Oct-4 mRNA and protein expression during human preimplantation development

Docosahexaenoic acid supplementation during porcine oocyte in vitro maturation improves oocyte quality and embryonic development by enhancing the homeostasis of energy metabolism

Although supplementation with docosahexaenoic acid (DHA) during porcine oocyte IVM is well-established, the available data are limited due to the lack of consistency. Moreover, to our knowledge, the anti-oxidant effects of DHA on porcine oocytes have not been reported. Hence, this study aimed to examine the effects of DHA supplementation on the regulation of energy metabolism during porcine oocyte maturation to improve oocyte maturation and embryonic development. By supplementing the IVM medium with various DHA concentrations, 25 μM DHA was identified as the optimal concentration which improved intraoocyte glutathione content and enhanced embryonic development after parthenogenesis. Compared to embryos derived from the control group, those derived from SCNT or IVF showed significantly improved blastocyst formation upon DHA supplementation during IVM. In addition, various transcription factors associated with oocyte development and apoptosis in mature oocytes were beneficially regulated in the DHA-treated oocytes. Moreover, DHA improved the AMP-activated protein kinase (AMPK)-regulatory ability of porcine oocytes and ameliorated nuclear maturation and embryonic development, which were decreased by artificially downregulating AMPK. To our knowledge, this is the first study to examine the effects of DHA as an AMPK regulator on oocyte maturation and embryo development in pigs. Furthermore, DHA addition to the IVM medium upregulated the relative expression of genes associated with mitochondrial potential and lipid metabolism. Therefore, the membrane potential of mitochondria (evaluated based on the JC-1 aggregate/JC-1 monomer ratio) and the levels of fatty acids and lipid droplets in matured oocytes increased, resulting in increased ATP synthesis. In conclusion, the DHA treatment of porcine oocytes with 25 μM DHA during IVM enhances the homeostasis of energy metabolism by improving mitochondrial function and lipid metabolism, leading to improved quality of matured oocytes and enhanced embryonic developmental potential of in vitro produced (IVP) embryos. Thus, 25 μM DHA supplementation could serve as a tool for improving the quality of IVP embryos. The study findings provide a basis for further research on improving the production efficiency of cloned animals by securing high-quality matured oocytes and enhancing energy metabolism in mammalian oocytes, including those of pigs.

Piperine improves the quality of porcine oocytes by reducing oxidative stress

Oxidative stress caused by light and high temperature arises during in vitro maturation (IVM), resulting in low-quality embryos compared with those obtained in vivo. To overcome this problem, we investigated the influence of piperine (PIP) treatment during maturation of porcine oocytes on subsequent embryo development in vitro. Porcine oocytes were cultured in IVM medium supplemented with 0, 50, 100, 200, or 400 μM PIP. After parthenogenetic activation, the blastocyst (BL) formation was significantly higher and the apoptosis rate was significantly lower using 200 μM PIP-treated oocytes (200 PIP). In the 200 PIP group, the level of reactive oxygen species at the metaphase II stage was decreased, accompanied by an increased level of glutathione and increased expression of antioxidant processes (Nrf2, CAT, HO-1, SOD1, and SOD2). Consistently, chromosome misalignment and aberrant spindle organization were alleviated and phosphorylated p44/42 mitogen-activated protein kinase activity was increased in the 200 PIP group. Expression of development-related (CDX2, NANOG, POU5F1, and SOX2), anti-apoptotic (BCL2L1 and BIRC5), and pro-apoptotic (BAK, FAS, and CASP3) processes was altered in the 200 PIP group. Ultimately, embryo development was improved in the 200 PIP group following somatic cell nuclear transfer. These findings suggest that PIP improves the quality of porcine oocytes by reducing oxidative stress, which inevitably arises via IVM. In-depth mechanistic studies of porcine oocytes will improve the efficiencies of assisted reproductive technologies.

Ellagic acid treatment during in vitro maturation of porcine oocytes improves development competence after parthenogenetic activation and somatic cell nuclear transfer

Ellagic acid (EA) is a natural polyphenol and a free radical scavenger with antioxidant properties. This study investigated the protective effects of EA during in vitro maturation (IVM) of porcine oocytes. To determine the optimal concentration, IVM medium was supplemented with various concentrations of EA. Treatment with 10 μM EA (10 EA) resulted in the highest cleavage rate, blastocyst formation rate, and total cell number per blastocyst and the lowest percentage of apoptotic cell in parthenogenetic blastocysts. In the 10 EA group, abnormal spindle and chromosome misalignment were rescued and the ratio of phosphorylated p44/42 to total p44/42 was increased. Furthermore, the reactive oxygen species and glutathione levels were significantly decreased and increased, respectively, and antioxidant genes (Nrf2, HO-1, CAT, and SOD1) were significantly upregulated in the 10 EA group. mRNA expression of developmental-related (CDX2, POU5F1, and SOX2) and anti-apoptotic (BCL2L1) genes was significantly upregulated in the 10 EA group, while mRNA expression of pro-apoptotic genes (BAK, FAS, and CASP3) was significantly downregulated. Ultimately, following somatic cell nuclear transfer, the blastocyst formation rate was significantly increased and the percentage of apoptotic cell in blastocysts was significantly decreased in the 10 EA group. In conclusion, addition of 10 EA to IVM medium improved oocyte maturation and the subsequent embryo development capacity through antioxidant mechanisms. These findings suggest that EA can enhance the efficiencies of assisted reproductive technologies.

Histone remodeling reflects conserved mechanisms of bovine and human preimplantation development

How histone modifications regulate changes in gene expression during preimplantation development in any species remains poorly understood. Using CUT&Tag to overcome limiting amounts of biological material, we profiled two activating (H3K4me3 and H3K27ac) and two repressive (H3K9me3 and H3K27me3) marks in bovine oocytes, 2-, 4-, and 8-cell embryos, morula, blastocysts, inner cell mass, and trophectoderm. In oocytes, broad bivalent domains mark developmental genes, and prior to embryonic genome activation (EGA), H3K9me3 and H3K27me3 co-occupy gene bodies, suggesting a global mechanism for transcription repression. During EGA, chromatin accessibility is established before canonical H3K4me3 and H3K27ac signatures. Embryonic transcription is required for this remodeling, indicating that maternally provided products alone are insufficient for reprogramming. Last, H3K27me3 plays a major role in restriction of cellular potency, as blastocyst lineages are defined by differential polycomb repression and transcription factor activity. Notably, inferred regulators of EGA and blastocyst formation strongly resemble those described in humans, as opposed to mice. These similarities suggest that cattle are a better model than rodents to investigate the molecular basis of human preimplantation development.

NBMA Promotes Spermatogenesis by Mediating Oct4 Pathway

Non-obstructive azoospermia is one of the most common causes of male infertility, but there is still no specific treatment drug. Given that the Oct4 (Octamer-binding transcription factor 4) has an important regulatory effect on spermatogenesis, activating it can effectively promote spermatogenesis, so it is of great value to develop Oct4-targeted drug design and elucidating its mechanism of action. Here, we screened out the Oct4-targeted drug molecule NBMA (N-benzyl-4-methoxy-2-(1-(4-(trifluoromethyl)phenyl)vinyl)aniline) by computer-assisted technology, and found that it has a significant promoting effect on spermatogenesis in the established mouse azoospermia model. Subsequently, through transcriptome sequencing and enrichment analysis, real-time fluorescent quantitative PCR (qPCR) and western blot experiments revealed that NBMA promotes the differentiation of spermatogonial stem cells by activating the Oct4 pathway, thereby promoting spermatogenesis. This study proves that NBMA is a molecule with great potential to be developed as a therapeutic drug for azoospermia. It also shows that computer-assisted, chemical and biological multidisciplinary methods play a very important role in innovative drug discovery.

Expression of the cancer stem cell marker OCT4 is associated with worse prognosis and survival in cutaneous melanoma

Cutaneous melanoma has an aggressive clinical presentation, showing rapid rate of growth and metastatic dissemination due to the permanence of cancer stem cells. The present study was to evaluate the expression of the self-renewal regulatory factor and the clinical significance of the transcription factor OCT4 in melanoma. Melanoma tissues were stained by immunohistochemistry and the correlation between the expression of this marker was determined through clinical-pathological variables and survival outcomes. Positive expression of nuclear and cytoplasmic OCT4 was observed in 49% and 41.2% of cases, respectively. The positive expression of nuclear OCT4 in melanoma was significantly associated with prognostic factors, such as Breslow depth, Clark's level, ulceration and metastasis. Survival of patients was 56% compared to positive nuclear OCT4 expression and 94.2% when compared to the low expression of the gene. Nuclear OCT4 positive genotype indicated aggressive tumor behavior with a worse clinical outcome, which indicates OCT4 as a useful biomarker in the prognosis of melanoma.

The safety of VASApos presumptive adult ovarian stem cells

Isolation and characterization of presumptive human adult ovarian stem cells (OSC) has broken the long standing dogma of the absence of postnatal neo-oogenesis. Human adult OSC have been immunosorted by antibodies reacting against the RNA helicase VASA and have been reported to engraft into appropriate stem cell niches to promote neo-oogenesis. Analysis of published research, however, questions some of the findings on isolation, characterization, in-vitro self-renewal and clinical safety of the presumptive human adult OSC. In the present study, human VASA^pos embryo-fetal primordial germ cells and presumptive adult OSC are shown to share several pluripotency and early germ cell markers not ascertained in the initial characterization of adult OSC. A new hypothesis is made that the restoration of fertility claimed to result from presumptive human adult OSC may be attributed instead to VASA^pos embryo-fetal primordial germ cell remnants in the adult ovary, or alternatively to earlier VASA^neg germ cells generated by in-vitro de-differentiation of the presumptive OSC. The suggested hypotheses have extensive implications for the practice and safety of adult OSC in the development of new treatments aimed at rescuing the ovarian reserve.

Lineage Differentiation Markers as a Proxy for Embryo Viability in Farm Ungulates

Embryonic losses constitute a major burden for reproductive efficiency of farm animals. Pregnancy losses in ungulate species, which include cattle, pigs, sheep and goats, majorly occur during the second week of gestation, when the embryo experiences a series of cell differentiation, proliferation, and migration processes encompassed under the term conceptus elongation. Conceptus elongation takes place following blastocyst hatching and involves a massive proliferation of the extraembryonic membranes trophoblast and hypoblast, and the formation of flat embryonic disc derived from the epiblast, which ultimately gastrulates generating the three germ layers. This process occurs prior to implantation and it is exclusive from ungulates, as embryos from other mammalian species such as rodents or humans implant right after hatching. The critical differences in embryo development between ungulates and mice, the most studied mammalian model, have precluded the identification of the genes governing lineage differentiation in livestock species. Furthermore, conceptus elongation has not been recapitulated in vitro, hindering the study of these cellular events. Luckily, recent advances on transcriptomics, genome modification and post-hatching in vitro culture are shedding light into this largely unknown developmental window, uncovering possible molecular markers to determine embryo quality. In this review, we summarize the events occurring during ungulate pre-implantation development, highlighting recent findings which reveal that several dogmas in Developmental Biology established by knock-out murine models do not hold true for other mammals, including humans and farm animals. The developmental failures associated to in vitro produced embryos in farm animals are also discussed together with Developmental Biology tools to assess embryo quality, including molecular markers to assess proper lineage commitment and a post-hatching in vitro culture system able to directly determine developmental potential circumventing the need of experimental animals.

Porcine OCT4 Reporter System Can Monitor Species-Specific Pluripotency During Somatic Cell Reprogramming

This study examined the activity and function of pig OCT4 enhancer in porcine reprogramming cells. Dual fluorescent protein reporter systems controlled by the upstream regulatory region of OCT4, which is one of the master regulators for pluripotency, are widely used in studies of the mechanism of pluripotency. We analyzed how this reporter system functions in fibroblast growth factor (FGF)- or leukemia inhibitory factor (LIF)-dependent reprogrammed porcine pluripotent stem cells using the previously established porcine-specific reporter system. Porcine embryonic fibroblasts were coinfected with the pOCT4-ΔPE-eGFP (distal enhancer [DE]-green fluorescent protein [GFP]) and pOCT4-ΔDE-DsRed2 (proximal enhancer [PE]-red fluorescent protein [RFP]) vectors, and GFP and RFP expression were verified during a DOX-dependent reprogramming process. We demonstrated that the porcine OCT4 DE and PE were activated in different expression patterns simultaneously as changes in the expression of pluripotent marker genes during the establishment of porcine-induced pluripotent stem cells (iPSCs). Porcine OCT4 upstream region-derived dual fluorescent protein reporter systems confirmed that porcine iPSCs are in primed state after reprogramming in FGF2- or LIF-containing media. This work demonstrates the applicability of porcine OCT4 upstream region-derived dual fluorescence reporter system, which may be applied to investigations of species-specific pluripotency in porcine-origin cells. These reporter systems may be useful tools for studies of porcine-specific pluripotency, early embryo development, and embryonic stem cells.

The unknown human trophectoderm: implication for biopsy at the blastocyst stage

Trophectoderm biopsy is increasingly performed for pre-implantation genetic testing of aneuploidies and considered a safe procedure on short-term clinical outcome, without strong assessment of long-term consequences. Poor biological information on human trophectoderm is available due to ethical restrictions. Therefore, most studies have been conducted in vitro (choriocarcinoma cell lines, embryonic and pluripotent stem cells) and on murine models that nevertheless poorly reflect the human counterpart. Polarization, compaction, and blastomere differentiation (e.g., the basis to ascertain trophectoderm origin) are poorly known in humans. In addition, the trophectoderm function is poorly known from a biological point of view, although a panoply of questionable and controversial microarray studies suggest that important genes overexpressed in trophectoderm are involved in pluripotency, metabolism, cell cycle, endocrine function, and implantation. The intercellular communication system between the trophectoderm cells and the inner cell mass, modulated by cell junctions and filopodia in the murine model, is obscure in humans. For the purpose of this paper, data mainly on primary cells from human and murine embryos has been reviewed. This review suggests that the trophectoderm origin and functions have been insufficiently ascertained in humans so far. Therefore, trophectoderm biopsy should be considered an experimental procedure to be undertaken only under approved rigorous experimental protocols in academic contexts.

Cancer Stem Cell Subpopulations Are Present Within Metastatic Head and Neck Cutaneous Squamous Cell Carcinoma

Cancer stem cells (CSCs) have been identified in many cancer types including primary head and neck cutaneous squamous cell carcinoma (HNcSCC). This study aimed to identify and characterize CSCs in metastatic HNcSCC (mHNcSCC). Immunohistochemical staining performed on mHNcSCC samples from 15 patients demonstrated expression of the induced pluripotent stem cell (iPSC) markers OCT4, SOX2, NANOG, KLF4, and c-MYC in all 15 samples. In situ hybridization and RT-qPCR performed on four of these mHNcSCC tissue samples confirmed transcript expression of all five iPSC markers. Immunofluorescence staining performed on three of these mHNcSCC samples demonstrated expression of c-MYC on cells within the tumor nests (TNs) and the peri-tumoral stroma (PTS) that also expressed KLF4. OCT4 was expressed on the SOX2+/NANOG+/KLF4+ cells within the TNs, and the SOX2+/NANOG+/KLF4+ cells within the PTS. RT-qPCR demonstrated transcript expression of all five iPSC markers in all three mHNcSCC-derived primary cell lines, except for SOX2 in one cell line. Western blotting showed the presence of SOX2, KLF4, and c-MYC but not OCT4 and NANOG in the three mHNcSCC-derived primary cell lines. All three cell lines formed tumorspheres, at the first passage. We demonstrated an OCT4+/NANOG+/SOX2+/KLF4+/c-MYC+ CSC subpopulation and an OCT4+/NANOG-/SOX2+/KLF4+/c-MYC+ subpopulation within the TNs, and an OCT4+/NANOG+/SOX2+/KLF4+/c-MYC+ subpopulation within the PTS of mHNcSCC.

Effects of cobalamin on meiotic resumption and developmental competence of growing porcine oocytes

This study was performed to explore the effects of cobalamin treatment during in vitro maturation (IVM) of porcine oocytes. Specifically, the effects of cobalamin exposure on nuclear and cytoplasmic maturation of oocytes, diameter, glutathione (GSH) and reactive oxygen species (ROS) levels of matured oocytes, as well as development and gene expression of porcine parthenogenetic and cloned embryos were assessed. Cumulus-oocyte complexes were exposed to 200 pM cobalamin for 22 h or incubated for 22 h without cobalamin (controls). The mean diameter of cobalamin-treated oocytes was greater than that of control oocytes (160.0 vs. 154.5 μm; p < 0.05). GSH level increased but ROS level decreased in the cobalamin-treated oocyte group. Parthenogenetic embryos derived from cobalamin-treated oocytes showed improved oocyte maturation (91.3% vs. 83.8%), cleavage (88.9% vs. 82.1%), and blastocyst formation (38.7% vs. 31.9%) rates compared with control embryos (p < 0.05). Similarly, cloned embryos derived from cobalamin-treated oocytes showed higher oocyte maturation (89.2% vs. 82.2%), cleavage (87.5% vs. 80.3%), and blastocyst formation (30.0% vs. 23.8%) rates than control embryos (p < 0.05). Furthermore, in parthenogenetic and cloned embryos, total cell number, inner cell mass (ICM), trophectoderm (TE) expression, and ICM: TE ratio were higher in the cobalamin-treated group compared to that in the control group (p < 0.05). Cloned embryos in the cobalamin-treated group showed higher mRNA expression levels of POU5F1, DPPA2, and NDP52IL than control group embryos. Together, these results demonstrate that cobalamin treatment during IVM improves the developmental competence of porcine oocytes by neutralizing the free radicals produced in the IVM medium.

Role of Oct3/4 in Cervical Cancer Tumorigenesis

Cervical cancer (CC) is the fourth most common type of cancer that affects women. Compared to other types of cancer, CC has a high mortality rate in women worldwide. Several factors contribute to the development of CC, but persistent high-risk human papillomavirus infection is the main etiologic agent associated with the development of CC. Moreover, several studies reported that alterations in the expression of transcription factors present in a small subpopulation of cells within tumors called cancer stem cells (CSCs), which contribute to the development of CC by promoting tumorigenicity and metastasis. These transcription factors affect self-renewal and maintenance of pluripotency and differentiation in stem cells. OCT3/4 belongs to the family of transcription factors with the POU domain. It consists of five exons and can be edited by alternative splicing into three main transcripts: OCT3/4A, OCT3/4B, and OCT3/4B1. The OCT3/4 expression in CSCs promotes carcinogenesis and the development of malignant tumors, and the loss of expression leads to the loss of self-renewal and proliferation and favors apoptosis. This review describes the main roles of OCT3/4 in CC and its importance in several biological processes that contribute to the development of CC and may serve as molecular targets to improve prognosis of CC.

Regulation of Cell Fate Decisions in Early Mammalian Embryos

Early embryogenesis is characterized by the segregation of cell lineages that fulfill critical roles in the establishment of pregnancy and development of the fetus. The formation of the blastocyst marks the emergence of extraembryonic precursors, needed for implantation, and of pluripotent cells, which differentiate toward the major lineages of the adult organism. The coordinated emergence of these cell types shows that these processes are broadly conserved in mammals. However, developmental heterochrony and changes in gene regulatory networks highlight unique evolutionary adaptations that may explain the diversity in placentation and in the mechanisms controlling pluripotency in mammals. The incorporation of new technologies, including single-cell omics, imaging, and gene editing, is instrumental for comparative embryology. Broadening the knowledge of mammalian embryology will provide new insights into the mechanisms driving evolution and development. This knowledge can be readily translated into biomedical and biotechnological applications in humans and livestock, respectively.

Quality of vitrified porcine immature oocytes is improved by coculture with fresh oocytes during in vitro maturation

It is essential to enhance the in vitro maturation (IVM) condition for immature oocytes after cryopreservation, particularly if limited numbers of oocytes collected from specific donors. The objective of this study was to determine if quality of vitrified porcine immature oocytes was enhanced by coculturing with fresh oocytes during IVM. To distinguish fresh versus vitrified oocytes, we used two types of coculture systems: (a) transwell two-chamber coculture; (b) labeling and tracing fresh oocytes with CellTracker™ Green CMFDA during conventional culture. Coculture systems significantly accelerated meiotic progression of vitrified oocytes and significantly increased blastocyst formation rates following parthenogenetic activation and somatic cell nuclear transfer. Reactive oxygen species generation in vitrified oocytes was ameliorated by the coculture conditions, with no significant difference between fresh and vitrified oocytes for intracellular glutathione level. Both coculture systems significantly increased rate of normal mitochondrial distribution in vitrified oocytes, but did not affect fluorescence intensity of mitochondria. The percentage of oocytes with normal endoplasmic reticulum (ER) distribution and ER fluorescence intensity were significantly higher in vitrified oocytes cocultured with fresh oocytes. After 20 hr of IVM, mRNA expression of COX2, HAS2, PTX3, and TNFAIP6 remained significantly higher in cumulus cells derived from vitrified oocytes and coculture systems significantly decreased the expression of these genes. Additionally, coculture methods prevented the reduction of mRNA expression for BMP15, ZAR1, POU5F1, and DNMT3A in vitrified oocytes. In conclusion, oocyte quality and subsequent embryo development of vitrified porcine immature oocytes were significantly improved by fresh oocyte coculture during IVM.

GDF8 enhances SOX2 expression and blastocyst total cell number in porcine IVF embryo development

Growth differentiation factor 8 (GDF8) is a member of the transforming growth factor-β family and a physiological regulator. According to recent studies, GDF8 can be detected in follicular fluid and the uterus, suggesting that GDF8 may affect preimplantation embryonic development and act in a paracrine manner to improve the success of late-blastocyst implantation in vivo. We investigated the effect of GDF8 supplementation during in vitro culture (IVC) of porcine embryos derived from in vitro fertilization (IVF) and parthenogenetic activation (PA) on cleavage, blastocyst formation rate, and total cell number and analysed gene transcription levels and cell linage specification in the resulting blastocysts. First, the concentration of GDF8 in porcine oviductal fluid was determined to be 139.8 pg/mL. Then, 0, 0.2, 2, or 20 ng/mL GDF8 was added to embryos throughout the entire IVC period. Our results showed that supplementation with GDF8 during porcine preimplantation embryo IVC enhanced blastocyst formation and total cell number and altered the transcriptional patterns of genes that regulate pluripotency and cavitation. Furthermore, using differential immunostaining, we demonstrated that supplementation with GDF8 enhanced the expression of the genuine inner cell mass (ICM) marker SOX2 and the ICM/trophectoderm ratio, improving IVF blastocyst quality. In conclusion, for the first time, we demonstrated the presence of the in vivo oviductal factor GDF8 in oviductal fluid. Furthermore, we found that GDF8 supplementation at 0.2 ng/mL increased the blastocyst total cell number and ICM/trophectoderm ratio by inducing the transcription of genes involved in developmental competence and the expression of genuine ICM marker SOX2 during porcine IVF embryo development in vitro.

Comparative aspects of early lineage specification events in mammalian embryos - insights from reverse genetics studies

Within the mammalian class, formation of the blastocyst is morphologically highly conserved among different species. The molecular and cellular events during preimplantation embryo development have been studied extensively in the mouse as model organism, because multiple genetically defined strains and a plethora of reverse genetics tools are available to dissect specific gene functions and regulatory networks. However, major differences in preimplantation developmental kinetics, implantation, and placentation exist among mammalians, and recent studies in species other than mouse showed, that even regulatory mechanisms of the first lineage differentiation events and maintenance of pluripotency are not always conserved. Here, we focus on the first and the second lineage segregation in mouse and bovine embryos, when the first differentiated cell types emerge. We outline their common features and differences in the regulation of these essential events during embryonic development with a glance at further species. In addition, we show how new reverse genetics strategies aid the study of regulatory circuits in embryos of domestic species, enhancing our overall understanding of mammalian preimplantation development.

OCT4/POU5F1 is required for NANOG expression in bovine blastocysts

Mammalian preimplantation development involves two lineage specifications: first, the CDX2-expressing trophectoderm (TE) and a pluripotent inner cell mass (ICM) are separated during blastocyst formation. Second, the pluripotent epiblast (EPI; expressing NANOG) and the differentiated primitive endoderm (PrE; expressing GATA6) diverge within the ICM. Studies in mice revealed that OCT4/POU5F1 is at the center of a pluripotency regulatory network. To study the role of OCT4 in bovine preimplantation development, we generated OCT4 knockout (KO) fibroblasts by CRISPR-Cas9 and produced embryos by somatic cell nuclear transfer (SCNT). SCNT embryos from nontransfected fibroblasts and embryos produced by in vitro fertilization served as controls. In OCT4 KO morulae (day 5), ∼70% of the nuclei were OCT4 positive, indicating that maternal OCT4 mRNA partially maintains OCT4 protein expression during early development. In contrast, OCT4 KO blastocysts (day 7) lacked OCT4 protein entirely. CDX2 was detected only in TE cells; OCT4 is thus not required to suppress CDX2 in the ICM. Control blastocysts showed a typical salt-and-pepper distribution of NANOG- and GATA6-positive cells in the ICM. In contrast, NANOG was absent or very faint in the ICM of OCT4 KO blastocysts, and no cells expressing exclusively NANOG were observed. This mimics findings in OCT4-deficient human blastocysts but is in sharp contrast to Oct4-null mouse blastocysts, where NANOG persists and PrE development fails. Our study supports bovine embryogenesis as a model for early human development and exemplifies a general strategy for studying the roles of specific genes in embryos of domestic species.

Changes in chromosome territory position within the nucleus reflect alternations in gene expression related to embryonic lineage specification

Loss of totipotentcy in an early embryo is directed by molecular processes responsible for cell fate decisions. Three dimensional genome organisation is an important factor linking chromatin architecture with stage specific gene expression patterns. Little is known about the role of chromosome organisation in gene expression regulation of lineage specific factors in mammalian embryos. Using bovine embryos as a model we have described these interactions at key developmental stages. Three bovine chromosomes (BTA) that differ in size, number of carried genes, and contain loci for key lineage regulators OCT4, NANOG and CDX2, were investigated. The results suggest that large chromosomes regardless of their gene density (BTA12 gene-poor, BTA5 gene-rich) do not significantly change their radial position within the nucleus. Gene loci however, may change its position within the chromosome territory (CT) and relocate its periphery, when stage specific process of gene activation is required. Trophectoderm specific CDX2 and epiblast precursor NANOG loci tend to locate on the surface or outside of the CTs, at stages related with their high expression. We postulate that the observed changes in CT shape reflect global alternations in gene expression related to differentiation.

OCT4B1 Regulates the Cellular Stress Response of Human Dental Pulp Cells with Inflammation

Introduction. Infection and apoptosis are combined triggers for inflammation in dental tissues. Octamer-binding transcription factor 4-B1 (OCT4B1), a novel spliced variant of OCT4 family, could respond to the cellular stress and possess antiapoptotic property. However, its specific role in dental pulpitis remains unknown. Methods. To investigate the effect of OCT4B1 on inflammation of dental pulp cells (DPCs), its expression in inflamed dental pulp tissues and DPCs was examined by in situ hybridization, real-time PCR, and FISH assay. OCT4B1 overexpressed DPCs model was established, confirmed by western blot and immunofluorescence staining, and then stimulated with Lipopolysaccharide (LPS). Apoptotic rate was determined by Hoechst/PI staining and FACS. Cell survival rate was calculated by CCK8 assay. Results. In situ hybridization, real-time PCR, and FISH assay revealed that OCT4B1 was extensively expressed in inflamed dental pulp tissues and DPCs with LPS stimulation. Western blot and immunofluorescence staining showed the expression of OCT4B1 and OCT4B increased after OCT4B1 transfection. Hoechst/PI staining and FACS demonstrated that less red/blue fluorescence was detected and apoptotic percentage decreased (3.45%) after transfection. CCK8 demonstrated that the survival rate of pCDH-OCT4B1-flag cells increased. Conclusions. OCT4B1 plays an essential role in inflammation and apoptosis of DPCs. OCT4B might operate synergistically with OCT4B1 to reduce apoptosis.

CDX2 is essential for cell proliferation and polarity in porcine blastocysts

The role of CDX2 in trophectoderm (TE) cells has been extensively studied, yet the results are contradictory and species specific. Here, CDX2 expression and function were explored in early porcine embryos. Notably, siRNA-mediated gene knockdown and lentivirus-mediated TE-specific gene regulation demonstrated that CDX2 is essential for the maintenance of blastocyst integrity by regulating the BMP4-mediated blastocyst niche and classic protein kinase C (PKC)-mediated TE polarity in mammalian embryos. Mechanistically, CDX2-depleted porcine embryos stalled at the blastocyst stage and exhibited apoptosis and inactive cell proliferation, possibly resulting from BMP4 downregulation. Moreover, TE cells in CDX2-depleted blastocysts displayed defective F-actin apical organization associated with downregulation of PKCα (PRKCA). Collectively, these results provide further insight into the functional diversity of CDX2 in early mammalian embryos.

Master regulators in development: Views from the Drosophila retinal determination and mammalian pluripotency gene networks

Among the mechanisms that steer cells to their correct fate during development, master regulatory networks are unique in their sufficiency to trigger a developmental program outside of its normal context. In this review we discuss the key features that underlie master regulatory potency during normal and ectopic development, focusing on two examples, the retinal determination gene network (RDGN) that directs eye development in the fruit fly and the pluripotency gene network (PGN) that maintains cell fate competency in the early mammalian embryo. In addition to the hierarchical transcriptional activation, extensive positive transcriptional feedback, and cooperative protein-protein interactions that enable master regulators to override competing cellular programs, recent evidence suggests that network topology must also be dynamic, with extensive rewiring of the interactions and feedback loops required to navigate the correct sequence of developmental transitions to reach a final fate. By synthesizing the in vivo evidence provided by the RDGN with the extensive mechanistic insight gleaned from the PGN, we highlight the unique regulatory capabilities that continual reorganization into new hierarchies confers on master control networks. We suggest that deeper understanding of such dynamics should be a priority, as accurate spatiotemporal remodeling of network topology will undoubtedly be essential for successful stem cell based therapeutic efforts.

Derivation of Induced Trophoblast Cell Lines in Cattle by Doxycycline-Inducible piggyBac Vectors

Trophectoderm lineage specification is one of the earliest differentiation events in mammalian development. The trophoblast lineage, which is derived from the trophectoderm, mediates implantation and placental formation. However, the processes involved in trophoblastic differentiation and placental formation in cattle remain unclear due to interspecies differences when compared with other model systems and the small repertoire of available trophoblast cell lines. Here, we describe the generation of trophoblast cell lines (biTBCs) from bovine amnion-derived cells (bADCs) using an induced pluripotent stem cell technique. bADCs were introduced with piggyBac vectors containing doxycycline (Dox)-inducible transcription factors (Oct3⁄4(POU5F1), Sox2, Klf4, and c-Myc). Colonies that appeared showed a flattened epithelial-like morphology similar to cobblestones, had a more definite cell boundary between cells, and frequently formed balloon-like spheroids similar to trophoblastic vesicles (TVs). biTBCs were propagated for over 60 passages and expressed trophoblast-related (CDX2, ELF5, ERRβ, and IFN-τ) and pluripotency-related genes (endogenous OCT3/4, SOX2, KLF4, and c-MYC). Furthermore, when biTBCs were induced to differentiate by removing Dox from culture, they formed binucleate cells and began to express pregnancy-related genes (PL, PRP1, and PAG1). This is the first report demonstrating that the induction of pluripotency in bovine amniotic cells allows the generation of trophoblastic cell lines that possess trophoblast stem cell-like characteristics and have the potential to differentiate into the extra-embryonic cell lineage. These cell lines can be a new cell source as a model for studying trophoblast cell lineages and implantation processes in cattle.

Construction of a Dual-Fluorescence Reporter System to Monitor the Dynamic Progression of Pluripotent Cell Differentiation

Oct4 is a crucial germ line-specific transcription factor expressed in different pluripotent cells and downregulated in the process of differentiation. There are two conserved enhancers, called the distal enhancer (DE) and proximal enhancer (PE), in the 5' upstream regulatory sequences (URSs) of the mouse Oct4 gene, which were demonstrated to control Oct4 expression independently in embryonic stem cells (ESCs) and epiblast stem cells (EpiSCs). We analyzed the URSs of the pig Oct4 and identified two similar enhancers that were highly consistent with the mouse DE and PE. A dual-fluorescence reporter was later constructed by combining a DE-free-Oct4-promoter-driven EGFP reporter cassette with a PE-free-Oct4-promoter-driven mCherry reporter cassette. Then, it was tested in a mouse ESC-like cell line (F9) and a mouse EpiSC-like cell line (P19) before it is formally used for pig. As a result, a higher red fluorescence was observed in F9 cells, while green fluorescence was primarily detected in P19 cells. This fluorescence expression pattern in the two cell lines was consistent with that in the early naïve pluripotent state and late primed pluripotent state during differentiation of mouse ESCs. Hence, this reporter system will be a convenient tool for screening out ESC-like naïve pluripotent stem cells from other metastable state cells in a heterogenous population.

Studying the expression patterns of OCT4 and SOX2 proteins in regenerating rabbit ear tissue

Epimorphic regeneration in New Zealand rabbit ear is an interesting example of mammalian wound healing in which blastema formation is involved in replacement of injured tissues. It has been suggested that isolated cells from regenerating rabbit ear possess stem-like properties. In this study, we aimed to determine the expression of stemness markers, OCT4 and SOX2 proteins, in regenerating rabbit tissues by immunohistochemistry. Results indicated that both proteins could be detected in epithelial cells, hair follicle cells and perichondrium cells. Expression pattern analysis of OCT4 and SOX2 proteins showed no clear differences between regenerative and non-regenerative control tissues. According to several reports of OCT4 and SOX2 proteins expression in adult stem cells, it could be proposed that OCT4 and SOX2 expressing cells in regenerating rabbit ear tissues are progenitor/adult stem cells which are resident in these tissues, and other markers should be used for detection of blastema cells.

Conservation of spermatogonial stem cell marker expression in undifferentiated felid spermatogonia

Spermatogonial stem cells (SSCs) are distinct in their ability to self-renew, transmit genetic information, and persist throughout the life of an individual. These characteristics make SSCs a useful tool for addressing diverse challenges such as efficient transgenic production in nonrodent, biomedical animal models, or preservation of the male genome for species in which survival of frozen-thawed sperm is low. A requisite first step to access this technology in felids is the establishment of molecular markers. This study was designed to evaluate, in the domestic cat (Felis catus), the expression both in situ and following enrichment in vitro of six genes (GFRA1, GPR125, ZBTB16, POU5F1, THY1, and UCHL1) that had been previously identified as SSC markers in other species. Antibodies for surface markers glial cell line-derived neurotrophic factor family receptor alpha 1, G protein-coupled receptor 125, and thymus cell antigen 1 could not be validated, whereas Western blot analysis of prepubertal, peripubertal, and adult cat testis confirmed protein expression for the intracellular markers ubiquitin carboxy-terminal hydrolase 1, zinc finger and BTB domain-containing protein 16, and POU domain, class 5, transcription factor 1. Colocalization of the markers by immunohistochemistry revealed that several cells within the subpopulation adjacent to the basement membrane of the seminiferous tubules and identified morphologically as spermatogonia, expressed all three intracellular markers. Studies performed on cheetah (Acinonyx jubatus) and Amur leopard (Panthera pardus orientalis) testis exhibited a conserved expression pattern in protein molecular weights, relative abundance, and localization of positive cells within the testis. The expression of the three intracellular SSC marker proteins in domestic and wild cat testes confirms conservation of these markers in felids. Enrichment of marker transcripts after differential plating was also observed. These markers will facilitate further studies in cell enrichment and IVC of felid SSCs enabling both production of transgenic domestic cats and preservation of the male genome from rare and endangered felids.

Cdx2 represses Oct4 function via inducing its proteasome-dependent degradation in early porcine embryos

Reciprocal repression of inner cell mass specific factor OCT4 and trophectoderm specific factor CDX2 promotes mouse first lineage segregation. Studies in mouse embryonic stem (ES) cells revealed that they bind to each other's regulatory regions to reciprocally suppress transcription, additionally they form protein complex for mutual antagonism. However, so far the molecular interaction of Oct4 and Cdx2 in other mammal's early embryo is not yet investigated. Here, over-expression of Cdx2 in early porcine embryo showed CDX2 represses Oct4 through neither the transcriptional repression nor forming repressive complex, but promoting OCT4 nuclear export and proteasomal degradation. The results showed novel molecular regulation of CDX2 on Oct4, and provided important clues for clarifying the mechanism of interaction between CDX2 and Oct4 in embryo of mammals other than mouse.

Antioxidant Capacity of Melatonin on Preimplantation Development of Fresh and Vitrified Rabbit Embryos: Morphological and Molecular Aspects

Embryo cryopreservation remains an important technique to enhance the reconstitution and distribution of animal populations with high genetic merit. One of the major detrimental factors to this technique is the damage caused by oxidative stress. Melatonin is widely known as an antioxidant with multi-faceted ways to counteract the oxidative stress. In this paper, we investigated the role of melatonin in protecting rabbit embryos during preimplantation development from the potential harmful effects of oxidative stress induced by in vitro culture or vitrification. Rabbit embryos at morula stages were cultured for 2 hr with 0 or 10⁻³ M melatonin (C or M groups). Embryos of each group were either transferred to fresh culture media (CF and MF groups) or vitrified/devitrified (CV and MV groups), then cultured in vitro for 48 hr until the blastocyst stage. The culture media were used to measure the activity of antioxidant enzymes: glutathione-s-transferase (GST) and superoxide dismutase (SOD), as well as the levels of two oxidative substrates: lipid peroxidation (LPO) and nitric oxide (NO). The blastocysts from each group were used to measure the expression of developmental-related genes (GJA1, POU5F1 and Nanog) and oxidative-stress-response-related genes (NFE2L2, SOD1 and GPX1). The data showed that melatonin promoted significantly (P<0.05) the blastocyst rate by 17% and 12% in MF and MV groups compared to their controls (CF and CV groups). The GST and SOD activity significantly increased by the treatment of melatonin in fresh or vitrified embryos, while the levels of LPO and NO decreased (P<0.05). Additionally, melatonin considerably stimulated the relative expression of GJA1, NFE2L2 and SOD1 genes in MF and MV embryos compared to CF group. Furthermore, melatonin significantly ameliorated the reduction of POU5F1 and GPX1 expression induced by vitrification. The results obtained from the current investigation provide new and clear molecular aspects regarding the mechanisms by which melatonin promotes development of both fresh and vitrified rabbit embryos.

Lanosterol influences cytoplasmic maturation of pig oocytes in vitro and improves preimplantation development of cloned embryos

Lanosterol is a precursor of meiosis-activating sterols in the cholesterol biosynthetic pathway and induces a physiological signal that instructs the oocyte to reinitiate meiosis. In this study, we examined the effect of lanosterol on IVM of porcine oocytes, specifically on nuclear maturation, cytoplasmic maturation by investigating intracellular glutathione (GSH) levels and lipid content, embryonic development after parthenogenetic activation and somatic cell nuclear transfer (SCNT), and on gene expression in cumulus cells, oocytes, and SCNT-derived blastocysts. There was no significant difference in nuclear maturation rates between the control and treatment groups (10, 50, and 100 μM of lanosterol added to IVM culture medium). Supplementation with 50-μM lanosterol significantly increased lipid content and GSH levels and decreased reactive oxygen species levels compared with the control. In addition, oocytes treated with 50 μM of lanosterol exhibited significantly increased blastocyst formation rates and total cell numbers after parthenogenetic activation (30.3% and 63.9 vs. 21.6% and 36.5, respectively) and SCNT (18.2% and 53.7 vs. 12.6% and 37.5, respectively), when compared with the control group. Cumulus cells treated with 50 μM of lanosterol showed significantly increased 14α-demethylase, Δ14-reductase, and Δ7-reductase mRNA transcript levels. Significantly increased PPARγ, SREBF1, GPX1, and Bcl-2 and decreased Bax transcript levels were observed in mature oocytes treated with 50 μM of lanosterol compared with the control. SCNT blastocysts derived from 50-μM lanosterol-treated oocytes had significantly higher POU5F1, FGFR2, and Bcl-2 transcript levels than control SCNT-derived blastocysts. In conclusion, supplementation with 50 μM of lanosterol during IVM improves preimplantation development of SCNT embryos by elevating lipid content of oocytes, increasing GSH levels, decreasing reactive oxygen species levels, and regulating genes related to the cholesterol biosynthetic pathway in cumulus cells, to lipid metabolism and apoptosis in oocytes, and their developmental potential and apoptosis in blastocysts.

Direct Reprogramming of Human Primordial Germ Cells into Induced Pluripotent Stem Cells: Efficient Generation of Genetically Engineered Germ Cells

Primordial germ cells (PGCs) share many properties with embryonic stem cells (ESCs) and innately express several key pluripotency-controlling factors, including OCT4, NANOG, and LIN28. Therefore, PGCs may provide a simple and efficient model for studying somatic cell reprogramming to induced pluripotent stem cells (iPSCs), especially in determining the regulatory mechanisms that fundamentally define pluripotency. Here, we report a novel model of PGC reprogramming to generate iPSCs via transfection with SOX2 and OCT4 using integrative lentiviral. We also show the feasibility of using nonintegrative approaches for generating iPSC from PGCs using only these two factors. We show that human PGCs express endogenous levels of KLF4 and C-MYC protein at levels similar to embryonic germ cells (EGCs) but lower levels of SOX2 and OCT4. Transfection with both SOX2 and OCT4 together was required to induce PGCs to a pluripotent state at an efficiency of 1.71%, and the further addition of C-MYC increased the efficiency to 2.33%. Immunohistochemical analyses of the SO-derived PGC-iPSCs revealed that these cells were more similar to ESCs than EGCs regarding both colony morphology and molecular characterization. Although leukemia inhibitory factor (LIF) was not required for the generation of PGC-iPSCs like EGCs, the presence of LIF combined with ectopic exposure to C-MYC yielded higher efficiencies. Additionally, the SO-derived PGC-iPSCs exhibited differentiation into representative cell types from all three germ layers in vitro and successfully formed teratomas in vivo. Several lines were generated that were karyotypically stable for up to 24 subcultures. Their derivation efficiency and survival in culture significantly supersedes that of EGCs, demonstrating their utility as a powerful model for studying factors regulating pluripotency in future studies.

Effect of zinc on in vitro development of porcine embryos

This study aimed to investigate the effect of zinc on in vitro development of porcine embryos. We evaluated the effects of zinc on blastocysts formation and investigated gene expression at zinc-deficient and supplemented conditions. Zinc-deficient in vitro condition was induced by 10-μM N,N,N',N'-tetrakis-(2-pyridylmethyl)-ethylendiamine (TPEN) (zinc chelator) treatment during IVC. On parthenogenetic activated embryos, this treatment significantly decreased cleavage rate and blastocyst formation compared with the control (0.0% and 0.0% vs. 69.0% and 36.0%, respectively). And time effect of the zinc deficiency exposure is observed. Blastocyst formation rate was significantly decreased as zinc-deficient time increases (54.1%, 31.0%, 9.0%, and 1.2% for zinc deficiency during 0, 3, 5, and 7 hours). However, zinc supplementation during IVC supported in vitro embryonic development. On parthenogenetic activated embryos, supplementation of 0.8 μg/mL of zinc during IVC significantly increased blastocyst formation compared with other groups (43.9%, 57.8%, 67.1%, 51.4%, and 52.6% for zinc supplementation of 0, 0.4, 0.8, 1.2, and 1.6 μg/mL). In vitro-fertilized (IVF) embryos showed similar results. The blastocyst formation rate was significantly higher in the 0.8 μg/mL of zinc-supplemented group than in the other groups (21.3%, 24.1%, 36.1%, 25.9%, and 25.2% for zinc supplementation of 0, 0.4, 0.8, 1.2, and 1.6 μg/mL). PCNA, POU5F1, and Bcl2 messenger RNA expressions were unregulated in IVF-derived blastocysts in the 0.8 μg/mL of zinc-supplemented group compared with the control. These results suggest that zinc is required for embryonic development, and supplementation with adequate zinc concentrations during IVC improved the viability of porcine embryos, possibly by increasing PCNA, POU5F1, and Bcl2 gene expression of embryos.

Cloning and characterization of rabbit POU5F1, SOX2, KLF4, C-MYC and NANOG pluripotency-associated genes

While the rabbit (Oryctolagus cuniculus) is an important research model for aspects of human development and disease that cannot be studied in rodents, the lack of data on the genetic regulation of rabbit preimplantation development is a limitation. To assist in the understanding of this process, our aim was to isolate and characterize genes necessary for the induction and maintenance of cellular pluripotency. We are the first to report the isolation of complete coding regions of rabbit SOX2, KLF4, C-MYC and NANOG, which encode transcription factors that play crucial regulatory roles during early mammalian embryonic development. We determined the exon-intron boundaries and chromosomal localization of these genes using computational analysis. The sequences of mRNA and translated protein of the newly identified genes and those of POU5F1 were aligned to their mammalian orthologs to determine the degree of evolutionary conservation. Furthermore, the expression of these genes in embryonic and adult cells was studied at the mRNA and protein levels. We found the sequences and the expression pattern of these pluripotency-associated genes to be highly conserved between human and rabbit, indicating that the rabbit would be a valuable model for human preimplantation development. Implementing the newly identified genes either as biomarkers or as reprogramming factors might also pave the way towards the creation of stable pluripotent rabbit cell lines.

The differential expression of OCT4 isoforms in cervical carcinoma

OCT4 is a transcription factor involved in maintaining stem cell phenotype and pluripotential. However, it remains unclear the expression pattern and biological function of OCT4 isoforms in cervical cancer. Here, we reported that both nuclear OCT4A and cytoplasmic OCT4B were overexpressed in CC. OCT4A was responsible for self-renewal of cervical cancer stem–like cells (CCSCs). Furthermore, OCT4B overexpression in SiHa cervical cancer cell line significantly increased cell proliferation and tumorigenesis by inhibiting apoptosis. Moreover, OCT4B enhanced angiogenesis by the upregulation of CD34, VEGF, HIF-1α and IL-6, and promoted tumor cell mobility to the surrounding tissue by the upregulation of MMP2 and MMP9, and the induction of epithelial-mesenchymal transition (EMT). In conclusion, nuclear OCT4A may serve as a marker of CCSCs and the driving force for cervical cancer metastasis and recurrence, while cytoplasmic OCT4B may cooperate with OCT4A to regulate the progression of cervical cancer through inducing angiogenesis and EMT.

Upregulation of pluripotency markers in adipose tissue-derived stem cells by miR-302 and leukemia inhibitory factor

The expression pattern of pluripotency markers in adipose tissue-derived stem cells (ADSCs) is a subject of controversy. Moreover, there is no data about the signaling molecules that regulate these markers in ADSCs. In the present study, we studied the roles of leukemia inhibitory factor (LIF) and miR-302 in this regard. Freshly isolated mouse ADSCs expressed hematopoietic, mesenchymal, and pluripotency markers. One day after plating, ADSCs expressed OCT4 and Sox2 proteins. After three passages, the expression of hematopoietic and pluripotency markers decreased, while the expression of mesenchymal stem cell markers exhibited a striking rise. Both supplementation of culture media with LIF and transfection of the ADSCs with miR-302 family upregulated the expression levels of OCT4, Nanog, and Sox2 mRNAs. These findings showed that mouse adipose tissue contains a population of cells with molecular resemblance to embryonic stem cells, and LIF and miR-302 family positively affect the expression of pluripotency markers.

Derivation of human embryonic stem cells (hESC)

Stem cells are characterized by their absolute or relative lack of specialization their ability for self-renewal, as well as their ability to generate differentiated progeny through cellular lineages with one or more branches. The increased availability of embryonic tissue and greatly improved derivation methods have led to a large increase in the number of hESC lines.

Totipotency: what it is and what it is not

There is surprising confusion surrounding the concept of biological totipotency, both within the scientific community and in society at large. Increasingly, ethical objections to scientific research have both practical and political implications. Ethical controversy surrounding an area of research can have a chilling effect on investors and industry, which in turn slows the development of novel medical therapies. In this context, clarifying precisely what is meant by "totipotency" and how it is experimentally determined will both avoid unnecessary controversy and potentially reduce inappropriate barriers to research. Here, the concept of totipotency is discussed, and the confusions surrounding this term in the scientific and nonscientific literature are considered. A new term, "plenipotent," is proposed to resolve this confusion. The requirement for specific, oocyte-derived cytoplasm as a component of totipotency is outlined. Finally, the implications of twinning for our understanding of totipotency are discussed.

Expression and differentiation between OCT4A and its Pseudogenes in human ESCs and differentiated adult somatic cells

The POU5F1 gene codes for the OCT4 transcription factor, which is one of the key regulators of pluripotency. Its transcription, alternative splicing, and alternative translation leading to the synthesis of the active, nuclear localized OCT4A has been described in detail. Much less, however, is known about actively transcribed OCT4 pseudogenes, several of which display high homology to OCT4A and can be expressed and translated into proteins. Using RT-PCR followed by pseudogene-specific restriction digestion, cloning, and sequencing we discriminate between OCT4A and transcripts for pseudogenes 1, 3 and 4. We show that expression of OCT4 and its pseudogenes follows a developmentally-regulated pattern in differentiating hESCs, indicating a tight regulatory relationship between them. We further demonstrate that differentiated human cells from a variety of tissues express exclusively pseudogenes. Expression of OCT4A can, however be triggered in adult differentiated cells by oxygen and FGF2-dependent mechanisms.