Oct-6: a POU transcription factor expressed in embryonal stem cells and in the developing brain

An integrated view of the structure and function of the human 4D nucleome

The dynamic three-dimensional (3D) organization of the human genome (the "4D Nucleome") is closely linked to genome function. Here, we integrate a wide variety of genomic data generated by the 4D Nucleome Project to provide a detailed view of human 3D genome organization in widely used embryonic stem cells (H1-hESCs) and immortalized fibroblasts (HFFc6). We provide extensive benchmarking of 3D genome mapping assays and integrate these diverse datasets to annotate spatial genomic features across scales. The data reveal a rich complexity of chromatin domains and their sub-nuclear positions, and over one hundred thousand structural loops and promoter-enhancer interactions. We developed 3D models of population-based and individual cell-to-cell variation in genome structure, establishing connections between chromosome folding, nuclear organization, chromatin looping, gene transcription, and DNA replication. We demonstrate the use of computational methods to predict genome folding from DNA sequence, uncovering potential effects of genetic variants on genome structure and function. Together, this comprehensive analysis contributes insights into human genome organization and enhances our understanding of connections between the regulation of genome function and 3D genome organization in general.

Oct4 redox sensitivity potentiates reprogramming and differentiation

The transcription factor Oct4/Pou5f1 is a component of the regulatory circuitry governing pluripotency and is widely used to induce pluripotency from somatic cells. Here we used domain swapping and mutagenesis to study Oct4's reprogramming ability, identifying a redox-sensitive DNA binding domain, cysteine residue (Cys48), as a key determinant of reprogramming and differentiation. Oct4 Cys48 sensitizes the protein to oxidative inhibition of DNA binding activity and promotes oxidation-mediated protein ubiquitylation. Pou5f1 C48S point mutation has little effect on undifferentiated embryonic stem cells (ESCs) but upon retinoic acid (RA) treatment causes retention of Oct4 expression, deregulated gene expression, and aberrant differentiation. Pou5f1 C48S ESCs also form less differentiated teratomas and contribute poorly to adult somatic tissues. Finally, we describe Pou5f1 C48S (Janky) mice, which in the homozygous condition are severely developmentally restricted after E4.5. Rare animals bypassing this restriction appear normal at birth but are sterile. Collectively, these findings uncover a novel Oct4 redox mechanism involved in both entry into and exit from pluripotency.

The transcription factor OCT6 promotes the dissolution of the naïve pluripotent state by repressing Nanog and activating a formative state gene regulatory network

In the mouse embryo, the transition from the preimplantation to the postimplantation epiblast is governed by changes in the gene regulatory network (GRN) that lead to transcriptional, epigenetic, and functional changes. This transition can be faithfully recapitulated in vitro by the differentiation of mouse embryonic stem cells (mESCs) to epiblast-like cells (EpiLCs), that reside in naïve and formative states of pluripotency, respectively. However, the GRN that drives this conversion is not fully elucidated. Here we demonstrate that the transcription factor OCT6 is a key driver of this process. Firstly, we show that Oct6 is not expressed in mESCs but is rapidly induced as cells exit the naïve pluripotent state. By deleting Oct6 in mESCs, we find that knockout cells fail to acquire the typical morphological changes associated with the formative state when induced to differentiate. Additionally, the key naïve pluripotency TFs Nanog, Klf2, Nr5a2, Prdm14, and Esrrb were expressed at higher levels than in wild-type cells, indicating an incomplete dismantling of the naïve pluripotency GRN. Conversely, premature expression of Oct6 in naïve cells triggered a rapid morphological transformation mirroring differentiation, that was accompanied by the upregulation of the endogenous Oct6 as well as the formative genes Sox3, Zic2/3, Foxp1, Dnmt3A and FGF5. Strikingly, we found that OCT6 represses Nanog in a bistable manner and that this regulation is at the transcriptional level. Moreover, our findings also reveal that Oct6 is repressed by NANOG. Collectively, our results establish OCT6 as a key TF in the dissolution of the naïve pluripotent state and support a model where Oct6 and Nanog form a double negative feedback loop which could act as an important toggle mediating the transition to the formative state.

Oct4 redox sensitivity potentiates reprogramming and differentiation

The transcription factor Oct4/Pou5f1 is a component of the regulatory circuitry governing pluripotency and is widely used to induce pluripotency from somatic cells. Here we use domain swapping and mutagenesis to study Oct4s reprogramming ability, identifying a redox-sensitive DNA binding domain cysteine residue (Cys48) as a key determinant of reprogramming and differentiation. Oct4 Cys48 sensitizes the protein to oxidative inhibition of DNA binding activity and promotes oxidation-mediated protein ubiquitylation. Pou5f1C48S point mutation has little effect on undifferentiated embryonic stem cells (ESCs), but upon retinoic acid (RA) treatment causes retention of Oct4 expression, deregulated gene expression and aberrant differentiation. Pou5f1C48S ESCs also form less differentiated teratomas and contribute poorly to adult somatic tissues. Finally, we describe Pou5f1C48S (Janky) mice, which in the homozygous condition are severely developmentally restricted after E4.5. Rare animals bypassing this restriction appear normal at birth but are sterile. Collectively, these findings uncover a novel Oct4 redox mechanism involved in both entry into and exit from pluripotency.

Distinct prefrontal projection activity and transcriptional state conversely orchestrate social competition and hierarchy

Social animals compete for limited resources, resulting in a social hierarchy. Although different neuronal subpopulations in the medial prefrontal cortex (mPFC), which has been mechanistically implicated in social dominance behavior, encode distinct social competition behaviors, their identities and associated molecular underpinnings have not yet been identified. In this study, we found that mPFC neurons projecting to the nucleus accumbens (mPFC-NAc) encode social winning behavior, whereas mPFC neurons projecting to the ventral tegmental area (mPFC-VTA) encode social losing behavior. High-throughput single-cell transcriptomic analysis and projection-specific genetic manipulation revealed that the expression level of POU domain, class 3, transcription factor 1 (Pou3f1) in mPFC-VTA neurons controls social hierarchy. Optogenetic activation of mPFC-VTA neurons increases Pou3f1 expression and lowers social rank. Together, these data demonstrate that discrete activity and gene expression in separate mPFC projections oppositely orchestrate social competition and hierarchy.

Integration of spatial and single-cell transcriptomic data elucidates mouse organogenesis

Molecular profiling of single cells has advanced our knowledge of the molecular basis of development. However, current approaches mostly rely on dissociating cells from tissues, thereby losing the crucial spatial context of regulatory processes. Here, we apply an image-based single-cell transcriptomics method, sequential fluorescence in situ hybridization (seqFISH), to detect mRNAs for 387 target genes in tissue sections of mouse embryos at the 8-12 somite stage. By integrating spatial context and multiplexed transcriptional measurements with two single-cell transcriptome atlases, we characterize cell types across the embryo and demonstrate that spatially resolved expression of genes not profiled by seqFISH can be imputed. We use this high-resolution spatial map to characterize fundamental steps in the patterning of the midbrain-hindbrain boundary (MHB) and the developing gut tube. We uncover axes of cell differentiation that are not apparent from single-cell RNA-sequencing (scRNA-seq) data, such as early dorsal-ventral separation of esophageal and tracheal progenitor populations in the gut tube. Our method provides an approach for studying cell fate decisions in complex tissues and development.

Stop codon readthrough alters the activity of a POU/Oct transcription factor during Drosophila development

Background

A number of cellular processes have evolved in metazoans that increase the proteome repertoire in relation to the genome, such as alternative splicing and translation recoding. Another such process, translational stop codon readthrough (SCR), generates C-terminally extended protein isoforms in many eukaryotes, including yeast, plants, insects, and humans. While comparative genome analyses have predicted the existence of programmed SCR in many species including humans, experimental proof of its functional consequences are scarce.

Results

We show that SCR of the Drosophila POU/Oct transcription factor Ventral veins lacking/Drifter (Vvl/Dfr) mRNA is prevalent in certain tissues in vivo, reaching a rate of 50% in the larval prothoracic gland. Phylogenetically, the C-terminal extension is conserved and harbors intrinsically disordered regions and amino acid stretches implied in transcriptional activation. Elimination of Vvl/Dfr translational readthrough by CRISPR/Cas9 mutagenesis changed the expression of a large number of downstream genes involved in processes such as chromatin regulation, neurogenesis, development, and immune response. As a proof-of-principle, we demonstrate that the C-terminal extension of Vvl/Dfr is necessary for correct timing of pupariation, by increasing the capacity to regulate its target genes. The extended Vvl/Dfr isoform acts in synergy with the transcription factor Molting defective (Mld) to increase the expression and biosynthesis of the steroid hormone ecdysone, thereby advancing pupariation. Consequently, late-stage larval development was prolonged and metamorphosis delayed in vvl/dfr readthrough mutants.

Conclusions

We demonstrate that translational recoding of a POU/Oct transcription factor takes place in a highly tissue-specific and temporally controlled manner. This dynamic and regulated recoding is necessary for normal expression of a large number of genes involved in many cellular and developmental processes. Loss of Vvl/Dfr translational readthrough negatively affects steroid hormone biosynthesis and delays larval development and progression into metamorphosis. Thus, this study demonstrates how SCR of a transcription factor can act as a developmental switch in a spatiotemporal manner, feeding into the timing of developmental transitions between different life-cycle stages.

Graphical abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s12915-021-01106-0.

Biological importance of OCT transcription factors in reprogramming and development

Ectopic expression of Oct4, Sox2, Klf4 and c-Myc can reprogram somatic cells into induced pluripotent stem cells (iPSCs). Attempts to identify genes or chemicals that can functionally replace each of these four reprogramming factors have revealed that exogenous Oct4 is not necessary for reprogramming under certain conditions or in the presence of alternative factors that can regulate endogenous Oct4 expression. For example, polycistronic expression of Sox2, Klf4 and c-Myc can elicit reprogramming by activating endogenous Oct4 expression indirectly. Experiments in which the reprogramming competence of all other Oct family members tested and also in different species have led to the decisive conclusion that Oct proteins display different reprogramming competences and species-dependent reprogramming activity despite their profound sequence conservation. We discuss the roles of the structural components of Oct proteins in reprogramming and how donor cell epigenomes endow Oct proteins with different reprogramming competences.

Cells can be reprogrammed into induced pluripotent stem cells (iPSCs), embryonic-like stem cells that can turn into any cell type and have extensive potential medical uses, without adding the transcription factor OCT4. Although other nearly identical OCT family members had been tried, only OCT4 could induce reprogramming and was previously thought to be indispensable. However, it now appears that the reprogramming can be induced by multiple pathways, as detailed in a review by Hans Schöler, Max Planck Institute for Biomolecular Medicine, Münster, and Johnny Kim, Max Planck Institute for Heart and Lung Research, Bad Nauheim, in Germany. They report that any factors that trigger cells to activate endogeous OCT4 can produce iPSCs without exogeously admistration of OCT4. The mechanisms for producing iPSCs can differ between species. These results illuminate the complex mechanisms of reprogramming.

Reprogramming competence of OCT factors is determined by transactivation domains

OCT4 (also known as POU5F1) plays an essential role in reprogramming. It is the only member of the POU (Pit-Oct-Unc) family of transcription factors that can induce pluripotency despite sharing high structural similarities to all other members. Here, we discover that OCT6 (also known as POU3F1) can elicit reprogramming specifically in human cells. OCT6-based reprogramming does not alter the mesenchymal-epithelial transition but is attenuated through the delayed activation of the pluripotency network in comparison with OCT4-based reprogramming. Creating a series of reciprocal domain-swapped chimeras and mutants across all OCT factors, we clearly delineate essential elements of OCT4/OCT6-dependent reprogramming and, conversely, identify the features that prevent induction of pluripotency by other OCT factors. With this strategy, we further discover various chimeric proteins that are superior to OCT4 in reprogramming. Our findings clarify how reprogramming competences of OCT factors are conferred through their structural components.

New Neuronal Subtypes With a "Pre-Pancreatic" Signature in the Sea Urchin Stongylocentrotus purpuratus

Neurons and pancreatic endocrine cells have a common physiology and express a similar toolkit of transcription factors during development. To explain these common features, it has been hypothesized that pancreatic cells most likely co-opted a pre-existing gene regulatory program from ancestral neurons. To test this idea, we looked for neurons with a "pre-pancreatic" program in an early-branched deuterostome, the sea urchin. Only vertebrates have a proper pancreas, however, our lab previously found that cells with a pancreatic-like signature are localized within the sea urchin embryonic gut. We also found that the pancreatic transcription factors Xlox/Pdx1 and Brn1/2/4 co-localize in a sub-population of ectodermal cells. Here, we find that the ectodermal SpLox+ SpBrn1/2/4 cells are specified as SpSoxC and SpPtf1a neuronal precursors that become the lateral ganglion and the apical organ neurons. Two of the SpLox+ SpBrn1/2/4 cells also express another pancreatic transcription factor, the LIM-homeodomain gene islet-1. Moreover, we find that SpLox neurons produce the neuropeptide SpANP2, and that SpLox regulates SpANP2 expression. Taken together, our data reveal that there is a subset of sea urchin larval neurons with a gene program that predated pancreatic cells. These findings suggest that pancreatic endocrine cells co-opted a regulatory signature from an ancestral neuron that was already present in an early-branched deuterostome.

Diversity among POU transcription factors in chromatin recognition and cell fate reprogramming

The POU (Pit-Oct-Unc) protein family is an evolutionary ancient group of transcription factors (TFs) that bind specific DNA sequences to direct gene expression programs. The fundamental importance of POU TFs to orchestrate embryonic development and to direct cellular fate decisions is well established, but the molecular basis for this activity is insufficiently understood. POU TFs possess a bipartite 'two-in-one' DNA binding domain consisting of two independently folding structural units connected by a poorly conserved and flexible linker. Therefore, they represent a paradigmatic example to study the molecular basis for the functional versatility of TFs. Their modular architecture endows POU TFs with the capacity to accommodate alternative composite DNA sequences by adopting different quaternary structures. Moreover, associations with partner proteins crucially influence the selection of their DNA binding sites. The plentitude of DNA binding modes confers the ability to POU TFs to regulate distinct genes in the context of different cellular environments. Likewise, different binding modes of POU proteins to DNA could trigger alternative regulatory responses in the context of different genomic locations of the same cell. Prominent POU TFs such as Oct4, Brn2, Oct6 and Brn4 are not only essential regulators of development but have also been successfully employed to reprogram somatic cells to pluripotency and neural lineages. Here we review biochemical, structural, genomic and cellular reprogramming studies to examine how the ability of POU TFs to select regulatory DNA, alone or with partner factors, is tied to their capacity to epigenetically remodel chromatin and drive specific regulatory programs that give cells their identities.

Yangjing Capsule extract promotes proliferation of GC-1 spg cells via up-regulated POU3F1 pathway

As is similar to glial cell line-derived neurotrophic factor (GDNF), the Yangjing Capsule (YC) extract could also lead to proliferation of spermatogonial stem cells (SSCs) by stimulating the phosphoinositide 3-kinase (PI3K)/protein kinase B (AKT) pathway; however, the regulatory effect of YC extract on the expression of POU3F1 still remains unknown. The objective of this study is to determine whether the transcription factor POU3F1 is up-regulated by YC extract through the PI3K/AKT signaling pathway to regulate SSCs survival and proliferation. Cultured GC-1 spermatogonial (spg) cells were treated with 0.01, 0.1, and 1 mg/mL YC extract for 48 h. Cell viability was analyzed using MTT assay, while POU3F1 expression was quantitatively detected using real time-polymerase chain reaction and Western blot analysis. POU3F1, GDNF family receptor alpha1 (GFRα1) short interfering ribonucleic acid (siRNA), and LY294002 (PI3K inhibitor) were applied as blockers to explore the underlying pathway. After 48 h treatment with YC extract, GC-1 spg cells proliferated and POU3F1 expression was significantly increased in a dose-dependent manner. POU3F1 siRNA partially blocked those effects of YC extract. Both GFRα1 siRNA and LY294002, as upstream blockers, reduced POU3F1 expression induced by YC extract. The conclusion is that YC extract promotes proliferation of GC-1 spg cells via up-regulation of POU3F1. The potential mechanism is that YC extract triggers the activation of the PI3K/AKT pathway and then up-regulates POU3F1 expression.

Quantitative profiling of selective Sox/POU pairing on hundreds of sequences in parallel by Coop-seq

Cooperative binding of transcription factors is known to be important in the regulation of gene expression programs conferring cellular identities. However, current methods to measure cooperativity parameters have been laborious and therefore limited to studying only a few sequence variants at a time. We developed Coop-seq (cooperativity by sequencing) that is capable of efficiently and accurately determining the cooperativity parameters for hundreds of different DNA sequences in a single experiment. We apply Coop-seq to 12 dimer pairs from the Sox and POU families of transcription factors using 324 unique sequences with changed half-site orientation, altered spacing and discrete randomization within the binding elements. The study reveals specific dimerization profiles of different Sox factors with Oct4. By contrast, Oct4 and the three neural class III POU factors Brn2, Brn4 and Oct6 assemble with Sox2 in a surprisingly indistinguishable manner. Two novel half-site configurations can support functional Sox/Oct dimerization in addition to known composite motifs. Moreover, Coop-seq uncovers a nucleotide switch within the POU half-site when spacing is altered, which is mirrored in genomic loci bound by Sox2/Oct4 complexes.

Characterization of a Novel Endoplasmic Reticulum Protein Involved in Tubercidin Resistance in Leishmania major

BACKGROUND

Tubercidin (TUB) is a toxic adenosine analog with potential antiparasitic activity against Leishmania, with mechanism of action and resistance that are not completely understood. For understanding the mechanisms of action and identifying the potential metabolic pathways affected by this drug, we employed in this study an overexpression/selection approach using TUB for the identification of potential targets, as well as, drug resistance genes in L. major. Although, TUB is toxic to the mammalian host, these findings can provide evidences for a rational drug design based on purine pathway against leishmaniasis.

METHODOLOGY/PRINCIPAL FINDINGS

After transfection of a cosmid genomic library into L. major Friedlin (LmjF) parasites and application of the overexpression/selection method, we identified two cosmids (cosTUB1 and cosTU2) containing two different loci capable of conferring significant levels of TUB resistance. In the cosTUB1 contained a gene encoding NUPM1-like protein, which has been previously described as associated with TUB resistance in L. amazonensis. In the cosTUB2 we identified and characterized a gene encoding a 63 kDa protein that we denoted as tubercidin-resistance protein (TRP). Functional analysis revealed that the transfectants were less susceptible to TUB than LmjF parasites or those transfected with the control vector. In addition, the trp mRNA and protein levels in cosTUB2 transfectants were higher than LmjF. TRP immunolocalization revealed that it was co-localized to the endoplasmic reticulum (ER), a cellular compartment with many functions. In silico predictions indicated that TRP contains only a hypothetical transmembrane domain. Thus, it is likely that TRP is a lumen protein involved in multidrug efflux transport that may be involved in the purine metabolic pathway.

CONCLUSIONS/SIGNIFICANCE

This study demonstrated for the first time that TRP is associated with TUB resistance in Leishmania. The next challenge is to determine how TRP mediates TUB resistance and whether purine metabolism is affected by this protein in the parasite. Finally, these findings may be helpful for the development of alternative anti-leishmanial drugs that target purine pathway.

Isolation and characterisation of a novel trophoblast side-population from first trimester placentae

The placenta is responsible for all nutrient and gas exchange between mother and baby during pregnancy. The differentiation of specialised placental epithelial cells called trophoblasts is essential for placental function, but we understand little about how these populations arise. Mouse trophoblast stem cells have allowed us to understand many of the factors that regulate murine trophoblast lineage development, but the human placenta is anatomically very different from the mouse, and it is imperative to isolate a human trophoblast stem cell to understand human placental development. Here we have developed a novel methodology to isolate a Hoechst side-population of trophoblasts from early gestation placentae and compared their transcriptome to differentiated trophoblast populations (cytotrophoblasts and extravillous trophoblasts) using microarray technology. Side-population trophoblasts clustered as a transcriptomically distinct population but were more closely related to cytotrophoblasts than extravillous trophoblasts. Side-population trophoblasts up-regulated a number of genes characteristic of trophectoderm and murine trophoblast stem cells in comparison to cytotrophoblasts or extravillous trophoblasts and could be distinguished from both of these more mature populations by a unique set of 22 up-regulated genes, which were enriched for morphogenesis and organ development and the regulation of growth functions. Cells expressing two of these genes (LAMA2 and COL6A3) were distributed throughout the cytotrophoblast layer at the trophoblast/mesenchymal interface. Comparisons to previously published trophoblast progenitor populations suggest that the side-population trophoblasts isolated in this work are a novel human trophoblast population. Future work will determine whether these cells exhibit functional progenitor/stem cell attributes.

Transduction of Oct6 or Oct9 gene concomitant with Myc family gene induced osteoblast-like phenotypic conversion in normal human fibroblasts

INTRODUCTION

Osteoblasts play essential roles in bone formation and regeneration, while they have low proliferation potential. Recently we established a procedure to directly convert human fibroblasts into osteoblasts (dOBs). Transduction of Runx2 (R), Osterix (X), Oct3/4 (O) and L-myc (L) genes followed by culturing under osteogenic conditions induced normal human fibroblasts to express osteoblast-specific genes and produce calcified bone matrix both in vitro and in vivo Intriguingly, a combination of only two factors, Oct3/4 and L-myc, significantly induced osteoblast-like phenotype in fibroblasts, but the mechanisms underlying the direct conversion remains to be unveiled.

MATERIALS AND METHODS

We examined which Oct family genes and Myc family genes are capable of inducing osteoblast-like phenotypic conversion.

RESULTS

As result Oct3/4, Oct6 and Oct9, among other Oct family members, had the capability, while N-myc was the most effective Myc family gene. The Oct9 plus N-myc was the best combination to induce direct conversion of human fibroblasts into osteoblast-like cells.

DISCUSSION

The present findings may greatly contribute to the elucidation of the roles of the Oct and Myc proteins in osteoblast direct reprogramming. The results may also lead to establishment of novel regenerative therapy for various bone resorption diseases.

Intrinsic regulations in neural fate commitment

Neural fate commitment is an early embryonic event that a group of cells in ectoderm, which do not ingress through primitive streak, acquire a neural fate but not epidermal or mesodermal lineages. Several extracellular signaling pathways initiated by the secreted proteins bone morphogenetic proteins (BMPs), fibroblast growth factors (FGFs), wingless/int class proteins (WNTs) and Nodal play essential roles in the specification of the neural plate. Accumulating evidence from the studies on mouse and pluripotent embryonic stem cells reveals that except for the extracellular signals, the intracellular molecules, including both transcriptional and epigenetic factors, participate in the modulation of neural fate commitment as well. In the review, we mainly focus on recent findings that the initiation of the nervous system is elaborately regulated by the intrinsic programs, which are mediated by transcriptional factors such as Sox2, Zfp521, Sip1 and Pou3f1, as well as epigenetic modifications, including histone methylation/demethylation, histone acetylation/deacetylation, and DNA methylation/demethylation. The discovery of the intrinsic regulatory machineries provides better understanding of the mechanisms by which the neural fate commitment is ensured by the cooperation between extracellular factors and intracellular molecules.

The transcription factor Pou3f1 promotes neural fate commitment via activation of neural lineage genes and inhibition of external signaling pathways

The neural fate commitment of pluripotent stem cells requires the repression of extrinsic inhibitory signals and the activation of intrinsic positive transcription factors. However, how these two events are integrated to ensure appropriate neural conversion remains unclear. In this study, we showed that Pou3f1 is essential for the neural differentiation of mouse embryonic stem cells (ESCs), specifically during the transition from epiblast stem cells (EpiSCs) to neural progenitor cells (NPCs). Chimeric analysis showed that Pou3f1 knockdown leads to a markedly decreased incorporation of ESCs in the neuroectoderm. By contrast, Pou3f1-overexpressing ESC derivatives preferentially contribute to the neuroectoderm. Genome-wide ChIP-seq and RNA-seq analyses indicated that Pou3f1 is an upstream activator of neural lineage genes, and also is a repressor of BMP and Wnt signaling. Our results established that Pou3f1 promotes the neural fate commitment of pluripotent stem cells through a dual role, activating internal neural induction programs and antagonizing extrinsic neural inhibitory signals.

Importin alpha subtypes determine differential transcription factor localization in embryonic stem cells maintenance

We recently demonstrated that the expression of the importin α subtype is switched from α2 to α1 during neural differentiation in mouse embryonic stem cells (ESCs) and that this switching has a major impact on cell differentiation. In this study, we report a cell-fate determination mechanism in which importin α2 negatively regulates the nuclear import of certain transcription factors to maintain ESC properties. The nuclear import of Oct6 and Brn2 was inhibited via the formation of a transport-incompetent complex of the cargo bound to a nuclear localization signal binding site in importin α2. Unless this dominant-negative effect was downregulated upon ESC differentiation, inappropriate cell death was induced. We propose that although certain transcription factors are necessary for differentiation in ESCs, these factors are retained in the cytoplasm by importin α2, thereby preventing transcription factor activity in the nucleus until the cells undergo differentiation.

Oct transcription factors in development and stem cells: insights and mechanisms

The POU domain family of transcription factors regulates developmental processes ranging from specification of the early embryo to terminal differentiation. About half of these factors display substantial affinity for an 8 bp DNA site termed the octamer motif, and are hence known as Oct proteins. Oct4 (Pou5f1) is a well-known Oct factor, but there are other Oct proteins with varied and essential roles in development. This Primer outlines our current understanding of Oct proteins and the regulatory mechanisms that govern their role in developmental processes and concludes with the assertion that more investigation into their developmental functions is needed.

Gbx2 directly restricts Otx2 expression to forebrain and midbrain, competing with class III POU factors

Otx2 plays essential roles in rostral brain development, and its counteraction with Gbx2 has been suggested to determine the midbrain-hindbrain boundary (MHB) in vertebrates. We previously identified the FM enhancer that is conserved among vertebrates and drives Otx2 transcription in forebrain/midbrain from the early somite stage. In this study, we found that the POU homeodomain of class III POU factors (Brn1, Brn2, Brn4, and Oct6) associates with noncanonical target sequence TAATTA in the FM enhancer. MicroRNA-mediated knockdown of Brn2 and Oct6 diminished the FM enhancer activity in anterior neural progenitor cells (NPCs) differentiated from P19 cells. The class III POU factors associate with the FM enhancer in forebrain and midbrain but not in hindbrain. We also demonstrated that the Gbx2 homeodomain recognizes the same target TAATTA in the FM enhancer, and Gbx2 associates with the FM enhancer in hindbrain. Gbx2 misexpression in the anterior NPCs repressed the FM enhancer activity and inhibited Brn2 association with the enhancer, whereas Gbx2 knockdown caused ectopic Brn2 association in the posterior NPCs. These results suggest that class III POU factors and Gbx2 share the same target site, TAATTA, in the FM enhancer and that their region-specific binding restricts Otx2 expression at the MHB.

Gene expression profile of adult human olfactory bulb and embryonic neural stem cell suggests distinct signaling pathways and epigenetic control

Global gene expression profiling was performed using RNA from human embryonic neural stem cells (hENSC), and adult human olfactory bulb-derived neural stem cells (OBNSCs), to define a gene expression pattern and signaling pathways that are specific for each cell lineage. We have demonstrated large differences in the gene expression profile of human embryonic NSC, and adult human OBNSCs, but less variability between parallel cultures. Transcripts of genes involved in neural tube development and patterning (ALDH1A2, FOXA2), progenitor marker genes (LMX1a, ALDH1A1, SOX10), proliferation of neural progenitors (WNT1 and WNT3a), neuroplastin (NPTN), POU3F1 (OCT6), neuroligin (NLGN4X), MEIS2, and NPAS1 were up-regulated in both cell populations. By Gene Ontology, 325 out of 3875 investigated gene sets were scientifically different. 41 out of the 307 investigated Cellular Component (CC) categories, 45 out of the 620 investigated Molecular Function (MF) categories, and 239 out of the 2948 investigated Biological Process (BP) categories were significant. KEGG Pathway Class Comparison had revealed that 75 out of 171 investigated gene sets passed the 0.005 significance threshold. Levels of gene expression were explored in three signaling pathways, Notch, Wnt, and mTOR that are known to be involved in NS cell fates determination. The transcriptional signature also deciphers the role of genes involved in epigenetic modifications. SWI/SNF DNA chromatin remodeling complex family, including SMARCC1 and SMARCE1, were found specifically up-regulated in our OBNSC but not in hENSC. Differences in gene expression profile of transcripts controlling epigenetic modifications, and signaling pathways might indicate differences in the therapeutic potential of our examined two cell populations in relation to in cell survival, proliferation, migration, and differentiation following engraftments in different CNS insults.

Comprehensive gene expression analysis of human embryonic stem cells during differentiation into neural cells

Global gene expression analysis of human embryonic stem cells (hESCs) that differentiate into neural cells would help to further define the molecular mechanisms involved in neurogenesis in humans. We performed a comprehensive transcripteome analysis of hESC differentiation at three different stages: early neural differentiation, neural ectoderm, and differentiated neurons. We identified and validated time-dependent gene expression patterns and showed that the gene expression patterns reflect early ESC differentiation. Sets of genes are induced in primary ectodermal lineages and then in differentiated neurons, constituting consecutive waves of known and novel genes. Pathway analysis revealed dynamic expression patterns of members of several signaling pathways, including NOTCH, mTOR and Toll like receptors (TLR), during neural differentiation. An interaction network analysis revealed that the TGFβ family of genes, including LEFTY1, ID1 and ID2, are possible key players in the proliferation and maintenance of neural ectoderm. Collectively, these results enhance our understanding of the molecular dynamics underlying neural commitment and differentiation.

Optimization and scale-up of Wharton's jelly-derived mesenchymal stem cells for clinical applications

MSCs are promising candidates for stem cell therapy and regenerative medicine. Umbilical cord is the easiest obtainable biological source of MSCs and the Wharton's jelly of the umbilical cord is a rich source of fetus-derived stem cells. However, the use of MSCs for therapeutic application is based on their subsequent large-scale in vitro expansion. A fast and efficient protocol for generation of large quantities of MSCs is required to meet the clinical demand and biomedical research needs. Here we have optimized conditions for scaling up of WJ-MSCs. Low seeding density along with basic fibroblast growth factor (bFGF) supplementation in the growth medium, which is DMEM-KO, resulted in propagation of more than 1 x 10(8) cells within a time period of 15 days from a single umbilical cord. The upscaled WJ-MSCs retained their differentiation potential and immunosuppressive capacity. They expressed the typical hMSC surface antigens and the addition of bFGF in the culture medium did not affect the expression levels of HLA-DR and CD 44. A normal karyotype was confirmed in the large-scale expanded WJ-MSCs. Hence, in this study we attempted rapid clinical-scale expansion of WJ-MSCs which would allow these fetus-derived stem cells to be used for various allogeneic cell-based transplantations and tissue engineering.

The POU domain transcription factor POU3F1 is an important intrinsic regulator of GDNF-induced survival and self-renewal of mouse spermatogonial stem cells

Continual spermatogenesis relies on a pool of spermatogonial stem cells (SSCs) that possess the capacity for self-renewal and differentiation. Maintenance of this pool depends on survival of SSCs throughout the lifetime of a male. Response to extrinsic stimulation from glial cell line-derived neurotrophic factor (GDNF), mediated by the PIK3/AKT signaling cascade, is a key pathway of SSC survival. In this study, we found that expression of the POU domain transcription factor POU3F1 in cultured SSCs is up-regulated via this mechanism. Reduction of Pou3f1 gene expression by short interfering RNA (siRNA) treatment induced apoptosis in cultured germ cell populations, and transplantation analyses revealed impaired SSC maintenance in vitro. POU3F1 expression was localized to spermatogonia in cross-sections of prepubertal and adult testes, implying a similar role in vivo. Through comparative analyses, we found that expression of POU5F1, another POU transcription factor implicated as essential for SSC self-renewal, is not regulated by GDNF in cultured SSCs. Transplantation analyses following siRNA treatment showed that POU5F1 expression is not essential for SSC maintenance in vitro. Additionally, expression of NODAL, a putative autocrine regulator of POU5F1 expression in mouse germ cells, could not be detected in SSCs isolated from testes or cultured SSCs. Collectively, these results indicate that POU3F1, but not POU5F1, is an intrinsic regulator of GDNF-induced survival and self-renewal of mouse SSCs.

The role of the nuclear transport system in cell differentiation

The eukaryotic cell nuclear transport system selectively mediates molecular trafficking to facilitate the regulation of cellular processes. The components of this system include diverse transport factors such as importins and nuclear pore components that are precisely organized to coordinate cellular events. A number of studies have demonstrated that the nuclear transport system is indispensible in many types of cellular responses. In particular, the nuclear transport machinery has been shown to be an important regulator of development, organogenesis, and tissue formation, wherein altered nuclear transport of key transcription factors can lead to disease. Importantly, precise switching between distinct forms of importin alpha is central to neural lineage specification, consistent with the hypothesis that importin expression can be a key mediator of cell differentiation.

Epigenetic regulation and downstream targets of the Rhox5 homeobox gene

The discovery of the Rhox homeobox gene cluster on the X chromosome opens up new vistas in the regulation of reproductive processes in mammals. In mice, this cluster comprises more than 30 genes that are selectively expressed in reproductive tissues. A subset of Rhox genes are androgen and AR regulated in postnatal and adult Sertoli cells, making them candidates to mediate androgen-dependent steps during spermatogenesis. The best characterized of these androgen/AR-regulated genes is Rhox5 (Pem), the founding member of the Rhox gene cluster. Targeted deletion of Rhox5 in mice causes male subfertility marked by increased germ-cell apoptosis and decreased sperm count and motility. Microarray analyses identified a wide variety of genes regulated by Rhox5 in Sertoli cells. One of them is the tumour suppressor UNC5C, a pro-apoptotic molecule previously only known to be involved in brain development. Targeted deletion of Unc5c causes decreased germ-cell apoptosis in postnatal and adult testes, indicating that it also has a role in spermatogenesis and supporting a model in which Rhox5 promotes germ-cell survival by downregulating Unc5c. Rhox5 has two independently regulated promoters that have distinct expression patterns. The unique tissue-specific and developmentally regulated transcription pattern of these two promoters appear to be controlled by DNA methylation. Both promoters are methylated in tissues in which they are not expressed, suggesting that DNA methylation serves to repress Rhox5 expression in inappropriate cell types and tissues. In summary, the Rhox gene cluster is an epigenetically regulated set of genes encoding a large number of transcription factors that are strong candidates to regulate gametogenesis and other aspects of reproduction.

Transcriptional control of oligodendrogenesis

Oligodendrocytes (OGs) assemble the myelin sheath around axons in the central nervous system. Specification of cells into the OG lineage is largely the result of interplay between bone morphogenetic protein, sonic hedgehog and Notch signaling pathways, which regulate expression of transcription factors (TFs) dictating spatial and temporal aspects of oligodendrogenesis. Many of these TFs and others then direct OG development through to a mature myelinating OG. Here we describe signaling pathways and TFs that are inductive, inhibitory, and/or permissive to OG specification and maturation. We develop a basic transcriptional network and identify similarities and differences between regulation of oligodendrogenesis in the spinal cord and brain.

Isolation and characterization of the murine Nanog gene promoter

Nanog protein is expressed in the interior cells of compacted morulae and maintained till epiblasts but downregulated by implantation stage. It is also expressed in embryonic stem cells, embryonic carcinoma cells and embryonic germ cells but disappeared in differentiated ES cells. In this study, we have isolated, sequenced, and performed the first characterization of the Nanog promoter. The transcription start sites were mapped by primer extension analysis. Two promoter regions were found upstream the transcription start sites and the expression of major Nanog promoter/reporter gene construct is abolished in differentiated F9 EC cells as compared to the undifferentiated counterpart. We also showed that a putative octamer motif (ATGCAAAA) is necessary for the major promoter activity. Gel shift and supershift assays showed that Oct-1, Oct-4 and Oct-6 protein selectively bind to the octamer motif.

TOR-induced resistance to toxic adenosine analogs in Leishmania brought about by the internalization and degradation of the adenosine permease

TOR is an atypical multidrug resistance protein present in the human protozoan parasite, Leishmania. Resistance to the toxic adenosine analog tubercidin was brought about by redirecting the adenosine permease from the plasma membrane to the multivesicular tubule lysosome. The cells became resistant to tubercidin because they were unable to take up and accumulate this toxic purine. The domain, which was recognized by TOR in this internalization pathway, was identified by expressing portions of this transporter in Leishmania and assessing whether they were capable of hindering the multidrug resistance capability of TOR. This approach identified the adenosine permease region spanning Met289 to Trp305. This region was also the epitope recognized by the internalization mechanism. An internal deletion mutant lacking Met289-Trp305 was functionally active but could no longer be internalized in cells with high TOR levels. The internalization and altered trafficking of the adenosine permease by TOR was observed in yeast and human embryonic kidney cells co-expressing these two Leishmania proteins indicating that the internalization process was conserved in evolutionary diverse organisms. The inability of Saccharomyces with a temperature-sensitive ubiquitin ligase to internalize adenosine permease suggested that ubiquitination was involved in this altered trafficking.

Potential treatment of cerebral global ischemia with Oct-4+ umbilical cord matrix cells

Potential therapeutic effects of Oct-4-positive rat umbilical cord matrix (RUCM) cells in treating cerebral global ischemia were evaluated using a reproducible model of cardiac arrest (CA) and resuscitation in rats. Animals were randomly assigned to four groups: A, sham-operated; B, 8-minute CA without pretreatment; C, 8-minute CA pretreated with defined media; and D, 8-minute CA pretreated with Oct-4(+) RUCM cells. Pretreatment was done 3 days before CA by 2.5-microl microinjection of defined media or approximately 10(4) Oct-4(+) RUCM cells in left thalamic nucleus, hippocampus, corpus callosum, and cortex. Damage was assessed histologically 7 days after CA and was quantified by the percentage of injured neurons in hippocampal CA1 regions. Little damage (approximately 3%-4%) was found in the sham group, whereas 50%-68% CA1 pyramidal neurons were injured in groups B and C. Pretreatment with Oct-4(+) RUCM cells significantly (p < .001) reduced neuronal loss to 25%-32%. Although the transplanted cells were found to have survived in the brain with significant migration, few were found directly in CA1. Therefore, transdifferentiation and fusion with host cells cannot be the predominant mechanisms for the observed protection. The Oct-4(+) RUCM cells might repair nonfocal tissue damage by an extracellular signaling mechanism. Treating cerebral global ischemia with umbilical cord matrix cells seems promising and worthy of further investigation.

Bovine Embryonic Stem Cells

Bovine embryonic stem (bES) cell lines reported to date vary in morphology and marker expression, such as alkaline phosphatase (ALPL), stage-specific embryonic antigen 4 (SSEA4), and octamer-binding transcription factor-4 (OCT4), that normally are associated with the undifferentiated, pluripotent state. This chapter introduces the methods of isolating and maintaining bovine ES cells. These bovine ES cells grow in large, multicellular colonies resembling the mouse ES and embryonic germ (EG) cells, as well as human EG cells. Throughout the culture period, most of the cells within the colonies stain positive for ALPL and cell surface markers SSEA4 and OCT4. The staining patterns of the bES cells are identical to those of the blastocysts fertilized in vitro (IVF), yet different from most previously reported bovine ES cell lines, which are either negative or not detected. After undifferentiated culture for more than 1 year, these cells maintained the ability to differentiate into embryoid bodies and derivatives of all three EG layers, thus demonstrating their pluripotency. In addition to bES from IVF, this chapter introduces two methods of generating blastocyst stage embryos other than in vitro fertilization, which are parthenogenetic activation and somatic cell nuclear transfer for the potential application of generation "patient-specific" ES cells.

Octamer and Sox elements are required for transcriptional cis regulation of Nanog gene expression

The pluripotential cell-specific gene Nanog encodes a homeodomain-bearing transcription factor required for maintaining the undifferentiated state of stem cells. However, the molecular mechanisms that regulate Nanog gene expression are largely unknown. To address this important issue, we used luciferase assays to monitor the relative activities of deletion fragments from the 5'-flanking region of the gene. An adjacent pair of highly conserved Octamer- and Sox-binding sites was found to be essential for activating pluripotential state-specific gene expression. Furthermore, the 5'-end fragment encompassing the Octamer/Sox element was sufficient for inducing the proper expression of a green fluorescent protein reporter gene even in human embryonic stem (ES) cells. The potential of OCT4 and SOX2 to bind to this element was verified by electrophoretic mobility shift assays with extracts from F9 embryonal carcinoma cells and embryonic germ cells derived from embryonic day 12.5 embryos. However, in ES cell extracts, a complex of OCT4 with an undefined factor preferentially bound to the Octamer/Sox element. Thus, Nanog transcription may be regulated through an interaction between Oct4 and Sox2 or a novel pluripotential cell-specific Sox element-binding factor which is prominent in ES cells.

Identification of the facilitative glucose transporter 12 gene Glut12 in mouse preimplantation embryos

In this study we report the cloning and characterisation of the mouse Glut12 gene and examine for the first time its expression pattern in the earliest stages of development. Mouse Glut12 (mGlut12) was cloned from preimplantation embryos by 5'RACE RT-PCR using primers designed from an EST clone corresponding to a human GLUT12 antigenic sequence after positive immunoreactivity was observed in mouse two-cell embryos by western immunoblotting. The mGlut12 gene contains an open reading frame of 1869 base pairs, potentially encoding a polypeptide of 622 amino acids. The predicted mGLUT12 protein bears all the hallmarks of the SLC2A family of hexose transporters and shares an 83% sequence homology to human GLUT12. Consistent with its human homolog mGlut12 mRNA is found highly expressed in skeletal and cardiac muscle and fat. Additionally, it was also found in the uterus and during early embryogenesis. During early development in the mouse, Glut12 expression is clearly apparent in ovulated oocytes and two-cell embryos but declines in day 3 morulae. With the exception of some Glut12 expression apparent in blastocysts, Glut12 mRNA remains at low to undetectable levels until E11.

Generation and characterization of pluripotent stem cells from cloned bovine embryos

Bovine embryonic stem (ES) cell lines reported to date vary in morphology and marker expression (e.g., alkaline phosphatase [ALPL], stage-specific embryonic antigen 4 [SSEA4], and OCT4) that normally are associated with the undifferentiated, pluripotent state. These observations suggest that the proper experimental conditions for consistently producing bovine ES cells have not been identified. Here, we report three bovine ES cell lines, one from in vitro-fertilized and two from nuclear transfer embryos. These bovine ES cells grew in large, multicellular colonies resembling the mouse ES and embryonic germ (EG) cells and human EG cells. Throughout the culture period, most of the cells within the colonies stained positive for ALPL and the cell surface markers SSEA4 and OCT4. The staining patterns of nuclear transfer ES cells were identical to those of the blastocysts generated in vitro yet different from most previously reported bovine ES cell lines, which were either negative or not detected. After undifferentiated culture for more than 1 yr, these cells maintained the ability to differentiate into embryoid bodies and derivatives of all three EG layers, thus demonstrating their pluripotency. However, unlike the mouse and human ES cells, following treatment with trypsin, type IV collagenase, or protease E, our bovine ES cells failed to self-renew and became spontaneously differentiated. Presumably, this resulted from an interruption of the self-renewal pathway. In summary, we generated pluripotent bovine ES cells with morphology similar to those of established ES cells in humans and mice as well as marker-staining patterns identical to those of the bovine blastocysts.

Gender and age related expression of Oct-6--a POU III domain transcription factor, in the adult mouse brain

Oct-6 is a POU III domain transcription factor whose primary role is thought to be developmental. It is expressed in embryonic stem cells, Schwann cells, and in neuronal subpopulations during telencephalic development. Its best characterised role is in Schwann cells where it is thought to regulate myelin specific gene expression. Expression of Oct-6 was recently discovered in neurons in post-mortem human schizophrenic specimens while being undetectable in matched controls. This study of human tissue contrasted in a number of regards with earlier studies of rodent brain, and questioned what we can consider to be normal adult expression of this gene. In this study, we have investigated Oct-6 expression via in situ hybridisation and Western blot analysis in normal adult female mice of different ages. We show that both RNA and protein levels of Oct-6 expression are highly sustained in the adult and aging cerebellum, whereas they are attenuated in the telencephalon by PW30 (postnatal week 30). These observations suggest that Oct-6 expression takes place in a sex and age dependent way.

Expression of the POU domain transcription factor, Oct-6, is attenuated in the adult mouse telencephalon, but increased by neurotoxic damage

Oct-6 is a POU III domain transcription factor expressed in embryonic stem cells, Schwann cells, and neuronal subpopulations during telencephalic development. Its role is unknown except in Schwann cells where it is thought to regulate myelin-specific gene expression. Expression of Oct-6 was recently discovered in neurons in postmortem human schizophrenic brain while being undetectable in matched controls. This study of human tissue contrasted in a number of regards with earlier studies of rodent brain and questioned what we can consider to be normal adult expression of this gene. In this study, we have investigated Oct-6 expression in normal adult mice and in mice treated with neuractive compounds. We show that Oct-6 is widely expressed in young adults but that its expression subsequently becomes restricted to specific neuronal subpopulations. Contrary to earlier reports, however, this specific expression is transient and is eventually completely lost from telencephalic neurons. The OCT-6 protein, somewhat surprisingly, is found to be cytoplasmic as well as nuclear in certain neuronal subpopulations. Finally, we report that neurotoxic doses of anticonvulsants reactivate OCT-6 expression in adult mouse brain.

Involvement of Oct-1 in transcriptional regulation of beta-casein gene expression in mouse mammary gland

Mouse beta-casein gene promoter contains a region termed block C which is crucial for its gene transcription induced by lactogenic hormones. Nuclear extracts from mouse mammary glands contain at least two binding complexes (DS1 and DS2) which specifically bind to double-stranded block C region DNA. The binding sequence of these complexes was identified to be 5'-AAATTAGCATGT-3' which contains a sequence element related to the consensus octamer motif's complement ATTTGCAT. In the present study, we demonstrate that this sequence element indeed is the binding site for octamer-binding transcription factors (Octs) and Octs represent the double-stranded DNA binding proteins specifically binding to the block C region. Formation of the specific double-stranded binding complexes can be completely blocked by Oct binding motif oligonucleotides and anti-rOct-1 antiserum. We also show that Oct-1B represents at least partial, if not all, double-stranded binding protein, DS1, in mammary nuclear extract. Oct-1B may function as a transcriptional activator on casein gene promoter. The Oct binding activity to beta-casein gene promoter in the mammary gland is affected under influence of hormones both in vitro and in vivo. The DS1 binding activity can be induced by the combination of lactogenic hormones insulin, hydrocortisone and prolactin in organ culture of virgin mouse mammary gland. The binding activity in vivo can be induced by injection of progesterone or its combination with estradiol in virgin mice.

POU domain factors in the neuroendocrine system: lessons from developmental biology provide insights into human disease

POU domain factors are transcriptional regulators characterized by a highly conserved DNA-binding domain referred to as the POU domain. The structure of the POU domain has been solved, facilitating the understanding of how these proteins bind to DNA and regulate transcription via complex protein-protein interactions. Several members of the POU domain family have been implicated in the control of development and function of the neuroendocrine system. Such roles have been most clearly established for Pit-1, which is required for formation of somatotropes, lactotropes, and thyrotropes in the anterior pituitary gland, and for Brn-2, which is critical for formation of magnocellular and parvocellular neurons in the paraventricular and supraoptic nuclei of the hypothalamus. While genetic evidence is lacking, molecular biology experiments have implicated several other POU factors in the regulation of gene expression in the hypothalamus and pituitary gland. Pit-1 mutations in humans cause combined pituitary hormone deficiency similar to that found in mice deleted for the Pit-1 gene, providing a striking example of how basic developmental biology studies have provided important insights into human disease.

Molecular cloning and characterization of DEC2, a new member of basic helix-loop-helix proteins

DEC1 is a basic helix-loop-helix (bHLH) protein related to Drosophila Hairy, Enhancer of split and HES, and involved in the control of proliferation and/or differentiation of chondrocytes, neurons, etc. We report here the identification and characterization of human, mouse and rat DEC2, a novel member of the DEC subfamily. DEC2 had high (97%) and moderate (52%) similarities in the bHLH region and the Orange domain with DEC1, respectively. However, DEC2, but not DEC1, had alanine and glycine-rich regions in the C-terminal half. Unlike Hairy, Enhancer of split and HES, DEC2 lacked the WRPW motif for interaction with the corepressor Groucho. The DEC2 gene was mapped to human chromosome 12p11.23-p12.1, mouse chromosome 6 G2-G3 and rat chromosome 4q43 distal-q4, where the conserved linkage homology has been identified among these species. Unlike DEC1, which was broadly expressed in many tissues, DEC2 showed a more restricted pattern of mRNA expression. The DEC subfamily proteins may play an important role in tissue development.

The POU domain transcription factor Tst-1 activates somatostatin receptor 1 gene expression in pancreatic beta -cells

The peptide hormone somatostatin inhibits the release of insulin. The gene encoding somatostatin receptor 1 is expressed in pancreatic beta-cells and insulinoma RIN 1046-38 cells. In the present study the mechanisms underlying the regulation of the somatostatin receptor 1 gene in pancreatic beta-cells were investigated. Transient transfections of RIN 1046-38 cells with promoter/reporter gene constructs and footprint analysis revealed two regions, fp1 and fp2, that were necessary for the observed promoter activity. Mutagenesis of the fp2 region delineated the cis-acting element to the motif 5'-TTAATCATT-3'. The POU domain transcription factor Tst-1 was identified as trans-activator mediating the 5'-TTAATCATT-3' motif-dependent transcription in RIN 1046-38 cells and heterologous CV1 cells. Tst-1, known as a transcriptional regulator in keratinocytes, glial cells, and neurons, has been detected by immunohistochemistry in pancreatic islets. Altogether, we demonstrate Tst-1 as transcriptional regulator in pancreatic neuroendocrine cells.

Combinatorial expression of zebrafish Brn-1- and Brn-2-related POU genes in the embryonic brain, pronephric primordium, and pharyngeal arches

Vertebrate class III POU genes are widely expressed in the embryonic and adult central nervous system, where they act as transcriptional regulators of cell- and/or region-specific gene expression. We isolated four zebrafish class III POU genes, named zp-12, zp-23, zp-47 and zp-50. In this study, we examined the developmental expression patterns of the Brn-1- and Brn-2-related zp-12, zp-23 and zp-47 genes by means of whole-mount in situ hybridization. Similarly to their mammalian orthologues, the major expression site of all zebrafish zp genes is the CNS. Neurectodermal expression was first detected at the beginning of somitogenesis in spatially restricted segment-like domains in different parts of the neural plate. During somitogenesis transcript distributions changed from highly restricted to widespread but nevertheless distinct patterns found in all major subdivisions of the CNS. While zp-47 expression was detected exclusively in the CNS, localized expression of zp-12 and zp-23 was also found in the pronephric primordium and in cell clusters within the mandibular and hyoid arches. Furthermore, zp-23 transcripts were transiently detected in a restricted region of the paraxial mesendoderm and, at late embryogenesis stages, in the auditory vesicles. The early regionalized expression of all three zp genes is compatible with roles in regional specification of the neural plate. Comparison of the distinct yet overlapping expression of zp-12, zp-23, zp-47 and the previously characterized zp-50 gene implies both unique, as well as redundant functions for each family member. We propose that coordinate expression of particular combinations of class III POU genes contribute to pattern formation or cell fate determination in the developing CNS and other structures.

qBrain-2, a POU domain gene expressed in quail embryos

We isolated a quail class III POU domain gene, qBrain-2, which was cloned from a cDNA library of E5 embryos. Northern blot and in situ hybridization analyses showed that qBrain-2 was expressed in developing central nervous system and adult brain. Moreover, qBrain-2 transcripts showed a dynamic distribution in embryonic central nervous system. Its transcripts were dominantly detected in the ventricular zone of the developing brain and spinal cord, but rarely in the differentiated region of mantle zone as well as the non-neuronal roof plate and floor plate. This suggests that qBrain-2 is involved in proliferation and differentiation of the neuroepithelial cells of quail central nervous system.

A dual role of erbB2 in myelination and in expansion of the schwann cell precursor pool

Neuregulin-1 provides an important axonally derived signal for the survival and growth of developing Schwann cells, which is transmitted by the ErbB2/ErbB3 receptor tyrosine kinases. Null mutations of the neuregulin-1, erbB2, or erbB3 mouse genes cause severe deficits in early Schwann cell development. Here, we employ Cre-loxP technology to introduce erbB2 mutations late in Schwann cell development, using a Krox20-cre allele. Cre-mediated erbB2 ablation occurs perinatally in peripheral nerves, but already at E11 within spinal roots. The mutant mice exhibit a widespread peripheral neuropathy characterized by abnormally thin myelin sheaths, containing fewer myelin wraps. In addition, in spinal roots the Schwann cell precursor pool is not correctly established. Thus, the Neuregulin signaling system functions during multiple stages of Schwann cell development and is essential for correct myelination. The thickness of the myelin sheath is determined by the axon diameter, and we suggest that trophic signals provided by the nerve determine the number of times a Schwann cell wraps an axon.

Graded and areal expression patterns of regulatory genes and cadherins in embryonic neocortex independent of thalamocortical input

The differentiation of areas of the mammalian neocortex has been hypothesized to be controlled by intrinsic genetic programs and extrinsic influences such as those mediated by thalamocortical afferents (TCAs). To address the interplay between these intrinsic and extrinsic mechanisms in the process of arealization, we have analyzed the requirement of TCAs in establishing or maintaining graded or areal patterns of gene expression in the developing mouse neocortex. We describe the differential expression of Lhx2, SCIP, and Emx1, representatives of three different classes of transcription factors, and the type II classical cadherins Cad6, Cad8, and Cad11, which are expressed in graded or areal patterns, as well as layer-specific patterns, in the cortical plate. The differential expression of Lhx2, SCIP, Emx1, and Cad8 in the cortical plate is not evident until after TCAs reach the cortex, whereas Cad6 and Cad11 show subtle graded patterns of expression before the arrival of TCAs, which later become stronger. We find that these genes exhibit normal-appearing graded or areal expression patterns in Mash-1 mutant mice that fail to develop a TCA projection. These findings show that TCAs are not required for the establishment or maintenance of the graded and areal expression patterns of these genes and strongly suggest that their regulation is intrinsic to the developing neocortex.

Oligodendrocyte programmed cell death and central myelination deficiency induced in transgenic mice by synergism between c-Myc and Oct-6

The basic helix-loop-helix transcription factor c-Myc is a potent trigger of programmed cell death when overexpressed during late oligodendrocyte development in transgenic mice. Here we provide evidence that c-Myc can act synergistically with the Pit, Oct, Unc homeodomain transcription factor Oct-6 to produce myelin disease pathogenesis in transgenic mice. More than 70% of c-myc/Oct-6 bitransgenic mice, obtained from crosses between phenotypically normal heterozygous mice of various My (c-Myc) and Oc (Oct-6) transgenic strains that express c-myc and oct-6 transgenes under transcriptional control of the myelin basic protein gene, developed severe neurological disturbances characterized by action tremors, recurrent seizures, and premature death. Affected bitransgenic mice exhibited multiple hypomyelinated lesions in the white matter that did not stain with myelin-specific antibodies against myelin basic protein, proteolipid protein, CNPase, and myelin-associated glycoprotein. The mice also exhibited a larger number of terminal deoxynucleotidyltransferase-mediated dUTP-biotin nick end-labeling positive cells in the white matter as well as ultrastructural evidence of glial cell death and astrogliosis. These observations indicate that the myelin lesions observed in the c-myc/oct-6 bitransgenic mice result from the untimely programmed cell death of oligodendroglia and that the c-myc and oct-6 transgenes act synergistically in producing the lesions.

The gene for the embryonic stem cell coactivator UTF1 carries a regulatory element which selectively interacts with a complex composed of Oct-3/4 and Sox-2

UTF1 is a transcriptional coactivator which has recently been isolated and found to be expressed mainly in pluripotent embryonic stem (ES) cells (A. Okuda, A. Fukushima, M. Nishimoto, et al., EMBO J. 17:2019-2032, 1998). To gain insight into the regulatory network of gene expression in ES cells, we have characterized the regulatory elements governing UTF1 gene expression. The results indicate that the UTF1 gene is one of the target genes of an embryonic octamer binding transcription factor, Oct-3/4. UTF1 expression is, like the FGF-4 gene, regulated by the synergistic action of Oct-3/4 and another embryonic factor, Sox-2, implying that the requirement for Sox-2 by Oct-3/4 is not limited to the FGF-4 enhancer but is rather a general mechanism of activation for Oct-3/4. Our biochemical analyses, however, also reveal one distinct difference between these two regulatory elements: unlike the FGF-4 enhancer, the UTF1 regulatory element can, by its one-base difference from the canonical octamer-binding sequence, selectively recruit the complex comprising Oct-3/4 and Sox-2 and preclude the binding of the transcriptionally inactive complex containing Oct-1 or Oct-6. Furthermore, our analyses reveal that these properties are dictated by the unique ability of the Oct-3/4 POU-homeodomain that recognizes a variant of the Octamer motif in the UTF1 regulatory element.