VPA
Mouse and human cells can both be reprogrammed with one cluster of specific miRNAs
The miRNA302/367 cluster was first found to be a direct target for the stem cell-specific factors Oct4 and Sox2, recently Anokye-Danso et al. showed that by overexpressing this miRNA cluster mouse and human cells can be reprogrammed without the OSKM factors. Moreover, according to the publication in Cell Stem Cell, miRNA-mediated reprogramming is “up to two orders of magnitude” more efficient than OSKM overexpression (but the authors used individual Oct4, Sox2, Klf4, and c-Myc lentiviruses, instead of a polycistronic virus such as Allele’s lenti-iPS-4-in-1).
To reprogram mouse embryonic fibroblasts (MEFs), suppression of chromatin remodeling factor Hdac2 is necessary when using miRNA for iPSC isolation. Surprisingly, the Hdac2 level is low in human fibroblasts, which do not need an Hdac inhibitor such as valproic acid (VPA) for reprogramming. Oct4-GFP positive cells (stem cells) are observed only 7 days post infecting MEFs with the miRNA302/367, and hundreds colonies appear per 10 thousand cells. When using human fibroblasts, iPSCs form at 18 to 26 days, at an efficiency of approximately 10%, which is significantly higher than using individual OSKM viruses.
The high efficiency from using miRNA for reprogramming is likely due to the fact that miRNAs can target hundreds of mRNAs, compared to providing one mRNA at a time. Although this study concluded that the miRNA302/367 expressing lentivirus was eventually silenced post stem cell induction, emphasis must still be placed on finding a non-integrating method to deliver this miRNA cluster.
New Product of the Week: Chemically synthesized miRNAs by your own design, email oligo@allelebiotech.com for details.
Promotion of the week: Promotion of the week: save 10% on AlleleBalanced Luciferase Assay Kits. Email the code Luc10 to abbashussain@allelebiotech.com to redeem this offer.
mRNA Transfection for Better Transgene Expression
Different approaches have been developed to over-express or ectopically express a protein in cells: peptide or full length recombinant protein transfer, viral gene transfer, non-viral DNA transfer and non-viral mRNA transfer.
1) Peptide transfection can be efficient, yet it is limited to only a small part of the protein, limiting the functional potential. Protein transfection is not consistent enough so far, because of the complicated properties of different proteins. Allele Biotech has tested dozens of proteins with several proprietary reagents, leader peptides, etc. but we have decided not to carry a protein transfection product line due to its instability. Furthermore, protein production is an expensive and laborious process.
2) Viral gene transfer is very effective, such as the HIV-based lentivirus or MMLV-based retrovirus, adenovirus, adeno-like virus or baculovirus, etc. However, the potent side-effect will still need to be considered for certain applications, especially involving clinical studies. Nevertheless, as research tools, viral gene transfer is still a highly preferred method. Allele Biotech has been providing the most effective platform for both MMLV-based and HIV-1-based retrovirus packaging. Check out our product website for details.
3) Non-viral DNA transfer is the most widely used transgene method in the biological research community, due to the simplicity of the procedure. There are many commercial kits on the market. However, the low efficiency for transfecting most primary cells significantly limits their use. In recent years, several leading biotech companies have developed various electroporation systems to improve the transfection efficiency and cell viability; although these improvements help with getting DNA inside the cytoplasm, they hardly help transport it into nucleus where DNA is transcribed.
4) Non-viral mRNA transfer has been around for a long time, but it is not widely used. It made a big splash recently through its use for iPSCs reprogramming. IPSCs factor mRNAs greatly improved the iPSCs induction efficiency and completely avoided the viral integration. Other well-known examples of mRNA transfection include loading special cancer antigens or HIV antigens to dendritic cells (DCs) in vitro for personal immunotherapy. PSA antigen expressing DCs transfected by mRNA has moved on to Phrase I Clinical Trials for this purpose.
New Product of the Week: 3C protease immobilized on beads for GST, His tag removal, email oligo@allelebiotech.com for details.
Promotion of the week: 10% off on all fluorescent proteins. To redeem, email oligo@allelebiotech.com along with PROMO code: JELLYFISH
Telling Good iPSCs from Bad iPSCs
Since its discovery pluripotent stem cells (iPSCs) have been known to differ somewhat from embryonic stem cells (ESCs) in term of gene expression profiles. It also appears that only a small percentage of iPSCs have the full potential of stem cells defined by being able to develop into adult animals. Instead of a global pattern of variations, surprisingly, the difference between iPSC and ESC was found to localize in a small region of one chromosome in mouse, 12qF1, which could account for most iPS cells’ lack of complete pluripotency (Stadtfeld et al, Nature 2010). In this region resides an imprinted gene cluster that includes 2 non-coding genes, Gtl2 and Rian, that remain silenced in most iPSCs. The underlining mechanism is hypermethylation and hypoacetylation, resulting in “paternalizaition” of the region. The effects are manifested around the mid-gestation stage.
By adding histone deacetylase inhibitor valproic acid (VPA) the silenced gene cluster may be reactivated and the iPSCs so treated show increased Gtl2 expression and ability to give rise to normal embryos. Expression of other imprinted genes showed clone-to-clone variations, as was previously reported by a number of groups, but no consistent differences between ESCs cells and iPSCs. Therefore, by analyzing the expression levels of just two genes, Gtl2 and Rian, the potential of iPSCs to be fully pluripotent can be assessed.
The relationships between stem cell status and epigenetic repressions also include the recent finding that Oct4 and Sox2, which are both germ cell-specific and critical reprogramming factors, may be implicated in the regulation of Xist and Tsix RNAs that control epigenetic silencing of X chromosome in female embryos.
New Product of the Week 05-17-10 to 05-23-10: RT-PCR primer set, ABP-SC-iPSh4NX $49, for identifying exogenous iPS factor expression from 4-in-1 iPS lentivirus
Promotion of the Week 05-17-10 to 05-23-10: $85 off IceCube dry bath 0-75C variable temp
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