A fiber-FISH contig spanning the non-recombining region of the human Y chromosome

High Resolution Fiber-Fluorescence In Situ Hybridization

High resolution fiber-Fluorescence in situ hybridization (FISH) is an advanced FISH technology that can effectively bridge the resolution gap between probe hybridizing on DNA molecules and chromosomal regions. Since various types of DNA and chromatin fibers can be generated reflecting different degrees of DNA/chromatin packaging status, fiber-FISH technology has been successfully used in diverse molecular cytogenetic/cytogenomic studies. Following a brief review of this technology, including its major development and increasing applications, typical protocols to generate DNA/chromatin fiber will be described, coupled with rationales, as well as technical tips. These released DNA/chromatin fibers are suitable for an array of cytogenetic/cytogenomic analyses.

Extended Chromatin and DNA Fibers from Active Plant Nuclei for High-resolution FISH

The conventional protocol for isolation of cell wall free nuclei for release of DNA fibers for plants involves mechanical removal of the cell wall and separation of debris by sieve filtration. The mechanical grinding pressure applied during the process leaves only the more tolerant G(1) nuclei intact, and all other states of active nuclei that may be present in the target tissues (e.g., leaf) are simply crushed/disrupted during the isolation process. Here we describe an alternative enzymatic protocol for isolation of nuclei from root tip tissue. Cell wall free nuclei at a given stage of cell cycle, free of any cell debris, could be realized in suspension that are fit for preparation of extended fibers suitable for fiber FISH applications. The protocol utilizes selective harvest of active nuclei from root tip tissue in liquid suspension under the influence of cell wall-degrading enzymes, and provides opportunities to target cell cycle-specific nuclei from interphase through division phase for the release of extended DNA fibers. Availability of cell cycle-specific fibers may have added value in transcriptional analysis, DNA:RNA hybridization, visualization of DNA replication and replication forks, and improved FISH efficiency.

47,X,idic(Y),inv dup(Y): a non-mosaic case of a phenotypically normal boy with two different Y isochromosomes and neocentromere formation

A de novo aberrant karyotype with 47 chromosomes including 2 different-sized markers was identified during prenatal diagnosis. Fluorescence in situ hybridization (FISH) with a Y painting probe tagged both marker chromosomes which were supposed to be isochromosomes of the short and the long arm, respectively. A normal boy was born in time who shows normal physical and mental development. To characterize both Y markers in detail, we postnatally FISH-mapped a panel of Y chromosomal probes including SHOX (PAR1), TSPY, DYZ3 (Y centromere), UTY, XKRY, CDY, RBMY, DAZ, DYZ1 (Yq12 heterochromatin), SYBL1 (PAR2), and the human telomeric sequence (TTAGGG)(n). The smaller Y marker turned out to be an isochromosome containing an inverted duplication of the entire short arm, the original Y centromere, and parts of the proximal long arm, including AZFa. The bigger Y marker was an isochromosome of the rest of the Y long arm. Despite a clearly visible primary constriction within one of the DAPI- and DYZ1-positive heterochromatic regions, hybridization of DYZ3 detected no Y-specific alphoid sequences in that constriction. Because of its stable mitotic distribution, a de novo formation of a neocentromere has to be assumed.

Heterogeneity of pericentric inversions of the human y chromosome

Pericentric inversions of the human Y chromosome (inv(Y)) are the result of breakpoints in Yp and Yq. Whether these breakpoints occur recurrently on specific hotspots or appear at different locations along the repeat structure of the human Y chromosome is an open question. Employing FISH for a better definition and refinement of the inversion breakpoints in 9 cases of inv(Y) chromosomes, with seemingly unvarying metacentric appearance after banding analysis, unequivocally resulted in heterogeneity of the pericentric inversions of the human Y chromosome. While in all 9 inv(Y) cases the inversion breakpoints in the short arm fall in a gene-poor region of X-transposed sequences proximal to PAR1 and SRY in Yp11.2, there are clearly 3 different inversion breakpoints in the long arm. Inv(Y)-types I and II are familial cases showing inversion breakpoints that map in Yq11.23 or in Yq11.223, outside the ampliconic fertility gene cluster of DAZ and CDY in AZFc. Inv(Y)-type III shows an inversion breakpoint in Yq11.223 that splits the DAZ and CDY fertility gene-cluster in AZFc. This inversion type is representative of both familial cases and cases with spermatogenetic impairment. In a further familial case of inv(Y), with almost acrocentric morphology, the breakpoints are within the TSPY and RBMY repeat in Yp and within the heterochromatin in Yq. Therefore, the presence of specific inversion breakpoints leading to impaired fertility in certain inv(Y) cases remains an open question.

Role of the Y-located putative gonadoblastoma gene in human spermatogenesis

The gonadoblastoma locus on the human Y chromosome (GBY) is postulated to serve normal functions in spermatogenesis, but could exert oncogenic properties in predisposing susceptible germ cells to tumorigenesis in incompatible niches such as streaked gonads in XY sex reversed patients or dysfunctional testis in males. The testis-specific protein Y-linked (TSPY) repeat gene has recently been demonstrated to be the putative gene for GBY, based on its location on the GBY critical region, expression patterns in early and late stages of gonadoblastoma and ability to induce gonadoblastoma-like structures in the ovaries of transgenic female mice. Over-expression of TSPY accelerates G(2)/M progression in the cell cycle by enhancing the mitotic cyclin B-CDK1 kinase activities. Currently the normal functions of TSPY in spermatogenesis are uncertain. Expression studies of TSPY, and its X-homologue, TSPX, in normal human testis suggest that TSPY is co-expressed with cyclin B1 in spermatogonia and various stages of spermatocytes while TSPX is principally expressed in Sertoli cells in the human testis. The co-expression pattern of TSPY and cyclin B1 in spermatogonia and spermatocytes suggest respectively that 1) TSPY is important for male spermatogonial cell replication and renewal in the testis; and 2) TSPY could be a catalyst/meiotic factor essential for augmenting the activities of cyclin B-cyclin dependent kinases, important for the differentiation of the spermatocytes in prophase I and in preparation for consecutive rounds of meiotic divisions without an intermediate interphase during spermatogenesis.

High-resolution FISH analysis

Map order, orientation, and gap or overlap distance of closely linked DNA probes may be determined using fluorescent hybridization to decondensed DNA. The linear arrangement of released chromatin fibers not only simplifies the task of gene ordering, but also provides higher resolution with probes separated by greater distances than can be achieved in FISH with intact interphase nuclei. The Basic Protocol 1 of this unit describes an alkaline lysis procedure for generating free chromatin from cultured cells for FISH analysis. A support protocol describes an empirical approach to optimize conditions for preparation of free chromatin. An Alternate Protocol 1 provides a method for producing free chromatin from cultured lymphocytes with drug treatment. The Basic Protocol 2, high-resolution FISH mapping with free chromatin, is a modification of the method used for FISH mapping of interphase nuclei.

Molecular characterization of the bovine chromodomain Y-like genes

The human chromodomain protein, Y-like (CDYL) gene family consists of three members, one on the Y chromosome (CDY) and two on autosomes (CDYL and CDYL2). Studies in the human and mouse showed that genes in the CDYL family are abundantly expressed in testis and play an important role in spermatogenesis. In this study, we have characterized the bovine CDYL (bCDYL) and CDYL2 (bCDYL2) genes. We found that bCDYL and bCDYL2 are very similar to the human orthologues at both mRNA (79% and 85%) and protein (89% and 93%) levels. However, the similarity between the bCDYL and bCDYL2 proteins is low (41%). The bCDYL gene is composed of nine exons, and the bCDYL2 has seven exons. The bCDYL and bCDYL2 genes were mapped by radiation hybrid mapping to bovine chromosomes (BTA) 24 and 18 respectively. The bCDYL gene has four transcript variants that produce four protein isoforms. RT-PCR expression analysis in 12 bovine tissues showed that bCDYL variant 2 was expressed in the testis only, bCDYL variants 1, 3 and 4 were expressed predominantly in the testis and at very low or undetectable levels in the remaining tissues and bCDYL2 was expressed ubiquitously. Examination of bovine testis with in situ hybridization revealed that the bCDYL and bCDYL2 transcripts were found mainly in spermatids, though the amounts of transcripts varied among genes/variants. In addition, antisense transcripts were detected in bCDYL variants 2/3 and 4, as well as in the bCDYL2 gene.

Phenotypic variability in isodicentric Y patients: study of nine cases

Isodicentric chromosomes are the most commonly reported aberrations of the human Y chromosome. As they are unstable during cell division and can generate various types of cell lines, most reported patients are chromosomal mosaics, generally including a 45,X cell line. Phenotypes depend on the location of the breakpoints as well as on the proportion of each cell line and vary from male to abnormal female or individual with ambiguous genitalia. Although phenotypic variability is known to also depend on the degree of mosaicism in the various tissues, gonads are rarely studied. We report nine cases of isodicentric Y chromosomes studied by conventional and molecular cytogenetic: three males, five females, and one individual with sexual ambiguity. Two males had a non-mosaic karyotype, while the third male was a mosaic with a predominant 46,XY cell line. Three of the females had a major 45,X cell line, while the last two females and the patient with ambiguous genitalia had a major 46,X,idic(Y) cell line. Analyses of gonadal tissues from the individual with sexual ambiguity and of three of the five female patients gave results concordant with their phenotype, allowing us to better understand the sexual differentiation of these patients.

New approaches to fluorescence in situ hybridization

Fluorescence in situ hybridization (FISH) is a nonisotopic labeling and detection method that provides a direct way to determine the relative location or copy number of specific DNA sequences in nuclei or chromosomes. With recent advancements, this technique has found increased application in a number of research areas, including cytogenetics, prenatal diagnosis, cancer research and diagnosis, nuclear organization, gene loss and/or amplification, and gene mapping. The availability of different types of probe and the increasing number of FISH techniques has made it a widespread and diversely applied technology. Multicolor karyotyping by multicolor FISH and spectral karyotyping interphase FISH and comparative genomic hybridization allow genetic analysis of previously intractable targets. We present a brief overview of FISH technology and describe in detail methods of probe labeling and detection for different types of tissue sample, including microdissected nuclei from formalin-fixed paraffin-embedded tissue sections.

Cytogenetic mapping and orientation of the rhesus macaque MHC

Applying fluorescence in situ hybridisation (FISH), six cosmid clones of rhesus macaque origin containing the genes SACM2L, RING1, BAT1 and MIC2, MIC3, MICD, and MOG of the major histocompatibility complex (MHC) were localised to the long arm of the rhesus macaque chromosome 6 in 6q24, the orthologous region to human 6p21.3. Furthermore, centromere to telomere orientation of the rhesus macaque MHC as well as the internal order of the MHC genes tested are the same as in human. Fiber-FISH allows a rough estimate of distances between these MHC genes in the rhesus macaque, and, as in the human, the rhesus macaque MHC comprises about 3 to 4 Mb.

Expression pattern of a gonadoblastoma candidate gene suggests a role of the Y chromosome in prostate cancer

The contribution of specific genes on the Y chromosome in the etiology of prostate cancer has been undefined. Genetic mapping studies have identified a gonadoblastoma locus on the human Y chromosome (GBY) that predisposes the dysgenetic gonads of XY sex-reversed patients to tumorigenesis. Recently a candidate gene, the testis-specific protein Y-encoded (TSPY) that resides on the GBY critical region, has been demonstrated to express preferentially in tumor cells in gonadoblastoma and testicular germ cell tumors. TSPY shares high homology to a family of cyclin B binding proteins and has been considered to possibly play a role in cell cycle regulation or cell division. To address the possible involvement of the TSPY gene in prostate cancer, both in situ mRNA hybridization and immunohistochemistry techniques were used to study the expression of this putative GBY gene in prostate specimens. Our results demonstrated that TSPY was expressed at low levels in normal epithelial cells and benign prostatic hyperplasia (BPH), but at elevated levels in tumor cells of prostate cancers at various degrees of malignancy. Sequence analysis of RT-PCR products obtained from both prostatic and testicular tissues using specific primers flanking the open reading frame of the TSPY mRNA revealed a complex pattern of RNA processing of the TSPY transcripts involving cryptic intron splicing and/or intron skipping. The variant transcripts encode a variety of polymorphic isoforms or shortened versions of the TSPY protein, some of which might possess different biochemical and/or functional properties. The abbreviated transcripts were more abundant in prostatic cancer tissues than the testicular ones. Although the exact nature of such variant TSPY transcripts and proteins is still unclear, their differential expression suggests that the TSPY gene may also be involved in the multi-step prostatic oncogenesis besides its putative role in gonadoblastoma and testicular seminoma.