Active demethylation of individual genes in intracytoplasmic sperm injection rabbit embryos

Maternal and Live-birth Outcomes of Pregnancies following Assisted Reproductive Technology: A Retrospective Cohort Study

This study was carried out to explore associations between assisted reproductive technology (ART) and maternal and neonatal outcomes compared with similar outcomes following spontaneously conceived births. We conducted a retrospective cohort study of pregnancies conceived by ART (N = 2641) during 2006–2014 compared to naturally conceived pregnancies (N = 5282) after matching for maternal age and birth year. Pregnancy complications, perinatal complications and neonatal outcomes of enrolled subjects were investigated and analysed by multivariate logistic regression. We found that pregnancies conceived by in vitro fertilization (IVF) were associated with a significantly increased incidence of gestational diabetes mellitus, gestational hypertension, preeclampsia, intrahepatic cholestasis of pregnancy, placenta previa, placental abruption, preterm premature rupture of membranes, placental adherence, postpartum haemorrhage, polyhydramnios, preterm labour, low birth weight, and small-for-date infant compared with spontaneously conceived births. Pregnancies conceived by intracytoplasmic sperm injection (ICSI) showed similar elevated complications, except some of the difference narrowed or disappeared. Singleton pregnancies or nulliparous pregnancies following ART still exhibited increased maternal and neonatal complications. Therefore, we conclude that pregnancies conceived following ART are at increased risks of antenatal complications, perinatal complications and poor neonatal outcomes, which may result from not only a higher incidence of multiple pregnancy, but also the manipulation involved in ART processes.

Improving efficiencies of locus-specific DNA methylation assessment for bovine in vitro produced embryos

Characterization of DNA methylation is one assessment of chromatin remodeling in early embryos. Unfortunately, evaluation at specific loci is hindered by their small cell numbers. Our objective was to determine if bisulfite sequencing could be optimized for preimplantation embryos, comparing conversion times, primer design, and DNA amplification methods. Methylation at three loci, SATI, OCT4, and IGF2, was investigated in bovine in vitro produced (IVP) embryos, somatic cells, and no template controls. Bisulfite treatment for 15-16 h gave higher quality DNA than treatment for 18 h. Three step primer design improved bisulfite primer specificity, yielding more PCR product than primers previously reported. Following optimization, methylation data were obtained from as few as 4 cell equivalents. Finally, DNA amplification efficiencies were evaluated using miniprep, TempliPhi, or 96-well glycerol stocks with automated TempliPhi. While TempliPhi was better than standard minipreps, the 96-well format proved most efficient. Preliminary methylation profiles of bovine IVP 2-cell, 8-cell, blastocyst stage embryos and somatic cells were 25, 10, 22, and 74% for SATI and 88, 88, 79, and 88% for OCT4, respectively, suggesting that SATI is demethylated during early embryonic reprogramming, while OCT4 remains hypermethylated. IGF2 methylation was 84, 28, and 84% for bovine IVP 8-cell, blastocyst stage embryos and somatic cells; blastocyst stage embryos exhibited more variability, ranging from 0 to 80%. This new assay will enhance assessment of chromatin remodeling in embryos, and be especially useful for evaluating those produced by assisted reproductive technologies.

Active demethylation of paternal genome in mammalian zygotes

Epigenetic reprogramming in early preimplantation embryos, that refers to erasing and remodeling epigenetic marks such as DNA methylation, is essential for differentiation and development. In many species, paternal genome is subjected to genome-wide active demethylation before the DNA replication commences, while maternal genome maintains its methylation status until being demethylated passively during the subsequent cleavage divisions. The purpose of this manuscript was to review the available knowledge about the paternal genome active demethylation process concerning the possible mechanisms, species variation and the factors affecting the active demethylation dynamics such as in vitro protocols for production of pronuclear-stage zygotes. Better understanding the mechanisms by which the epigenetic reprogramming is occurred may contribute to clarify the biological significance of this process.

Changes in histone methylation during human oocyte maturation and IVF- or ICSI-derived embryo development

OBJECTIVE

To characterize the histone methylation pattern during human oocyte maturation and embryo development after conventional IVF and ICSI.

DESIGN

Experimental study.

SETTING

Reproductive center of hospital.

PATIENT(S)

Women underwent IVF or ICSI.

INTERVENTION(S)

Immature and mature oocytes were collected from patients undergoing ICSI. Tripronuclear and normally fertilized embryos were obtained from patients undergoing IVF or ICSI.

MAIN OUTCOME MEASURE(S)

The distribution patterns of dimethylated histone H3 lysine 9 (H3K9) and histone H4 arginine 3 (H4R3) in oocytes and embryos were observed by indirect immunofluorescent staining and scanning confocal microscopy.

RESULT(S)

H3K9 and H4R3 were dimethylated throughout the meiotic maturation of human oocytes and the tripronuclear embryo development from two-cell to blastocyst stage. However, at the pronuclear stage, approximately half of the tripronuclear IVF zygotes displayed strong staining of MeH3K9 in one pronucleus, whereas MeH4R3 staining was always uniform in all three pronuclei. In the other half of the tripronuclear zygotes, all three pronuclei were strongly stained with MeH3K9 in some cases, and the remaining zygotes were completely unstained. Moreover, with progressively increasing fragmentation of blastomeres in ICSI-derived 2PN embryos with low morphological grade, H3K9 dimethylation decreased when compared with that of IVF embryos.

CONCLUSION(S)

Asymmetric distribution of the dimethylation form of H3K9 exists in human zygote pronuclei. The ICSI-derived embryos with low morphological grade are more likely to display H3K9 demethylation than their IVF counterparts.

Evidence for conserved DNA and histone H3 methylation reprogramming in mouse, bovine and rabbit zygotes

BACKGROUND

In mammals the parental genomes are epigenetically reprogrammed after fertilization. This reprogramming includes a rapid demethylation of the paternal (sperm-derived) chromosomes prior to DNA replication in zygotes. Such active DNA demethylation in the zygote has been documented for several mammalian species, including mouse, rat, pig, human and cow, but questioned to occur in rabbit.

RESULTS

When comparing immunohistochemical patterns of antibodies against 5-methyl-cytosine, H3K4me3 and H3K9me2 modifications we observe similar pronuclear distribution and dynamics in mouse, bovine and rabbit zygotes. In rabbit DNA demethylation of the paternal chromosomes occurs at slightly advanced pronuclear stages. We also show that the rabbit oocyte rapidly demethylates DNA of donor fibroblast after nuclear transfer.

CONCLUSION

Our data reveal that major events of epigenetic reprogramming during pronuclear maturation, including mechanisms of active DNA demethylation, are apparently conserved among mammalian species.

Long-term effects of mouse intracytoplasmic sperm injection with DNA-fragmented sperm on health and behavior of adult offspring

Genetic and environmental factors produce different levels of DNA damage in spermatozoa. Usually, DNA-fragmented spermatozoa (DFS) are used with intracytoplasmic sperm injection (ICSI) treatments in human reproduction, and use of DFS is still a matter of concern. The purpose of the present study was to investigate the long-term consequences on development and behavior of mice generated by ICSI with DFS. Using CD1 and B6D2F1 mouse strains, oocytes were injected with fresh spermatozoa or with frozen-thawed spermatozoa without cryoprotector. This treatment increased the percentage of TUNEL-positive spermatozoa, tail length as measured by comet assay, and loss of telomeres as measured by quantitative PCR. The ICSI-generated embryos were cultured for 24 h in KSOM, and 2-cell embryos were transferred into CD1 females. The DFS reduced both the rate of preimplantation embryo development and number of offspring. Immunofluorescence staining with an antibody against 5-methylcytosine showed a delay of 2 h on the active demethylation of male pronucleus in the embryos produced by ICSI. Moreover, ICSI affected gene transcription and methylation of some epigenetically regulated genes like imprinting, X-linked genes, and retrotransposon genes. At 3 and 12 mo of age, ICSI with DFS-produced animals and in vivo-fertilized controls were submitted to behavioral tests: locomotor activity (open field), exploratory/anxiety behavior (elevated plus maze, open field), and spatial memory (free-choice exploration paradigm in Y maze). Females produced by ICSI showed increased anxiety, lack of habituation pattern, deficit in short-term spatial memory, and age-dependent hypolocomotion in the open-field test (P<0.05). Postnatal weight gain of mice produced by ICSI with fresh or frozen sperm was higher than that of their control counterparts from 16 wk on (P<0.01). Anatomopathological analysis of animals at 16 mo of age showed some large organs and an increase in pathologies (33% of CD1 females produced with DFS presented some solid tumors in lungs and dermis of back or neck). Moreover, 20% of the B6D2F1 mice generated with DFS died during the first 5 mo of life, with 25% of the surviving animals showing premature aging symptoms, and 70% of the B6D2F1 mice generated with DFS died earlier than controls with different kind of tumors. We propose that depending on the level of DFS, oocytes may partially repair fragmented DNA, producing blastocysts able to implant and produce live offspring. The incomplete repair, however, may lead to long-term pathologies. Our data indicate that use of DFS in ICSI can generate effects that only emerge during later life, such as aberrant growth, premature aging, abnormal behavior, and mesenchymal tumors.

Suboptimal in vitro culture conditions: an epigenetic origin of long-term health effects

The foetal origins of adult diseases or Barker hypothesis suggests that there can be adverse in uterus effects on the foetus that can lead to certain diseases in adults. Extending this hypothesis to the early stages of embryo development, in particular, to preimplantation stages, it was recently demonstrated that, long-term programming of postnatal development, growth and physiology can be irreversibly affected during this period of embryo development by suboptimal in vitro culture (IVC). As an example, it was found in two recent studies that, mice derived from embryos cultured in suboptimal conditions can suffer from obesity, increased anxiety, and deficiencies on their implicit memory system. In addition, it was observed that suboptimal IVC can cause disease in mature animals by promoting alterations in their genetic imprinting during preimplantation development. Imprinting and other epigenetic mechanisms control the establishment and maintenance of gene expression patterns in the embryo, placenta and foetus. The previously described observations, suggest that the loss of epigenetic regulation during preimplantation development may lead to severe long-term effects. Although mostly tested in rodents, the hypothesis that underlies these studies can also fit assisted reproductive technology (ART) procedures in other species, including humans. The lack of information on how epigenetic controls are lost during IVC, and on the long-term consequences of ART, underscore the necessity for sustained epigenetic analysis of embryos produced in vitro and long-term tracking of the health of the human beings conceived using these procedures.

The constant variation: DNA methylation changes during preimplantation development

Studies on the DNA methylation changes in the mouse preimplantation embryo suggested a simple and attractive model explaining the process believed to be general in mammals. However, recent reports revealed marked differences between different species that abrogates the universal validity of the model. In order to find an explanation to the differences, we have analyzed the published mouse data and compared them to the observations available in other species. The emerging common theme is the high variability of the methylation at all scales of observation and all levels of organization. This variability is the likely consequence of a dynamic and active redistribution process of the cytosine methylation in the genome.

Human lactoferrin transgenic rabbits produced efficiently using dimethylsulfoxide - sperm-mediated gene transfer

Transgenic animal mammary gland bioreactors are used to produce recombinant proteins. However, it is difficult to validate whether these transgenic domestic animals are able to express the recombinant protein efficiently in their mammary glands before the birth of transgenic offspring. In the present study, a simple and efficient method was established to evaluate the functionality of animal mammary gland tissue-expressed cassettes. The gene transfer vector pGBC2LF was constructed, and the expression of human lactoferrin (LF) gene was controlled by the goat β-casein gene 5′ flanking sequence. To obtain the most efficient transfection, the influence of DNA concentration, dimethylsulfoxide (DMSO) concentration, and the ratio of linear-to-circular DNA required for associating DNA with spermatozoa were evaluated. Transfection of exogenous DNA into rabbit spermatozoa was found to be efficient using 30 μg mL–1 DNA, DMSO at a final concentration of 3%, and a 3 : 1 ratio of linear-to-circular DNA, with 29 of 85 (34.1%) in vitro-fertilised embryos being transgenic. Using DMSO–sperm-mediated gene transfer (DMSO-SMGT), 89 rabbit offspring were produced, with 46 of these (57.1%) being transgenic. As mammary gland bioreactor models, 17 of 21 (81%) transgenic female rabbits could express human LF protein in their glands. During lactation of the transgenic rabbits, the highest level of human LF protein expressed was 153 ± 31 μg mL–1, and the mean expression level in all of the transgenic rabbits was 103 ± 20 μg mL–1 in the third week, declining gradually after this time. Our results demonstrate that transgenic rabbits produced by DMSO–SMGT were able to express human LF protein in the correct tissue.

The significance of mitochondria for embryo development in cloned farm animals

The role of mitochondria in remodeling of the donor cell nucleus in cloned animals has gained increased attention, as mitochondria interact in direct or indirect ways with the donor cell nuclear DNA. Mitochondria comprise 1% of the genetic material that is contributed to the developing embryo by the recipient oocyte and provide the energy that is required for embryo development. In this review we compare mitochondria distribution in various species and the importance of mitochondria distribution for embryo development. We also compare the inheritance pattern of mitochondria in cloned embryos that remains unresolved, as the donor cell nucleus is typically transferred with surrounding cytoplasm including mitochondria which become destroyed in some but not all species. We review the role of mitochondria in cloned farm animals with emphasis on nucleo-cytoplasmic interactions and consequences for embryo development.