Early experiments by takahashi and yamanaka showed that a set of four genes introduced by retroviral expression are capable of transforming somatic cells into induced pluripotent stem cells. the four proteins encoded by these genes were all:
a. g-protein coupled receptors.
b. calcium-binding proteins.
c. tyrosine kinases.
d. transcription factors.

D. transcription factors.

Explanation:

Transcription factors include activators and repressor proteins. They are the cytosolic proteins and are involved in the regulation of gene expression in eukaryotes. The transcription factor may increase the expression of a gene by serving as an activator or may inhibit the gene expression. The pluripotent stem cells are the embryonic and adult stem cells that have the ability to give rise to many but not all the cell types of an organism.

Transformation of somatic cells into the pluripotent stem cells requires the expression of the genes involved in the production of different cell types. Therefore, during their experiments, Takahashi and Yamanaka introduced the genes of the transcription factors involved in the expression of the genes that are otherwise expressed in pluripotent stem cells but not in the somatic cells.

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