Pot1b -/- tumors activate G-quadruplex-induced DNA damage to promote telomere hyper-elongation.

Malignant cancers must activate telomere maintenance mechanisms to achieve replicative immortality. Mutations in the human Protection of Telomeres 1 (POT1) gene are frequently detected in cancers with abnormally long telomeres, suggesting that the loss of POT1 function disrupts the regulation of telomere length homeostasis to promote telomere elongation. However, our understanding of the mechanisms leading to elongated telomeres remains incomplete. The mouse genome encodes two POT1 proteins, POT1a and POT1b possessing separation of hPOT1 functions. We performed serial transplantation of Pot1b-/- sarcomas to better understand the role of POT1b in regulating telomere length maintenance. While early-generation Pot1b-/- sarcomas initially possessed shortened telomeres, late-generation Pot1b-/- cells display markedly hyper-elongated telomeres that were recognized as damaged DNA by the Replication Protein A (RPA) complex. The RPA-ATR-dependent DNA damage response at telomeres promotes telomerase recruitment to facilitate telomere hyper-elongation. POT1b, but not POT1a, was able to unfold G-quadruplex present in hyper-elongated telomeres to repress the DNA damage response. Our findings demonstrate that the repression of the RPA-ATR DDR is conserved between POT1b and human POT1, suggesting that similar mechanisms may underly the phenotypes observed in human cancers harboring human POT1 mutations.

Distinct functions of POT1 proteins contribute to the regulation of telomerase recruitment to telomeres.

Human shelterin components POT1 and TPP1 form a stable heterodimer that protects telomere ends from ATR-dependent DNA damage responses and regulates telomerase-dependent telomere extension. Mice possess two functionally distinct POT1 proteins. POT1a represses ATR/CHK1 DNA damage responses and the alternative non-homologous end-joining DNA repair pathway while POT1b regulates C-strand resection and recruits the CTC1-STN1-TEN1 (CST) complex to telomeres to mediate C-strand fill-in synthesis. Whether POT1a and POT1b are involved in regulating the length of the telomeric G-strand is unclear. Here we demonstrate that POT1b, independent of its CST function, enhances recruitment of telomerase to telomeres through three amino acids in its TPP1 interacting C-terminus. POT1b thus coordinates the synthesis of both telomeric G- and C-strands. In contrast, POT1a negatively regulates telomere length by inhibiting telomerase recruitment to telomeres. The identification of unique amino acids between POT1a and POT1b helps us understand mechanistically how human POT1 switches between end protective functions and promoting telomerase recruitment.

The Replisome Mediates A-NHEJ Repair of Telomeres Lacking POT1-TPP1 Independently of MRN Function.

Telomeres use shelterin to protect chromosome ends from activating the DNA damage sensor MRE11-RAD50-NBS1 (MRN), repressing ataxia-telangiectasia, mutated (ATM) and ATM and Rad3-related (ATR) dependent DNA damage checkpoint responses. The MRE11 nuclease is thought to be essential for the resection of the 5' C-strand to generate the microhomologies necessary for alternative non-homologous end joining (A-NHEJ) repair. In the present study, we uncover DNA damage signaling and repair pathways engaged by components of the replisome complex to repair dysfunctional telomeres. In cells lacking MRN, single-stranded telomeric overhangs devoid of POT1-TPP1 do not recruit replication protein A (RPA), ATR-interacting protein (ATRIP), and RAD 51. Rather, components of the replisome complex, including Claspin, Proliferating cell nuclear antigen (PCNA), and Downstream neighbor of SON (DONSON), initiate DNA-PKcs-mediated p-CHK1 activation and A-NHEJ repair. In addition, Claspin directly interacts with TRF2 and recruits EXO1 to newly replicated telomeres to promote 5' end resection. Our data indicate that MRN is dispensable for the repair of dysfunctional telomeres lacking POT1-TPP1 and highlight the contributions of the replisome in telomere repair.

WRN helicase is a synthetic lethal target in microsatellite unstable cancers.

Synthetic lethality-an interaction between two genetic events through which the co-occurrence of these two genetic events leads to cell death, but each event alone does not-can be exploited for cancer therapeutics1. DNA repair processes represent attractive synthetic lethal targets, because many cancers exhibit an impairment of a DNA repair pathway, which can lead to dependence on specific repair proteins2. The success of poly(ADP-ribose) polymerase 1 (PARP-1) inhibitors in cancers with deficiencies in homologous recombination highlights the potential of this approach3. Hypothesizing that other DNA repair defects would give rise to synthetic lethal relationships, we queried dependencies in cancers with microsatellite instability (MSI), which results from deficient DNA mismatch repair. Here we analysed data from large-scale silencing screens using CRISPR-Cas9-mediated knockout and RNA interference, and found that the RecQ DNA helicase WRN was selectively essential in MSI models in vitro and in vivo, yet dispensable in models of cancers that are microsatellite stable. Depletion of WRN induced double-stranded DNA breaks and promoted apoptosis and cell cycle arrest selectively in MSI models. MSI cancer models required the helicase activity of WRN, but not its exonuclease activity. These findings show that WRN is a synthetic lethal vulnerability and promising drug target for MSI cancers.

CTC1-STN1 coordinates G- and C-strand synthesis to regulate telomere length.

Coats plus (CP) is a rare autosomal recessive disorder caused by mutations in CTC1, a component of the CST (CTC1, STN1, and TEN1) complex important for telomere length maintenance. The molecular basis of how CP mutations impact upon telomere length remains unclear. The CP CTC1L1142H mutation has been previously shown to disrupt telomere maintenance. In this study, we used CRISPR/Cas9 to engineer this mutation into both alleles of HCT116 and RPE cells to demonstrate that CTC1:STN1 interaction is required to repress telomerase activity. CTC1L1142H interacts poorly with STN1, leading to telomerase-mediated telomere elongation. Impaired interaction between CTC1L1142H :STN1 and DNA Pol-α results in increased telomerase recruitment to telomeres and further telomere elongation, revealing that C:S binding to DNA Pol-α is required to fully repress telomerase activity. CP CTC1 mutants that fail to interact with DNA Pol-α resulted in loss of C-strand maintenance and catastrophic telomere shortening. Our findings place the CST complex as an important regulator of both G-strand extensions by telomerase and C-strand synthesis by DNA Pol-α.

Structural insights into POT1-TPP1 interaction and POT1 C-terminal mutations in human cancer.

Mammalian shelterin proteins POT1 and TPP1 form a stable heterodimer that protects chromosome ends and regulates telomerase-mediated telomere extension. However, how POT1 interacts with TPP1 remains unknown. Here we present the crystal structure of the C-terminal portion of human POT1 (POT1C) complexed with the POT1-binding motif of TPP1. The structure shows that POT1C contains two domains, a third OB fold and a Holliday junction resolvase-like domain. Both domains are essential for binding to TPP1. Notably, unlike the heart-shaped structure of ciliated protozoan Oxytricha nova TEBPα-ß complex, POT1-TPP1 adopts an elongated V-shaped conformation. In addition, we identify several missense mutations in human cancers that disrupt the POT1C-TPP1 interaction, resulting in POT1 instability. POT1C mutants that bind TPP1 localize to telomeres but fail to repress a DNA damage response and inappropriate repair by A-NHEJ. Our results reveal that POT1 C terminus is essential to prevent initiation of genome instability permissive for tumorigenesis.

Correlations between serum levels of 25-hydroxyvitamin D and carotid atherosclerosis in patients with type 2 diabetes in Shanghai.

OBJECTIVE: To explore the potential association between the serum levels of 25-hydroxyvitamin D [25(OH)D] and carotid atherosclerosis in patients with type 2 diabetes. MATERIAL AND METHODS: Three hundred and fifty patients with type 2 diabetes were enrolled in this study in Shanghai, China. B-mode ultrasound was used to detect carotid plaques as indicators of atherosclerosis and measure carotid artery intima-media wall thickness (C-IMT) at two sites of carotid artery. Subjects were divided into group A (patients with carotid plaques) and group B (patients without carotid plaques) and be assessed clinically. Serum levels of 25(OH)D and other clinical parameters were measured. Multivariate logistic regression was performed to find predictors of carotid atherosclerosis in the entire group. RESULTS: The levels of serum 25(OH)D were lower in group A than in group B[19.60 (13.30-25.73) vs 23.19 (18.10-30.06)ng/ml, P<0.001]. The C-IMT levels [(1.00±0.17 vs 0.88±0.20)mm, Ptrend<0.001] and proportion of people with carotid plaques(44/88 vs 20/87, Ptrend<0.001) in the lowest quartile of 25(OH)D were higher than in the highest quartile. Vitamin D concentrations were inversely associated with HbA1c in women(r=-0.194, P=0.006), and C-IMT in men(r=-0.409, P<0.001). Logistic regression analysis showed age, male sex, current smoke, history of hypertension, SBP, LDL-C and lg[25(OH)D] (OR: 0.924, 95%CI: 0.893-0.955, P<0.001) were independently associated with the presence of carotid plaques in T2DM. CONCLUSIONS: Serum vitamin D level is significantly and independently associated with carotid atherosclerosis in patients with T2DM in Shanghai, China.

Serum levels of 25-hydroxyvitamin D are associated with cognitive impairment in type 2 diabetic adults.

Hypovitaminosis D is highly prevalent in type 2 diabetes. The aim of this study is to determine the serum levels of 25-hydroxyvitamin D [25(OH)D] in type 2 diabetic patients with and without mild cognitive impairment (MCI), and examine the relationship of 25(OH)D and MCI with other clinical factors. One hundred and sixty-five diabetic patients were enrolled in this study. Among whom, 95 patients were considered as MCI [Montreal Cognitive Assessment score (MoCA) < 26] and the other 70 as no MCI (MoCA ≥ 26). Subjects were assessed clinically. Diabetic patients with MCI had a longer duration of DM, fewer years of education, elevated fasting blood glucose (FBG), resistant index (RI) of carotid, and lower levels of 25(OH)D {[17.35 (13.02-25.92) vs 28.00 (19.67-34.30)] ng/ml, P < 0.001}. The MoCA score was positively correlated with log10[25(OH)D], education year, and inversely correlated with duration of DM, history of hypertension, intima-media thickness (IMT), FBG, max-RI, and min-RI. Log10[25(OH)D] was positively correlated with MoCA score, and inversely correlated with IMT, in multivariate regression analysis adjusted for age, sex, and education year, 25(OH)D (ß = 0.210, P = 0.003), history of hypertension (ß = -0.191, P = 0.007), IMT (ß = -0.194, P = 0.007), and FBG (ß = -0.157, P = 0.026) independently predicted MoCA score. In conclusion, our results suggest that levels of serum 25(OH)D are inversely associated with the cognitive impairment in diabetic patients. Vitamin D may be a potential protective factor for cognitive impairment in patients with type 2 diabetes.

SLX4 assembles a telomere maintenance toolkit by bridging multiple endonucleases with telomeres.

SLX4 interacts with several endonucleases to resolve structural barriers in DNA metabolism. SLX4 also interacts with telomeric protein TRF2 in human cells. The molecular mechanism of these interactions at telomeres remains unknown. Here, we report the crystal structure of the TRF2-binding motif of SLX4 (SLX4TBM) in complex with the TRFH domain of TRF2 (TRF2TRFH) and map the interactions of SLX4 with endonucleases SLX1, XPF, and MUS81. TRF2 recognizes a unique HxLxP motif on SLX4 via the peptide-binding site in its TRFH domain. Telomeric localization of SLX4 and associated nucleases depend on the SLX4-endonuclease and SLX4-TRF2 interactions and the protein levels of SLX4 and TRF2. SLX4 assembles an endonuclease toolkit that negatively regulates telomere length via SLX1-catalyzed nucleolytic resolution of telomere DNA structures. We propose that the SLX4-TRF2 complex serves as a double-layer scaffold bridging multiple endonucleases with telomeres for recombination-based telomere maintenance.

Functional characterization of human CTC1 mutations reveals novel mechanisms responsible for the pathogenesis of the telomere disease Coats plus.

Coats plus is a rare recessive disorder characterized by intracranial calcifications, hematological abnormalities, and retinal vascular defects. This disease results from mutations in CTC1, a member of the CTC1-STN1-TEN1 (CST) complex critical for telomere replication. Telomeres are specialized DNA/protein structures essential for the maintenance of genome stability. Several patients with Coats plus display critically shortened telomeres, suggesting that telomere dysfunction plays an important role in disease pathogenesis. These patients inherit CTC1 mutations in a compound heterozygous manner, with one allele encoding a frameshift mutant and the other a missense mutant. How these mutations impact upon telomere function is unknown. We report here the first biochemical characterization of human CTC1 mutations. We found that all CTC1 frameshift mutations generated truncated or unstable protein products, none of which were able to form a complex with STN1-TEN1 on telomeres, resulting in progressive telomere shortening and formation of fused chromosomes. Missense mutations are able to form the CST complex at telomeres, but their expression levels are often repressed by the frameshift mutants. Our results also demonstrate for the first time that CTC1 mutations promote telomere dysfunction by decreasing the stability of STN1 to reduce its ability to interact with DNA Polα, thus highlighting a previously unknown mechanism to induce telomere dysfunction.

Single strand DNA binding proteins 1 and 2 protect newly replicated telomeres.

Human single-strand (ss) DNA binding proteins 1 and 2 (hSSB1 and 2) are components of the hSSB1/2-INTS3-C9orf80 heterotrimeric protein complex shown to participate in DNA damage response and maintenance of genome stability. However, their roles at telomeres remain unknown. Here, we generated murine SSB1 conditional knockout mice and cells and found that mSSB1 plays a critical role in telomere end protection. Both mSSB1 and mSSB2 localize to a subset of telomeres and are required to repair TRF2-deficient telomeres. Deletion of mSSB1 resulted in increased chromatid-type fusions involving both leading- and lagging-strand telomeric DNA, suggesting that it is required for the protection of G-overhangs. mSSB1's interaction with INTS3 is required for its localization to damaged DNA. mSSB1 interacts with Pot1a, but not Pot1b, and its association with telomeric ssDNA requires Pot1a. mSSB1(Δ/Δ) mice die at birth with developmental abnormalities, while mice with the hypomorphic mSSB1(F/F) allele are born alive and display increased sensitivity to ionizing radiation (IR). Our results suggest that mSSB1 is required to maintain genome stability, and document a previously unrecognized role for mSSB1/2 in the protection of newly replicated leading- and lagging-strand telomeres.

Risk factors of mild cognitive impairment in middle aged patients with type 2 diabetes: a cross-section study.

UNLABELLED: The aim of this study was to evaluate the risk factors of mild cognitive impairment (MCI) in middle-aged patients with type 2 diabetes (T2DM). METHODS: Montreal Cognitive Assessment (MoCA) was applied as cognition assessment implement. One hundred and fifty-seven middle-aged type 2 diabetic patients were enrolled in this cross-section study (age 40~69, mean age 55 ± 7). There were 93 patients with MCI (MoCA score<26) in MCI group and 64 with normal cognitive function (MoCA score ≥ 26) in control group. Information of history of disease, family history, data of BMI, WHR, HbA1c, FINS, C-Peptide (C-P), SBP, DBP, blood lipid (TG, TC, LDL-C, HDL-C and carotid ultrasound (carotid IMT, carotid resistance index [RI]) was collected. RESULTS: There were significant differences in the rate of patients with hypertension ([40.63 vs. 58.06%], P=0.026), duration of diabetes mellitus ([3.09 ± 4.04 y vs. 4.80 ± 4.94 y], P=0.024), C-P ([2.79 ± 1.09 ng/ml vs. 2.26 ± 1.00 ng/ml], P=0.008), Max C-IMT ([0.81 ± 0.15 mm vs. 0.91 ± 0.15 mm], P<0.001), Min C-RI (0.71 ± 0.06 vs. 0.68 ± 0.06, P<0.05), and no significant differences in the duration of hypertension and hyperlipidemia, BMI, WHR, HbA1c, SBP, DBP and blood lipid between control group and MCI group. MoCA scores were positively correlated with C-P (r=0.252, P=0.005), and negatively correlated with the history of hypertension (r=-0.244, P=0.002), duration of DM (r=-0.161, P=0.044), Max C-IMT (r=-0.253, P=0.005) and Min C-RI (r=-0.183, P=0.023). Multiple regression analysis showed that history of hypertension (Beta=-0.267, P=0.002), C-P (Beta=0.281, P=0.001) and Min C-RI (Beta=-0.221, P=0.011) were significantly independent determinants for the MoCA scores. CONCLUSIONS: The longer duration of diabetes, history of hypertension, lower serum C-P levels, thickened C-IMT and higher C-RI could be risk factors of MCI in type 2 diabetic patients. This finding could have an important impact on the management of cognitive decline in diabetic patients.

CTC1 deletion results in defective telomere replication, leading to catastrophic telomere loss and stem cell exhaustion.

The proper maintenance of telomeres is essential for genome stability. Mammalian telomere maintenance is governed by a number of telomere binding proteins, including the newly identified CTC1-STN1-TEN1 (CST) complex. However, the in vivo functions of mammalian CST remain unclear. To address this question, we conditionally deleted CTC1 from mice. We report here that CTC1 null mice experience rapid onset of global cellular proliferative defects and die prematurely from complete bone marrow failure due to the activation of an ATR-dependent G2/M checkpoint. Acute deletion of CTC1 does not result in telomere deprotection, suggesting that mammalian CST is not involved in capping telomeres. Rather, CTC1 facilitates telomere replication by promoting efficient restart of stalled replication forks. CTC1 deletion results in increased loss of leading C-strand telomeres, catastrophic telomere loss and accumulation of excessive ss telomere DNA. Our data demonstrate an essential role for CTC1 in promoting efficient replication and length maintenance of telomeres.

miRNA regulatory circuits in ES cells differentiation: a chemical kinetics modeling approach.

MicroRNAs (miRNAs) play an important role in gene regulation for Embryonic Stem cells (ES cells), where they either down-regulate target mRNA genes by degradation or repress protein expression of these mRNA genes by inhibiting translation. Well known tables TargetScan and miRanda may predict quite long lists of potential miRNAs inhibitors for each mRNA gene, and one of our goals was to strongly narrow down the list of mRNA targets potentially repressed by a known large list of 400 miRNAs. Our paper focuses on algorithmic analysis of ES cells microarray data to reliably detect repressive interactions between miRNAs and mRNAs. We model, by chemical kinetics equations, the interaction architectures implementing the two basic silencing processes of miRNAs, namely "direct degradation" or "translation inhibition" of targeted mRNAs. For each pair (M,G) of potentially interacting miRMA gene M and mRNA gene G, we parameterize our associated kinetic equations by optimizing their fit with microarray data. When this fit is high enough, we validate the pair (M,G) as a highly probable repressive interaction. This approach leads to the computation of a highly selective and drastically reduced list of repressive pairs (M,G) involved in ES cells differentiation.

Differential recruitment of methyl CpG-binding domain factors and DNA methyltransferases by the orphan receptor germ cell nuclear factor initiates the repression and silencing of Oct4.

The pluripotency gene Oct4 encodes a key transcription factor that maintains self-renewal of embryonic stem cell (ESC) and is downregulated upon differentiation of ESCs and silenced in somatic cells. A combination of cis elements, transcription factors, and epigenetic modifications, such as DNA methylation, mediates Oct4 gene expression. Here, we show that the orphan nuclear receptor germ cell nuclear factor (GCNF) initiates Oct4 repression and DNA methylation by the differential recruitment of methyl-CpG binding domain (MBD) and DNA methyltransferases (Dnmts) to the Oct4 promoter. When compared with wild-type ESCs and gastrulating embryos, Oct4 repression is lost and its proximal promoter is significantly hypomethylated in retinoic acid (RA)-differentiated GCNF(-/-) ESCs and GCNF(-/-) embryos. Efforts to characterize mediators of GCNF's repressive function and DNA methylation of the Oct4 promoter identified MBD3, MBD2, and de novo Dnmts as GCNF interacting factors. Upon differentiation, endogenous GCNF binds to the Oct4 proximal promoter and differentially recruits MBD3 and MBD2 as well as Dnmt3A. In differentiated GCNF(-/-) ESCs, recruitment of MBD3 and MBD2 as well as Dnmt3A to Oct4 promoter is lost and subsequently Oct4 repression and DNA methylation failed to occur. Hypomethylation of the Oct4 promoter is also observed in RA-differentiated MBD3(-/-) and Dnmt3A(-/-) ESCs, but not in MBD2(-/-) and Dnmt3B(-/-) ESCs. Thus, recruitment of MBD3, MBD2, and Dnmt3A by GCNF links two events: gene-specific repression and DNA methylation, which occur differentially at the Oct4 promoter. GCNF initiates the repression and epigenetic modification of Oct4 gene during ESC differentiation.

SNMIB/Apollo protects leading-strand telomeres against NHEJ-mediated repair.

Progressive telomere attrition or deficiency of the protective shelterin complex elicits a DNA damage response as a result of a cell's inability to distinguish dysfunctional telomeric ends from DNA double-strand breaks. SNMIB/Apollo is a shelterin-associated protein and a member of the SMN1/PSO2 nuclease family that localizes to telomeres through its interaction with TRF2. Here, we generated SNMIB/Apollo knockout mouse embryo fibroblasts (MEFs) to probe the function of SNMIB/Apollo at mammalian telomeres. SNMIB/Apollo null MEFs exhibit an increased incidence of G2 chromatid-type fusions involving telomeres created by leading-strand DNA synthesis, reflective of a failure to protect these telomeres after DNA replication. Mutations within SNMIB/Apollo's conserved nuclease domain failed to suppress this phenotype, suggesting that its nuclease activity is required to protect leading-strand telomeres. SNMIB/Apollo(-/-)ATM(-/-) MEFs display robust telomere fusions when Trf2 is depleted, indicating that ATM is dispensable for repair of uncapped telomeres in this setting. Our data implicate the 5'-3' exonuclease function of SNM1B/Apollo in the generation of 3' single-stranded overhangs at newly replicated leading-strand telomeres to protect them from engaging the non-homologous end-joining pathway.

Novel microRNA candidates and miRNA-mRNA pairs in embryonic stem (ES) cells.

BACKGROUND: MicroRNAS (miRNAS: a class of short non-coding RNAs) are emerging as important agents of post transcriptional gene regulation and integral components of gene networks. MiRNAs have been strongly linked to stem cells, which have a remarkable dual role in development. They can either continuously replenish themselves (self-renewal), or differentiate into cells that execute a limited number of specific actions (pluripotence). METHODOLOGY/PRINCIPAL FINDINGS: In order to identify novel miRNAs from narrow windows of development we carried out an in silico search for micro-conserved elements (MCE) in adult tissue progenitor transcript sequences. A plethora of previously unknown miRNA candidates were revealed including 545 small RNAs that are enriched in embryonic stem (ES) cells over adult cells. Approximately 20% of these novel candidates are down-regulated in ES (Dicer(-/-)) ES cells that are impaired in miRNA maturation. The ES-enriched miRNA candidates exhibit distinct and opposite expression trends from mmu-mirs (an abundant class in adult tissues) during retinoic acid (RA)-induced ES cell differentiation. Significant perturbation of trends is found in both miRNAs and novel candidates in ES (GCNF(-/-)) cells, which display loss of repression of pluripotence genes upon differentiation. CONCLUSION/SIGNIFICANCE: Combining expression profile information with miRNA target prediction, we identified miRNA-mRNA pairs that correlate with ES cell pluripotence and differentiation. Perturbation of these pairs in the ES (GCNF(-/-)) mutant suggests a role for miRNAs in the core regulatory networks underlying ES cell self-renewal, pluripotence and differentiation.

Nanog and Oct4 associate with unique transcriptional repression complexes in embryonic stem cells.

Nanog and Oct4 are essential transcription factors that regulate self-renewal and pluripotency of ES cells. However, the mechanisms by which Nanog and Oct4 modulate ES cell fate remain unknown. Through characterization of endogenous Nanog and Oct4 protein complexes in mouse ES cells, we found that these transcription factors interact with each other and associate with proteins from multiple repression complexes, including the NuRD, Sin3A and Pml complexes. In addition, Nanog, Oct4 and repressor proteins co-occupy Nanog-target genes in mouse ES cells, suggesting that Nanog and Oct4 together may communicate with distinct repression complexes to control gene transcription. To our surprise, of the various core components in the NuRD complex with which Nanog and Oct4 interact, Mta1 was preferred, whereas Mbd3 and Rbbp7 were either absent or present at sub-stoichiometric levels. We named this unique Hdac1/2- and Mta1/2-containing complex NODE (for Nanog and Oct4 associated deacetylase). Interestingly, NODE contained histone deacetylase (HDAC) activity that seemed to be comparable to NuRD, and retained its association with Nanog and Oct4 in Mbd3(-/-) ES cells. In contrast to Mbd3 loss-of-function, knockdown of NODE subunits led to increased expression of developmentally regulated genes and ES-cell differentiation. Our data collectively suggest that Nanog and Oct4 associate with unique repressor complexes on their target genes to control ES cell fate.

Nuclear Receptors in Regulation of Mouse ES Cell Pluripotency and Differentiation.

Embryonic stem (ES) cells have great therapeutic potential because they are capable of indefinite self-renewal and have the potential to differentiate into over 200 different cell types that compose the human body. The switch from the pluripotent phenotype to a differentiated cell involves many complex signaling pathways including those involving LIF/Stat3 and the transcription factors Sox2, Nanog and Oct-4. Many nuclear receptors play an important role in the maintenance of pluripotence (ERRbeta, SF-1, LRH-1, DAX-1) repression of the ES cell phenotype (RAR, RXR, GCNF) and also the differentiation of ES cells (PPARgamma). Here we review the roles of the nuclear receptors involved in regulating these important processes in ES cells.