability of the cell population and in peculiarities of clone selection. Comparison of peculiarities of karyotypic variability of leukemic and tumor cells both in vitro and in vivo was made, and general regularities of their karyotypic evolution have been established, such as nonrandom changes in the number and structure of chromosomes and deletion of one of the sex chromosomes, as well as regularities characteristic only of cells in culture in most human and animal cell lines (at least 85%) of disomy on all autosomes. The rest of the cell lines, 15%, are characterized by either partial or total monosomies on certain autosomes during long-term cultivation. Three main compensatory mechanisms of maintaining viability of cell lines that have lost genetic material are discussed: polyploidization of the initial cell clone, amplification of oncogenes (predominantly of mys family), and extracopying of whole autosomes or of their fragments.

Cytogenetic differences between intestinal and diffuse types of human gastric carcinoma

This study concerns the cytogenetics of 23 gastric carcinomas, classified histologically as intestinal or diffuse types. In carcinomas of the diffuse type, the only numerical changes observed were Y chromosome loss associated with X-chromosome disomy in four of seven male patients. A 46, XX karyotype without recognizable alterations was observed in three of five female patients, and rare structural changes in diffuse carcinomas involved chromosomes 1 and 18. In contrast, intestinal type tumors were exclusively aneuploid, with chromosome modes ranging from 48 to 84. The most consistent change was trisomy 20 in seven of 11 patients, each of which displayed a number of both single and clonal structural aberrations. Frequent structural changes were translocations involving chromosome 13 (including a putative isochromosome 13q in three of 11 patients), and alterations in chromosomes 1, 6 and 12. This study therefore suggests that diffuse and intestinal types of gastric carcinomas do not share a common sequence of genetic changes. The tumor with the worse prognosis (diffuse type) is surprisingly diploid, with uniform X-disomy in both males and females. The clinically less aggressive tumors (intestinal type) show multiple changes, both numerical and structural, of which some are reminiscent of changes seen in tumors of the lower gastrointestinal tract. Cytogenetics may thus be a valuable adjunct in establishing the diagnosis, classification, and prognosis of gastric carcinomas.

Two identical active X chromosomes in human mammary carcinoma cells

Chromosome G-banding analysis of two human mammary carcinoma cell lines, Elco and MCF-7, showed the existence of two X chromosomes in both cell lines. To determine the state of activity of the X chromosomes, a methylation-sensitive restriction endonuclease, HpaII, was used to distinguish the active X from the hypermethylated, inactive X chromosome with a probe for the phosphogalactokinase locus by Southern blot hybridization. DNA digested with the restriction enzymes PstI and BstXI showed a band at either 1.05 or 0.9 kilobases. After HpaII digestion, a 50% reduction in intensity was observed in the female controls, whereas total reduction of the band was observed for the tumor cell lines and the male control. This indicates the absence of an inactive X and the presence of only active X chromosomes in the mammary carcinoma cell lines and the male control. To investigate the mechanisms involved in the alteration of the X chromosome composition and activity, restriction fragment length polymorphism analyses of seven additional X chromosome markers (L1.28, DX13, p52A, pX65H7, L782, pA13.RI, and pXG-12) were performed on the DNA isolated from the tumor cells and controls. Heterozygosity for at least one of the seven markers was detected in the six female controls whereas only homozygosity was detected for each marker in the tumor cell lines and the male control. These results indicate that the two active X chromosomes identified in each of the two tumor cell lines are identical, resulting from duplication or nondisjunction of the active X and loss of the inactive X chromosome.

Mitotic recombination can explain the apparent polyclonal origin of some tumors

Although most human tumors appear to be monoclonal in origin, a few express two G6PD types; on this basis they have been thought to be polyclonal in origin and exceptions to the general rule of monoclonality. In light of the recent discovery that mitotic recombination can cause a shift from genetic heterozygosity to homozygosity in tumor cells, we suggest that such a mechanism can also explain the occasional occurrence of two G6PD types in a monoclonal tumor.

Imbalance of sex chromosomes, with gain of early-replicating X, in human solid tumors

An imbalance of sex chromosomes was observed in several cases of solid tumors: colorectal, anal canal and breast carcinomas. Replication studies, using BUdR incorporation, show that in males there is a tendency towards a gain of early-replicating X and a deficiency of Y chromosomes. In females, there is a tendency towards a gain of early-replicating X and a loss of late-replicating X chromosomes. Although almost no replication studies have been published in the literature, making it impossible to distinguish between late- and early-replicating Xs, it is likely that a similar situation exists for several solid tumors other than those we have studied. A possible consequence of this imbalance is briefly discussed.

X chromatin, endomitoses, and mitotic abnormalities in human cervical cancer

The incidence of X chromatin bodies and mitotic modifications and aberrations has been analyzed using Feulgen-squash preparations in 47 cervical cancers from Helsinki and 35 from Madison. Sixteen of the 82 tumors did not display any X chromatin bodies, and some others showed a lower than normal frequency, especially in the large nuclei. Different hypotheses to explain the absence of Barr bodies in female tumors have been reviewed. A new observation is that 44/82 tumors contained endomitoses. The metaphase/prophase ratio (M/P) was higher than 1.5 in all but three cases, reaching values as high as 23.0 (Madison) and 34.2 (Helsinki), and in one exceptional case, 51.8. The different types of cells, mitotic, endomitotic, and those with large to giant nuclei, form their own strands or layers. Cervical cancer is diagnosed earlier in Finland than in Madison due to a Pap mass screening program, and consequently, the survival of the patients after 5 years was 27/47 in Helsinki and 6/35 in Madison. No correlation could be established between the M/P (or other mitotic phenomena) or the stage and grade of the tumor, the age of the patient, or survival time.

Trisomy X as a possible initial chromosome change in a gastric cancer

Primary and metastatic gastric tumors from a patient previously treated for five different cancers were cytogenetically examined by G-banding. Both types of tumors had cells with a 47,XX, +X karyotype; in addition, the primary tumor had a second clone with a 48,XX, +X, +12 karyotype. No other abnormality was found in either tumor. The lymphocytes of this patient revealed a normal female diploid karyotype.

Mitotic modifications and aberrations in human cervical cancer

Mitotic modifications and aberrations characteristic of human malignant tumors have been analyzed and illustrated in cervical cancer. Most of them can be explained by assuming that the coordination of the centrosomal and chromosomal mechanisms, typical of normal mitosis, is disturbed. When the spindle mechanism is ahead of the chromosomes, the prophase is relatively shortened. This expresses itself in an increase of the ratio of metaphases to prophases (M/P), which in normal tissues is around 1. With M/P values of 4-6, the first tripolar metaphases are formed, and with higher ratios, divisions having more and more poles appear. The spindle and the chromosomes are out of step in the opposite direction in endocycles, in which the spindle is slowed down or absent. The most common of the endocycles is endoreduplication, followed by endomitosis, which is found in more than half of the cervical cancers. Mitotic abnormalities include lagging chromosomes in metaphase and anaphase and bridges in anaphase, which, when numerous, may lead to restitution. More sporadically occurring are C-mitosis and other abnormalities, including cell and nuclear fusions. There is a wide range of variation in the occurrence and frequency of chromocenters within a tumor, and an even greater variation between tumors. About one-fifth of cervical cancers lack X chromatin bodies. The abnormal chromosome constitutions in cancer are the result of various mitotic modifications and aberrations, as well as chromosome rearrangements. New chromosome combinations are constantly created and selection promotes the fastest dividing ones, which, in turn, become new stem lines of the tumor.

The structure and origin of giant nuclei in human cancer cells

The structure and origin of giant nuclei in human cancer cells were studied in two cases of squamous cell carcinoma of the cervix. Feulgen-squash preparations of untreated biopsies showed the following types of nuclei: fairly evenly stained nuclei, nuclei with distinct chromocenters from which individual chromosomes sometimes seemed to radiate, and nuclei with banded structures which we tentatively interpret as some type of "polytene" chromosomes possibly showing prophase chromomeres. In neither tumor did either the small or large nuclei display any X chromatin bodies. The main processes giving rise to the different types of nuclei are endoreduplication, true endomitosis, and a kind of polytenization. The multichromosome chromocenters that fell apart possibly represent polytene chromosomes separating into individual chromosomes.

Specific terminal DNA replication sequence of X chromosomes in different tissues of a live-born triploid infant

Using the thymidine pulse method, DNA replication kinetics were studied on cells derived from cartilage, gonad, lymphocytes, and skin of a live-born triploid (69,XXY) infant with typical clinical findings. Replication studies showed that 3% of the lymphocytes had one early and one late replicating X, and 97% of the lymphocytes, and cartilage, gonad, and skin cells had two early replicating X's. Asynchronous DNA replication between the two early replicating X's was observed in all tissues (range 25-40%). The predominant terminal replication sequence of X chromosomes from chondrocytes, gonad, and skin fibroblast differed from that of the lymphocytes. Thus, a tissue-specific DNA replication pattern of the early-replicating X chromosome may be present. In every tissue, the last band to complete DNA replication was Xq21. Polymorphisms of metaphase chromosomes of parents and the patient were studied by Q-banding. The possible origin of the extra haploid set of chromosomes is discussed.

Chromosomal replication asynchrony of a human breast carcinoma cell line. I. studied by continuous BrdU incorporation and G-banding analysis

Continuous BrdU incorporation and the Giemsa staining technique were used to study the cell cycle kinetics of a human breast tumor cell line. It was found that the interchromosomal replication pattern of the neoplastic cell was significantly different from that of normal cells in two respects. First, the pattern is highly asynchronous; within a single cell there are chromosomes at different replication cycles; that is, some chromosomes complete their DNA replication before others begin. Second, the replication schedule for the chromosomes, as identified by superimposing the BrdU-Giemsa technique on the trypsin G-banding technique, is relatively consistent within the cell line but differs from that of normal cells. Some chromosomes that replicate late in normal human lymphocytes and fibroblasts replicate early in this cell line. In contrast to the unusual interchromosomal replication pattern, gross analysis of the intrachromosomal replication schedule shows no apparent difference from that reported for normal cells. The asynchrony phenomenon reported here may be associated with the etiology of aneuploidy in neoplasia.

Probable mechanism for the loss of Barr body in human female tumor with special reference to breast cancer

One of the X-chromosomes by a random inactivation process condenses to form X-chromatin (Barr body) in early embryonic life. Once this occurs, it is final and fixed for that cell and all its descendants (1,2). However, numerous investigators have observed extreme variations in Barr body frequency in tumour cells. For example, Sohval and Gains (3) reported an absence of the characteristic Barr body pattern of 19 of the 27 teratomas from females and Moore and Barr (4) observed significant variation in Barr body counts in breast cancer cells. Furthermore, a good correlation was made between the frequency of Barr body and prognosis (5,6,7,8,9). From a retrospective study, it was shown that tumours with low Barr body frequency (BBF) had a significant correlation with blood vessel invasion (BVI) and poor prognosis (10). But the reason why patients with low BBF in the tumor with BVI get early recurrence is not known. In this paper an attempt has been made to suggest a mechanism which may be involved in reducing the BBF with high malignant potentiality.