Intracytoplasmic sperm injection may increase the risk of imprinting defects

Strategies for preimplantation genetic diagnosis of Angelman syndrome caused by mutations in the UBE3A gene

Angelman syndrome (AS) is a neurodevelopmental disorder associated with the loss of maternal gene expression in chromosome region 15q11-q13. AS is caused by a wide variety of genetic mechanisms, including mutations in the UBE3A gene that have been identified in 10-15% of patients; when the mother is heterozygous for the causative mutation, the risk of recurrence in subsequent pregnancies is 50%. The present authors have developed a preimplantation genetic diagnosis (PGD) assay for a family displaying a 10 bp deletion in exon 9 of the UBE3A gene, which was shared by two affected children and their phenotypically normal mother. A duplex polymerase chain reaction protocol was established, allowing the efficient amplification of the mutation together with an informative microsatellite marker (D15S122) located in intron 1 of the UBE3A gene. As most of UBE3A mutations identified so far are unique to one family, the present authors have also developed an indirect single cell protocol based upon the co-amplification of two microsatellite markers located within (D15S122) and close to the UBE3A gene (D15S1506). This strategy may be applied to all informative families requesting PGD for Angelman syndrome associated with mutations in the UBE3A gene.

Intracytoplasmic injection of spermatozoa and spermatogenic cells: its biology and applications in humans and animals

Intracytoplasmic sperm injection (ICSI) has become the method of choice to overcome male infertility when all other forms of assisted fertilization have failed. Animals in which ICSI has produced normal offspring include many species. Success rate with normal spermatozoa is well above 50% in the mouse but ICSI success rates in other animals have been low, ranging from 0.3 to 16.5%. Mouse ICSI revealed that spermatozoa that cannot participate in normal fertilization can produce normal offspring by ICSI, provided their nuclei are genomically intact. Human ICSI using infertile spermatozoa has been highly successful perhaps because of the intrinsic instability of human sperm plasma membrane. The health of children born after ICSI and other assisted fertilization techniques is of major concern. Careful analyses suggest that higher incidences of congenital malformations and/or low birth weights after assisted fertilization are largely attributable to parental genetic background and increased incidence of multiple births, rather than to the techniques of assisted fertilization. Since the physiological and nutritional environments of developing embryos may cause persisting alteration in DNA methylation, extreme caution must be exercised in handling gametes and embryos in vitro. In the mouse, round spermatid injection (ROSI) has been routinely successful but its use in humans is controversial. Whether human ROSI and assisted fertilization involving younger spermatogenic cells are medically safe must be the subject of further investigations.

Epigenetic reprogramming throughout preimplantation development and consequences for assisted reproductive technologies

Knowledge about preimplantation development is important both for basic reproductive biology and for practical applications, including livestock breeding and regenerative medicine. During preimplantation development, epigenetic modifications such as DNA methylation and histone modifications are involved in the regulation of imprinted and non-imprinted genes, in the initiation of X chromosome inactivation, and the adjustment of telomere length. The underlying events are particularly vulnerable to external factors. Characterization of expression profiles in in vivo-derived embryos of different developmental stages and understanding the mechanisms and dynamics underlying the reprogramming process are the first steps towards the analysis of the complex gene regulatory networks. They provide a baseline for the analysis of manipulated embryos of all mammalian species, including humans, to improve embryo technologies and related therapeutic applications.

Assisted reproductive technologies and birth outcomes: overview of recent systematic reviews

Several systematic reviews have been published recently on birth outcomes of infants conceived through assisted reproductive technologies (ART), compared with infants conceived spontaneously. These outcomes include perinatal mortality, preterm birth, low birthweight and birth defects. Methodological limitations of many of the individual studies (including small sample size, potential for bias in ascertainment of outcomes and considering singletons and multiples together) were obviated in these reviews by excluding studies where methods were considered inadequate, by conducting meta-analyses using data from all methodologically sound studies (small and large) and by examining singletons separately. Overall, the reviews indicate few differences between outcomes in ART twins compared with twins conceived spontaneously. However, in singleton ART infants, there are around two-fold increases in risk of perinatal mortality, low birthweight and preterm birth, about a 50% increase in small for gestational age and a 30–35% increase in birth defects, compared with singletons conceived spontaneously. Couples considering ART should be counselled about the increased risk of adverse outcomes. Epidemiologists, in conjunction with clinical and laboratory colleagues, should now focus on large, methodologically sound studies with long-term follow up that seek to identify the reasons for these increased risks and their long-term consequences, whether they are associated with particular technologies and causes of infertility, and how they might be reduced.

Mechanisms for the environmental regulation of gene expression

The environment can play a significant role in the production of phenotypes. However, the developmental mechanisms by which the environment can affect normal development are only now being elucidated. At least three paths have been found through which the environment can modify gene expression. The first is the neuroendocrine route, wherein the nervous system transmits signals from the environment to the endocrine system and the hormones alter gene expression. The second pathway involves environmental agents that change the methylation pattern of genes, thereby altering their transcriptional capacities. The third route involves the direct induction of gene expression in the host by its microbial symbionts. The normal environmental regulation of phenotype production should be considered a normal component of development and developmental biology.

Perinatal outcome of ICSI pregnancies compared with a matched group of natural conception pregnancies in Flanders (Belgium): a cohort study

A retrospective cohort study was conducted with an intracytoplasmic sperm injection (ICSI) group and a naturally conceived comparison group. A total of 1655 singleton and 1102 twin ICSI births were studied with regard to perinatal outcome. Control subjects (naturally conceived pregnancies) were selected from a regional registry and were matched for maternal age, parity, place of delivery, year of birth and fetal sex. The main outcome measures were duration of pregnancy, birth weight, Apgar score <5 after 5 min, neonatal complications, perinatal death and congenital malformations. Twin births, when compared with singletons, carry a much higher risk of poor perinatal outcome. For both ICSI singletons and ICSI twins, no significant difference was found between ICSI and naturally conceived pregnancies for all investigated parameters. After excluding like-sex twin pairs, ICSI twin pregnancies were at increased risk for perinatal mortality (OR = 2.74, CI = 1.26-5.98), prematurity (OR = 1.38, CI = 1.10-1.75) and low birth weight (OR = 1.34, CI = 1.06-1.69) compared with spontaneously conceived different-sex twin pairs. In conclusion, the perinatal outcome of ICSI singleton and twin pregnancies was very similar to that of spontaneously conceived pregnancies in this large cohort study. After excluding like-sex twin pairs, ICSI twins were at increased risk for prematurity, low birth weight and higher perinatal mortality compared with the natural conception comparison group.

Idiopathic impaired spermatogenesis: genetic epidemiology is unlikely to provide a short-cut to better understanding

The aetiology of impaired spermatogenesis is unknown in the majority of subfertile men. From several studies of concordance for involuntary childlessness among men, we can conclude that there is a substantial familial component in male subfertility and that shared loci segregating through families can be assumed. We now know that deletions on the Y chromosome, which do not penetrate fully, account for some of these cases. There are good reasons to suspect that other cases result from mutations in genes located elsewhere in the genome. In this article, we discuss different approaches to unravelling the molecular basis of impaired spermatogenesis originating from genetic abnormalities in chromosomes other than the Y chromosome. Genetic mapping studies are in general a good approach to detect disease-causing genes that are segregating through a population; they can provide a shortcut to unravelling the biochemistry of a disease. In this paper, we explain our reasons for arguing that linkage and association studies are no promising means to identify the genes causing impaired spermatogenesis. We conclude that direct screening of candidate genes for mutations will be necessary to detect genes involved in impaired spermatogenesis. However, this approach requires studies of the biochemical pathways of normal and abnormal spermatogenesis. Since we have a poor understanding of these pathways, more research is needed into the biochemistry of spermatogenesis.

Epigenetics and human disease

Epigenetics is comprised of the stable and heritable (or potentially heritable) changes in gene expression that do not entail a change in DNA sequence. The role of epigenetics in the etiology of human disease is increasingly recognized with the most obvious evidence found for genes subject to genomic imprinting. Mutations and epimutations in imprinted genes can give rise to genetic and epigenetic phenotypes, respectively; uniparental disomy and imprinting defects represent epigenetic disease phenotypes. There are also genetic disorders that affect chromatin structure and remodeling. These disorders can affect chromatin in trans or in cis, as well as expression of both imprinted and nonimprinted genes. Data from Angelman and Beckwith-Wiedemann syndromes and other disorders indicate that a monogenic or oligogenic phenotype can be caused by a mixed epigenetic and genetic and mixed de novo and inherited (MEGDI) model. The MEGDI model may apply to some complex disease traits and could explain negative results in genome-wide genetic scans.

Genomic imprinting and assisted reproduction

Imprinted genes exhibit a parent-of-origin specific pattern of expression. Such genes have been shown to be targets of molecular defects in particular genetic syndromes such as Beckwith-Wiedemann and Angelman syndromes. Recent reports have raised concern about the possibility that assisted reproduction techniques, such as in vitro fertilization or intracytoplasmic sperm injection, might cause genomic imprinting disorders. The number of reported cases of those disorders is still too small to draw firm conclusions and the safety of these widely used assisted reproduction techniques needs to be further evaluated.

Expression of mRNAs for DNA methyltransferases and methyl-CpG-binding proteins in the human female germ line, preimplantation embryos, and embryonic stem cells

Recent evidence indicates that mammalian gametogenesis and preimplantation development may be adversely affected by both assisted reproductive and stem cell technologies. Thus, a better understanding of the developmental regulation of the underlying epigenetic processes that include DNA methylation is required. We have, therefore, monitored the expression, by PCR, of the mRNAs of DNA methyltransferases (DNMTs), methyl-CpG-binding domain proteins (MBDs), and CpG binding protein (CGBP) in a developmental series of amplified cDNA samples derived from staged human ovarian follicles, oocytes, preimplantation embryos, human embryonic stem (hES) cells and in similar murine cDNA samples. Transcripts of these genes were detected in human ovarian follicles (DNMT3A, DNMT3b1, DNMT3b4, DNMT1, MDBs1-4, MeCP2, CGBP), germinal vesicle (GV) oocytes (DNMT3A, DNMT3b1, DNMT1, MDBs1-4, MeCP2, CGBP), mature oocytes (DNMT3A, DNMT3b1, DNMT1, CGBP), and preimplantation embryos (DNMT3A, DNMT3b1, DNMT1, DNMT3L, MBD2, MDB4, CGBP). Differential expression of DNMT3B gene transcripts in undifferentiated (DNMT3b1) and in vitro differentiated human ES cells (DNMT3b3) further demonstrated an association of the DNMT3b1 transcript variant with totipotent and pluripotent human cells. Significantly, whilst the murine Dnmt3L gene is both expressed and essential for imprint establishment during murine oogenesis, transcripts of the human DNMT3L gene were only detected after fertilisation. Therefore, the mechanisms and/or the timing of imprint establishment may differ in humans.

Primate models for assisted reproductive technologies

Although the deliberate creation of human embryos for scientific research is complicated by ethical and practical issues, a detailed understanding of the cellular and molecular events occurring during human fertilization is essential, particularly for understanding infertility. It is clear from cytoskeletal imaging studies of mouse fertilization that this information cannot be extrapolated to humans because of unique differences in centrosomal inheritance. However, the cytoskeletal rearrangements during non-human primate fertilization are very similar to humans, providing a compelling animal model in which to examine sperm–egg interactions. In order to address this key step in primate fertilization and to avoid the complexities in working with fertilized human zygotes, studies are now exploring the molecular foundations of various assisted fertilization techniques in a monkey model. While intracytoplasmic sperm injection with ejaculated or testicular sperm is quite successful in primate models, there are some specific differences when compared with standard IVF that warrant further investigation, particularly in regards to nuclear remodeling, genomic imprinting, Y-chromosome deletions and developmental outcomes. Similarly, primate models have been useful for examining spermatid function during fertilization but these have met with limited success. One area of primate reproductive research that has yet to be mastered is reproductive cloning. Genetically identical primates would provide the ultimate approach for accelerating stem cell-based therapies for a number of neurodegenerative diseases such as Alzheimer’s and Parkinson’s disease, as well as targeted gene therapies for various metabolic disorders.

Use of the egg-share model to investigate the paternal influence on fertilization and embryo development after in vitro fertilization and intracytoplasmic sperm injection

OBJECTIVE

To investigate whether sperm from different males can influence fertilization and embryo development.

DESIGN

To use an egg-sharing model, in which the eggs from one woman are shared between herself and a recipient, and different spermatozoa are used to fertilize the eggs.

SETTING

Assisted Conception Unit, Birmingham Women's Hospital, Edgbaston, United Kingdom.

PATIENT(S)

Infertile women undergoing egg sharing.

INTERVENTION(S)

In vitro fertilization (IVF).

MAIN OUTCOME MEASURE(S)

Fertilization rates and the mean day 2 or 3 embryo score (cell number X grade) were examined for egg-sharing pairs. A comparison was also made for pairs in which intracytoplasmic sperm injection (ICSI) and IVF was used as the insemination method. A paired samples t-test was used to compare the sharer and recipient results.

RESULT(S)

Pregnancy rates did not differ between sharer and recipient couples. Interestingly, when comparing fertilization, there was a significant difference (P<.05) in favor of IVF over ICSI. When comparing embryo development between egg-sharing pairs, we found that approximately 30% of patients showed a difference in mean embryo score of >or= 5 in all embryo development and 14% in the quality of embryos available for transfer.

CONCLUSION(S)

We showed that the egg-sharing model is a successful alternative for the treatment of women who required donated eggs. More important, the egg-sharing model shows that, in a certain percentage of couples, differences in early embryo development are paternally influenced.

Epigenetic reprogramming in early embryonic development: effects of in-vitro production and somatic nuclear transfer

A considerable proportion of offspring, in particular in ruminants and mice, born from nuclear transfer (NT)-derived and in-vitro-produced (IVP) embryos is affected by multiple abnormalities of which a high birthweight and an extended gestation length are the predominant features; a phenomenon that has been called 'large offspring syndrome' (LOS). The underlying mechanisms are largely unknown at present, but alterations of epigenetic modifications of embryonic and fetal gene expression patterns, primarily caused by alterations in DNA methylation are thought to be involved in this syndrome. In mammals, DNA methylation is essential for the regulation of transcription during development and differentiation. This review summarizes results from studies in which mRNA expression patterns from IVP and NT-derived embryos were compared with those of their in-vivo counterparts. Numerous aberrations have been found ranging from suppression of expression to de-novo overexpression or more frequently to a significant up- or down-regulation of a specific gene. These observations emphasize the need for further epigenetic studies during preimplantation embryo development to gain insight into the molecular regulation correlated with an undisturbed embryonic and fetal development. Understanding molecular mechanisms will aid improvements in biotechnologies applied to early embryos in all species, including humans.

Selective loss of imprinting in the placenta following preimplantation development in culture

Preimplantation development is a period of dynamic epigenetic change that begins with remodeling of egg and sperm genomes, and ends with implantation. During this time, parental-specific imprinting marks are maintained to direct appropriate imprinted gene expression. We previously demonstrated that H19 imprinting could be lost during preimplantation development under certain culture conditions. To define the lability of genomic imprints during this dynamic period and to determine whether loss of imprinting continues at later stages of development, imprinted gene expression and methylation were examined after in vitro preimplantation culture. Following culture in Whitten's medium, the normally silent paternal H19 allele was aberrantly expressed and undermethylated. However, only a subset of individual cultured blastocysts (∼65%) exhibited biallelic expression, while others maintained imprinted H19 expression. Loss of H19 imprinting persisted in mid-gestation conceptuses. Placental tissues displayed activation of the normally silent allele for H19, Ascl2, Snrpn, Peg3 and Xist while in the embryo proper imprinted expression for the most part was preserved. Loss of imprinted expression was associated with a decrease in methylation at the H19 and Snrpn imprinting control regions. These results indicate that tissues of trophectoderm origin are unable to restore genomic imprints and suggest that mechanisms that safeguard imprinting might be more robust in the embryo than in the placenta.

Are children born after assisted reproductive technology at increased risk for adverse health outcomes?

As assisted reproductive technologies (ARTs) are increasingly used to overcome infertility, there is concern about the health of the children conceived. The empirical evidence for associations with outcomes related to child health is variable and should be evaluated with consideration of methodological shortcomings. Currently, there is convincing evidence that ART treatment may increase the risk of a few outcomes. Experimental laboratory studies document that various constituents in culture media affect various embryo characteristics both positively and negatively. Multiple-gestation pregnancy and birth are increased with ART, both because of multiple embryo transfer and embryo splitting. There is evidence of an increase in chromosomal abnormalities among pregnancies conceived using intracytoplasmic sperm injection and low birth weight and preterm delivery among singletons conceived with all types of ART; however, there remains uncertainty about whether these risks stem from the treatment or the parental infertility. For some outcomes, data of an increased risk with ART are suggestive at best largely because of lack of purposeful study of sufficient size and scope. These include specific perinatal morbidities, birth defects, developmental disabilities, and retinoblastoma. The evidence for an association between ART and spontaneous abortion is inconsistent and weak. There is inconclusive evidence that ART may be associated with genetic imprinting disorders. For childhood cancer, chronic conditions, learning and behavioral disorders, and reproductive effects there is insufficient empirical research to date, but given the data for more proximal outcomes, these outcomes merit further study. Future research needs to address the unique methodological challenges underlying study in this area.

Neuroblastoma, maternal valproic acid use, in-vitro fertilization and family history of mosaic chromosome 22: coincidence or causal relationship?

We report a family with co-occurring disorders including neuroblastoma in the first child conceived by in-vitro fertilization with history of sodium valproate use by the mother during pregnancy and mosaic trisomy 22 in the third child. We discuss the possibility of an association between the disorders but conclude that no firm aetiological connection can be established between the different disorders in this family.

Gene expression patterns in in vitro-produced and somatic nuclear transfer-derived preimplantation bovine embryos: relationship to the large offspring syndrome?

A considerable proportion of the offspring born from somatic nuclear transfer (sNT)-derived and in vitro-produced (IVP) embryos, particularly in ruminants and mice, is affected by multiple abnormalities of which a high birth weight is the predominant feature; a phenomenon that has been called "large offspring syndrome (LOS)". The underlying mechanisms are largely unknown at present, but changes in epigenetic modifications occurring during preimplantation development resulting in perturbed embryonic and fetal gene expression patterns are thought to be involved in the syndrome. This review summarizes results from studies comparing mRNA expression patterns from IVP and sNT-derived embryos to those of their in vivo counterparts, which are regarded as the "gold standard". Numerous aberrations have been observed ranging from suppression of expression to de novo overexpression or more frequently to a significant up- or down-regulation of a specific gene. These observations emphasize the need for further studies during preimplantation embryo development to gain insight in the molecular, preferentially epigenetic, mechanisms regulating embryonic and fetal development. Understanding these mechanisms will help to improve biotechnologies applied to early embryos in all species including humans.

Are major defects in children conceived in vitro due to innate problems in patients or to induced genetic damage?

Birth anomalies recently detected in epidemiological studies indicate greater risks following assisted human reproduction than with natural conception. Some of these conclusions and assumptions are questioned in this paper, and the effects of specific causative factors unique to some infertile couples are analysed. Other recent studies have identified imprinting defects as causes of birth disorders following IVF or intracytoplasmic sperm injection. While few in numbers, they apparently involve unusual factors in conception such as aberrant responses among preimplantation embryos to culture medium or serum. Various genetic and developmental factors in infertile couples influencing the origin of such birth outcomes are assessed, and the significance of imprinting and its embryological roles are discussed.

Epigenetics and assisted reproductive technology: a call for investigation

A surprising set of recent observations suggests a link between assisted reproductive technology (ART) and epigenetic errors--that is, errors involving information other than DNA sequence that is heritable during cell division. An apparent association with ART was found in registries of children with Beckwith-Wiedemann syndrome, Angelman syndrome, and retinoblastoma. Here, we review the epidemiology and molecular biology behind these studies and those of relevant model systems, and we highlight the need for investigation of two major questions: (1) large-scale case-control studies of ART outcomes, including long-term assessment of the incidence of birth defects and cancer, and (2) investigation of the relationship between epigenetic errors in both offspring and parents, the specific methods of ART used, and the underlying infertility diagnoses. In addition, the components of proprietary commercial media used in ART procedures must be fully and publicly disclosed, so that factors such as methionine content can be assessed, given the relationship in animal studies between methionine exposure and epigenetic changes.

Epigenetic regulation of mammalian genomic imprinting

Imprinted genes play important roles in development, and most are clustered in large domains. Their allelic repression is regulated by 'imprinting control regions' (ICRs), which are methylated on one of the two parental alleles. Non-histone proteins and nearby sequence elements influence the establishment of this differential methylation during gametogenesis. DNA methylation, histone modifications, and also polycomb group proteins are important for the somatic maintenance of imprinting. The way ICRs regulate imprinting differs between domains. At some, the ICR constitutes an insulator that prevents promoter-enhancer interactions, when unmethylated. At other domains, non-coding RNAs could be involved, possibly by attracting chromatin-modifying complexes. The latter silencing mechanism has similarities with X-chromosome inactivation.

Les enfants de l’ICSI sous la loupe

The debate concerning the health of children conceived by artificial reproduction technology (ART) continues. Among these techniques, intracytoplasmic sperm injection (ICSI) is the subject of most attention. Indeed, several studies have concentrated on the evaluation of risks associated with ICSI. The publication of a few recent articles on the subject is providing an opportunity to reconsider the situation. Generally, women conceiving via ART are older, more often primipar and present increased rates of uterine pathologies compared to women conceiving naturally. Furthermore, ART pregnancies are sources of anxiety resulting in a significant increase rates of caesarean section. ART children present an increased risk of low birth rate often linked to multiple pregnancy, but this is also true for singleton pregnancy. Major studies have not revealed a significantly increased rate of malformations in ICSI children. However, sporadic observations of errors in genomic imprinting or of rare tumors in children conceived by ICSI point to a need for increased vigilance of ICSI practices. Finally, the mental development, the family and social life of ICSI children appears similar to children conceived naturally.

Reproductive epigenetics

Epigenetics refers to covalent modifications of DNA and core histones that regulate gene activity without altering DNA sequence. To date, the best-characterized DNA modification associated with the modulation of gene activity is methylation of cytosine residues within CpG dinucleotides. Human disorders associated with epigenetic abnormalities include rare imprinting diseases, molar pregnancies, and childhood cancers. Germ cell development and early embryo development are critical times when epigenetic patterns are initiated or maintained. This review focuses on the epigenetic modification DNA methylation and discusses recent progress that has been made in understanding when and how epigenetic patterns are differentially established in the male and female germlines, the mouse, and human disorders associated with abnormalities in epigenetic programming in germ cells and early embryos, as well as genetic and other modulators (e.g. nutrition and drugs) of reproductive epigenetic events.

Influence of in vitro manipulation on the stability of methylation patterns in the Snurf/Snrpn-imprinting region in mouse embryonic stem cells

Recent work on embryonic stem (ES) cells showed that stem cell-derived tissues and embryos, cloned from ES cell nuclei, often fail to maintain epigenetic states of imprinted genes. This deregulation is frequently associated with in vitro manipulations and culture conditions which might affect the cells potential to develop into normal fetuses. Usually, epigenetic instability is reported in differentially methylated regions of mostly growth-related imprinted genes. However, little is known about the epigenetic stability of genes that function late in organogenesis. Hence, we set out to investigate the epigenetic stability of neuronal genes and analyzed DNA methylation patterns in the Snurf/Snrpn imprinted cluster in several cultured mouse ES cell lines. We also determined the effects of in vitro stress factors such as consecutive passaging, trypsination, mechanical handling, single cell cloning, centrifugation, staurosporine-induced neurogenesis and the insertion of viral (foreign) DNA into the host genome. Intriguingly, none of these in vitro manipulations interfered with the stability of the methylation patterns in the analyzed neuronal genes. These data imply that, in contrast to growth-related genes like Igf2, H19, Igf2r or Grb10, the methylation imprints of the analyzed neuronal genes in the Snurf/Snrpn cluster may be particularly stable in manipulated ES cells.

On a fallacious invocation of the Barker hypothesis of anomalies in newborn rats due to mothers' food restriction in preimplantation phases

A statistical re-evaluation indicates serious flaws in the paper by Kwong et al., reporting that low birthweight and impaired development, and perhaps anomalous preimplantation embryo growth, were associated with food restriction during the preimplantation period. This paper has been used to confirm that early forms of protein deprivation in the preimplantation phase carry risks to IVF children. Errors in interpreting the nature of their study and a failure to apply the correct principles of statistical analysis in their hierarchical data structure have led to their flawed investigation. It is therefore proposed that such serious flaws cast doubt on their conclusions. The findings reported in this study should be withdrawn, and a rigorous statistical evaluation should be carried out to provide a proper assessment of the data.

Gene-specific timing and epigenetic memory in oocyte imprinting

Imprinted genes are differentially marked during germ cell development to allow for their eventual parent-of-origin specific expression. A subset of imprinted genes becomes methylated during oocyte growth in both mouse and human. However the timing and mechanisms of methylation acquisition are unknown. Here, we examined the methylation of the Snrpn, Igf2r, Peg1 and Peg3 differentially methylated regions in postnatal growing mouse oocytes. Our findings indicate that methylation was acquired asynchronously at these different genes. Further analysis of Snrpn DMR1 revealed that parental alleles retain an epigenetic memory of their origin as the two alleles were recognized in a parental-specific manner in the absence of DNA methylation. In addition, we show that methylation acquisition was probably related to oocyte diameter and coincided with the accumulation of Dnmt3a, Dnmt3b and Dnmt3L transcripts. Methylation of the repetitive retroviral-like intracisternal A particle also occurred during this same window of oocyte growth. These findings contribute to our understanding of the epigenetic mechanisms underlying imprint acquisition during female germ cell development and have implications for the practice of assisted reproductive technologies.

Long-term effects of culture of preimplantation mouse embryos on behavior

Many procedures used in assisted reproductive technologies (ART) to treat human infertility entail culture of preimplantation embryos. Moreover, there is an increasing trend to culture embryos for longer periods of time before uterine transfer to identify the "best" embryos for transfer and to minimize multiple pregnancies. Embryo culture, however, can perturb embryo metabolism and gene expression, and the long-term consequences of culture are unknown. We have explored the behavioral consequences of embryo culture by using a 129S6/SvEvTac/C57BL/6J F(1) mouse model and find that adults derived from cultured embryos exhibit specific behavioral alterations in the elevated zero maze and Morris water maze tasks.

The primate embryo gene expression resource: a novel resource to facilitate rapid analysis of gene expression patterns in non-human primate oocytes and preimplantation stage embryos

Detailed molecular studies of preimplantation stage development in a suitable nonhuman primate model organism have been inhibited due to the cost and scarcity of embryos. To circumvent these limitations, we have created a new resource for the research community, designated as the Primate Embryo Gene Expression Resource (PREGER). The PREGER sample collection currently contains over 160 informative samples of oocytes, obtained from various sized antral follicles, and embryos obtained through a variety of different protocols. The PREGER makes it possible to undertake quantitative gene-expression studies in rhesus monkey oocytes and embryos through simple and cost-effective hybridization-based methods. The PREGER also makes available other molecular tools to facilitate nonhuman primate embryology. We used PREGER here to compare the temporal expression patterns of five housekeeping mRNAs and three transcription factor mRNAs between mouse and rhesus monkey. We observed noticeable differences in temporal expression patterns between species for some mRNAs, but clear similarities for others. Our results also provide new information related to genome activation and the effects of embryo culture conditions on gene expression in primate embryos. These results provide one illustration of how the PREGER can be employed to obtain novel insight into primate embryogenesis.

Medical follow-up study of 5-year-old ICSI children

Children born after intracytoplasmic sperm injection (ICSI) are still a matter of concern. The purposes of the present study were to investigate the physical outcome in 5-year-old children born after ICSI and compare them with children born after spontaneous conception. Three hundred singleton children from Belgium, Sweden and the USA, born after ICSI, were matched by maternal age, child age and gender. In one centre, matching was also performed for maternal education. The main end-point was growth. Secondary end-points were general health, e.g. common diseases, chronic illnesses, surgical interventions and physical/neurological examinations. Standard deviation scores assessed growth. Growth assessed as stature at follow-up was similar in the two groups, despite a higher rate of preterm birth and low birth weight in the ICSI children. Common diseases and chronic illnesses occurred at similar rates in both groups. More ICSI children underwent surgical interventions and required other therapy e. g. physiotherapy and dietary therapy. Physical/neurological examinations revealed few abnormalities in either group. In conclusion, infertility treatment by ICSI does not adversely affect growth during childhood. The children's general health seems satisfactory.

Procreative liberty and harm to offspring in assisted reproduction

Assisted reproductive technologies (“ARTs”) have enabled many infertile couples to have children but have long been controversial. Opposition initially focused on the “unnaturalness” of laboratory conception and the doubts that healthy children would result. Once children were born, ethical debate shifted to the status and ownership of embryos and the novel forms of family that could result.

The new century has brought forth both new and old ethical concerns. The growing capacity to screen the genomes of embryos has sparked fears of eugenic selection and alteration. In addition, concerns about safety have reasserted themselves. Several studies suggest that in vitro fertilization (“IVF”) may be associated with lower birth weights and major malformations. Ethical attention has also focused on whether all persons seeking ARTs should be granted access to them, regardless of their child-rearing ability, age, disability, health status, marital status, or sexual orientation.

Assisted reproductive technology and congenital overgrowth: Some speculations on a case of Pallister-Killian syndrome

We report on a boy with Pallister-Killian syndrome (PKS) who was conceived by assisted reproductive technology (ART), specifically in vitro fertilization (IVF) with parents' gametes. A prenatal diagnosis performed elsewhere by CVS failed to detect the presence of the isochromosome 12p that was demonstrated postnatally in approximately 50% of cultured skin fibroblasts. Given that the patient did not show the congenital overgrowth typical of PKS, we speculate that ART might have restricted overgrowth in this particular case. More broadly, we hypothesize that overgrowth might protect from early demise fetuses conceived by ART, a technology known to cause low and very low birth weight.

Genetic variation in oocyte phenotype revealed through parthenogenesis and cloning: correlation with differences in pronuclear epigenetic modification

Previous studies revealed that oocytes of different genetic strains (e.g, C57BL/6 and DBA/2) modify maternal and paternal pronuclei differently, affecting early preimplantation development. To determine whether these strain-dependent effects would also apply to oocyte modifications of somatic cell nuclei introduced during cloning procedures, we compared the efficiency of development of parthenogenetic and cloned embryos made with DBA/2, C57BL/6, and (B6D2)F1 oocytes. Our results reveal significant differences in the ability of oocytes of different genetic backgrounds to support parthenogenetic development in different culture media. Additionally, our results reveal oocyte strain-dependent differences in the ability to support cloned embryo development beyond what can be accounted for on the basis of differences in parthenogenesis. Thus, the previously documented differences in oocyte-directed parental genome modification are accompanied in the same strains by differences in the ability of oocytes to modify somatic cell nuclei and support clonal development, raising the possibility that these oocyte functions may be mediated by related mechanisms. These results provide a genetic basis for further studies seeking to identify specific genes that determine oocyte phenotype, as well as genes that determine the success of nuclear reprogramming and clonal development.

Nuclear transfer: progress and quandaries

Cloning mammals by nuclear transfer is a powerful technique that is quickly advancing the development of genetically defined animal models. However, the overall efficiency of nuclear transfer is still very low and several hurdles remain before the power of this technique will be fully harnessed. Among these hurdles include an incomplete understanding of biologic processes that control epigenetic reprogramming of the donor genome following nuclear transfer. Incomplete epigenetic reprogramming is considered the major cause of the developmental failure of cloned embryos and is frequently associated with the disregulation of specific genes. At present, little is known about the developmental mechanism of reconstructed embryos. Therefore, screening strategies to design nuclear transfer protocols that will mimic the epigenetic remodeling occurring in normal embryos and identifying molecular parameters that can assess the developmental potential of pre-implantation embryos are becoming increasingly important. A crucial need at present is to understand the molecular events required for efficient reprogramming of donor genomes after nuclear transfer. This knowledge will help to identify the molecular basis of developmental defects seen in cloned embryos and provide methods for circumventing such problems associated with cloning the future application of this technology.

Uniparental disomy and Robertsonian translocations: risk estimation and prenatal testing

BACKGROUND

Uniparental disomy (UPD) is defined by the inheritance of both homologous chromosomes from only one parent, resulting in an imbalance of the expression of imprinted genes. With the recent identification of several diseases associated with UPD, the diagnostic significance of this molecular finding is a focus of interest. Acrocentric chromosomes involved in Robertsonian translocations (RTs) are particularly prone to being affected by mis-segregation events, possibly resulting in UPD. While UPDs of chromosomes 13, 21, and 22 have no clinical consequences, and therefore have no diagnostic impact despite of homozygosity of recessive alleles, prenatal testing for UPDs 14 or 15 is becoming increasingly asked for.

METHODS

Thirty-one fetuses with nonhomologous balanced RTs involving chromosome 14 were tested for UPD14 by microsatellite typing.

RESULTS

No cases of maternal UPD14 were detected among the 31 fetuses analyzed.

CONCLUSIONS

Based on our own data from molecular testing in 31 prenatal RT cases and findings in the published literature, we delineated a risk of 0.3% for a UPD with clinical consequences for prenatally detected carriers of a nonhomologous RT. Prenatal UPD testing is not associated with any additional risk to the pregnancy once invasive prenatal testing has been carried out. However, the possibly conflicting consequences in the case of a prenatal UPD identification should be discussed in advance. Furthermore, risk figures in specific clinical cohorts, such as couples prior to intracytoplasmic sperm injection, as well as questions of prenatal diagnostic management, will be discussed.

Is intracytoplasmic sperm injection safe?

OBJECTIVE

To review the pregnancy and birth outcomes of patients undergoing intracytoplasmic sperm injection (ICSI).

DESIGN

Selective review of the literature.

SETTING

Couples undergoing either conventional IVF or ICSI and their resulting offspring.

PATIENT(S)

None.

MAIN OUTCOME MEASURE(S)

None.

INTERVENTION(S)

None.

RESULTS

These observational studies are unfortunately inherently biased. Regardless, the information and experiences from these large centers cannot be ignored. These experiences reveal that birth weight may be decreased by an amount that is generally not clinically relevant. Chromosomal and genetic abnormalities are increased probably only as a direct corollary to the underlying parental risk. Congenital malformations reveal no clustering of any single specific abnormality. Developmental assessment is available for up to 2 years, and no major delays have been identified in either motor or mental function.

CONCLUSION(S)

Intracytoplasmic sperm injection appears to be a safe alternative for couples who otherwise would be unable to achieve pregnancy. The inherent risks associated with these genetically "at risk" couples mandate thorough evaluation and counseling before undertaking ICSI.

Rare congenital disorders, imprinted genes, and assisted reproductive technology

CONTEXT

During the past two decades, assisted reproductive technologies (ARTs) have revolutionised the treatment of infertility. ARTs now account for between 1% and 3% of annual births in many western countries and in-vitro fertilisation (IVF) services are growing worldwide. In general, the incidence of abnormalities at birth is reassuringly low and children develop normally. Nevertheless, it is important to monitor the safety of ARTs as clinical protocols evolve and new technologies emerge.

STARTING POINT

Three recent studies all report an unexpectedly high incidence of Beckwith-Wiedemann syndrome (BWS) in children conceived with ARTs. Six of 149 cases were reported from a British BWS registry (J Med Genet 2003; 40: 62-64); the same numbers were recorded in a French registry (Am J Hum Genet 2003; 72: 1338-41), and a further seven children have been reported in the USA (Am J Hum Genet 2003; 72: 156-60). These frequencies are extraordinarily high for such a rare congenital condition and such findings are reminiscent of reports of sporadic cases of the imprinting disorder, Angelman syndrome, which has also been linked with ARTs. WHERE NEXT? Continuing surveillance of children conceived with ARTs is needed, including monitoring birth defects, development, and cancer. Studies will need to be prospective and multicentre, and should include molecular characterisation of epigenetic abnormalities, including the methylation status of imprinting control regions within imprinted gene clusters.

Imprinting evolution and the price of silence

In contrast to the biallelic expression of most genes, expression of genes subject to genomic imprinting is monoallelic and based on the sex of the transmitting parent. Possession of only a single active allele can lead to deleterious health consequences in humans. Aberrant expression of imprinted genes, through either genetic or epigenetic alterations, can result in developmental failures, neurodevelopmental and neurobehavioral disorders and cancer. The evolutionary emergence of imprinting occurred in a common ancestor to viviparous mammals after divergence from the egg-laying monotremes. Current evidence indicates that imprinting regulation in metatherian mammals differs from that in eutherian mammals. This suggests that imprinting mechanisms are evolving from those that were established 150 million years ago. Therefore, comparing genomic sequence of imprinted domains from marsupials and eutherians with those of orthologous regions in monotremes offers a potentially powerful bioinformatics approach for identifying novel imprinted genes and their regulatory elements. Such comparative studies will also further our understanding of the molecular evolution and phylogenetic distribution of imprinted genes.

Towards a more precise assay of sperm function in egg binding

Historically, the treatment of severe male factor infertility has relied on donor sperm insemination. A decade ago the option of treating severe male factor infertility with partner sperm became a viable alternative. With the introduction of intracytoplasmic sperm injection (ICSI) in conjunction with in vitro fertilization (IVF), only men who produce no sperm are denied the option of fathering their own children. The use of ICSI has been extended to couples with mild male factors. Despite the known genetic risks (both inherent and de novo) of ICSI to offspring, couples with male factors as part of their infertility problem often prefer ICSI to standard IVF, due to apprehension that their sperm might not otherwise succeed in fertilization. This apprehension would be alleviated if an assay for the egg binding capability of human sperm were available. We examine here the possibility that recombinant human zona pellucida 3 (rec hZP3), the primary sperm receptor sulfoglycoprotein of the egg zona pellucida (ZP), be used as a human ZP surrogate for assessing sperm ability to bind to the ZP. Unlike human eggs, which cannot be obtained for this purpose, rec hZP3 can be produced in quantity. An efficient assay can be established by incubating sperm with rec hZP3 coated to a microwell plate. Infertile men with sperm having ability to bind to rec hZP3 can be advised to select standard IVF or intrauterine insemination, which have fewer genetic and medical risks.