Meiotic maturation failure in primary ovarian insufficiency: insights from a bovine model.

PURPOSE: Oocytes from women presenting primary ovarian insufficiency (POI) generate viable embryos at a lower rate than non-POI women, but the mechanisms responsible for the lower oocyte quality remain elusive. Due to the scarcity of human oocytes for research, animal models provide a promising way forward. We aimed at investigating the molecular events characterizing final maturation in POI oocytes in a well-defined POI-like bovine model. METHODS: Single-cell RNA-sequencing of bovine control and POI-like, GV, and MII oocytes (n = 5 per group) was performed. DEseq2 was used to identify differentially expressed genes. Further, a Gene set enrichment analysis and a transcriptomic meta-analysis between bovine and human oocytes were performed. RESULTS: In control cows, we found 2223 differentially expressed genes between the GV and MII stages. Specifically, the affected genes were related to RNA processing and transport, protein synthesis, organelle remodeling and reorganization, and metabolism. The meta-analysis with a set of young human oocytes at different maturation stages revealed 315 conserved genes through the GV-MII transition in cows and humans, mostly related to meiotic progression and cell cycle. Gene expression analysis between GV and MII of POI-like oocytes showed no differences in terms of differentially expressed genes, pointing towards a substantial failure to properly remodel the transcriptome in the POI model, and with the clustering analysis indicating that the cow's genetic background had a higher impact than the oocyte's maturation stage. CONCLUSION: Overall, we have identified and characterized a valuable animal model of POI, paving the way to identifying new molecular mechanisms involved in POI.

Specific processing of meiosis-related transcript is linked to final maturation in human oocytes.

Human meiosis in oocytes entails an intricate regulation of the transcriptome to support late oocyte growth and early embryo development, both crucial to reproductive success. Currently, little is known about the co- and post-transcriptional mRNA processing mechanisms regulating the last meiotic phases, which contribute to transcriptome complexity and influence translation rates. We analyzed gene expression changes, splicing and pre-mRNA processing in an RNA sequencing set of 40 human oocytes at different meiotic maturation stages, matured both in vivo and in vitro. We found abundant untranslated region (UTR) processing, mostly at the 3' end, of meiosis-related genes between the germinal vesicle (GV) and metaphase II (MII) stages, supported by the differential expression of spliceosome and pre-mRNA processing related genes. Importantly, we found very few differences among GV oocytes across several durations of IVM, as long as they did not reach MII, suggesting an association of RNA processing and successful meiosis transit. Changes in protein isoforms are minor, although specific and consistent for genes involved in chromosome organization and spindle assembly. In conclusion, we reveal a dynamic transcript remodeling during human female meiosis, and show how pre-mRNA processing, specifically 3'UTR shortening, drives a selective translational regulation of transcripts necessary to reach final meiotic maturation.

Shared aspects of mRNA expression associated with oocyte maturation failure in humans and rhesus monkeys indicating compromised oocyte quality.

Oocyte maturation failure observed in assisted reproduction technology (ART) cycles can limit the number of quality oocytes obtained and present a pronounced barrier for some patients. The potential exists to use unmatured oocytes for ART through in vitro maturation. Understanding the molecular basis of oocyte maturation failure is pertinent to minimizing this loss of oocytes and considerations of whether such oocytes can be used safely for ART. We identified shared transcriptome abnormalities for rhesus monkey and human failed-to-mature (FTM) oocytes relative to healthy matured MII stage oocytes. We discovered that, although the number of shared affected genes was comparatively small, FTM oocytes in both species shared effects for several pathways and functions, including predicted activation of oxidative phosphorylation (OxPhos) with additional effects on mitochondrial function, lipid metabolism, transcription, nucleotide excision repair, endoplasmic reticulum stress, unfolded protein response, and cell viability. RICTOR emerged as a prominent upstream regulator with predicted inhibition across all analyses. Alterations in KDM5A, MTOR, MTORC1, INSR, CAB39L, and STK11 activities were implicated along with RICTOR in modulating mitochondrial activity and OxPhos. Defects in cell cycle progression were not a prominent feature of FTM oocytes. These results identify a common set of transcriptome abnormalities associated with oocyte maturation failure. While our results do not demonstrate causality, they indicate that fundamental aspects of cellular function are abnormal in FTM oocytes and raise significant concerns about the potential risks of using FTM oocytes for ART.

Human oocyte meiotic maturation is associated with a specific profile of alternatively spliced transcript isoforms.

The transition from a transcriptionally active state (GV) to a transcriptionally inactive state (mature MII oocytes) is required for the acquisition of oocyte developmental competence. We hypothesize that the expression of specific genes at the in vivo matured (MII) stage could be modulated by posttranscriptional mechanisms, particularly regulation of alternative splicing (AS). In this study, we examined the transcriptional activity of GV oocytes after ovarian stimulation followed by oocyte pick-up and the landscape of alternatively spliced isoforms in human MII oocytes. Individual oocytes were processed and analyzed for transcriptional activity (GV), gene expression (GV and MII), and AS signatures (GV and MII) on HTA 2.0 microarrays. Samples were grouped according to maturation stage, and then subgrouped according to women's age and antral follicular count (AFC); array results were validated by quantitative polymerase chain reaction. Differentially expressed genes between GV and MII oocytes clustered mainly in biological processes related to mitochondrial metabolism. Interestingly, 16 genes that were related to the regulation of transcription and mitochondrial translation showed differences in alternatively spliced isoform profiles despite not being differentially expressed between groups. Altogether, our results contribute to our understanding of the role of AS in oocyte developmental competence acquisition.

Trophoblast attachment to the endometrial epithelium elicits compartment-specific transcriptional waves in an in-vitro model.

RESEARCH QUESTION: Which are the early compartment-specific transcriptional responses of the trophoblast and the endometrial epithelium throughout early attachment during implantation? DESIGN: An endometrial epithelium proxy (cell line Ishikawa) was co-cultured with spheroids of a green fluorescent protein (GFP) expressing trophoblast cell line (JEG-3). After 0, 8 and 24 h of co-culture, the compartments were sorted by fluorescence-activated cell sorting; GFP+ (trophoblast), GFP- (epithelium) and non-co-cultured control populations were analysed (in triplicate) by RNA-seq and gene set enrichment analysis (GSEA). RESULTS: Trophoblast challenge induced a wave of transcriptional changes in the epithelium that resulted in 295 differentially regulated genes involving epithelial to mesenchymal transition (EMT), cell movement, apoptosis, hypoxia, inflammation, allograft rejection, myogenesis and cell signalling at 8 h. Interestingly, many of the enriched pathways were subsequently de-enriched by 24 h (i.e. EMT, cell movement, allograft rejection, myogenesis and cell signalling). In the trophoblast, the co-culture induced more transcriptional changes and regulation of a variety of pathways. A total of 1247 and 481 genes were differentially expressed after 8 h and from 8 to 24 h, respectively. Angiogenesis and hypoxia were over-represented at both stages, while EMT and cell signalling only were at 8 h; from 8 to 24 h, inflammation and oestrogen response were enriched, while proliferation was under-represented. CONCLUSIONS: Successful attachment produced a series of dynamic changes in gene expression, characterized by an overall early and transient transcriptional up-regulation in the receptive epithelium, in contrast to a more dynamic transcriptional response in the trophoblast.

Novel phospholipase C zeta 1 mutations associated with fertilization failures after ICSI.

STUDY QUESTION: Are phospholipase C zeta 1 (PLCZ1) mutations associated with fertilization failure (FF) after ICSI? SUMMARY ANSWER: New mutations in the PLCZ1 sequence are associated with FFs after ICSI. WHAT IS KNOWN ALREADY: FF occurs in 1-3% of ICSI cycles, mainly due to oocyte activation failure (OAF). The sperm PLCζ/PLCZ1 protein hydrolyzes phosphatidylinositol (4, 5)-bisphosphate in the oocyte, leading to intracellular calcium release and oocyte activation. To date, few PLCZ1 point mutations causing decreased protein levels or activity have been linked to FF. However, functional alterations of PLCζ/PLCZ1 in response to both described and novel mutations have not been investigated. STUDY DESIGN, SIZE, DURATION: We performed a study including 37 patients presenting total or partial FF (fertilization rate (FR), ≤25%) after ICSI occurring between 2014 and 2018. PARTICIPANTS/MATERIALS, SETTING, METHODS: Patients were divided into two groups based on oocyte evaluation 19 h post ICSI: FF due to a defect in oocyte activation (OAF, n = 22) and FF due to other causes ('no-OAF', n = 15). Samples from 13 men with good fertilization (FR, >50%) were used as controls. PLCζ/PLCZ1 protein localization and levels in sperm were evaluated by immunofluorescence and western blot, respectively. Sanger sequencing on genomic DNA was used to identify PLCZ1 mutations in exonic regions. The effect of the mutations on protein functionality was predicted in silico using the MODICT algorithm. Functional assays were performed by cRNA injection of wild-type and mutated forms of PLCZ1 into human in vitro matured metaphase II oocytes, and fertilization outcomes (second polar body extrusion, pronucleus appearance) scored 19 h after injection. MAIN RESULTS AND THE ROLE OF CHANCE: In the OAF group, 12 (54.6%) patients carried at least one mutation in the PLCZ1 coding sequence, one patient out of 15 (6.7%) in the no-OAF group (P < 0.05) and none of the 13 controls (P < 0.05). A total of six different mutations were identified. Five of them were single-nucleotide missense mutations: p.I120M, located at the end of the EF-hand domain; p.R197H, p.L224P and p.H233L, located at the X catalytic domain; and p.S500 L, located at the C2 domain. The sixth mutation, a frameshift variant (p.V326K fs*25), generates a truncated protein at the X-Y linker region. In silico analysis with MODICT predicted all the mutations except p.I120M to be potentially deleterious for PLCζ/PLCZ1 activity. After PLCZ1 cRNA injection, a significant decrease in the percentage of activated oocytes was observed for three mutations (p.R197H, p.H233L and p.V326K fs*25), indicating a deleterious effect on enzymatic activity. PLCZ1 protein localization and expression levels in sperm were similar across groups. FRs were restored (to >60%) in patients carrying PLCZ1 mutations (n = 10) after assisted oocyte activation (AOA), with seven patients achieving pregnancy and live birth. LIMITATIONS, REASONS FOR CAUTION: Caution should be exerted when comparing the cRNA injection results with fertilization outcomes after ICSI, especially in patients presenting mutations in heterozygosis. WIDER IMPLICATIONS OF THE FINDINGS: PLCZ1 mutations were found in high frequency in patients presenting OAF. Functional analysis of three mutations in human oocytes confirms alteration of PLCζ/PLCZ1 activity and their likely involvement in impaired oocyte activation. Our results suggest that PLCZ1 gene sequencing could be useful as a tool for the diagnosis and counseling of couples presenting FF after ICSI due to OAF. STUDY FUNDING/COMPETING INTEREST(S): This work was supported by intramural funding of Clínica EUGIN, by the Secretary for Universities and Research of the Ministry of Economy and Knowledge of the Government of Catalonia (GENCAT 2015 DI 049 to M. T.-M. and GENCAT 2015 DI 048 to D. C.-B.) and by the Torres Quevedo Program from the Spanish Ministry of Economy and Competitiveness to A. F.-V. No competing interest declared.

Children born after assisted reproduction more commonly carry a mitochondrial genotype associating with low birthweight.

Children conceived through assisted reproductive technologies (ART) have an elevated risk of lower birthweight, yet the underlying cause remains unclear. Our study explores mitochondrial DNA (mtDNA) variants as contributors to birthweight differences by impacting mitochondrial function during prenatal development. We deep-sequenced the mtDNA of 451 ART and spontaneously conceived (SC) individuals, 157 mother-child pairs and 113 individual oocytes from either natural menstrual cycles or after ovarian stimulation (OS) and find that ART individuals carried a different mtDNA genotype than SC individuals, with more de novo non-synonymous variants. These variants, along with rRNA variants, correlate with lower birthweight percentiles, independent of conception mode. Their higher occurrence in ART individuals stems from de novo mutagenesis associated with maternal aging and OS-induced oocyte cohort size. Future research will establish the long-term health consequences of these changes and how these findings will impact the clinical practice and patient counselling in the future.

ESHRE survey results and good practice recommendations on managing chromosomal mosaicism.

STUDY QUESTION: How should ART/preimplantation genetic testing (PGT) centres manage the detection of chromosomal mosaicism following PGT? SUMMARY ANSWER: Thirty good practice recommendations were formulated that can be used by ART/PGT centres as a basis for their own policy with regards to the management of 'mosaic' embryos. WHAT IS KNOWN ALREADY: The use of comprehensive chromosome screening technologies has provided a variety of data on the incidence of chromosomal mosaicism at the preimplantation stage of development and evidence is accumulating that clarifies the clinical outcomes after transfer of embryos with putative mosaic results, with regards to implantation, miscarriage and live birth rates, and neonatal outcomes. STUDY DESIGN SIZE DURATION: This document was developed according to a predefined methodology for ESHRE good practice recommendations. Recommendations are supported by data from the literature, a large survey evaluating current practice and published guidance documents. The literature search was performed using PubMed and focused on studies published between 2010 and 2022. The survey was performed through a web-based questionnaire distributed to members of the ESHRE special interest groups (SIG) Reproductive Genetics and Embryology, and the ESHRE PGT Consortium members. It included questions on ART and PGT, reporting, embryo transfer policy and follow-up of transfers. The final dataset represents 239 centres. PARTICIPANTS/MATERIALS SETTING METHODS: The working group (WG) included 16 members with expertise on the ART/PGT process and chromosomal mosaicism. The recommendations for clinical practice were formulated based on the expert opinion of the WG, while taking into consideration the published data and results of the survey. MAIN RESULTS AND THE ROLE OF CHANCE: Eighty percent of centres that biopsy three or more cells report mosaicism, even though only 66.9% of all centres have validated their technology and only 61.8% of these have validated specifically for the calling of chromosomal mosaicism. The criteria for designating mosaicism, reporting and transfer policies vary significantly across the centres replying to the survey. The WG formulated recommendations on how to manage the detection of chromosomal mosaicism in clinical practice, considering validation, risk assessment, designating and reporting mosaicism, embryo transfer policies, prenatal testing and follow-up. Guidance is also provided on the essential elements that should constitute the consent forms and the genetic report, and that should be covered in genetic counselling. As there are several unknowns in chromosomal mosaicism, it is recommended that PGT centres monitor emerging data on the topic and adapt or refine their policy whenever new insights are available from evidence. LIMITATIONS REASONS FOR CAUTION: Rather than providing instant standardized advice, the recommendations should help ART/PGT centres in developing their own policy towards the management of putative mosaic embryos in clinical practice. WIDER IMPLICATIONS OF THE FINDINGS: This document will help facilitate a more knowledge-based approach for dealing with chromosomal mosaicism in different centres. In addition to recommendations for clinical practice, recommendations for future research were formulated. Following up on these will direct research towards existing research gaps with direct translation to clinical practice. Emerging data will help in improving guidance, and a more evidence-based approach of managing chromosomal mosaicism. STUDY FUNDING/COMPETING INTERESTS: The WG received technical support from ESHRE. M.D.R. participated in the EQA special advisory group, outside the submitted work, and is the chair of the PGT WG of the Belgian society for human genetics. D.W. declared receiving salary from Juno Genetics, UK. A.C. is an employee of Igenomix, Italy and C.R. is an employee of Igenomix, Spain. C.S. received a research grant from FWO, Belgium, not related to the submitted work. I.S. declared being a Co-founder of IVFvision Ltd, UK. J.R.V. declared patents related to 'Methods for haplotyping single-cells' and 'Haplotyping and copy number typing using polymorphic variant allelic frequencies', and being a board member of Preimplantation Genetic Diagnosis International Society (PGDIS) and International Society for Prenatal Diagnosis (ISPD). K.S. reported being Chair-elect of ESHRE. The other authors had nothing to disclose. DISCLAIMER: This Good Practice Recommendations (GPR) document represents the views of ESHRE, which are the result of consensus between the relevant ESHRE stakeholders and are based on the scientific evidence available at the time of preparation.  ESHRE GPRs should be used for information and educational purposes. They should not be interpreted as setting a standard of care or be deemed inclusive of all proper methods of care, or be exclusive of other methods of care reasonably directed to obtaining the same results. They do not replace the need for application of clinical judgement to each individual presentation, or variations based on locality and facility type.  Furthermore, ESHRE GPRs do not constitute or imply the endorsement, or favouring, of any of the included technologies by ESHRE.

Single human oocyte transcriptome analysis reveals distinct maturation stage-dependent pathways impacted by age.

Female fertility is inversely correlated with maternal age due to a depletion of the oocyte pool and a reduction in oocyte developmental competence. Few studies have addressed the effect of maternal age on the human mature oocyte (MII) transcriptome, which is established during oocyte growth and maturation, however, the pathways involved remain unclear. Here, we characterize and compare the transcriptomes of a large cohort of fully grown germinal vesicle stage (GV) and in vitro matured (IVM-MII) oocytes from women of varying reproductive age. First, we identified two clusters of cells reflecting the oocyte maturation stage (GV and IVM-MII) with 4445 and 324 putative marker genes, respectively. Furthermore, we identified genes for which transcript representation either progressively increased or decreased with age. Our results indicate that the transcriptome is more affected by age in IVM-MII oocytes (1219 genes) than in GV oocytes (596 genes). In particular, we found that transcripts of genes involved in chromosome segregation and RNA splicing significantly increased representation with age, while genes related to mitochondrial activity showed a lower representation. Gene regulatory network analysis facilitated the identification of potential upstream master regulators of the genes involved in those biological functions. Our analysis suggests that advanced maternal age does not globally affect the oocyte transcriptome at GV or IVM-MII stages. Nonetheless, hundreds of genes displayed altered transcript representation, particularly in IVM-MII oocytes, which might contribute to the age-related quality decline in human oocytes.

Oxidative Stress in Reproduction: A Mitochondrial Perspective.

Mitochondria are fundamental organelles in eukaryotic cells that provide ATP through oxidative phosphorylation. During this process, reactive oxygen species (ROS) are produced, and an imbalance in their concentrations can induce oxidative stress (OS), causing cellular damage. However, mitochondria and ROS play also an important role in cellular homeostasis through a variety of other signaling pathways not related to metabolic rates, highlighting the physiological relevance of mitochondria-ROS interactions. In reproduction, mitochondria follow a peculiar pattern of activation, especially in gametes, where they are relatively inactive during the initial phases of development, and become more active towards the final maturation stages. The reasons for the lower metabolic rates are attributed to the evolutionary advantage of keeping ROS levels low, thus avoiding cellular damage and apoptosis. In this review, we provide an overview on the interplay between mitochondrial metabolism and ROS during gametogenesis and embryogenesis, and how OS can influence these physiological processes. We also present the possible effects of assisted reproduction procedures on the levels of OS, and the latest techniques developed to select gametes and embryos based on their redox state. Finally, we evaluate the treatments developed to manage OS in assisted reproduction to improve the chances of pregnancy.

Detection of Heteroplasmic Variants in the Mitochondrial Genome through Massive Parallel Sequencing.

Detecting heteroplasmies in the mitochondrial DNA (mtDNA) has been a challenge for many years. In the past, Sanger sequencing was the main option to perform this analysis, however, this method could not detect low frequency heteroplasmies. Massive Parallel Sequencing (MPS) provides the opportunity to study the mtDNA in depth, but a controlled pipeline is necessary to reliably retrieve and quantify the low frequency variants. It has been shown that differences in methods can significantly affect the number and frequency of the retrieved variants. In this protocol, we present a method involving both wet lab and bioinformatics that allows identifying and quantifying single nucleotide variants in the full mtDNA sequence, down to a heteroplasmic load of 1.5%. For this, we set up a PCR-based amplification of the mtDNA, followed by MPS using Illumina chemistry, and variant calling with two different algorithms, mtDNA server and Mutect. The PCR amplification is used to enrich the mitochondrial fraction, while the bioinformatic processing with two algorithms is used to discriminate the true heteroplasmies from background noise. The protocol described here allows for deep sequencing of the mitochondrial DNA in bulk DNA samples as well as single cells (both large cells such as human oocytes, and small-sized single cells such as human embryonic stem cells) with minor modifications to the protocol.

Uncovering low-level mosaicism in human embryonic stem cells using high throughput single cell shallow sequencing.

Human pluripotent stem cells (hPSCs) have significant levels of low-grade genetic mosaicism, which commonly used techniques fail to detect in bulk DNA. These copy number variations remain a hurdle for the clinical translation of hPSC, as their effect in vivo ranges from unknown to dangerous, and the ability to detect them will be necessary as the field advances. As such there is need for techniques which can efficiently analyse genetic content in single cells with higher throughput and lower costs. We report here on the use of the Fluidigm C1 single cell WGA platform in combination with shallow whole genome sequencing to analyse the genetic content of single hPSCs. From a hPSC line carrying an isochromosome 20, 56 single cells were analysed and found to carry a total of 50 aberrations, across 23% of cells, which could not be detected by bulk analysis. Aberrations were predominantly segmental gains, with a fewer number of segmental losses and aneuploidies. Interestingly, 40% of the breakpoints seen here correspond to known DNA fragile sites. Our results therefore demonstrate the feasibility of single cell shallow sequencing of hPSC and further expand upon the biological importance and frequency of single cell mosaicism in hPSC.

Genetic and epigenetic factors which modulate differentiation propensity in human pluripotent stem cells.

BACKGROUND: Human pluripotent stem cell (hPSC) lines are known to have a bias in their differentiation. This gives individual cell lines a propensity to preferentially differentiate towards one germ layer or cell type over others. Chromosomal aberrations, mitochondrial mutations, genetic diversity and epigenetic variance are the main drivers of this phenomenon, and can lead to a wide range of phenotypes. OBJECTIVE AND RATIONALE: Our aim is to provide a comprehensive overview of the different factors which influence differentiation propensity. Specifically, we sought to highlight known genetic variances and their mechanisms, in addition to more general observations from larger abnormalities. Furthermore, we wanted to provide an up-to-date list of a growing number of predictive indicators which are able to identify differentiation propensity before the initiation of differentiation. As differentiation propensity can lead to difficulties in both research as well as clinical translation, our thorough overview could be a useful tool. SEARCH METHODS: Combinations of the following key words were applied as search criteria in the PubMed database: embryonic stem cells, induced pluripotent stem cells, differentiation propensity (also: potential, efficiency, capacity, bias, variability), epigenetics, chromosomal abnormalities, genetic aberrations, X chromosome inactivation, mitochondrial function, mitochondrial metabolism, genetic diversity, reprogramming, predictive marker, residual stem cell, clinic. Only studies in English were included, ranging from 2000 to 2017, with a majority ranging from 2010 to 1017. Further manuscripts were added from cross-references. OUTCOMES: Differentiation propensity is affected by a wide variety of (epi)genetic factors. These factors clearly lead to a loss of differentiation capacity, preference towards certain cell types and oftentimes, phenotypes which begin to resemble cancer. Broad changes in (epi)genetics, such as aneuploidies or wide-ranging modifications to the epigenetic landscape tend to lead to extensive, less definite changes in differentiation capacity, whereas more specific abnormalities often have precise ramifications in which certain cell types become more preferential. Furthermore, there appears to be a greater, though often less considered, contribution to differentiation propensity by factors such as mitochondria and inherent genetic diversity. Varied differentiation capacity can also lead to potential consequences in the clinical translation of hPSC, including the occurrence of residual undifferentiated stem cells, and the transplantation of potentially transformed cells. WIDER IMPLICATIONS: As hPSC continue to advance towards the clinic, our understanding of them progresses as well. As a result, the challenges faced become more numerous, but also more clear. If the transition to the clinic is to be achieved with a minimum number of potential setbacks, thorough evaluation of the cells will be an absolute necessity. Altered differentiation propensity represents at least one such hurdle, for which researchers and eventually clinicians will need to find solutions. Already, steps are being taken to tackle the issue, though further research will be required to evaluate any long-term risks it poses.

Random Mutagenesis, Clonal Events, and Embryonic or Somatic Origin Determine the mtDNA Variant Type and Load in Human Pluripotent Stem Cells.

In this study, we deep-sequenced the mtDNA of human embryonic and induced pluripotent stem cells (hESCs and hiPSCs) and their source cells and found that the majority of variants pre-existed in the cells used to establish the lines. Early-passage hESCs carried few and low-load heteroplasmic variants, similar to those identified in oocytes and inner cell masses. The number and heteroplasmic loads of these variants increased with prolonged cell culture. The study of 120 individual cells of early- and late-passage hESCs revealed a significant diversity in mtDNA heteroplasmic variants at the single-cell level and that the variants that increase during time in culture are always passenger to the appearance of chromosomal abnormalities. We found that early-passage hiPSCs carry much higher loads of mtDNA variants than hESCs, which single-fibroblast sequencing proved pre-existed in the source cells. Finally, we show that these variants are stably transmitted during short-term differentiation.

Accurate and comprehensive analysis of single nucleotide variants and large deletions of the human mitochondrial genome in DNA and single cells.

Massive parallel sequencing (MPS) can accurately quantify mitochondrial DNA (mtDNA) single nucleotide variants (SNVs), but no MPS methods are currently validated to simultaneously and accurately establish the breakpoints and frequency of large deletions at low heteroplasmic loads. Here we present the thorough validation of an MPS protocol to quantify the load of very low frequency, large mtDNA deletions in bulk DNA and single cells, along with SNV calling by standard methods. We used a set of well-characterized DNA samples, DNA mixes and single cells to thoroughly control the study. We developed a custom script for the detection of mtDNA rearrangements that proved to be more accurate in detecting and quantifying deletions than pre-existing tools. We also show that PCR conditions and primersets must be carefully chosen to avoid biases in the retrieved variants and an increase in background noise, and established a lower detection limit of 0.5% heteroplasmic load for large deletions, and 1.5 and 2% for SNVs, for bulk DNA and single cells, respectively. Finally, the analysis of different single cells provided novel insights into mtDNA cellular mosaicism.

Higher-Density Culture in Human Embryonic Stem Cells Results in DNA Damage and Genome Instability.

Human embryonic stem cells (hESC) show great promise for clinical and research applications, but their well-known proneness to genomic instability hampers the development to their full potential. Here, we demonstrate that medium acidification linked to culture density is the main cause of DNA damage and genomic alterations in hESC grown on feeder layers, and this even in the short time span of a single passage. In line with this, we show that increasing the frequency of the medium refreshments minimizes the levels of DNA damage and genetic instability. Also, we show that cells cultured on laminin-521 do not present this increase in DNA damage when grown at high density, although the (long-term) impact on their genomic stability remains to be elucidated. Our results explain the high levels of genome instability observed over the years by many laboratories worldwide, and show that the development of optimal culture conditions is key to solving this problem.

Dissecting histone deacetylase role in pulmonary arterial smooth muscle cell proliferation and migration.

Pulmonary Arterial Hypertension (PAH) is a rare and devasting condition characterized by elevated pulmonary vascular resistance and pulmonary artery pressure leading to right-heart failure and premature death. Pathologic alterations in proliferation, migration and survival of all cell types composing the vascular tissue play a key role in the occlusion of the vascular lumen. In the current study, we initially investigated the action of selective class I and class II HDAC inhibitors on the proliferation and migration of pulmonary artery smooth muscle cells (PASMCs) after exposure to Platelet Derived Growth Factor (PDGF). Class I HDAC inhibitors were able to counteract the hyperproliferative response to PDGF, reducing both proliferation and migration in PASMCs, while class II were ineffective. Selective silencing with siRNAs targeted against different HDACs revealed a major role of class I, and within this class, of HDAC1 in mediating PDGF-induced Akt Phosphorylation and Cyclin D1 (CycD1) expression. These results from these combinatorial approaches were further confirmed by the ability of a specific HDAC1 inhibitor to antagonize the PDGF action. The finding that HDAC1 is a major conductor of PDGF-induced patterning in PAH-PASMCs prompts the development of novel selective inhibitors of this member of class I HDACs as a potential tool to control lung vascular homeostasis in PAH.

Sodium butyrate inhibits platelet-derived growth factor-induced proliferation and migration in pulmonary artery smooth muscle cells through Akt inhibition.

Sodium butyrate (BU) is a molecule that acts as a histone deacetylase inhibitor. As compared with its well-known antineoplastic/antiproliferative effects, little is known about BU action on vascular cell dynamics. An imbalance of proliferation and migration in pulmonary arterial smooth muscle cells (PASMCs) is essential in the onset and progression of pulmonary arterial hypertension (PAH), a disease that is characterized by vascular lung derangement and that frequently has an unfavorable outcome. Here, we show that, in PASMCs of PAH rats, BU counteracted platelet-derived growth factor (PDGF)-induced Ki67 expression, and arrested the cell cycle, mainly at G0 /G1 . BU decreased proliferating cell nuclear antigen, c-Myc and cyclin D1 transcription and protein expression, while increasing p21 expression. BU reduced the transcription of PDGF receptor-ß, and that of Ednra and Ednrb, two major receptors in PAH progression. Wound healing, migration and pulmonary artery ring assays indicated that BU inhibited PDGF-induced PASMC migration. BU strongly inhibited PDGF-induced Akt phosphorylation, an effect reversed by the phosphatase inhibitor calyculin A. BU-treated cells showed a remarkable increase in acetylated Akt, indicating an inverse relationship between the levels of acetylated Akt and phospho-Akt. These findings may provide novel perspectives on the use of histone deacetylase inhibitors in PAH.