iPS cells can be used to generate full term mice

Note: This is a review of the published article listed below. All information, quotes, figures, methods, and findings mentioned in this review are from that article, and are the property of its authors and/or the publication in which the article originally appeared.

Original Research Paper

iPS Cells Can Support Full-Term Development of Tetraploid Blastocyst-Complemented Embryos

Lan Kang, Jianle Wang, Yu Zhang, Zhaohui Kou and Shaorong Gao

Cell Stem Cell, Volume 5, Issue 2, 135-138, 23 July 2009

Review

Induced pluripotent stem cells (iPS cells) are derived from non-pluripotent cells, typically from adult skin cells, through introduction of genes that reprogram the cell and transform it into a pluripotent cell that has all the characteristics of an embryonic stem cell. iPS cells were first produced in 2006 from mouse cells and in 2007 from human cells. This was a breakthrough in stem cell research, as it allowed researchers to obtain pluripotent stem cells, for research and therapeutic use, without the controversial use of embryos.

However, the methods used to reprogram adult cells to obtain iPS cells pose significant risks including the use of oncogenes to transform the cells. In 2008, a technique was published on how to remove transgenes after induction of pluripotency and in 2009 it was demonstrated that the generation of iPS cells was possible without any genetic alteration of the adult cell by repeated treatments of certain proteins.

The latest advance comes from a group of scientists from China (Kang et.al. 2009; Cell Stem Cell) who for the first time have successfully demonstrated that a mouse iPS cell line induced by four transcription factors can be used to generate full-term mice via tetraploid complementation.

Stem cell-like colonies were produced by viral transduction of the transcription factors Oct4, Sox2, Klf4, and c-Myc into mouse embryonic fibroblast cells from ROSA26-M2rtTA transgenic mice. After propagation they selected five iPSC lines that exhibited typical embryonic stem cell morphology, positive AP activity and expressed pluripotency marker genes including Oct4, Sox2, and Nanog. The karyotypes of all five iPSC lines were normal, with 40 chromosomes. Further tests including in vitro differentiation, in vivo teratoma formation, and formation of chimeras validated the pluripotency of the five iPSC lines. These cell lines were then tested to see if they could generate full-term mice through tetraploid complementation.

The tetraploid embryos were generated by fusing late two cell-stage embryos to one cell stage embryos from a female mouse and were then mated with the male mice of the same strain. Ten to fifteen iPSCs were microinjected into the cavity of the tetraploid blastocysts and the complemented blastocysts were transferred into seven pseudo pregnant ICR female mice.

They were able to produce four full term pups of which one survived into adulthood. SSLP and rtTA analysis of the organs collected from the three dead pups and the tail tip of the live mouse confirmed that all pups were derived from the iPSCs and not from the tetraploid embryos.

Tetraploid complementation is the most stringent test of pluripotency. Although only 1.0% of complemented blastocysts produced full-term mice, this is the first report of an iPS cell line shown to be fully pluripotent.