Phenotypic drug discovery requires billions of cells for high-throughput screening (HTS) campaigns. Because up to several million different small molecules will be tested in a single HTS campaign, even small variability within the cell populations for screening could easily invalidate an entire campaign. Neurodegenerative assays are particularly challenging because neurons are post-mitotic and cannot be expanded for implementation in HTS. Therefore, HTS for neuroprotective compounds requires a cell type that is robustly expandable and able to differentiate into all of the neuronal subtypes involved in disease pathogenesis. Here, we report the derivation and propagation using only small molecules of human neural progenitor cells (small molecule neural precursor cells; smNPCs). smNPCs are robust, exhibit immortal expansion, and do not require cumbersome manual culture and selection steps. We demonstrate that smNPCs have the potential to clonally and efficiently differentiate into neural tube lineages, including motor neurons (MNs) and midbrain dopaminergic neurons (mDANs) as well as neural crest lineages, including peripheral neurons and mesenchymal cells. These properties are so far only matched by pluripotent stem cells. Finally, to demonstrate the usefulness of smNPCs we show that mDANs differentiated from smNPCs with LRRK2 G2019S are more susceptible to apoptosis in the presence of oxidative stress compared to wild-type. Therefore, smNPCs are a powerful biological tool with properties that are optimal for large-scale disease modeling, phenotypic screening, and studies of early human development.

Recent studies have shown that defined sets of transcription factors can directly reprogram differentiated somatic cells to a different differentiated cell type without passing through a pluripotent state, but the restricted proliferative and lineage potential of the resulting cells limits the scope of their potential applications. Here we show that a combination of transcription factors (Brn4/Pou3f4, Sox2, Klf4, c-Myc, plus E47/Tcf3) induces mouse fibroblasts to directly acquire a neural stem cell identity-which we term as induced neural stem cells (iNSCs). Direct reprogramming of fibroblasts into iNSCs is a gradual process in which the donor transcriptional program is silenced over time. iNSCs exhibit cell morphology, gene expression, epigenetic features, differentiation potential, and self-renewing capacity, as well as in vitro and in vivo functionality similar to those of wild-type NSCs. We conclude that differentiated cells can be reprogrammed directly into specific somatic stem cell types by defined sets of specific transcription factors.

Oct‐4 is a maternally expressed octamer‐binding protein encoded by the murine Oct‐4 gene. It is present in unfertilized oocytes, but also in the inner cell mass and in primordial germ cells. Here we show that the ectopic expression of Oct‐4 in HeLa cells is sufficient for transcriptional activation from the octamer motif, indicating that Oct‐4 is a transcription factor. Therefore, Oct‐4 is the first transcription factor described that is specific for the early stages of mouse development. The spatial and temporal expression patterns were further determined using in situ hybridization. With this technique Oct‐4 expression is detected in the oocyte, in the blastocyst and before gastrulation in the embryonic ectoderm. After day 8 Oct‐4 expression decreases and is restricted to primordial germ cells from about day 8.5 onwards. Therefore Oct‐4 is a transcription factor that is specifically expressed in cells participating in the generation of the germline lineage. Linkage analysis using B X D recombinant inbred mouse strains demonstrates that Oct‐4 maps to chromosome 17 in or near the major histocompatibility complex. Several mouse mutants in the distal region of the mouse t‐complex affecting blastocyst and embryonic ectoderm formation also map to this region.

The Pou domain containing transcription factor Oct4 is a well-established regulator of pluripotency in the inner cell mass of the mammalian blastocyst as well as in embryonic stem cells. While it has been shown that the Oct4 gene is inactivated through a series of epigenetic modifications following implantation, recent studies have detected Oct4 activity in a variety of somatic stem cells and tumor cells. Based on these observations it has been suggested that Oct4 may also function in maintaining self-renewal of somatic stem cells and, in addition, may promote tumor formation. We employed a genetic approach to determine whether Oct4 is important for maintaining pluripotency in the stem cell compartments of several somatic tissues including the intestinal epithelium, bone marrow (hematopoietic and mesenchymal lineages), hair follicle, brain, and liver. Oct4 gene ablation in these tissues revealed no abnormalities in homeostasis or regenerative capacity. We conclude that Oct4 is dispensable for both self-renewal and maintenance of somatic stem cells in the adult mammal.

We have analysed various adult organs and different developmental stages of mouse embryos for the presence of octamer‐binding proteins. A variety of new octamer‐binding proteins were identified in addition to the previously described Oct1 and Oct2. Oct1 is ubiquitously present in murine tissues, in agreement with cell culture data. Although Oct2 has been described as a B‐cell‐specific protein, similar complexes were also found with extracts from brain, kidney, embryo and sperm. In embryo and brain at least two other proteins, Oct3 and Oct7, are present. A new microextraction procedure allowed the detection of two maternally expressed octamer‐binding proteins, Oct4 and Oct5. Both proteins are present in unfertilized oocytes and embryonic stem cells, the latter containing an additional protein, Oct6. Whereas Oct4 was not found in sperm or testis, it is expressed in male and female primordial germ cells. Therefore Oct4 expression is specific for the female germline at later stages of germ cell development. Our results indicate that a family of octamer‐binding proteins is present during mouse development and is differentially expressed during early embryogenesis. Protease clipping experiments of Oct4 and Oct1 suggest that both proteins contain similar DNA‐binding domains.

Oct4 and Oct5 are two mouse maternally expressed proteins binding to the octamer motif. Both are found in unfertilized oocytes and embryonic stem cells, whereas Oct4 is also found in primordial germ cells. In this study, the activity of the octamer motif was analysed in two embryonic stem cell lines containing Oct4 and Oct5, the teratocarcinoma‐derived cell line F9 and the blastocyst‐derived cell line D3. It is known that oligomerization of the octamer motif creates a powerful B‐cell specific enhancer. As shown here, this oligomerized transcriptional element is also a very strong enhancer in F9 and D3 embryonic stem cells. After differentiation of the stem cells, both enhancer activity and the amount of the octamer binding proteins decrease. An intact octamer stimulates heterologous promoters in embryonic stem cells, whereas mutations in the octamer motif abolish transcriptional stimulation and binding of the octamer factors. The use of transgenic embryos demonstrates transcriptional activation in the inner cell mass but not in the trophoblast of blastocysts. The results indicate that Oct4 and Oct5 are active early in mouse development.

A family of octamer binding proteins is expressed during mouse development. Oct‐4 and Oct‐6 have been identified as two octamer binding proteins present in embryonal stem cells. Here we report the complementary DNA cloning and characterization of the mouse Oct‐6 gene. The protein of 448 amino acids contains a glycine/alanine‐rich amino terminal region, a histidine‐rich sequence with homology to a region of kininogen associated with clotting, a POU domain and a short proline/histidine‐rich carboxy terminal region. Expression of Oct‐6 in HeLa cells is sufficient for transcriptional activation from the octamer motif, identifying Oct‐6 as a transcription factor. The Oct‐6 expression is downregulated upon embryonic stem cell differentiation increasing again during brain development. Expression in brain is present in certain areas of telencephalon, mesencephalon and brain stem with abundant expression in the cortex anlagen and in the developing colliculi. Thus Oct‐6 is a new octamer binding transcription factor specifically regulated during mouse development.

Preimplantation development in the mouse is characterized by the occurrence of several critical genetic and epigenetic events. Until recently, very little was known about the regulation of these events. The search for genes which are involved in the control of the earliest stages of mouse development has so far resulted in only a few candidates. Oct-4, a member of the POU transcription factor family, is encoded by a gene belonging to this group. Initially present as a maternal factor in the oocyte, Oct-4 is expressed by the embryo throughout the preimplantation period, as well as in germ cell precursors of adult mice. Oct-4 expression is correlated with an undifferentiated phenotype, both in the embryo and in cell lines derived from it. Regulation of the Oct-4 gene is dependent on the activity of two separate enhancers, one of which is specifically active in pluri- and totipotent cells. Its function as a transcriptional regulator is supported by the identification of an increasing number of potential target genes, including some known to be essential for early embryonic development.