Background

Multipotent neural progenitor cells (NPCs) generate the major cell types of the central nervous system (CNS): neurons, astrocytes, and oligodendrocytes. Human pluripotent stem cells (hPSCs), including embryonic stem (ES) cells and induced pluripotent stem (iPS) cells, can be directed to differentiate into NPCs using a variety of methods. This process, known as ‘neural induction’, must be efficient and reliable, in order to generate high-quality NPCs for downstream applications. hPSC-derived NPCs are used extensively for studying human nervous system development, modeling neurological disorders, and screening potential therapeutic molecules.

For a number of years, the predominant methods for neural induction of human ES and iPS cells have involved either co-culture with a stromal cell line, or embryoid body (EB) formation. More recently, studies have shown that neural induction from human ES and iPS cells can also be achieved in a monolayer culture system, wherein human ES and iPS cells are plated onto a defined matrix, and exposed to inductive factors.^1,2

STEMdiff™ Neural Induction Medium is a defined, serum-free medium for the generation of NPCs from hPSCs. The standard protocol for this product involves EB formation and selection of neural rosettes, to obtain highly enriched cultures of CNS-type NPCs in 12 days (Figures 1A, 2A). In this technical bulletin, we describe a method for neural induction using STEMdiff™ Neural Induction Medium in a monolayer culture system (Figures 1B, 2B). Using this protocol, CNS-type NPCs can be generated from human ES or iPS cells in six to nine days.

Protocol: Rapid Neural Induction in a Monolayer Culture System

This procedure is for neural induction of ES or iPS cells cultured in 10 cm² culture dishes. If using alternative culture-ware, adjust volumes accordingly. This protocol was developed using H9 human ES cells and has been validated with the ES and iPS lines listed in Table 1. It may be necessary to modify some steps of the protocol, such as seeding density (step 12) or timing of first passage (step 14), to optimize performance for other cell lines.

*Only recommended for use when neural induction is performed using STEMdiff™ SMADi Neural Induction Kit

Materials

• STEMdiff™ Neural Induction Medium (Catalog #05835)
• Gentle Cell Dissociation Reagent (Catalog #07174)
• PBS without Ca++ and Mg++ (e.g. Catalog #37350)
• DMEM/F-12 with 15 mM HEPES (e.g. Catalog #36254)
• Y-27632 (Catalog #72302)
• Poly-Ornithine/Laminin- or Matrigel®-coated plates or coverslips
• 50 mL conical tube (e.g. Falcon® Conical Tubes, Catalog #38010)
• Hemocytometer
• Trypan blue (e.g. Catalog #07050)
• ACCUTASE™ (Catalog #07920)
• STEMdiff™ Neural Progenitor Medium (Catalog #05833)

Before beginning the experiment, prepare poly-Ornithine/Laminin- or Matrigel®-coated plates or coverslips (see STEMdiff™ Neural Induction Medium manual; Catalog #28782).

Procedure for Neural Induction

1. Pre-warm STEMdiff™ Neural Induction Medium, Gentle Cell Dissociation Reagent, PBS without Ca++ and Mg++, and DMEM/F-12 to 37°C.
2. Estimate volume of STEMdiff™ Neural Induction Medium required for initial seeding (see Table 2), and supplement with 10 μM Y-27632 (ROCK inhibitor).
   

   Table 2. Suggested Volumes of Medium and Cell Numbers Required to Achieve Recommended Seeding Densities

   
3. Inspect each 10 cm² plate of human ES or iPS cells (previously maintained in mTeSR™1, mTeSR™ Plus, or TeSR™-E8™) and aspirate any areas of differentiated cells.
4. Rinse each plate once with 5 - 10 mL of sterile PBS.
5. Add 3 mL of Gentle Cell Dissociation Reagent and incubate at 37°C for 8 - 10 minutes.
6. After incubation period, gently dislodge cells that are still attached, using a 5 mL pipet. Triturate cells by pipetting up and down 5 - 10 times.
7. Add 5 mL of DMEM/F-12 and collect cells into a 50 mL conical tube.
8. Optional: Add an additional 5 mL of DMEM/F-12 onto the 10 cm² plate to rinse off any remaining cells and add to the 50 mL tube.
9. Count viable cells using Trypan Blue and a hemocytometer.
10. Centrifuge cells at 300 x g for 10 minutes.
11. Resuspend cells in an appropriate volume of STEMdiff™ Neural Induction Medium supplemented with 10 μM Y-27632 to achieve a seeding density of 200,000 or 250,000 cells/cm², for ES cells and iPS cells respectively. See suggested volumes in Table 2.
12. Seed cells onto poly-Ornithine/Laminin- or Matrigel®-coated plates or coverslips.
13. Replace medium daily with fresh STEMdiff™ Neural Induction Medium. Y-27632 is not required after seeding. If performing further differentiation to neuronal lineage, see Important Notes below.
14. After six to nine days in STEMdiff™ Neural Induction Medium, cells will be OCT4-negative and PAX6-positive (Figures 3 - 5). At this point, cultures will be confluent and ready for passage using ACCUTASE™.

Passaging

• After the first passage, NPCs should be passaged once they reach 70 - 80% confluency, and seeded in the next passage at a density between 125,000 and 200,000 cells/cm³.
• Maintain NPCs in STEMdiff™ Neural Induction Medium until passage 3. At passage 3, transition cells into STEMdiff™ Neural Progenitor Medium.
• Supplement STEMdiff™ Neural Induction Medium with Y-27632 for the first day after each passage. Y-27632 is not required when maintaining cells in STEMdiff™ Neural Progenitor Medium.

Important Notes

• Cell density is critical for achieving success. If seeding at too low a density, the efficiency of neural induction will be reduced.
• Visual inspection of cultures is not a reliable method of confirming neural induction. We recommend assessing expression of markers for neural induction (PAX6) and/or undifferentiated ES or iPS cells (e.g. OCT4).
• We recommend maintaining NPCs in STEMdiff™ Neural Induction Medium until passage three, and in STEMdiff™ Neural Progenitor Medium thereafter.
• STEMdiff™ Neural Induction Medium should be supplemented with Y-27632 for the first day after each passage. Y-27632 is not required when maintaining cells in STEMdiff™ Neural Progenitor Medium.
• For differentiation to neuronal subtypes (e.g. dopaminergic, motor), inductive factors are added between days five and seven¹. Differentiation to glial subtypes requires NPCs at passage four or later³.

See more technical tips for neural induction using monolayer culture >

Results

STEMdiff™ Neural Induction Medium can be used for neural induction in a monolayer culture system, to generate highly enriched cultures of PAX6-positive NPCs. The confluent NPC monolayer generated using this method may feature rosette-like radial arrangements of cells, but the morphology is not sufficiently distinct to allow for neural rosette isolation (Figure 2).

Figure 2. Morphology of Neural Progenitor Cell Cultures Generated Using Embryoid Body and Monolayer Culture Protocols

(A) At day 12 in the EB neural induction protocol, distinct clusters of neural rosettes are clearly visible and can be isolated using STEMdiff™ Neural Rosette Selection Reagent. (B) NPCs in the monolayer culture protocol form a more morphologically homogenous confluent monolayer. Although rosette-like radial arrangements of cells may be observed (see higher magnification in inset), these are not sufficiently morphologically distinct to allow rosette isolation. Scale bar = 100 μm.

The time-course of neural induction is similar in the EB and monolayer culture procedures (Figure 3); however, the time-points at which NPCs are available as single cells differ. In the EB protocol, PAX6-positive single cells are available for passage at day 16 - 18, after rosette selection and replating (Figure 1A). In contrast, in the monolayer protocol, PAX6-positive single cells are available for passage at day 6 - 9, as soon as neural induction is complete (Figure 1B).

Immunocytochemistry and quantitative PCR data show that during neural induction of ES cells, OCT4 expression decreases rapidly in the first 3 - 4 days, after which PAX6 expression increases (Figures 4 - 5). This monolayer culture protocol can also be used for neural induction of human iPS cell lines, although the time-course of induction may be slightly longer. In addition, highly efficient neural induction of human ES and iPS cells can be achieved, regardless of whether they were previously maintained in mTeSR™1, mTeSR™ Plus, or TeSR™-E8™ hPSC culture media (data not shown).

Conclusions

Here we describe a procedure for neural induction using STEMdiff™ Neural Induction Medium in a monolayer culture-based system. Using this method, PAX6-positive NPCs can be generated efficiently. This simple protocol can be used to achieve rapid and efficient neural induction of ES or iPS cells maintained in either mTeSR™1, mTeSR™ Plus, or TeSR™-E8™.

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