The chromosome constitution of 1000 human spermatozoa

The sporophyte-to-gametophyte transition: The haploid generation comes of age

Flowering plants alternate between two multicellular generations: the diploid sporophyte and haploid gametophyte. Despite its small size, the gametophyte has significant impacts on plant genetics, evolution, and breeding. Each male pollen grain and female embryo sac is a multicellular organism with independent gene expression, a functioning metabolism, and specialized cell types. In this review, we describe recent progress in understanding the process in which the haploid genome takes over expression from its diploid parent - the sporophyte-to-gametophyte transition. The focus is on pollen, but similar concepts may also apply to the female gametophyte. Technological advances in single-cell genomics offer the opportunity to characterize haploid gene expression in unprecedented detail, positioning the field to make rapid progress.

New Biological Insights on X and Y Chromosome-Bearing Spermatozoa

A spermatozoon is a male germ cell capable of fertilizing an oocyte and carries genetic information for determining the sex of the offspring. It comprises autosomes and an X (X spermatozoa) or a Y chromosome (Y spermatozoa). The origin and maturation of both X and Y spermatozoa are the same, however, certain differences may exist. Previous studies proposed a substantial difference between X and Y spermatozoa, however, recent studies suggest negligible or no differences between these spermatozoa with respect to ratio, shape and size, motility and swimming pattern, strength, electric charge, pH, stress response, and aneuploidy. The only difference between X and Y spermatozoa lies in their DNA content. Moreover, recent proteomic and genomic studies have identified a set of proteins and genes that are differentially expressed between X and Y spermatozoa. Therefore, the difference in DNA content might be responsible for the differential expression of certain genes and proteins between these cells. In this review, we have compiled our present knowledge to compare X and Y spermatozoa with respect to their structural, functional, and molecular features. In addition, we have highlighted several areas that could be explored in future studies in this field.

Comprehensive Genome Profiling of Single Sperm Cells by Multiple Annealing and Looping-Based Amplification Cycles and Next-Generation Sequencing from Carriers of Robertsonian Translocation

Robertsonian translocation (RT) is a common cause for male infertility, recurrent pregnancy loss, and birth defects. Studying meiotic recombination in RT-carrier patients helps decipher the mechanism and improve the clinical management of infertility and birth defects caused by RT. Here we present a new method to study spermatogenesis on a single-gamete basis from two RT carriers. By using a combined single-cell whole-genome amplification and sequencing protocol, we comprehensively profiled the chromosomal copy number of 88 single sperms from two RT-carrier patients. With the profiled information, chromosomal aberrations were identified on a whole-genome, per-sperm basis. We found that the previously reported interchromosomal effect might not exist with RT carriers. It is suggested that single-cell genome sequencing enables comprehensive chromosomal aneuploidy screening and provides a powerful tool for studying gamete generation from patients carrying chromosomal diseases.

Seminal biomarkers for the evaluation of male infertility

For men struggling to conceive with their partners, diagnostic tools are limited and often consist of only a standard semen analysis. This baseline test serves as a crude estimation of male fertility, leaving patients and clinicians in need of additional diagnostic biomarkers. Seminal fluid contains the highest concentration of molecules from the male reproductive glands, therefore, this review focuses on current and novel seminal biomarkers in certain male infertility scenarios, including natural fertility, differentiating azoospermia etiologies, and predicting assisted reproductive technique success. Currently available tests include antisperm antibody assays, DNA fragmentation index, sperm fluorescence in situ hybridization, and other historical sperm functional tests. The poor diagnostic ability of current assays has led to continued efforts to find more predictive biomarkers. Emerging research in the fields of genomics, epigenetics, proteomics, transcriptomics, and metabolomics holds promise for the development of novel male infertility biomarkers. Seminal protein-based assays of TEX101, ECM1, and ACRV1 are already available or under final development for clinical use. Additional panels of DNA, RNA, proteins, or metabolites are being explored as we attempt to understand the pathophysiologic processes of male infertility. Future ventures will need to continue data integration and validation for the development of clinically useful infertility biomarkers to aid in male infertility diagnosis, treatment, and counseling.

The use of fluorescent in situ hybridization in male infertility

Male factors are implicated in up to 50% of couples being evaluated and treated for infertility with advanced assisted reproductive technologies. Genetic abnormalities, including sperm chromosome aneuploidy as well as structural aberrations, are one of the major causes of infertility. The use of chromosome-specific DNA probes labeled with fluorochromes, particularly the combination with multiple probes, has been used to indirectly study the sperm chromosome by fluorescent in situ hybridization (FISH). Clinically, this technique is also used to assess the sperm of men recovering from gonadotoxic treatment. Recent advances in this technology facilitate the evaluation of sperm aneuploidy. Sperm FISH is a widely used screening tool to aid in counseling couples with severe male factor infertility, especially in cases of prior repeated in vitro fertilization/intracytoplasmic sperm injection failure or recurrent pregnancy loss. Automation of FISH imaging and analysis, as well as the development of emerging techniques such as comparative genomic hybridization, will all contribute to the promise of future diagnostic approaches aimed at improving the quality, ease, and efficiency of aneuploidy analysis.

Cytogenetic determinants of male fertility

BACKGROUND

Cytogenetic abnormalities have been known to be important causes of male infertility for decades.

METHODS

Research publications from 1978 to 2008, from PubMed, have been reviewed.

RESULTS

These studies have greatly improved our information on somatic chromosomal abnormalities such as translocations, inversions and sex chromosomal anomalies, and their consequences to the cytogenetic make-up of human sperm. Also, we have learned that infertile men with a normal somatic karyotype have an increased risk of chromosomally abnormal sperm and children. New techniques such as single sperm typing and synaptonemal complex analysis have provided valuable insight into the association between meiotic recombination and the production of aneuploid sperm. These meiotic studies have also unveiled errors of chromosome pairing and synapsis, which are more common in infertile men.

CONCLUSIONS

These studies allow us to provide more precise information to infertile patients, and further our basic knowledge in the causes of male infertility.

Freezing-free preservation of human spermatozoa--a pilot study

This study tested a method for maintaining human spermatozoa without freezing for subsequent use in intracytoplasmic sperm injection (ICSI). We demonstrated that human sperm stored in electrolyte-free solution maintain their motility and viability for at least 4 and 6 weeks, respectively. We also have shown that preserved spermatozoa are fully functional in ICSI. Sperm chromosome analysis after injection of human sperm into mouse oocytes revealed that two weeks of storage does not negatively affect sperm DNA integrity. A mouse model was used to analyze the ability of preserved sperm to participate in normal embryogenesis. Mouse sperm preserved in electrolyte-free solution in a similar manner as human sperm maintained motility for up to 3 weeks. When mouse spermatozoa stored for 1 week were injected into the oocytes by ICSI, they yielded normal blastoctysts and normal viable fetuses. The results of the study bear significance for human assisted reproduction technologies (ART) and provide clinicians and infertile patients with a new method that can simplify sperm preparation for ICSI, assisting men who are unable to provide semen on the day of assisted fertilization.

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

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

Effect of paternal age on the frequency of cytogenetic abnormalities in human spermatozoa

Many surveys have been performed to find etiological relationships between pregnancy outcome and specific risk factors, such as exposure to chemicals and radiation or parental age. Advanced maternal age is a strong risk factor for trisomic pregnancies, albeit there are considerable variations among the different chromosomes. The definite incidence of the various structural and numerical chromosome aberrations in spontaneous abortions and liveborns is well known, as well as the rate of maternally and paternally derived rearrangements. Nevertheless studies have failed to assert an age-dependent risk for men fathering chromosomally abnormal children. New techniques using fluorescence in situ hybridization render it possible to analyze spermatozoa directly for numerical and, to some extent, for structural aberrations. This article compiles the findings of studies on human spermatozoa over the last few years.

Mechanisms of nondisjunction in human spermatogenesis

A reduction in recombination in the pseudoautosomal region is associated with an increased frequency of aneuploid 24,XY human sperm. Similarly, individuals with paternally derived Klinefelter syndrome (47,XXY) also have a paucity of recombination in the chromosomes that have undergone nondisjunction. Meiotic studies using newly developed immunocytogenetic techniques have demonstrated errors of chromosome synapsis and significantly reduced recombination in infertile men with nonobstructive azoospermia. These men have an increased risk of aneuploidy in sperm that have been surgically removed from the testes. Thus, evidence is starting to accumulate that reduced recombination has a marked effect on the generation of aneuploid sperm.

The epigenetic environment: secondary sex ratio depends on differential survival in embryogenesis

Live human births are usually more than half male, in spite of excess losses of males throughout fetal development. These observations together demand an excess of males near the beginning of pregnancy greater than that seen at birth. Reductions of the usual excess of males among human live births have widely been considered to represent consequences of untoward circumstances surrounding conception. Repeated competent research efforts have found no evidence for any bias in gametogenesis or fertilization in favour of Y-bearing sperm. Male embryogenesis is faster and more efficient, leaving females in excess among failures before the fetal period. Sex differences in speed and efficiency of embryogenesis, dependent for example on epigenetic differences such as genomic imprinting, produce an excess of males at the transition from embryogenesis to clinical pregnancy, that will survive the male excess of losses throughout the fetal period, to yield an excess of males among live births. Changes in, or mediated by, the epigenetic environment of embryogenesis provide the most plausible prospects for causes of changes in secondary sex ratio.

Effect of paternal age on human sperm chromosomes

OBJECTIVE

To investigate whether increased age alters the frequency and type of chromosomal anomalies in human spermatozoa.

DESIGN

Semen specimens were collected from donors via masturbation; cytogenetic studies were performed on sperm chromosomes after heterologous (human-hamster) in vitro fertilization.

SETTING

Cytogenetics Laboratory, Genetics Department, Faculty of Medicine of Ribeirão Preto, University of São Paulo, Brazil.

PATIENT(S)

Seven men ages 59-74 (older group) and five men ages 23-39 (control group).

MAIN OUTCOME MEASURE(S)

Frequency and types of chromosomal anomalies in older and control group donors.

RESULT(S)

The frequency of numerical and structural aberrations (acentric fragments and complex radial figures) was significantly greater in chromosomes of older donors when compared with those of the control group.

CONCLUSION(S)

The higher frequency of sperm chromosome aberrations in older men was mainly a result of increased nondisjunction, acentric fragments, and complex radial figures.

Sperm chromosome abnormalities in men with severe male factor infertility who are undergoing in vitro fertilization with intracytoplasmic sperm injection

OBJECTIVE

To investigate the potential paternal contribution to the risk of fetal chromosomal anomalies after intracytoplasmic sperm injection (ICSI).

DESIGN

Spermatozoa isolated from testicular tissue and ejaculated specimens of consenting patients undergoing testicular biopsy and ICSI were analyzed for chromosomes X, Y, and 18 by FISH.

SETTING

Assisted reproductive technology program.

PATIENT(S)

Consenting patients undergoing testicular biopsy and ICSI, severe oligozoospermic patients, and normal fertile donors.

INTERVENTION(S)

None.

MAIN OUTCOME MEASURE(S)

The rate of chromosome abnormalities in testicular sperm with regard to the type of azoospermia and ejaculated sperm compared to healthy men.

RESULT(S)

The mean serum levels of FSH in the groups with nonobstructive azoospermia (n = 9), obstructive azoospermia (n = 10), severe oligozoospermia (n = 9), and the normal donors (n = 6) were 17.5 +/- 8.2 (P<.05), 3.5 +/- 2.6, 14.6 +/- 3.5 (P<.05), and 3.1 +/- 0.4 IU/mL, respectively. The corresponding rates of sperm chromosome abnormalities among these groups were 19.6% (P<.001), 8.2% (P<.001), 13.0% (P<.001), and 1.6%, respectively. The corresponding rates of disomy among these groups were 7.8% (12 of 153 spermatozoa), 4.9% (18 of 367), 6.2% (109 of 1,751), and 1% (5 of 500 spermatozoa), respectively. Errors in chromosomes X and Y were significantly more common than in chromosome 18.

CONCLUSION(S)

The present findings demonstrate a linkage between gonadal failure (high serum FSH levels) and the occurrence of sperm chromosome aneuploidies. Our findings may explain the increased incidence of sex chromosome abnormalities found after IVF in the severe male factor patient population. Genetic screening during pregnancy or before embryo replacement should be considered carefully.

The rationale for a national prospective cohort study of environmental exposure and childhood development

Evidence is growing that pre- and perinatal exposures and factors play a role in not only childhood but adulthood disorders. Therefore, there is a compelling need to undertake a national cohort study to evaluate the effects of such factors, ideally through adult life. Several recent developments, including advancements in computer technology, the management, storage, and analysis of biological specimens, and the rapid growth of genetic markers, facilitate the evaluation of the influence of environmental exposures on the subsequent risk of developmental abnormalities and disease. The rationale behind the establishment of such a cohort is discussed.

An appreciation of modern ART

As we have entered into the new millennium, it is difficult not to recognize ART as one of the most dynamic and rapidly emerging fields in all of medicine. What began as an experimental procedure in animals has developed into a multidisciplinary technology. A great debt is owed to the field of animal husbandry. In humans, implantation is inefficient and has been recognized as the rate-limiting step in reproduction. In vitro fertilization has allowed the observation of human gamete interaction in the laboratory. A milestone was reached when ART allowed couples with infertility to have success rates that exceeded those associated with normal human fecundity. Continued innovations are improving the rate of embryonic implantation. Blastocyst transfer will have a major role in the future of ART. It is common for the couple with infertility to battle their problem by increasing the frequency of intercourse because it is the only weapon at their disposal. So, too, did clinicians increase the number of embryos transferred to the uterus. New developments promise to challenge the long-held contention that successful IVF/embryo transfer is positively correlated with the number of oocytes retrieved or the number of embryos transferred. More accurate reporting will enable us to measure the impact of technologic improvements that improve implantation rates and decrease multiple gestations. The future holds the promise of some tangible goals. The development of in vitro maturation of immature oocytes could lead to an era in which oocytes are harvested without the need for controlled ovarian hyperstimulation. This would provide for the possibility of the banking of gametes. Women could preserve or store their fertility at a young age in a manner similar to that which has been possible for men for decades. They could avoid the increased risk for aneuploidy seen with the age of 35, and theoretically, they should have a lower risk for miscarriage. The future is near. One day, ART will be perfected so that a single embryo transfer will be the standard of care. Soon it will be possible to know all about the genetic makeup of that embryo and it will be routinely selected from its cohort by virtue of those genetic traits.

The ratio of X- and Y-bearing sperm in ejaculates of men with three or more children of the same sex

PURPOSE

The present study evaluated the proportions of X-bearing and Y-bearing sperm within the semen of donors who were the declared fathers of three or more sons or daughters.

METHODS

The proportions of sperm were determined using dual-color fluorescence in situ hybridization to identify the X and Y chromosomes.

RESULTS

The only difference observed was in semen volume. There was no increase in the proportion of Y-bearing sperm for men with only sons (49.7 +/- 1.3%) or of X-bearing sperm for men with only daughters (44.8 +/- 2.6%).

CONCLUSIONS

A preponderance of either sons or daughters in a family cannot be explained simply by an altered ratio of X-bearing and Y-bearing sperm in the father's semen.

Simultaneous detection of X- and Y-bearing bull spermatozoa by double colour fluorescence in situ hybridization

Double colour fluorescence in situ hybridization with sex chromosome probes was applied on sperm cells of five Swedish Holstein-Friesian bulls. It was demonstrated that cosmids with strong fluorescence signals and scraped chromosomes can successfully be used as markers in this type of study. X and Y segregated as expected according to a 1:1 ratio, and there were no interindividual variations. There was a tendency for there to be more Y- than X-bearing spermatozoa, but this bias was assumed to be due to the markers used. Disomic spermatozoa occurred with a frequency of more than 0.1 % (0.067% XX, 0.029% YY, and 0.029% XY), which is considerably lower than the frequency in humans. Diploid sperm cells occurred with a frequency of 0.05 %.

Genetics of human sperm

PURPOSE

Chromosome abnormalities in sperm were studied by fluorescence in situ hybridization to determine the frequency and distribution of abnormalities in normal men and the effect of donor age on the frequency of abnormalities. Studies of chemotherapy and infertility patients assessed any increased risk in these populations.

METHODS

Multicolor fluorescence in situ hybridization was performed on the sperm samples to assess aneuploidy frequencies for chromosomes 1, 2, 4, 9, 12, 13, 15, 16, 18, 20, 21, X, and Y as well as "sex ratios" and frequencies of diploid sperm.

RESULTS

Most chromosomes yielded disomy estimates of approximately 0.1%, whereas the frequencies for chromosome 21 and the sex chromosomes were significantly elevated. The only chromosome to show a significant paternal age effect was YY disomy. Chemotherapy patients did not have an increased risk of aneuploid sperm 2-13 years after treatment. Infertility patients had an increased risk of disomy for chromosome 1, 13, 21, and XY.

CONCLUSIONS

Multicolor fluorescence in situ hybridization analysis allows comparison of sperm from various populations of men and has demonstrated that infertile patients have a significant increase in the frequency of aneuploid sperm.

DNA methylation of the extraembryonic tissues: an in situ study on human metaphase chromosomes

DNA methylation level and pattern of human metaphase chromosomes from extraembryonic tissues (chorionic villi and placental fibroblasts) were analysed in situ. The DNA methylation global level of these tissues was studied by comparing them with the one observed in fetal fibroblasts and adult lymphocytes. In order to assess the tissue specificity and significance of the observed differences, chromosomal preparations were then treated in parallel. They were first stained with distamycin A/DAPI and pictured, then treated with immunofluorescent staining using monoclonal antibodies raised against 5-methylcytosine. Compared with metaphases from lymphocytes or placental and fetal fibroblasts, distamycin-A/DAPI stained metaphases and constitutive heterochromatic regions with very similar intensities. In contrast, in chorionic villi, the immunofluorescent intensities revealing the presence of 5-methylcytosine was much duller than in the other tissues. In addition, in both chorionic villi and placental fibroblasts, large differences were observed between various chromosome structures within individual metaphases. In particular, the secondary constriction of chromosome 9, the distal segment of chromosome Y and the short arms of acrocentric chromosomes exhibited a much lower staining than the one observed for the secondary constrictions of chromosome 1 and 16 of the same metaphases. Because all these structures are known to be deeply methylated in other somatic tissues, this suggests that in extraembryonic tissues DNA methylation level remained hypomethylated and the pattern is under precise control.

Chromosome abnormalities in human beings

Constitutional chromosomal abnormalities are an important cause of miscarriage, infertility, congenital anomalies and mental retardation in humans. Most human constitutional chromosomal imbalance results from aneuploidy, a condition that appears to be much more frequent in humans than in any other species studied. Chromosomal rearrangements and segmental deletions and duplications also occur in humans, but much less often. Although treatment of human somatic cells with some environmental agents produces chromosomal damage, no measurable increase in the frequency of constitutional chromosomal abnormalities has been unequivocally demonstrated among the children of parents exposed to any agent. Recent work has provided insight into a variety of mechanisms by which chromosomal abnormalities can arise during gametogenesis and early embryogenesis. Mechanisms have also been recognized that can correct or partially compensate for chromosomal imbalance, sometimes permitting survival of conceptuses that would otherwise be lost early in gestation. This improved understanding can be used to refine future studies of the cytogenetic effects of environmental exposures.

Fluorescence in situ hybridization studies on the sex chromosome constitution of human sperm

More males are conceived than females and more males are born as a result of in vitro fertilization (IVF) and donor insemination procedures. All donor sperm samples are frozen for a minimum of 6 months before they are used. The ratio of more boys to girls has been consistently reported over the years. A similar finding has been noted in the Galway Fertility Unit at University College Hospital Galway, Ireland. Traditionally, it has been accepted that the reason for this excess is that a Y chromosome-bearing sperm swims faster than the X-bearing sperm because it contains less DNA and is therefore "lighter." To test this hypothesis, semen samples were collected at the Galway Fertility Unit from men presenting for routine semen assessments. Each sample was divided into a number of aliquots. The first aliquot was assessed as the "raw" ejaculate to measure the initial ratio of X to Y. The second aliquot was prepared using Percoll density gradients, which allows for greater recovery of sperm with higher motility and improved sperm function. The final aliquot was frozen. The frozen sample was later thawed and prepared using Percoll. The prepared sperm were kept for 48 h and sampled at the time of preparation and at 24 h and 48 h to establish if there was any differential survival over time. The X:Y ratio was analyzed using the technique of fluorescence in situ hybridization (FISH). This allowed the sex chromosomes to be specifically stained and identified simultaneously. No difference was found in the X:Y ratio of the sperm. Therefore, any selection for the Y sperm must take place at some later stage.

Aneuploidy detection in human sperm nuclei using PRINS technique

Rapid and specific identification of chromosomes can be attained in situ using the PRimed IN Situ (PRINS) labelling technique. We have adapted this technique to mature human sperm in combination with a protocol for simultaneous decondensation and denaturation of sperm nuclei. This strategy allowed us to obtain double labelling of human spermatozoa in a < 2-hr reaction. In the present study, we report the estimates of disomy for chromosomes 3, 7, 10, 11, and 17 on 64,642 spermatozoa from 2 normal males. The incidences of disomy ranged from 0.28-0.34%. There were no significant interindividual or interchromosomal differences in disomy rates.

Penetration of concanavalin-A-treated Chinese hamster oocytes by golden hamster spermatozoa in vitro, and chromosome analysis of hybrid 1-cell zygotes

Pretreatment of zona-free Chinese hamster (CH) oocytes with three kinds of lectin--concanavalin A (Con-A), phytohaemagglutinin-P (PHA) and wheat germ agglutinin (WGA)--was attempted in order to improve penetration by golden hamster (GH) spermatozoa in vitro. Con-A had no significant effect on penetration at 2 micrograms/ml, adequately facilitated oocyte-sperm fusion at 4 micrograms/ml, and caused excessive sperm binding and resultant severe polyspermy at 10 micrograms/ml. Neither PHA nor WGA had positive effects on sperm penetration at any concentrations (2-10 micrograms/ml) examined. Using the Con-A (4 micrograms/ml) pretreatment, high rates of interspecific fertilisation and subsequent chromosome analysis of hybrid 1-cell zygotes were achieved. Among 258 CH oocytes used, 212 (82.2%) were fertilised and 153 (72.2% of fertilised ova) developed to the first cleavage metaphase. Eventually, 132 CH-derived chromosome complements and 153 GH-derived ones were successfully karyoanalysed. Incidences of aneuploidy and structural anomaly were 3.1% and 2.3% in CH complements, and 1.4% and 6.5% in GH complements, respectively. These incidences were not significantly different from those obtained by intraspecific in vivo fertilisation, suggesting that our interspecific in vitro fertilisation system does not cause chromosome aberrations.

PRINS as a method for rapid chromosomal labeling on human spermatozoa

Direct in situ labeling of human spermatozoa was performed using the PRINS method. This technique is based on annealing of specific oligonucleotide primers, and subsequent primer extension by a Taq DNA polymerase. The reaction was carried out on a programmable temperature cycler, and labeling was obtained in a 1-hr reaction. The method was successfully tested with specific primers for chromosomes 13, 16, and 21. This suggests that PRINS may be a fast and reliable technique for detecting aneuploidies.

Chromosome investigation in in vitro fertilization failure

PURPOSE

A chromosomal complement of 227 human oocytes was studied to provide information on the frequency and type of chromosomal abnormalities in oocytes failing in vitro fertilization.

RESULTS

Normal haploid chromosome complement was found in 54.6%; chromosomal abnormalities consisting of diploid sets were identified in 16.7% and aneuploidy was observed in 26%. Premature condensation of sperm chromosomes of the GI-phase was observed in 22.9% oocytes. Male infertility was correlated with an increase in the rate of aneuploidy when compared with tubal infertility. The rate of chromosome abnormalities for the oocytes recovered from women who had no fertilized oocytes was significantly higher compared to those with at least one oocyte fertilized.

CONCLUSION

A high frequency of chromosome abnormalities in unfertilized oocytes suggests that natural selection against chromosome abnormalities may occur even prior to fertilization.

Identification of two human sperm populations using flow and image cytometry

Flow cytometric studies of human sperm from fertile men display a constant and characteristic bimodal nonartifactual DNA pattern confirming the existence of two distinct populations. The main population is represented by a peak followed by a shoulder ("marginal population"). The appearance of this marginal population fluctuates with either freezing and thawing or with Percoll gradient centrifugation. We have analyzed both the main and marginal sperm populations by flow cytometry after cell sorting, laser scanning cytometry, light microscopic evaluation, and their sensitivity to DNase digestion. We have observed that the marginal population detected in fertile men represents a sperm group altered in the nuclear condensation, yielding unstable chromatin which appears more stainable with propidium iodide.

Future of germ cell cytogenetics

The celebration of the 25th Anniversary of the Environmental Mutagen Society provides an excellent opportunity to assess the status of research in a broad range of areas, with an emphasis on the directions in which they are going. This chapter concentrates on the analysis of chromosomal alterations in mammalian germ cells. The future developments in germ cell cytogenetics research will build heavily upon techniques developed over the past 25 years. With these it is possible to assess numerical and structural alterations in the male in differentiating spermatogonia, spermatocytes, and post-meiotic cells (at the first cleavage division) and for the female in oocytes and the zygote. The most predictable advances will be in the identification of specific alterations through FISH of interphase spermatozoa in humans and further improvements with the human sperm/hamster egg in vitro fertilization technique. Of particular importance is the fact that this will allow for the study of effects in human germ cells. From a more speculative viewpoint it might be possible to assess the role of particular genomic organization on genetic outcomes by direct observation; these might include genomic imprinting and the visual separation of male and female genomes. The overall aim of germ cell cytogenetic studies will remain as improving our ability to identify and estimate the true genetic risk in humans.

Association between human in vitro fertilization rate and pregnancy outcome: a possible involvement of spermatozoal quality in subsequent embryonic viability

A conventional view of mammalian fertilization is that the active component of the process: the spermatozoon, by virtue of its progressive motility and acrosomal enzymes, penetrates an otherwise passive oocyte. This concept has placed bias on spermatozoal normality as largely determining the outcome of fertilization; once this has been achieved then the contribution of the spermatozoon is often forgotten, and attention switches to the maternally derived "blue-print" for early embryonic development. Paternal genomic contribution is known to start at the eight-cell stage in the human, but this is usually after the time when early cleavage stage (2 to 8-cell stage) embryos are replaced in human assisted reproductive technologies (ART) procedures such as in vitro fertilization and embryo transfer (IVF-ET). Hence, fundamental abnormal contributions to embryogenesis derived from the fertilizing spermatozoon have often been ignored. Human IVF-ET has permitted far greater powers of analysis of the fertilization event, and fertilization success appears to be determined in such a system by three main factors: spermatozoal quality, oocyte quality, and quality of in vitro culture conditions (the gamete environment). If the second two factors are more carefully controlled than the first, as is the usual emphasis in routine human IVF practice, then any large variation in fertilization rates that are also significantly related to embryonic viability and ultimately pregnancy outcome, may be thought to be more directly associated with original quality of the fertilizing spermatozoon. An analysis of results of 758 IVF cases provides preliminary evidence to show that there is a close association between human in vitro fertilization rate and subsequent embryo viability following replacement. In accepting this hypothesis as a possibility, we should drastically change our attitude from one of the spermatozoon as a robust, simple initiator of embryonic development, and embrace the idea of the vulnerability of such germ cells both during and after their production, and how detrimental influences on this might profoundly affect embryogenesis after successful fertilization.

High resolution mapping of interstitial long arm deletions of chromosome 16: relationship to phenotype

The breakpoints of seven interstitial deletions of the long arm of chromosome 16 and two ring chromosomes of this chromosome were mapped by in situ hybridisation or by analysis of mouse/human somatic cell hybrids containing the deleted chromosome 16. Use of a high resolution cytogenetic based physical map of chromosome 16 enabled breakpoints to be assigned to an average resolution of at least 1.6 Mb. In general, interstitial deletions involving q12 or q22.1 have broadly similar phenotypes though there are differences in specific abnormalities. Deletions involving regions more distal, from 16q22.1 to 16q24.1, were associated with relatively mild dysmorphism. One region of the long arm, q24.2 to q24.3, was not involved in any deletion, either in this study or in any previous report. Presumably, monosomy for this region is lethal. In contrast, patients with deletions of 16q21 have a normal phenotype. These results are consistent with the proposed distribution of genes, frequent in telomeric Giesma light band regions but infrequent in G positive bands.

Simultaneous detection of X- and Y-bearing human sperm by double fluorescence in situ hybridization

Double fluorescence in situ hybridization (FISH) was used to detect sex chromosomes in decondensed human sperm nuclei. Biotinylated X chromosome specific (TRX) and digoxigenin-labeled Y chromosome specific (HRY) probes were simultaneously hybridized to sperm preparations from 12 normal healthy donors. After the hybridization, the probes were detected immunocytochemically, using two different and independent affinity systems. Ninety-six percent of the 12,636 sperm showed fluorescent labeling, of which 47.4% were haploid X and 46.8% were haploid Y. A frequency of 0.46% of XX-bearing sperm (0.28% disomic, 0.18% diploid) and 0.38% YY-bearing sperm (0.21% disomic, 0.17% diploid) was found. The overall proportions of X- and Y-bearing sperm in the ejaculates were 47.9% and 47.2%, respectively, which was not significantly different from the expected 50:50 ratio. In addition 0.21% of cells appeared to be haploid XY-bearing sperm, 0.62% were diploid XY-bearing cells, and 0.05% of cells were considered to be tetraploid cells. The application of double FISH to human sperm using X-chromosome and Y-chromosome probes has allowed a more accurate assessment of the sex chromosal complements in sperm than single FISH method and quinacrine staining for Y-bodies.

The sex ratio of normal and manipulated human sperm quantitated by the polymerase chain reaction

OBJECTIVE

To establish the primary sex ratio, the relative abundance of X and Y chromosome-bearing sperm, in unselected sperm and in sperm selected by swim-up or Sephadex filtration (SpermPrep column; Fertility Technologies, Inc., Natick, MA). This was done to evaluate the possibility that these semen manipulations change the primary sex ratio.

DESIGN

Ninety-eight unmanipulated semen samples were analyzed for sex chromosome content using quantitative polymerase chain reaction (PCR). A smaller number of samples was analyzed before and after either swim-up or Sephadex filtration.

RESULTS

The mean percentage of all sex chromosomes identified as a Y chromosome in unmanipulated semen samples ranged from 41.9% to 56.7%, with a mean average of 50.3%. There was no significant change in sex chromosome composition after either swim-up (n = 17) or column filtration (n = 20).

CONCLUSIONS

The chromosome compositions of semen samples from a large number of men have equal numbers of X and Y. Swim-up and SpermPrep filtration do not appear to alter the primary sex ratio.

Detection of genetic damage in human sperm

Assessment of genetic damage in human sperm is now possible using the hamster oocyte/human sperm fusion technique. This cross-species in vitro assay provides precise human sperm karyotypes that can be banded for identification of individual chromosomes and numeric and structural abnormalities. This technique is time-consuming and difficult but there are now 11 laboratories in 7 different countries reporting results on normal men and men at increased risk of sperm chromosomal abnormalities. Men who have been exposed to radiotherapy and chemotherapy have been shown to have an increased frequency of chromosomal abnormalities in their sperm. A few laboratories have reported results on the use of fluorescence in situ hybridization (FISH) of interphase sperm nuclei. This appears to be a promising new technique for the assessment of aneuploidy and FISH results from our laboratory correlate well with our frequency of aneuploidy determined by sperm chromosome analysis. Thus it is possible that, in the future, FISH might be used as a simple rapid screen of potentially aneugenic agents.

The outcome of pregnancy and prenatal chromosomal diagnosis of fetuses in couples including a translocation carrier

In order to evaluate the relation between chromosomal translocation and the outcome of pregnancy, 50 couples were examined. Subjects consisted of 35 couples that included a reciprocal translocation carrier; 13 included a Robertsonian translocation carrier and 2 included a carrier of a mosaic reciprocal translocation. The reasons for performing chromosomal examinations were mainly infertility and abnormality of neonates. The rates of miscarriages and neonatal abnormalities in prior pregnancies were significantly higher than the birth rate of morphologically normal newborns. The presence of a translocation is closely related to reproductive failure because of the chromosomal imbalance. However, prenatal chromosomal examination after the 15th gestational week in subsequent pregnancies revealed that almost half of the fetuses showed normal karyotypes and only 12.8 per cent of the fetuses showed a chromosomal imbalance. Many chromosomally imbalanced fetuses are spontaneously aborted before amniocentesis. The risk of chromosomal imbalance is relatively low in prenatal diagnosis, but partial trisomies of small rearrangements tend to be preserved.

The genetic risks of in vitro fertilization techniques: the use of an animal model

PURPOSE

The influence of some technical and biological parameters on the genetic characteristics of embryos derived from in vitro fertilization (IVF) techniques was studied.

METHOD

Using a murine model, we assessed the effect of gamete manipulation, gamete maturation stage, and maternal age on the chromosome complements of first-cleavage embryos.

RESULTS AND CONCLUSIONS

We found a positive correlation between some of these parameters and the incidence of the different chromosome abnormalities studied. Regarding aneuploidy, we observed an influence of maternal age, using both prepubertal and old females. Polyspermy showed a positive correlation with in vitro fertilization, the immaturity and overmaturity of the oocytes employed, and the use of prepubertal females. The appearance of diploid female complements was related to oocyte immaturity and prepubertal females, while diploid male complements were directly related to in vitro fertilization. Premature chromosome condensation (PCC) had a direct relationship with oocyte immaturity and in vitro maturation of the oocyte. Finally, structural abnormalities were associated with the process of sperm aging in vitro.

The proliferation theory of rejuvenation

A theory concerning the molecular basis of rejuvenation is presented that postulates a central role for cell proliferation. This theory assumes that aging is due to the accumulation of multiple forms of molecular damage and that rejuvenation is due to repair. The advantages of proliferation as a means of repair are described and it is proposed that cell proliferation is required for full rejuvenation. This proliferation theory offers several advantages: a different perspective on the question of which organisms age; an explanation of aging-related phenomena that are not well handled by traditional aging theories; a novel approach to altering the aging rate; and testable implications for the design of new experimental systems and therapeutic interventions.

The implantation window

The implantation window is defined as that period when the uterus is receptive for implantation of the free-lying blastocyst. This period of receptivity is short and results from the programmed sequence of the action of oestrogen and progesterone on the endometrium. Implantation itself is a process that commences with apposition, continues through attachment to trophoblast outgrowth and decidualization. For maximal effectiveness of assisted reproductive technologies in women, it is important to know the optimal time for embryo transfer which implies a need to predict the period of uterine receptivity. At present there are no good markers of, or for prediction of, uterine receptivity. In cycles where endogenous hormonal activity is suppressed or absent, the optimal time for embryo transfer can be easily defined and lies between luteal days +3 to +5, where luteal day +1 is the first day of exogenous progesterone treatment. In the human, it is suggested that blastocyst apposition begins about LH day +6 and is complete by LH +10. Human embryos survive in vitro manipulation well, and the stage of development at which they are placed in the uterus seems less critical than in other species, provided they are at an earlier stage of development than that of the endometrium.

Survival of fetuses with 45,X: an instructive case and an hypothesis

The high (greater than 95%) fetal loss rate of 45,X embryos and fetuses has led to the suggestion that fetal survival with this karyotype requires the presence of mosaicism. However, in many instances, even given a "mild Ullrich-Turner syndrome" phenotype, mosaicism is not detected. In a pregnancy studied for advanced maternal age, CVS cultured cells showed 65% 45,X and 35% 46,X,r(X). After termination, 2 fetal tissues showed 95% 45,X cells. It is suggested that infants with the 45,X karyotype likely had mosaicism for a structurally abnormal X or Y chromosome during embryogenesis, but the abnormal cell line disappeared prior to birth.

Uniparental disomy, isodisomy, and imprinting: probable effects in man and strategies for their detection

The concept of uniparental disomy--the presence of a chromosome pair derived solely from one parent in a diploid offspring--was introduced in 1980 as a probable consequence of the high rate of germ cell aneuploidy in man, and has now been convincingly demonstrated through molecular analyses in several families. A most likely mechanism for the production of uniparental disomy is the chance reunion, and complementation, of 2 gametes aneuploid for the same chromosome member; uniparental disomy could also occur through other mechanisms including postzygotic non-segregation in a trisomic conceptus. Uniparental disomy may result in isodisomy, i.e., homozygosity of a series of contiguous alleles in a pair of homologues. The presence and degree of isodisomy in an offspring depend in turn on the occurrence, timing, and extent of the meiotic recombination that had occurred in the chromosome pair of the disomic gamete involved. Uniparental disomy with or without isodisomy can explain a number of unusual observations, such as the unexpected pattern of transmission of a genetic disorder. The two may be associated with an imprinting effect to produce pathological phenotypes, as has been observed in the mouse, and may be the basis for a number of syndromes of as yet unclear cause. The evidence for uniparental disomy, isodisomy, and imprinting in man is reviewed, and strategies for their detection presented.

The appropriate upper age limit for semen donors: a review of the genetic effects of paternal age

There is little evidence to support a correlation between increased paternal age and the incidence of chromosome anomalies. Though a few early studies demonstrated an increased risk of Down syndrome with advanced paternal age, especially after the age of 55, numerous later studies failed to confirm any paternal age effect. Among structural chromosome anomalies, only the inherited reciprocal translocations were found to be more common among children of older fathers. Chromosome analysis of semen donors would rule out this problem. There is evidence, however, that the incidence of serious nonchromosomal birth defects, especially those arising from new autosomal mutations, increases with paternal age. Risk estimates have been established for increased paternal age and contribution to new dominant mutations. The established association between increased paternal age and new autosomal mutations and the fact that most of the disorders associated with such mutations cannot be prenatally diagnosed may be important in establishing the upper age limit for semen donors. Recommendations from the literature are interpreted to advise men to have their children before age 40. This suggestion would obviously benefit immediate offspring and perhaps successive generations as well. The limit of 35 years set by AATB standards, therefore, is in harmony with such benefit, but may be too stringent in eliminating potential donors. Accordingly, the Reproductive Council of the AATB has initiated steps to modify its standards to the age limit of 40.

Preimplantation genetics: chromosomes of fragmented human embryos

STUDY OBJECTIVE

To examine the chromosome makeup of fragmented human embryos.

DESIGN

Prospective.

SETTING

Assisted reproductive technology (ART) program.

PATIENTS

One hundred twenty-one poor-quality embryos from 58 patients 31 to 40 years of age admitted for an ART program were examined for chromosome makeup.

RESULTS

Chromosome anomalies were observed in 31.9% (29/91) of poor-quality embryos, 19.8% (18/91) displayed mosaicism (diploid/haploid, diploid/triploid, diploid/aneuploid), 5.5% (5/91) showed polyploidy, 2.2% (2/91) had pulverized chromosomes, 2.2% (2/91) revealed aneuploidy, 1.1% (1/91) had prematurely condensed chromosomes, and 1.1% (1/91) had structural rearrangements involving chromosome number 2. The mean age of patients showing anomalies (36.5 years) was not significantly higher than the mean for the entire group (35.5 years).

CONCLUSIONS

The incidence of chromosome anomalies in fragmented human embryos is high. These anomalies originate either in the gametes or through mitotic nondisjunction within the embryos. It is not advisable to replace such embryos into patients going through in vitro fertilization.

A cytogenetic and molecular study of a series of 45,X fetuses and their parents

The parental origin of the single X chromosome in 10 45,X fetuses was studied using DNA restriction fragment length polymorphisms. In six the single X was maternal in origin, in one it was paternal, and in one the results were consistent with a paternal origin. Therefore the parental origin of the X in 45,X fetuses that survive to the second or third trimester of pregnancy is similar to that of spontaneous abortions and live births with a 45,X constitution. The mothers of two of the fetuses were themselves found to have an abnormal sex chromosome complement, but in neither case did it appear to be related to the chromosome abnormality in the fetus.

Role of embryonic factors in implantation: recent developments

The embryonic factors influencing implantation have been studied extensively in laboratory and domestic animals, but not in primates, including humans. Species differences make extrapolation inadvisable. Embryonic factors affecting implantation include intrinsic features of the embryo, such as its genetic constitution, morphology and hatching. Abnormal genetic constitutions or unsuccessful transitions from maternal to embryonic transcription could account for many failures of early embryonic growth and implantation. Morphology per se does not greatly influence implantation, except when it reflects an abnormal genetic constitution, e.g. in severe fragmentation, although subtle effects may be detected as experimental techniques are refined. The initiation of differentiation and intraembryonic communication between cells and cell types has been studied in animal embryos. Signals must be exchanged between the embryo and the mother to ensure satisfactory implantation. These could include platelet activating factor, prostaglandins, histamine related factors, steroids, proteins, metabolic products and immune-active factors. No one factor seems to be totally responsible for alerting the mother to the presence of an embryo, and a concerted action of these and other agents is probably responsible. The process of implantation itself is poorly understood because of a lack of adequate experimental models. The expression of complementary proteins and the role of specific enzymes and markers of endometrial and embryonic competence are factors well worthy of further study. Knowledge about human implantation is increasing because of recent developments in assisted reproductive technology, and concepts arising from many years of research in animals should find clinical applications in understanding and controlling human reproduction.

Analysis of the origin of Turner's syndrome using polymorphic DNA probes

Thirty-four families with a child or fetus with Turner's syndrome were studied using a series of polymorphic DNA probes. Analysis of the origin of the normal X chromosome was possible in all cases. In 16 families with 45,X (four fetuses and 12 livebirths), the observed X was maternal in each case, indicating a preferential loss of the paternal sex chromosome at, or before, conception. In the remaining 18 families with a variety of karyotypes, but especially in those where the child had an isochromosome of Xq or a ring X, there was again a strong tendency for the normal X to be maternal. Analysis of parental ages was performed with known origin of each abnormality, but no evidence for an increased or decreased parental age effect was detected.

Delayed fertilization and poor embryonic development associated with impaired semen quality

Delayed fertilization is common in cycles with immature oocytes. This phenomenon was observed in 42 of 423 with mature oocytes. Of the 42 cycles, 16 were excluded because of the presence of sperm autoantibodies. Sperm parameters of the remaining 26 (6.1%) cycles (group A) were compared with those in cycles with no fertilization at all (group B) and those in the control group (group C). The percentage of normal forms was 15% in group B and 24% in group A compared with 51% in group C. Fertilization rates were 32% in group A compared with 81% in group C. The incidence of poor embryonic morphology was 82% in group A compared with 29% in group C. Delayed fertilization and poor embryonic morphology associated with impaired sperm quality is of clinical and prognostic importance.

Chromosomal analysis of unfertilized oocytes and morphologically abnormal preimplantation embryos from an in vitro fertilization program

In vitro fertilization cycles yield a low percentage of pregnancies. Eighty-five to ninety percent of the transferred embryos do not implant, and the abortion rate approaches 30%. Aneuploidy is assumed to be responsible for a major portion of this pregnancy wastage. The purpose of this study was to determine if there was any correlation between morphology and chromosomal content of unfertilized oocytes and rejected embryos. To assess the chromosomal content of oocytes and embryos, we used the method described by Tarkowski in 1966. Sixty oocytes fron 28 women, aged between 27 and 41 years, were analyzed. Sixty-seven percent were aneuploid; of these, 23.35% were hyperhaploid, 23.35% were hypohaploid, 8.35% were hyperdiploid, 3.35% were diploid, and 8.35% showed premature chromosome condensation. Of 20 preimplantation embryos analyzed, 80% were aneuploid, 10% were diploid, 5% were haploid, and 5% showed structural anomaly. Correlation was found between maternal age and aneuploidy in oocytes and between morphology and genetic balance in preimplantation embryos.

Incidence and timing of pregnancy losses: relevance to evaluating safety of early prenatal diagnosis

Knowing the frequency and timing of pregnancy loss during normal gestation is integral to evaluating the safety of prenatal diagnostic techniques. That preclinical loss rates are high in humans has long been suspected, but in the past decade new data concerning these losses have become available. Cohort studies indicate that many women who show positive beta-HCG assays never show clinical evidence of pregnancy. Cytogenetic abnormalities have also recently been documented in 20% of ostensibly normal in vitro fertilization embryos. All the above are consistent with the sentinel studies of Hertig and Rock, who showed high frequencies of morphological abnormalities in preimplantation embryos. The frequency of fetal losses after clinical recognition of pregnancy is 12-15%; however, more sensitive (ultrasonographic) methods of detecting fetal demise now indicate that most clinically recognized pregnancies occur prior to 8-9 weeks, being retained in utero 2-3 weeks prior to expulsion. Loss rates are influenced by maternal age, smoking, alcohol, and other confounding variables that if not taken into account could yield spurious results concerning safety of prenatal diagnostic techniques. After 8 weeks gestation the likelihood of losing a viable pregnancy is only 3% and after 16 weeks only 1%.