The human Y chromosome.

Despite its central role in sex determination, genetic analysis of the Y chromosome has been slow. This poor progress has been due to the paucity of available genetic markers. Whereas the X chromosome is known to include at least 100 functional genetic loci, only three or four loci have been ascribed to the Y chromosome and even the existence of several of these loci is controversial. Other factors limiting genetic analysis are the small size of the Y chromosome, which makes cytogenetic definition difficult, and the absence of extensive recombination. Based on cytogenetic observation and speculation, a working model of the Y chromosome has been proposed. In this classical model the Y chromosome is defined into subregions; an X-Y homologous meiotic pairing region encompassing most of the Y chromosome short arm and, perhaps, including a pseudoautosomal region of sex chromosome exchange; a pericentric region containing the sex determining gene or genes; and a long arm heterochromatic genetically inert region. The classical model has been supported by studies on the MIC2 loci, which encode a cell surface antigen defined by the monoclonal antibody 12E7. The X linked locus MIC2X, which escapes X inactivation, maps to the tip of the X chromosome short arm and the homologous locus MIC2Y maps to the Y chromosome short arm; in both cases, these loci are within the proposed meiotic pairing region. MIC2Y is the first biochemically defined, expressed locus to be found on the human Y chromosome. The proposed simplicity of the classical model has been challenged by recent molecular analysis of the Y chromosome. Using cloned probes, several groups have shown that a major part of the Y chromosome short arm is unlikely to be homologous to the X chromosome short arm. A substantial block of sequences of the short arm are homologous to sequences of the X chromosome long arm but well outside the pairing region. In addition, the short arm contains sequences shared with the Y chromosome long arm and sequences shared with autosomes. About two-thirds of XX males contain detectable Y derived sequences. As the amount of Y sequences present varies in different XX males, DNA from these subjects can be used to construct a map of the region around the sex determining gene. Assuming that XX males are usually caused by simple translocation, the sex determining genes cannot be located in the pericentric region. Although conventional genetic analysis of the Y chromosome is difficult, this chromosome is particularly suited to molecular analysis. Paradoxically, the Y chromosome may soon become the best defined human chromosome at the molecular level and may become the model for other chromosomes.     

Cytogenetic, molecular and testicular tissue studies in an infertile 45,X male carrying an unbalanced (Y;22) translocation: case report

(Y;autosome) translocations have been reported in association with male infertility. Different mechanisms have been suggested to explain the male infertility, such as deletion of the azoospermic factor (AZF) on the long arm of the Y chromosome, or meiosis impairment. We describe a new case with a de novo unbalanced translocation t(Y;22) and discuss the genotype-phenotype correlation. A 36 year old male with azoospermia was found to have a mosaic 45,X/46,X, + mar karyotype. Fluorescence in situ hybridization (FISH) showed the presence of a derivative Y chromosome containing the short arm, the centromere and a small proximal part of the long-arm euchromatin of the Y chromosome and the long arm of chromosome 22. The unstable small marker chromosome included the short arm and the centromere of chromosome 22. This unbalanced translocation t(Y;22)(q11.2;q11.1) generated the loss of the long arm of the Y chromosome involving a large part of AZFb, AZFc and Yq heterochromatin regions. Testicular tissue analyses showed sperm in the wet preparation. Our case shows the importance of documenting (Y;autosome) translocations with molecular and testicular tissue analyses.     

Trisomy 10p produced by recombination involving complex paternal translocation between chromosomes 1 and 10

A complex and unique, apparently balanced translocation involving No. 1 long arm and No. 10 short and long arm, segregated in a family and produced an unbalanced progeny with recombination of t(10) translocation chromosome during paternal meiosis.     

Mosaicism presumably related to a Y/6 translocation in a boy with multiple congenital abnormalities.

A 3 1/2-year-old boy was referred for chromosomal evaluation because of mental and developmental retardation, peculiar facies, and abnormalities of the extremities. Karyotype analysis disclosed the presence of 46 and 47 chromosome cell lines. The 46 chromosome line contained 4 normal G group chromosomes and an abnormally small Y identified by G banding. Further investigation with Q and C band techniques revealed that the missing segment of the Y, the distal long arm, had been translocated to the end of the long arm of a number 6 chromosome. This de novo rearrangement appeared to be balanced and was found in all cells examined. The 47 chromosome line, which had a frequency of 10% in the patient's leucocytes, was identical to the 46 line except for the presence of an additional copy of the small chromosome. The morphology and banding patterns of the two small acrocentrics in the aneuploid line were found to correspond to those of the der (derivative) Y in the euploid line. The cytogenetic findings suggest that the translocation was followed by non-disjunction of one of its products resulting in mosaicism. Possible causes for the clinical and karyotypic abnormalities are discussed.     

Mouse Sycp1 functions in synaptonemal complex assembly, meiotic recombination, and XY body formation

In meiotic prophase, synaptonemal complexes (SCs) closely appose homologous chromosomes (homologs) along their length. SCs are assembled from two axial elements (AEs), one along each homolog, which are connected by numerous transverse filaments (TFs). We disrupted the mouse gene encoding TF protein Sycp1 to analyze the role of TFs in meiotic chromosome behavior and recombination. Sycp1(-/-) mice are infertile, but otherwise healthy. Sycp1(-/-) spermatocytes form normal AEs, which align homologously, but do not synapse. Most Sycp1(-/-) spermatocytes arrest in pachynema, whereas a small proportion reaches diplonema, or, exceptionally, metaphase I. In leptotene Sycp1(-/-) spermatocytes, gammaH2AX (indicative of DNA damage, including double-strand breaks) appears normal. In pachynema, Sycp1(-/-) spermatocytes display a number of discrete gammaH2AX domains along each chromosome, whereas gammaH2AX disappears from autosomes in wild-type spermatocytes. RAD51/DMC1, RPA, and MSH4 foci (which mark early and intermediate steps in pairing/recombination) appear in similar numbers as in wild type, but do not all disappear, and MLH1 and MLH3 foci (which mark late steps in crossing over) are not formed. Crossovers were rare in metaphase I of Sycp1(-/-) mice. We propose that SYCP1 has a coordinating role, and ensures formation of crossovers. Unexpectedly, Sycp1(-/-) spermatocytes did not form XY bodies.     

Unique t(Y;1)(q12;q12) reciprocal translocation with loss of the heterochromatic region of chromosome 1 in a male with azoospermia due to meiotic arrest: a case report

A de novo reciprocal translocation 46,X,t(Y;1)(q12;q12) was found in an azoospermic male with meiotic arrest. Cytogenetics and fluorescent in situ hybridization (FISH) were used to define the karyotype, translocation breakpoints and homologue pairing. SRY (Yp), Yq11.2-AZF regions, DAZ gene copies and the distal Yq12 heterochromatin were studied by PCR and restriction analysis using sequence-tagged sites and single nucleotide variants. High resolution GTL, CBL and DA-DAPI staining revealed a (Y;1) translocation in all metaphases and a normal karyotype in the patient's father. FISH showed the presence of the distal Yq12 heterochromatic region in der(1) and loss of the heterochromatic region of chromosome 1. PCR demonstrated the intactness of the Y chromosome, including the SRY locus, AZF regions, DAZ genes and distal heterochromatin. A significant decrease (P = 0.005) of Xp/Yp pairing (18.6%), as compared with controls (65.7%), was found in arrested primary spermatocytes, and cell culture and mRNA expression studies confirmed an irreversible arrest at meiosis I, with induction of apoptosis and removal of germ cells by Sertoli cells. We characterized a de novo t(Y;1)(q12;q12) balanced reciprocal translocation with loss of the heterochromatic region of chromosome 1, that caused unpairing of sex chromosomes followed by meiosis I arrest, apoptotic degeneration of germ cells and azoospermia.     

Crossover frequency and synaptonemal complex length: their variability and effects on human male meiosis

In this study, immunocytogenetics has been used in combination with the subtelomere-specific multiplex-fluorescent in-situ hybridization (stM-FISH) assay to identify 4681 autosomal synaptonemal complexes (SCs) of two fertile men. Comparisons of crossover maps for each individual SC between two men with extremely different meiotic crossover frequencies show that a low crossover frequency results in (i) a higher frequency of XY pairs and of small SCs without MLH1 foci and (ii) lower frequency of crossovers in the proximity of centromeres. In both cases, the bivalents which most frequently lacked MLH1 foci were the XY pair and the SC21. Analysis of SC length showed that SC arms can be longer or shorter than the corresponding mitotic one. Moreover, for a given SC, the variation in length found in one arm was independent of the variation observed in the other one (e.g. SC1p arms are longer than SC1q arms). The results confirmed that reduction in the crossover frequency may increase the risk of achiasmate small bivalents and that interindividual differences in crossover frequency could explain the variability in the frequencies of aneuploidy in human sperm. How MLH1 foci are positioned within the SC is discussed based on detailed MLH1 foci distributions and interfoci distances. Finally, evidence that the variation of the SC arm length may reflect the abundance of open and of compact chromatin fibers in the arm is shown.     

Malignant peripheral nerve sheath tumor with rhabdomyoblastic differentiation (malignant triton tumor) with balanced t(7;9)(q11.2;p24) and unbalanced translocation der(16)t(1;16)(q23;q13)

Malignant peripheral nerve sheath tumors (MPNST) with skeletal muscle differentiation are termed malignant triton tumors. A case of malignant triton tumor arising in a patient without signs of neurofibromatosis with two consistent chromosomal abnormalities is described. The first was of a balanced translocation between the long arm of chromosome 7 and the short arm of chromosome 9. The second was an unbalanced rearrangement between chromosomes 1 and 16, leading to partial trisomy for the long arm of chromosome 1 and partial monosomy for the long arm of chromosome 16. Review of previous reports on chromosomal abnormalities in malignant triton tumors revealed consistent abnormalities involving chromosome 1, regardless of the presence or absence of neurofibromatosis. This finding may relate to the observed poor prognostic outcome in this type of sarcoma. Also unique to our case is the translocation involving 7q and 9p, both regions may play a role in MPNST.     

综合应用分子细胞遗传学技术检测一例染色体微小易位

目的 综合应用分子细胞遗传学技术对1例染色体微小易位的病例进行检测.方法 按常规制备染色体,G显带进行核型分析,并先后进行光谱核型分析(spectral karyotyping,SKY),染色体涂染,双色荧光原位杂交技术(fluorescence in situ hybridisation,FISH)检测,亚端粒探针F...     

Analysis of chromosome segregation in sperm from a chromosome 2 inversion heterozygote and assessment of an interchromosomal effect

Using fluorescence in situ hybridization (FISH) analysis, the chromosome segregation of a pericentric inversion of chromosome 2 was studied in spermatozoa. An interchromosomal effect (ICE) was also determined for chromosomes 13, 21, X, and Y. This chromosome inversion included more than 2/3 of the total length of the chromosome and the breaks points were in G-light bands. The frequency of non-recombinant sperm was 55.9%, and that of recombinant sperm was 34.5% (with a 1:1 ratio of duplication of the p arm and deletion of the q arm and vice versa). There was a significantly increased frequency of disomy for chromosome 2 (0.6%) compared to the other autosomes, suggesting that pairing and recombination of the inversion may predispose to nondisjunction. There was no significant difference between the frequencies of aneuploidy for chromosomes 13, 21, X, and Y for the chromosome inversion heterozygote compared to control donors. Thus we did not find evidence for an ICE.     

Loss of the Y chromosome PAR2 region and additional rearrangements in two familial cases of satellited Y chromosomes: cytogenetic and molecular analysis

Two cases of rare structural aberrations of the Y chromosome were detected: a del(Y) (q12) chromosome in a child with mild dysmorphic features, obesity and psychomotor delay, and two identical satellited Y chromosomes (Yqs) in a normal twin, which were originally observed during routine prenatal diagnosis. In both cases a Yqs chromosome was detected in the father which had arisen from a reciprocal translocation involving the short arm of chromosome 15 and the heterochromatin of the long arm of the Y chromosome (Yqh). Cytogenetic and molecular studies demonstrated that in the reciprocal product of chromosomes 15 and Y PAR2 could not be detected, showing that PAR2 had been deleted. It is discussed whether the translocation of the short arm of an acrocentric chromosome to the heterochromatin of the long arm of the Y chromosome causes instability of this region which results either in loss of genetic material or interference with the normal mechanism of disjunction.     

Fluorescent in-situ hybridization and sequence-tagged sites for delineation of an X:Y translocation in a patient with secondary amenorrhoea

We describe a phenotypically normal female with secondary amenorrhoea due to a translocation of genetic material involving the long arm of chromosome X (Xq28) and the long arm of chromosome Y (Yq11). We used fluorescent in situ hybridization to localize the breakpoint on the Xq. The Y chromosome breakpoint was identified using polymerase chain reaction (PCR) detection of sequence-tagged sites (STS) specific for interval 5 at Yq11.21. The relationship between this X:Y translocation and premature ovarian failure is discussed.      

Complex relationship between meiotic recombination frequency and autosomal synaptonemal complex length per cell in normal human males

Although the relationship between meiotic recombination frequency and synaptonemal complex (SC) length has been of interest for a long time, how recombination frequency is related to SC length has not been carefully explored. To address this question, we have measured the meiotic recombination frequency as represented by MLH1 foci in 889 pachytene spermatocytes and measured the length of 19,558 autosomal SCs from 10 human males. A complex relationship between the number of MLH1 foci and total autosomal SC length per cell was observed. A positive correlation with significant correlation coefficients between the two variables was found in eight of the ten donors examined, with three donors showing weak correlation, and five showing moderate correlation. Two donors who did not show any correlation between the two variables were identified for the first time. Moreover, most cells with similar total autosomal SC length showed very different numbers of MLH1 foci both between individuals and even within an individual, and vice versa. Our data provide the first evidence for a complex relationship between the recombination frequency and total length of autosomal SCs per cell in human males.     

Structural analysis of a rare rearranged Y chromosome and its bearing on genotype-phenotype correlation

We report on a 9-year-old boy with a rare rearranged Y chromosome and borderline short stature (-2.0 SD). Standard metaphase chromosome analysis indicated a 46,X,i(Y)(q1O) karyotype, but high resolution G-banding showed an asymmetric band pattern for the rearranged Y chromosome. FISH and DNA studies for a total of 15 different Y chromosomal loci or regions showed that the rearranged Y chromosome was accompanied by: 1) a partial deletion of the short arm pseudoautosomal region (PAR1) involving SHOX, with the breakpoint distal to DXYS85; and 2) a partial duplication of Yq, with the breakpoint proximal to DAZ. The karyotype was determined as 46,X,?i(Y)(q1O).ish der(Y)(Yqter--> Yp11.3::Yq11.2-->Yqter)(DAZ++,DYZ3+,SRY +, SHOX-). The X chromosome and the autosomes were normal. The results suggest that haploinsufficiency of SHOX is primarily responsible for the borderline short stature, and that the deletion of the PAR1 may result in spermatogenic failure due to defective X-Y pairing and recombination in the PAR1.     

Variation in MLH1 distribution in recombination maps for individual chromosomes from human males

Meiotic recombination is essential for the segregation of homologous chromosomes and the formation of normal haploid gametes. Little is known about patterns of meiotic recombination in human germ cells or the mechanisms that control these patterns. Documentation of the normal range of variability of recombination distribution over the genome among individuals is an essential prerequisite for understanding abnormal recombination patterns, which may be associated with non-disjunction and chromosome rearrangements. In this article, variation in recombination maps for individual chromosomes among 10 normal human males is examined for the first time. An immunocytogenetic approach allowed analysis of pachytene cells, using antibodies to detect the mature synaptonemal complex (SCP1/SCP3), the centromere (CREST) and sites of crossing over (MLH1). Individual bivalents were identified with centromere-specific multicolor fluorescence in situ hybridization. Significant heterogeneity in MLH1 focus frequency across donors was observed for larger chromosome arms (P<0.05, one-way ANOVA). Significant inter-donor variation in the overall crossover frequency per cell was also found (P<0.0001, one-way ANOVA). Furthermore, several chromosome arms showed significant differences in crossover distribution along the SCs among donors. Inter-individual variation in interference distances was observed for all chromosomes. The significance of altered recombination patterns among individuals and the role of interference are discussed.     

Analysis of non-crossover bivalents in pachytene cells from 10 normal men

BACKGROUND: Bivalents with no recombination foci (possible achiasmates) are unable to orient properly on the metaphase plate or to segregate chromosomes to daughter cells. Non-crossover bivalents are known to cause meiotic arrest in various organisms. METHODS: Individual non-crossover bivalents were identified in 886 pachytene cells (19 492 bivalents) from testicular biopsies of 10 normal men. Fluorescence staining combined with centromere-specific multicolour fluorescence in situ hybridization (cenM-FISH) was used to identify mismatch repair gene mutation of human mutL homologue 1 (MLH1) recombination foci along each bivalent synaptonemal complex (SC). RESULTS: A total of 60 autosomal non-crossovers (SCs without an MLH1 focus) were found, and of these, chromosomes 21 (2.1%) and 22 (1.7%) had a significantly higher proportion than chromosomes 11, 12, 19 (each 0.1%), 13 (0.2%), 14 (0.6%), 16 (0.5%) and 15, 17, 18, 20 (each 0.3%) (P < 0.05). Sex chromosome univalents had a frequency of 27%, higher than that observed in any autosomal bivalent (P < 0.0001). CONCLUSIONS: These results suggest that G-group chromosomes and sex chromosomes are most susceptible to having no recombination foci and thus would be more susceptible to non-disjunction during spermatogenesis. This is consistent with previous observations from sperm karyotyping and FISH analysis, which demonstrate that chromosomes 21 and 22 and the sex chromosomes have a significantly increased frequency of aneuploidy compared with other autosomes.     

A malignant triton tumor with an unbalanced translocation (1;13)(q10;q10) and an isochromosome (8)(q10) as the sole karyotypic abnormalities

The karyotype of a malignant nerve sheath tumor with rhabdomyosarcomatous differentiation (malignant triton tumor) of a 58-year-old woman is reported. The tumor revealed an isochromosome for the long arm of chromosome 8 and an unbalanced translocation (1;13)(q10;q10) leading to a gain of the long arm of chromosome 1 as the sole karyotypic abnormalities.     

刺猬精母细胞联会丝复合体的结构、核型及行为研究

本文以改进的[固定液中加入一定浓度的十二烷基硫酸钠(SDS)]表面铺展技术制备刺猬精母细胞联会丝复合体(SC)标本,经硝酸银染色后,进行光镜和电镜观察。刺猬SC的3层结构中,侧线各宽50nm,两侧线间的距离为100nm。每一SC的相对长度和臂比几乎恒定。SC的核型和有丝分裂中期染色体核型基本一致。 X、Y染色体轴在减数分裂前期中有明显特征,易于与常染色体的SC区别。在粗线期中,X、Y染色体形成一定长度的SC,而未配对的染色体轴异固缩化,表现为多种不同的形态。刺猬中,这种分化程度较人和鼠为低。此外,X、Y染色体间出现扩大配对,其长度随减数分裂的进行而降低。     

A de novo complex chromosomal rearrangement with nine breakpoints characterised by FISH in a boy with mild mental retardation, developmental delay, short stature and microcephaly

A de novo complex chromosome rearrangement (CCR) involving chromosomes 1, 6, 7, 15 and Y was detected in a boy with mental retardation, short stature, and microcephaly. Fluorescence in situ hybridisation (FISH) with whole chromosome painting libraries, band-specific cosmids and telomeric probes was essential for the characterisation of the rearrangement. The CCR was shown to be the result of at least nine chromosomal breaks and involved the alternating insertion of two segments of the short arm of chromosome 1 and two segments of the long arm of chromosome 6 into a novel derived chromosome 7. A non-reciprocal translocation between the distal short arm of the same chromosome 7 and the distal long arm of the Y chromosome was also found, together with a paracentric inversion of the long arm of chromosome 15. The only detectable imbalance was a deletion of the heterochromatic Yq telomeric region. FISH investigations in this case have revealed an additional complexity in this CCR, which has implications for reproductive risk assessment and genetic counselling.     

Discontinuities and unsynapsed regions in meiotic chromosomes have a cis effect on meiotic recombination patterns in normal human males

During meiosis, homologous chromosome pairing is essential for subsequent meiotic recombination (crossover). Discontinuous chromosome regions (gaps) or unsynapsed chromosome regions (splits) in the synaptonemal complex (SC) indicate anomalies in chromosome synapsis. Recently developed immunofluorescence techniques (using antibodies against SC proteins and the crossover-associated MLH1 protein) were combined with fluorescence in situ hybridization (using centromere-specific DNA probes) to identify bivalents with gaps/splits and to examine the effect of gaps/splits on meiotic recombination patterns during the pachytene stage of meiotic prophase from three normal human males. Gaps were observed only in the heterochromatic regions of chromosomes 9 and 1, with 9q gaps accounting for 90% of these events. Most splits were also found in chromosomes 9 and 1, with 58% of splits occurring on 9q. Gaps and splits significantly altered the distribution of MLH1 foci on the SC. On gapped SC 9q, the frequency of MLH1 foci was decreased compared with controls, and single 9q crossovers tended toward a more distal distribution. Furthermore, the larger the gap the more distal the location of the MLH1 focus closest to the q arm's telomere. MLH1 foci on split SC 9 had distributions similar to those of gapped SC 9; however, splits did not change the frequencies of MLH1 foci on SC 9. This is the first demonstration that gaps and splits have an effect on meiotic recombination in humans.