Patent Publication Number: US-2022235331-A1

Title: Production method and kit of induced pluripotent stem cells

Description:
TECHNICAL FIELD 
     The present invention relates to a production method and a kit of induced pluripotent stem cells. Priority is claimed on Japanese Patent Application No. 2019-078907, filed Apr. 17, 2019, the content of which is incorporated herein by reference. 
     BACKGROUND ART 
     The technique for establishing iPS cells from human and mouse somatic cells has been improved and simplified, and the efficiency for establishing iPS cells has been increased as compared with that of the conventional techniques. Meanwhile, animals (pluripotency induction-resistant animals) for which establishing iPS cells from adult somatic cells is particularly difficult are present. As the pluripotency induction-resistant animals, dogs, pigs, marmosets, cats, cows, horses, and the like are known. 
     For example, canine iPS cells can be established by persistently expressing a reprogramming factor in canine fetus-derived fibroblasts (refer to, for example, Non Patent Document 1). In addition, canine iPS cells can be established from canine fetus-derived fibroblasts by using Sendai virus (refer to, for example, Non Patent Document 2). In addition, porcine iPS cells can be established by persistently expressing a reprogramming factor in porcine fetus-derived fibroblasts (refer to, for example, Non Patent Document 3). 
     CITATION LIST 
     Non Patent Document 1: Nishimura T et al., Feeder-independent canine induced pluripotent stem cells maintained under serum-free conditions. Mol. Reprod. Dev., Vol. 84, 329-339, 2017. 
     Non Patent Document 2: Tsukamoto M et al., Generation of Footprint-Free Canine Induced Pluripotent Stem Cells Using Auto-Erasable Sendai Virus Vector. Stem Cells Dev., 27, 1577-1586, 2018. 
     Non Patent Document 3: Du X et al., Barriers for Deriving Transgene-Free Pig iPS Cells with Episomal Vectors. Stem Cells, Vol. 33, 3228-3238, 2015. 
     SUMMARY OF INVENTION 
     An object of the present invention is to provide a new technique for establishing iPS cells from mammalian somatic cells. 
     The present invention includes the following aspects: 
     [1] A production method of induced pluripotent stem cells, the method including: a step of introducing a reprogramming factor into mammalian somatic cells and culturing the mammalian somatic cells in a neural stem cell culture medium to obtain induced neural stem cell-like cells; and a step of culturing the induced neural stem cell-like cells in a growth medium to obtain induced pluripotent stem cells, in which the reprogramming factor includes an OCT family, a SOX family, a KLF family, a MYC family, a LIN28 family, and a P53 function-inhibiting substance. 
     [2] The production method of induced pluripotent stem cells according to [1], in which the reprogramming factor further includes one or more selected from the group consisting of a KDM family, a GLIS family, and NANOG. 
     [3] The production method according to [1] or [2], in which the somatic cells are derived from an adult. 
     [4] The production method according to any one of [1] to [3], in which the neural stem cell culture medium contains a MAP kinase inhibitor, a GSK3β inhibitor, and a TGFβ inhibitor. 
     [5] The production method according to any one of [1] to [4], in which the growth medium contains bFGF. 
     [6] Induced pluripotent stem cells produced by the production method according to any one of [1] to [5]. 
     [7] A kit for producing induced pluripotent stem cells from somatic cells of a pluripotency induction-resistant animal, the kit including: a reprogramming factor including an OCT family, a SOX family, a KLF family, a MYC family, a LIN28 family, and a P53 function-inhibiting substance; and a neural stem cell culture medium containing a MAP kinase inhibitor, a GSK3β inhibitor, and a TGFβ inhibitor. 
     [8] The kit according to [7], in which the reprogramming factor the reprogramming factor further includes one or more selected from the group consisting of a KDM family, a GLIS family, and NANOG. 
     [9] The kit according to [7] or [8], further including a growth medium containing bFGF. 
     Advantageous Effects of Invention 
     According to the present invention, it is possible to provide a new technique for establishing iPS cells from mammalian somatic cells. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a diagram schematically showing an EP-A vector set for expressing a reprogramming factor. 
         FIG. 2  is a diagram schematically showing an EP-B vector set for expressing a reprogramming factor. 
         FIGS. 3( a ) and 3( b )  are photographs of cells in Experimental Example 1.  FIG. 3( a )  is a photograph obtained by imaging cells, into which the EP-A vector set was introduced and which were cultured in a growth medium for 4 days, in a bright field.  FIG. 3( b )  is a photograph obtained by imaging fluorescence of EGFP of cells into which the EP-A vector set was introduced and which were cultured in a growth medium for 4 days. 
         FIGS. 4( a ) and 4( b )  are photographs of cells in Experimental Example 1.  FIG. 4( a )  is a photograph of cells in which the EP-A vector set was introduced into E01F and which were cultured in a growth medium for 30 days.  FIG. 4( b )  is a photograph of cells in which the EP-A vector set was introduced into E02M and which were cultured in a growth medium for 30 days. 
         FIG. 5  is a diagram showing a process for establishing iPS cells from marmoset somatic cells. 
         FIGS. 6( a ) to 6( d )  are photographs of iNSL cells in Experimental Example 2.  FIG. 6( a )  is a photograph of a colony formed by introducing the EP-A vector set into E01F and then culturing in a neural stem cell culture medium.  FIG. 6( b )  is a photograph of a colony formed by introducing the EP-B vector set into E01F and then culturing in a neural stem cell culture medium.  FIG. 6( c )  is a photograph of a colony formed by introducing the EP-A vector set into E02M and then culturing in a neural stem cell culture medium.  FIG. 6( d )  is a photograph of a colony formed by introducing the EP-B vector set into E02M and then culturing in a neural stem cell culture medium. 
         FIG. 7  is a graph showing the results of calculating a colony forming ability when marmoset embryonic fibroblasts were used in Experimental Example 2. 
         FIGS. 8( a ) and 8( b )  are diagrams showing the results of staining with alkaline phosphatase in Experimental Example 2.  FIG. 8( a )  is a diagram showing the results of staining, with alkaline phosphatase, a colony obtained by introducing the EP-A vector set into E01F and culturing in a neural stem cell culture medium.  FIG. 8( b )  is a diagram showing the results of staining, with alkaline phosphatase, a colony obtained by introducing the EP-B vector set into E01F and culturing in a neural stem cell culture medium. 
         FIG. 9  shows photographs of iNSL cells and iPS cells in Experimental Example 3.  FIG. 9( a )  is a photograph of a colony formed by introducing the EP-A vector set into marmoset embryonic fibroblasts (E01F) and culturing in a neural stem cell culture medium.  FIG. 9( b )  is a photograph of a colony formed by introducing the EP-A vector set into marmoset embryonic fibroblasts (E01F), culturing in a neural stem cell culture medium, and then culturing in a growth medium.  FIG. 9( c )  is a photograph of a colony formed by introducing the EP-B vector set into marmoset embryonic fibroblasts (E02M) and culturing in a neural stem cell culture medium.  FIG. 9( d )  is a photograph of a colony formed by introducing the EP-B vector set into marmoset embryonic fibroblasts (E02M), culturing in a neural stem cell culture medium, and then culturing in a growth medium. 
         FIG. 10  shows diagrams showing the results of analyzing the expression of ES cell markers in marmoset iPS cells in Experimental Example 3. 
         FIG. 11  shows diagrams showing the results of subjecting marmoset iPS cells to alkaline phosphatase staining in Experimental Example 3. 
         FIG. 12  shows diagrams showing the results of analyzing the expression of ES cell markers in marmoset iPS cells in Experimental Example 3. 
         FIG. 13  shows diagrams showing the results of analyzing the expression of ES cell markers in marmoset iPS cells in Experimental Example 3. 
         FIG. 14  shows diagrams showing the results of analyzing the expression of ES cell markers in marmoset iPS cells in Experimental Example 3. 
         FIG. 15  shows diagrams showing the results of analyzing the presence or absence of an expression vector in marmoset iPS cells in Experimental Example 3. 
         FIG. 16  shows diagrams showing the results of analyzing the expression of markers in three germ layers differentiated from marmoset iPS cells in Experimental Example 4. 
         FIG. 17  is a diagram showing the results of analyzing the expression of AFP expressed by marmoset iPS cells cultured in a KSR medium in Experimental Example 4. 
         FIG. 18  is a diagram showing the results of analyzing the expression of AFP expressed by marmoset iPS cells cultured in a medium containing FBS in Experimental Example 4. 
         FIG. 19  shows diagrams showing the results of analyzing teratomas formed from marmoset iPS cells in Experimental Example 4. 
         FIG. 20  shows photographs of iNSL cells derived from fibroblasts of an adult marmoset in Experimental Example 5. 
         FIG. 21  is a diagram showing the colony forming ability of iNSL cells derived from fibroblasts of an adult marmoset in Experimental Example 5. 
         FIG. 22  shows diagrams showing the results of alkaline phosphatase staining of iNSL cells derived from fibroblasts of an adult marmoset in Experimental Example 5. 
         FIG. 23  shows photographs of colonies of marmoset iPS cells derived from fibroblasts of an adult marmoset in Experimental Example 5. 
         FIG. 24  shows diagrams showing the results of alkaline phosphatase staining of iPS cells derived from fibroblasts of an adult marmoset in Experimental Example 5. 
         FIG. 25  shows diagrams showing the results of analyzing the expression of ES cell markers in marmoset iPS cells derived from fibroblasts of an adult marmoset in Experimental Example 5. 
         FIG. 26  is a diagram showing the results of analyzing the expression of ES cell markers in marmoset iPS cells derived from fibroblasts of an adult marmoset in Experimental Example 5. 
         FIG. 27  is a diagram showing the results of analyzing the expression of ES cell markers in marmoset iPS cells derived from fibroblasts of an adult marmoset in Experimental Example 5. 
         FIG. 28  is a diagram showing the results of analyzing the expression of ES cell markers in marmoset iPS cells derived from fibroblasts of an adult marmoset in Experimental Example 5. 
         FIG. 29  is a diagram showing the results of analyzing the expression of ES cell markers in marmoset iPS cells derived from fibroblasts of an adult marmoset in Experimental Example 5. 
         FIG. 30  shows diagrams showing the results of analyzing the expression of markers in three germ layers differentiated from marmoset iPS cells derived from fibroblasts of an adult marmoset in Experimental Example 5. 
         FIG. 31  shows diagrams showing the results of analyzing the expression of markers in three germ layers differentiated from marmoset iPS cells derived from fibroblasts of an adult marmoset in Experimental Example 5. 
         FIG. 32  shows diagrams showing the results of analyzing teratomas formed from marmoset iPS cells derived from fibroblasts of an adult marmoset in Experimental Example 5. 
         FIG. 33  is a diagram showing the results of analyzing whether or not a vector remains in marmoset iPS cells derived from fibroblasts of an adult marmoset in Experimental Example 5. 
         FIG. 34  shows photographs of marmoset iNSL cells in Experimental Example 6. 
         FIG. 35  shows diagrams showing the results of analyzing a vector remaining in marmoset iNSL cells in Experimental Example 6. 
         FIG. 36  is a diagram showing the results of analyzing the expression of endogenous OCT4, NANOG, SOX2, KLKF4, and ZFP42 in marmoset iNSL cells in Experimental Example 6. 
         FIG. 37  is a diagram showing the results of analyzing the expression of DPPA5 and TERT in marmoset iNSL cells in Experimental Example 6. 
         FIG. 38  is a diagram showing the results of analyzing the expression of endogenous and exogenous OCT4, NANOG, KLF4, and Lin28 in marmoset iNSL cells in Experimental Example 6. 
         FIG. 39  is a diagram showing the results of analyzing the expression of PAX6 in marmoset iNSL cells in Experimental Example 6. 
         FIG. 40  is a diagram showing the results of analyzing the expression of SOX1 and ZFP521 in marmoset iNSL cells in Experimental Example 6. 
         FIG. 41  is a diagram showing the results of analyzing the expression of T and SOX17 in marmoset iNSL cells in Experimental Example 6. 
         FIG. 42  is a schedule of neural differentiation assays in Experimental Example 6. 
         FIG. 43  shows diagrams showing the results of immunostaining of cells differentiated from the obtained induced neural stem cells with a Hoechst stain and an anti-βIII-tubulin antibody in Experimental Example 6. 
         FIG. 44  is a graph showing the proportion of cells in which the expression of βIII-tubulin was recognized among cells differentiated into nerve cells in Experimental Example 6. 
         FIG. 45  is a diagram showing the results of clustering analysis in Experimental Example 7. 
         FIG. 46  is a diagram showing the results of analyzing the gene expression level in Experimental Example 7. 
         FIG. 47  is a diagram showing the results of principal component analysis in Experimental Example 7. 
         FIG. 48  shows photographs of colonies formed by canine iPS cells in Experimental Example 8. 
         FIG. 49  shows diagrams showing the results of analyzing the expression of OCT4, SOX2, and NANOG in canine iPS cells in Experimental Example 8. 
         FIG. 50  shows photographs of teratomas formed from canine iPS cells in Experimental Example 8. 
         FIG. 51  shows diagrams showing the results of analyzing the bone, cartilage, nerve cells, retina, sebaceous gland, hair follicle epithelium, and glandular tissue in teratomas formed from canine iPS cells in Experimental Example 8. 
         FIG. 52  shows diagrams showing the results of analyzing whether or not a vector remains in canine iPS cells in Experimental Example 8. 
         FIG. 53  is a photograph of a colony of porcine iPS cells in Experimental Example 9. 
         FIG. 54  shows diagrams showing the results of analyzing the expression of OCT4, SOX2, and NANOG in porcine iNSL cells and porcine iPS cells in Experimental Example 9. 
         FIG. 55  is a photograph of a colony of ferret iPS cells in Experimental Example 10. 
         FIG. 56  shows diagrams showing the results of analyzing the expression of OCT4, SOX2, and NANOG in ferret iNSL cells and ferret iPS cells in Experimental Example 10. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Notation of Gene Name and Protein Name 
     In the present specification, human genes and human proteins, and genes and proteins of pluripotency induction-resistant animals are represented by uppercase alphabets. However, in some cases, human genes and genes of other species may be represented by uppercase alphabets without strict distinction. In addition, human proteins and proteins of other species may be represented by uppercase alphabets without strict distinction. 
     In the present specification, for example, the notation “SOX2” means both the SOX2 protein and the nucleic acid encoding it. In addition, for example, the notation “reprogramming factor” means both the reprogramming protein and the nucleic acid encoding it. In addition, for example, the notation “SOX family” means both the SOX protein and the nucleic acid encoding it. 
     Notation of Cell Name 
     In the present specification, induced pluripotent stem cells may be referred to as iPS cells or iPSCs. In addition, induced neural stem cell-like cells may be referred to as iNSL cells or iNSLCs. 
     Production Method 
     In one embodiment, the present invention provides a production method of induced pluripotent stem cells, the method including: a step (a) of introducing a reprogramming factor into mammalian somatic cells and culturing the mammalian somatic cells in a neural stem cell culture medium to obtain induced neural stem cell-like cells; and a step (b) of culturing the induced neural stem cell-like cells in a growth medium to obtain induced pluripotent stem cells, in which the reprogramming factor includes an OCT family, a SOX family, a KLF family, a MYC family, a LIN28 family, and a P53 function-inhibiting substance. In the present embodiment, the mammal may be a pluripotency induction-resistant animal. 
     In the present specification, the pluripotency induction-resistant animal refers to a mammal that cannot establish iPS cells even when the reprogramming factors of an OCT family, a SOX family, a KLF family, and a MYC family are expressed in combination in somatic cells of the adult pluripotency induction-resistant animal. 
     Examples of the pluripotency induction-resistant animal include, but are not limited to, monkeys, pigs, ferrets, sheep, cats, dogs, horses, cows, goats, and rabbits. Examples of monkeys include marmosets. 
     In the present embodiment, examples of somatic cells of the pluripotency induction-resistant animal which are as a material for producing iPS cells include fetus-derived somatic cells and adult-derived somatic cells. Examples of somatic cells include fat cells, cartilage cells, osteoblasts, bone cells, muscle cells, vascular cells, immune cells, epithelial cells, nerve cells, liver cells, pancreatic cells, and precursor cells thereof. The above-mentioned somatic cells may be undifferentiated cells or differentiated cells. 
     Marmosets, dogs, pigs, and ferrets are typical pluripotency induction-resistant animals. As will be described later in Examples, iPS cells, which do not have an expression construct expressing a reprogramming factor within the cells, can be established by transiently expressing the reprogramming factor intracellularly from somatic cells of adult marmosets, dogs, pigs, and ferrets by the production method of the present embodiment. 
     In the present embodiment, it is preferable to introduce a non-episomal vector having a nucleic acid encoding EBNA-1 into mammalian somatic cells together with the reprogramming factor. 
     Reprogramming Factor 
     In the present embodiment, the reprogramming factor includes an OCT family, a SOX family, a KLF family, an MYC family, a LIN28 family, and a P53 function-inhibiting substance. 
     Examples of the OCT family include OCT3/4, OCT1, OCT2, and OCT6. As the OCT family, OCT3/4 is preferable. 
     Examples of the SOX family include SOX2, SOX1, SOX3, SOX15, and SOX17. 
     Examples of the KLF family include KLF1, KLF2, KLF4, and KLF5. 
     Examples of the MYC family include C-MYC, N-MYC, and L-MYC. 
     Examples of the LIN28 family include LIN28 and LIN28B. 
     NANOG is a transcription factor having a homeodomain. When NANOG is expressed in somatic cells together with OCT4, SOX2, and LIN28, it is possible to establish iPS cells (refer to, for example, Yu J et al., Science, 318, 1917-1920 (2007)). 
     In the present specification, the P53 function-inhibiting substance may be any substance as long as it is a substance suppressing the function of P53 protein or a substance suppressing the expression of a P53 gene (for example, PCT International Publication No. WO2009/157593). 
     Examples of the substance suppressing the function of P53 protein include dominant negative mutants of P53, chemical substances that inhibit the function of P53 protein, anti-P53 antagonist antibodies, decoy nucleic acids containing a consensus sequence of P53 response elements, and P53 pathway-inhibiting substances. Examples of the substance suppressing the expression of a P53 gene include siRNA and shRNA for P53. 
     As the dominant negative mutant of P53, P53DD in which the amino acid at the positions 14 to 301 of mouse P53 (corresponding to the positions 11 to 304 in human P53) is deleted is preferable (refer to, for example, Bowman, T., Genes &amp; Development, 10, 826-835 (1996)). 
     The reprogramming factor may further include one or more selected from the group consisting of a KDM family, a GLIS family, and NANOG. 
     The reprogramming factor preferably includes the OCT family, the SOX family, the KLF family, the MYC family, the LIN28 family, the P53 function-inhibiting substance, the KDM family, the GLIS family, and NANOG. 
     The KDM family has Lysine Demethylase activity and demethylates K9 of histone H3. As the KDM family, KDM1, KDM2, KDM3, KDM4, KDM5, and KDM6 are known. Forced expression of KDM4D or KDM4A demethylates the 9th lysine residue of histone H3 and promotes reprogramming of somatic cells (refer to, for example, Matoba et al., Cell, 159, 884-895 (2014); Chung Y G et al., Cell Stem Cell, 17, 758-766 (2015)). 
     The KDM family used as the reprogramming factor is not particularly limited, and examples thereof include KDM1, KDM2, KDM3, KDM4, KDM5, and KDM6. As the KDM family, KDM4A and KDM4D are preferable. 
     The GLIS family (GLI Similar family) is a zinc finger-type transcription factor. As the GLIS family, GLIS1, GLIS2, and GLIS3 are known. Forced expression of GLIS1 promotes the formation of iPS cells (refer to, for example, Maekawa et al., Nature, 474, 225-229 (2011)). In addition, GLIS1, GLIS2, and GLIS3 play various roles in stem cells (refer to, for example, Scoville D W et al., Stem Cell Investig, 4:80 (2017)). 
     The GLIS family used as the reprogramming factor is not particularly limited, and examples thereof include GLIS1, GLIS2, and GLIS3. As the GLIS family, GLIS1 is preferable. 
     The reprogramming factor may include an ESRR family. 
     The ESRR family (Estrogen-related receptor family) is a nuclear receptor. As the ESRR family, ESRRA, ESRRB, and ESRRG are known. When ESRRB or ESRRG is forcibly expressed together with OCT4 and SOX2, somatic cells can be reprogrammed (refer to, for example, Feng B et al., Nat. Cell. Biol., vol. 11, 197-203 (2009)). 
     The ESRR family used as the reprogramming factor is not particularly limited, and examples thereof include ESRRB and ESRRG. 
     Examples of combinations of the reprogramming factors include, but are not limited to, combinations exemplified in Table 1 as disclosed in PCT International Publication No. WO2015/056804. 
     
       
         
           
               
             
               
                 TABLE 1 
               
               
                   
               
               
                 Combination of reprogramming factors 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
            
               
                   
                 OCT3/4, KLF4, C-MYC 
               
               
                   
                 OCT3/4, KLF4, C-MYC, SOX2 
               
               
                   
                 OCT3/4, KLF4, SOX2 
               
               
                   
                 OCT3/4, SOX2, NANOG, LIN28 
               
               
                   
                 OCT3/4, KLF4, C-MYC, SOX2, NANOG, LIN28 
               
               
                   
                 OCT3/4, KLF4 
               
               
                   
                 OCT3/4, C-MYC 
               
               
                   
                 OCT3/4, SOX2 
               
               
                   
                 OCT3/4, SOX2, NANOG 
               
               
                   
                 OCT3/4, SOX2, LIN28 
               
               
                   
                 OCT3/4, SOX2, C-MYC, ESRRB 
               
               
                   
                 OCT3/4, SOX2, ESRRB 
               
               
                   
                 OCT3/4, KLF4, L-MYC 
               
               
                   
                 OCT3/4, NANOG 
               
               
                   
                 OCT3/4 
               
               
                   
                 OCT3/4, KLF4, C-MYC, SOX2, NANOG, LIN28 
               
               
                   
                 OCT3/4, SOX2, KLF4, L-MYC, LIN28 
               
               
                   
                 OCT3/4, SOX2, KLF4, L-MYC, LIN28, GLIS1 
               
               
                   
               
            
           
         
       
     
     The reprogramming factor may have a mutation as long as the reprogramming factor has the activity to reprogram pluripotency induction-resistant somatic cells. When the reprogramming factor has a mutation, the reprogramming factor preferably has 80% or more sequence identity, more preferable has 90% or more sequence identity, and further preferable has 95% or more sequence identity with respect to proteins or mRNAs specified by the NCBI accession numbers exemplified in Table 1. 
     The sequence identity of an amino acid sequence is a value indicating a proportion in which an amino acid sequence of a target (target amino acid sequence) matches an amino acid sequence as a reference (reference amino acid sequence). The sequence identity of a target amino acid sequence with respect to a reference amino acid sequence can be obtained as follows, for example. First, a reference amino acid sequence and a target amino acid sequence are aligned. Each amino acid sequence may contain a gap so as to maximize the sequence identity. Subsequently, the number of amino acids matched in the reference amino acid sequence and the target amino acid sequence can be calculated to obtain the sequence identity according to Formula (1). 
       Sequence identity (%)=number of amino acids matched/total number of amino acids in target amino acid sequence×100  (1)
 
     Similarly, the sequence identity of a target base sequence with respect to a reference base sequence can be obtained as follows, for example. First, a reference base sequence and a target base sequence are aligned. Each base sequence may contain a gap so as to maximize the sequence identity. Subsequently, the number of bases matched in the reference base sequence and the target base sequence can be calculated to obtain the sequence identity according to Formula (2). 
       Sequence identity (%)=number of bases matched/total number of bases in target base sequence×100  (2)
 
     In the present embodiment, the animal species from which the reprogramming factor is derived may be the same as or different from the animal species from which somatic cells into which the reprogramming factor is introduced are derived. Those skilled in the art can obtain the amino acid sequence or mRNA sequence of the reprogramming factor of the desired animal species from the database. 
     The reprogramming factor may be mRNA specified by the NCBI accession number exemplified in Table 2, a protein encoded by the mRNA, or a gene that transcribes the mRNA (refer to, for example, Japanese Patent No. 5098028, Japanese Patent No. 6381442, PCT International Publication No. WO2015/030111, and PCT International Publication No. WO2015/056804). The accession numbers shown in Table 1 are human cDNA sequences. 
     
       
         
           
               
               
               
             
               
                   
                 TABLE 2 
               
               
                   
                   
               
               
                   
                 Name 
                 Accession number 
               
               
                   
                   
               
             
            
               
                   
                 OCT3/4 
                 NM_002701 
               
               
                   
                 OCT1 
                 NM_002697 
               
               
                   
                 OCT2 
                 NM_002698 
               
               
                   
                 OCT6 
                 NM_002699 
               
               
                   
                 SOX2 
                 NM_003106 
               
               
                   
                 SOX1 
                 NM_005986 
               
               
                   
                 SOX3 
                 NM_005634 
               
               
                   
                 SOX15 
                 NM_006942 
               
               
                   
                 SOX17 
                 NM_022454 
               
               
                   
                 KLF1 
                 NM_006563 
               
               
                   
                 KLF4 
                 NM_004235 
               
               
                   
                 KLF2 
                 NM_016270 
               
               
                   
                 KLF5 
                 NM_001730 
               
               
                   
                 C-MYC 
                 NM_002467 
               
               
                   
                 N-MYC 
                 NM_005378 
               
               
                   
                 L-MYC 
                 NM_005376 
               
               
                   
                 LIN28 
                 NM_024674 
               
               
                   
                 LIN28B 
                 NM_001004317 
               
               
                   
                 KDM1 
                 NM_015013 
               
               
                   
                 KDM2 
                 NM_012308 
               
               
                   
                 KDM3 
                 NM_018433 
               
               
                   
                 KDM4A 
                 NM_014663 
               
               
                   
                 KDM4D 
                 NM_018039 
               
               
                   
                 KDM5 
                 NM_001042603 
               
               
                   
                 KDM6 
                 NM_001291415 
               
               
                   
                 GLIS1 
                 NM_147193 
               
               
                   
                 GLIS2 
                 NM_032575 
               
               
                   
                 GLIS3 
                 NM_001042413 
               
               
                   
                 NANOG 
                 NM_152676 
               
               
                   
                 ESRRB 
                 NM_004452 
               
               
                   
                 ESRRG 
                 NM_001438 
               
               
                   
                   
               
            
           
         
       
     
     The reprogramming factor of the present embodiment may be introduced in the form of a protein, or may be introduced in the form of mRNA encoding the protein or a nucleic acid such as an expression vector. 
     As will be described later in Examples, the reprogramming factor preferably includes OCT4, SOX2, KLF4, L-MYC, LIN28, and mP53DD. 
     In addition, as will be described later in Examples, the reprogramming factor preferably includes OCT4, SOX2, KLF4, L-MYC, LIN28, mP53DD, KLF2, KDM4D, GLIS1, and NANOG. 
     Step (a) 
     In the present step, a reprogramming factor is introduced into mammalian somatic cells, and culturing is performed in a neural stem cell culture medium to obtain induced neural stem cell-like cells. The mammal may be a pluripotency induction-resistant animal. 
     When the reprogramming factor is protein or RNA, a conventional method such as microinjection or electroporation can be used as a method of incorporating the reprogramming factor into cells. 
     When the reprogramming factor is a protein, examples of the method of incorporating the reprogramming factor into cells include a method using protein transduction reagent, a method using protein transduction domain (PTD) fusion proteins, and a microinjection method. 
     As the protein transduction reagent, for example, it is possible to use known reagents such as cationic lipid type introduction reagents such as BioPORTER (Gelantis), Pro-DeliverIN (OZ Bioscience), Ab-DeliverIN (OZ Bioscience), PULSin Kit (Polyplus-transfection SAS), Proteinfectin (Targeting Systems), and Fuse-It P (NIPPON Genetics); membrane-permeable peptide type introduction reagents such as Chariot (Active motif), Xfect Protein (Clontech), JBS Transduction Kit (Jena Bioscience), and Cellvader (GE Healthcare); lipid type introduction reagents such as Profect-1 (Targeting Systems); and HVJ envelope type introduction reagents such as GenomONE™-Neo (FD) (Cosmo Bio). 
     As a reagent for introducing mRNA, for example, it is possible to use known reagents such as TransIT-mRNA Transfection Reagent (TaKaRa), Lipofectamine Messenger MAX™ (Thermo Fisher Scientific), and Xfect™ RNA Transfection Reagent (Clonetech). 
     The reprogramming factor may be an expression construct in which DNA encoding the reprogramming factor and a promoter are linked. The promoter may be one having activity in a target cell or may be an expression-inducible promoter capable of inducing activity by a drug or the like. 
     For example, the promoter may be a cytomegalovirus promoter (CMV promoter) or a CMV early enhancer/chicken beta actin (CAG promoter) which has strong promoter activity in almost all cells, or may be a promoter having tissue-specific promoter activity. 
     Examples of the expression-inducible promoter include, but are not limited to, a doxycycline-inducible promoter, a Cumate-inducible promoter, a heat shock promoter, and a light-induced promoter. In addition, it may be a system in which expression is induced during Cre recombinant enzyme action by a protein translation stop codon or polyadenylation sequence sandwiched between loxP sites. 
     The above-mentioned expression construct may be one incorporated into, for example, a transposon vector, an adenovirus vector, an adeno-associated virus vector, a plasmid vector, an episomal vector, or the like. 
     The vector is preferably one in which the vector is not incorporated into the genome, or a vector in which the vector is temporarily incorporated into the genome but can be removed from the genome by an artificial operation. 
     For example, when the above-mentioned construct is incorporated into a transposon vector, it can be easily incorporated into the chromosome of a cell by introducing it into a cell to cause a transposase to act. In addition, by causing the transposase to act, the above-mentioned construct incorporated into the chromosome can be excised from the chromosome and removed without leaving a trace. The transposon may be, for example, piggyBac, Sleeping Beauty, Tol II, mariner, or the like. 
     Alternatively, after loxP sequences are disposed at both ends of the above-mentioned construct and iPS cells are established, Cre recombinase may be caused to act to remove the sequence sandwiched between the loxP sequences. 
     As the vector, an episomal vector is preferable. Examples of the episomal vector include a vector which is derived from EBV, SV40, or the like and contains a sequence required for autonomous replication within mammalian cells. 
     Examples of the sequence required for autonomous replication within mammalian cells include a replication initiation point that functions within mammalian cells, and a gene that encodes a protein that binds to a replication initiation point and controls replication. 
     Specifically, regarding the vector derived from EBV, a replication initiation point oriP and an EBNA-1 gene are exemplary examples. Regarding the vector of SV40, a replication initiation point ori and an SV40 large T antigen gene are exemplary examples. 
     Examples of methods of introducing the vector into cells include a lipofection method, a DEAE-dextran method, a calcium phosphate method, a microinjection method, an electroporation method, a gene gun method, and a viral vector method. 
     Examples of devices for performing the electroporation method include NEPA21 (Nepa Gene Co., Ltd.), 4D-Nucleofector (Lonza), Neon (Thermo Fisher Scientific), Gene Pulser Xcell (Bio-Rad Laboratories, Inc.), and ECM839 (BTX, Harvard Apparatus). 
     A reagent for transfection may be used as a method of introducing the vector into cells. As the reagent for transfection, it is possible to use, for example, Lipofectamine 2000 (Thermo Fisher Scientific), StemFect (STEMGEN S.p.A.), FuGENE 6/HD (Promega), CRISPRMAX (Thermo Fisher Scientific), jetPRIME Kit (Polyplus Transfection), DreamFect (OZ Biosciences), GenePorter 3000 (OZ Biosciences), a reagent for calcium phosphate method, and the like. 
     Subsequently, in the step (a), somatic cells of a pluripotency induction-resistant animal into which the reprogramming factor has been introduced are cultured in a neural stem cell culture medium. The neural stem cell culture medium preferably contains a MAP kinase inhibitor, a GSK3β inhibitor, and a TGFβ inhibitor. 
     The neural stem cell culture medium may further contain Leukemia Inhibitory Factor (LIF) as a differentiation inhibiting factor, and a basic fibroblast growth factor (bFGF) as a growth factor. 
     Examples of the GSK3β inhibitor include CHIR99021, SB-415286, SB-2167, indirubin-3′-Monoxime, and Kenpaullone, and among these, CHIR99021 and Kenpaullone are particularly preferable. In addition, the addition concentration of the GSK inhibitor to the medium is, for example, 0.1 to 10 μM, preferably 1 to 3 μM. 
     Examples of the TGF-β inhibitor include A83-01, SB-431542, SB-505124, SB-525334, SD-208, LY-36494, and SJN-2511. Among these, A83-01 is preferable. In addition, the addition concentration of the TGF-β inhibitor to the medium is, for example, 0.1 to 10 μM, preferably 0.5 to 1 μM. 
     The MAP kinase inhibitor may be, for example, one inhibiting constituent factors of the MAP kinase pathway such as MAPK, ERK, MEK, MEKK, ERK1, ERK2, Raf, MOS, p21ras, GRB2, SOS, JNK, c-jun, SAPK, JNKK, PAK, RAC, and p38. 
     Examples of the MAP kinase inhibitor include PD0325901, PD184352, VX-745, SB202190, anisomycin, PD98059, SB203580, U0126, AG126, apigenin, an HSP25 kinase inhibitor, 5-iodotubercidin, MAP kinase antisense oligonucleotide, control MAP kinase oligonucleotide, a MAP kinase cascade inhibitor, a MAP kinase inhibitor set 1, a MAP kinase inhibitor set 2, a MEK inhibitor set, olomoucine, iso-olomoucine, N9-isopropyl-olomoucine, a p38 MAP kinase inhibitor, PD169316, SB202474, SB202190 hydrochloride, SB202474 dihydrochloride, SB203580 sulfone, Ioto-SB203580, SB220025, SC68376, SKF-86002, Tyrphostin AG 126, U0124, U0125, and ZM336372 (refer to, for example, Japanese Patent No. 6218229). Among these, PD0325901 is preferable. In addition, the addition concentration of the MAP kinase inhibitor to the medium is, for example, 0.01 to 10 μM, preferably 0.03 to 1 μM. 
     Step (b) 
     In the present step, the induced neural stem cell-like cells obtained in the step (a) are cultured in a growth medium to obtain induced pluripotent stem cells. 
     As will be described later in Examples, induced pluripotent stem cells can be obtained by culturing the induced neural stem cell-like cells obtained in the step (a) in a growth medium. As the growth medium, a known medium for culturing ES cells can be used, but the growth medium is not limited thereto and may be any medium as long as it is suitable for culturing ES cells. As will be described later in Examples, the growth medium may contain bFGF (FGF2). 
     As will be described later in Examples, the growth medium may be a Dulbecco&#39;s modified Eagle&#39;s medium containing 20% Knockout serum replacement (KSR, Thermo Fisher Scientific) and 4 to 10 ng/mL bFGF. 
     Induced Pluripotent Stem Cells 
     In one embodiment, the present invention provides induced pluripotent stem cells produced by the production method described above. 
     As will be described later in Examples, the iPS cells of the present embodiment endogenously express OCT4, NANOG, SOX2, KLF4, LIN28, ZFP42, TRA-1-60, and SSEA4, which are pluripotent stem cell markers. In addition, the iPS cells of the present embodiment can be differentiated into endoderm, mesoderm, and ectoderm. In addition, the iPS cells of the present embodiment can form teratomas and differentiate into differentiated glandular epithelium, blood vessels, cartilage, fat cells, and nerve cells. 
     The iPS cells of the present embodiment are produced by expressing the above-mentioned reprogramming factor in somatic cells. Therefore, a gene encoding the reprogramming factor may be introduced. 
     However, for example, when a gene is introduced using an episomal vector or the like and the gene is removed in the middle of culturing, it is impossible to detect the reprogramming factor. 
     A difference in gene expression patterns and the like may be present between the iPS cells of the present embodiment and, for example, ES cells. However, it is uncertain whether or not such a difference is present, and in order to specify such a difference to specify the iPS cells of the present embodiment by gene expression patterns and the like, a significantly large number of trials and errors is required, which is substantially impossible. Therefore, it can be said that it is practical to specify the iPS cells of the present embodiment by them being produced by the above-mentioned production method. 
     The efficiency for establishing the iPS cells may be improved by bringing, in addition to the reprogramming factors described above, an efficiency-improving substance, which is capable of improving the efficiency for establishing known iPS cells, into contact with somatic cells of a pluripotency induction-resistant animal in the step (a). 
     As described in PCT International Publication No. WO2015/056804, examples of the substance for improving the efficiency of establishing iPS cells include, but are not limited to, a histone deacetylase (HDAC) inhibitor [for example, valproic acid (VPA) (Nat. Biotechnol., 26(7): 795-797 (2008)), small molecule inhibitors such as tricostatin A, sodium butyrate, MC 1293, and M344, and nucleic acid expression inhibitors such as siRNA and shRNA for HDAC (for example, HDAC1 siRNA Smartpool™ (Millipore), HuSH 29mer shRNA Constructs against HDAC1 (OriGene), and the like)], DNA methyltransferase inhibitors (for example, 5′-azacytidine) (Nat. Biotechnol., 26(7): 795-797 (2008)), G9a histone methyltransferase inhibitors [for example, small molecule inhibitors such as BIX-01294 (Cell Stem Cell, 2: 525-528 (2008)), and nucleic acid expression inhibitors such as siRNA and shRNA for G9a (for example, G9a siRNA (human) (Santa Cruz Biotechnology) and the like)], L-channel calcium agonist (for example, Bayk8644) (Cell Stem Cell, 3, 568-574 (2008)), UTF1 (Cell Stem Cell, 3, 475-479 (2008)), Wnt Signaling activators (for example, soluble Wnt3a) (Cell Stem Cell, 3, 132-135 (2008)), 2i/LIF (where 2i is an inhibitor of mitogen-activated protein kinase signalling and glycogen synthase kinase-3, PloS Biology, 6(10), 2237-2247 (2008)), ES cell-specific miRNA (for example, miR-302-367 cluster (Mol. Cell. Biol. doi: 10.1128/MCB.00398-08), miR-302 (RNA (2008) 14: 1-10), miR-291-3p, miR-294, and miR-295 (which are in Nat. Biotechnol. 27: 459-461 (2009))), 3′-phosphoinositide-dependent kinase-1 (PDK1) acitvators (for example, PS48 (Cell Stem Cell, 7: 651-655 (2010))), neuropeptide Y (WO2010/147395), and prostaglandins (for example, prostaglandin E2 and prostaglandin J2) (WO2010/068955). 
     In the above-described step (a) and step (b), the efficiency for establishing iPS cells may be improved by culturing somatic cells, iNSL cells, and iPS cells under hypoxic conditions. For example, a condition in which the oxygen concentration in the atmosphere when culturing cells is 18% or less is an exemplary example. 
     Kit 
     In one embodiment, the present invention provides a kit for producing induced pluripotent stem cells from somatic cells of a pluripotency induction-resistant animal, the kit including: a reprogramming factor including an OCT family, a SOX family, a KLF family, a MYC family, a LIN28 family, and a P53 function-inhibiting substance; and a neural stem cell culture medium containing a MAP kinase inhibitor, a GSK3β inhibitor, and a TGFβ inhibitor. 
     For example, iPS cells can be produced by introducing the reprogramming factor attached to the kit of the present embodiment into the somatic cells of a pluripotency induction-resistant animal and thereafter culturing the cells in the neural stem cell culture medium attached to the kit of the present embodiment. The above-mentioned MAP kinase inhibitor, GSK3β inhibitor, and TGFβ inhibitor may be the above-mentioned inhibitors in the production method. 
     The kit described above may further include a growth medium containing bFGF. The growth medium may be any medium as long as it can culture ES cells, and may be a known medium. 
     By using the kit of the present embodiment, induced pluripotent stem cells can be easily produced even in the case of somatic cells of a pluripotency induction-resistant animal. 
     The reprogramming factor attached to the kit of the present embodiment may further include one or more selected from the group consisting of a KDM family, a GUS family, and NANOG. 
     The reprogramming factor preferably includes the OCT family, the SOX family, the KLF family, the MYC family, the LIN28 family, the P53 function-inhibiting substance, the KDM family, the GLIS family, and NANOG. 
     The reprogramming factor described above may be a protein or a nucleic acid encoding the protein, as described above in the production method. 
     The P53 function-inhibiting substance attached to the kit of the present embodiment may be any substance as long as it is a substance suppressing the function of P53 protein or a substance suppressing the expression of a P53 gene, as described above in the production method. 
     The kit of the present embodiment may include a non-episomal vector having an expression construct for expressing the reprogramming factor and a nucleic acid encoding EBNA-1. Examples of the expression construct include one in which a gene fragment encoding a reprogramming factor is linked downstream of a promoter, as described above in the production method. 
     EXAMPLES 
     Hereinafter, the present invention will be described with reference to examples, but the present invention is not limited to the following examples. 
     In  FIGS. 1 to 56  of Examples, E01F and E02M mean the line names of embryonic fibroblasts of marmosets, and I5061F and CM421F mean the line names of fibroblasts of adult marmosets. In addition, the description of these line names may mean cells from which iPS cells and iNSL cells are derived. In addition, EP-A means an EP-A vector set, and EP-B means an EP-B vector set. In addition, the description of EP-A and EP-B may mean a vector set introduced into cells. 
     Experimental Example 1 
     Introduction of Reprogramming Factor and Culture in Growth Medium 
     After introducing a reprogramming factor into somatic cells of a marmoset, the obtained cells were directly cultured in a growth medium (ES cell culture medium) without being cultured in a neural stem cell culture medium. 
     First, a reprogramming gene expression construct inserted into the vector described below was prepared. The reprogramming genes are OCT4, SOX2, KLF4, L-MYC, LIN28, mP53DD, KLF2, NANOG, KDM4D, and GLIS1. 
     OCT4, SOX2, KLF4, L-MYC, LIN28, KLF2, NANOG, KDM4D, and GLIS1 are human genes. An mP53DD protein is a dominant negative form in which the C-terminus of a mouse P53 protein has been deleted (Okita K et al., An Efficient Non-viral Method to Generate Integration-Free Human iPS Cells from Cord Blood and Peripheral Blood Cells, Stem Cells, vol. 31, 458-466, 2013). 
     Expression constructs introduced into the marmoset somatic cells are shown in  FIGS. 1 and 2 . The expression constructs have the structure described below. 
     pCE-hOCT3/4 expressing OCT4 has ORF of an OCT4 gene downstream of a CAG promoter, and further has ORF of an EBNA1 gene (EBV Nuclear Antigen 1) downstream of an EBV (Epstein-Barr Virus) promoter, and a replication origin point OriP of EBV. 
     pCE-hSK expressing SOX2 and KLF4 has ORF of SOX2, a 2A sequence of foot-and-mouth disease virus, and ORF of KLF4 downstream of a CAG promoter, and has ORF of an EBNA1 gene downstream of an EBV promoter and a replication origin point OriP of EBV. 
     pCE-hUL expressing L-MYC and LIN28 has ORF of L-MYC, a 2A sequence of foot-and-mouth disease virus, and ORF of LIN28 downstream of a CAG promoter, and has ORF of an EBNA1 gene downstream of an EBV promoter and a replication origin point OriP of EBV. 
     pCE-mP53DD expressing mP53DD has ORF of mP53DD downstream of a CAG promoter, and has ORF of an EBNA1 gene downstream of an EBV promoter and a replication origin point OriP of EBV. 
     pCXLE-EGFP expressing EGFP has ORF of EGFP downstream of a CAG promoter, and has ORF of an EBNA1 gene downstream of an EBV promoter and a replication origin point OriP of EBV. 
     pCXB-EBNA1 expressing EBNA1 has ORF of an EBNA1 gene downstream of a CAG promoter. 
     pCE-K2N expressing KLF2 and NANOG has ORF of KLF2, a 2A sequence of foot-and-mouth disease virus, and ORF of NANOG downstream of a CAG promoter, and has ORF of an EBNA1 gene downstream of an EBV promoter and a replication origin point OriP of EBV. 
     pCE-KdGI expressing KDM4D and GLIS1 has ORF of KDM4D, a 2A sequence of foot-and-mouth disease virus, and ORF of GLIS1 downstream of a CAG promoter, and has ORF of an EBNA1 gene downstream of an EBV promoter and a replication origin point OriP of EBV. 
     The EP-A vector set consists of pCE-hOCT3/4, pCE-hSK, pCE-hUL, pCE-mP53DD, pCXLE-EGFP, and pCXB-EBNA1. 
     The EP-B vector set consists of pCE-hOCT3/4, pCE-hSK, pCE-hUL, pCE-mP53DD, pCXLE-EGFP, pCXB-EBNA1, pCE-K2N, and pCE-KdGI. 
     As the growth medium, a Dulbecco&#39;s modified Eagle&#39;s medium (DMEM medium) containing 20% Knockout serum replacement (KSR, Thermo Fisher Scientific) and 4 to 10 ng/mL bFGF was used. The composition of the growth medium is shown in Table 3 below. 
     
       
         
           
               
               
               
             
               
                   
                 TABLE 3 
               
               
                   
                   
               
             
            
               
                   
                   
                 DMEM medium 
               
               
                   
                   
                 20% KSR (Thermo Fisher Scientific) 
               
               
                   
                   
                 10 ng/mL bFGF 
               
               
                   
                   
                 1% NEAA (Thermo Fisher Scientific) 
               
               
                   
                   
                 2 mM L-glutamine 
               
               
                   
                   
                 0.1 mM 2-mercaptoethanol 
               
               
                   
                   
               
            
           
         
       
     
     The EP-A vector set was introduced into marmoset embryonic fibroblasts (E01F), and culturing was directly performed in the growth medium without culturing in a neural stem cell culture medium.  FIG. 3  shows the results. 
       FIG. 3( a )  is a photograph obtained by imaging cells, into which the EP-A vector set was introduced and which were cultured in the growth medium for 4 days, in a bright field.  FIG. 3( b )  is a photograph obtained by imaging fluorescence of EGFP of cells into which the EP-A vector set was introduced and which were cultured in the growth medium for 4 days. 
     As a result, it was confirmed that the EP-A vector set was introduced into the marmoset cells and expressed EGFP which is a marker. 
     The EP-A vector set was introduced into marmoset embryonic fibroblasts (E01F and E02M), and the obtained cells were cultured in a medium for ES cell culture for 30 days.  FIG. 4  shows the results.  FIG. 4( a )  is a photograph of cells in which the EP-A vector set was introduced into E01F and which were cultured in the growth medium for 30 days.  FIG. 4( b )  is a photograph of cells in which the EP-A vector set was introduced into E02M and which were cultured in the growth medium for 30 days. 
     As a result, even when the marmoset cells into which the EP-A vector set was introduced were directly cultured in the medium for ES cell culture without being cultured in a neural stem cell culture medium, a cell colony and cell mass could not be confirmed. From this result, it became clear that marmoset iPS cells are not formed even when the reprogramming factor is expressed in the marmoset cells and thereafter culturing is performed in the medium for ES cell culture. 
     Experimental Example 2 
     Introduction of Reprogramming Factor and Culture in Neural Stem Cell Culture Medium 
     The reprogramming factor was introduced into marmoset embryonic fibroblasts, and culturing was performed in a neural stem cell culture medium to dedifferentiate marmoset cells. 
     The process for establishing iPS cells from marmoset somatic cells is shown in  FIG. 5 . First, a reprogramming factor expression construct was introduced into marmoset somatic cells by electroporation. Subsequently, the obtained cells were cultured in a Dulbecco&#39;s modified Eagle&#39;s medium containing 10% fetal bovine serum (FBS). 
     Subsequently, the obtained cells were cultured using MEF as a feeder cell. Subsequently, the obtained cells were cultured in a neural stem cell culture medium. 
     As the neural stem cell culture medium, a medium containing a MAP kinase inhibitor (PD0325901), a GSK3β inhibitor (CHIR99021), and a TGFβ inhibitor (A83-01) was used. The composition of the neural stem cell culture medium is shown in Table 4 below. 
     
       
         
           
               
               
               
             
               
                   
                 TABLE 4 
               
               
                   
                   
               
             
            
               
                   
                   
                 DMEM/F12 medium:Neurobasal medium 1:1 
               
               
                   
                   
                 1% N2 supplement (Thermo Fisher Scientific) 
               
               
                   
                   
                 2% B27 supplement (Thermo Fisher Scientific) 
               
               
                   
                   
                 0.05% AlubuMAX (Thermo Fisher Scientific) 
               
               
                   
                   
                 1% NEAA (Thermo Fisher Scientific) 
               
               
                   
                   
                 2 mM L-glutamine 
               
               
                   
                   
                 0.1 mM 2-mercaptoethanol 
               
               
                   
                   
                 1% KSR (Thermo Fisher Scientific) 
               
               
                   
                   
                 0.1 μM PD0325901 (CAS: 391210-10-9) 
               
               
                   
                   
                 1 μM CHIR99021 (CAS: 252917-06-9) 
               
               
                   
                   
                 0.5 μM A83-01 (CAS: 909910-43-6) 
               
               
                   
                   
                 10 μM Forskolin (CAS: 66575-29-9) 
               
               
                   
                   
                 10 ng/ml hLIF (Thermo Fisher Scientific) 
               
               
                   
                   
               
            
           
         
       
     
     In Table 4, the DMEM/F12 medium is a medium in which DMEM and Ham&#39;s F-12 were mixed at the ratio of 1:1. The Neurobasal medium is manufactured by Thermo Fisher Scientific. 
     The EP-A vector set or EP-B vector set was introduced into marmoset embryonic fibroblasts (E01F and E02M), and culturing was performed in a neural stem cell culture medium.  FIG. 6  shows the results. 
       FIG. 6( a )  is a photograph of a colony formed by introducing the EP-A vector set into E01F and then culturing in the neural stem cell culture medium.  FIG. 6( b )  is a photograph of a colony formed by introducing the EP-B vector set into E01F and then culturing in the neural stem cell culture medium.  FIG. 6( c )  is a photograph of a colony formed by introducing the EP-A vector set into E02M and then culturing in the neural stem cell culture medium.  FIG. 6( d )  is a photograph of a colony formed by introducing the EP-A vector set into E02M and then culturing in the neural stem cell culture medium. 
     As a result, it became clear that all the marmoset cells into which the EP-A vector set or the EP-B vector set was introduced formed colonies. 
     Furthermore, the colony forming ability of the marmoset cells into which the EP-A vector set or the EP-B vector set was introduced was calculated.  FIG. 7  shows the results.  FIG. 7  is a graph showing the results of calculating the colony forming ability when marmoset embryonic fibroblasts were used. 
     In addition, the above-mentioned colonies were subjected to alkaline phosphatase staining.  FIG. 8  shows the results.  FIG. 8( a )  is a diagram showing the results of staining, with alkaline phosphatase, a colony obtained by introducing E01F into the EP-A vector set and culturing in a neural stem cell culture medium.  FIG. 8( b )  is a diagram showing the results of staining, with alkaline phosphatase, a colony obtained by introducing E01F into the EP-B vector set and culturing in a neural stem cell culture medium. 
     As a result, it became clear that the colonies of marmoset cells into which the EP-A vector set or the EP-B vector set was introduced were stained by alkaline phosphatase staining. 
     This result suggests that these colonies have been dedifferentiated and are in an undifferentiated state. Hereinafter, the cells forming these colonies may be referred to as induced Neural Stem Cell Like Cells (iNSLC), that is iNSL cells. 
     Experimental Example 3 
     Establishment of Marmoset iPS Cells 
     The reprogramming factor was introduced into marmoset embryonic fibroblasts, and culturing was performed in a neural stem cell culture medium. Thereafter, culturing was performed in a growth medium (ES cell culture medium) to establish marmoset iPS cells. As the neural stem cell culture medium and the growth medium, the same media as in Experimental Examples 1 and 2 were used. 
     The EP-A vector set or EP-B vector set was introduced into marmoset embryonic fibroblasts (E01F and E02M). Subsequently, the obtained cells were cultured in the neural stem cell culture medium, and then cultured in the growth medium. 
       FIG. 9  shows the results.  FIG. 9( a )  is a photograph of a colony formed by introducing the EP-A vector set into marmoset embryonic fibroblasts (E01F) and culturing in the neural stem cell culture medium.  FIG. 9( b )  is a photograph of a colony formed by introducing the EP-A vector set into marmoset embryonic fibroblasts (E01F), culturing in the neural stem cell culture medium, and then culturing in the growth medium.  FIG. 9( c )  is a photograph of a colony formed by introducing the EP-B vector set into marmoset embryonic fibroblasts (E02M) and culturing in the neural stem cell culture medium.  FIG. 9( d )  is a photograph of a colony formed by introducing the EP-B vector set into marmoset embryonic fibroblasts (E02M), culturing in the neural stem cell culture medium, and then culturing in the growth medium. 
     As a result, when the reprogramming factor was introduced into marmoset embryonic fibroblasts, culturing was performed in the neural stem cell culture medium, and thereafter culturing was performed in the growth medium, colonies having the shape similar to colonies formed by ES cells were observed. 
     Subsequently, the colonies of marmoset ES cells (No. 40 ESC) and the above-mentioned marmoset iPS cells (A-2-2, A-2-6, and A-2-7 derived from E01F, and B-0-6, B-0-7, and B-0-11 derived from E02M) were subjected to Hoechst staining and immunostaining using an anti-TRA-1-60 antibody and an anti-SSEA4 antibody. TRA-1-60 and SSEA4 are genes expressed in ES cells.  FIG. 10  shows the results. 
       FIG. 10  shows diagrams showing the results of analyzing the expression of ES cell markers in marmoset iPS cells. As a result, it became clear that these marmoset iPS cells express TRA-1-60 and SSEA4 as in the case of ES cells. 
     Subsequently, the colonies of the above-mentioned marmoset iPS cells were subjected to alkaline phosphatase staining.  FIG. 11  shows the results.  FIG. 11  shows diagrams showing the results of subjecting marmoset iPS cells to alkaline phosphatase staining. As a result, it became clear that these colonies were stained by alkaline phosphatase staining in the same manner as undifferentiated cells. 
     Subsequently, the colonies of the above-mentioned marmoset iPS cells were subjected to Hoechst staining and immunostaining using an anti-OCT4 antibody and an anti-NANOG antibody.  FIG. 12  shows the results.  FIG. 12  shows diagrams showing the results of analyzing the expression of ES cell markers in marmoset iPS cells. As a result, it became clear that these marmoset iPS cell colonies expressed OCT4 and NANOG as in the case of ES cells. 
     Subsequently, for the above-mentioned marmoset iPS cells, marmoset ES cells (No. 40, DSY127), and marmoset embryonic fibroblasts, the expression of endogenous OCT4, endogenous NANOG, endogenous SOX2, and endogenous KLF4 gene, and the expression of a Zinc finger protein 42 (ZFP42) gene, a Developmental Pluripotency Associated 2 (DPPA) gene, and a Telomerase Reverse Transcriptase (TERT) gene were analyzed by qRT-PCR.  FIG. 13  and  FIG. 14  show the results. 
       FIG. 13  and  FIG. 14  show diagrams showing the results of analyzing the expression of ES cell markers in marmoset iPS cells. As a result, it became clear that the marmoset iPS cells endogenously express the OCT4, NANOG, SOX2, KLF4, DRPA5, ZFP42, and TERT genes as in the case of the marmoset ES cells. 
     Subsequently, whether or not the vector contained in the EP-A vector set or the EP-B vector set remained in the marmoset iPS cells was analyzed by a PCR method.  FIG. 15  shows the results.  FIG. 15  shows diagrams showing the results of analyzing the presence or absence of an expression vector in marmoset iPS cells. 
     As a result, regarding E01F A-2-2 iPSC, E01F A-2-3 iPSC, E01F A-2-5 iPSC, E01F A-2-6 iPSC, E01F A-2-7 iPSC, E02M B-0-6 iPSC, and E02M B-0-7 iPSC, it became clear that the EP-A vector set or the EP-B vector set did not remain in the cells. 
     Based on the above results, it became clear that, when marmoset cells into which the EP-A vector set or the EP-B vector set was introduced were cultured in the neural stem cell culture medium and thereafter cultured in the growth medium, the marker gene of ES cells is expressed even when the vector set is lost. 
     Experimental Example 4 
     Pluripotency of Marmoset iPS Cells 
     The marmoset iPS cells obtained in Experimental Example 3 were differentiated into endoderm, mesoderm, and ectoderm, and the expression of marker genes in each of the germ layers was analyzed to verify the pluripotency of the marmoset iPS cells. 
     First, the marmoset iPS cells (A-2-2, A-2-6, A-2-7, and B-0-7) were suspension-cultured and differentiated into each of the germ layers. 
     Subsequently, the expression of Alpha-fetoprotein (AFP) for endoderm, α-Smooth muscle actin (αSMA) for mesoderm, and Microtubule associated protein 2 (MAP2) and βIII-tubulin for ectoderm was analyzed using antibodies against each of the proteins. Furthermore, at the same time, Hoechst staining was also performed.  FIG. 16  shows the results. 
       FIG. 16  shows diagrams showing the results of analyzing the expression of markers in three germ layers differentiated from marmoset iPS cells. As a result, it became clear that each of the germ layers formed from the marmoset iPS cells expresses a marker gene characteristic of each of the germ layers. 
     In addition, after culturing the embryoid body formed from the marmoset iPS cells for 2 weeks or 4 weeks using a KnockOut Serum Replacement Medium (KSR medium) or a medium containing 10% fetal bovine serum, the expression of AFP was analyzed by qRT-PCR.  FIG. 17  and  FIG. 18  show the results. 
       FIG. 17  is a diagram showing the results of analyzing the expression of AFP expressed by marmoset iPS cells cultured in the KSR medium.  FIG. 18  is a diagram showing the results of analyzing the expression of AFP in marmoset iPS cells cultured in the medium containing FBS. 
     In  FIGS. 17 and 18 , EB indicates the embryoid body, 2 w indicates after 2 weeks, and 4 w indicates after 4 weeks. As a result, it became clear that the embryoid body formed from the marmoset iPS cells expresses AFP. 
     Furthermore, the obtained marmoset iPS cells (A-2-2, A-2-7, and B-0-7) were injected into the testicle of an immunodeficient mouse (NOD/SCID), and after 2 to 3 months, teratomas formed inside the testicle were excised to observe tissues differentiated from endoderm, mesoderm, and ectoderm. 
     More specifically, glandular epithelium differentiated from the endoderm, and blood vessels, cartilage, and fat cells differentiated from the mesoderm were observed by hematoxylin and eosin staining (HE staining), and nerve cells differentiated from the ectoderm were observed by HE staining and immunostaining with an antibody against neurofilament 200 kDa.  FIG. 19  shows the results. 
       FIG. 19  shows diagrams showing the results of analyzing teratomas formed from marmoset iPS cells. As a result, it became clear that the differentiated glandular epithelium, blood vessels, cartilage, fat cells, and nerve cells are formed in the teratomas. 
     Experimental Example 5 
     Establishment of iPS Cells from Adult Marmoset Cells 
     The EP-A vector set or the EP-B vector set was introduced into adult marmoset fibroblasts, and culturing was performed in a neural stem cell culture medium to establish iNSL cells. Furthermore, iPS cells were established by culturing the obtained iNSL cells in a growth medium. 
     Using the adult marmoset fibroblasts (15061F and CM421F), marmoset iNSL cells were established by the method described above.  FIG. 20  shows the results.  FIG. 20  shows photographs of iNSL cells derived from fibroblasts of an adult marmoset. 
     As a result, it became clear that iNSL cells derived from adult marmoset fibroblasts form cell masses and colonies. 
     Subsequently, the colony forming ability of iNSL cells derived from adult marmoset fibroblasts was calculated.  FIG. 21  shows the results.  FIG. 21  is a diagram showing the colony forming ability of iNSL cells derived from fibroblasts of an adult marmoset. 
     In  FIG. 21 , “+ VPA” indicates that a histone deacetylase inhibitor (Valproic Acid) was added for 2 days. As a result, it became clear that iNSL cells can be established with good reproducibility from the adult marmoset fibroblasts. 
     Subsequently, alkaline phosphatase staining was performed on the above-mentioned iNSL cells.  FIG. 22  shows the results.  FIG. 22  shows diagrams showing the results of alkaline phosphatase staining of iNSL cells derived from fibroblasts of an adult marmoset. 
     As a result, it became clear that iNSL cells derived from adult marmoset fibroblasts express alkaline phosphatase. That is, it became clear that iNSL cells derived from adult marmoset fibroblasts have an undifferentiation property. 
     Subsequently, in the same manner as in Experimental Example 3, the above-mentioned iNSL cells were cultured in a growth medium to obtain marmoset iPS cells.  FIG. 23  shows the results.  FIG. 23  shows photographs of colonies of marmoset iPS cells derived from fibroblasts of an adult marmoset. As a result, it became clear that the marmoset iPS cells cultured in the growth medium form colonies similar to the colonies of ES cells. 
     Subsequently, the obtained marmoset iPS cells were subjected to alkaline phosphatase staining.  FIG. 24  shows the results.  FIG. 24  shows diagrams showing the results of alkaline phosphatase staining of iPS cells derived from fibroblasts of an adult marmoset. As a result, it was suggested that the established marmoset iPS cells were undifferentiated. 
     Subsequently, the obtained marmoset iPS cells were immunostained using an anti-TRA-1-60 antibody and an anti-SSEA4 antibody. At the same time, staining was performed using Hoechst.  FIG. 25  shows the results. 
       FIG. 25  shows diagrams showing the results of analyzing the expression of ES cell markers in marmoset iPS cells derived from fibroblasts of an adult marmoset. As a result, it became clear that the obtained marmoset iPS cells express TRA-1-60 and SSEA4 as in the case of ES cells. 
     Subsequently, for the obtained marmoset iPS cells, the expression of endogenous OCT4, NANOG, SOX2, KLF4, and Lin28 genes, and the expression of the ZFP42 gene, DPPA gene, and TERT gene were analyzed by qRT-PCR.  FIGS. 26 to 29  show the results. 
       FIGS. 26 to 29  are diagrams showing the results of analyzing the expression of ES cell markers in marmoset iPS cells derived from fibroblasts of an adult marmoset. 
     As a result, it became clear that the obtained marmoset iPS cells express the above-mentioned genes as in the case of the marmoset ES cells. 
     Subsequently, the obtained marmoset iPS cells were differentiated into endoderm, mesoderm, and ectoderm by the same method as in Experimental Example 4, and the expression of a marker gene in each of the germ layers was analyzed. 
     Subsequently, the expression of AFP for endoderm, αSMA for mesoderm, and MAP2 and βIII-tubulin for ectoderm was analyzed using antibodies against each of the proteins. Furthermore, at the same time, Hoechst staining was also performed.  FIGS. 30 and 31  show the results. 
       FIG. 30  and  FIG. 31  show diagrams showing the results of analyzing the expression of markers in three germ layers differentiated from marmoset iPS cells derived from fibroblasts of an adult marmoset. As a result, it became clear that each of the germ layers formed by being differentiated from the obtained marmoset iPS cells expresses a marker gene characteristic of each of the germ layers. 
     Furthermore, teratomas were produced from the obtained marmoset iPS cells in the same manner as in Experimental Example 4, and tissues differentiated from endoderm, mesoderm, and ectoderm were observed. Glandular epithelium differentiated from the endoderm and blood vessels differentiated from the mesoderm were observed by HE staining, and nerve cells differentiated from the ectoderm were observed by HE staining and immunostaining with an antibody against neurofilament 200 kDa.  FIG. 32  shows the results. 
       FIG. 32  shows diagrams showing the results of analyzing teratomas formed from marmoset iPS cells derived from fibroblasts of an adult marmoset. As a result, it became clear that the differentiated glandular epithelium, blood vessels, and nerve cells are formed in the teratomas. 
     In addition, regarding the obtained marmoset iPS cells, whether or not the vector contained in the EP-A vector set or the EP-B vector set remained was analyzed by a PCR method.  FIG. 33  shows the results. 
       FIG. 33  is a diagram showing the results of analyzing whether or not a vector remains in marmoset iPS cells derived from fibroblasts of an adult marmoset. As a result, it became clear that the vector did not remain in the obtained marmoset iPS cells. 
     Experimental Example 6 
     Analysis of Gene Expression Pattern in iNSL Cells 
     The EP-A vector set or the EP-B vector set was introduced into marmoset embryonic fibroblasts or adult marmoset fibroblasts. Thereafter, culturing was performed in a neural stem cell culture medium to obtain induced neural stem cell-like cells (iNSL cells). The gene expression pattern and the differentiation potential into nerve cells of the obtained iNSL cells were analyzed. 
     First, the EP-A vector set or EP-A vector set was introduced into marmoset embryonic fibroblasts, and thereafter, culturing was performed in a neural stem cell culture medium.  FIG. 34  shows the results.  FIG. 34  shows photographs of marmoset iNSL cells. As a result, it was confirmed that iNSL cells were obtained. 
     Subsequently, whether or not the EP-A vector set or the EP-B vector set remained in the obtained iNSL cells was analyzed by a PCR method.  FIG. 35  shows the results.  FIG. 35  shows diagrams showing the results of analyzing a vector remaining in iNSL cells. 
     As a result, it became clear that the EP-A vector set or the EP-B vector set remained in the iNSL cells passaged 10 times after the introduction of the vector set. 
     Subsequently, the gene expression pattern of the obtained iNSL cells was analyzed by qRT-PCR.  FIG. 36  and  FIG. 37  show the results.  FIG. 36  is a diagram showing the results of analyzing the expression of endogenous OCT4, NANOG, SOX2, KLKF4, and ZFP42 in iNSL cells.  FIG. 37  is a diagram showing the results of analyzing the expression of DPPA5 and TERT in iNSL cells. 
     As a result, it became clear that the obtained iNSL cells endogenously express SOX2 and TERT, but do not endogenously express OCT4, NANOG, KLF4, ZFP42, and DPPA5. 
     Subsequently, the gene expression level of the obtained iNSL cells, in which the endogenous gene expression and the exogenous (gene expression by the vector set) gene expression were combined, was analyzed by qRT-PCR.  FIG. 38  is a diagram showing the results of analyzing the expression of endogenous and exogenous OCT4, NANOG, KLF4, and Lin28 in iNSL cells. 
     As a result, it became clear that in the gene expression level in which the endogenous gene expression and the exogenous gene expression were combined, OCT4, KLF4, and Lin28 were expressed, but NANOG was not expressed. 
     Subsequently, for the obtained iNSL cells, the expression of PAX6 (Paired box 6), SOX1 (Sry-type HMG box 1), and ZFP521 (Zinc Finger Protein 521), which are neural stem cell markers, was analyzed by qRT-PCR.  FIG. 39  and  FIG. 40  show the results. 
       FIG. 39  is a diagram showing the results of analyzing the expression of PAX6 in iNSL cells.  FIG. 40  is a diagram showing the results of analyzing the expression of SOX1 and ZFP521 in iNSL cells. As a result, it became clear that PAX6 is not expressed in marmoset ES cells, but the obtained induced neural stem cells express PAX6, SOX1, and ZFP521. 
     Subsequently, for the obtained induced neural stem cells, the expression of T (TBX T), which is a mesoderm marker, and SOX17 (Sry-type HMG box 17), which is an endoderm marker, was analyzed by qRT-PCR.  FIG. 41  shows the results. 
       FIG. 41  is a diagram showing the results of analyzing the expression of T and SOX17 in iNSL cells. As a result, it was confirmed that T and SOX17 are expressed in marmoset ES cells but not in the obtained induced neural stem cells. 
     Subsequently, the marmoset ES cells, marmoset iPS cells, and marmoset-induced neural stem cells were analyzed for the differentiation potential into neural stem cells by unbiased neuronal differentiation assay.  FIG. 42  is a schedule of neural differentiation assays. Specifically, suspension culture was performed for 7 days, and thereafter adhesion culture was performed for 7 days.  FIG. 43  and  FIG. 44  show the results. 
       FIG. 43  shows diagrams showing the results of immunostaining of cells differentiated from the obtained induced neural stem cells with a Hoechst stain and an anti-βIII-tubulin antibody. As a result, it became clear that the cells differentiated from the obtained induced neural stem cells differentiated into nerve cells. 
       FIG. 44  is a graph showing the proportion of cells in which the expression of βIII-tubulin was recognized among cells differentiated into nerve cells. As a result, it became clear that cells differentiated from marmoset ES cells and marmoset iPS cells do not express βIII-tubulin, but cells differentiated from marmoset-induced neural stem cells express βIII-tubulin. 
     From the above results, it became clear that the iNSL cells, which were obtained by introducing the EP-A vector set or EP-B vector set into adult marmoset fibroblasts and performing culturing in a neural stem cell culture medium, acquire the traits of neural stem cells. 
     In addition, it became clear that, when iNSL cells are continuously cultured in the neural stem cell culture medium without being transferred to the growth medium, the iNSL cells retain the traits of neural stem cells and do not acquire the traits of ES cells even though the iNSL cells continue to retain the vector. 
     From this result, it became clear that it is not possible to directly produce iPS cells from adult somatic cells of a pluripotency induction-resistant animal, but it is possible to cause dedifferentiation into neural stem cells once and thereafter further dedifferentiation into iPS cells. 
     Experimental Example 7 
     Gene Profiling of Marmoset iPS Cells and iNSL Cells 
     Clustering analysis was performed on the gene expression profiles of ES cells, iPS cells, and iNSL cells of marmosets. 
     Clustering analysis was performed on the ES cells, iPS cells, and iNSL cells of marmosets based on a comprehensive gene expression profile.  FIG. 45  shows the results. As a result, it became clear that the marmoset iPS cells have high similarity to the marmoset ES cells, and the marmoset iNSL cells have high similarity to the marmoset fibroblasts. 
     Subsequently, the expression levels of 40 genes, reflecting the similarity of each cluster, in each of the cells were analyzed.  FIG. 46  shows the results. As a result, genes having characteristic expression levels could be extracted from the marmoset iPS cells and the marmoset-induced neural stem cells. 
     Principal component analysis was performed on the gene expression profile of each of the cells.  FIG. 47  shows the results. As a result, it became clear that each of the cells was divided into a group of fibroblasts, ES cells and iPS cells, and induced neural stem cells. 
     Experimental Example 8 
     Establishment of Canine iPS Cells 
     The EP-B vector set was introduced into canine fibroblasts to establish canine iPS cells. 
       FIG. 48  shows the results.  FIG. 48  shows photographs of colonies formed by canine iPS cells. As a result, it became clear that the canine iPS cells form colonies similar to the colonies formed by ES cells. 
     The expression of markers of ES cells was analyzed for the obtained canine iPS cells.  FIG. 49  shows the results.  FIG. 49  shows diagrams showing the results of analyzing the expression of OCT4, SOX2, and NANOG in canine iPS cells by RT-PCR. 
     As a result, it became clear that the canine iPS cells express OCT4, SOX2, and NANOG. That is, it was suggested that the canine iPS cells have the traits similar to those of ES cells. 
     The canine iPS cells were injected into the testicle of an immunodeficient mouse (NOD/SCID), and after 2 to 3 months, teratomas formed inside the testicle were excised to observe the teratomas.  FIG. 50  shows the results. 
     The obtained teratomas were subjected to hematoxylin and eosin staining to observe each tissue.  FIG. 51  shows the results.  FIG. 51  shows diagrams showing the results of analyzing the bone, cartilage, nerve cells, retina, sebaceous gland, hair follicle epithelium, and glandular tissue. 
     Whether or not the vector introduced into the obtained canine iPS cells remained was analyzed by a PCR method.  FIG. 52  shows the results. As a result, it was confirmed that the expression vector did not remain in the canine iPS cells. 
     Experimental Example 9 
     Establishment of Porcine iPS Cells 
     The EP-B vector set was introduced into porcine fibroblasts to establish porcine iNSL cells and porcine iPS cells. 
       FIG. 53  is a photograph of a colony of porcine iPS cells. It became clear that the porcine iPS cells form colonies similar to the colonies formed by ES cells. 
     Subsequently, the expression of markers of ES cells in the porcine iPS cells and porcine iNSL cells was analyzed by RT-PCR.  FIG. 54  shows diagrams showing the results of analyzing the expression of OCT4, SOX2, and NANOG in porcine iNSL cells and porcine iPS cells. 
     As a result, it became clear that the porcine iPS cells express OCT4, SOX2, and NANOG. Furthermore, it also became clear that the porcine iNSL cells express SOX2. 
     Experimental Example 10 
     Establishment of Ferret iPS Cells 
     The EP-B vector set was introduced into ferret fibroblasts to establish ferret iNSL cells and ferret iPS cells. 
       FIG. 55  is a photograph of a colony of the obtained ferret iPS cells. It became clear that the ferret iPS cells form colonies similar to the colonies formed by ES cells. 
     Subsequently, the expression of markers of ES cells in the ferret iPS cells was analyzed.  FIG. 56  shows diagrams showing the results of analyzing the expression of OCT4, SOX2, and NANOG in ferret iNSL cells and ferret iPS cells by RT-PCR. 
     As a result, it became clear that the ferret iPS cells express OCT4, SOX2, and NANOG. Furthermore, it also became clear that the ferret iNSL cells express SOX2. 
     INDUSTRIAL APPLICABILITY 
     According to the present invention, it is possible to provide a new technique for establishing iPS cells from mammalian somatic cells.