Section 9: Discovering the Yamanaka Factors

What were the three scientific streams that led to iPSCs? [?]

(1) SCNT/cloning (Gurdon, Wilmut),

(2) Master transcription factor function (Antennapedia, MYOD),

(3) Pluripotency factors in ESC (Evans, Martin, Smith, Thompson, Tada).

How many candidate factors did Yamanaka start with?

Yamanaka started with 24 candidate genes that were expressed in embryonic stem cells.

What were the 24 candidate genes?

They included Ecat1, Dppa5, Fbxo15, Nanog, Eras, Dnmt3, Ecat8, Gdf3, Sox15, Dppa2, Dppa3, Dppa4, Fthl17, Sall4, Oct4, Sox2, Rex1, Utf1, Tcl1, Klf4, β-catenin, c-Myc, Stat3, and Grb2.

What was Yamanaka's experimental strategy?

They transduced all 24 factors into mouse fibroblasts and looked for colonies that activated an ESC-specific gene (Fbx15).

Did any single factor work alone?

No, no single candidate gene was sufficient to activate the Fbx15 gene.

What happened when all 24 factors were used together?

All 24 factors together generated 22 G418-resistant colonies with ESC-like morphology.

How did Yamanaka identify the critical factors?

They withdrew individual factors from the pool of 24 and observed which withdrawals prevented colony formation.

Which factors were identified as essential?

Oct4, Sox2, Klf4, and c-Myc were identified as the essential factors for iPSC generation.

What are the Yamanaka factors?

The Yamanaka factors are Oct4, Sox2, Klf4, and c-Myc.

What role do Oct4, Klf4, Sox2, and c-Myc play?

They play important roles in the generation of iPS cells from mouse embryonic fibroblasts (MEF