Isodicentric X chromosome in a patient with Turner syndrome--implications for localization of the X-inactivation center

Additional activation of the AR gene may be involved in the development of the castration resistance phenotype in prostate cancer

INTRODUCTION

Several studies have already shown that changes in the AR gene may be associated with a more aggressive disease phenotype and even castration-resistant prostate cancer. Thus, we investigated cytogenetic and molecular alterations linked to AR.

MATERIALS AND METHODS

To evaluate AR methylation, we performed a cytogenetic-molecular analysis using fluorescence in situ hybridization that uses specific probes for the AR gene (Xq11.12) and the X chromosome centromere. For AR activity, we performed a qualitative analysis of human androgen receptor activity. To analyze the expression of AR in PC3 and LNCaP cell lines, we used qPCR assays.

RESULTS

In the qPCR assay, we found downregulation of AR in the PC3 cell line compared with the LNCaP. We found the presence of X chromosome polysomy in PC-3 and LNCaP cell lines by FISH assay. In the HUMARA-Q assay, we found two X chromosomes/cell and the activity of both AR in the PC-3 cell line. In LNCaP cells, we found two X chromosomes/cell and methylation of only one AR.

CONCLUSION

Castration-resistant prostate cancer phenotype represents a significant challenge in the setting of urological management. The X chromosomes and AR-linked alterations may contribute to a better understanding of the disease. However, further studies should be performed in an attempt to elucidate as much as possible the role of AR in the castration-resistant prostate cancer phenotype.

Characterization of chromatin at structurally abnormal inactive X chromosomes reveals potential evidence of a rare hybrid active and inactive isodicentric X chromosome

X chromosome structural abnormalities are relatively common in Turner syndrome patients, in particular X isochromosomes. Reports over the last five decades examining asynchronous DNA replication between the normal X and isochromosome have clearly established that the structurally abnormal chromosome is the inactive X chromosome (Xi). Here the organization of chromatin at a deleted X chromosome, an Xq isochromosome, and two isodicentric chromosomes were examined. Consistent with previous differential staining methods, at interphase, the X isochromosome and isodicentric X chromosomes frequently formed bipartite Barr bodies, observed by fluorescence microscopy using numerous independent bona fide markers of Xi heterochromatin. At metaphase, with the exception of the pseudoautosomal region and the duplicated locus of the macrosatellite DXZ4 (if present on the abnormal X chromosome based on break points), euchromatin markers were absent from the Xi, whereas histone variant macroH2A formed reproducible banded mirror-image chromosomes. Unexpectedly, the isodicentric chromosome in 46,X,idic(X)(q28) cells, which carry a near full-length q-arm-to-q-arm fused chromosome, showed at interphase very rare instances of Xi chromatin bodies that were separated by large distances in the nucleus. Further examination using immunofluorescence and FISH support the possibility that these rare cells may represent ones in which one half of the isodicentric chromosome is active and the other half is inactive.

Three patients with a 45,X/46,X,psu dic(Xp) karyotype

Few cases of isochromosomes for the short arm of the X have been reported and all are dicentric with variable portions of the long arms interposed between the two centromeres. This paper reports three cases of complete short arm duplication of one X chromosome in unrelated female patients. All patients also have a 45,X cell line and present with some characteristic features of Turner syndrome. We used conventional cytogenetics, in situ hybridisation, and molecular genetics to describe all three structurally abnormal chromosomes and the parental origin of two of them. We briefly discuss the "inactivation enhancement" theory; however, any genotype-phenotype correlation is complicated by the presence of the 45,X cell line.

Macrocephaly and chromosome disorders: a case report

We report the case of a young patient with macrocephaly. After excluding the most frequent causes of macrocephaly (hereditary disorders, degenerative, osseous and metabolic diseases, neurocutaneous syndromes and cerebral malformations), the likelihood of a chromosome disorder was investigated, revealing an unbalanced de novo translocation: 46,X,der(X),t(X;7) (q13 or q13.2; q11.23 or q21.11), i.e., a partial trisomy of the long arm of chromosome 7, associated with a partial monosomy of the long arm of chromosome X. Though this chromosome disorder is relatively rare, it should be considered in the differential diagnosis of patients under one year of age presenting with macrocephaly, scoliosis and non-progressive psychomotor retardation.

Prenatal detection of short arm deletion and isochromosome 18 formation investigated by molecular techniques

A patient was referred for amniocentesis because of advanced maternal age and polyhydramnios. The fetal karyotype was a mosaic 46,XX,del(18)(p11.1)/46,XX,-18,+i(18q)de novo. The deletion appeared to encompass the whole short arm as evidenced by G banding and in situ hybridisation. However, telomere sequences were found on both ends of the deleted chromosome as well as the isochromosome. The normal 18 and the isochromosome showed more alphoid sequences than the del(18). Subsequent passages of the cell lines showed an increase in the frequency of the isochromosome from 20% to about 30%. Possible mechanisms are discussed.

Mammalian X-chromosome inactivation and the XIST gene

X-chromosome inactivation is a unique developmental event that results in the cis-limited transcriptional inactivation of most genes on one of the two X chromosomes in female mammals. Studies in both human and mouse have demonstrated that X inactivation requires the presence in cis of a locus, the X-inactivation center, that is thought to be involved in the initiation and/or spreading of the inactivation signal in early development. Identification and characterization of a gene, XIST, which is located at or near the X-inactivation center and which is expressed specifically from the inactive X chromosome in both humans and mouse, suggests that it may be involved in X inactivation.

Physical mapping of 60 DNA markers in the p21.1----q21.3 region of the human X chromosome

Using a panel of human/rodent somatic cell hybrids and human lymphoblast lines segregating 18 different human X-chromosome rearrangements and deletions, we have assigned 60 DNA markers to the physical map of the X chromosome from Xp21.1 to Xq21.3. Data from Southern blot hybridization and polymerase chain reaction (PCR) amplification assign these markers to 15 primary map intervals. This provides a basis for further long-range cloning and mapping of the pericentromeric region of the X chromosome.