A mitotically unstable human dicentric Y chromosome in a male pseudohermaphrodite

A patient with a mitotically unstable dic(Y)(p11) chromosome is reported. Physical examination revealed a small penis with severe hypospadia, undescended testes, rudimetary vagina, uterus, left fallopian tube, and no stigmata of Turner syndrome. Longitudinal chromosome studies over a four-year period, including blood, skin, foreskin, and testicular tissue, revealed 45,X/46,X,dic(Y)(p11)/46,X,del(dic Y) mosaicism. The proportions of these cells varied in the different tissues, and only 45,X and 46,X,del(dic Y) were major cell lines in testicular tissue. Additional minor cell lines were present mainly in peripheral blood: 47,X,dicY,dicY; 47,X,dicY,del(dicY); and 47,X,del(dicY),del(DICY). Premature disjunction of one of the centromeres in a high percentage of the dicentric Y chromosomes in metaphase was observed by Q- and C-banding. Lymphocytes at anaphase and telophase showed lagging Y chromosomes, fragments, and nondisjunction. These observations indicate a high degree of mitotic instability and thus raise the question of the effect of premature centromeric disjunction on mitotic instability of dicentric chromosomes.     

A stable marker chromosome with a cryptic centromere: evidence for centromeric sequences associated with an inverted duplication

Centromere activation, an important mechanism in karyotype evolution, is occasionally observed in some human chromosome rearrangements. We report a possible occurrence of centromere activation in a marker chromosome containing an atypical centromere associated with an inverted duplication of the region 14q32 --> qter. The marker chromosome's reduced centromere lacks both the alpha and beta satellite sequences usually found at normal centromeres. In an attempt to identify the centromeric sequences, the marker chromosome was flow-sorted and amplified by a degenerate oligonucleotide primer polymerase chain reaction. Reverse chromosome painting experiments showed that the marker chromosome contains sequences that are unique to the distal region of chromosome 14, as well as a low copy number of (centromeric) sequences that are also highly represented in the centromeres of chromosomes 18 and 19. These data suggest the activation of a novel centromere in the 14q32 --> qter region, very likely consequent to the duplication of the region itself.     

Assay of centromere function using a human artificial chromosome

In order to define a functional human centromere sequence, an artificial chromosome was constructed as a reproducible DNA molecule. Mammalian telomere repeats and a selectable marker were introduced into yeast artificial chromosomes (YACs) containing alphoid DNA from the centromere region of human chromosome 21 in a recombination-deficient yeast host. When these modified YACs were introduced into cultured human cells, a YAC with the alphoid DNA from the alpha21-I locus, containing CENP-B boxes at a high frequency and a regular repeat array, efficiently formed minichromosomes that were maintained stably in the absence of selection and bound CENP-A, CENP-B, CENP-C and CENP-E. The minichromosomes, 1-5 Mb in size and composed of multimers of the introduced YAC DNA, aligned at metaphase plates and segregated to opposite poles correctly in anaphase. Extensive cytological analyses strongly suggested that the minichromosomes had not acquired host sequences and were formed in all cases by a de novo mechanism. In contrast, minichromosomes were never produced with a modified YAC containing alphoid DNA from the alpha21-II locus, which contains no CENP-B boxes and has a less regular sequence arrangement. We conclude that alpha21-I alphoid DNA can induce de novo assembly of active centromere/kinetochore structures on minichromosomes.     

A de novo satellited short arm of the Y chromosome possibly resulting from an unstable translocation

A satellited long arm of the Y chromosome (Yqs) is considered a normal variation, whereas the presence of a satellite on the short arm of the Y (Yps) has never been described in the literature. A Yps chromosome could be clinically significant if the translocation resulting in Yps has relocated the testis-determining gene, SRY, to another chromosome. A carrier of such a translocation would therefore be at increased risk for having XX male and XY female offspring. Here we describe the first reported case of de novo Yps present in a phenotypically normal male. This Yps chromosome was positive for C-banding and nucleolus organizer region (NOR) staining and showed a hybridization signal for the beta-satellite sequence. Fluorescence in situ hybridization (FISH) analysis indicated that SRY was retained on the Yps and the translocation breakpoint on Yps was distal to the pseudoautosomal region. At prenatal diagnosis, a normal appearing Y chromosome was found in his son, and thus the satellite on Yps was lost during meiotic Xp-Yp pairing. This Yps chromosome was likely the product of an "unstable" translocation.     

Corrected centromere orientation for mouse chromosome 19 MIT markers

The Author demonstrates the use of dextranomer beads (Debrisan) in an extended upper and lower lid laceration. He found the dextranomer beads helpful in the treatment of lid lacerations. The mechanism of action of dextranomer beads is described as well. He is not aware of any publications about the use of dextranomer beads in ophthalmology.     

Y chromosome and spermatogenesis

The authors present two patients affected by scars resulting from burning of over 60 per cent of the total body area, in which the pre-expansion of a free flap has been used to increase the tissue surface useful for transfer from the only area of residual healthy skin (left forearm, left parascapular region). In both cases it was possible to transfer abundant healthy tissue into the desired areas, obtaining a rapid release of the region, which made possible an early physical rehabilitation of the patient starting after the second postoperative week. One of the main problems encountered, when facing surgical rehabilitation for the seriously burned patient, is the poor availability of skin donor areas suitable for reconstructive flaps. The pre-expansion of free flaps provides an advantage in that it allows the few integral residual areas to be used, improving vascularization and therefore increasing the available surface. Furthermore, as pre-expansion reduces tension on the margins, it allows for the easier closing of the donor area, with a minor risk of complications and a better scar outcome.     

The mammalian Y chromosome: a new perspective

If pityriasis lichenoides et varioliformis acuta (PLAVA) exists in the vagina or cervical os of the uterus, it may cause premature labor and premature rupture of the membranes.     

Ring Y chromosome without mosaicism

A 53-year-old man with a short stocky build, mild mental retardation, gynecomastia and hypogonadism was found to have a small ring Y chromosome unassociated with mosaicism. The ring Y was represented by a minute portion of chromatin or sometimes paired dots which were no larger than the short arm of the normally expected Y. No brightly fluorescent segment of the ring Y was present nor was it observed elsewhere in the karyotype. A primary medical problem was severe osteoarthritis, necessitating bilateral hip arthroplasties. Plasma testosterone was markedly decreased and plasma gonadotropins were increased. Potency was improved following testosterone injections. We conclude that genes responsible for testicular differentiation, maleness and possibly height are located close to the centromere of the Y chromosome, possibly on both the short and long arm. We also conclude that multiple genes are required for a fully developed male phenotype and apparently some of these genes were deleted or not expressed in this patient.     

Applications of microsatellite-based Y chromosome haplotyping

Y-chromosomal microsatellites have been investigated for the purposes of application to male identification, population genetics and population history. With nine markers, every male in a German population sample (n = 70) could be identified by an individual-specific Y microsatellite haplotype. The analysis of 474 unrelated males of nine human populations with seven markers revealed 301 different Y haplotypes. The analysis of molecular variance (AMOVA) approach was used to detect male population characteristics of Y microsatellite haplotypes. With pairwise comparisons of inter-population variance, most of the populations could be distinguished significantly. Sixty individuals from different male populations in Asia and Northern Europe carrying a novel Y-chromosomal T-->C transition show reduced microsatellite variability together with haplotype similarities. Microsatellite data suggest that the mutation occurred recently in Asia, supporting the hypothesis of Asian ancestry of some northern European populations.     

Y chromosome polymorphisms in native American and Siberian populations: identification of native American Y chromosome haplotypes

We have initiated a study of ancient male migrations from Siberia to the Americas using Y chromosome polymorphisms. The first polymorphism examined, a C-->T transition at nucleotide position 181 of the DYS199 locus, was previously reported only in Native American populations. To investigate the origin of this DYS199 polymorphism, we screened Y chromosomes from a number of Siberian, Asian, and Native American populations for this and other markers. This survey detected the T allele in all five Native American populations studied at an average frequency of 61%, and in two of nine native Siberian populations, the Siberian Eskimo (21%) and the Chukchi (17%). This finding suggested that the DYS199 T allele may have originated in Beringia and was then spread throughout the New World by the founding populations of the major subgroups of modern Native Americans. We further characterized Native American Y chromosome variation by analyzing two additional Y chromosome polymorphisms, the DYS287 Y Alu polymorphic (YAP) element insertion and a YAP-associated A-->G transition at DYS271, both commonly found in Africans. We found neither African allele associated with the DYS199 T allele in any of the Native American or native Siberian populations. However, we did find DYS287 YAP+ individuals who harbored the DYS199 C allele in one Native American population, the Mixe, and in one Asian group, the Tibetans. A correlation of these Y chromosome alleles in Native Americans with those of the DYS1 locus, as detected by the p49a/p49f (p49a,f) probes on TaqI-digested genomic DNA, revealed a complete association of DYS1 alleles (p49a,f haplotypes) 13, 18, 66, 67 and 69 with the DYS199 T allele, while DYS1 alleles 8 and 63 were associated with both the DYS199 C and T allele.     

Y chromosome microdeletions in male infertility

A new protocol for computed tomography (CT) imaging of the midfoot is described. This imaging technique places the CT cuts parallel to and perpendicular to the talus-first metatarsal axis, as viewed on the lateral CT scout image. For imaging the midfoot, this technique is an improvement over previously described hindfoot or midfoot protocols.     

Linkage of familial Wilms' tumor predisposition to chromosome 19 and a two-locus model for the etiology of familial tumors

Familial predisposition to Wilms' tumor (WT), a childhood kidney tumor, is inherited as an autosomal dominant trait. For most WT families studied, the 11p13 gene WT1 and genomic regions implicated in tumorigenesis in a subset of tumors can be ruled out as the site of the familial predisposition gene. Following a genome-wide genetic linkage scan, we have obtained strong evidence (log of the odds ratio = 4.0) in five families for an inherited WT predisposition gene (FWT2) at 19q13.3-q13.4. In addition, we observed loss of heterozygosity at 19q in tumors from individuals from two families in which 19q can be ruled out as the site of the inherited predisposing mutation. From these data, we hypothesize that alterations at two distinct loci are critical rate-limiting steps in the etiology of familial WTs.     

Molecular cytogenetic evidence for a common breakpoint in the largest inverted duplications of chromosome 15

Chromosomes from 20 patients were used to delineate the breakpoints of inverted duplications of chromosome 15 (inv dup[15]) that include the Prader-Willi syndrome/Angelman syndrome (PWS/AS) chromosomal region (15q11-q13). YAC and cosmid clones from 15q11-q14 were used for FISH analysis, to detect the presence or absence of material on each inv dup(15). We describe two types of inv dup(15): those that break between D15S12 and D15S24, near the distal boundary of the PWS/AS chromosomal region, and those that share a breakpoint immediately proximal to D15S1010. Among the latter group, no breakpoint heterogeneity could be detected with the available probes, and one YAC (810f11) showed a reduced signal on each inv dup(15), compared with that on normal chromosomes 15. The lack of breakpoint heterogeneity may be the result of a U-type exchange involving particular sequences on either homologous chromosomes or sister chromatids. Parent-of-origin studies revealed that, in all the cases analyzed, the inv dup(15) was maternal in origin.     

The azoospermic factor on the Y chromosome

Azoospermia is the most frequent cause of male infertility. After excluding the obvious urological reasons and the effect of Klinefelter's syndrome, azoospermia may be caused by an abnormality in the crucial gene(s) expressed during male germ cell differentiation. Recently, two candidate genes for azoospermia have been cloned from the azoospermic factor (AZF) locus on the Y chromosome long arm (Yq). One is YRRM (Y chromosome RNA recognition motif) gene, and the other is DAZ (deletion in azoospermia) gene. Both genes encode RNA binding protein and their expression is restricted to the testis. Therefore they are good candidates for AZF, although their function remains unclear. Here, the genes on the Y chromosome possibly involved in spermatogenesis and the role of the Y chromosome in evolution are discussed.     

Enigma of Y chromosome degeneration: neo-Y and neo-X chromosomes of Drosophila miranda a model for sex chromosome evolution

Y chromosome degeneration is characterized by structural changes in the chromosome architecture and expansion of genetic inertness along the Y chromosome. It is generally assumed that the heteromorphic sex chromosome pair has developed from a pair of homologues. Several models have been suggested. We use the unique situation of the secondary sex chromosome pair, neo-Y and neo-X (X2), in Drosophila miranda to analyze molecular mechanisms involved in the evolutionary processes of Y chromosome degeneration. Due to the fusion of one of the autosomes to the Y chromosome (about 2 Mya), a neo-Y chromosome and a neo-X chromosome, designated X2, were formed. Thus, formerly autosomal genes are inherited now on a pair of sex chromosomes in D. miranda. Analyzing DNA sequences from the X2 and neo-Y region, we observed a massive accumulation of DNA insertions on the neo-Y chromosome. From the analysis of several insertion elements, we present compelling evidence that the first step in Y chromosome degeneration is driven by the accumulation of transposable elements, especially retrotransposons. An enrichment of these elements along an evolving Y chromosome could account for the switch from a euchromatic into a heterochromatic chromatin structure.     

Loss of heterozygosity for chromosome 1p in familial neuroblastoma

Loss of heterozygosity (LOH) and deletion of chromosome 1p are very often found in sporadic neuroblastoma. Nevertheless, very few data are available concerning 1p LOH in familial neuroblastoma. Families with recurrent neuroblastoma are rare and analysis of chromosome 1p in these families might give useful information for identifying the putative neuroblastoma suppressor gene. We used combined cytogenetic and molecular techniques to study 1p LOH in two neuroblastoma families. Family M has 2 out of 3 children with neuroblastoma and family C has 2 children, 1 of whom has neuroblastoma and type 1 neurofibromatosis (NF1). All patients of both families showed tumour cells with chromosome 1p deletion (1pdel), but only the patient from family C also had MYCN gene amplification. In all cases the deleted chromosome 1 was of maternal origin.     

Molecular structure of a functional Drosophila centromere

Centromeres play a critical role in chromosome inheritance but are among the most difficult genomic components to analyze in multicellular eukaryotes. Here, we present a highly detailed molecular structure of a functional centromere in a multicellular organism. The centromere of the Drosophila minichromosome Dp1187 is contained within a 420 kb region of centric heterochromatin. We have used a new approach to characterize the detailed structure of this centromere and found that it is primarily composed of satellites and single, complete transposable elements. In the rest of the Drosophila genome, these satellites and transposable elements are neither unique to the centromeres nor present at all centromeres. We discuss the impact of these results on our understanding of heterochromatin structure and on the determinants of centromere identity and function.