3.1 Introduction
3.1.1 Differentiation potential of stem cells
One of definitions of stem cells is multidifferentiation potential. Also the degree of their stemness is determined by their differentiation potential. According to results of section 2, sphere forming cells expressed pluripotent cell markers. Therefore in this section, we aimed to confirm their differentiation potential in vivo and in vitro.
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3.2 Experimental<→Experiment>
3.2.1 In vitro Differentiation Assays.
In vitro differentiation assays were examined following the published differentiation culture conditions for murin ES cells.
Mesoderm lineage differentiation assay. Dissociated muscle cells were stained with anti-αmooth muscle actin antibody, anti-Myosin antibody and anti-Desmin antibody. Chondrocyte were stained with Safranin-0 and Fast Green. Osteocytes were stained with ALIZARIN RED S. After 21 days, adipocytes were stained with Oil Re 0.
Ectoderm lineage (Neural lineage) differentiation assay. Cells were plated on ortinin-coated chamber slides and incubated with anti-βIII Tubuin mouse monoclonal, anti-O4 mouse monoclonal antibody and anti-GFAP mouse monoclonal antibody.
Endoderm lineage (Hepatic) differentiation assay. Differentiated cells were detected by immunohistochemistory using anti-αfetoprotein mouse monoclonal antibody, anti-Albumin goat polyclonal antibody and anti-Cytokeratin 18 mouse monoclonal antibody. Results from immunohistochemistry were confirmed by RT-PCR.
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3.2.2 In Vivo Differentiation.
Spheres were seeded onto biodegradable scaffolds and implanted into subcutaneous of NOD/SCID mice (Charles River laboratories). After 6 weeks, the implants were harvested and fixed with 10% formaldehyde, then examined by immunocytochemistry.
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3.3Results
3.3.1 Differentiation potential of cells in vitro
When representative bone marrow derived spheres were dissociated into single cells and exposed to three different differentiation media, the cells differentiated to express specific genes of the three lineages, Map2 (ectoderm), MyoD (mesoderm) and alpha-fetoprotein (AFP, endoderm) (Fig. 10).The addition of a neural differentiation medium to the in vitro environment of cells from bone marrow spheres, resulted in expression of pIII tubulin (a marker for neuron) (Fig. 11).
Alternatively, the addition of 20% fetal calf serum to the media resulted in the expression of markers representative of mesoderm; that is, a-smooth muscle actin (Fig. 11) as well as the mesenchymal cells, chondrocytes, osteocytes and adipocytes (Fig. 12). Thus, cells from spheres differentiated into all cell types of neural (neurons, oligodendrocytes and ghas) and mesenchymal stem cell lineage (chondrocytes, osteocytes and adipocytes). When exposed to a hepatocyte differentiation media the expression of a-fetoprotein (Fig. 11), was seen, suggestive of differentiation into endodermal tissue.
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3.3.2 Differentiation potential in vivo.
Bone marrow spheres and ES cells were transplanted subcutaneously into immune deficient mice to examine their tumor-initiating capacity. As a result, after 6 weeks ES cells formed a tumor. Spheres did not form tumor as big as ES cells did. We concluded that the proliferative potential of sphere cells was much weaker than that of ES cells (Fig. 13).
Next, we investigated if transplanted cells differentiated in vivo after transplantation. Transplanted cells were harvested after 6 weeks, and processed for immunohistochemical analyses. According to results of immunohistochemical analyses, spheres differentiated into tissues derived from three germ layers in vivo (Fig. 14).
3.3.2 生体内分化能<訳注:目次では3.3.2 Differentiation potential of cells in vivoとなっているので、小保方さんがいろいろと編集中であることがわかる。これを見て草稿だと気づけない頭というのもどうなのか。>
骨髄のスフィア及びES細胞が、それらの腫瘍形成能力を調べるために、免疫欠損マウスに皮下移植された。その結果、6週間後にES細胞は腫瘍を形成した。我々はスフィア細胞の増殖能がES細胞よりもはるかに弱かったと結論付けた（図13）。
次に我々は移植された細胞が移植後に生体内で分化するかどうかを調査した。移植された細胞は6週間後に回収され、免疫組織化学的分析に供された。免疫組織化学的分析の結果によると、スフィアは生体内で三胚葉に由来した組織に分化した（図14）。
