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a Division of Laboratory Animal Science, Central Institute for Experimental Animals, Kawasaki, Kanagawa, Japan;
b Department of Urology, Urayasu Hospital, Juntendo University, Urayasu, Chiba, Japan;
c Department of Molecular Genetics, Division of Molecular and Clinical Genetics, Medical Institute of Bioregulation, Kyushu University, Hakata, Fukuoka, Japan;
d Tokai University School of Medicine, Isehara, Kanagawa, Japan;
e Department of Physiology, Keio University School of Medicine, Shinjuku-ku, Tokyo, Japan;
f Research Project Center,
g Department of Genetics, Central Institute for Experimental Animals, Kawasaki, Kanagawa, Japan;
h Division of Molecular Therapy, Institute of Medical Science, University of Tokyo,
i Institute of Obstetrics & Gynecology in Clinical Medicine, University of Tsukuba,
j Laboratory of Embryonic Stem Cell Research, Stem Cell Research Center,
k Department of Development and Differentiation, Institute for Frontier Medical Sciences, Kyoto University, Kyoto, Japan
Key Words. Embryonic stem cells • Common marmoset • Embryoid body • Nonhuman primate • Teratoma formation
Correspondence: Kenzaburo Tani, M.D., Ph.D., Department of Molecular Genetics, Division of Molecular and Clinical Genetics, Medical Institute of Bioregulation, Kyushu University, Hakata, Fukuoka 812-8582, Japan. Telephone: 81-92-642-6434; Fax: 81-92-642-6444; e-mail: taniken{at}bioreg.kyushu-u.ac.jp; for CMES cell distribution, contact Erika Sasaki at esasaki{at}ciea.or.jp
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ABSTRACT |
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INTRODUCTION |
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The common marmoset (Callithrix jacchus) is a New World primate species with reproductive characteristics that are appropriate for ESC studies. More specifically, these animals are small (weighing approximately 350–400 g), they have a short gestation period (approximately 144 days), and reach sexual maturity at 12–18 months. Unlike macaques, marmosets routinely deliver twins or triplets for each pregnancy. In addition, it is possible to synchronize the marmoset ovarian cycle with prostaglandin analogs, collect age-matched embryos from multiple females, and transfer embryos to synchronized recipients with success rates in the range of 70%–80% [1–3]. Because these reproductive characteristics allow routine efficient transfer of multiple embryos, marmosets constitute an excellent primate species for the generation of transgenic and knockout animal models of human diseases.
In addition to these reproductive benefits, we have shown previously that marmosets are suitable laboratory animals for preclinical studies of stem cell therapies, owing to the similarities between the hematopoietic and immune systems of humans and marmosets [4, 5]. In 1996, Thomson et al. [6] established pluripotent common marmoset cell lines, which are considered powerful tools for understanding the regulatory mechanisms of ESC differentiation both in vitro and in vivo. However, the differentiation abilities of the pluripotent common marmoset cells in terms of in vitro teratoma formation assays and certain common properties of ESC lines, such as differentiation to the cell lineages of three germ layers, have not been defined fully. The establishment of totipotent common marmoset ESC (CMESC) lines would facilitate the construction, by gene targeting, of nonhuman primate models for human disease. To achieve our goal of establishing the common marmoset as a human disease model, we have established novel CMESC lines and characterized their differentiation capacities.
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MATERIALS AND METHODS |
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Embryo Collection
Fifteen female animals were divided into three groups. The ovulation cycles of each group of animals were synchronized with the prostaglandin (PG) F2
analogue cloprostenol (0.75 mg/head Estrumate; Schering-Plough Animal Health, Union, NJ, http://www.spah.com) which was administered more than 10 days after the luteal phase, as reported previously [7]. Plasma samples (0.1 ml) were collected from the femoral vein at 2, 9, 11, and 13 days after the injection of cloprostenol, and the day of ovulation was determined by the plasma progesterone concentration, using an enzyme immunoassay (EIA), as described below. The day of ovulation (day 0) was defined as the day before the serum progesterone level reached 10 ng/ml [8]. Embryos were collected 7–10 days after ovulation, after anesthesia by intramuscular injection of 0.05 mg per head of medetomidine hydrochloride (Domitor; Meiji Techno, Tokyo, http://www.meijitechno.co.jp) or 0.25–0.5 mg per head of flunitrazepam (Silece; Eisai Co., Ltd., Tokyo, http://www.eisai.co.jp/index-e.html) and 70 mg per head of ketamine hydrochloride (veterinary Ketalar 50; Sankyo Lifetech Co., Ltd., Tokyo, http://www.sankyo-lifetech.co.jp/english). The cervix and both oviducts were exteriorized by midline laparotomy and clamped, and the uterine lumen was flushed from the proximal end to the cervix with 2.5 ml of Dulbecco’s modified Eagle’s medium (DMEM; Invitrogen, Tokyo, http://www.invitrogen.com) that contained 10% fetal bovine serum (FBS; JRH, Tokyo, http://www.jrhbio.com). The flushed medium was collected using a 23-gauge needle that was placed in the uterine lumen through the uterine fundus. Cloprostenol was also administered 4 days after embryo collection. The plasma progesterone concentration was determined using the DPC Progesterone Kit (Diagnostic Products Corporation, Los Angeles, http://www.dpcweb.com) according to the recommendations of the manufacturer.
Isolation and Culture of ESC Lines
Inner cell masses (ICMs) were isolated by immunosurgery, as described previously [9]. Briefly, the zona pellucida of the marmoset blastocyst was removed by the addition of 0.5% pronase (Sigma, Tokyo, http://www.sigmaaldrich.com) in DMEM, and the blastocysts were washed three times with DMEM. To remove the trophectoderm, the blastocysts were incubated for 45 minutes at 37°C in 5% CO2 with a 10-fold dilution of anti-marmoset fibroblast rabbit serum in DMEM. After three washes with DMEM, the blastocysts were incubated with a fivefold dilution of guinea pig complement (Invitrogen) in DMEM for 30 minutes at 37°C in 5% CO2. After immunosurgery, the trophectoderm was removed by pipetting, and the ICMs were isolated. The ICMs were plated on 3,500-rad 
-irradiated mouse embryonic fibroblast (MEF) feeder layer. After 10–14 days, the ICMs were dissociated in trypsin-EDTA and replated on a fresh MEF feeder layer. The ICMs and their expanded cells were cultured using CMESC medium that consisted of 80% Knockout DMEM supplemented with 20% Knockout Serum Replacement (KSR; Invitrogen), 1 mM L-glutamine, 0.1 mM MEM nonessential amino acids, 0.1 mM ß-mercaptoethanol (2-ME; Sigma), 100 IU/ml penicillin, 100 µg/ml streptomycin sulfate, 250 ng/ml amphotericin B, and 10 ng/ml leukemia inhibitory factor. For cell splitting, undifferentiated CMESC colonies were detached from the feeder cells, using 0.25% trypsin that was supplemented with 1 mM CaCl2 and 20% KSR. The removed colonies were mechanically dissociated into 10 to 50 cells and replated on new irradiated MEF feeder layer.
Immunohistochemical Staining
To examine the expression of cell surface markers on cultured marmoset ICMs, alkaline phosphatase was detected using the Alkaline Phosphatase Staining Kit (Sigma) according to the manufacturer’s instructions. For immunostaining, ESCs were fixed with 4% paraformaldehyde in phosphate-buffered saline (PBS) for 10 minutes at room temperature and then incubated with 0.3% H2O2 for 10 minutes at room temperature. The primary antibodies against stage-specific embryonic antigen (SSEA)-1, SSEA-3, SSEA-4 (Developmental Studies Hybridoma Bank, Iowa City, IA, http://www.uiowa.edu/~dshbwww), TRA-1-60, and TRA-1-81 (Chemicon, Temecula, CA, http://www.chemicon.com) were diluted with Antibody Diluent (DAKO ChemMate; DakoCytomation, Glostrup, Denmark, http://www.dakocytomation.dk) and incubated for 1 hour at room temperature. The following primary antibodies (dilutions) were used: anti-SSEA-1 (1:50), anti-SSEA-3 (1:10), anti-SSEA-4 (1:50), anti-TRA-1-60, and anti-TRA-1-81 (10 µg/ml). After three washes with PBS, the biotinylated secondary antibody Simple Stain PO Multi system (Nichirei Corporation, Tokyo, http://www.nichirei.co.jp/english) was incubated with the cells for 30 minutes at room temperature. The samples were washed three times with PBS, and the localization of the bound monoclonal antibodies was detected using the DAB (3,3'-diaminobenzidine tetrahydrochloride) horseradish peroxidase complex.
For immunohistochemical analysis of tumors that formed after transplantation into immunodeficient mice, the collected tumors were fixed in neutral buffered formalin and embedded in paraffin. The paraffin blocks were sectioned and subjected to immunohistochemical staining. Primary antibodies against keratin wide specific screening (WSS), desmin, CD31, and glial fibrillary acidic protein (GFAP) (all purchased from DakoCytomation, Tokyo) were incubated with the paraffin sections at dilutions of 1:200, 1:200, 1:10, and 1:50, respectively. The localization of the bound monoclonal antibodies was detected using the Envision System (DakoCytomation).
For immunofluorescence staining of in vitro–differentiated neural cells, the slides and sections were preincubated with 10% normal goat serum plus 0.3% Triton X-100 in PBS, followed by over-night incubation in 10% normal goat serum plus 0.3% Triton X-100 in PBS that contained rabbit polyclonal anti-TH antibody (AB152; Chemicon). AlexaTM 488 goat anti-rabbit IgG antibody and AlexaTM 568 goat anti-mouse IgG antibody (Jackson ImmunoResearch Laboratories, Inc., West Grove, PA, http://www.jacksonimmuno.com) were added as secondary antibodies for 2 hours. Finally, the specimens were soaked in 2 µg/ml Hoechst 33528 in distilled water. All of the micrographs were analyzed on the Zeiss AxioCam imaging system (Carl Zeiss, Jena, Germany, http://www.zeiss.com).
Karyotypic Analysis
ESCs were prepared by passaging a confluent culture from a 25-cm2 bottle. After a 3-hour incubation with fresh medium, a colce-mid (Invitrogen) was added to a final concentration of 0.02 µg/ml for 20 minutes. The cells were then washed in PBS, dissociated using trypsin, and spun down. The pellet was resuspended carefully in 0.56% KCl at room temperature. After centrifugation, the hypotonic solution was removed, and the pellet was fixed with methanol/acetic acid, 3:1 (vol/vol) via gently pipetting. After centrifuging at 1,000 rpm, 5-minute fixation was performed twice before spreading the cells on slides. The slides were air-dried overnight, stained in freshly made 5% Giemsa for 10 minutes, and rinsed with distilled water. In the Giemsa (G)-banding analysis, the numbers of chromosomes as well as karyotypic analysis were performed using 30 and five metaphase spreads, respectively.
Telomerase Activity
Telomerase activity was determined using the TRAPEZE Telomerase Detection Kit (Chemicon, Tokyo) according to the manufacturer’s instructions. Briefly, cell extracts were obtained from approximately 1 x 106 cells, and the protein concentrations were normalized using the Coomassie blue–stained protein assay reagent bovine serum albumin standards (Pierce, Inc., Rockford, IL, http://www.piercenet.com). Heat-inactivated controls were obtained by incubating the samples at 85°C for 10 minutes. Aliquots (1.5 µg) of the cell extracts were used for polymerase chain reaction (PCR), which was performed according to the manufacturer’s instructions. The PCR products were electrophoresed on a 12.5% nondenaturing polyacrylamide gel, and telomerase activity was detected by SYBR green staining (Invitrogen).
PCR–Single Strand Conformation Polymorphism (PCR-SSCP)
SSCP analysis of the major histocompatibility complex-DRB genes was performed as described previously [10]. The following PCR primers were used: MA-DR-2r, 5'-CTCTCCGCGGCAC-TAGGAAC-3'; and MA-DR-4s, 5'-GCACGTTTCTTGGAG-TATAGC-3'.
Reverse Transcription (RT)–PCR
Poly(A)+ RNA was isolated using the QuickPrep Micro mRNA Purification Kit (GE Healthcare, Toyko, http://www4.amershambioscience.com) according to the manufacturer’s instructions. First-strand cDNA was synthesized from 1 µg of poly(A)+ RNA from the undifferentiated ESCs, or the embryoid bodies (EBs), using the ImProm-II cDNA Synthesis Kit (Promega, Tokyo, http://www.promega.com). As negative controls, 1 µg of the poly(A)+ RNA was allowed to react with the cDNA synthesis reaction mixture in the absence of the ImProm-II RT. After cDNA synthesis, 1/20 of the cDNA synthesis reaction mixture was used as the template for the PCR. For RT-PCR analysis of fresh ICMs, ICMs were obtained from seven blastocysts and used for poly(A)+ RNA isolation. Half of the isolated poly(A)+ RNA was then used for first-strand cDNA synthesis, and the other half was used as a negative control, as described above.
Individual primers were designed for the target genes. The following (forward and reverse) primer pairs were used: Nanog, 5'-A A ACAGA AGACCAGA ACTGTG -3' and 5'-AGTTGTTTTTCTGCCACCTCT-3'; Oct3/4, 5'- CCTGGGGGTTCTATTTGGGA-3' and 5'-T T T-GAATGCATGGGAGAGCC-3'; FoxD3, 5'-CGACGAC-GGGCTGGAGGAGAA-3' and 5'-ATGAGCGCGATGTAC-GAGTA-3'; Sox-2, 5'-AGAACCCCAAGATGCACAAC-3' and 5'-GGGCAGCGTGTACTTATCCT-3'; CD34, 5'-AGCCT-GTCACCTGGAAATGC-3' and 5'-CGTGTTGTCTTGCT-GAATGGC-3'; Nestin, 5'-GCCCTGACCACTCCAGTTTA-3' and 5'-GGAGTCCTGGATTTCCTTCC-3'; -fetoprotein, 5'-GCTGGATTGTCTGCAGGATGGGGAA-3' and 5'-TCCCCTGAAGAAAATTGGTTAAAAT-3'; marmoset chorionic gonadotropin (mCG) ß, 5'-CCCTGT-GTGTGTCGCCTTT-3' and 5'-CTAATGGAGGGTCT-GCTGGC-3'; Bex1/Rex3, 5'-ACAGGCAAGGATGAGA-GAAG-3' and 5'-CCCACGTAAACAAGTGACAG-3'; HEB, 5'-ACTGAAACAAAGAAAGGATGAAAACC-3' and 5'-CCCTTTCTATCTTCTGTTCAGGGTTC-3'; gp130, 5'-AAA-CAGAACAGCATCCAGTC-3' and 5'-AGTTGAGGCATCTTT-GGTCC-3'; leukemia inhibitory factor receptor (LIFR), 5'-TTTCTTGGCATTTACCAGG-3' and 5'-GCTATTTT-GGAAGGTGGTG-3'; ß-actin, 5'-TCCTGACCCTSAAG-TACCCC-3' and 5'-GTGGTGGTGAAGCTGTAGCC-3'. Except for CD34, -fetoprotein, and mCG, the expected sizes of the PCR products were estimated from human sequences. The expected PCR products were ~190 bp (nanog), ~530 bp (oct3/4), ~200 bp (Sox-2), ~356 bp (FoxD3), ~200 bp (nestin), 627 bp (CD34), 200 bp (-fetoprotein), ~559 bp (gp130), ~269 bp (Bex1/Rex3), ~165 bp (HEB), 286 bp (mCG), ~514 bp (LIFR), and 418 bp (ß-actin). The PCR reaction mixture (25 µl) contained x1 PCR buffer (10 mM Tris-HCl [pH 9.0], 1.5 mM MgCl2, 50 mM KCl), 0.2 mM dNTP, 0.5 µM of each primer, and 2.5 U Taq polymerase. The amplification was performed for 35 cycles of denaturation at 95°C for 1 minute, annealing at 60°C for 30 seconds, and elongation at 72°C. Representative RT-PCR products for each gene were verified by DNA sequencing (data not shown).
Analysis of Differentiation Potency
EB Formation To study EB formation, undifferentiated ESCs were removed from the MEF feeder layer, dissociated using 0.25% trypsin in PBS with 20% KSR and 1 mM CaCl2, and cultured in bacterial Petri dishes for 10–21 days using DMEM supplemented with 10% FBS. The medium was changed every 2 days.
In Vivo Differentiation Analysis: Teratoma Formation
To examine teratoma formation in mice, between 1–5 x 106 CMESCs were injected subcutaneously into the abdomen of 5-week-old immunodeficient mice, NOD/shiscid, IL-2Rnull (NOG) mice [11]. Four to eight weeks after the injection, tumors were resected from the mice. The resected tumors were fixed in buffered formaldehyde, embedded in paraffin blocks, and subjected to immunohistochemical and histological examinations.
In Vitro Differentiation
Neural Cells
Stromal PA6 cells were plated on 12-mm coverslips and grown to semiconfluence. On day 0, 5 x 104 ESCs were cocultured with the PA6 cells on coverslips in Glasgow’s modified Eagle’s medium (GMEM) supplemented with 10% KSR, 0.1 mM 2-ME, and 10–7 M ascorbate. For the first 10 days of coculture, the medium was changed every 2 days. On day 12, the medium was exchanged for GMEM plus N-2 supplement (Invitrogen) that contained 0.1 mM 2-ME and 10–7 M ascorbate, and the culture was continued until day 20. The cells were then fixed with 4% paraformaldehyde in PBS.
Hematopoietic Cells
CMESCs were differentiated into hematopoietic cells by EB formation in Iscove’s modified Dulbecco’s medium (Invitrogen) that contained 15% FBS, 200 µg/ml transferrin, 10 µg/ml insulin, 50 µg/ml ascorbic acid, and 0.45 mM monothioglycerol. The CMESCs (104 cells per 9-cm dish) were cultured without cytokines for 14–18 days and then subjected to hematopoietic colony assays. Hematopoietic colonies were examined by growing differentiated ESC-derived cells (105 cells) in Methocult GF+ medium (StemCell Technologies, Vancouver, British Columbia, Canada, http://www.stemcell.com) according to the manufacturer’s instructions. After 10–14 days, the colony-forming units (CFU) were counted, and cellular morphology was confirmed microscopically using May-Giemsa staining of cytospun samples.
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RESULTS |
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administration. Our ovarian cycle control system made it possible to obtain fertilized eggs every 3 weeks from the same animals. Sixty immunosurgically isolated ICMs from 70 blastocysts (the ICM isolation rate was 85.7%) were plated on the irradiated MEF feeder layer, and 11 ICMs were cultured for more than 10 passages (18.3% derivation rate). To date, 3/11 ICM-derived cells have been cultured for more than 1 year. All ICM-derived cells showed flat, packed, and tight colony morphology and a high nucleus:cytoplasm ratio (Figs. 1A, 1B
). The morphology of these derived cells was very similar to that of reported primate ESCs, including those from humans and from rhesus and cynomolgus monkeys [12–16]. It has been reported that primate ESCs exhibit spontaneous differentiation during culture and that leukemia inhibitory factor does not maintain the ESCs in the undifferentiated state [13, 14]. The common marmoset ICM-derived cell lines also showed low frequency of differentiation. However, most ICM-derived cells maintained undifferentiated morphology of the cells. It is known that the quality of FBS is critical to the maintenance of undifferentiated primate ESCs; different lots of FBS from the same manufacturer can vary in this respect. Therefore, the chemically defined serum-free supplement KSR was used for the establishment and culture of the marmoset ESCs. The CMESC colonies appeared more packed and tight when KSR was used in the culture; they were flatter in appearance when FBS was used in the medium. To maintain stem cells, the dissociation procedure for cynomolgus ESCs was adopted for subculture of the marmoset ICM-derived cells [14]. With this culture system, continuous cultures of CMESCs have been sustained for more than 1 year.
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, the ICM-derived cell lines showed alkaline phosphatase activity (Fig. 1C) and expressed SSEA-3 (Fig. 1E), SSEA-4 (Fig. 1F), TRA-1-60 (Fig. 1G), and TRA-1-81 (Fig. 1H) but not SSEA-1 (Fig. 1D). All three cell lines retained the normal 46, XX karyotype (Fig. 2) and telomerase (Fig. 3A) activity. These three ICM-derived cell lines also expressed Nanog, Oct3/4, Sox2, gp130, mCG, HEB, and Bex1/Rex3 mRNA and low levels of FoxD3 and Nestin mRNA (Fig. 4A). Conversely, LIFR mRNA was not detected by RT-PCR. All three lines showed identical expression patterns of the genes. Therefore, we believe that these cells are CMESCs. To compare the gene expression patterns of fresh ICMs and the ICM-derived cell lines, RT-PCR analysis was conducted using fresh ICMs. As a result, the expression of Nanog, Oct3/4, and Sox2 mRNA was observed, whereas FoxD3 and Nestin mRNA was not detected in fresh ICMs (Fig. 4B).
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, the three CMESC lines were confirmed, based on different SSCP patterns, as having been established independently. Of these three CMESC lines, nos. 30 and 40 were derived from the same parents.
Differentiation Potency
Similar to other primate ESCs, CMESCs differentiate spontaneously during culturing on MEF feeder layer. However, the complete differentiation of CMESCs was suppressed by some growth factors or inhibitory factors from MEF feeder layer. To estimate the degree of differentiation, 50 CMESC clusters were seeded onto MEF feeder layer. As a result, 22%–74% (n = 6) of the colonies (average 42.6%) were morphologically undifferentiated ESCs (data not shown). However, the differentiation rate of each cell was unclear because CMESCs need to be cell clusters to maintain undifferentiated status.
To assess the spontaneous differentiation potency of CMESCs, the formation of EBs and teratomas was examined. The suspension cultures of all three CMESC lines formed EBs (Figs. 5A, 5B). Simple EBs formed several days after the start of the suspension culture, and cystic EBs formed within 2 weeks. These EBs expressed mRNA for the Nestin, CD34, and -fetoprotein genes, which are marker genes for the three germ layers, and mCG, Bex1/Rex3, and Heb, which are marker genes for trophectoderm (Fig. 4A). Furthermore, expression of LIFR and gp130 was observed. However, Nanog, Oct3/4, and Sox2 gene expression was shut off after 2 weeks of EB culture. In contrast, the expression level of FoxD3 in EBs was greater than in undifferentiated CMESCs. To examine the differentiation potency in more detail, cells of CMESC 20 were injected subcutaneously into five immunodeficient NOG mice [11]. Eight weeks after injection, subcutaneous tumors were rescued from these mice and subjected to histological analysis. The tumor formation rate was 100% (5/5). The tumors were found to be teratomas that consisted of embryonic germ layers of ectodermal, mesodermal, and endodermal tissues (Figs. 6A–6M). Teratomas formed in all five NOG mice (100% teratoma formation rate). In the teratomas, the ectodermal tissue consisted of keratinized epidermis (Figs. 6B, 6G, and 7F) and neuronal cells (Fig. 6M); the mesodermal tissue was comprised of muscle (Figs. 6C, 6H) and blood vessels (Figs. 6I, 6J), and the endodermal tissue contained columnar epithelium (Figs. 6A, 6K, and 6L). Furthermore, cartilage-like tissue (Figs. 6A, 6D, and 6E) and adipose-like tissue (Fig. 6D) were also observed. These blood vessels were distinguished from murine blood vessels by immunohistochemical staining with human anti-CD31 antibody. Bronchus-like structures and gut-like structures were occasionally found in the teratomas (Figs. 6A, 6K, and 6L). Differentiation was confirmed by immunohistochemical analysis with several tissue-specific antibodies. As evidence for ESC differentiation into ectodermal cells, the GFAP-positive cells were observed as neuronal cells (Fig. 6M), and the keratinized epidermis-like structures in the teratomas expressed WSS keratin (Fig. 6G). The teratomas differentiated frequently into mesodermal tissues such as muscle, blood vessels, and cartilage. The muscle-like structure showed desmin expression, and CD31-positive cells were located in the hemangioendothelium of the blood vessel–like structures (Fig. 6J). The presence of the gut-like structures suggests endodermal differentiation. Alcian blue and periodic acid-Schiff (PAS) staining revealed mucus secretion from the columnar epithelium (Fig. 6L).
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). SDIA has been reported to induce the production of tyrosine hydroxylase (TH)–positive dopaminergic neurons in mouse and cynomolgus monkey ESCs and hESCs [17–19]. Therefore, we tested the marmoset cells for similar activities. After 2 weeks of induction, 14% of the class III ß-tubulin–positive postmitotic neurons were TH-positive at the cellular level (n = 50). These cells were plated from trypsinized ESCs at passage. Most of the cells were derived from single cells, but only 15% of them expressed the TH protein. In the teratoma-like tumor induced by subcutaneous transplantation into NOG mice, some III ß-tubulin–positive cells were found in colonies. Among III ß-tublin–positive neurons, TH-positive neurons were found in 21% of them (n = 113; data not shown).
To induce hematopoietic cells, EB formation was allowed to proceed in the cytokine-free medium, and CFU assays were performed. CFU-M (CFU-monocyte/macrophage) colonies were mainly observed under these conditions (Fig. 8A), and the main population of macrophages was confirmed microscopically using May-Giemsa staining of cytospun preparations (Fig. 8B).
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DISCUSSION |
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analogue cloprostenol. Thus, embryo collection from the same animal was carried out routinely, every 3 weeks, using cloprostenol administration. Using our embryo collection system, we recently established CMESC lines. In this study, we used a reported method of immunosurgery [9]. Although there was a high ICM isolation rate (85.7%) from blastocysts, the CMESC derivation rate was 18.3%, which is comparable to previous reports on other primate ESC lines, including 35.7% for human and 12.5% for cynomolgus monkey [14, 15]. The derivation rate of CMESC lines was considered to be dependent on the expansion procedure used for the cultured ICMs, including the in vitro developmental ability of embryos or the passage technique used for expanded ICMs. The results of immunohistochemical analysis, enzymatic activity assays, RT-PCR analysis, and karyotype analysis show that the CMESC lines maintain their undifferentiated status. The RT-PCR results indicate that the gene expression patterns of undifferentiated CMESCs are similar to that of hESCs and different from those of mouse ESCs. In undifferentiated CMESCs, the expression patterns of Oct3/4, Nanog, Sox2, mCG, HEB, and Bex1/REX3 gene mRNA were identical to hESCs or marmoset ESCs [6, 20]. In contrast, a very low level of FoxD3 expression was observed in undifferentiated CMESCs. In fresh ICMs, the expression of Nanog, Oct3/4, and Sox2 was observed, whereas that of FoxD3 and Nestin was not. The presence of Nanog, Oct3/4, and Sox2 mRNA expression in both fresh ICMs and CMESCs suggests that these genes are required to maintain stemness of cells in vitro and in vivo. Because FoxD3 and Nestin were expressed at very low levels in undifferentiated CMESCs, it is possible that these genes in fresh ICMs are expressed under the detection level of our RT-PCR analysis. Another possibility is that the FoxD3 and Nestin genes were amplified from spontaneously differentiated CMESCs in the cultured CMESCs. The latter possibility is supported by increased FoxD3 gene expression in EBs. As the FoxD3 gene expressed in murine undifferentiated ESCs [20], the different FoxD3 expression patterns in primate and murine ESCs suggests that FoxD3 plays a different role in respective ESCs. The expression of mCG and Bex1/REX3 reflects the ability of CMESCs to differentiate into trophectodermal cells. These results match the ability of other primate ESCs to differentiate into trophectodermal cells.
The molecular mechanisms that maintain undifferentiated primate ESCs are largely unknown, and MEF feeder layer is essential to maintain undifferentiated primate ESCs. CMESCs also differentiated spontaneously on MEF feeder layer at low frequency. The expression of gp130 and the absence of LIFR in CMESCs were identical to hESCs. These results indicate that maintaining undifferentiated CMESCs is not dependent on LIF signals. However, the expression of gp130 suggested that other gp130-STAT3 signals, such as interleukin (IL)-6, oncostatin M, or IL-11, play a role in CMESC proliferation or differentiation. The MEF feeder layer dependency of primate ESCs is considered one significant obstacle to using hESCs for stem therapy. Elucidation of the molecular mechanisms for the maintenance or development of MEF feeder layer–free culture systems of undifferentiated primate ESCs is one of the important themes of ESC research. Combined, these results suggest that the cellular characteristics and activities of CMESCs are similar to those of human and other primate ESCs [6, 12–16, 21, 22].
The spontaneous differentiation abilities of the CMESCs were verified by EB formation (Fig. 5) and teratoma formation (Fig. 6). RT-PCR analysis of EBs showed that the CMESCs differentiated into three germ layers in vitro. Furthermore, when the CMESCs were transplanted subcutaneously into immunodeficient NOG mice, teratomas that consisted of three-dimensional tissue structures were formed with high efficiency (100%). When SCID mice were used for the teratoma formation experiment, the teratoma formation rate was also 100% (two of two NOD/SCID mice, data not shown). Therefore, the formation of teratomas indicates that CMESCs have multipotent differentiation ability. The teratomas were also examined by immunohistochemistry, using several tissue-specific antibodies. The most frequently observed tissue type in the teratomas was mesodermal, which included cartilage (Figs. 6A, 6D, and 6E), muscle (Figs. 6C, 6H), and blood vessels (Fig. 6I). Although the frequency of endodermal tissue differentiation was lower than the frequencies of ectodermal and mesodermal tissue differentiation, endodermal tissue differentiation was clearly demonstrated with one of our CMESC lines (no. 20). Interestingly, Alcian blue and PAS staining of columnar epithelium showed the secretion of mucus from the cells, which indicates that CMESCs can differentiate into functional endodermal cells (Fig. 6L). Teratoma formation was not demonstrated for the marmoset ESC line (cj 11) established by Thomson et al. [6]. Both CMESC and cj 11 showed similar morphology and identical marker expression patterns. However, when we examined teratoma formation with a marmoset ESC line purchased from the WiCell Research Institute, Inc. (Madison, WI, http://www.wicell.org), we obtained fibrosarcomas, but no teratomas, in NOD/SCID mice (data not shown). The reasons for successful in vivo teratoma formation with our ESCs remain to be elucidated.
SDIA caused CMESC lines 20 and 40 to differentiate into TH-positive neurons in vitro (Fig. 7). In vitro differentiation into hematopoietic cells from EBs was measured in colony assays. Although other types of hematopoietic colonies were not seen in all experiments (n > 7), other conditions, such as gene-transfer methods, make it possible to induce various hematopoietic colonies from CMESCs (Kurita et al., personal communication), which suggests that CMESCs have the ability to differentiate into multiple hematopoietic lineages. These results support our finding that CMESCs have the capacity to differentiate into functional cells both in vitro and in vivo. Therefore, CMESCs can be used in preclinical studies aimed at developing regenerative medicines.
In this study, the teratoma formation and in vitro differentiation experiments show the strong differentiating potency of our CMESC lines; in addition, this is the first report to demonstrate the pluripotency of CMESCs. Our pluripotent CMESC lines should be very useful in establishing a preclinical animal model system for predicting the safety and efficacy of regenerative therapies using hESCs. Chimerism and the germ line transmission ability of CMESCs are not yet known. The mechanisms of the germ line transmission of ESCs are unknown, and in primates and other mammals, except mice, germ line transmission of ESCs has not been reported. Therefore, it is possible that germ line transmission of CMESCs will not occur in chimeras. If CMESCs do not transmit into the germ line, somatic cell nuclear transfer from the chimera or gametogenesis from CMESCs is one way to solve the problem [23–25].
Recently, various types of cells differentiated from hESCs or nonhuman ESCs have been reported [18, 26–36]. For example, hematopoietic cells, dopaminergic neurons, and insulin-producing cells have been generated from hESCs or primate ESCs. However, reports of transplantation of these differentiated ESCs into nonhuman primates are very rare [37]. There are various difficulties involved in using nonhuman primates as experimental animals. For example, rhesus or cynomolgus monkeys in which the ESC line has already been established are too expensive and cumbersome. Furthermore, immunological incompatibility between ESCs and animals may represent a significant obstacle to ESC transplantation. Taking this situation into consideration, the common marmoset has advantages, such as low cost and ease of maintenance. Importantly, marmosets are immunogenetically closed because they have been bred in large closed colonies. Thus, the common marmoset and CMESCs provide an excellent experimental model system for studies into the mechanism of cell differentiation, as well as for the development of regenerative therapies using hESCs.
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ACKNOWLEDGMENTS |
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DISCLOSURES
The authors indicate no potential conflicts of interest.
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