The impact of chromosomal alteration on embryo development

Telomere Shortening and Fusions: A Link to Aneuploidy in Early Human Embryo Development

Importance

It is known that oocytes undergo aging that is caused by exposure to an aged ovarian microenvironment. Telomere length in mouse and bovine oocytes declines with age, and age-associated telomere shortening in oocytes is considered a sign of poor development competency. Women with advanced age undergoing assisted reproductive technologies have poor outcomes because of increasing aneuploidy rates with age. Research has shown that aneuploidy is associated with DNA damage, reactive oxygen species, and telomere dysfunction.

Objective

In this review, we focus on the possible relationship between telomere dysfunction and aneuploidy in human early embryo development and several reproductive and perinatal outcomes, discussing the mechanism of aneuploidy caused by telomere shortening and fusion in human embryos.

Evidence Acquisition

We reviewed the current literature evidence concerning telomere dysfunction and aneuploidy in early human embryo development.

Results

Shorter telomeres in oocytes, leukocytes, and granulosa cells, related to aging in women, were associated with recurrent miscarriage, trisomy 21, ovarian insufficiency, and decreasing chance of in vitro fertilization success. Telomere length and telomerase activity in embryos have been related to the common genomic instability at the cleavage stage of human development. Complications of assisted reproductive technology pregnancies, such as miscarriage, birth defects, preterm births, and intrauterine growth restriction, also might result from telomere shortening as observed in oocytes, polar body, granulosa cells, and embryos.

Conclusions and Relevance

Telomere length clearly plays an important role in the development of the embryo and fetus, and the abnormal shortening of telomeres is likely involved in embryo loss during early human development. However, telomere fusion studies have yet to be performed in early human development.

Establishment of TP53-knockout canine cells using optimized CRIPSR/Cas9 vector system for canine cancer research

Background

Genetic engineering technology such as clustered regularly interspaced short palindromic repeats (CRISPR)/Cas9 system provides a powerful tool for developing disease models and determining gene functions. Recent interests in canine cancer models have highlighted the necessity of developing genetic engineering tools for dogs. In this study, we attempted to generate optimized CRISPR/Cas9 system to target canine tumor protein 53 (TP53), one of the most crucial tumor suppressor genes, to establish TP53 knockout canine cells for canine cancer research.

Results

We constructed CRISPR/Cas9 vectors using each of three TP53 gene-targeting guide RNAs (gRNAs) with minimal off-target potential. After transfection, we obtained several clones of TP53 knockout cells containing “indel” mutations in the targeted locus which had infinite cellular life span, resistance to genotoxicity, and unstable genomic status in contrast to normal cells. Of the established TP53 knockout cells, TP53KO#30 cells targeted by TP53 gRNA #30 showed non-cancerous phenotypes without oncogenic activation both in vitro and in vivo. More importantly, no off-target alteration was detected in TP53KO#30 cells. We also tested the developmental capacity of TP53 knockout cells after application of the somatic cell nuclear transfer technique.

Conclusions

Our results indicated that TP53 in canine cells was effectively and specifically targeted by our CRISPR/Cas9 system. Thus, we suggest our CRISPR/Cas9-derived canine TP53 knockout cells as a useful platform to reveal novel oncogenic functions and effects of developing anti-cancer therapeutics.

Electronic supplementary material

The online version of this article (10.1186/s12896-018-0491-5) contains supplementary material, which is available to authorized users.

Thyroid hormones alter the transcriptome of in vitro-produced bovine blastocysts

Thyroid hormones (THs) have been shown to improve in vitro embryo production in cattle by increasing blastocyst formation rate, and the average cell number of blastocysts and by significantly decreasing apoptosis rate. To better understand those genetic aspects that may underlie enhanced early embryo development in the presence of THs, we characterized the bovine embryonic transcriptome at the blastocyst stage, and examined differential gene expression profiles using a bovine-specific microarray. We found that 1212 genes were differentially expressed in TH-treated embryos when compared with non-treated controls (>1.5-fold at P < 0.05). In addition 23 and eight genes were expressed uniquely in control and treated embryos, respectively. The expression of genes specifically associated with metabolism, mitochondrial function, cell differentiation and development were elevated. However, TH-related genes, including those encoding TH receptors and deiodinases, were not differentially expressed in treated embryos. Furthermore, the over-expression of 52 X-chromosome linked genes in treated embryos suggested a delay or escape from X-inactivation. This study highlights the significant impact of THs on differential gene expression in the early embryo; the identification of TH-responsive genes provides an insight into those regulatory pathways activated during development.

Trends, fads and ART!

Morphological selection techniques of gametes and embryos are of current interest to clinical practice in ART. Although intracytoplasmic morphologically selected sperm injection (IMSI), time lapse imaging morphometry (TLIM) or quantification of chromosome numbers (PGS) are potentially useful in research, they have not been shown to be of statistically predictive value and, thus, have only limited clinical usefulness. We make the point that morphological markers alone cannot predict the success of the early embryo, which depends on the correct orchestration of a myriad of physiological and biochemical activation events that progress independently of the maternal or zygotic genome. Since previous attempts to identify metabolic markers for embryo quality have failed and there is no evidence that the intrinsic nature of gametes and embryos can be improved in the laboratory, embryologists can only minimize environmental or operator induced damage while these cells are manipulated ex vivo.

Detecting somatic mosaicism: considerations and clinical implications

Human disease is rarely a matter of all or nothing; variable expressivity is generally observed. Part of this variability is explained by somatic mosaicism, which can arise by a myriad of genetic alterations. These can take place at any stage of development, possibly leading to unusual features visible at birth, but can also occur later in life, conceivably leading to cancer. Previously, detection of somatic mosaicism was extremely challenging, as many gold standard tests lacked the necessary resolution. However, with the advances in high-throughput sequencing, mosaicism is being detected more frequently and at lower levels. This raises the issue of normal variation within each individual vs mosaicism leading to disease, and how to distinguish between the two. In this article, we will define somatic mosaicism with a brief overview of its main mechanisms in concrete clinical examples, discuss the impact of next-generation sequencing technologies in its detection, and expand on the clinical implications associated with a discovery of somatic mosaicism in the clinic.

Compounds used to produce cloned animals are genotoxic and mutagenic in mammalian assays in vitro and in vivo

The compounds 6-dimethylaminopurine and cycloheximide promote the successful production of cloned mammals and have been used in the development of embryos produced by somatic cell nuclear transfer. This study investigated the effects of 6-dimethylaminopurine and cycloheximide in vitro, using the thiazolyl blue tetrazolium bromide colorimetric assay to assess cytotoxicity, the trypan blue exclusion assay to assess cell viability, the comet assay to assess genotoxicity, and the micronucleus test with cytokinesis block to test mutagenicity. In addition, the comet assay and the micronucleus test were also performed on peripheral blood cells of 54 male Swiss mice, 35 g each, to assess the effects of the compounds in vivo. The results indicated that both 6-dimethylaminopurine and cycloheximide, at the concentrations and doses tested, were cytotoxic in vitro and genotoxic and mutagenic in vitro and in vivo, altered the nuclear division index in vitro, but did not diminish cell viability in vitro. Considering that alterations in DNA play important roles in mutagenesis, carcinogenesis, and morphofunctional teratogenesis and reduce embryonic viability, this study indicated that 6-dimethylaminopurine and cycloheximide utilized in the process of mammalian cloning may be responsible for the low embryo viability commonly seen in nuclear transfer after implantation in utero.

Effects of oocyte quality, incubation time and maturation environment on the number of chromosomal abnormalities in IVF-derived early bovine embryos

Chromosomal aberrations are one of the major causes of embryo developmental failures in mammals. The occurrence of these types of abnormalities is higher in in vitro-produced (IVP) embryos. The aim of the present study was to investigate the effect of oocyte morphology and maturation conditions on the rate of chromosomal abnormalities in bovine preimplantational embryos. To this end, 790 early cattle embryos derived from oocytes with different morphologies and matured under different conditions, including maturation period (24 v. 36 h) and maturation media (five different serum supplements in TCM-199), were evaluated cytogenetically in three sequential experiments. The rates of normal diploidy and abnormal haploidy, polyploidy and aneuploidy were determined in each embryo. Throughout all the experiments, the rate of chromosomal abnormalities was significantly (P < 0.05) affected by oocyte morphology and maturation conditions (maturation time and culture medium). Lower morphological quality was associated with a high rate of chromosome abnormalities (P < 0.05). Moreover, polyploidy was associated with increased maturation time (P < 0.01), whereas the maturation medium significantly (P < 0.05) affected the rates of haploidy and polyploidy. In general, supplementing the maturation medium with oestrous cow serum or fetal calf serum resulted in higher rates of chromosomal aberrations (P < 0.05) compared with the other serum supplements tested (bovine steer serum, anoestroues cow serum, bovine amniotic fluid and bovine serum albumin). On the basis of the results of the present study, we conclude that the morphological quality of oocytes and the maturation conditions affect the rate of chromosomal abnormalities in IVP bovine embryos.

Uncoupled embryonic and extra-embryonic tissues compromise blastocyst development after somatic cell nuclear transfer

Somatic cell nuclear transfer (SCNT) is the most efficient cell reprogramming technique available, especially when working with bovine species. Although SCNT blastocysts performed equally well or better than controls in the weeks following embryo transfer at Day 7, elongation and gastrulation defects were observed prior to implantation. To understand the developmental implications of embryonic/extra-embryonic interactions, the morphological and molecular features of elongating and gastrulating tissues were analysed. At Day 18, 30 SCNT conceptuses were compared to 20 controls (AI and IVP: 10 conceptuses each); one-half of the SCNT conceptuses appeared normal while the other half showed signs of atypical elongation and gastrulation. SCNT was also associated with a high incidence of discordance in embryonic and extra-embryonic patterns, as evidenced by morphological and molecular “uncoupling”. Elongation appeared to be secondarily affected; only 3 of 30 conceptuses had abnormally elongated shapes and there were very few differences in gene expression when they were compared to the controls. However, some of these differences could be linked to defects in microvilli formation or extracellular matrix composition and could thus impact extra-embryonic functions. In contrast to elongation, gastrulation stages included embryonic defects that likely affected the hypoblast, the epiblast, or the early stages of their differentiation. When taking into account SCNT conceptus somatic origin, i.e. the reprogramming efficiency of each bovine ear fibroblast (Low: 0029, Med: 7711, High: 5538), we found that embryonic abnormalities or severe embryonic/extra-embryonic uncoupling were more tightly correlated to embryo loss at implantation than were elongation defects. Alternatively, extra-embryonic differences between SCNT and control conceptuses at Day 18 were related to molecular plasticity (high efficiency/high plasticity) and subsequent pregnancy loss. Finally, because it alters re-differentiation processes in vivo, SCNT reprogramming highlights temporally and spatially restricted interactions among cells and tissues in a unique way.

Incidence of chromosomal abnormalities in bovine blastocysts derived from unsorted and sex-sorted spermatozoa

The aim of the present study was to examine the incidence of chromosomal abnormalities in bovine blastocysts produced by IVF with unsorted, X-sorted or Y-sorted spermatozoa. In Experiment 1, individual blastocysts were processed to examine the incidence of mixoploidy using fluorescent in situ hybridisation. Overall, 80% (44/55) of blastocysts were mixoploid (10/15, 14/15 and 20/25 for X-sorted, Y-sorted and unsorted spermatozoa, respectively; P > 0.05). However, the prevalence of abnormal XY chromosome complements was relatively low in all groups; on average, only a small fraction of the total nuclei per embryo appeared polyploid (1.64%, 5.62% and 6.0% for X-sorted, Y-sorted and unsorted spermatozoa, respectively). Interestingly, 20% (5/25) of blastocysts derived from unsorted spermatozoa were found to be chimeric (XX/XY). In Experiment 2, chimeric embryos were detected among the blastocysts derived from two of five sires tested. In addition, one chimeric blastocyst was detected among nine in vivo-derived blastocysts obtained following AI. In conclusion, based on the results of the present study, the incidence of chromosomal abnormalities did not different between blastocysts derived from sex-sorted or unsorted spermatozoa. In addition, the occurrence of mixed sex chimeras was not limited to a single sire and was not unique to blastocysts derived from IVF.

Serial cloning of pigs by somatic cell nuclear transfer: restoration of phenotypic normality during serial cloning

Somatic cell nuclear transfer (scNT) is a useful way to create cloned animals. However, scNT clones exhibit high levels of phenotypic instability. This instability may be due to epigenetic reprogramming and/or genomic damage in the donor cells. To test this, we produced transgenic pig fibroblasts harboring the truncated human thrombopoietin (hTPO) gene and used them as donor cells in scNT to produce first-generation (G1) cloned piglets. In this study, 2,818 scNT embryos were transferred to 11 recipients and five G1 piglets were obtained. Among them, a clone had a dimorphic facial appearance with severe hypertelorism and a broad prominent nasal bridge. The other clones looked normal. Second-generation (G2) scNT piglets were then produced using ear cells from a G1 piglet that had an abnormal nose phenotype. We reasoned that, if the phenotypic abnormality of the G1 clone was not present in the G2 and third-generation (G3) clones, or was absent in the G2 clones but reappeared in the G3 clones, the phenotypic instability of the G1 clone could be attributed to faulty epigenetic reprogramming rather than to inherent/accidental genomic damage to the donor cells. Blastocyst rates, cell numbers in blastocyst, pregnancy rates, term placenta weight and ponderal index, and birth weight between G1 and G2 clones did not differ, but were significantly (P < 0.05) lower than control age- and sex-matched piglets. Next, we analyzed global methylation changes during development of the preimplantation embryos reconstructed by donor cells used for the production of G1 and G2 clones and could not find any significant differences in the methylation patterns between G1 and G2 clones. Indeed, we failed to detect the phenotypic abnormality in the G2 and G3 clones. Thus, the phenotypic abnormality of the G1 clone is likely to be due to epigenetic dysregulation. Additional observations then suggested that expression of the hTPO gene in the transgenic clones did not appear to be the cause of the phenotypic abnormality in the G1 clones and that the abnormality was acquired by only a few of the G1 clone's cells during its gestational development.

Cloning in companion animal, non-domestic and endangered species: can the technology become a practical reality?

Somatic cell nuclear transfer (SCNT) can provide a unique alternative for the preservation of valuable individuals, breeds and species. However, with the exception of a handful of domestic animal species, successful production of healthy cloned offspring has been challenging. Progress in species that have little commercial or research interest, including many companion animal, non-domestic and endangered species (CANDES), has lagged behind. In this review, we discuss the current and future status of SCNT in CANDES and the problems that must be overcome to improve pre- and post-implantation embryo survival in order for this technology to be considered a viable tool for assisted reproduction in these species.

Role of chromosome stability and telomere length in the production of viable cell lines for somatic cell nuclear transfer

Background

Somatic cell nuclear transfer (SCNT) provides an appealing alternative for the preservation of genetic material in non-domestic and endangered species. An important prerequisite for successful SCNT is the availability of good quality donor cells, as normal embryo development is dependent upon proper reprogramming of the donor genome so that embryonic genes can be appropriately expressed. The characteristics of donor cell lines and their ability to produce embryos by SCNT were evaluated by testing the effects of tissue sample collection (DART biopsy, PUNCH biopsy, post-mortem EAR sample) and culture initiation (explant, collagenase digestion) techniques.

Results

Differences in initial sample size based on sample collection technique had an effect on the amount of time necessary for achieving primary confluence and the number of population doublings (PDL) produced. Thus, DART and PUNCH biopsies resulted in cultures with decreased lifespans (<30 PDL) accompanied by senescence-like morphology and decreased normal chromosome content (<40% normal cells at 20 PDL) compared to the long-lived (>50 PDL) and chromosomally stable (>70% normal cells at 20 PDL) cultures produced by post-mortem EAR samples. Chromosome stability was influenced by sample collection technique and was dependent upon the culture's initial telomere length and its rate of shortening over cell passages. Following SCNT, short-lived cultures resulted in significantly lower blastocyst development (≤ 0.9%) compared to highly proliferative cultures (11.8%). Chromosome stability and sample collection technique were significant factors in determining blastocyst development outcome.

Conclusion

These data demonstrate the influence of culture establishment techniques on cell culture characteristics, including the viability, longevity and normality of cells. The identification of a quantifiable marker associated with SCNT embryo developmental potential, chromosome stability, provides a means by which cell culture conditions can be monitored and improved.