Bivalent 15 regularly associates with the sex vesicle in normal male meiosis

Verification of a cryptic t(Y;15) translocation in a male with an apparent 45,X karyotype

Background

A rare disease is that an individual with a non-chimeric karyotype of 45,X develops into a male. We explored the genetic aetiology of an infertile male with an apparent 45,X karyotype, which was subsequently verified as cryptic translocation between chromosomes Y and 15.

Methods

DNA was extracted from the patient's peripheral blood. A range of genetic testing was performed, including conventional chromosomal karyotyping, short tandem repeat (STR) analysis for azoospermia factor (AZF) region, fluorescence in situ hybridization (FISH) with specific probes groups of DXZ1/DYZ3, DYZ3/D15Z1/PML and SRY/D15Z1/PML, and chromosomal microarray analysis (CMA) for genomic copy number variations (CNVs).

Results

The patient was found to have an apparent 45,X karyotype. STR analysis showed that he possessed a short arm of the Y chromosome, including the SRY gene; however, he was missing the long arm of the Y chromosome, including AZFa + b + c and Yqter. A FISH assay of DXZ1 and DYZ3 probes showed a green signal of the X centromere and a red of the Y centromeric signal on a D-group-sized chromosome. By FISH assaying with D15Z1 and DYZ3 probes, chromosomes 15 and Y centromeric signals appeared closely on a single chromosome, as the PML control probe ascertained. A further FISH assay with D15Z1 and SRY probes revealed a signal of the SRY gene at the end of one arm of chromosome 15. The result of the CMA indicated a deletion with an approximate size of 45.31 Mb spanning from Yq11 to Yter.

Conclusion

Our study enriched the karyotype-phenotype correlation of Y and 15 chromosomes translocation. It strengthened the critical roles of molecular genetic techniques in identifying the chromosomal breakpoints and regions involved. Genetic aetiology can guide early intervention in childhood and assisted reproduction in adulthood.

How much, if anything, do we know about sperm chromosomes of Robertsonian translocation carriers?

In men with oligozoospermia, Robertsonian translocations (RobTs) are the most common type of autosomal aberrations. The most commonly occurring types are rob(13;14) and rob(14;21), and other types of RobTs are described as 'rare' cases. Based on molecular research, all RobTs can be broadly classified into Class 1 and Class 2. Class 1 translocations produce the same breakpoints within their RobT type, but Class 2 translocations are predicted to form during meiosis or mitosis through a variety of mechanisms, resulting in variation in the breakpoint locations. This review seeks to analyse the available data addressing the question of whether the molecular classification of RobTs into Classes 1 and 2 and/or the type of DD/GG/DG symmetry of the involved chromosomes is reflected in the efficiency of spermatogenesis. The lowest frequency value calculated for the rate of alternate segregants was found for rob(13;15) carriers (Class 2, symmetry DD) and the highest for rob(13;21) carriers (Class 2, DG symmetry). The aneuploidy values for the rare RobT (Class 2) and common rob(14;21) (Class 1) groups together exhibited similarities while differing from those for the common rob(13;14) (Class 1) group. Considering the division of RobT carriers into those with normozoospermia and those with oligoasthenozoospermia, it was found that the number of carriers with elevated levels of aneuploidy was unexpectedly quite similar and high (approx. 70%) in the two subgroups. The reason(s) that the same RobT does not always show a similar destructive effect on fertility was also pointed out.

Small supernumerary marker chromosomes (sSMC) and male infertility: characterization of five new cases, review of the literature, and perspectives

PURPOSE

To characterize small supernumerary marker chromosomes (sSMC) in infertile males RESEARCH QUESTION: Are molecular cytogenetic methods still relevant for the identification and characterization of sSMC in the era of next-generation sequencing?

METHODS

In this paper, we report five males with oligoasthenozoospermia or azoospermia with a history of recurrent pregnancy loss in partnership in four cases. R-banding karyotyping and fluorescence in situ hybridization (FISH) analysis were performed and showed sSMC in all five cases. Microdissection and reverse-FISH were performed in one case.

RESULTS

One sSMC, each, was derived from chromosome 15 and an X-chromosome; two sSMC were derivatives of chromosome 22. The fifth sSMC was a ring chromosome 4 complemented by a deletion of the same region 4p14 to 4p16.1 in one of the normal chromosomes 4. All markers were mosaics except one of sSMC(22).

CONCLUSION

Through this study, we emphasize the necessity of a proper combination of high-throughput techniques with conventional cytogenetic and FISH methods. This could provide a personalized diagnostic and accurate results for the patients suffering from infertility or RPL. We also highlight FISH analyses, which are essential tools for detecting sSMC in infertile patients. In fact, despite its entire composition of heterochromatin, sSMC can have effects on spermatogenesis by producing mechanical perturbations during meiosis and increasing meiotic nondisjunction rate. This would contribute to understand the exact chromosomal mechanism disrupting the natural and the assisted reproduction leading to offer a personalized support.

Chromosome positioning and male infertility: it comes with the territory

The production of functional spermatozoa through spermatogenesis requires a spatially and temporally highly regulated gene expression pattern, which in case of alterations, leads to male infertility. Changes of gene expression by chromosome anomalies, gene variants, and epigenetic alterations have been described as the main genetic causes of male infertility. Recent molecular and cytogenetic approaches have revealed that higher order chromosome positioning is essential for basic genome functions, including gene expression. This review addresses this issue by exposing well-founded evidences which support that alterations on the chromosome topology in spermatogenetic cells leads to defective sperm function and could be considered as an additional genetic cause of male infertility.

Prenatal diagnosis of the maternal derivative chromosome der(15)t(Y;15)(q12;p13) in a dizygotic twin pregnancy

Sex chromosome translocations are unique and must be considered separately from translocations between autosomes. Here, we describe the first prenatal case of one twin fetus with an unbalanced translocation between chromosome Y and chromosome 15, presenting a 46,XY,der(15)t(Y;15) karyotype. The other twin had a normal 46,XY karyotype. Cytogenetic analysis of the parental chromosomes revealed that the father had a normal 46,XY karyotype, whereas the mother exhibited a 46,XX,der(15) t(Y;15) karyotype. Thus, the proband inherited this translocation from the mother. Fluorescence in situ hybridization analyses demonstrated that the breakpoint on chromosome Y involved a heterochromatin region (Yq12), while that on chromosome 15 involved a p-arm region (15p13). At 37 gestational weeks, healthy twins were delivered vaginally. We conclude that accurate identification of der(15) chromosomal content can facilitate not only prenatal diagnosis of a chromosomal aberration in one twin, but also prediction of the fetal phenotype.

Genetic dosage and position effect of small supernumerary marker chromosome (sSMC) in human sperm nuclei in infertile male patient

Chromosomes occupy specific distinct areas in the nucleus of the sperm cell that may be altered in males with disrupted spermatogenesis. Here, we present alterations in the positioning of the human chromosomes 15, 18, X and Y between spermatozoa with the small supernumerary marker chromosome (sSMC; sSMC⁺) and spermatozoa with normal chromosome complement (sSMC⁻), for the first time described in the same ejaculate of an infertile, phenotypically normal male patient. Using classical and confocal fluorescent microscopy, the nuclear colocalization of chromosomes 15 and sSMC was analyzed. The molecular cytogenetic characteristics of sSMC delineated the karyotype as 47,XY,+der(15)(pter->p11.2::q11.1->q11.2::p11.2->pter)mat. Analysis of meiotic segregation showed a 1:1 ratio of sSMC⁺ to sSMC⁻ spermatozoa, while evaluation of sperm aneuploidy status indicated an increased level of chromosome 13, 18, 21 and 22 disomy, up to 7 × (2.7 − 15.1). Sperm chromatin integrity assessment did not reveal any increase in deprotamination in the patient’s sperm chromatin. Importantly, we found significant repositioning of chromosomes X and Y towards the nuclear periphery, where both chromosomes were localized in close proximity to the sSMC. This suggests the possible influence of sSMC/XY colocalization on meiotic chromosome division, resulting in abnormal chromosome segregation, and leading to male infertility in the patient.

The human sex ratio from conception to birth

We describe the trajectory of the human sex ratio from conception to birth by analyzing data from (i) 3- to 6-d-old embryos, (ii) induced abortions, (iii) chorionic villus sampling, (iv) amniocentesis, and (v) fetal deaths and live births. Our dataset is the most comprehensive and largest ever assembled to estimate the sex ratio at conception and the sex ratio trajectory and is the first, to our knowledge, to include all of these types of data. Our estimate of the sex ratio at conception is 0.5 (proportion male), which contradicts the common claim that the sex ratio at conception is male-biased. The sex ratio among abnormal embryos is male-biased, and the sex ratio among normal embryos is female-biased. These biases are associated with the abnormal/normal state of the sex chromosomes and of chromosomes 15 and 17. The sex ratio may decrease in the first week or so after conception (due to excess male mortality); it then increases for at least 10-15 wk (due to excess female mortality), levels off after ∼20 wk, and declines slowly from 28 to 35 wk (due to excess male mortality). Total female mortality during pregnancy exceeds total male mortality. The unbiased sex ratio at conception, the increase in the sex ratio during the first trimester, and total mortality during pregnancy being greater for females are fundamental insights into early human development.

Acrocentric bivalents positioned preferentially nearby to the XY pair in metaphase I human spermatocytes

OBJECTIVE

To analyze whether the preferential proximity between acrocentric bivalents and the XY pair described at pachytene was maintained in metaphase I human spermatocytes.

DESIGN

Proximity frequencies of autosomic bivalents to the sex bivalent were evaluated with the analysis of meiotic preparations combining sequentially standard techniques and multiplex fluorescence in situ hybridization.

SETTING

Assisted reproduction centers.

PATIENT(S)

Thirty-seven men consulting for fertility problems.

INTERVENTION(S)

Unilateral testicular biopsies.

MAIN OUTCOME MEASURE(S)

Proximity frequencies analysis to the XY pair, evaluated individually and grouping bivalents, was carried out using a logistical regression model with repeated measures.

RESULT(S)

Bivalents 22 and 15 were observed more frequently near to the sex bivalent than the others. Significant interindividual differences were not observed.

CONCLUSION(S)

Results suggest that bivalents distribution to the metaphase plate is nonrandom. The maintenance of the acrocentric chromosomes' proximity to the sex bivalent from pachytene to metaphase I would indicate that the relative bivalents position would be notably preserved. The observation of non-interindividual variability, despite different infertility etiology, suggests that the nuclear organization pattern remains largely unaffected even if spermatogenesis is compromised.

46,XX, der(15),t(Y;15)(q12;p11) karyotype in an azoospermic male

We report on a Yq/15p translocation in a 23-year-old infertile male referred for Klinefelter Syndrome testing, who had azoospermia and bilateral small testes. Hormonal studies revealed hypergonadotropic hypogonadism. Conventional cytogenetic procedures giemsa trypsin giemsa (GTG) and high resolution banding (HRB) and molecular cytogenetic techniques Fluorescence In Situ Hybridization (FISH) performed on high-resolution lymphocyte chromosomes revealed the karyotype 46,XX, t(Y;15)(q12;p11). SRY-gene was confirmed to be present by classical Polymerase Chain Reaction (PCR) methods. His father carried de novo derivative chromosome 15 [45,X, t(Y;15)(q12;p11)] and was fertile; the karyotype of the father using G-band technique confirmed a reciprocal balanced translocation between chromosome Y and 15. In the proband, the der (15) has been inherited from the father because the mother had a normal karyotype (46,XX). In the proband, the der (15) could have produced genetic imbalance leading to unbalanced robertson translocation between chromosome Y and 15, which might have resulted in azoospermia and infertility in the proband. The paternal translocation might have lead to formation of imbalanced ova, which might be resulted infertility in the proband. Sister's karyotypes was normal (46,XX) while his brother was not analyzed.

Interchromosomal effect analyses by sperm FISH: incidence and distribution among reorganization carriers

Structural reorganization carriers usually present compromised fertility accompanied by an increased risk of producing gametes with chromosomal abnormalities that can be transmitted to the offspring. In part these imbalances are ascribed to result from the occurrence of meiotic disturbances produced by the rearrangements in the proper segregation of other chromosome pairs. This phenomenon of interference has been called interchromosomal effect (ICE). Several studies have been performed to assess the occurrence of ICE in structural reorganization carriers by analyzing the frequencies of numerical abnormalities in the gametes. Nevertheless, the occurrence and distribution of these disturbing events still is a controversial issue. In this work we present compiled data from 130 sperm fluorescent in situ hybridization (FISH) studies performed in carriers of the most frequent structural rearrangements in humans: 44 Robertsonian translocations, 66 reciprocal translocations and 13 inversions. Data from 7 complex/multiple rearrangements will be considered in a separate group. Significant increases of gametes with numerical abnormalities have been detected in all types of reorganization carriers. Among the groups of non-complex/multiple rearrangements, Robertsonian translocations appear to be the most prone to produce such interference (54.5%) closely followed by reciprocal translocations (43.9%). In contrast, ICE's were only detected in 7.7% of the inversion carriers analyzed. The presence of complex/multiple rearrangements seems to be an important factor for promoting ICE, as 71.4% of these carriers presented increased rates of gametes with numerical abnormalities. Altogether, almost half of the structural reorganization carriers (45.4%) present a higher reproductive risk of producing aneuploid/diploid spermatozoa compared to the general population. This high incidence has been obtained by analyzing a small set of chromosomes, suggesting that underlying meiotic disorders could be present in these individuals. Further ICE studies in structural reorganization carriers will help to clarify the still unknown predisposing cytogenetic features that promote this phenomenon.

A normal birth following preimplantation genetic diagnosis by FISH determination in the carriers of der(15)t(Y;15)(Yq12;15p11) translocations: two case reports

PURPOSE

To investigate the clinical application of fluorescence in situ hybridization (FISH) for assessing chromosome disorders of embryos in preimplantation diagnosis of carriers with der(15)t(Y;15)(q12;p11) translocations.

METHODS

Multicolor FISH was performed using directly-labelled DNA probes, chromosome X with one (DXZ1, Xp11.1-q11.1), but Y with two (DYZ3, Yp11.1-q11.1 and DYZ1, Yq12). Normal embryos were transferred on day 6 at blastocyst stage.

RESULTS

Couple A: Three of 6 biopsied embryos were normal. Two normal blastocysts were transferred, but no pregnancy was achieved. Couple B: Three of 6 biopsied embryos were normal. Two normal blastocysts were transferred. A normal male infant weighing 3,230 g was born by cesarean section on the 39th week of gestation. All of the remaining nonreplaced embryos showed mosaic or der(15).

CONCLUSION

Embryos from carries of der(15)t(Y;15)(q12;p11) translocation showed a high frequency of chromosome abnormalities. PGD is a valuable screen tool for those couples to treat their infertility and break the transmission of der(15) chromosome for their offspring.

A family case of fertile human 45,X,psu dic(15;Y) males

We report on a familial case including four male probands from three generations with a 45,X,psu dic(15;Y)(p11.2;q12) karyotype. 45,X is usually associated with a female phenotype and only rarely with maleness, due to translocation of small Y chromosomal fragments to autosomes. These male patients are commonly infertile because of missing azoospermia factor regions from the Y long arm. In our familial case we found a pseudodicentric translocation chromosome, that contains almost the entire chromosomes 15 and Y. The translocation took place in an unknown male ancestor of our probands and has no apparent effect on fertility and phenotype of the carrier. FISH analysis demonstrated the deletion of the pseudoautosomal region 2 (PAR2) from the Y chromosome and the loss of the nucleolus organizing region (NOR) from chromosome 15. The formation of the psu dic(15;Y) chromosome is a reciprocal event to the formation of the satellited Y chromosome (Yqs). Statistically, the formation of 45,X,psu dic(15;Y) (p11.2;q12) is as likely as the formation of Yqs. Nevertheless, it has not been described yet. This can be explained by the dicentricity of this translocation chromosome that usually leads to mitotic instability and meiotic imbalances. A second event, a stable inactivation of one of the two centromeres is obligatory to enable the transmission of the translocation chromosome and thus a stably reduced chromosome number from father to every son in this family.

Studying meiosis: a review of FISH and M-FISH techniques used in the analysis of meiotic processes in humans

It is well known that chromosome in situ hybridization allows the unequivocal identification of targeted human somatic chromosomes. Different fluorescent in situ hybridization (FISH) techniques have been developed throughout the years and, following the mitotic studies, meiotic analyses have been performed using these different techniques. The introduction of M-FISH techniques to the analysis of meiotic cells has allowed the study of meiotic processes for every individual human chromosome. In this paper, we review the different FISH and M-FISH techniques that have been used on human meiotic cells in both men and women.

SUMO-1, human male germ cell development, and the androgen receptor in the testis of men with normal and abnormal spermatogenesis

Sumoylation affects multiple cellular events, including chromatin inactivation and transcriptional repression. Our data provide the first characterization of small ubiquitin-related modifier-1 (SUMO-1) expression during human spermatogenesis by the use of high-resolution cellular SUMO-1 bioimaging. During human meiotic prophase, SUMO-1 localizes to sex chromosomes and centromeric and pericentromeric chromatin. As human spermatocytes progress toward the end of prophase in meiosis I, SUMO-1 is no longer detected within the sex body and pericentromeric heterochromatin but localizes exclusively to centromeres. SUMO-1 localization along sex chromosome axes, pseudoautosomal region, and centromeres of both chromosomes supports a role for SUMO-1 sumoylation in epigenetic events occurring over the entire sex body, e.g., meiotic sex chromosome inactivation and chromatin condensation. Centromeric SUMO-1 throughout meiotic prophase suggests a role in centromeric chromatin condensation and/or other centromere/kinetochore functions. SUMO-1 is likely involved in both facultative and constitutive heterochromatin processes in spermatocytes. Haploid round spermatids show a consistent association of SUMO-1 with centromeric clusters. During spermatid elongation, SUMO-1 localizes in the manchette perinuclear ring. Steroidogenic Leydig cells show some cytoplasmic but strong nuclear and perinuclear SUMO-1. Peritubular myoepithelial cell SUMO-1 colocalizes with centromeric heterochromatin. In epithelial Sertoli cells, when associated with centromeric heterochromatin, SUMO-1 is adjacent but not colocalized with the nucleolus. Male germ cells demonstrate no SUMO-1 nucleolar association. Human and rodent Sertoli cells consistently show an inverse correlation between androgen receptor (AR) and SUMO-1 expression and compartmentalization. Sertoli cells from certain infertile patients, however, showed greatly decreased SUMO-1 and AR. Our data suggest that human testicular SUMO-1 has specific functions in heterochromatin organization, meiotic centromere function, and gene expression.

Behaviour of human heterochromatic regions during the synapsis of homologous chromosomes

BACKGROUND

Alterations of synapsis can disturb or arrest meiosis and result in infertility. Synaptic abnormalities are frequently observed in infertile patients but also in fertile men.

METHODS

The subtelomere-specific multiplex fluorescence in-situ hybridization (stM-FISH) has been applied in combination with immunofluorescence to identify all synaptonemal complexes (SCs) and to analyse those presenting synaptic anomalies in fertile and infertile men.

RESULTS

SCs with heterochromatin blocks other than centromere (noncentromeric heterochromatin) presented a higher frequency of gaps (SC discontinuities) and splits (unsynapsed SC regions) at pachytene, the incidences for 9qh, 1qh, 15p and 21p being the highest ones. Inter-individual variability in the incidence of synaptic anomalies in these regions has been observed. In addition, synaptic anomalies in other SC regions are more frequent in infertile cases than in controls. Clear association of the SC15 and SC21 to the XY pair has been seen.

CONCLUSION

Noncentromeric heterochromatic regions are the last to synapse. The inter-individual variation observed in the incidence of gaps and splits in these regions may be explained by the heteromorphism of these regions in the general population. The presence of synaptic anomalies in other SC regions may indicate nuclei with a severely affected synapsis. Noncentromeric heterochromatic regions might play a role in the association of autosomal SC15 and SC21 with the XY pair.

Establishment of male-specific epigenetic information

The setting of male-specific epigenetic information is a complex process, which involves a major global re-organisation, as well as localized changes of the nucleus structure during the pre-meiotic, meiotic and post-meiotic stages of the male germ cell differentiation. Although it has long been known that DNA methylation in targeted regions of the genome is associated with male-specific genomic imprinting, or that most core histones are hyperacetylated and then replaced by sperm-specific proteins during the post-meiotic condensation of the nucleus, many questions remain unanswered. How these changes interact, how they affect the epigenetic information and how the paternal epigenetic marks contribute to the future genome are indeed major issues remaining to be explored.

HP1beta and HP1gamma, but not HP1alpha, decorate the entire XY body during human male meiosis

During meiosis in male mammals, the X and Y chromosomes become heterochromatic and transcriptionally silent, and form the XY body. Although the HP1 proteins are known to be involved in the packaging of chromosomal DNA into repressive heterochromatin domains, their involvement in facultative heterochromatinization has not been precisely determined. Here, we analyse, for the first time in humans, the subcellular distribution of the heterochromatin protein HP1alpha, HP1beta and HP1gamma isoforms, in male pachytene spermatocytes, and the XY body facultative heterochromatin in particular. Our results demonstrate that HP1beta and HP1gamma, but not the HP1alpha isoforms, decorate the entire XY body in half the pachytene nuclei observed. In some nuclei, the XY body appears to be only partially labelled. In these cases, the HP1beta and HP1gamma signals are adjacent to the Yq12 constitutive heterochromatin and signal appears to originate in this region before spreading over the entire XY body. This distribution suggests that HP1beta and HP1gamma proteins, which are components of the constitutive heterochromatin, may also be involved in the facultative heterochromatinization of the XY body. Nevertheless, their absence from the early pachytene substage, even though the XY body is already condensed, suggests that these proteins are not involved in the initiation of this process.

Recurrent trisomy 15 in a female carrier of der(15)t(Y;15)(q12;p13)

We report on a female carrier of der(15) t(Y;15)(q12;p13) who had two pregnancy losses with trisomy 15 and one with tetraploidy. Molecular analysis showed that both non-disjunction events resulting in the trisomy 15 pregnancies occurred in maternal meiosis I. This finding raises the possibility that there may be an increased risk for trisomy 15 in some carriers of unbalanced t(Y;15) which, if followed by trisomic zygote rescue, may lead to uniparental disomy (UPD).

Organization of the X and Y chromosomes in human, chimpanzee and mouse pachytene nuclei using molecular cytogenetics and three-dimensional confocal analyses

We used multicolour fluorescence in-situ hybridization on air-dried pachytene nuclei to analyse the structural and functional domains of the sex vesicle (SV) in human, chimpanzee and mouse. The same technology associated with 3-dimensional analysis was then performed on human and mouse pachytene nuclei from cytospin preparations and tissue cryosections. The human and the chimpanzee SVs were very similar, with a consistently small size and a high degree of condensation. The mouse SV was most often seen to be large and poorly condensed, although it did undergo progressive condensation during pachynema. These results suggest that the condensation of the sex chromosomes is not a prerequisite for the formation of the mouse SV, and that a different specific mechanism could be responsible for its formation. We also found that the X and Y chromosomes are organized into two separate and non-entangled chromatin domains in the SV of the three species. In each species, telomeres of the X and Y chromosomes remain clustered in a small area of the SV, even those without a pseudoautosomal region. The possible mechanisms involved in the organization of the sex chromosomes and in SV formation are discussed.

Evaluation of meiotic impairment of azoospermic men by fluorescence in situ hybridization

OBJECTIVE

To identify predictive criteria for the existence of spermatogenesis in nonobstructive azoospermic men.

DESIGN

Prospective study.

SETTING

Andrology laboratory at a teaching hospital.

PATIENT(S)

Twenty-two azoospermic men were divided into three groups by qualitative testicular histopathology and the presence of spermatozoa in minced biopsies.

INTERVENTION(S)

Testicular biopsies evaluation.

MAIN OUTCOME MEASURE(S)

The presence of spermatozoa and/or mature spermatids, the percentage of sex vesicle formation (X and Y chromosomes in proximity), and the pairing of the two 18 homologous chromosomes.

RESULT(S)

Spermatozoa and mature spermatids were found in 17 study patients. Whenever few mature spermatids and/or spermatozoa were found, the rates of X-Y and 18 bivalents were significantly higher (mean +/- SD, 73% +/- 13. 3% and 91% +/- 7.1%) than those in cases of spermatocyte maturation arrest (23% +/- 8.0% and 60% +/- 11.8%, respectively).

CONCLUSION(S)

Pairing of chromosomes during meiosis is apparently related to the progression of spermatogenesis. Consequently, high rates of bivalent formation increase the prospect of focal spermatogenesis in the testis, despite the failure to identify mature spermatids in the specific testicular biopsy under examination.