Medaka Oct4 is essential for pluripotency in blastula formation and ES cell derivation.

The origin and evolution of molecular mechanisms underlying cellular pluripotency is a fundamental question in stem cell biology. The transcription factor Oct4 or Pou5f1 identified in mouse features pluripotency expression and activity in the inner cell mass and embryonic stem (ES) cells. Pou2 identified in zebrafish is the non-mammalian homolog prototype of mouse Oct4. The genes oct4 and pou2 have reportedly evolved by pou5 gene duplication in the common ancestor of vertebrates. Unlike mouse oct4, however, zebrafish pou2 lacks pluripotency expression and activity. Whether the presence of pluripotency expression and activity is specific for mammalian Oct4 or common to the ancestor of vertebrate Oct4 and Pou2 proteins has remained to be determined. Here we report that Oloct4, the medaka oct4/pou2, is essential for early embryogenesis and pluripotency maintenance. Oloct4 exists as a single copy gene and is orthologous to pou2 by sequence and chromosome synteny. Oloct4 expression occurs in early embryos, germ stem cells and ES cells like mouse oct4 but also in the brain and tail bud like zebrafish pou2. Importantly, OlOct4 depletion caused blastula lethality or blockage. We show that Oloct4 depletion abolishes ES cell derivation from midblastula embryos. Thus, Oloct4 has pluripotency expression and is essential for early embryogenesis and pluripotency maintenance. Our results demonstrate the conservation of pluripotency expression and activity in vertebrate Oct4 and Pou2 proteins. The finding that Oloct4 combines the features of mouse oct4 and zebrafish pou2 in expression and function suggests that Oloct4 might represent the ancestral prototype of vertebrate oct4 and pou2 genes.

Counteracting activities of OCT4 and KLF4 during reprogramming to pluripotency.

Differentiated cells can be reprogrammed into induced pluripotent stem cells (iPSCs) after overexpressing four transcription factors, of which Oct4 is essential. To elucidate the role of Oct4 during reprogramming, we investigated the immediate transcriptional response to inducible Oct4 overexpression in various somatic murine cell types using microarray analysis. By downregulating somatic-specific genes, Oct4 induction influenced each transcriptional program in a unique manner. A significant upregulation of pluripotent markers could not be detected. Therefore, OCT4 facilitates reprogramming by interfering with the somatic transcriptional network rather than by directly initiating a pluripotent gene-expression program. Finally, Oct4 overexpression upregulated the gene Mgarp in all the analyzed cell types. Strikingly, Mgarp expression decreases during the first steps of reprogramming due to a KLF4-dependent inhibition. At later stages, OCT4 counteracts the repressive activity of KLF4, thereby enhancing Mgarp expression. We show that this temporal expression pattern is crucial for the efficient generation of iPSCs.

A hypothetical relationship between the nuclear reprogramming factors for induced pluripotent stem (iPS) cells generation--bioinformatic and algorithmic approach.

A hypothetical evolutionary relationship was generated between the nuclear reprogramming factors for induced pluripotent stem (iPS) cells generation. Utilizing bioinformatics techniques, sequence analyses and phylogenetic tree algorithms, a comparative study has been performed to understand the evolutionary relationship of human nuclear reprogramming factors of induced pluripotent stem cells (iPSCs) generation. Among the total six nuclear reprogramming factors, the four reprogramming factors (SOX2, C-MYC, KLF4, and LIN28) have significant evolutionary origin. Our study shows SOX2 and C-MYC have evolutionary relationship and common point of origin. Likewise, KLF4 and LIN28 are having evolutionary relationship and have common point of origin. Based on these evidences, we propose that our study may be a great help to the future researchers to understand the mechanism(s) as well as pathway of nuclear reprogramming process.

Stem cells, stress, metabolism and cancer: a drama in two Octs.

It is a classic story of two related transcription factors. Oct4 is a potent regulator of pluripotency during early mammalian embryonic development, and is notable for its ability to convert adult somatic cells to pluripotency. The widely expressed Oct1 protein shares significant homology with Oct4, binds to the same sequences, regulates common target genes, and shares common modes of upstream regulation, including the ability to respond to cellular stress. Both proteins are also associated with malignancy, yet Oct1 cannot substitute for Oct4 in the generation of pluripotency. The molecular underpinnings of these phenomena are emerging, as are the consequences for adult stem cells and cancer, and thereby hangs a tale.

Expression of stem cell pluripotency factors during regeneration in newts.

In this study, we present data indicating that mammalian stem cell pluripotency-inducing factors are expressed during lens and limb regeneration in newts. The apparent expression even in intact tissues and the ensued regulation during regeneration raises the possibility that these factors might regulate tissue-specific reprogramming and regeneration. Furthermore, these factors should enable us to understand the similarities and differences between animal regeneration in the newt and stem cell strategies in mammals. Developmental Dynamics 238:1613-1616, 2009. (c) 2009 Wiley-Liss, Inc.