During mammalian development pluripotent stem cells produce a myriad of structurally and functionally distinct somatic cells. The reprogramming of somatic into pluripotent cells is fundamental to the development of patient-specific cell sources applicable to biomedical science and regenerative medicine. Different experimental approaches can reprogram somatic into pluripotent cells: the induced pluripotent stem cell (iPSC) technique, somatic cell nuclear transfer (SCNT), and cell-cell fusion. However, the factors and mechanism underlying somatic cell reprogramming remain elusive. Extract cell reprogramming is a suitable system to identify factors and mechanisms responsible for somatic cell reprogramming because it is amenable to biochemical assays and manipulations that can identify factors and therefore mechanisms involved in the reprogramming process. One prerequisite for the biochemical dissection of cell reprogramming is the development of a large scale reprogramming system, which uses potent but inexpensive extract sources to reprogram large numbers of somatic cells. Here, I describe the development of a cell extract-based reprogramming system, which uses protein extract isolated from the oocytes of salmon (Oncorhynchus tshawytscha). The developed system supports the digitonin-mediated permeabilization and survival of somatic cells as well as the uptake and retention of large molecules such as proteins within somatic cells. Salmon oocyte extract can at least partially reprogram mouse somatic cells into pluripotent cells. The established extract-based reprogramming system provides evidence that salmon oocytes are a suitable cell source for the identification of factors and the dissection of mechanisms involved in somatic cell reprogramming.

The general transcription factor II D (TFIID) nucleates the assembly of general transcription factors (GTF) and RNA polymerase II at the promoters to form the pre-initiation complex (PIC). TBP-associated factor I (TAF1), the scaffold of TFIID, not only interacts with other factors to stabilize the protein complex but also has several enzymatic activities.

In this study, genome-wide ChIP-on-chip analysis revealed that TAF1 recognizes and binds in vivo to more than 1,800 of core promoters. From the transcription profiling, 4,531 genes have been identified with more than 1.25 folds change in transcriptional level, including 2,780 genes with reduced transcription and 1,751 with an enhanced transcription level. Among TAF1 target genes, 53% of genes were directly down-regulated by TAF1, especially cyclins and cell cycle regulators. Genes such as members of the heat shock protein family were associated with direct TAF1 upregulation. This study suggests that TAF1 is essential protein and involved in various biological processes including cell cycle progression and stress response.