Defect in the nuclear pore membrane glycoprotein 210-like gene is associated with extreme uncondensed sperm nuclear chromatin and male infertility: a case report

After the two meiotic divisions, haploid round spermatids undergo dramatic changes to become mature spermatozoa. One of the main transformations consists of compacting the cell nucleus to confer the sperm its remarkable hydrodynamic property and to protect its DNA from the oxidative stress it will encounter during its reproductive journey. Here, we studied an infertile subject with low sperm count, poor motility and highly abnormal spermatozoa with strikingly large heads due to highly uncondensed nuclear sperm DNA. Whole-exome sequencing was performed on the subject's DNA to identify the genetic defect responsible for this severe sperm anomaly. Bioinformatics analysis of exome sequence data uncovered a homozygous loss of function variant, ENST00000368559.7:c.718-1G>A, altering a consensus splice site expected to prevent the synthesis of the nucleoporin 210 like (NUP210L) protein. High-resolution mass spectrometry of sperm protein extracts did not reveal any NUP210L peptide sequence in the patient's sperm, contrary to what was observed in control donors, thus confirming the absence of NUP210L in the patient's sperm. Interestingly, homozygous Nup210l knock-out mice have been shown to be infertile due to a reduced sperm count, a high proportion of round-headed sperm, other head and flagella defects and a poor motility. NUP210L is almost exclusively expressed in the testis and sequence analogy suggests that it encodes a nuclear pore membrane glycoprotein. The protein might be crucial to regulate nuclear trafficking during and/or before spermiogenesis, its absence potentially impeding adequate nuclear compaction by preventing the entry of histone variants/transition proteins/protamines into the nucleus and/or by preventing the adequate replacement of core histones. This work describes a new gene necessary for male fertility, potentially improving the efficiency of the genetic diagnosis of male infertility. The function of NUP210L still remains to be resolved and its future investigation will help to understand the complex mechanisms necessary for sperm compaction.

Homozygous deletion of SUN5 in three men with decapitated spermatozoa

A recent study of 17 men with decapitated spermatozoa found that 8 carried two rare SUN5 alleles, and concluded that loss of SUN5 function causes the acephalic spermatozoa syndrome. Consistent with this, the SUN5 protein localises to the head-tail junction in normal spermatozoa, and SUN proteins are known to form links between the cytoskeleton and the nucleus. However, six of the ten SUN5 variants reported were missense with an unknown effect on function, and only one man carried two high confidence loss-of-function (LOF) alleles: p.Ser284* homozygozity. One potential exonic splice mutation, homozygous variant p.Gly114Arg, was not tested experimentally. Thus, definitive proof that loss of SUN5 function causes the acephalic spermatozoa syndrome is still lacking. Based on these findings, we determined the sequence of the SUN5 gene in three related men of North African origin with decapitated spermatozoa. We found all three men to be homozygous for a deletion-insertion variant (GRCh38 - chr20:32995761_32990672delinsTGGT) that removes 5090 base pairs including exon 8 of SUN5, predicting the frameshift, p.(Leu143Serfs*30), and the inactivation of SUN5. We therefore present the second case where the acephalic spermatozoa syndrome is associated with two LOF alleles of SUN5. We also show that the p.Gly114Arg variant has a strong inhibitory effect on splicing in HeLa cells, evidence that homozygozity for p.Gly114Arg causes acephalic spermatozoa syndrome through loss of SUN5 function. Our results, together with those of the previous study, show that SUN5 is required for the formation of the sperm head-tail junction and male fertility.

Exposure to low-dose bisphenol A impairs meiosis in the rat seminiferous tubule culture model: a physiotoxicogenomic approach

BACKGROUND

Bisphenol A (BPA) is one of the most widespread chemicals in the world and is suspected of being responsible for male reproductive impairments. Nevertheless, its molecular mode of action on spermatogenesis is unclear. This work combines physiology and toxicogenomics to identify mechanisms by which BPA affects the timing of meiosis and induces germ-cell abnormalities.

METHODS

We used a rat seminiferous tubule culture model mimicking the in vivo adult rat situation. BPA (1 nM and 10 nM) was added to the culture medium. Transcriptomic and meiotic studies were performed on the same cultures at the same exposure times (days 8, 14, and 21). Transcriptomics was performed using pangenomic rat microarrays. Immunocytochemistry was conducted with an anti-SCP3 antibody.

RESULTS

The gene expression analysis showed that the total number of differentially expressed transcripts was time but not dose dependent. We focused on 120 genes directly involved in the first meiotic prophase, sustaining immunocytochemistry. Sixty-two genes were directly involved in pairing and recombination, some of them with high fold changes. Immunocytochemistry indicated alteration of meiotic progression in the presence of BPA, with increased leptotene and decreased diplotene spermatocyte percentages and partial meiotic arrest at the pachytene checkpoint. Morphological abnormalities were observed at all stages of the meiotic prophase. The prevalent abnormalities were total asynapsis and apoptosis. Transcriptomic analysis sustained immunocytological observations.

CONCLUSION

We showed that low doses of BPA alter numerous genes expression, especially those involved in the reproductive system, and severely impair crucial events of the meiotic prophase leading to partial arrest of meiosis in rat seminiferous tubule cultures.

Decline of semen quality among 10 932 males consulting for couple infertility over a 20-year period in Marseille, France

Semen from 10 932 male partners of infertile couples was analysed and sperm parameter trends were evaluated at the Reproduction Biology Laboratory of the University Hospital of Marseille (France) between 1988 and 2007. After 3-6 days of abstinence, semen samples were collected. Measurements of seminal fluid volume, pH, sperm concentration, total sperm count, motility and detailed morphology of spermatozoa were performed. Sperm parameters were analysed on the entire population and in men with normal total numeration (≥40 million per ejaculate). The whole population demonstrated declining trends in sperm concentration (1.5% per year), total sperm count (1.6% per year), total motility (0.4% per year), rapid motility (5.5% per year) and normal morphology (2.2% per year). In the group of selected samples with total normal sperm count, the same trends of sperm quality deterioration with time were observed. Our results clearly indicate that the quality of semen decreased in this population over the study period.

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.

Chronology of meiosis & synaptonemal complex abnormalities in normal & abnormal spermatogenesis

BACKGROUND & OBJECTIVES

The study was taken up to define criteria of normality for meiosis by assessing the frequency of meiotic prophase cell types, the frequency of pachytene substage in normal and abnormal spermatogenesis and to determine what synaptonemal complex.

METHODS

A quantitative and qualitative analysis of the first meiotic prophase was performed in 10 patients presenting with non-obstructive infertility and 10 controls, using dual colour immunocytochemistry with SCP3 and BRCA1 which visualise axial elements and synaptonemal complexes (SC). The respective frequencies of the leptotene, zygotene and pachytene stages as well as the frequencies of the four substages of pachytene were evaluated. The frequencies of the main types of meiotic abnormalities at pachytene were also assessed.

RESULTS

The frequencies of leptotene and zygotene stages were significantly higher in patients (7.95 and 9.75%) than in controls (2.30 and 1.45%), whereas the frequency of pachytene was significantly higher in controls than in patients (96.25 vs. 75.30%). Detailed analysis of the sex chromosomes revealed that the controls showed a presence of late pachytene substages (P3 + P4 = 64.40%), whereas the patients showed a early pachytene substages (P1 + P2 = 63.40%). From these results, a new index was defined to evaluate spermatogenesis: the Pachytene Index, or PI (PI = P1 + P2 / P1 + P2 + P3 + P4). The same abnormalities (asynapsis, fragmented SC, dotted SC, thin SC) were observed in controls and in patients, but with different frequencies. The most frequent abnormality was fragmented SC, with a significant difference between patients and controls (15.28 vs. 9.74%). There was a significant difference between patients and controls for the frequency of asynapsed nuclei (7.97 vs. 2.95%) while the difference in other abnormalities were not significant.

INTERPRETATION & CONCLUSION

The accumulation of early primary spermatocytes is an indication that progression of meiosis is defective in spermatogenesis failures. The value of the PI less than 0.50 indicates that the kinetic of meiosis is normal at pachytene. There is no normal spermatogenesis when the frequency of one or several SC abnormalities is significantly higher than in controls and/ or when the PI is more than 0.50.

Meiotic abnormalities in patients bearing complete AZFc deletion of Y chromosome

BACKGROUND

We studied meiosis in three infertile patients presenting complete AZFc microdeletion and three controls.

METHODS

Primary spermatocytes were immunolabeled with SCP3, BRCA1 and gammaH2AX. We quantified the leptotene, zygotene and pachytene stages, and pachytene abnormalities: asynapsis and fragmented and dotted synaptonemal complexes (SCs).

RESULTS

SCP3 level was significantly higher in leptotene and zygotene (bouquet) stages in patients, suggesting AZFc may have a direct effect on early prophase. SCs were abnormal in 77.3% of pachytene nuclei of patients versus 30.8% of controls. The two groups differed significantly (P < 0.001) in asynapsed nuclei, fragmented SC and dotted SCs. In patients, asynapsis were short and limited to a few bivalents. Staging of pachytene nuclei based on the morphology of the XY pair with BRCA1 revealed a prevalence of early pachytene substages (70.7%) in patients. H2AX was normally phosphorylated.

CONCLUSIONS

In the absence of the AZFc region, the transient zygotene stage is extended, and chromosome condensation is reduced. The low level of limited asynapsis, the normal H2AX staining and the incomplete loss of germ cells at the pachytene checkpoint indicate that the AZFc region is not critical for meiotic recombination. We suggest that the pachytene phenotype develops secondarily to a primary defect that influences meiosis.

Meiotic arrest at the midpachytene stage in a patient with complete azoospermia factor b deletion of the Y chromosome

OBJECTIVE

To study the meiosis of a patient with complete azoospermia factor (AZF)b deletion of the Y chromosome.

DESIGN

Case report.

SETTING

La Conception University Hospital, Marseille, France.

PATIENT(S)

One azoospermic patient.

INTERVENTION(S)

Yq deletion testing, testicular sperm extraction, and meiotic study with immunocytochemistry.

MAIN OUTCOME MEASURE(S)

Abnormal synapsis rates in spermatocytes.

RESULT(S)

We found that most spermatocytes were at an early stage of meiosis. Half of the meiotic germ cells analyzed showed asynapsis, which was mostly extended or total. Discontinuity in the synaptonemal complex was seen in one third of the meiotic cells analyzed. An unusually small number of normal pachytene nuclei were found, all at early pachytene substages.

CONCLUSION(S)

This is the first demonstration that the synaptic process is impaired in a man with complete deletion of the AZFb interval. Our findings provide evidence that the pachytene checkpoint is situated at the midpachytene substage in humans.

Meiotic anomalies in infertile men with severe spermatogenic defects

BACKGROUND

This study was aimed at evaluating the rate of pairing failure in pachytene spermatocytes of patients presenting either an obstructive (O) or a non-obstructive (NO) infertility.

METHODS

Forty-one patients and 13 controls underwent testicular biopsy. Among the patients, 19 had an O infertility and 22 a NO infertility. Preparations of all patients and controls were Giemsa-stained, and synaptonemal complexes from nine of these patients and one control were immunostained.

RESULTS

In all, 2931 pachytene nuclei were analysed. The mean rate of asynapsed nuclei from the NO group (25.4%) was significantly higher than that of the O group (9.8%). There was no significant difference between the O group and the controls (10.6%). Immunocytochemistry showed that the number of pachytene nuclei decreased from the early to late pachytene sub-stage in all patients. Two NO patients, one azoospermic and one oligozoospermic, had a high percentage of asynapsed nuclei (86 and 91.8% respectively); one of these patients also presented a precocious localized separation of sister chromatids.

CONCLUSION

high levels of extended asynapsis could arise from a primary meiotic defect which may be responsible for 9% of the NO male infertilities at our centre. The prevalence of early pachytene substages suggests that the pachytene checkpoint is localized at the mid-pachytene stage in humans.

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.

Pregnancies after ICSI using sperm with abnormal head-tail junction from two brothers: case report

We report ICSI pregnancies in two couples with a history of long standing primary infertility in which the sperm of the male partner were either acephalic or had abnormal head-midpiece attachments. The two couples, in which the men are brothers, underwent ICSI. Sperm were analysed by transmission electron microscopy and immunocytochemistry with an anti-MPM2 monoclonal antibody. The first couple underwent two ICSI cycles, each consisting of the injection of two mature oocytes and the transfer of two embryos. A successful pregnancy occurred after the second transfer and led to the birth to a healthy girl. The second couple underwent three ICSI cycles, each consisting of the injection of 18 oocytes and the transfer of two embryos; the last of these led to a triple ongoing pregnancy which included two identical twins. Caesarean section led to the birth of three fetal-growth restricted children. This case report demonstrates that ongoing pregnancies can be achieved in cases of abnormal development of the head-neck attachment. The genetic origin of this syndrome is generally accepted, but the phenotypic heterogeneity observed by light and electron microscopy among published cases suggests that there are a variety of genetic causes of this syndrome.

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.

[Morphological aspect of embryos obtained after fertilization in vitro for male factor or ICSI]

OBJECTIVE

In order to study the eventual impact on fertilization and embryo characteristics of the microinjection procedure we compared the quality of the embryos obtained by ICSI with those of in vitro fertilization with male factors (MF IVF).

MATERIAL AND METHODS

One hundred thirty-four cycles of IVF treatment (group 1) were selected with oligoasthenozoospermia according to WHO criteria with a total number of motile spermatozoa between 500,000 and 1 million. One thousand eighty-eight mature oocytes and 486 embryos were obtained. One hundred forty-three cycles of intracytoplasmic sperm injection (group 2) were performed in couples whose in vitro fertilization was imparticable because of extreme sperm impairment. One thousand one hundred forty-seven mature oocytes were injected and 626 embryos were obtained.

RESULTS

In group 1, the pregnancy rate per embryo transfer and the implantation rate were respectively 22.7% and 12.3%. In group 2, the pregnancy rate per embryo transfer was 37.1% and the implantation rate was 17%. The statistical analysis of the embryos obtained in the two different groups did not demonstrate any difference in the distribution of the more regular and less fragmented embryos (group A) and those of the more irregular and fragmented embryos (group B). No statistical difference was demonstrated in the chronology of the division of these embryos (groups 1 and 2).

CONCLUSION

The pregnancy rate by cycle and by transfer reported by ICSI (p < 0.003 and p < 0.015 respectively) could be related to a significantly higher mean number of transferred embryos (2.65 vs 2.02) in probable relation with a higher cleavage rate (p < 0.00001).

A simple and reliable method for meiotic studies on testicular samples used for intracytoplasmic sperm injection

OBJECTIVE

To develop a reliable and simple method allowing meiotic studies to be performed on testicular samples used for ICSI.

DESIGN

Evaluation of meiotic abnormalities in patients with severe spermatogenic impairment.

SETTING

Centre de Médecine de la Reproduction, Marseille.

PATIENT(S)

Two azoospermic men undergoing testicular biopsy for ICSI and one control individual with normal testicular histology.

INTERVENTION(S)

The immature germ cells from the patients came from testicular biopsy used for ICSI, after dispersal into a thin cell suspension. Cells were cytocentrifuged to obtain well-spread spermatocytes and then immunocytochemical techniques were performed. We used rabbit polyclonal antibodies against the specific meiotic proteins Cor1 and Syn1 and a human CREST anti-kinetochore antibody.

MAIN OUTCOME MEASURE(S)

Synapsis abnormalities in patients with severe spermatogenesis impairment.

RESULT(S)

Pachytene spermatocytes are easily analyzed with this technique, without damage of the axial core and synaptonemal complex. The loss of germ cells is limited.

CONCLUSION(S)

The cytocentrifugation method is the most suitable technique for meiotic studies in patients with severe spermatogenic failure, because it can be used on the testicular cell suspension remaining after ICSI with testicular spermatozoa.

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

Using fluorescent in-situ hybridization, we investigated the positioning of different human bivalents at the pachytene stage of normal male meiosis. We showed that, in about 35% of nuclei, the pericentromeric region of bivalent 15 is closely associated with the sex vesicle (SV). This behaviour may be linked to the presence of three domains in the pericentromeric region of chromosome 15: a large imprinted domain, a nucleolar organizing region (NOR), and a heterochromatic block. In order to define the domains of chromosome 15 involved in this association, we analysed the meiotic behaviour of other bivalents with similar domains: human bivalent 11 and mouse bivalent 7, bearing imprinted domains, other human acrocentric bivalents bearing a NOR, and the human bivalents 1, 9 and 16 containing a heterochromatic region. None of these bivalents were as frequently associated with the SV as the human bivalent 15. Nevertheless, we suggest that the bivalent 15 heterochromatin may be responsible for the association because of two properties: its telomeric location on chromosome 15 and its strong sequence homology with the Yq heterochromatin. This phenomenon could explain the high frequency of translocations between the chromosome 15 and the X or Y chromosomes.

Failure of pregnancy after intracytoplasmic sperm injection with decapitated spermatozoa: case report

The case of a couple with a history of long standing primary infertility is reported in which the man presented with a decapitated sperm defect. The woman had a normal history and presented with normal clinical characteristics. The couple underwent one unsuccessful conventional in-vitro fertilization (IVF). Subsequently, embryos were obtained and transferred after assisted fertilization attempts: in all, three subzonal inseminations and four intracytoplasmic sperm injections. A total of 49 mature oocytes was injected in both studies, 25 embryos obtained and 20 embryos transferred, three of them after freezing and thawing. Despite the good embryo morphology, implantation was unsuccessful and no pregnancy occurred. The failure of implantation may have resulted from an arrest in early embryonic development related to the sperm anomaly. One hypothesis is that transferred embryos may carry a chromosomal imbalance that prevents them from progressing to the blastocyst stage. Nevertheless, we cannot exclude the possibility that the woman is responsible for the implantation failure. Co-culture associated with a further attempt could provide information regarding the ability of embryos to progress to the blastocyst stage and implant.

Rapid chromosomal analysis of germ-line cells by FISH: an investigation of an infertile male with large-headed spermatozoa

A rapid fluorescence in-situ hybridization (FISH) technique was used for direct chromosomal analysis on germ cells from an infertile male with large-headed spermatozoa. The interphase chromosomes were fluorescently-labelled using an extremely bright cyanine dye during a 5-15 min FISH procedure. Germ cells were analysed using a battery of chromosome-specific DNA probes in several consecutive rapid FISH experiments. It was found that the majority of large-headed spermatozoa contained a diploid chromosome number probably due to errors in meiosis I or II divisions, whereas the majority of spermatozoa with normal sized heads are haploid and may be utilized for selective in-vitro fertilization procedures. Rapid FISH may be useful for the detection of major chromosomal aneuploidies in germ cells as an alternative technique to standard or multicolour FISH, and may find an additional application for the chromosomal analysis of human preimplantation embryos.

[Quality of embryos in unexplained sterility]

In our study, the rate of pregnancy by transfer and puncture was not significantly different in unexplained and in tubal infertility, but the mean number of transferred embryos was significantly higher in the first group. To explain these data, we compared the quality of embryos in 32 punctures realized among 29 women with unexplained infertility and in 171 punctures planned among 156 women with tubal infertility. The percentage of embryos with 4 or more blastomeres was significantly lower in the unexplained infertility group than in the pure tubal infertility group.

[Genetic aspects of male infertility]

Cytogenetic investigations in sterile males showed that autosomal and sex chromosome anomalies can be responsible of the defect of spermatogenesis. Specific alteration of genes controlling spermatogenesis is excluded because all chromosomes are involved in the anomaly and breakpoints are distributed at random. In the aim to explain the spermatogenic failure, three mechanisms are proposed: X-autosome interaction, asynapsis, somatic lesion of the gonad, each mechanism might act alone or with the other. Beside chromosomal infertility, meiotic or sperm anomalies suggest the presence of gene mutations which interfere with the evolution of spermatogenesis or lead to the formation of abnormal spermatozoa. Insertion of technics of molecular biology in our researches could demonstrate the existence of these mutations; the same technics will allow to resolve the problem of the failure of a germ cell bearing a chromosomal anomaly particularly when this anomaly is balanced and involves the autosomes and not the sex chromosomes.

[Male infertility of chromosomal origin]

Cytogenetic studies in infertile men showed that chromosomal anomalies were more frequent in these patients than in general population. Sex chromosome anomalies, specially 47, XYY karyotype, are predominant by their frequency at the severity of testicular impair. Nevertheless, balanced autosomal rearrangements can also induce spermatogenic failure; they were of great interest in perfecting the hypothesis which try to explain germ cells atresia. Three mechanisms are proposed: --X-autosome interaction; --synaptic failure; both could lead to a metabolic disorder and death of the germ cell; --somatic lesions of the gonad could also induce this degenerative process. Techniques of molecular biology joined up to cytogenetic investigations of meiosis will lead to a better understanding of the chromosomal male sterility.

Infertility in human males with autosomal translocations. II. Meiotic studies in three reciprocal rearrangements, one showing tertiary monosomy in a 45-chromosome individual and his father

The meiotic prophase behavior of three human reciprocal autosomal translocations is presented. Each translocation was ascertained among men attending an infertility clinic. Two involved chromosomes 3 and 5, with breakpoints in different places. Quadrivalents were seen in every cell. The third translocation was a rare t(11q;15q) rearrangement in a 45-chromosome individual with tertiary monosomy. The long product of the translocation was retained in the karyotype over two generations of the family, the short product having been lost. At meiotic prophase, a trivalent was seen in every cell; in 60% of the nuclei, the short arm of the trivalent was closely associated with the XY bivalent. The transmission and phenotypic effects of tertiary monosomy in man and the mouse are discussed.

Three dimensional reconstruction of human pachytene spermatocyte nuclei of a 17;21 reciprocal translocation carrier: study of XY-autosome relationships

A study of XY-autosome relationships at the pachytene stage in an infertile 17-21 reciprocal translocation carrier was undertaken by means of three dimensional reconstruction. Synaptonemal complexes and the sex vesicle were analysed on electron microscopic serial sections and the reconstruction was performed on transparent sheets and on a Samba 2000 (Alcatel TITN) image analysis system. All asynapsed segments were entirely included in the sex vesicle, the chromatin fibre of the autosomes and sex chromosomes being tightly intermingled. In one nucleus, the four arms of the quadrivalent were paired, except around the breakpoints where an interstitial asynapsis was observed. In the other nuclei, a terminal asynapsis involving one or two arms of the quadrivalent was found. In the sex vesicle, autosomal asynapsed segments showed the same morphological characteristics as those of X and Y chromosomes. This observation agrees with the hypothesis of the extension of gene inactivation from sex chromosomes to autosomes.

Infertility in human males with autosomal translocations: meiotic study of a 14;22 Robertsonian translocation

Pachytene analysis was undertaken in a male patient heterozygous for a 14q22q Robertsonian translocation. The relatively low rate of XY autosome association led us to examine the relationships existing between the chromosomes involved in the translocation, the rate of XY-autosome association and the degree of spermatogenic failure. Cytogenetic investigations in infertile men and the results of the meiotic studies suggest a direct correlation between the frequency of XY-autosome association at pachytene and the degree of spermatogenic failure. Whether associations arise as a consequence or cause of germ cell failure is still not certain.

Differential associative behaviour of mitotic and meiotic acrocentric chromosomes

A comparative study of the association of mitotic acrocentric chromosomes and acrocentric bivalents at the pachytene stage shows that at least two factors can act in the associative behaviour of these chromosomes: (1) Nor activity and (2) the presence of satellite DNA in the short arms of these chromosomes. These factors do not act with the same intensity in the two cell lines studied. In lymphocytes, Nor activity prevails, whereas satellite DNA plays the main role in the association of acrocentric chromosomes in germ cells at the pachytene stage.

Precise in situ localization of NCAM, ETS1, and D11S29 on human meiotic chromosomes

In order to sublocalize NCAM, ETS1, and the anonymous DNA fragment D11S29 within 11q23, in situ hybridization was performed on pachytene bivalents. Analysis of the grain distribution within the band 11q23 indicated that the chromosomal sublocalization of both NCAM and D11S29 was in 11q23.1, whereas ETS1 was found to be localized in 11q23.3. These results clearly demonstrate the usefulness of in situ hybridization applied to pachytene bivalents to obtain accurate gene sublocalization.

Differential elongation of autosomal pachytene bivalents related to their DNA content in human spermatocytes

The establishment of the complete karyotype of human pachytene spermatocytes reveals differences in stretching of chromosomes between meiosis and mitosis. Bivalents or specific regions of bivalents which exhibit many R-bands are particularly elongated. In mitotic chromosomes, the DNA contained in such bands is known to be early replicating. The study of variations in the total length and the centromeric index of bivalent 1 suggests that differential elongation of pachytene bivalents is a premeiotic event, taking place during the last DNA replication.

Pachytene analysis in a 17;21 reciprocal translocation carrier: role of the acrocentric chromosomes in male sterility

Pachytene analysis was undertaken in an infertile male, heterozygous for a 17;21 reciprocal translocation. The quadrivalent was identified by its configuration and chromomere pattern. A non-random association was found between the quadrivalent and the sex vesicle in 77% of the pachytene nuclei analysed. In 13.1% of the cells the contact with the sex vesicle was established by the terminal chromomere of the two chromosomes 21; in 63.9% of the cells, the entire region of the breakpoints was completely hidden by the sex vesicle. In some nuclei asynapsis was found in the region of the breakpoints. The nature of the contact between the quadrivalent and the sex vesicle is discussed in this paper. It is proposed that the acrocentric chromosome favours the contact between the quadrivalent and the sex vesicle, and increases the risk of sterility in male carriers of Robertsonian translocations and of reciprocal translocations involving one acrocentric chromosome.

Loop formation and synaptic adjustment in a human male heterozygous for two pericentric inversions

Pachytene analysis was undertaken in an infertile male heterozygous for two pericentric inversions of chromosomes 1 and 9. The synaptic behaviour of the bivalent 1 inversion was the most informative. Analysis of the chromomere pattern combined with centromeric heterochromatin staining allowed precise description of synaptic initiation and extension leading to the homosynapsed loop. These techniques also allowed demonstration of the existence of heterosynapsis following alignment of the inverted segments. Non-homologous synapsed bivalents had the morphological aspects of straight bivalents with two distant blocks of centromeric heterochromatin. The numbering of the autosomal bivalent chromomeres at various successive phases of the inversion loop behaviour of bivalent 1 permitted us an alternative approach to the timing of pachytene.

Synapsis and synaptic adjustment in an infertile human male heterozygous for a pericentric inversion in chromosome 1

Synapsis and "synaptic adjustment" were analyzed, using electron microscopy in silver stained surface microspreads of inversion-bearing spermatocytes, in an infertile human male with an inherited pericentric inversion in chromosome 1. Possible reasons for his infertility are discussed.

Random acrocentric bivalent associations in human pachytene spermatocytes. Molecular implications in the occurrence of Robertsonian translocations

Acrocentric bivalent associations were studied in 232 human male germ cells at pachytene in order to understand better the preferential involvement of chromosomes 13, 14, and 21 in Robertsonian translocations. The tendency of each acrocentric bivalent to associate with another was not correlated with NOR activity, as measured by silver staining. Good agreement was noticed between their ability to associate and the amount of satellite DNA in human acrocentric chromosomes. The distribution of two-by-two acrocentric bivalent associations was random. In order to reconcile this result with the nonrandom distribution of Robertsonian translocations, a molecular hypothesis is proposed. The model is based on homology of recombinational sites, interspersed at regular interval in satellite DNA, which could increase the probability of accidental unequal crossing-over between two specific acrocentric chromosomes.

Complete pachytene chromomere karyotypes of human spermatocyte bivalents

Well-spread human pachytene spermatocyte bivalents were obtained allowing specific identification of each bivalent within its total complement according to its chromomere sequence combined with further staining of its centromeric heterochromatin. The total number of chromomeres was found to be related to the degree of bivalent contraction: 396 in condensed bivalents and 511 in decondensed bivalents. A striking correspondence between chromomeres and mitotic G-bands was observed; on account of the variability of bivalent contraction, condensed bivalents corresponded to prometaphase somatic chromosomes and decondensed bivalents to mid/late prophase chromosomes.

Pachytene analysis of a man with a 13q;14q translocation and infertility. Behavior of the trivalent and nonrandom association with the sex vesicle

Pachytene analysis was undertaken in a sterile 13q;14q heterozygous translocation carrier in an attempt to follow the segregational behavior of the trivalent and to evaluate the relationship of Robertsonian translocations in man to the impairment of spermatogenesis. Well-spread bivalents from pachytene nuclei were identified by their chromomere patterns. The trivalent was found always in cis configuration. Silver staining demonstrated the loss of nucleolar organizer regions from the translocated chromosomes. A nonrandom association was found between the trivalent configuration and the sex vesicle in 61% of the pachytene nuclei examined. Such an association has been described before in mice heterozygous for Robertsonian or reciprocal translocations, and may thus represent a general phenomenon. As in mice, this contact was restricted to the centromeric region of the trivalent. A hypothesis relating the association of the trivalent with the sex vesicle to impairment of normal X-chromosome inactivation and subsequent spermatogenic breakdown is discussed. Other chromosomal abnormalities in which sex-vesicle anomalies are associated with male sterility (such as X-or Y-autosomal translocations) are also considered. It is proposed that any process interfering with normal X-chromosome inactivation in pachytene spermatocytes could disturb subsequent meiotic or postmeiotic germ cells development.