An azoospermic man with a de novo point mutation in the Y-chromosomal gene USP9Y

Current concepts of human azoospermia and its causes

Infertility is a serious social problem in advanced nations today. One of the most important causes is the male factor. Striking progress has been achieved in recent years in elucidating the mechanisms of spermatogenesis in mice by experimental methods represented by the knockout mouse. Although many factors associated with male infertility are known in mice, the translation of this information to people has been slow. This is because the knockout mouse phenotype cannot necessarily be reproduced faithfully in humans. However, it is known that environmental factors, chromosomal defects and several specific gene mutations result in human male infertility. In this review, we first discuss the environmental factors considered likely to be involved in male infertility, and secondly we describe the Y chromosome and several important genes on the Y chromosome that play critical roles in spermatogenesis in humans. Then, we demonstrate the three critical genes identified in our laboratory in autosomes involved in human spermatogenesis, the SYCP3, MEI1 and PARP-2. Finally, we explain the future directionality and possibilities of research in this field.

A biopsy sample reduction approach to identify significant alterations of the testicular transcriptome in the presence of Y-chromosomal microdeletions that are independent of germ cell composition

Y-chromosomal microdeletions (YCMD) are the major genetic cause of male infertility. To date, it is not known which global changes are induced by the presence of AZFc or AZFb + c deletions in the human testicular transcriptome. We investigated this question by microarray analysis in which we had to eliminate the ‘germ cell effect’, i.e., the dominating effect of germ cell transcripts due to the quantitative difference in germ cell composition in samples with/without YCMD. This problem was tackled by selecting 26 samples from an initial cohort of 34 samples by their homogeneity in respect to cellular composition as obtained from gene expression clustering. This way, the ‘germ cell effect’ was minimized, and a distinct ‘deletion effect’ became more apparent. Several hundred genes are influenced by YCMD as shown on the three different phenotypes hypospermatogenesis, meiotic arrest, and Sertoli-cell only syndrome. We validated on an independent cohort of samples five genes by quantitative real-time PCR that are expressed in germ cells or the somatic compartment and which are exclusively altered by the presence of YCMD. We conclude that the deletion of Y-chromosomal genes has a significant effect on spermatogenesis by modulating the transcriptional network of the germ cell and somatic compartment.

Aneuploidies in embryos and spermatozoa from patients with Y chromosome microdeletions

In patients with Y chromosome microdeletions and high percentage of numeric chromosome abnormalities detected by fluorescence in situ hybridization on sperm, a high percentage of abnormal embryos was observed compared with oligozoospermic patients without Y chromosome microdeletions, with a significant increase in the percentage of embryos with monosomy X. Differences in fertilization rates between the different patient groups were not observed; however, blastocyst rates were significantly impaired in patients with Y chromosome microdeletions.

Genetic dissection of the AZF regions of the human Y chromosome: thriller or filler for male (in)fertility?

The azoospermia factor (AZF) regions consist of three genetic domains in the long arm of the human Y chromosome referred to as AZFa, AZFb and AZFc. These are of importance for male fertility since they are home to genes required for spermatogenesis. In this paper a comprehensive analysis of AZF structure and gene content will be undertaken. Particular care will be given to the molecular mechanisms underlying the spermatogenic impairment phenotypes associated to AZF deletions. Analysis of the 14 different AZF genes or gene families argues for the existence of functional asymmetries between the determinants; while some are prominent players in spermatogenesis, others seem to modulate more subtly the program. In this regard, evidence supporting the notion that DDX3Y, KDM5D, RBMY1A1, DAZ, and CDY represent key AZF spermatogenic determinants will be discussed.

Examination of disease-based selection, demographic history and population structure in European Y-chromosome haplogroup I

We attempted to refine the understanding of an association of Y-chromosomal haplogroup I (hg-I) with enhanced AIDS progression that had been previously reported. First, we compared the progression phenotype between hg-I and its phylogenetically closest haplogroup J (hg-J). Then, we took a candidate gene approach resequencing DDX3Y, a crucial autoimmunity gene, in hg-I and other common European Y- chromosome haplogroups looking for functional variants. We extended the genetic analyses to CD24L4 and compared and contrasted the roles of disease based selection, demographic history, and population structure shaping the contemporary genetic landscape of hg-I chromosomes. Our results confirmed and refined the AIDS progression signal to hg-I, though no gene variant was identified that can explain the disease association. Molecular evolutionary and genetic analyses of the examined loci suggested a unique evolutionary history in hg-I, probably shaped by complex interactions of selection, demographic history, and high geographical differentiation leading to the formation of distinct hg-I subhaplogroups that today are associated with HIV/AIDS onset. Clearly, further studies on Y chromosome candidate loci sequencing to discover functional variants and discern the roles of evolutionary factors are warranted.

[Male infertility and gene defects]

About 15% of the couples at reproductive age worldwide suffer from infertility. It is estimated that 50% of the entity result from male itself. The mechanism of male infertility is quite complicated, attributing to inherent and environment factors of the infertility patients, of which defects of fertility-related genes are of importance for its occurrence. The clinical features of male infertility vary from azoospermia to oligoasthenoteratozoospermia. This paper presents the relationship between the known defects in genes and male infertility.

Expression and localization of the deubiquitinating enzyme mUBPy in wobbler mouse testis during spermiogenesis

Mouse ubiquitin-specific processing protease (mUBPy) is a deubiquitinating enzyme highly expressed in both brain and testis. In testis, it interacts with the DnaJ protein, MSJ-1; both mUBPy and MSJ-1 are located on the cytoplasmic surface of the developing acrosome and in the centrosomal region during spemiogenesis. Present data show the first appearance in testis of mUbpy mRNA and protein at 10 days post-partum (d.p.p.). In addition, to investigate on a possible role of mUBPy in sperm formation, we took advantage of mutant wr/wr (wobbler) mice characterized by male infertility, which is likely due to the lack of a real, functional acrosome. RT-PCR and Northern blot analyses show that mUbpy is up-regulated in adult wobbler testis. Furthermore, in wild-type testis mUBPy protein is primarily detected by Western blot in the soluble (cytosolic/nuclear) fraction during the first round of spermatogenesis and in the adult. By contrast, mUBPy is primarily detected in membranous/insoluble protein fraction when wobbler phenotype is clearly shown (30 d.p.p.) and in adult wobbler testis. By immunohistochemistry, whereas in wild-type animals mUBPy marks the profile of the acrosomic vesicle in differentiating spermatids, in wobbler mice only a detergent pre-treatment procedure allows to detect mUBPy immunoreactivity, which results in diffuse spotted granules inside the cytoplasm and around the nuclear shape. In conclusion, in wobbler testis expression of mUbpy is up-regulated, while a differential sorting of the protein characterizes wobbler spermatids where acrosome formation is impaired.

Alterations in the steroid hormone receptor co-chaperone FKBPL are associated with male infertility: a case-control study

BACKGROUND

Male infertility is a common cause of reproductive failure in humans. In mice, targeted deletions of the genes coding for FKBP6 or FKBP52, members of the FK506 binding protein family, can result in male infertility. In the case of FKBP52, this reflects an important role in potentiating Androgen Receptor (AR) signalling in the prostate and accessory glands, but not the testis. In infertile men, no mutations of FKBP52 or FKBP6 have been found so far, but the gene for FKBP-like (FKBPL) maps to chromosome 6p21.3, an area linked to azoospermia in a group of Japanese patients.

METHODS

To determine whether mutations in FKBPL could contribute to the azoospermic phenotype, we examined expression in mouse and human tissues by RNA array blot, RT-PCR and immunohistochemistry and sequenced the complete gene from two azoospermic patient cohorts and matching control groups. FKBPL-AR interaction was assayed using reporter constructs in vitro.

RESULTS

FKBPL is strongly expressed in mouse testis, with expression upregulated at puberty. The protein is expressed in human testis in a pattern similar to FKBP52 and also enhanced AR transcriptional activity in reporter assays. We examined sixty patients from the Japanese patient group and found one inactivating mutation and one coding change, as well as a number of non-coding changes, all absent in fifty-six controls. A second, Irish patient cohort of thirty showed another two coding changes not present in thirty proven fertile controls.

CONCLUSIONS

Our results describe the first alterations in the gene for FKBPL in azoospermic patients and indicate a potential role in AR-mediated signalling in the testis.

LMTK2 and PARP-2 gene polymorphism and azoospermia secondary to meiotic arrest

PURPOSE

To investigate whether the human LMTK2 and PARP-2 gene defects are associated with azoospermia by meiotic arrest, mutational analysis was performed on Japanese men with azoospermia.

METHODS

Via direct sequencing, mutational screening was carried out on the exon region of the genes, using genomic DNAs from 18 Japanese men. Statistical analysis was done on the detected single nucleotide polymorphisms (SNPs) in the patients and normal controls.

RESULTS

Nine SNPs were detected in LMTK2 and five SNPs were detected in PARP-2. There were no significant differences in the genotype distribution and allele frequencies between the two groups in LMTK2. However, the genotype frequency of heterozygotes in SNP1 of PARP-2 was higher in the patient group. The haplotype analysis revealed that SNP1-SNP4 (T-A) of PARP-2 was significantly more frequent in the patient group.

CONCLUSION

The PARP-2 gene might be associated with azoospermia by meiotic arrest in humans.

A single nucleotide polymorphism in SPATA17 may be a genetic risk factor for Japanese patients with meiotic arrest

Genetic mechanisms have been implicated as a cause of some cases of male infertility. Recently, 10 novel genes involved in human spermatogenesis were identified by microarray analysis of human testicular tissue. One of these is spermatogenesis-associated 17 (SPATA17). To investigate whether defects in the SPATA17 gene are associated with azoospermia due to meiotic arrest, a mutational analysis was conducted, in which the SPATA17 coding regions of 18 Japanese patients with this condition were sequenced. A statistical analysis was carried out that included 18 patients with meiotic arrest, 20 patients with Sertoli-cell-only syndrome (SCOS) and 96 healthy control men. No mutations were found in SPATA17. However, three coding single nucleotide polymorphisms (cSNPs: SNP1-SNP3) were detected in the patients with meiotic arrest. No significant differences in the genotype or allele frequencies of SNP1 and SNP2 were found between patients with meiotic arrest and the others. However, the frequency of the SNP3 allele was significantly elevated in the meiotic arrest group (P < 0.05). This study suggests that SPATA17 may play a critical role in human spermatogenesis, especially in meiosis.

Two novel mouse genes mapped to chromosome Yp are expressed specifically in spermatids

The male-specific region of the Y chromosome is evolutionarily predisposed to accumulate genes important for spermatogenesis. Recent work in this laboratory identified two novel Y-linked transcripts that were upregulated in the testis in response to deletions on the chromosome arm Yq. This article reports the further characterisation of these two transcripts and their comparison to related X and autosomal genes. Both map to chromosome arm Yp, outside the Sxr ( b ) deletion interval, both are present in at least two copies on the Y, and both are expressed specifically in spermatids. Given the testicular phenotype of mice with deletions on the Y chromosome, both genes are therefore likely to function in spermatid differentiation. AK006152 is a novel mouse-specific gene with a single potential open reading frame, and it is unusual in that there appears to be no X-linked relative. H2al2y is a novel histone in the H2A superfamily and has multiple X-linked relatives and a single autosomal relative in mouse. The presence of a single X-linked copy in rat suggests that H2al amplification is mouse-specific, with the alternative explanation being an earlier amplification followed by gene loss. A phylogenetic analysis of H2al genes together with other H2A genes indicates that H2al is most closely related to the mammalian-specific H2A.Bbd family of histones. Interestingly, K (a)/K (s) analysis indicates that the X and Y members of the H2al family may be under positive selection in mouse, while the autosomal copy is under purifying selection and presumably retains the ancestral function.

Spermatogenesis in a man with complete deletion of USP9Y

Deletions in the azoospermia factor region AZFa on the human Y chromosome and, more specifically, in the region that encompasses the ubiquitin-specific peptidase 9, Y-linked gene USP9Y have been implicated in infertility associated with oligospermia and azoospermia. We have characterized in detail a deletion in AZFa that results in an absence of USP9Y in a normospermic man and his brother and father. The association of this large deletion with normal fertility shows that USP9Y, hitherto considered a candidate gene for infertility and azoospermia, does not have a key role in male reproduction. These results suggest that it may not be necessary to consider USP9Y when screening the Y chromosome of infertile or subfertile men for microdeletions.

Two single nucleotide polymorphisms in PRDM9 (MEISETZ) gene may be a genetic risk factor for Japanese patients with azoospermia by meiotic arrest

PURPOSE

To investigate whether defects in human PRDM9, CDK2 and PSMC3IP are associated with azoospermia Mutational analysis was performed in Japanese patients with azoospermia caused by meiotic arrest.

METHODS

Mutational screening of the coding regions of human PRDM9, CDK2 and PSMC3IP was done by direct sequencing using genomic DNA from 18 Japanese patients. Statistical analysis of the detected coding single nucleotide polymorphisms (cSNPs) in patients and normal control men was then carried out.

RESULTS

One cSNP was detected in CDK2 and PSMC3IP. There were no significant differences in genotype distribution and allele frequencies between the patient and control groups in these two genes. However, three novel cSNPs were detected in the PRDM9. The genotype and allele frequencies of heterozygotes in SNP2 and SNP3 of PRDM9 were significantly higher in the patient group than in the control group.

CONCLUSION

We found a possible association between PRDM9 and azoospermia by meiotic arrest.

Transgenic rescue of ataxia mice reveals a male-specific sterility defect

Homozygous ataxia (ax(J)) mice have reduced expression of ubiquitin-specific protease 14 (Usp14), resulting in severe neuromuscular defects and death by 2 months of age. Transgenic expression of Usp14 exclusively in the nervous system of ax(J) mice (ax(J)-Tg) prevents early lethality and restores motor system function to the ax(J) mice, enabling an analysis of the reproductive capabilities of Usp14-deficient mice. Although female ax(J)-Tg mice had a 75% reduction of Usp14 in the ovaries, they were able to produce normal litters. Ovary transfer experiments also demonstrated that the ovaries of ax(J) mice were capable of producing viable pups. In contrast, male ax(J) and ax(J)-Tg mice displayed a 50% reduction in testicular Usp14 levels and were infertile, indicating that Usp14 is required for development and function of the male reproductive system. Immunohistochemistry experiments showed that Usp14 is found in the redundant nuclear envelope and cytoplasmic droplet of epididymal spermatozoa. Analysis of ax(J) testes demonstrated a 50% reduction in testis weight, a 100-fold reduction in sperm number and the presence of abnormal spermatozoa in the epididymis. Histological examination of the Usp14-deficient testes revealed abnormal spermatogenesis and the presence of degenerating germ cells, indicating that Usp14 and the ubiquitin proteasome system are required for spermatid differentiation during spermiogenesis.

An evolutionary perspective on Y-chromosomal variation and male infertility

Genetic variation on the Y chromosome is one of the best-documented causes of male infertility, but the genes responsible have still not been identified. This review discusses how an evolutionary perspective may help with interpretation of the data available and suggest novel approaches to identify key genes. Comparison with the chimpanzee Y chromosome indicates that USP9Y is dispensable in apes, but that multiple copies of TSPY1 may have an important role. Comparisons between infertile and control groups in search of genetic susceptibility factors are more complex for the Y chromosome than for the rest of the genome because of population stratification and require unusual levels of confirmation. But the extreme population stratification exhibited by the Y also allows populations particularly suitable for some studies to be identified, such as the partial AZFc deletions common in Northern European populations where further dissection of this complex structural region would be facilitated.

The AZF proteins

The azoospermia factor (AZF) locus in Yq11 is now functionally subdivided in three distinct spermatogenesis loci: AZFa, AZFb and AZFc. After knowledge of the complete genomic Y sequence in Yq11, 14 Y genes encoding putatively functional proteins and expressed in human testis are found to be located in one of the three AZF intervals. Therefore, a major question for each infertility clinic performing molecular screening for AZF deletions has now raised concerning the functional contribution of the encoded AZF proteins to human spermatogenesis. Additionally, it has been shown that distinct chromatin regions in Yq11 overlapping with the genomic AZFb and AZFc intervals are probably involved in the pre-meiotic X and Y chromosome pairing process. An old hypothesis on the germ line function of AZF becomes therefore revitalized. It proposed a specific chromatin folding code in Yq11, which controls the condensation cycle of the Y chromosome in the male germ line. Thus, with the exception of AZF proteins functionally expressed during the pre-meiotic differentiation and proliferation of spermatogonia, the need for AZF proteins functionally expressed at meiosis or during the post-meiotic spermatid maturation process is difficult to assess before the identification of specific mutations in the corresponding AZF gene causing male infertility.

The genetic basis of male reproductive failure

Evolving therapies have allowed the use of sperm from men with spermatogenic compromise, obstructive azoospermia, and sperm functional deficiency, enabling these men to procreate when unable to do so naturally. The genetic basis of only a portion of these conditions is known and research must be pursued into the genetic underpinnings of those that have not yet been delineated. Education and provision of information to patients is the responsibility of all involved in the care of men with reproductive failure. The author concentrates on some of the known causes of nonobstructive azoospermia and obstructive azoospermia with a well-established genetic cause such as congenital bilateral absence of the vas deferens.

Gene polymorphisms/mutations relevant to abnormal spermatogenesis

Despite the identification of an increasing number of candidate genes involved in spermatogenesis, the armamentarium of diagnostic genetic tests in male infertility remains extremely limited. A number of new causative mutations have been reported for hypogonadotrophic hypogonadism but still the genetic diagnosis in this pathological condition is made only in about 20% of cases. The sole molecular genetic test that is routinely proposed in severe spermatogenic disturbances is screening for Yq microdeletion. The search for causative mutations in the Y chromosome, and in autosomal and X-linked genes, has mostly been unsuccessful. The paucity of gene mutations raises questions about the appropriateness of the currently used screening approaches. Among the proposed genetic risk factors, gr/gr deletion of the Y chromosome seems to be the most promising polymorphism. Other polymorphisms are awaiting further confirmation, whereas for some (POLG, DAZL, USP26, FSHR) a lack of association with abnormal spermatogenesis has now been ascertained. It is likely that some polymorphisms lead to testicular dysfunction only when in association with a specific genetic background or with environmental factors. Future large-scale studies with stringent study design may provide a more efficient way to identify clinically relevant genetic factors of male infertility.

Study of azoospermia factor-a deletion caused by homologous recombination between the human endogenous retroviral elements and population-specific alleles in Japanese infertile males

OBJECTIVE

To evaluate the relationship between the status of homologous recombination and population-specific alleles in infertile Japanese males with azoospermia factor (AZF)-a deletions and to characterize the clinical features of these patients.

DESIGN

Retrospective deletion study in infertile Japanese men.

SETTING

University hospital and reproductive clinic.

PATIENT(S)

A total of 931 consecutive patients visiting a male-infertility clinic were genetically evaluated.

INTERVENTION(S)

Patients were analyzed for Y-chromosomal microdeletions and the breakpoints of intrachromosomal homologous recombination of human endogenous retrovirus (HERV) 15qy; in addition, Y-haplogroup typing on the basis of polymerase chain reaction also was performed. Endogenous retroviruses contribute to the evolution of the host genome and can be associated with disease.

MAIN OUTCOME MEASURE(S)

Presence or absence of appropriately sized polymerase chain reaction products.

RESULT(S)

Four cases of AZFa deletions were found. All patients with AZFa deletions had an azoospermia and breakpoints in the ID2 region of HERV15qy. Three of the four cases were derived from Y-haplogroup D2b. Testicular sperm extraction procedures were performed in three of these four patients, and elongated spermatids were recovered in two. However, no pregnancies were successfully achieved.

CONCLUSION(S)

Y-haplotype D2b, specific for some Japanese clade, may be associated with HERV breakpoints that lead to intrachromosomal homologous recombination. From the clinical point of view, the testicular sperm extraction procedure is not applicable to males with complete AZFa deletions.

New binary polymorphisms reshape and increase resolution of the human Y chromosomal haplogroup tree

Markers on the non-recombining portion of the human Y chromosome continue to have applications in many fields including evolutionary biology, forensics, medical genetics, and genealogical reconstruction. In 2002, the Y Chromosome Consortium published a single parsimony tree showing the relationships among 153 haplogroups based on 243 binary markers and devised a standardized nomenclature system to name lineages nested within this tree. Here we present an extensively revised Y chromosome tree containing 311 distinct haplogroups, including two new major haplogroups (S and T), and incorporating approximately 600 binary markers. We describe major changes in the topology of the parsimony tree and provide names for new and rearranged lineages within the tree following the rules presented by the Y Chromosome Consortium in 2002. Several changes in the tree topology have important implications for studies of human ancestry. We also present demography-independent age estimates for 11 of the major clades in the new Y chromosome tree.

Reconstructing phylogenies and phenotypes: a molecular view of human evolution

This review broadly summarizes how molecular biology has contributed to our understanding of human evolution. Molecular anthropology began in the 1960s with immunological comparisons indicating that African apes and humans were closely related and, indeed, shared a common ancestor as recently as 5 million years ago. Although initially dismissed, this finding has proven robust and numerous lines of molecular evidence now firmly place the human-ape divergence at 4-8 Ma. Resolving the trichotomy among humans, chimpanzees and gorillas took a few more decades. Despite the readily apparent physical similarities shared by African apes to the exclusion of modern humans (body hair, knuckle-walking, thin tooth enamel), the molecular support for a human-chimpanzee clade is now overwhelming. More recently, whole genome sequencing and gene mapping have shifted the focus of molecular anthropology from phylogenetic analyses to phenotypic reconstruction and functional genomics. We are starting to identify the genetic basis of the morphological, physiological and behavioural traits that distinguish modern humans from apes and apes from other primates. Most notably, recent comparative genomic analyses strongly indicate that the marked differences between modern humans and chimpanzees are likely due more to changes in gene regulation than to modifications of the genes themselves, an idea first proposed over 30 years ago. Almost weekly, press releases describe newly identified genes and regulatory elements that seem to have undergone strong positive selection along the human lineage. Loci involved in speech (e.g. FOXP2), brain development (e.g. ASPM), and skull musculature (e.g. MYH16) have been of particular interest, but some surprising candidate loci (e.g. those involved in auditory capabilities) have emerged as well. Exciting new research avenues, such as the Neanderthal Genome Project, promise that molecular analyses will continue to provide novel insights about our evolution. Ultimately, however, these molecular findings can only be understood in light of data from field sites, morphology labs, and museum collections. Indeed, molecular anthropology depends on these sources for calibrating molecular clocks and placing genetic data within the context of key morphological and ecological transitions in human evolution.

Evolutionary and expression analysis of the zebrafish deubiquitylating enzyme, usp9

Mouse Usp9x/Fam (fat facets in mouse) and its Drosophila ortholog faf (fat facets) encode substrate-specific deubiquitylating enzymes and are essential for early embryonic development. The zebrafish (Danio rerio) is a powerful tool for studying embryonic gene expression patterns and function, and to that end, we sought to characterize the zebrafish Usp9 ortholog. Zebrafish usp9 was identified from database searches, and the predicted Usp9 protein is very highly conserved in mouse (90% identical and 94% similar) over its entire length. Phylogenetic analysis indicated that vertebrate Usp9s are highly clustered and separate from the USP9Y and Drosophila forms. We examined the developmental expression of usp9 from fertilization to 2 days postfertilization. usp9 is initially expressed ubiquitously but later restricted to the cephalic central nervous system, the developing lens, distal tips of the pectoral fin bud, and migrating endoderm. The extraordinary level of conservation between the mouse and zebrafish genes, coupled with equivalent expression patterns, makes zebrafish an appropriate complementary system for the study of usp9 in development.

DDX3Y encodes a class I MHC-restricted H-Y antigen that is expressed in leukemic stem cells

The Y chromosome encodes male-specific minor histocompatibility (H-Y) antigens that stimulate T- and B-lymphocyte responses after sex-mismatched allogeneic hematopoietic cell transplantation (HCT). A CD8(+) cytotoxic T lymphocyte (CTL) clone that recognizes a novel HLA-B*2705-restricted H-Y antigen encoded by the DDX3Y gene was isolated from a male who had received a hematopoietic cell graft from his human leukocyte antigen (HLA)-identical sister. The antigenic peptide is a decamer that differs from the homologous DDX3X-encoded peptide at 4 positions. Expression of DDX3Y and of the H-Y epitope that it encodes was examined by quantitative polymerase chain reaction (PCR) and by CTL recognition assays. Expression of DDX3Y is detected in all myeloid and lymphoid leukemic cells that carry an intact Y chromosome. Moreover, the DDX3Y-encoded H-Y epitope is presented on the surface of both myeloid and lymphoid leukemic cells from male HLA-B*2705(+) patients. DDX3Y-specific CTLs prevent engraftment of human acute leukemia in nonobese diabetic/severe combined immune deficient mice, demonstrating that the DDX3Y-encoded H-Y antigen is also expressed in leukemic stem cells. These results demonstrate that CD8(+) T-cell responses against DDX3Y have the potential to contribute to graft-versus-leukemia (GVL) activity after female into male allogeneic HCT. This study is registered at http://clinicaltrials.gov as NCT00107354.

A rare Y chromosome missense mutation in exon 25 of human USP9Y revealed by pyrosequencing

Ubiquitin-specific protease 9, Y-linked (USP9Y), is a protein encoded by the Y chromosome. Its precise function in the cell is unknown, although a role in the regulation of protein turnover has been postulated. Nonetheless, mutations in this gene could result in the over- or under-abundance of proteins involved in the regulation of spermatogenesis. We have identified a novel mutation, SM1, located in exon 25 of USP9Y (c.3642G-->A), which results in an amino acid substitution (p.V1214I). The mutation is in close linkage (four bases distant) from a silent mutation, referred to as M222 (p.E1212E, c.3636G-->A). In our male population (n = 374), SM1 was found in one individual (0.3%) who belongs to the recently described haplogroup R1b3h, defined by the U152 SNP. This new mutation is expected to represent a new haplogroup, (R1b1c10a); therefore, within our population of individuals from haplogroup R1b3h (R1b110) (n = 16), it has a frequency of 6.3% (95% CI: 2.7-9.9%).

Molecular and clinical characterization of Y chromosome microdeletions in infertile men: a 10-year experience in Italy

CONTEXT

An explosive growth in Y chromosome long arm (Yq) microdeletion testing demand for male infertility occurred in the past few years. However, despite the progresses in the biology of this chromosome, a number of molecular and clinical concerns are not supported by definitive data.

OBJECTIVE

The objective was to provide information on the type and prevalence of microdeletions in infertile males, indication for testing, genotype-phenotype correlation, sperm aneuploidies, and genetic counseling.

DESIGN AND SETTING

We performed a prospective study from January 1996 to December 2005 in an academic clinic.

PATIENTS

We studied 3073 consecutive infertile men, of which 625 were affected by nonobstructive azoospermia and 1372 were affected by severe oligozoospermia. Ninety-nine patients with microdeletions are described here.

MAIN OUTCOME MEASURES

Yq microdeletions, seminal analysis, reproductive hormones, testicular cytology/histology, and sperm sex chromosomes aneuploidies were used as outcome measures.

RESULTS

The prevalence of microdeletions was 3.2% in unselected infertile men, 8.3% in men with nonobstructive azoospermia, and 5.5% in men with severe oligozoospermia. Only 2 of 99 deletions were found in men with more than 2 million sperm/ml. No clinical data are useful to identify a priori patients with higher risk of Yq microdeletions. Most deletions are of the AZFc-b2/b4 subtype and are associated with variable spermatogenic phenotype, with sperm present in 72% of the cases. Complete AZFa and AZFb (P5/Proximal P1) deletions are associated with Sertoli cell-only syndrome and alterations in spermatocyte maturation, respectively, whereas partial deletions in these regions are associated with milder phenotype and frequent presence of sperm. Men with AZFc-b2/b4 deletions produce a higher percentage of sperm with nullisomy for the sex chromosomes and XY-disomy.

CONCLUSIONS

This extensive clinical research expands the knowledge on genotype-phenotype relationships and confirms that the identification of Yq microdeletions has significant diagnostic and prognostic value, adding useful information for genetic counseling in these patients.

A simplified gene-specific screen for Y chromosome deletions in infertile men

OBJECTIVE

To test the diagnostic efficiency of a gene-specific, five-marker screening strategy for the detection of Y chromosome deletions.

DESIGN

Prospective case study.

SETTING

University genetics laboratory and reproductive clinics.

PATIENT(S)

Six hundred twenty-seven infertile men and 212 fertile men.

INTERVENTION(S)

Peripheral blood samples were screened for Y chromosome deletions in a triple-blind fashion using three protocols: protocol I consisted of five gene-specific markers, including USP9Y, DBY, SMCY, RBM1, and DAZ; protocol II included 14 gene-specific markers; and protocol III consisted of six sequence-tagged sites (STSs) markers recommended by EAA/EMQN.

MAIN OUTCOME MEASURE(S)

Deletion status of Y chromosome genes or sequence-tagged sites.

RESULT(S)

Protocols I and II identified the same 41 infertile patients with Y deletions. Protocol III identified 38 infertile patients with Y deletions, and all 38 patients were also identified by protocols I and II. One patient with isolated USP9Y deletion and two patients with isolated DBY deletions, as detected by protocols I and II, could not be identified by protocol III.

CONCLUSION(S)

We observed mostly consistent results between our protocols and the EAA/EMQN protocol. This gene-specific, five-marker screening panel provides the same diagnostic efficiency as the EAA/EMQN protocol and may be considered an alternative to the EAA/EMQN protocol.

Polymorphisms of the humanPUMILIO2 gene and male sterility

The highly conserved Pumilio protein plays crucial roles in fertility of many organisms acting as a repressor of translation, and causing infertility when mutated. Although one of two human Pumilio homologs, PUMILIO2 is expressed mainly in the germ line, its role in mammalian germ cell development has not been reported yet. To shed light on the role of PUMILIO2 in development of the human male germ line, we screened this gene for mutations in 137 patients presenting a variety of phenotypes with spermatogenic failure. The first variant, we identified was a single base substitution within intron 15 (IVS15 + 6G > A). This variant was found in three azoospermic males, the second allele being the wild type. However, this variant was also present among fertile males, as frequently as in the patients. Although location of IVS15 + 6G > A substitution in close proximity to the canonical donor splice site GT, indicates that its influence on splicing cannot be excluded, our preliminary cDNA analysis has not revealed evidence of a splicing abnormality of PUMILIO2 pre-mRNA carrying this variant. Nevertheless, this study provides new interesting variant containing a donor splice site variant, which can be relevant for understanding of splicing mechanism of mammalian genes. The second variant, c.774 C > T transversion (Y258Y) in exon 6 was found only in one patient, but an influence on PUMILIO2 function is not obvious. Altogether, this study shows that variation in the PUMILIO2 gene is very low and it seems improbable that mutations of this gene significantly contribute to male infertility in humans.

Is a genetic defect in Fkbp6 a common cause of azoospermia in humans?

FK506-binding protein 6 (Fkbp6) is a member of a gene family containing a prolyl isomerase/FK506-binding domain and tetratricopeptide protein-protein interaction domains. Recently, the targeted inactivation of Fkbp6 in mice has been observed to result in aspermic males and the absence of normal pachytene spermatocytes. The loss of Fkbp6 results in abnormal pairing and a misalignment of the homologous chromosomes, and in non-homologous partner switches and autosynapsis of the X chromosome cores in meiotic spermatocytes. In this study, we analyzed whether human FKBP6 gene defects might be associated with human azoospermia. We performed a mutation analysis in all the coding regions of the human FKBP6 gene in 19 patients with azoospermia resulting from meiotic arrest. The expression of the human FKBP6 gene was specific to the testis, and a novel polymorphism site, 245C --> G (Y60X) could be found in exon 3. Our findings suggest that the human FKBP6 gene might be imprinted in the testis based on an analysis using two polymorphism sites.

Expression profile of AZF genes in testicular biopsies of azoospermic men

BACKGROUND

The Y-chromosome AZF regions include genes whose functions and specific roles in spermatogenesis have not been fully clarified. This study investigated the expression of several AZF (USP9Y, DDX3Y/DDX3Yt1, EIF1AY and PRY) and USP9X transcripts in testicular biopsies of 89 azoospermic men who had been classified by histology and cytology assessments.

METHODS

Expression was analysed by RT-PCR, and some biopsies were evaluated by multiplex RT-PCR. Quantitative PCR was performed in some biopsies to determine the ratio of the testis-specific transcript DDX3Yt1 to the total DDX3Y transcription.

RESULTS

The expression of USP9Y, USP9X and DDX3Y was found in all the specimens tested, whereas DDX3Yt1 expression was diminished or undetectable in several biopsies with impaired spermatogenesis. EIF1AY was detected in all except two of the specimens. Noteworthy, PRY expression was detected mainly in biopsies with germ cells, and this association was significant (P < 0.001). An identical expression profile was obtained by either single or multiplex RT-PCR.

CONCLUSIONS

These findings suggest that PRY is usually expressed in germ cells, whereas the other transcripts are also expressed in testicular somatic cells. The absence of EIF1AY expression might sporadically contribute to azoospermia. The decreased ratio of DDX3Yt1/DDX3Y transcript in impaired spermatogenesis suggests that the DDX3Yt1 transcript is under-expressed in impaired spermatogenesis. The findings contribute to the search and selection of the most valuable gene markers potentially useful as additional tools for predicting complete spermatogenesis by multiplex expression analysis.

Mutations in the testis-specific NALP14 gene in men suffering from spermatogenic failure

BACKGROUND

Because of the common use of ICSI and the potential genetic aetiology of spermatogenic failure, concern has been raised about transmitting genetic disorders to ICSI offspring. However, to date, in only approximately 15% of all cases of spermatogenic failure, an underlying genetic cause can be identified. We have previously established an association between spermatogenic failure and chromosomal region 11p15. In this study, we set out to explore whether NALP14, a gene recently mapped to 11p15, has a function in spermatogenesis and whether mutations in NALP14 can cause spermatogenic failure.

METHODS

We applied two different multiple tissue northern (MTN) blots to determine tissue specificity of NALP14 and performed immunohistochemistry on human testis with anti-NALP14 antiserum. To determine imprinting status of NALP14, we tested the expression pattern of two single-nucleotide polymorphisms (SNPs) in human testis. Finally, we performed a mutation screen of the NALP14 gene in 157 men with azoospermia or severe oligozoospermia by direct sequencing; 158 normospermic men served as controls.

RESULTS

NALP14 was, as are the three other genes in 11p15, exclusively expressed in testis. Within the testis, the NALP14 protein was mainly expressed in A dark spermatogonia, mid and late spermatocytes and spermatids. The mutation screen revealed five mutations that occurred only in the patient group. One of these unique mutations introduced an early stop codon in the NALP14 sequence, predicted to result in a severely truncated protein.

CONCLUSION

Our data suggest that NALP14 has a function in spermatogenesis and that mutations in this gene might cause spermatogenic failure.

Natural transmission of USP9Y gene mutations: a new perspective on the role of AZFa genes in male fertility

Deletions of the azoospermia factor (AZF) regions of the Y chromosome are associated with severe spermatogenic failure and represent the most frequent molecular genetic cause of azoospermia and severe oligozoospermia. The exact role of the candidate AZF genes is largely unknown due to both the extreme rarity of naturally occurring AZF gene-specific mutations and the lack of functional assays. Here, we report the fine characterization of two different deletions in the USP9Y gene (one of the two candidate genes in the AZFa region), which have been transmitted through natural conception in two unrelated families. The associated mild testicular phenotype, in both cases, is in sharp contrast with that of the two previously reported infertile patients bearing a mutation of the same gene. In conclusion, to date, the USP9Y gene has been considered as one of the major Y-linked spermatogenesis genes, based on both its position within the AZFa region and previous reports that correlated USP9Y mutation to severe spermatogenic failure and infertility. This view is now substantially changed because our findings clearly demonstrate that during human spermatogenesis, USP9Y is more likely a fine tuner that improves efficiency, rather than a provider of an essential function. More importantly, the observed natural conceptions suggest that the protein is not required for the final sperm maturation process or for the acquisition of sperm fertilizing ability, providing a new perspective on the role played by the USP9Y gene in male fertility.

The human Y chromosome: a masculine chromosome

Once considered to be a genetic wasteland of no scientific interest beyond sex determination, the human Y chromosome has made a significant comeback in the past few decades and is currently implicated in multiple diseases, including spermatogenic failure - absent or very low levels of sperm production. The Y chromosome contains over one hundred testis-specific transcripts, and several deletions have been described that remove some of these transcripts, thereby causing spermatogenic failure. Screening for such deletions in infertile men is now a standard part of clinical evaluation. Many other Y-chromosome structural variants, some of which affect gene copy number, have been reported recently, and future research will be necessary to address the phenotypic effect of these structural variants.

The genetic and molecular bases of monogenic disorders affecting proteolytic systems

Complete and limited proteolysis represents key events that regulate many biological processes. At least 5% of the human genome codes for components of proteolytic processes if proteases, inhibitors, and cofactors are taken into account. Accordingly, disruption of proteolysis is involved in numerous pathological conditions. In particular, molecular genetic studies have identified a growing number of monogenic disorders caused by mutations in protease coding genes, highlighting the importance of this class of enzymes in development, organogenesis, immunity, and brain function. This review provides insights into the current knowledge about the molecular genetic causes of these disorders. It should be noted that most are due to loss of function mutations, indicating absolute requirement of proteolytic activities for normal cellular functions. Recent progress in understanding the function of the implicated proteins and the disease pathogenesis is detailed. In addition to providing important clues to the diagnosis, treatment, and pathophysiology of disease, functional characterisation of mutations in proteolytic systems emphasises the pleiotropic functions of proteases in the body homeostasis.

Polymorphic alleles of the human MEI1 gene are associated with human azoospermia by meiotic arrest

Genetic mechanisms are implicated as a cause of some male infertility, yet are poorly understood. Mouse meiotic mutant mei1 (meiosis defective 1) was isolated by a screening of infertile mice. Male mei1 mice have azoospermia due to meiotic arrest, and the mouse Mei1 gene is responsible for the mei1 phenotype. To investigate whether human MEI1 gene defects are associated with azoospermia by meiotic arrest, we isolated the human MEI1 cDNA based on the mouse Mei1 amino acid sequence. MEI1 is expressed specifically in the testis. Mutational analysis by direct sequencing of all MEI1 coding regions was performed in 27 men (13 European Americans, 13 Israeli and 1 Japanese) having azoospermia due to complete early meiotic arrest. This identified four novel, coding single-nucleotide-polymorphisms (cSNPs), i.e., SNP1 (T909G), SNP2 (A1582G), SNP3 (C1791A) and SNP4 (C2397T) in exons 4, 8, 9 and 14, respectively. Using these cSNPs, an association study was carried out between 26 non-Japanese patients with azoospermia and two sets of normal control men (61 normal European Americans and 60 Israelis). Consequently, SNP3 and SNP4 were shown to be associated with azoospermia among European Americans (P =0.0289 and P =0.0299 for genotype and allele frequencies at both the polymorphic sites, respectively), although no such association was observed among Israelis (P >0.05). Haplotype estimation revealed that the frequencies of SNP3-SNP4 (C-T), SNP3-SNP4 (A-C) and SNP3-SNP4 (A-T) were higher in the European American patients, and the frequency of SNP3-SNP4 (A-T) was also higher than in both control groups. These results suggest that MEI1 may play a role in meiosis during spermatogenesis, especially in European Americans.

A genomic and functional inventory of deubiquitinating enzymes

Posttranslational modification of proteins by the small molecule ubiquitin is a key regulatory event, and the enzymes catalyzing these modifications have been the focus of many studies. Deubiquitinating enzymes, which mediate the removal and processing of ubiquitin, may be functionally as important but are less well understood. Here, we present an inventory of the deubiquitinating enzymes encoded in the human genome. In addition, we review the literature concerning these enzymes, with particular emphasis on their function, specificity, and the regulation of their activity.

A rapid and simple system of detecting deletions on the Y chromosome related with male infertility using multiplex PCR

Around 10% of males with idiopathic azoospermia or oligozoospermia, which are important causes of male infertility, have partial deletions on the long arm of the Y chromosome. To develop a rapid and accurate detection system for screening major Y deletions found in infertile men, we developed a multiplex PCR system that can simultaneously amplify five loci on the Y chromosome, SRY, AMELY, DBY, RBMY, DAZ and one locus on the X chromosome, AMELX. The size of the PCR products was designed to increase gradually from the distal Yp to the distal Yq. Our system could detect deletions of three major candidate regions for the azoospermic factor, AZFa, AZFb and AZFc on the Y chromosome together with sex. The gradual increase in the size of the PCR products was convenient for imaging the location of deletions on the Y chromosome. Moreover, the multiplex PCR system was combined with microchip-based electrophoresis, and the PCR products derived from each locus were separated within 4 min. Our system is useful for screening Y chromosomes bearing the structural anomalies including three major AZF deletions found among azoospermic or oligozoospermic males.

Human Y-chromosome variation and male dysfunction

The Y-chromosome is responsible for sex determination in mammals, which is triggered by the expression of the SRY gene, a testis-determining factor. This particular gene, as well as other genes related to male fertility, are located in the non-recombining portion of the Y (NRY), a specific region that encompasses 95% of the human Y-chromosome. The other 5% is composed of the pseudo-autosomal regions (PARs) at the tips of Yp and Yq, a X-chromosome homologous region used during male meiosis for the correct pairing of sexual chromosomes. Despite of the large size of the human NRY (about 60 Mb), only a few active genes are found in this region, most of which are related to fertility. Recently, several male fertility dysfunctions were associated to microdeletions by STS mapping. Now that the complete genetic map of the human Y-chromosome is available, the role of particular NRY genes in fertility dysfunctions is being investigated. Besides, along with the description of several nucleotide and structural variations in the Y-chromosome, the association between phenotype and genotype is being addressed more precisely. Particularly, several research groups are investigating the association between Y-chromosome types and susceptibility to certain male dysfunctions in different population backgrounds. New insights on the role of the Y-chromosome and maleness are being envisaged by this approach.

Mutations in the chromosome pairing gene FKBP6 are not a common cause of non-obstructive azoospermia

Although it is generally thought that spermatogenic failure has a genetic background, to date only a limited percentage of men with non-obstructive azoospermia (NOA) are diagnosed with a genetic defect. The only common and well-established genetic causes of NOA in humans are numerical and structural chromosomal abnormalities and Y-chromosome deletions. In addition, some infrequent mutations have been identified in the ubiquitin-specific protease 9, Y-linked (USP9Y) and the synaptonemal complex protein 3 (SYCP3) gene that cause azoospermia. FK506-binding protein 6 (Fkbp6) is a newly discovered component of the synaptonemal complex (SC), which is essential for proper chromosome pairing and meiotic division. A null mutation of the Fkbp6 gene causes azoospermia in mice as well as in rats. We tested the hypothesis whether mutations in this gene can also cause azoospermia in humans. We performed a mutation screen in 51 men with NOA through direct sequencing methods. No homozygous mutations were identified. Two heterozygous mutations (T173T and R183C) were identified, which are likely to disrupt FKBP6 protein function. However, both mutations were also found in a group of 218 normospermic controls indicating that one FKBP6 allele appears to be sufficient for normal spermatogenesis. In conclusion, our results suggest that genetic defects in FKBP6 can be excluded as a common cause of azoospermia in humans.

Conservation of Y-linked genes during human evolution revealed by comparative sequencing in chimpanzee

The human Y chromosome, transmitted clonally through males, contains far fewer genes than the sexually recombining autosome from which it evolved. The enormity of this evolutionary decline has led to predictions that the Y chromosome will be completely bereft of functional genes within ten million years. Although recent evidence of gene conversion within massive Y-linked palindromes runs counter to this hypothesis, most unique Y-linked genes are not situated in palindromes and have no gene conversion partners. The 'impending demise' hypothesis thus rests on understanding the degree of conservation of these genes. Here we find, by systematically comparing the DNA sequences of unique, Y-linked genes in chimpanzee and human, which diverged about six million years ago, evidence that in the human lineage, all such genes were conserved through purifying selection. In the chimpanzee lineage, by contrast, several genes have sustained inactivating mutations. Gene decay in the chimpanzee lineage might be a consequence of positive selection focused elsewhere on the Y chromosome and driven by sperm competition.

The genetic and cytogenetic basis of male infertility

Despite the difficulties in determining the relative maternal vs. paternal contributions to infertility it is often suggested that a male factor problem is implicated in 50% of cases. This review is concerned specifically with male fertility disorders that have a clearly defined genetic component. The genetic causes of infertility can be broken down into Y chromosome deletions (specifically deletions in the AZF a, b, and c regions), single gene disorders (particularly those relating to the CFTR gene), multifactorial causes and chromosome abnormalities. Chromosome abnormalities can be numerical (such as trisomy--full blown or mosaic) or structural (such as inversions or translocations). Of especial interest at present is the incidence of levels of numerical chromosome abnormalities in the sperm of infertile men; prospects for screening sperm for such abnormalities are discussed.

Bipolar affective disorder in a male with a deletion of Y chromosome -- a case report

We report on a 25-year-old male with bipolar disorder, dysmorphic features and a deletion of the long arm of Y chromosome. A potential association between sex chromosome abnormalities and a susceptibility to major psychiatric disorders has been documented. However there have been very few reports on the coincidence of Y chromosome aberrations with bipolar disorder. Cytogenetic studies have contributed to the identification of several disease genes. Karyotyping of patients with bipolar disorder in order to identify candidate regions for linkage studies has been recommended.