Publications by authors named "Maja Okuka"

17 Publications

  • Page 1 of 1

Sidestream Smoke Affects Dendritic Complexity and Astrocytes After Model Mild Closed Head Traumatic Brain Injury.

Cell Mol Neurobiol 2021 Jan 8. Epub 2021 Jan 8.

Laboratory of Molecular Biology, Research and Development 151, Bay Pines VA Healthcare System, Bay Pines, FL, 33744, USA.

Mild traumatic brain injuries can have long-term consequences that interfere with the life of the patient and impose a burden on our health care system. Oxidative stress has been identified as a contributing factor for the progression of neurodegeneration following TBI. A major source of oxidative stress for many veterans is cigarette smoking and second-hand smoke, which has been shown to have an effect on TBI recovery. To examine the potential influences of second-hand smoke during recovery from TBI, we utilized a mouse model of closed head injury, followed by repeated exposure to cigarette smoke and treatment with a neuroprotective antioxidant. We found that neither the mild injuries nor the smoke exposure produced axonal damage detectable with amino cupric silver staining. However, complexity in the dendritic arbors was significantly reduced after mild TBI plus smoke exposure. In the hippocampus, there were astrocytic responses, including Cyp2e1 upregulation, after the injury and tobacco smoke insult. This study provides useful context for the importance of lifestyle changes, such as reducing or eliminating cigarette smoking, during recovery from TBI.
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http://dx.doi.org/10.1007/s10571-020-01036-5DOI Listing
January 2021

Inflammatory biomarkers and telomere length in women with polycystic ovary syndrome.

Fertil Steril 2015 Feb 20;103(2):542-7.e2. Epub 2014 Nov 20.

Department of Obstetrics and Gynecology, Ribeirao Preto Medical School, University of Sao Paulo, Ribeirao Preto, Sao Paulo, Brazil. Electronic address:

Objective: To analyze whether leukocyte telomere length (LTL) is impaired in women with polycystic ovary syndrome (PCOS).

Design: Case-control study.

Setting: Hospital.

Patient(s): A total of 274 women, including 150 patients with PCOS and 124 controls.

Intervention(s): None.

Main Outcome Measure(s): Body mass index (BMI), waist circumference, systemic arterial pressure, lipid profile, E(2), LH, T, androstenedione, PRL, TSH, sex hormone-binding globulin, C-reactive protein (CRP), homocysteine, free androgen index, and the homeostatic model of insulin sensitivity (HOMA-IR) index were analyzed. The LTL evaluation was measured by quantitative polymerase chain reaction.

Result(s): The PCOS group had higher values for weight, BMI, waist circumference, systolic arterial pressure, triglycerides, LH, T, insulin, CRP, free androgen index, and HOMA-IR compared with the control group. Sex hormone-binding globulin and E(2) levels were lower in the PCOS group than in the control group. The LTL did not differ between groups. Age, BMI, and HOMA-IR had no significant effect on LTL. The inflammatory biomarkers CRP and homocysteine were negatively correlated with LTL in patients with PCOS.

Conclusion(s): Our results showed no differences in LTL between patients with PCOS and controls, but CRP and homocysteine biomarkers negatively correlated with LTL in the PCOS group.
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http://dx.doi.org/10.1016/j.fertnstert.2014.10.035DOI Listing
February 2015

Telomere elongation and naive pluripotent stem cells achieved from telomerase haplo-insufficient cells by somatic cell nuclear transfer.

Cell Rep 2014 Dec 20;9(5):1603-1609. Epub 2014 Nov 20.

Center for Advanced Models for Translational Sciences and Therapeutics, University of Michigan Medical Center, Ann Arbor, MI 48109, USA. Electronic address:

Haplo-insufficiency of telomerase genes in humans leads to telomere syndromes such as dyskeratosis congenital and idiopathic pulmonary fibrosis. Generation of pluripotent stem cells from telomerase haplo-insufficient donor cells would provide unique opportunities toward the realization of patient-specific stem cell therapies. Recently, pluripotent human embryonic stem cells (ntESCs) have been efficiently achieved by somatic cell nuclear transfer (SCNT). We tested the hypothesis that SCNT could effectively elongate shortening telomeres of telomerase haplo-insufficient cells in the ntESCs with relevant mouse models. Indeed, telomeres of telomerase haplo-insufficient (Terc(+/-)) mouse cells are elongated in ntESCs. Moreover, ntESCs derived from Terc(+/-) cells exhibit naive pluripotency as evidenced by generation of Terc(+/-) ntESC clone pups by tetraploid embryo complementation, the most stringent test of naive pluripotency. These data suggest that SCNT could offer a powerful tool to reprogram telomeres and to discover the factors for robust restoration of telomeres and pluripotency of telomerase haplo-insufficient somatic cells.
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http://dx.doi.org/10.1016/j.celrep.2014.10.052DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4268138PMC
December 2014

Rif1 maintains telomere length homeostasis of ESCs by mediating heterochromatin silencing.

Dev Cell 2014 Apr;29(1):7-19

State Key Laboratory of Medicinal Chemical Biology, Department of Cell Biology and Genetics, College of Life Sciences, Nankai University, Tianjin 300071, China. Electronic address:

Telomere length homeostasis is essential for genomic stability and unlimited self-renewal of embryonic stem cells (ESCs). We show that telomere-associated protein Rif1 is required to maintain telomere length homeostasis by negatively regulating Zscan4 expression, a critical factor for telomere elongation by recombination. Depletion of Rif1 results in terminal hyperrecombination, telomere length heterogeneity, and chromosomal fusions. Reduction of Zscan4 by shRNA significantly rescues telomere recombination defects of Rif1-depleted ESCs and associated embryonic lethality. Further, Rif1 negatively modulates Zscan4 expression by maintaining H3K9me3 levels at subtelomeric regions. Mechanistically, Rif1 interacts and stabilizes H3K9 methylation complex. Thus, Rif1 regulates telomere length homeostasis of ESCs by mediating heterochromatic silencing.
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http://dx.doi.org/10.1016/j.devcel.2014.03.004DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4720134PMC
April 2014

Roles for Tbx3 in regulation of two-cell state and telomere elongation in mouse ES cells.

Sci Rep 2013 Dec 13;3:3492. Epub 2013 Dec 13.

State Key Laboratory of Medicinal Chemical Biology; Department of Cell Biology and Genetics, College of Life Sciences, Nankai University, Tianjin 300071, China.

Mouse embryonic stem (ES) cell cultures exhibit heterogeneity and recently are discovered to sporadically enter the 2-cell (2C)-embryo state, critical for ES potency. Zscan4 could mark the sporadic 2C-state of ES cells. However, factors that regulate the Zscan4(+)/2C state remain to be elucidated. We show that Tbx3 plays a novel role in regulation of Zscan4(+)/2C state. Tbx3 activates 2-cell genes including Zscan4 and Tcstv1/3, but not vise versa. Ectopic expression of Tbx3 results in telomere elongation, consistent with a role for Zscan4 in telomere lengthening. Mechanistically, Tbx3 decreases Dnmt3b and increases Tet2 protein levels, and reduces binding of Dnmt3b to subtelomeres, resulting in reduced DNA methylation and derepression of genes at subtelomeres, e.g. Zscan4. These data suggest that Tbx3 can activate Zscan4(+)/2C state by negative regulation of DNA methylation at repeated sequences, linking to telomere maintenance and self-renewal of ES cells.
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http://dx.doi.org/10.1038/srep03492DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3861804PMC
December 2013

Telomere reprogramming and maintenance in porcine iPS cells.

PLoS One 2013 30;8(9):e74202. Epub 2013 Sep 30.

State Key Laboratory of Medicinal Chemical Biology, College of Life Sciences, Nankai University, Tianjin, China.

Telomere reprogramming and silencing of exogenous genes have been demonstrated in mouse and human induced pluripotent stem cells (iPS cells). Pigs have the potential to provide xenotransplant for humans, and to model and test human diseases. We investigated the telomere length and maintenance in porcine iPS cells generated and cultured under various conditions. Telomere lengths vary among different porcine iPS cell lines, some with telomere elongation and maintenance, and others telomere shortening. Porcine iPS cells with sufficient telomere length maintenance show the ability to differentiate in vivo by teratoma formation test. IPS cells with short or dysfunctional telomeres exhibit reduced ability to form teratomas. Moreover, insufficient telomerase and incomplete telomere reprogramming and/or maintenance link to sustained activation of exogenous genes in porcine iPS cells. In contrast, porcine iPS cells with reduced expression of exogenous genes or partial exogene silencing exhibit insufficient activation of endogenous pluripotent genes and telomerase genes, accompanied by telomere shortening with increasing passages. Moreover, telomere doublets, telomere sister chromatid exchanges and t-circles that presumably are involved in telomere lengthening by recombination also are found in porcine iPS cells. These data suggest that both telomerase-dependent and telomerase-independent mechanisms are involved in telomere reprogramming during induction and passages of porcine iPS cells, but these are insufficient, resulting in increased telomere damage and shortening, and chromosomal instability. Active exogenes might compensate for insufficient activation of endogenous genes and incomplete telomere reprogramming and maintenance of porcine iPS cells. Further understanding of telomere reprogramming and maintenance may help improve the quality of porcine iPS cells.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0074202PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3787036PMC
May 2014

Association of telomere instability with senescence of porcine cells.

BMC Cell Biol 2012 Dec 15;13:36. Epub 2012 Dec 15.

State Key Laboratory of Medicinal Chemical Biology; College of Life Sciences, Nankai University, Tianjin 300071, China.

Background: Telomeres are essential for the maintenance of genomic stability, and telomere dysfunction leads to cellular senescence, carcinogenesis, aging, and age-related diseases in humans. Pigs have become increasingly important large animal models for preclinical tests and study of human diseases, and also may provide xeno-transplantation sources. Thus far, Southern blot analysis has been used to estimate average telomere lengths in pigs. Telomere quantitative fluorescence in situ hybridization (Q-FISH), however, can reveal status of individual telomeres in fewer cells, in addition to quantifying relative telomere lengths, and has been commonly used for study of telomere function of mouse and human cells. We attempted to investigate telomere characteristics of porcine cells using telomere Q-FISH method.

Results: The average telomere lengths in porcine cells measured by Q-FISH correlated with those of quantitative real-time PCR method (qPCR) or telomere restriction fragments (TRFs) by Southern blot analysis. Unexpectedly, we found that porcine cells exhibited high incidence of telomere doublets revealed by Q-FISH method, coincided with increased frequency of cellular senescence. Also, telomeres shortened during subculture of various porcine primary cell types. Interestingly, the high frequency of porcine telomere doublets and telomere loss was associated with telomere dysfunction-induced foci (TIFs). The incidence of TIFs, telomere doublets and telomere loss increased with telomere shortening and cellular senescence during subculture.

Conclusion: Q-FISH method using telomere PNA probe is particularly useful for characterization of porcine telomeres. Porcine cells exhibit high frequency of telomere instability and are susceptible to telomere damage and replicative senescence.
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http://dx.doi.org/10.1186/1471-2121-13-36DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3563453PMC
December 2012

Conservation and characterization of unique porcine interstitial telomeric sequences.

Sci China Life Sci 2012 Dec 12;55(12):1029-37. Epub 2012 Dec 12.

State Key Laboratory of Medicinal Chemical Biology, College of Life Sciences, Nankai University, Tianjin 300071, China.

Telomeres are composed of TTAGGG repeats and located at the ends of chromosomes. Telomeres protect chromosomes from instability in mammals, including mice and humans. Repetitive TTAGGG sequences are also found at intrachromosomal sites, where they are named as interstitial telomeric sequences (ITSs). Aberrant ITSs are implicated in chromosomal instability and found in cancer cells. Interestingly, in pigs, vertebrate telomere sequences TTAGGG (vITSs) are also localized at the centromeric region of chromosome 6, in addition to the end of all chromosomes. Surprisingly, we found that botanic telomere sequences, TTTAGGG (bITSs), also localize with vITSs at the centromeric regions of pig chromosome 6 using telomere fluorescence in situ hybridization (FISH) and by comparisons between several species. Furthermore, the average lengths of vITSs are highly correlated with those of the terminal telomeres (TTS). Also, pig ITSs show a high incidence of telomere doublets, suggesting that pig ITSs might be unstable and dynamic. Together, our results show that pig cells maintain the conserved telomere sequences that are found at the ITSs from of plants and other vertebrates. Further understanding of the function and regulation of pig ITSs may provide new clues for evolution and chromosomal instability.
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http://dx.doi.org/10.1007/s11427-012-4420-xDOI Listing
December 2012

Zscan4 promotes genomic stability during reprogramming and dramatically improves the quality of iPS cells as demonstrated by tetraploid complementation.

Cell Res 2013 Jan 13;23(1):92-106. Epub 2012 Nov 13.

Group of Epigenetic Reprogramming, State Key Laboratory of Cell Biology, Institute of Biochemistry and Cell Biology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai 200031, China.

Induced pluripotent stem (iPS) cells generated using Yamanaka factors have great potential for use in autologous cell therapy. However, genomic abnormalities exist in human iPS cells, and most mouse iPS cells are not fully pluripotent, as evaluated by the tetraploid complementation assay (TCA); this is most likely associated with the DNA damage response (DDR) occurred in early reprogramming induced by Yamanaka factors. In contrast, nuclear transfer can faithfully reprogram somatic cells into embryonic stem (ES) cells that satisfy the TCA. We thus hypothesized that factors involved in oocyte-induced reprogramming may stabilize the somatic genome during reprogramming, and improve the quality of the resultant iPS cells. To test this hypothesis, we screened for factors that could decrease DDR signals during iPS cell induction. We determined that Zscan4, in combination with the Yamanaka factors, not only remarkably reduced the DDR but also markedly promoted the efficiency of iPS cell generation. The inclusion of Zscan4 stabilized the genomic DNA, resulting in p53 downregulation. Furthermore, Zscan4 also enhanced telomere lengthening as early as 3 days post-infection through a telomere recombination-based mechanism. As a result, iPS cells generated with addition of Zscan4 exhibited longer telomeres than classical iPS cells. Strikingly, more than 50% of iPS cell lines (11/19) produced via this "Zscan4 protocol" gave rise to live-borne all-iPS cell mice as determined by TCA, compared to 1/12 for lines produced using the classical Yamanaka factors. Our findings provide the first demonstration that maintaining genomic stability during reprogramming promotes the generation of high quality iPS cells.
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http://dx.doi.org/10.1038/cr.2012.157DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3541664PMC
January 2013

Telomere shortening and DNA damage of embryonic stem cells induced by cigarette smoke.

Reprod Toxicol 2013 Jan 21;35:89-95. Epub 2012 Jul 21.

Department of Biochemistry, State Key Laboratory of Biocontrol, School of Life Sciences, Sun Yat-Sen University, Guangzhou 510275, China.

Embryonic stem cells (ESCs) provide a valuable in vitro model for testing toxicity of chemicals and environmental contaminants including cigarette smoke. Mouse ESCs were acutely or chronically exposed to smoke components, cigarette smoke condensate (CSC), or cadmium, an abundant component of CSC, and then evaluated for their self-renewal, apoptosis, DNA damage and telomere function. Acute exposure of ESCs to high dose of CSC or cadmium increased DNA damage and apoptosis. Yet, ESCs exhibited a remarkable capacity to recover following absence of exposure. Chronic exposure of ESCs to low dose of CSC or cadmium resulted in shorter telomeres and DNA damage. Together, acute exposure of ESCs to CSC or cadmium causes immediate cell death and reduces pluripotency, while chronic exposure of ESCs to CSC or cadmium leads to DNA damage and telomere shortening. Notably, a sub-proportion of ESCs during passages is selected to resist to smoke-induced oxidative damage to telomeres.
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http://dx.doi.org/10.1016/j.reprotox.2012.07.003DOI Listing
January 2013

Molecular insights into the heterogeneity of telomere reprogramming in induced pluripotent stem cells.

Cell Res 2012 Apr 20;22(4):757-68. Epub 2011 Dec 20.

College of Life Sciences, Nankai University, Tianjin 300071, China.

Rejuvenation of telomeres with various lengths has been found in induced pluripotent stem cells (iPSCs). Mechanisms of telomere length regulation during induction and proliferation of iPSCs remain elusive. We show that telomere dynamics are variable in mouse iPSCs during reprogramming and passage, and suggest that these differences likely result from multiple potential factors, including the telomerase machinery, telomerase-independent mechanisms and clonal influences including reexpression of exogenous reprogramming factors. Using a genetic model of telomerase-deficient (Terc(-/-) and Terc(+/-)) cells for derivation and passages of iPSCs, we found that telomerase plays a critical role in reprogramming and self-renewal of iPSCs. Further, telomerase maintenance of telomeres is necessary for induction of true pluripotency while the alternative pathway of elongation and maintenance by recombination is also required, but not sufficient. Together, several aspects of telomere biology may account for the variable telomere dynamics in iPSCs. Notably, the mechanisms employed to maintain telomeres during iPSC reprogramming are very similar to those of embryonic stem cells. These findings may also relate to the cloning field where these mechanisms could be responsible for telomere heterogeneity after nuclear reprogramming by somatic cell nuclear transfer.
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http://dx.doi.org/10.1038/cr.2011.201DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3317559PMC
April 2012

Association of telomere length with authentic pluripotency of ES/iPS cells.

Cell Res 2011 May 1;21(5):779-92. Epub 2011 Feb 1.

School of Life Sciences, Sun Yat-sen University, Guangzhou 510275, China.

Telomerase and telomeres are important for indefinite replication of stem cells. Recently, telomeres of somatic cells were found to be reprogrammed to elongate in induced pluripotent stem cells (iPSCs). The role of telomeres in developmental pluripotency in vivo of embryonic stem cells (ESCs) or iPSCs, however, has not been directly addressed. We show that ESCs with long telomeres exhibit authentic developmental pluripotency, as evidenced by generation of complete ESC pups as well as germline-competent chimeras, the most stringent tests available in rodents. ESCs with short telomeres show reduced teratoma formation and chimera production, and fail to generate complete ESC pups. Telomere lengths are highly correlated (r > 0.8) with the developmental pluripotency of ESCs. Short telomeres decrease the proliferative rate or capacity of ESCs, alter the expression of genes related to telomere epigenetics, down-regulate genes important for embryogenesis and disrupt germ cell differentiation. Moreover, iPSCs with longer telomeres generate chimeras with higher efficiency than those with short telomeres. Our data show that functional telomeres are essential for the developmental pluripotency of ESCs/iPSCs and suggest that telomere length may provide a valuable marker to evaluate stem cell pluripotency, particularly when the stringent tests are not feasible.
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http://dx.doi.org/10.1038/cr.2011.16DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3203670PMC
May 2011

Telomere susceptibility to cigarette smoke-induced oxidative damage and chromosomal instability of mouse embryos in vitro.

Free Radic Biol Med 2010 Jun 8;48(12):1663-76. Epub 2010 Apr 8.

Department of Obstetrics and Gynecology, University of South Florida College of Medicine, Tampa, FL 33612, USA.

Cigarette smoke is associated with high risk of lung, cardiovascular, and degenerative diseases, reduced fertility, and possibly the health of newborns. Cigarette smoke contains many components and exerts its genotoxicity in part by generating reactive oxidative stress. Telomeres consist of repeated 'G' rich sequences and associated proteins located at the chromosomal ends that maintain chromosomal integrity. We tested the hypothesis that telomere shortening and dysfunction are implicated in smoke associated oxidative damage and chromosomal instability using early mouse embryos in vitro and short-telomere mouse model. Mouse embryos exposed to smoke components, cigarette smoke condensate (CSC) at the concentration of 0.02 mg/ml continuously or 0.1mg/ml for 20 h, or cadmium at 5-100 microM, exhibited increased oxidative stress and telomere shortening and loss, associated with chromosomal instability, apoptosis, and compromised embryo cleavage and development. Remarkably, reduction of oxidative stress by an antioxidant N-acetyl-L-cysteine (NAC) greatly reduced these toxicities. Notably, cadmium led to more severe oxidative damage and telomere dysfunction, which could be more effectively rescued by antioxidant treatment, than did CSC. Moreover, short telomeres predisposed embryos to smoke component-induced oxidative damage. These data further extend our understanding of mechanisms underlying smoke-induced oxidative damage to include telomere dysfunction and chromosomal instability.
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http://dx.doi.org/10.1016/j.freeradbiomed.2010.03.026DOI Listing
June 2010

Telomere elongation in induced pluripotent stem cells from dyskeratosis congenita patients.

Nature 2010 Mar 17;464(7286):292-6. Epub 2010 Feb 17.

Division of Hematology/Oncology, Children's Hospital Boston, Massachusetts 02115, USA.

Patients with dyskeratosis congenita (DC), a disorder of telomere maintenance, suffer degeneration of multiple tissues. Patient-specific induced pluripotent stem (iPS) cells represent invaluable in vitro models for human degenerative disorders like DC. A cardinal feature of iPS cells is acquisition of indefinite self-renewal capacity, which is accompanied by induction of the telomerase reverse transcriptase gene (TERT). We investigated whether defects in telomerase function would limit derivation and maintenance of iPS cells from patients with DC. Here we show that reprogrammed DC cells overcome a critical limitation in telomerase RNA component (TERC) levels to restore telomere maintenance and self-renewal. We discovered that TERC upregulation is a feature of the pluripotent state, that several telomerase components are targeted by pluripotency-associated transcription factors, and that in autosomal dominant DC, transcriptional silencing accompanies a 3' deletion at the TERC locus. Our results demonstrate that reprogramming restores telomere elongation in DC cells despite genetic lesions affecting telomerase, and show that strategies to increase TERC expression may be therapeutically beneficial in DC patients.
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http://dx.doi.org/10.1038/nature08792DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3058620PMC
March 2010

Generation of pluripotent stem cells from eggs of aging mice.

Aging Cell 2010 Apr 8;9(2):113-25. Epub 2009 Dec 8.

Department of Obstetrics and Gynecology, University of South Florida College of Medicine, Tampa, FL 33647, USA.

Oocytes can reprogram genomes to form embryonic stem (ES) cells. Although ES cells largely escape senescence, oocytes themselves do senesce in the ovaries of most mammals. It remains to be determined whether ES cells can be established using eggs from old females, which exhibit reproductive senescence. We attempted to produce pluripotent stem cell lines from artificial activation of eggs (also called pES) from reproductive aged mice, to determine whether maternal aging affects pES cell production and pluripotency. We show that pES cell lines were generated with high efficiency from reproductive aged (old) mice, although parthenogenetic embryos from these mice produced fewer ES clones by initial two passages. Further, pES cell lines generated from old mice showed telomere length, expression of pluripotency molecular markers (Oct4, Nanog, SSEA1), alkaline phosphatase activity, teratoma formation and chimera production similar to young mice. Notably, DNA damage was reduced in pES cells from old mice compared to their progenitor parthenogenetic blastocysts, and did not differ from that of pES cells from young mice. Also, global gene expression differed only minimally between pES cells from young and old mice, in contrast to marked differences in gene expression in eggs from young and old mice. These data demonstrate that eggs from old mice can generate pluripotent stem cells, and suggest that the isolation and in vitro culture of ES cells must select cells with high levels of DNA and telomere integrity, and/or with capacity to repair DNA and telomeres.
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http://dx.doi.org/10.1111/j.1474-9726.2009.00539.xDOI Listing
April 2010

Effects of cigarette smoke on fertilization and embryo development in vivo.

Fertil Steril 2009 Oct 18;92(4):1456-1465. Epub 2008 Nov 18.

Department of Obstetrics and Gynecology, University of South Florida College of Medicine, Tampa, Florida; College of Life Science, Nankai University, Tianjin, People's Republic of China. Electronic address:

Objective: To determine the effects of smoking on eggs and subsequent embryo development by maternal exposure to cigarette smoke.

Design: Mice were exposed to cigarette smoke or cigarette smoke condensate (CSC) for 4 weeks and then examined for development and telomere function of embryos in vitro after fertilization. In addition, the effects of continuous smoke on embryo development and telomere length were determined by treating mice for 4 weeks, followed by continuous exposure to cigarette smoke or CSC after fertilization.

Setting: Laboratory study.

Animal(s): CD1 mice.

Intervention(s): Mice were exposed to cigarette smoke or CSC.

Main Outcome Measure(s): The percentage (rate) of blastocyst development, quality of embryos assessed by total cell number, apoptosis, Oct4 expression (a molecular marker of embryonic stem cells), telomere length and loss, and chromosomal instability were compared between smoke- and CSC- treated mice and sham-treated mice.

Result(s): Mice exposed to cigarette smoke or CSC for 4 weeks exhibited increased egg fragmentation or delayed fertilization, thus reducing development to blastocysts in vitro. Fragmented eggs showed increased reactive oxygen species. Mice exposed to smoke or CSC showed increased apoptosis and altered expression of Oct4 in developed embryos. The effects of smoke or CSC on embryo development showed a dose-dependent relationship to exposure time. Exposure to smoke or CSC beginning 4 weeks before fertilization altered expression of Oct4 and increased apoptosis in blastocysts. Notably, the rate of abnormal embryos significantly increased in the smoke and CSC groups. Smoke and CSC shortened telomeres in embryos, but their telomere shortening was not enough to induce major chromosome abnormalities in mice, which have unusually long telomeres.

Conclusion(s): Together, the whole animal exposure model shows that cigarette smoke induces oxidative stress, telomere shortening, and apoptosis, and compromises embryo development in vivo.
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http://dx.doi.org/10.1016/j.fertnstert.2008.07.1781DOI Listing
October 2009

Telomere lengthening early in development.

Nat Cell Biol 2007 Dec 4;9(12):1436-41. Epub 2007 Nov 4.

Laboratory for Reproductive Medicine, Department of Obstetrics and Gynecology, University of South Florida College of Medicine, Tampa, Florida 33612, USA.

Stem cells and cancer cells maintain telomere length mostly through telomerase. Telomerase activity is high in male germ line and stem cells, but is low or absent in mature oocytes and cleavage stage embryos, and then high again in blastocysts. How early embryos reset telomere length remains poorly understood. Here, we show that oocytes actually have shorter telomeres than somatic cells, but their telomeres lengthen remarkably during early cleavage development. Moreover, parthenogenetically activated oocytes also lengthen their telomeres, thus the capacity to elongate telomeres must reside within oocytes themselves. Notably, telomeres also elongate in the early cleavage embryos of telomerase-null mice, demonstrating that telomerase is unlikely to be responsible for the abrupt lengthening of telomeres in these cells. Coincident with telomere lengthening, extensive telomere sister-chromatid exchange (T-SCE) and colocalization of the DNA recombination proteins Rad50 and TRF1 were observed in early cleavage embryos. Both T-SCE and DNA recombination proteins decrease in blastocyst stage embryos, whereas telomerase activity increases and telomeres elongate only slowly. We suggest that telomeres lengthen during the early cleavage cycles following fertilization through a recombination-based mechanism, and that from the blastocyst stage onwards, telomerase only maintains the telomere length established by this alternative mechanism.
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http://dx.doi.org/10.1038/ncb1664DOI Listing
December 2007