feeder cells

Creating ground-state human iPSCs

Murine pluripotent stem cells can exist in two distinct states, blastocyst-derived LIF-dependent embryonic stem cells (ESCs) and epiblast-derived bFGF-dependent stem cells (EpiSCs). Murine ESCs and similar iPSC lines are more of the “ground-state” in terms of developmental status, as reflected by the lack of X chromosome inactivation in female cells and their abilities to pass as single cells. Human iPSCs, like human ES cells, are more similar to mouse EpiSCs. Unfortunately these human pluripotent stem cells are difficult to genetically manipulate, e.g. knockin or knockout. They also grow slowly, with doubling time averaging 36 hours. In order to create ground-state human iPSCs, several approaches have been tested, including reprogramming iPSC-derived fibroblasts, continuously expressing 5 iPS factors (Oct4, Sox2, Nanog, c-Myc, and Klf4), or using chemicals to inhibit chromatin modifying enzyme HDAC. While these approaches succeeded to certain degrees, the resulting cell lines seem to have some limitations, such as limited passage numbers.

Retinoic acid (RA) signaling is involved in many aspects of embryonic development. RA receptor (RAR), together with one of its heterodimerization partners, steroid hormone receptor Lrh-1, was recently found to be able to synergize with the 4 common iPS factors (Oct4, Sox2, Klf4, and c-Myc) to induce mouse and human fibroblasts into ground-state iPSCs. The pluripotent cells created by the so-called F6 factor combination show no X chromosome inactivation if from female origin, can fully activate the endogenous Oct4 promoter, express Rex1 (which is specific to mouse ESCs, not EpiSCs), and grow with a 16 hour doubling time. All these mouse ESC-like features were achieved without detectable expression of the exogenous factors once iPSC colonies formed, indicating transient F6 expression is capable of effectively initiating endogenous stem cell factors. Remarkably, these stem cells can maintain their undifferentiated status in mouse ESC medium for 50 passages or more. This work, published this month in Proceedings of National Academy of Science USA [1], provided the stem cell research and application field with a very desirable choice of human stem cells.

As opposed to ~16 days with F4, it appears that the time required to induce adult fibroblasts into pluripotent stem cells is as short as 4 days if F6 factors are introduced on a murine stem cell virus (MSCV) vector with an integrated piggyback transposon. As the authors noted in their discussion, the speed-up benefit should be particularly advantageous for transient transfection approaches such as mRNA reprogramming. The bottom line from this paper and the engineered factor papers (see the previous AlleleBlog article under “iPS and other Stem Cells”) is that iPSC reprogramming is only going to get faster, which means that hopefully in the near future creating iPSCs will become a routine experiment as easy as a simple transfection.

Wang, W., J. Yang, et al. (2011). “Rapid and efficient reprogramming of somatic cells to induced pluripotent stem cells by retinoic acid receptor gamma and liver receptor homolog 1.” Proc Natl Acad Sci U S A.

New Products of the week: ARCA, modified cap analog for in vitro transcription of mRNA.

Promotion of the week: Friday special this week, 15% off all iPS viral particle products if using code “ViraliPS” when ordering online at allelebiotech.com, by email, or fax.

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Thursday, October 27th, 2011 iPSCs and other stem cells No Comments

How do you produce your iPS cells?

From AlleleForum: First off, thank you for choosing Allele Biotech for your iPSC experiment needs. Now onto your questions

You asked Q1: How many human fibroblast cells you normally to start for transfection. I understand you use 12-well plate? How many days you wait till the cells grow confluent? If the cells never grow confluent, should I still transfer them to feeder plate? Is it critical for the cells to reach confluent, if it is, could you suggest the reasons to me

We usually plate at 70% or about 10e4-10e5 cells and transduce the cells for 2-3 days. It should become confluent in 2-3 days. There is no need for the cells to become confluent before splitting onto feeder cells. Please note for primary cells, do not wait for the cells to get too confluent because contact inhibition may induce growth senescence before cells are reprogrammed.

Q2: How many cells you plate on the feeder plate, let’s say it is 6-well plate, and how many clones would normally pup out from each well?

From one well of a 12 well plate, you can plate 1/5 onto a well of a 6 well feeder cell plate. From there, you should get plenty of colonies.

Q3: At the time when you need to cut the Loxp sites, what passage number you do, do you have to dispense the iPS into single cell? Do you have a detailed protocol for that? Other than virus, do you have any other means to do the job, like plasmid?

Never dispense iPSC into single cells. They do not grow back well if split into single cells. iPSC colonies should be passaged in patches of cells. To excise loxP, the suggested timing is after 12-14 days when the cells are reprogrammed into iPSC colonies. Just transduce the iPSC colonies with Cre virus.

Q4: Is it true, that the 4-in-1 is more powerful than individual ones? Do you have the construct(4-in-one) for sale?

The 4-in-1 is somewhat more effective than 4 individual ones. For license issues, we do not distribute the construct to customers because we only offer packaging service. Similar type of plasmid DNAs may be accessible from other sources.

If you have any other questions or concerns, please let us know. Thanks again.

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Protocols for Using Human Fibroblasts Expressing Human bFGF as Feeder Cells for iPSCs

New Product of the Week: Anti-GFP Polyclonal Antibody 100ug ABP-PAB-PAGFP10 $175.00.

Allele Biotech has introduced the highly efficient GFP-Trap for GFP fusion protein pull-down, and a monoclonal anti-GFP antibody for detecting GFP-fusion proteins after Immunoprecipitation with GFP-Trap. Just launched this week, the anti-GFP polyclonal antibodies provide an alternative method for analyzing the isolated proteins.

Pre-announcement: Allele Biotech will launch a FAQ and a User Forum online where you can also find common protocols in focus areas and exchange ideas with us or others.

1. Thaw one vial of irradiated feeder cells by swirling gently in 37oC water bath until all of the contents are thawed. One vial of 2×10^6 cells is sufficient to prepare two10-cm dishes, or two 6-well or 12-well plates (about 3-4×10^4/cm2).
2. Spray vial with 70% ethanol and wipe dry before placing in tissue culture hood.
3. Gently add 1 ml prewarmed feeder cell medium (alphaMEM or DMEM/F12 with 10% FBS), mix with contents of cryovial and transfer into 15-ml conical tube containing 4 ml prewarmed feeder cell medium.
4. Centrifuge the cells at 200g at room temperature for 5 min and discard the supernatant.
5. Resuspend the feeder cells in 12 ml feeder cell medium. If using a 6-well plate: add 1 ml of feeder cell suspension to each well of the 6-well plate containing 1 ml fresh feeder cell media per well. If using a 10-cm tissue culture dish: add 6 ml of feeder cell suspension to 10-cm tissue culture dish containing 6 ml fresh feeder cell media. If using a 12-well plate: add 0.5 ml feeder cell suspension to each well of 12-well plate containing 1 ml fresh feeder cell media per well. Gently shake the dish left/right and up/down 10-20 times without swirling the plate to evenly distribute the cells across the plate.
6. Incubate the cells in 37 1C, 5% CO2, overnight.
CRITICAL STEP When moving the feeder cell plates from the tissue culture hood to incubator, do not swirl the medium, as this tends to cause the cells to accumulate in the center. Immediately after placing the plates in the incubator, slide the plates forward and backward (2–3 cm) two times, then left to right (2–3 cm) two times to ensure equal distribution of the cells. Use within 5–7 days.
7. Split stem cells (~2.5 x 10^5 to 5 x 10^5 cells, or ~10% confluence) into plate with feeder cells: aspirate medium from ESC or iPSC, wash with PBS and add 0.5 ml of 0.05% trypsin. Incubate at 37oC, 5% CO2, for 5 min.
8. Inactivate trypsin with 3 ml stem cell medium (e.g. DMEM + 20% knockout serum replacement), and collect cell clumps in 15-ml conical tube avoiding making single cell suspension because ESC tends to die in single cell form.
9. Centrifuge at 200g at room temperature for 4 min.
10. Aspirate feeder medium from feeder plates (cells incubated in Step 6), rinse with one ml of stem cell medium and add 5 ml of stem cell medium and return to incubator.
11. Aspirate and discard supernatant from the conical tube in Step 8, resuspend cells in 5 ml stem cell medium, gently dispense the cell pellet three times, add to feeder cell wells or dishes.
12. Incubate stem cells grown on feeder cells at 37oC, 5% CO2, for 48 h.
13. Aspirate medium and replace with stem cell medium every day; if iPSC colony number is low, replace medium every two days.

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Wednesday, October 14th, 2009 iPSCs and other stem cells, Open Forum No Comments

FAQ About Feeder Cells for Stem Cells –Part One

The cost of preparing feeder cells for induced pluripotent stem cells (iPSCs) or embryonic stem cells (ESCs) is mainly due to 1. serum and media, 2. labor for growing and treating cells, and 3. expenses for freezing media and vials. Ready-to-use feeder cells saves one important labor-intensive step of iPSC generation, it should be an important help for iPSC and stem cell researchers. We know that most of our colleagues are tired of preparing fresh early passages of MEFs and treating them with expensive mitomycin C or finding an irradiator to pre-treat the MEFs. A lot of iPSC researchers lost iPS stem cells due to the lack of patience in handling MEF feeders. The offering of Allele’s feeder cell product line is really an easy solution and convenience to iPSC researchers.

Question 1: There are companies offering drug-resistant feeder cells such as MEF cells expressing neo-, puro-, or hygromycin-resistance genes. Is it important to have such drug-resistance genes when choosing feeder cells?

Adding drug resistant markers to these cells should not be necessary because iPSCs grown on feeder cells are usually not cultured in antibiotics-containing medium. The feeder cells will not be selected by drug resistance nor will they contaminate iPS cells since they can not propagate after irradiation. However, for those who do need to use drug selection for any reason, we will provide drug-resistant feeder cells upon request.

Question 2: There are publications showing the use of cells lines as feeder cells instead of primary fibroblasts, e.g. SL10, MRC-5, STO. Are there any advantages of using these cell lines?

Not really. Handling primary cells requires certain amount of experience and may be tedious; using cell lines, on the other hand, would be easier for preparing feeder cells. We provide feeder cells from immortalized early passage human foreskin fibroblasts at prices often lower than those from cell lines.

Question 3: Should I choose fluorescent protein expressing feeder cells for easy separation from iPSCs?

You do not need to include fluorescent protein in feeder cells, as feeder cells are quite different in morphology from iPS cells or ES cells. In fact, many labs use iPS factors that are co-expressed with fluorescent markers, in which cases feeder cell expressed fluorescent proteins will confuse the readout.

Question 4: What are the main advantages of using bFGF-expressing feeder cells?

Our bFGF-feeder cells not only eliminate the needs for added recombinant bFGF to stem cell cultures, but also form very nice cell lawn to serve iPSC colony formation because of their strictly controlled passage and growth conditions. We have used these cells without coating dishes with gelatin and obtained nice iPSC colonies.

Preview: Next Part of FAQ on Feeder Cells: choosing mouse or human fibroblasts, selecting iPSC colonies…

Announcement: An audience-orientated User Forum will be added to Allele Biotech webpages so that people can freely discuss or review products and technologies. A distilled version of discussions will be presented in a related but separate FAQ section, which will also include all Allele eNewsletters sent to our contacts about every quarter. Look for the links on www.allelebiotech.com in coming weeks.

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Wednesday, October 7th, 2009 iPSCs and other stem cells No Comments

Feeder Cells for Stem Cells

Allele’s entire iPSC product line is designed for the ease of the researcher. Each component in our iPSC catalog will shave priceless time off your protocol by eliminating the tedious steps in iPS induction so you can get down to work.

Allele is adding a major component to its iPSC line: pre-irradiated, ready-to-use, system specific, bFGF-Producing Feeder Cells for iPSC propagation!

Using Allele’s bFGF-Producing Feeder Cells avoids the usual problems associated with MEF cell lines. They are maintained at low passages, come pre-irradiated and ectopically express bFGF so there is no need to supplement your medium with additional growth factors.

Additionally, Allele Biotech is introducing human fibroblasts to the market for iPSC work. MEF is good for mouse iPSC reprogramming but human fibroblast feeders are preferred when creating human iPSCs due to their secreted factors. Propagate human iPSC with greater efficiency while eliminating non-human cells for therapeutic use of human iPSCs!

As always we encourage customer feed back. We are interested to hear about your stem cell work, needs, and requests for new products. We also welcome those who have new ideas and potential products to collaborate with us. We are here to help advance your research and get your technologies to the public.

If you are enjoying AlleleNews and AlleleBlogs: come back and check out our new Forum and FAQ Sections soon to be added to our blogs for quick product/service related exchange and messages of more user control.

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Wednesday, September 9th, 2009 iPSCs and other stem cells, State of Research No Comments