Yq deletion,aspermia, and short stature

Summary A large Yq deletion involving both the fluorescent and part of the non-fluorescent segment in a 36-year-old phenotypic normal male is presented. His short stature and aspermia gives strong support, after a complete review of the literature, to the existence of factors involved in the control of both characteristics in the non-fluorescent segment of the long arm of chromosome Y, distally within band 11.     

Relevance to prenatal diagnosis of the identification of a human Y/autosome translocation by Y-chromosome-specific in situ hybridisation

Routine cytogenetic analysis of an amniotic fluid sample revealed a large brightly fluorescent region in the short arm of chromosome 14 in an otherwise normal male karyotype (46,XY,14p+ + +). This site was also present in the paternal karyotype. In situ hybridisation to a Y-chromosome-specific DNA probe confirmed that the father had a Y/14 translocation. The incidence of two hybridisation bodies (large hybridisation sites), detecting both the translocated Y chromatin and the normal Y chromosome, was lower in interphase nuclei (44.3%) than in metaphase spreads (95.2%). The relevance of these observations to the potential use of in situ hybridisation to interphase nuclei for prenatal diagnosis is discussed.     

Parallel occurrence of asynaptic sex chromosomes in gray voles (Microtus Schrank, 1798)

In many eutherian species, pairing and recombination of X and Y chromosomes are indispensable for normal meiotic progression and correct segregation of sex chromosomes. The rodent subfamily Arvicolinae provides an interesting exception. The majority of arvicoline species with asynaptic sex chromosomes belong to the genus Microtus sensu lato. However, some vole species of the genus Microtus and other genera display normal X-Y pairing in meiosis. These observations indicate that synaptic condition was typical for the common ancestor of all voles, but the gaps in taxonomic sampling makes impossible to identify a lineage or lineages, in which the asynapsis occurred. The methods of electron and fluorescent microscopy were used to study the synapsis of sex chromosomes in males of some additional species of the subfamily Arvicolinae. This extended taxonomic list allowed us to identify asynaptic species in every large lineage of the tribe Microtini. Apparently, the ability of sex chromosomes to pair and recombine in male meiosis was lost in arvicoline evolution for at least three times independently. Our results indirectly suggest the unnecessity of sex chromosome pairing in male meiosis of arvicoline rodents, and presence of alternate molecular mechanism of sex chromosome segregation in this large mammalian tribe.     

Recombination in the pseudoautosomal region in a 47,XYY male

Males with a 47,XYY karyotype generally have chromosomally normal children, despite the high theoretical risk of aneuploidy. Studies of sperm karyotypes or FISH analysis of sperm have demonstrated that the majority of sperm are chromosomally normal in 47,XYY men. There have been a number of meiotic studies of XYY males attempting to determine whether the additional Y chromosome is eliminated during spermatogenesis, with conflicting results regarding the pairing of the sex chromosomes and the presence of an additional Y. We analyzed recombination in the pseudoautosomal region of the XY bivalent to determine whether this is perturbed in a 47,XYY male. A recombination frequency similar to normal 46,XY men would indicate normal pairing within the XY bivalent, whereas a significantly altered frequency would suggest other types of pairing such as a YY bivalent or an XYY trivalent. Two DNA markers, STS/STS pseudogene and DXYS15, were typed in sperm from a heterozygous 47,XYY male. Individual sperm (23,X or Y) were isolated into PCR tubes using a FACStarPlus flow cytometer. Hemi-nested PCR analysis of the two DNA markers was performed to determine the frequency of recombination. A total of 108 sperm was typed with a 38% recombination frequency between the two DNA markers. This is very similar to the frequency of 38.3% that we have observed in 329 sperm from a normal 46,XY male. Thus our results suggest that XY pairing and recombination occur normally in this 47,XYY male. This could occur by the production of an XY bivalent and Y univalent (which is then lost in most cells) or by loss of the additional Y chromosome in some primitive germ cells or spermatogonia and a proliferative advantage of the normal XY cells.     

Purifying human Y chromosomes by flow cytometry and sorting

A method of producing an enriched sample of human Y chromosomes from peripheral blood lymphocytes is described. Metaphase chromosomes were prepared from peripheral blood lymphocytes donated by 17 normal male individuals. A suspension of chromosomes in a polyamine buffer was produced from each sample, stained with the fluorescent dye Hoechst 33258, and passed through a flow cytometer and sorter. Following analysis of the 17 fluorescence distributions, a single donor was found giving a separate peak corresponding to the Y chromosome. Seventy percent of the chromosomes sorted from this peak were identified as Y chromosomes. Batches of a million Y chromosomes were produced from each of several 40 ml donations of peripheral blood. These were assessed for the amount of Y DNA present and used to construct a DNA library.     

Spermatogenesis in XO,Sxr mice: role of the Y chromosome

The goal of this investigation was to evaluate the role of the Y chromosome in spermatogenesis by a quantitative and qualitative analysis of spermatogenesis as it occurs in the absence of a significant portion of the Y chromosome, i.e., in XO,Sxr male mice. Although these mice have the testis-determining portion of the Y chromosome on their single X chromosome, they lack most of the Y chromosome. Since it was found that all sperm-specific structures were assembled in a normal spatial and temporal pattern in spermatids of XO,Sxr mice, the genes controlling these structures cannot be located on the Y chromosome outside of the Sxr region, and are more likely to be on autosomes or on the X chromosome. In spite of the assembly of the correct sperm-specific structures, spermatogenesis was not quantitatively normal in XO,Sxr mice and significantly reduced numbers of spermatids were found in the seminiferous tubules of these mice. Furthermore, two size classes of spermatids were found in the testes of XO,Sxr mice, normal and twice-normal size. These findings are suggestive of abnormalities of meiosis in XO,Sxr spermatocytes, which lack one of the two sex chromosomes, and may not implicate function of specific genes on the Y chromosome. Morphological abnormalities of spermatids, which were not unique to XO,Sxr mice, were observed and these may be due to either a defective testicular environment because of reduced numbers of germ cells or to the lack of critical Y chromosome-encoded products. Since pachytene spermatocytes of XO,Sxr mice exhibited a sex vesicle, it can be concluded that the assembly of this structure does not depend on the presence of either a complete Y chromosome or the pairing partner for the X chromosome.     

A 45,X male with translocation of euchromatic Y chromosome material

Summary A phenotypically normal 32-year-old male with azoospermia was found to have a 45,X karyotype with presence of excess euchromatic material on 14p. The parents' karyotypes are normal. This observation is interpreted as a Y/14 translocation with loss of the heterochromatic Y chromosome material.     

The contribution of the y chromosome to hybrid male sterility in house mice

Hybrid sterility in the heterogametic sex is a common feature of speciation in animals. In house mice, the contribution of the Mus musculus musculus X chromosome to hybrid male sterility is large. It is not known, however, whether F(1) male sterility is caused by X-Y or X-autosome incompatibilities or a combination of both. We investigated the contribution of the M. musculus domesticus Y chromosome to hybrid male sterility in a cross between wild-derived strains in which males with a M. m. musculus X chromosome and M. m. domesticus Y chromosome are partially sterile, while males from the reciprocal cross are reproductively normal. We used eight X introgression lines to combine different X chromosome genotypes with different Y chromosomes on an F(1) autosomal background, and we measured a suite of male reproductive traits. Reproductive deficits were observed in most F(1) males, regardless of Y chromosome genotype. Nonetheless, we found evidence for a negative interaction between the M. m. domesticus Y and an interval on the M. m. musculus X that resulted in abnormal sperm morphology. Therefore, although F(1) male sterility appears to be caused mainly by X-autosome incompatibilities, X-Y incompatibilities contribute to some aspects of sterility.     

Synapsis and obligate recombination between the sex chromosomes of male laboratory mice carrying the Y* rearrangement.

The synaptic and recombinational behavior of the sex chromosomes in male laboratory mice carrying the Y* rearrangement was analyzed by light and electron microscopy. Examination of zygotene and pachytene X-Y* configurations revealed a surprising paucity of the staggered pairing configuration predicted from the distal position of the X pseudoautosomal region and the subcentromeric position of the Y* pseudoautosomal region. When paired at pachynema, the X and Y* chromosomes usually assumed configurations similar to those of typical sex bivalents from normal male laboratory mice. The X and Y* chromosomes were present as univalents in more than half of the early- and mid-pachytene nuclei, presumably as a result of steric difficulties associated with homologous alignment of the pseudoautosomal regions. When paired at diakinesis and metaphase I, the X and Y* chromosomes exhibited an asymmetrical chiasmatic association indicative of recombination within the staggered synaptic configuration. Both pairing disruption and recombinational failure apparently contribute to diakinesis/metaphase I sex-chromosome univalency, as most cells at these stages possessed X and Y* univalents lacking evidence of prior recombination. Recombinant X or Y* chromosomes were detected in all metaphase II complements examined, thus substantiating the hypothesis that X-Y recombination is a prerequisite for the normal progression of male meiosis.     

Differential frequency of human X and Y chromatin as related to cell density in vitro

The relationship between cell density in vitro and the frequency of fluorescent X chromatin and/or Y chromatin-positive interphase nuclei was studied in cultured cells from three human male and female subjects. It was found that altough the frequency of fluorescent X chromatin-positive cells was proportional to cell density, the frequency of fluorescent Y chromatin-postitive cells was independent of cell density. Our results are compared with those of other investigators.     

Cytogenetic characterization and description of an XX/XY1Y2 sex chromosome system in catfish Harttia carvalhoi (Siluriformes, Loricariidae)

Karyotypic and cytogenetic characteristics of catfish Harttia carvalhoi (Paraíba do Sul River basin, S?o Paulo State, Brazil) were investigated using differential staining techniques (C-banding, Ag-staining) and fluorescent in situ hybridization (FISH) with 18S and 5S rDNA probes. The diploid chromosome number of females was 2n = 52 and their karyotype was composed of nine pairs of metacentric, nine pairs of submetacentric, four pairs of subtelocentric and four pairs of acrocentric chromosomes. The diploid chromosome number of males was invariably 2n = 53 and their karyotype consisted of one large unpaired metacentric, eight pairs of metacentric, nine pairs of submetacentric, four pairs of subtelocentric, four pairs of acrocentric plus two middle-sized acrocentric chromosomes. The differences between female and male karyotypes indicated the presence of a sex chromosome system of XX/XY1Y2 type, where the X is the largest metacentric and Y1 and Y2 are the two additional middle-sized acrocentric chromosomes of the male karyotype. The major rDNA sites as revealed by FISH with an 18S rDNA probe were located in the pericentromeric region of the largest pair of acrocentric chromosomes. FISH with a 5S rDNA probe revealed two sites: an interstitial site located in the largest pair of acrocentric chromosomes, and a pericentromeric site in a smaller metacentric pair of chromosomes. Translocations or centric fusions in the ancestral 2n = 54 karyotype is hypothesized for the origin of such multiple sex chromosome systems where females are fixed translocation homozygotes whereas males are fixed translocation heterozygotes. The available cytogenetic data for representatives of the genus Harttia examined so far indicate large kayotype diversity.     

Incidence of 47,XYY karyotype in a consecutive series of newborn males in Tokyo

Summary A series of 3545 newborn males, born consecutively at a maternity hospital in the western suburbs of Tokyo and with no detectable physical abnormalities, were studied for fluorescent Y-chromatin. Buccal cell smears from each infant were screened. Cases with ambiguous results were subjected to a second test by blood smears, which were found to be more reliable. After the second test, chromosomal analysis was carried out in five infants: three had a 47,XYY karyotype; one, the karyotype 46,XY-D,t(D:Y) (Iijima et al., in preparation); and one, a normal male karyotype. The XYY karyotype occurred in 0.11% of newborn males in this series.     

Comparison of gene expression in male and female mouse blastocysts revealed imprinting of the X-linked gene, Rhox5/Pem, at preimplantation stages

Mammalian male preimplantation embryos develop more quickly than females . Using enhanced green fluorescent protein (EGFP)-tagged X chromosomes to identify the sex of the embryos, we compared gene expression patterns between male and female mouse blastocysts by DNA microarray. We detected nearly 600 genes with statistically significant sex-linked expression; most differed by 2-fold or less. Of 11 genes showing greater than 2.5-fold differences, four were expressed exclusively or nearly exclusively sex dependently. Two genes (Dby and Eif2s3y) were mapped to the Y chromosome and were expressed in male blastocysts. The remaining two (Rhox5/Pem and Xist) were mapped to the X chromosome and were predominantly expressed in female blastocysts. Moreover, Rhox5/Pem was expressed predominantly from the paternally inherited X chromosome, indicating sex differences in early epigenetic gene regulation.     

Fluorescence in situ hybridization and Y ring chromosome

Summary Investigations by fluorescence in situ hybridization and a Y-specific probe (Y190) of a male patient with a Y ring chromosome, 46,X,r(Y) showed four bright fluorescent spots within the ring. Thus, using this technique, it is possible to suggest that the ring originates from the duplication of the short arms of the Y chromosome.     

H-Y antigen-positive male pseudohermaphroditism with 45,X/46,XYq-mosaicism

Summary A 42-year-old male had short stature, microphallus, hypospadias, a bifid scrotum, abdominal undifferentiated testes, a uterus, bilateral fallopian tubes, and 45,X/46,XYq-mosaicism in his blood, skin, and germinal tissue and tissue surrounding the testes as determined by means of G-, Q-, and C-banding. An H-Y antigen assay on skin fibroblasts was positive, indicating that the locus for this antigen is not located in the brightly fluorescent region of the Y chromosome.     

Recombination is suppressed over a large region of the rainbow trout Y chromosome

The previous genetic mapping data have suggested that most of the rainbow trout sex chromosome pair is pseudoautosomal, with very small X-specific and Y-specific regions. We have prepared an updated genetic and cytogenetic map of the male rainbow trout sex linkage group. Selected sex-linked markers spanning the X chromosome of the female genetic map have been mapped cytogenetically in normal males and genetically in crosses between the OSU female clonal line and four different male clonal lines as well as in outcrosses involving outbred OSU and hybrids between the OSU line and the male clonal lines. The cytogenetic maps of the X and Y chromosomes were very similar to the female genetic map for the X chromosome. Five markers on the male maps are genetically very close to the sex determination locus ( SEX ), but more widely spaced on the female genetic map and on the cytogenetic map, indicating a large region of suppressed recombination on the Y chromosome surrounding the SEX locus. The male map is greatly extended at the telomere. A BAC clone containing the SCAR (sequence characterized amplified region) Omy - 163 marker, which maps close to SEX , was subjected to shotgun sequencing. Two carbonyl reductase genes and a gene homologous to the vertebrate skeletal ryanodine receptor were identified. Carbonyl reductase is a key enzyme involved in production of trout ovarian maturation hormone. This brings the number of type I genes mapped to the sex chromosome to six and has allowed us to identify a region on zebrafish chromosome 10 and medaka chromosome 13 which may be homologous to the distal portion of the long arm of the rainbow trout Y chromosome.     

Y-autosome translocation and infertility: usefulness of molecular, cytogenetic and meiotic studies

An apparently balanced reciprocal translocation 46,X,t(Y;6) (q11.23 ∼ q12;p11.1) was observed in an infertile man with severe oligozooteratozoospermia. Different mitotic chromosome banding patterns were performed and fluorescence in situ hybridization indicated a breakpoint in the fluorescent Yq heterochromatin. Molecular genetic deletion experiments for the azoospermia factor region in distal Yq11 showed the retention of the DAZ gene and meiotic pairing configurations suggested that the man’s infertility could be due to the pairing behaviour of the Y;6 translocation chromosome with the X chromosome visualised by synaptonemal complex analysis at the electron microscopy level. The morphological appearance of the normal chromosome 6 and the Y;6 translocated chromosome included in the compartment of the sex vesicle may allow an explanation of the degeneration of most spermatocytes after the pachytene stage. Received: 1 August 1997 / Accepted: 25 September 1997     

Familial mosaicism of del(Y) and inv del(Y)

Molecular cytogenetic investigation of a male proband showing oligozoospermia (OAT I-II degrees ) has led to the detection of a Y-chromosome mosaicism. This mosaicism consists of a deleted Y chromosome with deletion of most of the long-arm heterochromatin, including the PAR2, del(Y), and a Y chromosome, which, in addition to that deletion, shows a paracentric long-arm inversion, inv del(Y), with breakpoints in the DAZ gene cluster in deletion interval 6 and within the remainder of the long-arm heterochromatin of the Y. The Y mosaicism is not confined to the sterile proband but is also detected in both his father and his fertile brother. Interestingly, the percentage of inv del(Y) is highest (80%) in the proband showing oligozoospermia.     

H-Y antigen: localization of the H-Y gene

Testicular development in a patient with deletion of the distal (fluorescent) segment of the Y chromosome is described. The presence of a normal dose of H-Y antigen was demonstrated by Goldberg's cytotoxicity test. It is concluded that the distal fluorescent segment of the Y chromosome is void of genes regulating H-Y antigen activity.     

Aberrations of the synaptonemal complexes in a male 46,XY,-14,+der(14)t(Y;14)

An unbalanced translocation 46,XY,-14,+der(14)t(Y;14)(q11;p11) was observed in an azoospermic male, with reduced spermatogenesis and absent spermiogenesis. At the pachytene stage of spermatocyte 1, the segments of the 2 Y chromosomes, fluorescent with quinacrine mustard, were always found close together. This proximity was also demonstrated by the study of synaptonemal complexes, which showed, in addition, an unusual hypercondensation of the proximal segment of bivalent 14, adjacent to the translocated Y chromosome. This allows us to propose that this hypercondensation might correspond to an inactivation of the translocated autosome, which could be responsible of the degeneration of the germ cells.