Xist Expression Research Articles

Ftx is dispensable for imprinted X-chromosome inactivation in preimplantation mouse embryos.

X-chromosome inactivation (XCI) equalizes gene expression between the sexes by inactivating one of the two X chromosomes in female mammals. Xist has been considered as a major cis-acting factor that inactivates the paternally derived X chromosome (Xp) in preimplantation mouse embryos (imprinted XCI). Ftx has been proposed as a positive regulator of Xist. However, the physiological role of Ftx in female animals has never been studied. We recently reported that Ftx is located in the cis-acting regulatory region of the imprinted XCI and expressed from the inactive Xp, suggesting a role in the imprinted XCI mechanism. Here we examined the effects on imprinted XCI using targeted deletion of Ftx. Disruption of Ftx did not affect the survival of female embryos or expression of Xist and other X-linked genes in the preimplantation female embryos. Our results indicate that Ftx is dispensable for imprinted XCI in preimplantation embryos.

Maternal bias and escape from X chromosome imprinting in the midgestation mouse placenta

To investigate the epigenetic landscape at the interface between mother and fetus, we provide a comprehensive analysis of parent-of-origin bias in the mouse placenta. Using F1 interspecies hybrids between mus musculus (C57BL/6J) and mus musculus castaneus, we sequenced RNA from 23 individual midgestation placentas, five late stage placentas, and two yolk sac samples and then used SNPs to determine whether transcripts were preferentially generated from the maternal or paternal allele. In the placenta, we find 103 genes that show significant and reproducible parent-of-origin bias, of which 78 are novel candidates. Most (96%) show a strong maternal bias which we demonstrate, via multiple mathematical models, pyrosequencing, and FISH, is not due to maternal decidual contamination. Analysis of the X chromosome also reveals paternal expression of Xist and several genes that escape inactivation, most significantly Alas2, Fhl1, and Slc38a5. Finally, sequencing individual placentas allowed us to reveal notable expression similarity between littermates. In all, we observe a striking preference for maternal transcription in the midgestation mouse placenta and a dynamic imprinting landscape in extraembryonic tissues, reflecting the complex nature of epigenetic pathways in the placenta.

22 OXAMFLATIN TREATMENT ENHANCES NUCLEAR REPROGRAMMING BY INHIBITING XIST EXPRESSION AND REDUCING DNA METHYLATION IN PORCINE SOMATIC CELL NUCLEAR TRANSFER EMBRYOS

Treatment of cloned embryos with histone deacetylase inhibitors (HDACi) enhances developmental potential by alteration of epigenetic status. Oxamflatin is one of the potent HDACi. In our previous study, development to Day 7 blastocysts was enhanced when the porcine somatic cell nuclear transfer (SCNT) embryos were treated with oxamflatin for 16 h. The objective of the present study was to investigate the effect of oxamflatin treatment on XIST gene expression and DNA methylation of XIST gene and centromeric repeat element in Day 7 SCNT blastocysts. Somatic cell nuclear transfer was performed on enucleated metaphase II oocytes using a transgene female cell line. Cloned embryos were electrically fused and activated, treated with 150 nM oxamflatin for 16 h and cultured in PZM3 under 5% CO2, 5% oxygen, and 90% N2 for 7 days. Clones without Oxamflatin treatment were used as controls. For XIST methylation, IVF blastocysts at Day 7 were used as controls. Blastocysts at Day 7 were pooled from each treatment group and processed for methylation analysis by bisulfite sequencing and gene expression by quantitative real-time PCR. This experiment was replicated 4 times. The percent of CpG methylation in donor cells before SCNT was also determined. Data were analysed by using SAS version 9.3 (SAS Institute Inc., Cary, NC, USA). In donor cells, 45.3 ± 5.8% of CpGs in a centromeric repeat element (9 CpGs in GenBank Z75640) were methylated. In the SCNT embryos, oxamflatin treatment reduced methylation from 27.3 ± 3.1% in the control to 18.2 ± 3.2% (P < 0.05). The average methylation in XIST (11 CpGs in GenBank KC149530.1) in donor cells was 42.4 ± 6.4%. This CpG island had 2 sites that were not methylated in any of the samples. However, the remaining 9 CpGs were methylated in 8 of 15 samples; for example, showing a parental imprint of ~50%. This implied that the CpG island studied represented the real-time status of the XIST locus in the cell and provides a good marker for reprogramming studies. XIST methylation level in Day 7 blastocysts was not different between oxamflatin (11.8 ± 3.2%) and control (11.8 ± 3.2%). However, XIST methylation in SCNT embryos was higher than in the same age IVF blastocysts (11.7 ± 1.7 v. 0.6 ± 2.4%; P < 0.01). Oxamflatin treatment tended to decrease XIST expression in Day 7 blastocysts compared with controls (18.8 ± 0.8 v. 21.7 ± 0.8; P < 0.1) as measured by real-time PCR. Interestingly, XIST gene expression was positively correlated with its methylation (P < 0.05). In conclusion, these results indicate that during nuclear reprogramming there was a dramatic decrease in DNA methylation from donor cells to Day 7 SCNT embryos. The higher methylation of XIST in SCNT embryos compared with IVF embryos suggests that the reprogramming of donor cells was not completed, which may be a contributor to low cloning efficiency. Oxamflatin treatment of SCNT embryos may enhance nuclear reprogramming by inhibiting XIST expression and reducing DNA methylation, resulting in better embryo development.

The Histone Deacetylase Inhibitor Abexinostat Induces Cancer Stem Cells Differentiation in Breast Cancer with Low Xist Expression

Cancer stem cells (CSC) are the tumorigenic cell population that has been shown to sustain tumor growth and to resist conventional therapies. The purpose of this study was to evaluate the potential of histone deacetylase inhibitors (HDACi) as anti-CSC therapies. We evaluated the effect of the HDACi compound abexinostat on CSCs from 16 breast cancer cell lines (BCL) using ALDEFLUOR assay and tumorsphere formation. We performed gene expression profiling to identify biomarkers predicting drug response to abexinostat. Then, we used patient-derived xenograft (PDX) to confirm, in vivo, abexinostat treatment effect on breast CSCs according to the identified biomarkers. We identified two drug-response profiles to abexinostat in BCLs. Abexinostat induced CSC differentiation in low-dose sensitive BCLs, whereas it did not have any effect on the CSC population from high-dose sensitive BCLs. Using gene expression profiling, we identified the long noncoding RNA Xist (X-inactive specific transcript) as a biomarker predicting BCL response to HDACi. We validated that low Xist expression predicts drug response in PDXs associated with a significant reduction of the breast CSC population. Our study opens promising perspectives for the use of HDACi as a differentiation therapy targeting the breast CSCs and identified a biomarker to select patients with breast cancer susceptible to responding to this treatment.

Potential Mechanisms of Aberrant DNA Hypomethylation on the X Chromosome in Uterine Leiomyomas

. We recently found that aberrant DNA hypomethylation is more common on the X chromosome than on other chromosomes in uterine leiomyomas by genome-wide DNA methylation profiling. To investigate the mechanism of aberrant hypomethylation on the X chromosome in uterine leiomyomas, we analyzed methylome and transcriptome data from three cases of leiomyomas and the adjacent myometrium. We found that eleven of the aberrantly hypomethylated genes on the X chromosome were common to the three cases. None of these 11 genes were transcriptionally upregulated in the leiomyoma. However, one of them, TSPYL2, was hypomethylated in 68% of multiple leiomyoma specimens. The incidence of aberrant hypomethylation of TSPYL2 was comparable to that of the MED12 mutation (68%), which is known to be detected at a high frequency in uterine leiomyomas. We also analyzed the aberration of the X chromosome inactivation (XCI) mechanism in uterine leiomyomas. Hypomethylation was not enriched in the imprinted genes, suggesting that dysfunction of polycomb repressive complexes is not involved in the aberrant hypomethylation on the X chromosome. The expression analysis of XCI-related genes revealed that the XIST and SATB1 expression was downregulated in 36% and 46% of 11 leiomyoma specimens, respectively, while the HNRNPU and SMCHD1 expression was not altered. In conclusion, the aberration of XCI-related genes such as SATB1 or XIST may be involved in aberrant hypomethylation on the X chromosome in a certain population of the patients with uterine leiomyomas. TSPYL2 of the aberrantly hypomethylated genes on the X chromosome can be used as a biomarker of uterine leiomyomas.

X-Reactivation Impacts Human iPSC Differentiation Potential Towards Blood

To determine novel key regulators that direct ES/iPS cell differentiation to hematopoietic lineages, we compared the gene expression profiles of multiple iPS cell lines with defferential blood forming capacity. We generated multiple iPS cell lines from amniotic fluid derived mesenchymal stromal cells (AF-iPS) which differentiated towards hematopoietic lineages using our standardized and highly reproducible differentiation protocol. Of the 9 AF-iPS cell lines derived from an individual female patient, the average efficiency of CD45+ hematopoietic cells was 14.2 +/- 9% (range 1.6 to 26.3%).To elucidate the possible reasons for this diversity in efficiency, we grouped the AF-iPS cell lines on the basis of lowest and highest blood differentiation capacity and compared their gene expression profiles by microarray. We found very few changes above 1.5-fold, but interestingly, among the 11 genes that were over-expressed in the AF-iPSC lines with poor blood differentiation efficiency 10 were located on X chromosome, and the remaining one reported to be involved in Notch signalling.A combination of cumulative sum analysis and the location of differentially expressed genes on the X chromosome identified putative regions of reactivation at multiple, but distinct locations. The possibility of X-reactivation in these female lines was reinforced further where lower levels of XIST were seen in AF-iPSC lines shown to have low blood forming potential, however only half of the iPS cell lines with high blood differentiation capacity showed normal XIST expression when compared to the amniotic fluid mesenchymal starting cell material.To determine whether the block in differentiation was tissue specific we tested the differentiation capacity of the AF-iPSC lines towards neuronal lineages. Intriguingly we found neural cell differentiation was not hampered within all lines with poor blood potential suggesting that the over-expression of genes as a consequence of X-reactivation can impart a specific negative effect on differentiation towards the blood lineages from pluripotency stage, while not having an effect on neuronal cell development.To further define the source of this block, we have begun working knocking down the overexpressed genes on X chromosome in lines with poor blood differentiation potential to determine whether the efficiency can be increased (or fully rescued) with one, or a combination of these 11 candidate genes. These results have implications for the identification and selection of female iPS lines suitable for therapeutic purposes. Disclosures:No relevant conflicts of interest to declare.

Sex‐dependent regulation of cytochrome P450 family members Cyp1a1, Cyp2e1, and Cyp7b1 by methylation of DNA

Sexual differences are only partially attributable to hormones. Cultured male or female cells, even from embryos before sexual differentiation, differ in gene expression and sensitivity to toxins, and these differences persist in isolated primary cells. Male and female cells from Swiss Webster CWF mice manifest sex-distinct patterns of DNA methylation for X-ist and for cytochrome P450 (CYP; family members 1a1, 2e1m, and 7b1. Dnmt3l is differentially expressed but not differentially methylated, and Gapdh is neither differentially methylated nor expressed. CYP family genes differ in expression in whole tissue homogenates and cell cultures, with female Cyp expression 2- to 355-fold higher and Dnmt3l 12- to 32-fold higher in males. DNA methylation in the promoters of these genes is sex dimorphic; reducing methylation differences reduces to 1- to 6-fold differences in the expression of these genes. Stress or estradiol alters both methylation and gene expression. We conclude that different methylation patterns partially explain the sex-based differences in expression of CYP family members and X-ist, which potentially leads to inborn differences between males and females and their different responses to chronic and acute changes. Sex-differential methylation may have medical effects.

X Chromosome Inactivation and Epigenetic Responses to Cellular Reprogramming

Reprogramming somatic cells to derive induced pluripotent stem cells (iPSCs) has provided a new method to model disease and holds great promise for regenerative medicine. Although genetically identical to their donor somatic cells, iPSCs undergo substantial changes in the epigenetic landscape during reprogramming. One such epigenetic process, X chromosome inactivation (XCI), has recently been shown to vary widely in human female iPSCs and embryonic stem cells (ESCs). XCI is a form of dosage compensation whose chief regulator is the noncoding RNA Xist. In mouse iPSCs and ESCs, Xist expression and XCI strictly correlate with the pluripotent state, but no such correlation exists in humans. Lack of XIST expression in human cells is linked to reduced developmental potential and an altered transcriptional profile, including upregulation of genes associated with cancer, which has therefore led to concerns about the safety of pluripotent stem cells for use in regenerative medicine. In this review, we describe how different states of XIST expression define three classes of female human pluripotent stem cells and explore progress in discovering the reasons for these variations and how they might be countered.

75P - Expression of XIST and 53BP1 as Predictive Markers in BRCA1 Deficient Breast Cancer

The identification and validation of predictive biomarkers has often been hampered by issues in retrospective clinical study design, for example missing control groups and small or biased patient series. Despite a wealth of preclinical mechanistic insights and finished randomized controlled trials (RCT), translation to the clinic is infrequent. XIST and 53BP1 are two genes that were previously identified in preclinical studies to predict resistance to therapy targeting BRCA1 deficiency. We studied the expression of these two genes in the context of an RCT randomizing between conventional (5 cycles fluorouracil, epirubicin, cyclophosphamide (FEC)) and BRCA1 defect targeting chemotherapy (4 cycles FEC + 1 cycle of high dose carboplatin, thiotepa, cyclophosphamide).

XACT, a long non-coding transcript coating the active X chromosome in human pluripotent cells

X-chromosome inactivation (XCI), the dosage compensation process that equalizes X-linked gene expression between sexes, has mostly been studied in the mouse, where the central role for the non-coding RNA Xist in the initiation and spreading of the process was demonstrated. Although Xist is conserved in humans [1], very little is known concerning its regulation and function in this species. Several lines of evidence moreover suggest that different strategies have been adopted in the human to control XCI as compared to the mouse. In particular, in human pre-implantation development, XIST RNA coats the X chromosome(s) in both male and female embryos without inducing X-chromosome silencing [2]. This indicates that XIST expression and X-inactivation can be uncoupled during human embryogenesis and that other elements likely participate to the control of X chromosome activity in humans. XCI is established early during embryonic development, and embryonic stem cells can be used to decipher the kinetics and the molecular actors of the process. Human female embryonic stem cells (hESC) can be found in different configurations regarding XIST expression: most female hESC have already undergone XCI but tend to spontaneously lose XIST expression [3]. In the course of an RNA-seq analysis of female hESC, we identified an extended and un-annotated transcribed region producing a long unspliced, likely non-coding nuclear RNA. RNA-FISH analysis reveals that this transcript is expressed from, and coats the active X chromosome. We called this transcript XACT, for X-active coating transcript. In female hESC in which XIST is repressed, XACT is expressed from and coats both Xs, and this correlates with significant reactivation of the inactive X chromosome. Expression of XACT appears to be specific for pluripotent cells as its expression decreases during differentiation. Finally, we provide evidence that XACT is not conserved in the mouse. In conclusion, we have identified XACT as the first long ncRNA that coats the active X chromosome in human. Given its expression profile and lack of conservation, it is tempting to speculate that XACT is involved in the peculiar control of XCI initiation in human.

A prominent and conserved role for YY1 in Xist transcriptional activation

Dosage compensation for X-linked genes in female mammals relies on X-chromosome inactivation. This process involves monoallelic up-regulation of the non-coding Xist RNA which coats in cis the chromosome and triggers epigenetic reprogramming that will prevent chromosome-wide transcription. Xist transcription is controlled, directly and/or indirectly, by several ncRNA (Tsix, Jpx, Ftx) and factors (Sox2, Oct4, Nanog, Rex1, Rnf12). However, mechanisms leading to Xist monoallelic regulation remain poorly understood. Using mouse ES and differentiating cells, we identified specific YY1 and CTCF interacting sites on the Xist locus of the inactive X-chromosome. We show that this monoallelic binding is controlled by DNA methylation. To gain further insights into YY1 functional role on the Xist locus, we conducted YY1 knockdown experiments. We show by RNA-FISH that depletion of YY1 in female somatic cells impairs the accumulation of Xist on the inactive X-chromosome. This is likely due to a transcriptional effect as we observe a drastic reduction of both spliced and unspliced Xist RNA levels. This hypothesis is further reinforced by the in vitro analysis Xist promoter activity, which displays strict dependency on the YY1 binding sites. Importantly, YY1 is also necessary for the upregulation of Xist that triggers X-chromosome inactivation. Taken together, these results suggest a strong requirement for YY1 in the upregulation and maintenance of Xist transcription. Importantly, we demonstrate that the function of YY1 in the control of Xist expression is conserved in humans and predicted in other mammalian species. These results highlight the importance of YY1 both in the monoallelic upregulation of Xist at the exit of pluripotency and in the maintenance of its expression in somatic cells. Taken together with previous studies, we propose that through its dual action on Tsix and Xist, YY1 acts as a bimodal transcriptional regulator of X-inactivation.

Feeder-Free Generation and Long-Term Culture of Human Induced Pluripotent Stem Cells Using Pericellular Matrix of Decidua Derived Mesenchymal Cells

Human ES cells (hESCs) and human induced pluripotent stem cells (hiPSCs) are usually generated and maintained on living feeder cells like mouse embryonic fibroblasts or on a cell-free substrate like Matrigel. For clinical applications, a quality-controlled, xenobiotic-free culture system is required to minimize risks from contaminating animal-derived pathogens and immunogens. We previously reported that the pericellular matrix of decidua-derived mesenchymal cells (PCM-DM) is an ideal human-derived substrate on which to maintain hiPSCs/hESCs. In this study, we examined whether PCM-DM could be used for the generation and long-term stable maintenance of hiPSCs. Decidua-derived mesenchymal cells (DMCs) were reprogrammed by the retroviral transduction of four factors (OCT4, SOX2, KLF4, c-MYC) and cultured on PCM-DM. The established hiPSC clones expressed alkaline phosphatase, hESC-specific genes and cell-surface markers, and differentiated into three germ layers in vitro and in vivo. At over 20 passages, the hiPSCs cultured on PCM-DM held the same cellular properties with genome integrity as those at early passages. Global gene expression analysis showed that the GDF3, FGF4, UTF1, and XIST expression levels varied during culture, and GATA6 was highly expressed under our culture conditions; however, these gene expressions did not affect the cells’ pluripotency. PCM-DM can be conveniently prepared from DMCs, which have a high proliferative potential. Our findings indicate that PCM-DM is a versatile and practical human-derived substrate that can be used for the feeder-cell-free generation and long-term stable maintenance of hiPSCs.

RNAi-mediated Knockdown of <i>Xist</i> Does Not Rescue the Impaired Development of Female Cloned Mouse Embryos

In mice, one of the major epigenetic errors associated with somatic cell nuclear transfer (SCNT) is ectopic expression of Xist during the preimplantation period in both sexes. We found that this aberrant Xist expression could be impeded by deletion of Xist from the putative active X chromosome in donor cells. In male clones, it was also found that prior injection of Xist-specific siRNA could significantly improve the postimplantation development of cloned embryos as a result of a significant repression of Xist at the morula stage. In this study, we examined whether the same knockdown strategy could work as well in female SCNT-derived embryos. Embryos were reconstructed with cumulus cell nuclei and injected with Xist-specific siRNA at 6–7 h after oocyte activation. RNA FISH analysis revealed that siRNA treatment successfully repressed Xist RNA at the morula stage, as shown by the significant decrease in the number of cloud-type Xist signals in the blastomere nuclei. However, blastomeres with different sizes (from “pinpoint” to “cloud”) and numbers of Xist RNA signals remained within single embryos. After implantation, the dysregulated Xist expression was normalized autonomously, as in male clones, to a state of monoallelic expression in both embryonic and extraembryonic tissues. However, at term there was no significant improvement in the survival of the siRNA-injected cloned embryos. Thus, siRNA injection was largely effective in repressing the Xist overexpression in female cloned embryos but failed to rescue them, probably because of an inability to mimic consistent monoallelic Xist expression in these embryos. This could only be achieved in female embryos by applying a gene knockout strategy rather than an siRNA approach.

Fetal exposure to diesel exhaust affects X-chromosome inactivation factor expression in mice

Several studies have shown effects of diesel exhaust (DE) on the central nervous system, but the mechanism is unclear. Fetal mice were exposed to whole DE (contains gases and particles) in an inhalation chamber, and cerebrum gene expression changes were examined by gene assay (microarray and quantitative real-time PCR). By microarray, upregulation of Xist, B-raf and Drwms2 were detected. Especially, mRNA expression of Xist was increased in a concentration-dependent manner in male and female mice. Xist (X-inactive specific transcript) is a major effector of the X-inactivation process, and X-linked genes are highly expressed in brain tissue and consistent with a role in brain developments. By quantitative real-time PCR, Tsix (crucial noncoding antisense partner of Xist) and other X-linked genes (Mecp2, Hprt1, and Sts) were examined; Tsix was upregulated, and other X-linked genes were unaffected in the male and female mice. Our findings suggest that exposure to DE increases Xist and Tsix gene expression in utero without influencing X-linked gene expression. An examination of Xist gene expression changes may provide an important biomarker for DE-induced effects. The possibility of avoiding X-chromosome inactivation (XCI) mechanisms by minimizing exposure to DE is expected.

Human Decidua-Derived Mesenchymal Cells Are a Promising Source for the Generation and Cell Banking of Human Induced Pluripotent Stem Cells.

Placental tissue is a biomaterial with remarkable potential for use in regenerative medicine. It has a three-layer structure derived from the fetus (amnion and chorion) and the mother (decidua), and it contains huge numbers of cells. Moreover, placental tissue can be collected without any physical danger to the donor and can be matched with a variety of HLA types. The decidua-derived mesenchymal cells (DMCs) are highly proliferative fibroblast-like cells that express a similar pattern of CD antigens as bone marrow-derived mesenchymal cells (BM-MSCs). Here we demonstrated that induced pluripotent stem (iPS) cells could be efficiently generated from DMCs by retroviral transfer of reprogramming factor genes. DMC-hiPS cells showed equivalent characteristics to human embryonic stem cells (hESCs) in colony morphology, global gene expression profile (including human pluripotent stem cell markers), DNA methylation status of the OCT3/4 and NANOG promoters, and ability to differentiate into components of the three germ layers in vitro and in vivo. The RNA expression of XIST and the methylation status of its promoter region suggested that DMC-iPSCs, when maintained undifferentiated and pluripotent, had three distinct states: (1) complete X-chromosome reactivation, (2) one inactive X-chromosome, or (3) an epigenetic aberration. Because DMCs are derived from the maternal portion of the placenta, they can be collected with the full consent of the adult donor and have considerable ethical advantages for cell banking and the subsequent generation of human iPS cells for regenerative applications.

Sex-dependent insulin like growth factor-1 expression in preattachment equine embryos

An adjustment of sex ratio of offspring to the conditions present at conception is seen in many mammals including horses. This depends on preferential survival of male embryos under conditions of high energy intake. In several species, growth factors including insulin like growth factor (IGF)-1 have been shown to promote embryonic development by decreasing apoptosis and increasing cell proliferation. We hypothesized that sex-related differences in IGF-1 expression in equine embryos during the phase of maternal recognition of pregnancy might exist and thus contribute to preferential survival of embryos from either of both sexes under specific environmental conditions. Insulin like growth factor-1 mRNA expression of in vivo-produced equine embryos on different days of pregnancy (Day 8, N = 6; Day 10, N = 8; Day 12, N = 14) was analyzed. Insulin like growth factor-1 mRNA expression was evaluated by reverse transcription quantitative polymerase chain reaction. The sex of the embryo was determined by detection of X-inactivation specific transcript (Xist) RNA and equine sex determining region of the Y chromosome DNA. Embryos positive for Xist expression were classified as female, and Xist negative and equine sex determining region of the Y chromosome positive embryos were classified as male. From 28 embryos tested, 15 (54%) showed positive Xist expression and were thus classified as female. Insulin like growth factor-1 mRNA expression was influenced by sex (P = 0.01) but not by day of pregnancy (relative expression of IGF-1 in relation to β-actin, Day 8: male 5.1 ± 2.1, female 11.4; Day 10: male 5.2 ± 1.6, female 17.4 ± 6.7; Day 12: male 2.6 ± 0.3, female 11.6 ± 2.4). Results demonstrate an increased expression of IGF-1 in female equine embryos. Sex-related influences on expression of the IGF system are probably related to a gradual X chromosome inactivation.

HDAC inhibition decreases XIST expression on female IVP bovine blastocysts

During initial development, both X chromosomes are active in females, and one of them must be silenced at the appropriate time in order to dosage compensate their gene expression levels to male counterparts. Silencing involves epigenetic mechanisms, including histone deacetylation. Major X chromosome inactivation (XCI) in bovine occurs between hatching and implantation, although in vitro culture conditions might disrupt the silencing process, increasing or decreasing X-linked gene expression. In this study, we aimed to address the roles of histone deacetylase inhibition by trichostatin A (TSA) on female preimplantation development. We tested the hypothesis that by enhancing histone acetylation, TSA would increase the percentage of embryos achieving 16-cell stage, reducing percentage of embryos blocked at 8-cell stage, and interfere with XCI in IVF embryos. We noticed that after TSA treatment, acetylation levels in individual blastomeres of 8-16 cell embryos were increased twofold on treated embryos, and the same was detected for blastocysts. Changes among blastomere levels within the same embryo were diminished on TSA group, as low-acetylated blastomeres were no longer detected. The percentage of embryos that reached the 5th cleavage cycle 118 h after IVF, analyzed by Hoechst staining, remained unaltered after TSA treatment. Then, we assessed XIST and G6PD expression in individual female bovine blastocysts by quantitative real-time PCR. Even though G6PD expression remained unaltered after TSA exposure, XIST expression was eightfold decreased, and we also detected a major decrease in the percentage of blastocysts expressing detectable XIST levels after TSA treatment. Based on these results, we conclude that HDAC is involved on XCI process in bovine embryos, and its inhibition might delay X chromosome silencing and attenuate aberrant XIST expression described for IVF embryos.

Evaluation of Xist expression in preattachment equine embryos

Until now, sex determination in equine embryos has been performed by detection of Y-chromosome-specific sequences only. In the present study, expression of a Barr-body-specific marker, the X-inactivated-specific transcript (Xist) gene, whose gene product consists of RNA which coats and thereby inactivates one of the X chromosomes, was investigated in equine embryos produced in vivo. Preattachment embryos at different times after ovulation (Day 8: n = 9; Day 10: n = 12; Day 12: n = 15) were analyzed for Xist RNA expression using quantitative and qualitative reverse transcription-polymerase chain reaction (RT-PCR). Female and male primary equine dermal cell cultures were used as positive and negative controls, respectively. Embryos tested negative for Xist were evaluated for expression of the male-specific eSRY gene by qualitative PCR at the DNA level. From 36 embryos assessed by qualitative RT-PCR, 18 showed positive Xist expression (50%). From 29 embryos tested by quantitative RT-PCR, 16 showed positive Xist expression (55%). All of the Xist-negative equine embryos tested by quantitative PCR were positive for eSRY. We also demonstrated by strand-specific RT-PCR that in the horse, as in humans, the counter transcript Tsix seems to be truncated not reaching Exon 1. In contrast to many other species, neither Xist nor Tsix was expressed in equine male testicular tissue. The results demonstrate that expression of Xist is restricted to female equine embryos. Xist can thus be considered an X-inactivation-specific marker which can be used in concert with Y-specific markers for sex determination.

Molecular Signatures of Human Induced Pluripotent Stem Cells Highlight Sex Differences and Cancer Genes

Although human induced pluripotent stem cells (hiPSCs) have enormous potential in regenerative medicine, their epigenetic variability suggests that some lines may not be suitable for human therapy. There are currently few benchmarks for assessing quality. Here we show that X-inactivation markers can be used to separate hiPSC lines into distinct epigenetic classes and that the classes are phenotypically distinct. Loss of XIST expression is strongly correlated with upregulation of X-linked oncogenes, accelerated growth rate invitro, and poorer differentiation invivo. Whereas differences in X-inactivation potential result in epigenetic variability of female hiPSC lines, male hiPSC lines generally resemble each other and do not overexpress the oncogenes. Neither physiological oxygen levels nor HDAC inhibitors offer advantages to culturing female hiPSC lines. We conclude that female hiPSCs may be epigenetically less stable in culture and caution that loss ofXIST may result in qualitatively less desirable stem cell lines.

Evidence for production of early pregnancy factor (Hsp10), microRNAs and exosomes by day 8 equine embryos

would be very suitable for life cell fluorescence. This technique could also be used to detect aberrant ratios of sex chromosomes. In the present study, Xist RNA expression of in vivo produced equine embryos at different times of pregnancy (day8: n1⁄4 9); day10: n1⁄4 12; day 12: n1⁄4 15)was analysed. Xist RNAexpressionwas evaluatedbyquantitative and qualitative RT-PCR. Female and male primary equine skin tissue cultures were used as positive and negative controls, respectively. Embryos testednegative for Xistwere evaluated for expression of the male specific eSRY gene by qualitative PCR at the DNA level. From 36 embryos assessed by qualitative RT-PCR, 19 showed positive Xist expression (52.7% female). From 29 embryos tested by quantitative RTPCR, 16 showed positive Xist expression (55.2% female). All of the Xist negative equine blastocysts were positive for eSRY signals by qualitative PCR. The results demonstrate that expression of Xist is restricted to female equine embryos. Xist can thus be considered a female specific marker. Further research may allow applying this method for gender detection in equine embryos before transfer.