Group leader: 

Keisuke Kaji

Position: 

Dr

Contact: 

keisuke [dot] kaji [at] ed [dot] ac [dot] uk

Aims
Recently a technology to generate pluripotent stem cells from differentiated somatic cells has been developed using defined factors. However, the biological mechanism underlying the process of reprogramming has not been elucidated at all. Our group aims to understand the mechanism of the reprogramming, improve the technology and enable to control cell fate.

Background
In 2006 Yamanaka and Takahashi demonstrated that forced expression of four factors, Oct4, Sox2, Klf4 and c-Myc, can reprogram adult somatic cells from mice to a pluripotent state, which can be maintained as induced pluripotent stem (iPS) cells. This technology has since been utilized to produce human iPS cells, which have the exciting potential to be used as platforms of in vitro disease models, desease specific drug screening, and sauce of patient specific tissue in regenerative medicine, etc. However the original technology requires viral gene transduction and resulting multiple viral vector integration and permanent existance of the exogenous genes in the genome can cause unexpectred abnormalities in the iPS cells and re-differentiated cells. In additon, the efficiency of reprograming is still very low and the process takes a long time. To improve the technology it is essential to understand the mechanism.

Approaches and progress
We have developed non-viral one vector reprogramming system. In this system we can generate iPS cells with only one vector integration, and from which all the exogenous factors are subsequently removed using a Cre-loxP recombination system. Based on the one vector system we are generating iPS cell lines which has inducible expression of all the reprogramming factors. Because all of the differentiated cells from the iPS cells can induce the reprogramming factors without additional gene derively, we can achieve high reprogramming efficiency, which is essential to analyze the molecular mechanism of the reprogramming process. We perform gene expression profiling and analyze epigenetic modification change during the process using the system. Based on the knowledge, we aim to understand the mechanism of the reprogramming and improve the technology.

Selected publications

• O'Malley J, Woltjen K, Kaji K. 2009. New strategies to generate induced pluripotent stem cells. Curr Opin Biotechnol, Epub PMID 19837580.
• Kaji K, Norrby K, Paca A, Mileikovsky M, Mohseni P, Woltjen K. 2009. Virus-free induction of pluripotency and subsequent excision of reprogramming factors. Nature 458:771-775. Press release.
• Woltjen K, Michael IP, Mohseni P, Desai R, Mileikovsky M, Hämäläinen R, Cowling R, Wang W, Liu P, Gertsenstein M, Kaji K, Sung HK, Nagy A. 2009. PiggyBac transposition reprograms fibroblasts to induced pluripotent stem cells. Nature 458:766-770. Press release.
• Kaji K, Nichols J, Hendrich B. 2007. Mbd3, a component of the NuRD co-repressor complex, is required for development of pluripotent cells. Development. 134:1123-1132.
• Kaji K, Caballero IM, Macleod R, Nichols J, Wilson VA, Hendrich B. 2006. The NuRD component Mbd3 is required for pluripotency of embryonic stem cells. Nat Cell Biol 8:285-292.
• Kaji K and Kudo A. 2004. The mechanisms underlying sperm-egg fusion at fertilization. Reproduction 127:423-429.
• Kaji K, Oda S, Miyazaki S, Kudo A. 2002. Infertility of CD9-deficient mouse eggs is reversed by mouse CD9, human CD9 or mouse CD81; Polyadenylated mRNA injection developed for molecular analysis of sperm-egg fusion. Dev Biol 247:327-334.
• Kaji K, Katogi R, Azuma Y, Naito A, Inoue JI, Kudo A. 2001. Tumor necrosis factor alpha-induced osteoclastogenesis requires tumor necrosis factor receptor-associated factor 6. J Bone Miner Res 16:1593-1599.
• Kaji K, Takeshita S, Miyake K, Takai T, Kudo A. 2001. Functional association of CD9 with the Fc gamma receptors in macrophages. J. Immunol. 166:3256-3265.
• Kaji K, Oda S, Shikano T, Ohnuki T, Uematsu Y, Sakagami J, Tada N, Miyazaki S, Kudo A. 2000. The gamete fusion process is defective in eggs of Cd9-deficient mice. Nat Genet 24:279-282.

Funding

• European Research Council Starting Grant
• Medical Research Council