SPINK2 deficiency causes infertility by inducing sperm defects in heterozygotes and azoospermia in homozygotes

Azoospermia, characterized by the absence of spermatozoa in the ejaculate, is a common cause of male infertility with a poorly characterized etiology. Exome sequencing analysis of two azoospermic brothers allowed the identification of a homozygous splice mutation in SPINK2, encoding a serine protease inhibitor believed to target acrosin, the main sperm acrosomal protease. In accord with these findings, we observed that homozygous Spink2 KO male mice had azoospermia. Moreover, despite normal fertility, heterozygous male mice had a high rate of morphologically abnormal spermatozoa and a reduced sperm motility. Further analysis demonstrated that in the absence of Spink2, protease-induced stress initiates Golgi fragmentation and prevents acrosome biogenesis leading to spermatid differentiation arrest. We also observed a deleterious effect of acrosin overexpression in HEK cells, effect that was alleviated by SPINK2 coexpression confirming its role as acrosin inhibitor. These results demonstrate that SPINK2 is necessary to neutralize proteases during their cellular transit toward the acrosome and that its deficiency induces a pathological continuum ranging from oligoasthenoteratozoospermia in heterozygotes to azoospermia in homozygotes.

Human and mouse ZFY genes produce a conserved testis-specific transcript encoding a zinc finger protein with a short acidic domain and modified transactivation potential

Mammalian ZFY genes are located on the Y chromosome, and code putative transcription factors with 12–13 zinc fingers preceded by a large acidic (activating) domain. In mice, there are two genes, Zfy1 and Zfy2, which are expressed mainly in the testis. Their transcription increases in germ cells as they enter meiosis, both are silenced by meiotic sex chromosome inactivation (MSCI) during pachytene, and Zfy2 is strongly reactivated later in spermatids. Recently, we have shown that mouse Zfy2, but not Zfy1, is involved in triggering the apoptotic elimination of specific types of sex chromosomally aberrant spermatocytes. In humans, there is a single widely transcribed ZFY gene, and there is no evidence for a specific role in the testis. Here, we characterize ZFY transcription during spermatogenesis in mice and humans. In mice, we define a variety of Zfy transcripts, among which is a Zfy2 transcript that predominates in spermatids, and a Zfy1 transcript, lacking an exon encoding approximately half of the acidic domain, which predominates prior to MSCI. In humans, we have identified a major testis-specific ZFY transcript that encodes a protein with the same short acidic domain. This represents the first evidence that ZFY has a conserved function during human spermatogenesis. We further show that, in contrast to the full acidic domain, the short domain does not activate transcription in yeast, and we hypothesize that this explains the functional difference observed between Zfy1 and Zfy2 during mouse meiosis.

Complete deletion of the AZFb interval from the Y chromosome in an oligozoospermic man

BACKGROUND

Deletion of the entire AZFb interval from the Y chromosome is strictly associated with azoospermia arising from maturation arrest during meiosis. Here, we describe the exceptional case of an oligozoospermic man, 13-1217, with an AZFb + c (P5/distal-P1) deletion. Through the characterization of this patient, and two AZFb (P5/proximal-P1) patients with maturation arrest, we have explored three possible explanations for his exceptionally progressive spermatogenesis.

METHODS AND RESULTS

We have determined the precise breakpoints of the deletion in 13-1217, and shown that 13-1217 is deleted for more AZFb material than one of the AZFb-deleted men (13-5349). Immunocytochemical analysis of spermatocytes with an antibody against a synaptonemal complex component indicates synapsis to be largely unaffected in 13-1217, in contrast to 13-5349 where extended asynapsis is frequent. Using PCR-based analyses of RNA and DNA from the same testicular biopsy, we show that 13-1217 expresses post-meiotic germ cell markers in the absence of genomic DNA and transcripts from the AZFb and AZFc intervals. We have determined the Y chromosome haplogroup of 13-1217 to be HgL-M185.

CONCLUSIONS

Our results indicate that the post-meiotic spermatogenesis in 13-1217 is not a consequence of mosaicism or retention of a key AZFb gene. On the contrary, since the Hg-L Y chromosome carried by 13-1217 is uncommon in Western Europe, a Y-linked modifier locus remains a possible explanation for the oligozoospermia observed in patient 13-1217. Further cases must now be studied to understand how germ cells complete spermatogenesis in the absence of the AZFb interval.

[Spermiogenesis: histone acetylation triggers male genome reprogramming]

During their post-meiotic maturation, male germ cells undergo an extensive reorganization of their genome, during which histones become globally hyperacetylated, are then removed and progressively replaced by transition proteins and finally by protamines. The latter are known to tightly associate with DNA in the mature sperm cell. Although this is a highly conserved and fundamental biological process, which is a necessary prerequisite for the transmission of the male genome to the next generation, its molecular basis remains mostly unknown. We have identified several key factors involved in this process, and their detailed functional study has enabled us to propose the first model describing molecular mechanisms involved in post-meiotic male genome reprogramming. One of them, Bromodomain Testis Specific (BRDT), has been the focus of particular attention since it possesses the unique ability to specifically induce a dramatic compaction of acetylated chromatin. Interestingly, a mutation was found homozygous in infertile men which, according to our structural and functional studies, disrupts the function of the protein. A combination of molecular structural and genetic approaches has led to a comprehensive understanding of new major actors involved in the male genome reprogramming and transmission.

Clinical data and parenthood of 63 infertile and Y-microdeleted men

OBJECTIVE

To collect follow-up data for infertile men with Y microdeletion.

DESIGN

Retrospective, observational survey.

SETTING

Multicenter IVF units associated with genetics laboratories.

PATIENT(S)

Sixty-three patients with Y microdeletion.

INTERVENTION(S)

Karyotype analysis, Y microdeletion screening, and assisted reproductive technology.

MAIN OUTCOME MEASURES

Medical history, karyotype, nature of the AZF deletion, semen parameters, testis biopsy results, choice of assisted reproductive technology, and results of intracytoplasmic sperm injection (ICSI).

RESULTS

Abnormal karyotypes were found in 8 men (12.7%), who were azoospermic except 1. Of these 8 men, 5 presented a combined AZFb+c deletion, and 3 had a deletion in AZFc only. Most men (39 of 63) were azoospermic, 3 were cryptoazoospermic, and 19 had extreme oligozoospermia (sperm concentration </=1.10(6)/mL). Sperm concentration above 1.10(6)/mL was found for 2 men (3.1%). A testis biopsy was performed in 27 azoospermic men, resulting in positive sperm extraction in 6 cases. To date, 42 ICSI cycles with either testicular (n = 5) or ejaculated spermatozoa (n = 37) have been carried out in 23 couples with male partners with AZFc deletion. Eighteen clinical pregnancies were obtained, leading to the birth of 14 babies. Donor insemination had been chosen by 28 couples, leading to the birth of 9 children.

CONCLUSION

Karyotype analysis should be systematically performed in Y microdeleted men. Intracytoplasmic sperm injection can be offered to half of AZFc-deleted patients, providing real opportunities to have a child.

Phenotypic variation within European carriers of the Y-chromosomal gr/gr deletion is independent of Y-chromosomal background

BACKGROUND

Previous studies have compared sperm phenotypes between men with partial deletions within the AZFc region of the Y chromosome and non-carriers, with variable results. In this study, a separate question was investigated, the basis of the variation in sperm phenotype within gr/gr deletion carriers, which ranges from normozoospermia to azoospermia. Differences in the genes removed by independent gr/gr deletions, the occurrence of subsequent duplications or the presence of linked modifying variants elsewhere on the chromosome have been suggested as possible causal factors. This study set out to test these possibilities in a large sample of gr/gr deletion carriers with known phenotypes spanning the complete range.

RESULTS

In total, 169 men diagnosed with gr/gr deletions from six centres in Europe and one in Australia were studied. The DAZ and CDY1 copies retained, the presence or absence of duplications and the Y-chromosomal haplogroup were characterised. Although the study had good power to detect factors that accounted for >or=5.5% of the variation in sperm concentration, no such factor was found. A negative effect of gr/gr deletions followed by b2/b4 duplication was found within the normospermic group, which remains to be further explored in a larger study population. Finally, significant geographical differences in the frequency of different subtypes of gr/gr deletions were found, which may have relevance for the interpretation of case control studies dealing with admixed populations.

CONCLUSIONS

The phenotypic variation of gr/gr carriers in men of European origin is largely independent of the Y-chromosomal background.

Preliminary study on the role of the human IZUMO gene in oocyte-spermatozoa fusion failure

We studied the IZUMO gene 9 coding exons sequence in four groups of patients including those with fertilization failure by conventional IVF. We observed in our populations two combinations of four polymorphisms that appeared to be preferentially linked (CGG-CG and TAA-TT) without any significant difference between different genotype repartitions.

Fine mapping of re-arranged Y chromosome in three infertile patients with non-obstructive azoospermia/cryptozoospermia

BACKGROUND

Cytogenetically detectable aberrations of the Y chromosome, such as isodicentrics, rings or translocations are sometimes associated with male non-obstructive infertility. This report presents a detailed analysis of the clinical, cytogenetic and molecular data in three patients with a re-arranged Y chromosome.

METHODS

Patients A and B were azoospermic, whereas patient C was cryptozoospermic. All had a somatic mosaic karyotype including a population of 45,X cells and a cell line with a re-arranged Y chromosome. A molecular and FISH analysis of their re-arranged Y was undertaken, which specifically focussed on the presence of the AZFa, b and c regions.

RESULTS

The AZFa region was present in all the three patients. The AZFb and AZFc regions were absent in patients A and B, whereas, in patient C, the distal part of AZFb and the whole AZFc region were deleted. Moreover, in this patient, the AZF FISH analysis revealed a mosaicism for the size of the AZF deletion within the re-arranged Y, suggesting a progressive enlargement of the deletion during cell mitotic divisions.

CONCLUSIONS

This investigation allowed not only a more precise description of the abnormal Y, but also shed light on how this re-arrangement could be involved in the infertility phenotype.

Predictive factors for an increased risk of sperm aneuploidies in oligo-astheno-teratozoospermic males

Patients with severe spermatogenesis impairment can now successfully father a child thanks to the use of intracytoplasmic sperm injection (ICSI). In oligozoospermic patients, many studies have reported significantly higher sperm aneuploidy rates and therefore an increased risk of transmitting a chromosomal abnormality via the injection of abnormal spermatozoa. However, the frequency of aneuploidy is highly variable between patients. The aim of the present work was to identify clinical and biological factors, which, together with non-obstructive oligozoospermia, could be predictive of elevated sperm aneuploidies. The sperm aneuploidy rates for chromosomes X, Y, 13, 18 and 21 were assessed in 31 infertile men with well-characterized spermatogenesis impairment, and in a population of control men with proven fertility. The frequency of sperm aneuploidy was compared between several patient subgroups according to their clinical and biological factors. Nearly half of the oligozoospermic males (15/31) had a significantly increased disomy rate for at least one of the five chromosomes compared with that observed in the control population (mean disomy rates + 1.96 standard deviation). Factors significantly associated with higher numbers of aneuploid sperm were cigarette smoking, an elevated follicle-stimulating hormone level, a sperm concentration less than 1 m/mL, and a severe teratozoospermia. Hence, several factors predictive of an increased risk of sperm aneuploidy rates were identified in ICSI male candidates with a non-obstructive oligozoospermia.

Évaluation d’une technique simple et rapide de détection de microdélétions du bras long du chromosome Y

OBJECTIVES

Recent investigations showed a high prevalence of Y chromosome microdeletions in men with severely impaired spermatogenesis. Screening for these men is recommended prior to assisted reproduction techniques. The aim of this study was to set up a simple method to detect Y deletion in infertile men. First, we tested the feasibility of cytobrush to collect oral cells as source of DNA. Second, we compared a classic PCR corresponding to European recommendations to the Promega kit.

PATIENTS AND METHODS

Seventeen infertile male patients with previously characterized deletions were included in the present study, after fully informed written consent. Both oral cells and blood were used for DNA extraction. A specific DNA extraction protocol was carried out on the buccal cells. The DNAs were tested for Y deletion screening by two different methods.

RESULTS

We retrieved between 4 and 10 microg of DNA per brush from buccal cells, allowing several multiplex PCR. The Promega kit detected all the deletions but one: an AZFa deletion was not detected by the two markers of the kit covering this region. In addition, sY130, sY133 and SY153, included in the kit, are not reliable.

DISCUSSION AND CONCLUSIONS

Buccal cells represent a convenient substitute for blood in testing for Y microdeletions. Both false negative and false positive results were obtained with Promega Kit. On the opposite, PCR according to the European recommendations allow the accurate detection of Y microdeletion in our 17 cases, at a lower cost.