We would like to thank all members of the Stem Cell and Regenerative Medicine Group of the University of W&#252;rzburg for helpful suggestions and Martina Gebhardt as well as Heike Arthen for excellent technical support. This work was supported by grants from the Deutsche Forschungsgemeinschaft DFG (ED79/1-2), the German Ministry of Education and Research BMBF (01 GN 0813), the Bavarian Research Network Induced Pluripotent Stem Cells &#8220;forIPS&#8221; and the &#8220;Stiftung Sibylle Assmus&#8221;. Figure 1 was produced using Servier Medical Art, available from www.servier.com.

The human fibroblasts used in this study were obtained from a skin punch biopsy after getting informed consent and ethical clearance by the ethics committee of the University of W&#252;rzburg, Germany (ethical report no: 96/11 dated 10.06.2011).
1. Punch Biopsy
<ol>
	<li>Disinfect skin of patient. Anesthetize skin part of which biopsy will be taken from (preferentially a less sun-exposed area) using 0.5 to 1 ml mepivacaine hydrochloride intracutaneously and prepare skin biopsy using a sterile 3mm biopsy punch, rinse biopsy with DPBS + 1 &#181;l/1ml Gentamicin and remove fat. Rinse biopsy twice with DPBS + Gentamicin, aspirate DPBS completely and cover biopsy with Dispase II (2.4 U/ml) and incubate 16 - 18 hr&#160;at 4 &#176;C.</li>
	<li>Aspirate Dispase completely, wash twice with DPBS and remove epidermis with tweezers. Wash biopsy twice with DPBS, add 2 ml Collagenase Type 2 (500 U/ml CDU), transfer in 15 ml tube and add Collagenase up to 5 ml total volume. Incubate for 45 min at 37 &#176;C, 5% CO2.</li>
	<li>Centrifuge 5 min at 180 x g and discard supernatant afterwards. Resuspend pellet in 10 ml DMEM-FCS-Gentamicin-media (10% FCS, 1 &#181;l/ml Gentamicin) and centrifuge again for 5 min at 180 x g. Discard supernatant and resuspend pellet in 1.5 ml DMEM-FCS-Gentamicin-media. Transfer to T25 adherent tissue culture flask and incubate at 37 &#176;C, 5% CO2.</li>
	<li>Change media every 3 days.</li>
	<li>After approximately 2 weeks, when cells are confluent around skin parts, split cells using Trypsin/EDTA (0.05%): wash cells once with DPBS, incubate 5 min at 37 &#176;C, 5% CO2 after addition of 2 ml Trypsin/EDTA (0.05%), add 2 ml of DMEM-FCS-Gentamicin-media, transfer to 15 ml tube and centrifuge at 180 x g for 5 min; discard supernatant and resuspend pellet in appropriate amount of DMEM-FCS-Gentamicin-media.</li>
	<li>Further expand the cells by changing the medium every 3rd day and splitting as described above when cells are confluent; addition of Gentamicin can be stopped after passage 2.</li>
	<li>Before using the cells for direct conversion experiments, make sure to exclude mycoplasma contamination by standard assays.</li>
	<li>When cells have been expanded, you may directly start conversion or freeze cells down using 10% DMSO and 90% FCS. Cells should be stored in -80 &#176;C for 2 days and then transferred to liquid nitrogen for long-term storage.</li>
	<li>For preparation of conversion, wash cells once with DPBS, aspirate DPBS and add 2.5 ml Trypsin/EDTA (0.05%). Keep for 5 min at 37 &#176;C, 5% CO2. Tap flask gently to detach cells, resuspend in 2.5 ml of fibroblast media (DMEM incl. L-Glu + 10% FCS + 1% NEAA + 1% Sodium pyruvate)&#160;and transfer to 15 ml tube. Centrifuge at 180 x g for 5 min and aspirate the supernatant. Resuspend cells in 1 ml fibroblast media &#160;and pipette up and down to generate single cell suspension.</li>
	<li>Count the number of cells using a Fuchs-Rosenthal- or Neubauer-cell counting chamber and plate 3 x 104 cells per well of a 24 well-plate. Incubate O/N at 37 &#176;C, 5% CO2.</li>
</ol>
2. Infection of Human Fibroblasts with Sendai Virus and Transdifferentiation
NOTE: To ensure safety, the following steps handling virus have to be performed in a biological safety cabinet and a laminar flow hood, and with appropriate personal safety equipment, especially a surgical mask, to prevent mucosal exposure.
<ol>
	<li>Switch cells to 100 &#181;l fibroblast media (Step 1.9). Thaw aliquots of Oct4-, Klf4-, Sox2- and c-myc-Sendai virus and resuspend each virus in 1 ml fibroblast media. Add each virus with a MOI of 3 to cells (virus titer varies from lot to lot, but one aliquot of each virus can generally be used for infection of 10 wells of a 24 well-plate) and mix gently. Incubate O/N at 37 &#176;C, 5% CO2.</li>
	<li>After 24 hr&#160;aspirate the medium and add 500 &#181;l of neuroinduction media (1:1 DMEM/F-12 : Neurobasal, 1x N2, 1x B27, 1% GlutaMAX, 10 ng/ml hLIF, 3 &#181;M CHIR99021, 2 &#181;M SB431542) and culture at 39 &#176;C, 5% CO2 from now on. Change the media every other day.</li>
	<li>On day 6 after infection prepare laminin-coated 6-well-plates: dilute laminin to 1 &#181;g/ml in DPBS, add 1 ml of solution onto 6 well-plates and keep at 4 &#176;C for 24 hr.</li>
	<li>On day 7 after infection split the cells using DPBS/EDTA: aspirate the media and wash cells once with DPBS, then add 500 &#181;l of DPBS/EDTA and incubate for 10 min at 37 &#176;C, 5% CO2.</li>
	<li>Add 500 &#181;l of DMEM/F12 and remove suspension from plate in a 15 ml tube and centrifuge at 180 x g for 5 min.</li>
	<li>Aspirate the supernatant and resuspend the pellet in 1.5 ml of neuroinduction media, plate on laminin-coated 6 well-plates and add ROCK inhibitor Y27632 in a final concentration of 10 &#181;M to the cells, culture at 39 &#176;C, 5% CO2.</li>
	<li>Change the media every other day.</li>
	<li>From day 14 after infection culture the cells at 37 &#176;C, 5% CO2. Neuroepithelial colonies become apparent around day 17 after infection by phase contrast microscopy. They should be large enough to be picked around day 20 after infection.</li>
</ol>
3. Isolation of Putative iNPC Colonies
<ol>
	<li>One day before picking, coat one 48 well-plate with laminin: dilute laminin to 1 &#181;g/ml in DPBS, add 300 &#181;l of solution onto plates and keep at 4 &#176;C for 24 hr. One day later aspirate laminin from plates and add 200 &#181;l of neuroinduction media to the wells.</li>
	<li>Wash the 6 well-plates containing the colonies to be picked once with DPBS and add 2 ml DPBS per well of 6 well-plate. Pick the colonies mechanically: scrape around colonies using a thin needle to get rid of surrounding cells; set the 200 &#181;l pipetman on 50 &#181;l and pick the colonies using the respective pipette tips.</li>
	<li>Transfer one colony each into one well of a laminin-coated 48 well-plate and generate a single cell suspension mechanically by pipetting up and down 10 times. Add ROCK inhibitor Y27632 in a final concentration of 10 &#181;M to the cells.</li>
	<li>Grow the cells on the 48 well-plate at 37 &#176;C, 5% CO2 for 2 days. Change the media every second day until cells reach 80 - 90% confluency (approx. 3 - 4 days).</li>
</ol>
4. Expansion and Cryo-preservation of iNPCs
<ol>
	<li>Passaging and Expansion of iNPCs
	<ol>
		<li>Aspirate the medium and wash the cells with DPBS. Aspirate the DPBS and add 200 &#181;l DPBS/EDTA and incubate for 10 min at 37 &#176;C, 5% CO2, add 200 &#181;l of DMEM/F12 and remove suspension from plate in a 15 ml tube, centrifuge at 180 x g for 5 min.</li>
		<li>Aspirate the supernatant and resuspend the pellet in 0.5 ml of neuroinduction media (Step 2.2), plate on laminin-coated 12 well-plates and add ROCK inhibitor Y27632 in a final concentration of 10 &#181;M to the cells, culture at 37 &#176;C, 5% CO2. After cells reach 80 - 90% confluency they can be either further expanded or frozen down as follows.</li>
	</ol>
	</li>
	<li>Freezing of iNPCs
	<ol>
		<li>Aspirate the medium and wash the cells with DPBS. Aspirate the DPBS and add 300&#181;l DPBS/EDTA and incubate for 10 min at 37 &#176;C, 5% CO2, add 300 &#181;l of DMEM/F12 and remove suspension from plate in a 15 ml tube, centrifuge at 180 x g for 5 min.</li>
		<li>Aspirate the supernatant and resuspend the pellet in 0.5 ml of commercial NSC freezing medium. Transfer suspension to freezing vials and put in cell-freezing container. Store at -80 &#176;C for 2 days, then transfer to liquid nitrogen for long-term storage.</li>
	</ol>
	</li>
</ol>
5. Differentiation of iNPCs
<ol>
	<li>Differentiation towards neuronal lineage
	<ol>
		<li>Culture cells on laminin-coated plates as described above. Change media to neuro-diff-media (DMEM/F-12, 1x N2, 1x B27, 300 ng/ml cAMP, 200 &#181;M vitamin C, 10 ng/ml BDNF, 10 ng/ml GDNF) when cells are approximately 70% confluent. Change media every other day for three weeks. Do not split cells during differentiation.</li>
		<li>After three weeks cells should express the neuronal marker TUJ1. To gain more mature neurons and neuronal subtypes continue differentiation up to 3 months.</li>
	</ol>
	</li>
	<li>Differentiation towards glial lineage
	<ol>
		<li>Change media to glial induction media (1:1 DMEM/F-12 : Neurobasal, 1x N2, 1x B27, 10 &#181;M &#946;-mercaptoethanol, 100 &#181;M non-essential amino acids, 1.5 mM L-Glutamine, 5 &#181;g/ml insulin, 40 ng/ml T3) including 20 ng/ml EGF to induce differentiation into glial precursor cells. Remove half of the media and replace by fresh media every other day for about 2 weeks. During this period cells should be split 1:3 in presence of 10 &#181;M ROCK inhibitor Y27632 when 100% confluency is reached.</li>
		<li>After 2 weeks differentiate cells further into astrocytes: when cells are nearly confluent change media to commercial available astrocyte media, change media every second day. After about 7 days cells start to express astrocyte markers (e.g., GFAP). If cells get 100% confluent during the differentiation protocol, split them in a 1:2 ratio in presence of 10 &#181;M ROCK inhibitor Y27632.</li>
	</ol>
	</li>
</ol>

The authors declare that they have no competing financial interests.

Here we show the isolation and direct conversion of human fibroblasts into expandable transgene-free neural progenitor cells and their differentiated progeny as a putative basis for cell-replacement therapy or application in drug screening analyses. Direct lineage conversion of somatic cells into NPCs has been achieved by forced expression of lineage-specific transcription factors 26,33,34. Nevertheless, in many cases fetal fibroblasts were used for transdifferentiation experiments33,34. For biomedi...

In 2006 Yamanaka and colleagues could show for the first time the possibility of reprogramming of somatic cells into a pluripotent state1. This dedifferentiation was achieved by overexpression of four transcription factors Oct4, Sox2, Klf4, and c-Myc in murine fibroblasts. The generated so-called induced pluripotent stem cells (iPSCs) show functional equivalence to embryonic stem cells (ESCs) and can thus be differentiated into all cell types of the adult organism. One year later reprogramming to iPSCs could also be achieved for human fibroblasts2. Experiments in animal models demonstrate that iPSC-derived cells can generally be used for cell replacement therapy, e.g., in Parkinson&#8217;s Disease (PD) 3-5. However, several limitations associated with the use of iPSCs represent roadblocks for the full realization of their therapeutic potential. First of all, reprogramming of cells into a pluripotent state and subsequent quality control is generally a time-consuming and inefficient process yielding in extensive and thus costly cell culture procedures. Second, iPSCs need to be re-differentiated into the desired cell type of interest before biomedical application and the probability of residual pluripotent cells in the differentiated population harbors a significant tumorigenic potential and thus displays a high risk after cell transplantation6. Third, the reprogramming process is usually achieved by inducing the reprogramming factors by lenti- or retroviral infection. The integration of these viruses into the host genome might lead to insertional mutagenesis and/or uncontrolled reactivation of the transgenes7,8. Non-integrative systems have been developed to deliver the reprogramming factors to target cells, which minimize the risk of insertional mutagenesis and transgene reactivation. Examples for these transgene-free approaches are the reprogramming of cells using non-integrating Adeno or Sendai virus9,10, DNA-based vectors11 or the application of DNA-free methods, like transfection of synthetic mRNA12 or transduction of recombinant proteins13,14. Another promising method for the derivation of transgene-free iPSC is the use of loxP-modified lentiviral reprogramming constructs and subsequent deletion of transgenes using the Cre-loxP DNA recombination system15,16.
A more straightforward approach to generate neural cells for cell replacement therapy represents direct conversion of fibroblasts into post-mitotic neurons17-20. Vierbuchen et al. reported that the overexpression of transcription factors Ascl1, Brn2 and Myt1l results in the generation of 20% neurons from murine fibroblasts17. In 2011 it was shown, that the same three transcription factors in combination with overexpression of NeuroD1 enable transdifferentiation of human fibroblasts into neurons19. Human induced neurons could also be generated by overexpression of Ascl1 and Ngn2 under dual SMAD- and GSK3&#946;- inhibition20. Notably, direct conversion of fibroblasts into neurons generates a non-proliferative, post-mitotic cell population that does not allow further expansion and biobanking.
Recently, the direct conversion of fibroblasts into a proliferating neural stem/progenitor cell population was reported21-26. For sake of clarity, all these cell types will be named as induced neural progenitor cells (iNPCs) in this report. Han et al. overexpressed Brn4, Sox2, c-Myc and Klf4 to generate iNPCs. Like their neural stem cell counterparts derived from either primary tissue or pluripotent cells these iNPCs are tripotential and could be differentiated into neurons, astrocytes and oligodendrocytes21. Our group reported a slightly different conversion protocol involving overexpression of Sox2, Klf4, and c-Myc and induced Oct4-expression for 5 days only. With this approach we could generate stably proliferating iNPCs from murine embryonic and adult fibroblasts that exhibit complete silencing of the reprogramming factors22. In contrast to iPSCs, iNPCs do not exhibit a tumorigenic potential after transplantation27. We used converted cells successfully in an animal model of demyelination, myelin deficient rats, demonstrating that iNPCs are clinically useful22. Until then, NPCs could be only generated from pluripotent stem cells or primary neural tissue28-32. iNPCs are stably expandable cells that can be cryopreserved and are able to differentiate into neurons, astrocytes and oligodendrocytes. Much effort has been made to adapt the direct conversion protocol from mouse to human cells23,26,33,34. In 2012 it was published that overexpression of the single factor Sox2 in fibroblasts is sufficient to generate murine and human iNPCs33. The authors reported generation of human iNPCs from fetal foreskin fibroblasts and characterized them by staining against Sox2 and Nestin. However, the target cells used for reprogramming represent a very particular cell type that won&#8217;t be available in clinical practice and there was no functional characterization of converted cells by transplantation in an animal model performed. A more recent publication describes the generation of neuronal restricted progenitors from human fetal fibroblasts by overexpression of Sox2, c-Myc and either Brn2 or Brn434. The generated cell lines showed self-renewal capacity and could be differentiated into various types of terminal neurons. However, the usage of fetal fibroblasts is unfavorable, as these cells are of heterogeneous origin and one cannot exclude the presence of residual e.g., neural crest stem cells in the preparations. In 2014, Zhu et al. reported the direct conversion of human adult and neonatal fibroblasts into tripotential neural progenitor cells by overexpression of Sox2 together with Oct4 or Oct4 alone and addition of small molecules to the cell culture media. Notably, based on their studies Sox2 alone was insufficient to induce direct conversion26. More recently, Lu et al. reported that the overexpression of the Yamanaka factors Oct4-, Sox2-, Klf4-, c-Myc by Sendai virus for 24 hr and subsequent inactivation of the virus by increased temperature results in the generation of expandable tripotential neural precursor cells23. In conclusion, although the conversion protocols published for human cells thus far have in common the overexpression of at least one or more of the Yamanaka factors, often in a timely restricted manner, there is no clear indication of the minimal molecular factors needed to drive direct conversion into iNPCs. The timely restricted overexpression of Oct4 by either genetic means, transfection with synthetic mRNA, or cell-permeant protein together with constitutive expression of Sox2, Klf-4, and c-Myc did not result in stable human iNPC lines yet. Thus, the application of Sendai virus to overexpress all Yamanaka factors and timely restrict their activity by heat inactivation of the virus23 together with optimized neural media induction conditions22,31 represents the preferred strategy thus far.
Several studies demonstrate the cellular functionality of NSCs or their differentiated counterparts in different animal disease models. Neural progenitors from human pluripotent stem cells have been transplanted in mouse models of the neuroinflammatory disorder multiple sclerosis35,36. The applicability of hESC-derived neural progenitor cells in EAE (experimental autoimmune encephalomyelitis)-mice was first shown in 2008 35. Multipotent neural precursor cells were injected into the ventricles of mouse brain, and the transplantation resulted in the reduction of clinical signs of EAE. Kim et al. generated oligodendroglial precursors from hESCs and transplanted those intracerebroventricularly into EAE-mice. Although transplants did not survive for more than 10 days, mice showed significant improvement of neurological function and reduction of proinflammatory immune cells in the white matter36. Stem cell therapy has also been applied for preclinically targeting of Parkinson&#8217;s Disease as NPCs could be successfully employed in the respective animal models. For this, progenitor cells were either derived from fetal brain tissue37 differentiated from pluripotent stem cells38-40 or mesenchymal stem cells41 were used. In 2012 we showed that mouse iNPCs are able to produce proteolipid protein, the major myelin protein component, after transplantation into the brains of myelin-deficient (md) rats22. By that proof-of-principle experiment the therapeutic applicability of iNPCs was firstly proven and soon confirmed by another study32. However, the full potential of therapeutic use of human iNPCs remains to be explored.
Here we show an robust and integrated process of (i) derivation of human primary cells from adult patients via skin biopsy, (ii) direct conversion of human fibroblasts into a neural progenitor state and (iii) the ability of iNPCs to be differentiated into neuronal and glial lineages. Usage of this protocol will help to speed up generation of autologous human cells for therapeutic applications.

<table border="0" cellpadding="0" cellspacing="0">
	<tbody>
		<tr>
			<td>Astrocyte media</td>
			<td>ScienCell</td>
			<td align="right">1801</td>
			<td></td>
		</tr>
		<tr>
			<td>B27</td>
			<td>LifeTechnologies</td>
			<td>17504-044</td>
			<td></td>
		</tr>
		<tr>
			<td>BDNF</td>
			<td>Peprotech</td>
			<td>450-02</td>
			<td></td>
		</tr>
		<tr>
			<td>Biopsy Punch</td>
			<td>pfm medical</td>
			<td align="right">48301</td>
			<td></td>
		</tr>
		<tr>
			<td>cAMP</td>
			<td>Sigma</td>
			<td>A6885</td>
			<td></td>
		</tr>
		<tr>
			<td>CHIR99021</td>
			<td>Axon medchem</td>
			<td align="right">1386</td>
			<td></td>
		</tr>
		<tr>
			<td>Collagenase Type2</td>
			<td>Worthington Biochemical</td>
			<td>LS004177</td>
			<td></td>
		</tr>
		<tr>
			<td>Dispase</td>
			<td>PAN&#160;</td>
			<td>P10-032100</td>
			<td></td>
		</tr>
		<tr>
			<td>DMEM</td>
			<td>LifeTechnologies</td>
			<td>41966-029</td>
			<td></td>
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			<td>DMEM F12</td>
			<td>LifeTechnologies</td>
			<td>11320-033</td>
			<td></td>
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		<tr>
			<td>DMSO</td>
			<td>Roth</td>
			<td align="right">4720</td>
			<td></td>
		</tr>
		<tr>
			<td>DPBS</td>
			<td>LifeTechnologies</td>
			<td>14190-094</td>
			<td></td>
		</tr>
		<tr>
			<td>EGF</td>
			<td>Life Technologies</td>
			<td>PHG0313</td>
			<td></td>
		</tr>
		<tr>
			<td>FCS</td>
			<td>Biochrom AG</td>
			<td align="right">50115</td>
			<td></td>
		</tr>
		<tr>
			<td>GDNF</td>
			<td>Peprotech</td>
			<td>450-10</td>
			<td></td>
		</tr>
		<tr>
			<td>Gentamicin</td>
			<td>Sigma</td>
			<td>G1397</td>
			<td></td>
		</tr>
		<tr>
			<td>GFAP-antibody</td>
			<td>Dako</td>
			<td>Z0334</td>
			<td></td>
		</tr>
		<tr>
			<td>GlutaMAX</td>
			<td>LifeTechnologies</td>
			<td>35050-038</td>
			<td></td>
		</tr>
		<tr>
			<td>hLIF</td>
			<td>Peprotech</td>
			<td>300-05</td>
			<td></td>
		</tr>
		<tr>
			<td>Insulin</td>
			<td>Seralab</td>
			<td>GEM-700-112-P</td>
			<td></td>
		</tr>
		<tr>
			<td>Ki67-antibody</td>
			<td>NeoMarkers</td>
			<td>RM-9106-S</td>
			<td></td>
		</tr>
		<tr>
			<td>L-Glutamine</td>
			<td>LifeTechnologies</td>
			<td>25030-024</td>
			<td></td>
		</tr>
		<tr>
			<td>Laminin</td>
			<td>Sigma</td>
			<td>L2020</td>
			<td></td>
		</tr>
		<tr>
			<td>N2</td>
			<td>LifeTechnologies</td>
			<td>17502-048</td>
			<td></td>
		</tr>
		<tr>
			<td>Nestin-antibody</td>
			<td>R&#38;D Systems</td>
			<td>MAB1259</td>
			<td></td>
		</tr>
		<tr>
			<td>Neurobasal</td>
			<td>LifeTechnologies</td>
			<td>21103-049</td>
			<td></td>
		</tr>
		<tr>
			<td>Non-essential amino acids</td>
			<td>LifeTechnologies</td>
			<td>11140-050</td>
			<td></td>
		</tr>
		<tr>
			<td>NSC freezing media</td>
			<td>Sigma</td>
			<td>C6295</td>
			<td></td>
		</tr>
		<tr>
			<td>Oct4-antibody</td>
			<td>Santa Cruz</td>
			<td>sc9081</td>
			<td></td>
		</tr>
		<tr>
			<td>Pax6-antibody</td>
			<td>Covance</td>
			<td>PRB-278P</td>
			<td></td>
		</tr>
		<tr>
			<td>SB431542</td>
			<td>Invivogen</td>
			<td>inh-sb43</td>
			<td></td>
		</tr>
		<tr>
			<td>Sendai virus: CytoTune Sendai Reprogramming Kit</td>
			<td>&#160;LifeTechnologies</td>
			<td>A1378001</td>
			<td></td>
		</tr>
		<tr>
			<td>Sodiumpyruvate</td>
			<td>Life Technologies</td>
			<td>11360-039</td>
			<td></td>
		</tr>
		<tr>
			<td>Sox1-antibody</td>
			<td>R&#38;D Systems</td>
			<td>AF3369</td>
			<td></td>
		</tr>
		<tr>
			<td>Sox2-antibody</td>
			<td>R&#38;D Systems</td>
			<td>MAB2018</td>
			<td></td>
		</tr>
		<tr>
			<td>T3</td>
			<td>Santa Cruz</td>
			<td>sc-205725</td>
			<td></td>
		</tr>
		<tr>
			<td>Trypsin/EDTA</td>
			<td>Life Technologies</td>
			<td>15400-054</td>
			<td></td>
		</tr>
		<tr>
			<td>TUJ1-antibody</td>
			<td>Covance</td>
			<td>MMS-435P-250</td>
			<td></td>
		</tr>
		<tr>
			<td>Vitamin C</td>
			<td>Sigma</td>
			<td>A4544</td>
			<td></td>
		</tr>
		<tr>
			<td>Y27632</td>
			<td>Calbiochem</td>
			<td>CAS 146986-50-7</td>
			<td></td>
		</tr>
		<tr>
			<td>&#946;-Mercaptoethanol</td>
			<td>LifeTechnologies</td>
			<td align="right">21985023</td>
			<td></td>
		</tr>
	</tbody>
</table>

derivation of adult human fibroblasts and their direct conversion into expandable neural progenitor cells

Generation of&#160;induced pluripotent stem cell (iPSCs) from adult skin fibroblasts and subsequent differentiation into somatic cells provides fascinating prospects for the derivation of autologous transplants that circumvent histocompatibility barriers. However, progression through a pluripotent state and subsequent complete differentiation into desired lineages remains a roadblock for the clinical translation of iPSC technology because of the associated neoplastic potential and genomic instability. Recently, we and others showed that somatic cells cannot only be converted into iPSCs but also into different types of multipotent somatic stem cells by using defined factors, thereby circumventing progression through the pluripotent state. In particular, the direct conversion of human fibroblasts into induced neural progenitor cells (iNPCs) heralds the possibility of a novel autologous cell source for various applications such as cell replacement, disease modeling and drug screening. Here, we describe the isolation of adult human primary fibroblasts by skin biopsy and their efficient direct conversion into iNPCs by timely restricted expression of Oct4, Sox2, Klf4, as well as c-Myc. Sox2-positive neuroepithelial colonies appear after 17 days of induction and iNPC lines can be established efficiently by monoclonal isolation and expansion. Precise adjustment of viral multiplicity of infection and supplementation of leukemia inhibitory factor during the induction phase represent critical factors to achieve conversion efficiencies of up to 0.2%. Thus far, patient-specific iNPC lines could be expanded for more than 12 passages and uniformly display morphological and molecular features of neural stem/progenitor cells, such as the expression of Nestin and Sox2. The iNPC lines can be differentiated into neurons and astrocytes as judged by staining against TUJ1 and GFAP, respectively. In conclusion, we report a robust protocol for the derivation and direct conversion of human fibroblasts into stably expandable neural progenitor cells that might provide a cellular source for biomedical applications such as autologous neural cell replacement and disease modeling.

Here we present description of an integrated process that allows generation of induced neural progenitor cells (iNPCs) from human fibroblasts that have been obtained by a punch biopsy from skin within less than 8&#160;weeks (Figure 1). Patient-specifc iNPCs can be further differentiated into neuronal and glial lineages and harbor huge potential for cell replacement therapy and disease modeling.
Infection of the fibroblasts with Oct4-, Klf4-, Sox2- and c-myc- Sendai viruses<sup...

Watch this Scientific Journal Video about Derivation of Adult Human Fibroblasts and their Direct Conversion into Expandable Neural Progenitor Cells at JoVE.com

Derivation of Adult Human Fibroblasts and their Direct Conversion into Expandable Neural Progenitor Cells

Generation of induced pluripotent stem cells provides fascinating prospects for the derivation of autologous transplants. However, progression through a pluripotent state and laborious re-differentiation still hinders clinical translation. Here we describe the derivation of adult human fibroblasts and their direct conversion into induced neural progenitor cells and the subsequent differentiation into neural lineages.

Generation of&#160;induced pluripotent stem cell (iPSCs) from adult skin fibroblasts and subsequent differentiation into somatic cells provides ...

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JoVE Journal

Neuroscience

15.3K Views.  University of Würzburg. Generation of induced pluripotent stem cells provides fascinating prospects for the derivation of autologous transplants. However, progression through a pluripotent state and laborious re-differentiation still hinders clinical translation. Here we describe the derivation of adult human fibroblasts and their direct conversion into induced neural progenitor cells and the subsequent differentiation into neural lineages.

Video: Derivation of Adult Human Fibroblasts and their Direct Conversion into Expandable Neural Progenitor Cells

Time-lapse Live Imaging of Clonally Related Neural Progenitor Cells in the Developing Zebrafish Forebrain

Precise patterns of division, migration and differentiation of neural progenitor cells are crucial for proper brain development and function1,2. To understand the behavior of neural progenitor cells in the complex in vivo environment, time-lapse live imaging of neural progenitor cells in an intact brain is critically required. In this video, we exploit the unique features of zebrafish embryos to visualize the development of forebrain neural progenitor cells in vivo. We use electroporation to genetically and sparsely label individual neural progenitor cells. Briefly, DNA constructs coding for fluorescent markers were injected into the forebrain ventricle of 22 hours post fertilization (hpf) zebrafish embryos and electric pulses were delivered immediately. Six hours later, the electroporated zebrafish embryos were mounted with low melting point agarose in glass bottom culture dishes. Fluorescently labeled neural progenitor cells were then imaged for 36hours with fixed intervals under a confocal microscope using water dipping objective lens. The present method provides a way to gain insights into the in vivo development of forebrain neural progenitor cells and can be applied to other parts of the central nervous system of the zebrafish embryo.

The present video demonstrates a method which takes advantage of the combination of electroporation and confocal microscopy to perform live imaging on individual neural progenitor cells in the developing zebrafish forebrain. In vivo analysis of the development of forebrain neural progenitor cells at a clonal level can be achieved in this way.

Precise patterns of division, migration and differentiation of neural progenitor cells are crucial for proper brain development and function1,2. To ...

Neural-Colony Forming Cell Assay: An Assay To Discriminate Bona Fide Neural Stem Cells from Neural Progenitor Cells

The neurosphere assay (NSA) is one of the most frequently used methods to isolate, expand and also calculate the frequency of neural stem cells (NSCs). Furthermore, this serum-free culture system has also been employed to expand stem cells and determine their frequency from a variety of tumors and normal tissues. It has been shown recently that a one-to-one relationship does not exist between neurosphere formation and NSCs. This suggests that the NSA as currently applied, overestimates the frequency of NSCs in a mixed population of neural precursor cells isolated from both the embryonic and adult mammalian brain. This video practically demonstrates a novel collagen based semi- solid assay, the neural-colony forming cell assay (N-CFCA), which has the ability to discriminate stem from progenitor cells based on their long-term proliferative potential, and thus provides a method to enumerate NSC frequency. In the N-CFCA, colonies &ge;2 mm in diameter are derived from cells that meet all the functional criteria of a NSC, while colonies &lt; 2mm are derived from progenitors. The N-CFCA procedure can be used for cells prepared from different sources including primary and cultured adult or embryonic mouse CNS cells. Here we use cells prepared from passage one neurospheres generated from embryonic day 14 mice brain to perform N-CFCA. The cultures are replenished with proliferation medium every seven days for three weeks to allow the plated cells to exhibit their full proliferative potential and then the frequency of neural progenitor and bona fide neural stem cells is calculated respectively by counting the number of colonies that are &lt; 2mm and the ones that are &ge;2mm in reference to the number of cells that were initially plated.

This video protocol demonstrates how to discriminate and enumerate bona fide neural stem cells in a mixed population of neural precursor cells using the neural colony-forming cell assay.

The neurosphere assay (NSA) is one of the most frequently used methods to isolate, expand and also calculate the frequency of neural stem cells (NSCs). ...

Live-cell Imaging of Sensory Organ Precursor Cells in Intact Drosophila Pupae

Since the discovery of Green Fluorescent Protein (GFP), there has been a revolutionary change in the use of live-cell imaging as a tool for understanding fundamental biological mechanisms. Striking progress has been particularly evident in Drosophila, whose extensive toolkit of mutants and transgenic lines provides a convenient model to study evolutionarily-conserved developmental and cell biological mechanisms. We are interested in understanding the mechanisms that control cell fate specification in the adult peripheral nervous system (PNS) in Drosophila. Bristles that cover the head, thorax, abdomen, legs and wings of the adult fly are individual mechanosensory organs, and have been studied as a model system for understanding mechanisms of Notch-dependent cell fate decisions. Sensory organ precursor (SOP) cells of the microchaetes (or small bristles), are distributed throughout the epithelium of the pupal thorax, and are specified during the first 12 hours after the onset of pupariation. After specification, the SOP cells begin to divide, segregating the cell fate determinant Numb to one daughter cell during mitosis. Numb functions as a cell-autonomous inhibitor of the Notch signaling pathway.
Here, we show a method to follow protein dynamics in SOP cell and its progeny within the intact pupal thorax using a combination of tissue-specific Gal4 drivers and GFP-tagged fusion proteins 1,2.This technique has the advantage over fixed tissue or cultured explants because it allows us to follow the entire development of an organ from specification of the neural precursor to growth and terminal differentiation of the organ. We can therefore directly correlate changes in cell behavior to changes in terminal differentiation. Moreover, we can combine the live imaging technique with mosaic analysis with a repressible cell marker (MARCM) system to assess the dynamics of tagged proteins in mitotic SOPs under mutant or wildtype conditions. Using this technique, we and others have revealed novel insights into regulation of asymmetric cell division and the control of Notch signaling activation in SOP cells (examples include references 1-6,7 ,8).

Live-cell Imaging of Sensory Organ Precursor Cells in Intact Drosophila Pupae

In this video, we describe a method for live cell imaging of asymmetrically dividing sensory organ progenitor cells and epidermal cells in intact Drosophila pupae

Since the discovery of Green Fluorescent Protein (GFP), there has been a revolutionary change in the use of live-cell imaging as a tool for understanding ...

Lineage-reprogramming of Pericyte-derived Cells of the Adult Human Brain into Induced Neurons

Direct lineage-reprogramming of non-neuronal cells into induced neurons (iNs) may provide insights into the molecular mechanisms underlying neurogenesis and enable new strategies for in vitro modeling or repairing the diseased brain. Identifying brain-resident non-neuronal cell types amenable to direct conversion into iNs might allow for launching such an approach in situ, i.e. within the damaged brain tissue. Here we describe a protocol developed in the attempt of identifying cells derived from the adult human brain that fulfill this premise. This protocol involves: (1) the culturing of human cells from the cerebral cortex obtained from adult human brain biopsies; (2) the in vitro expansion (approximately requiring 2-4 weeks) and characterization of the culture by immunocytochemistry and flow cytometry; (3) the enrichment by fluorescence-activated cell sorting (FACS) using anti-PDGF receptor-&#946; and anti-CD146 antibodies; (4) the retrovirus-mediated transduction with the neurogenic transcription factors sox2 and ascl1; (5) and finally the characterization of the resultant pericyte-derived induced neurons (PdiNs) by immunocytochemistry (14 days to 8 weeks following retroviral transduction). At this stage, iNs can be probed for their electrical properties by patch-clamp recording. This protocol provides a highly reproducible procedure for the in vitro lineage conversion of brain-resident pericytes into functional human iNs.

Targeting brain-resident cells for direct lineage-reprogramming offers new perspectives for brain repair. Here we describe a protocol of how to prepare cultures enriched for brain-resident pericytes from the adult human cerebral cortex and convert these into induced neurons by retrovirus-mediated expression of the transcription factors Sox2 and Ascl1.

Direct lineage-reprogramming of non-neuronal cells into induced neurons (iNs) may provide insights into the molecular mechanisms underlying neurogenesis ...

Feeder-free Derivation of Neural Crest Progenitor Cells from Human Pluripotent Stem Cells

Human pluripotent stem cells (hPSCs) have great potential for studying human embryonic development, for modeling human diseases in the dish and as a source of transplantable cells for regenerative applications after disease or accidents. Neural crest (NC) cells are the precursors for a large variety of adult somatic cells, such as cells from the peripheral nervous system and glia, melanocytes and mesenchymal cells. They are a valuable source of cells to study aspects of human embryonic development, including cell fate specification and migration. Further differentiation of NC progenitor cells into terminally differentiated cell types offers the possibility to model human diseases in vitro, investigate disease mechanisms and generate cells for regenerative medicine. This article presents the adaptation of a currently available in vitro differentiation protocol for the derivation of NC cells from hPSCs. This new protocol requires 18 days of differentiation, is feeder-free, easily scalable and highly reproducible among human embryonic stem cell (hESC) lines as well as human induced pluripotent stem cell (hiPSC) lines. Both old and new protocols yield NC cells of equal identity.

Neural crest (NC) cells derived from human pluripotent stem cells (hPSC) have great potential for modeling human development and disease and for cell replacement therapies. Here, a feeder-free adaptation of the currently widely used in vitro differentiation protocol for the derivation of NC cells from hPSCs is presented.

Human pluripotent stem cells (hPSCs) have great potential for studying human embryonic development, for modeling human diseases in the dish and as a ...

Cell Sorting of Neural Stem and Progenitor Cells from the Adult Mouse Subventricular Zone and Live-imaging of their Cell Cycle Dynamics

Neural stem cells (NSCs) in the subventricular zone of the lateral ventricles (SVZ) sustain olfactory neurogenesis throughout life in the mammalian brain. They successively generate transit amplifying cells (TACs) and neuroblasts that differentiate into neurons once they integrate the olfactory bulbs. Emerging fluorescent activated cell sorting (FACS) techniques have allowed the isolation of NSCs as well as their progeny and have started to shed light on gene regulatory networks in adult neurogenic niches. We report here a cell sorting technique that allows to follow and distinguish the cell cycle dynamics of the above-mentioned cell populations from the adult SVZ with a LeX/EGFR/CD24 triple staining. Isolated cells are then plated as adherent cells to explore in details their cell cycle progression by time-lapse video microscopy. To this end, we use transgenic Fluorescence Ubiquitination Cell Cycle Indicator (FUCCI) mice in which cells are red-fluorescent during G1 phase due to a G1 specific red-Cdt1 reporter. This method has recently revealed that proliferating NSCs progressively lengthen their G1 phase during aging, leading to neurogenesis impairment. This method is easily transposable to other systems and could be of great interest for the study of the cell cycle dynamics of brain cells in the context of brain pathologies.

We report a Fluorescent Activated Cell Sorting (FACS)-based method to isolate neural stem cells (NSCs) and their progeny from the subventricular zone (SVZ) of the adult mouse brain. Applied to Fluorescence Ubiquitination Cell Cycle Indicator (FUCCI) transgenic mice, it allows the study of cell cycle progression by live imaging.

Neural stem cells (NSCs) in the subventricular zone of the lateral ventricles (SVZ) sustain olfactory neurogenesis throughout life in the mammalian brain. ...

Development of a Refined Protocol for Trans-scleral Subretinal Transplantation of Human Retinal Pigment Epithelial Cells into Rat Eyes

Degenerative retinal diseases such as age-related macular degeneration (AMD) are the leading cause of irreversible vision loss worldwide. AMD is characterized by the degeneration of retinal pigment epithelial (RPE) cells, which are a monolayer of cells functionally supporting and anatomically wrapping around the neural retina. Current pharmacological treatments for the non-neovascular AMD (dry AMD) only slow down the disease progression but cannot restore vision, necessitating studies aimed at identifying novel therapeutic strategies. Replacing the degenerative RPE cells with healthy cells holds promise to treat dry AMD in the future. Extensive preclinical studies of stem cell replacement therapies for AMD involve the transplantation of stem cell-derived RPE cells into the subretinal space of animal models, in which the subretinal injection technique is applied. The approach most frequently used in these preclinical animal studies is through the trans-scleral route, which is made difficult by the lack of direct visualization of the needle end and can often result in retinal damage. An alternative approach through the vitreous allows for direct observation of the needle end position, but it carries a high risk of surgical traumas as more eye tissues are disturbed. We have developed a less risky and reproducible modified trans-scleral injection method that uses defined needle angles and depths to successfully and consistently deliver RPE cells into the rat subretinal space and avoid excessive retinal damage. Cells delivered in this manner have been previously demonstrated to be efficacious in the Royal College of Surgeons (RCS) rat for at least 2 months. This technique can be used not only for cell transplantation but also for delivery of small molecules or gene therapies.

Subretinal injection has been widely applied in preclinical studies of stem cell replacement therapy for age-related macular degeneration. In this visualized article, we describe a less risky, reproducible and precisely modified subretinal injection technique via the trans-scleral approach to deliver cells into rat eyes.

Degenerative retinal diseases such as age-related macular degeneration (AMD) are the leading cause of irreversible vision loss worldwide. AMD is ...

Homochronic Transplantation of Interneuron Precursors into Early Postnatal Mouse Brains

Neuronal fate determination and maturation requires an intricate interplay between genetic programs and environmental signals. However, disentangling the roles of intrinsic vs. extrinsic mechanisms that regulate this differentiation process is a conundrum for all developmental neurobiologists. This issue is magnified for GABAergic interneurons, an incredibly heterogeneous cell population that is born from transient embryonic structures and undergo a protracted migratory phase to disperse throughout the telencephalon. To explore how different brain environments affect interneuron fate and maturation, we developed a protocol for harvesting fluorescently labeled immature interneuron precursors from specific brain regions in newborn mice (P0-P2). At this age, interneuron migration is nearly complete and these cells are residing in their final resting environments with relatively little synaptic integration. Following collection of single cell solutions via flow cytometry, these interneuron precursors are transplanted into P0-P2 wildtype postnatal pups. By performing both homotopic (e.g., cortex-to-cortex) or heterotopic (e.g., cortex-to-hippocampus) transplantations, one can assess how challenging immature interneurons in new brain environments affects their fate, maturation, and circuit integration. Brains can be harvested in adult mice and assayed with a wide variety of posthoc analysis on grafted cells, including immunohistochemical, electrophysiological and transcriptional profiling. This general approach provides investigators with a strategy to assay how distinct brain environments can influence numerous aspects of neuron development and identify if specific neuronal characteristics are primarily driven by hardwired genetic programs or environmental cues.

Challenging young neurons in new brain regions can reveal important insights into how the environment sculpts neuronal fate and maturation. This protocol describes a procedure to harvest interneuron precursors from specific brain regions and transplant them either homotopically or heterotopically into the brain of postnatal pups.

Neuronal fate determination and maturation requires an intricate interplay between genetic programs and environmental signals. However, disentangling the ...

Identifying Cell Surface Markers of Primary Neural Stem and Progenitor Cells by Metabolic Labeling of Sialoglycan

Neural stem and progenitor cells (NSPCs) are the cellular basis for the complex structures and functions of the brain. They are located in specialized niches in vivo and can be isolated and expanded in vitro, serving as an important resource for cell transplantation to repair brain damage. However, NSPCs are heterogeneous and not clearly defined at the molecular level or purified due to a lack of specific cell surface markers. The protocol presented, which has been previously reported, combines a neural-endothelial co-culture system with a metabolic glycan labeling method to identify the surface sialoglycoproteome of primary NSPCs. The NSPC-endothelial co-culture system allows self-renewal and expansion of primary NSPCs in vitro, generating a sufficient number of NSPCs. Sialoglycans in cultured NSPCs are labeled using an unnatural sialic acid metabolic reporter with bioorthogonal functional groups. By comparing the sialoglycoproteome from self-renewing NSPCs expanded in an endothelial co-culture with differentiating neural culture, we identify a list of membrane proteins that are enriched in NSPCs. In detail, the protocol involves: 1) set-up of an NSPC-endothelial co-culture and NSPC differentiating culture; 2) labeling with azidosugar per-O-acetylated N-azidoacetylmannosamine (Ac4ManNAz); and 3) biotin conjugation to modified sialoglycan for imaging after fixation of neural culture or protein extraction from neural culture for mass spectrometry analysis. Then, the NSPC-enriched surface marker candidates are selected by comparative analysis of mass spectrometry data from both the expanded NSPC and differentiated neural cultures. This protocol is highly sensitive for identifying membrane proteins of low abundance in the starting materials, and it can be applied to marker discovery in other systems with appropriate modifications

Presented here is a protocol that combines an in vitro neural-endothelial co-culture system and metabolic incorporation of sialoglycan with bioorthogonal functional groups to expand primary neural stem and progenitor cells and label their surface sialoglycoproteins for imaging or mass-spectrometry analysis of cell surface markers.

Neural stem and progenitor cells (NSPCs) are the cellular basis for the complex structures and functions of the brain. They are located in specialized ...

Conversion of Human Induced Pluripotent Stem Cells (iPSCs) into Functional Spinal and Cranial Motor Neurons Using PiggyBac Vectors

We describe here a method to obtain functional spinal and cranial motor neurons from human induced pluripotent stem cells (iPSCs). Direct conversion into motor neuron is obtained by ectopic expression of alternative modules of transcription factors, namely Ngn2, Isl1 and Lhx3 (NIL) or Ngn2, Isl1 and Phox2a (NIP). NIL and NIP specify, respectively, spinal and cranial motor neuron identity. Our protocol starts with the generation of modified iPSC lines in which NIL or NIP are stably integrated in the genome via a piggyBac transposon vector. Expression of the transgenes is then induced by doxycycline and leads, in 5 days, to the conversion of iPSCs into MN progenitors. Subsequent maturation, for 7 days, leads to homogeneous populations of spinal or cranial MNs. Our method holds several advantages over previous protocols: it is extremely rapid and simplified; it does not require viral infection or further MN isolation; it allows generating different MN subpopulations (spinal and cranial) with a remarkable degree of maturation, as demonstrated by the ability to fire trains of action potentials. Moreover, a large number of motor neurons can be obtained without purification from mixed populations. iPSC-derived spinal and cranial motor neurons can be used for in vitro modeling of Amyotrophic Lateral Sclerosis and other neurodegenerative diseases of the motor neuron. Homogeneous motor neuron populations might represent an important resource for cell type specific drug screenings.

Conversion of Human Induced Pluripotent Stem Cells iPSCs into Functional Spinal and Cranial Motor Neurons Using PiggyBac Vectors

This protocol allows rapid and efficient conversion of induced pluripotent stem cells into motor neurons with a spinal or cranial identity, by ectopic expression of transcription factors from inducible piggyBac vectors.

We describe here a method to obtain functional spinal and cranial motor neurons from human induced pluripotent stem cells (iPSCs). Direct conversion into ...