POU transcription factors control expression of CNS stem cell-specific genes

Brain fatty acid binding protein (Fabp7) is diurnally regulated in astrocytes and hippocampal granule cell precursors in adult rodent brain

Brain fatty acid binding protein (Fabp7), which is important in early nervous system development, is expressed in astrocytes and neuronal cell precursors in mature brain. We report here that levels of Fabp7 mRNA in adult murine brain change over a 24 hour period. Unlike Fabp5, a fatty acid binding protein that is expressed widely in various cell types within brain, RNA analysis revealed that Fabp7 mRNA levels were elevated during the light period and lower during dark in brain regions involved in sleep and activity mechanisms. This pattern of Fabp7 mRNA expression was confirmed using in situ hybridization and found to occur throughout the entire brain. Changes in the intracellular distribution of Fabp7 mRNA were also evident over a 24 hour period. Diurnal changes in Fabp7, however, were not found in postnatal day 6 brain, when astrocytes are not yet mature. In contrast, granule cell precursors of the subgranular zone of adult hippocampus did undergo diurnal changes in Fabp7 expression. These changes paralleled oscillations in Fabp7 mRNA throughout the brain suggesting that cell-coordinated signals likely control brain-wide Fabp7 mRNA expression. Immunoblots revealed that Fabp7 protein levels also underwent diurnal changes in abundance, with peak levels occurring in the dark period. Of clock or clock-regulated genes, the synchronized, global cycling pattern of Fabp7 expression is unique and implicates glial cells in the response or modulation of activity and/or circadian rhythms.

Rapid promoter analysis in developing mouse brain and genetic labeling of young neurons by doublecortin-DsRed-express

Characterization of neural promoter/enhancers is essential for understanding gene regulation during brain development and provides useful genetic tools. However, it relies on the use of transgenic mice. We report a method for the rapid in vivo analysis of neural promoter/enhancers in the developing mouse brain and its application in the isolation of the doublecortin (DCX) promoter/enhancer for genetic labeling of young neurons. In the present study, we demonstrated that reporter genes introduced into the developing mouse cerebral cortex by in utero electroporation can achieve promoter/enhancer-specific patterns of expression. We used the in utero electroporation system to isolate a genomic fragment of the doublecortin gene that can direct reporter expression faithful to doublecortin in young neurons of the cerebral cortex. Finally, we showed that the DCX promoter identified via electroporation could reproduce doublecortin expression in the entire central nervous system in DCX-DsRed-express transgenic mice. The results of our study provide a convenient, reliable, and rapid method for in vivo analysis of neural promoter/enhancers in the developing mouse brain.

Identifying and quantitating neural stem and progenitor cells in the adult brain

Adult brain contains neural stem and progenitor cells that are capable of generating new neurons. Active continuous neurogenesis is limited to the subventricular zone of the lateral ventricles and the subgranular zone of the hippocampal dentate gyrus. Newborn neurons gradually become fully functional and integrated into the existing circuitry of the olfactory bulb and the hippocampus. Transition from stem cells to fully differentiation neurons, the neuronal differentiation cascade, occurs through defined steps, and different classes of neuronal precursors can be distinguished by their morphology, expressed markers, and mitotic activity. Cells in these classes can be identified by immunophenotyping, labeling with thymidine analogues, and infection with retro- and lentiviral vectors. We here describe a transgenic approach that allows identification, in vivo visualization, isolation, and accurate enumeration of various classes of stem and progenitor cells in the adult brain. We generated a series of reporter mouse lines in which neural stem and progenitor cells express various fluorescent proteins (GFP, CFPnuc, H2B-GFP, DsRedTimer, and mCherry) under the control of the regulatory elements of the nestin gene. Using these lines, we were able to dissect the neuronal differentiation cascade into several discrete steps and to evaluate the changes induced by various neurogenic and antineurogenic stimuli. In particular, nuclear localization of the fluorescent signal in nestin-CFPnuc mice greatly simplifies the distribution pattern of neural stem and progenitor cells and allows accurate quantitation of changes induced by neurogenic agents in distinct classes of neuronal precursors. We present protocols for applying confocal microscopy, stereology, and electron microscopy to evaluate changes in the neurogenic compartments of the adult brain.

Normal distribution and medullary-to-cortical shift of Nestin-expressing cells in acute renal ischemia

Nestin, a marker of multi-lineage stem and progenitor cells, is a member of intermediate filament family, which is expressed in neuroepithelial stem cells, several embryonic cell types, including mesonephric mesenchyme, endothelial cells of developing blood vessels, and in the adult kidney. We used Nestin-green fluorescent protein (GFP) transgenic mice to characterize its expression in normal and post-ischemic kidneys. Nestin-GFP-expressing cells were detected in large clusters within the papilla, along the vasa rectae, and, less prominently, in the glomeruli and juxta-glomerular arterioles. In mice subjected to 30 min bilateral renal ischemia, glomerular, endothelial, and perivascular cells showed increased Nestin expression. In the post-ischemic period, there was an increase in fluorescence intensity with no significant changes in the total number of Nestin-GFP-expressing cells. Time-lapse fluorescence microscopy performed before and after ischemia ruled out the possibility of engraftment by the circulating Nestin-expressing cells, at least within the first 3 h post-ischemia. Incubation of non-perfused kidney sections resulted in a medullary-to-cortical migration of Nestin-GFP-positive cells with the rate of expansion of their front averaging 40 microm/30 min during the first 3 h and was detectable already after 30 min of incubation. Explant matrigel cultures of the kidney and aorta exhibited sprouting angiogenesis with cells co-expressing Nestin and endothelial marker, Tie-2. In conclusion, several lines of circumstantial evidence identify a sub-population of Nestin-expressing cells with the mural cells, which are recruited in the post-ischemic period to migrate from the medulla toward the renal cortex. These migrating Nestin-positive cells may be involved in the process of post-ischemic tissue regeneration.

A global genomic transcriptional code associated with CNS-expressed genes

Highly conserved non-coding DNA regions (HCNR) occur frequently in vertebrate genomes, but their functional roles remain unclear. Here, we provide evidence that a large portion of HCNRs are enriched for binding sites for Sox, POU and Homeodomain transcription factors, and such HCNRs can act as cis-regulatory regions active in neural stem cells. Strikingly, these HCNRs are linked to several hundreds of genes expressed in the developing CNS and they may exert locus-wide regulatory effects on multiple genes flanking their genomic location. Moreover, these data imply a unifying transcriptional logic for a large set of CNS-expressed genes in which Sox and POU proteins act as generic promoters of transcription while Homeodomain proteins control the spatial expression of genes through active repression.

Putative "stemness" gene jam-B is not required for maintenance of stem cell state in embryonic, neural, or hematopoietic stem cells

Many genes have been identified that are specifically expressed in multiple types of stem cells in their undifferentiated state. It is generally assumed that at least some of these putative "stemness" genes are involved in maintaining properties that are common to all stem cells. We compared gene expression profiles between undifferentiated and differentiated embryonic stem cells (ESCs) using DNA microarrays. We identified several genes with much greater signal in undifferentiated ESCs than in their differentiated derivatives, among them the putative stemness gene encoding junctional adhesion molecule B (Jam-B gene). However, in spite of the specific expression in undifferentiated ESCs, Jam-B mutant ESCs had normal morphology and pluripotency. Furthermore, Jam-B homozygous mutant mice are fertile and have no overt developmental defects. Moreover, we found that neural and hematopoietic stem cells recovered from Jam-B mutant mice are not impaired in their ability to self-renew and differentiate. These results demonstrate that Jam-B is dispensable for normal mouse development and stem cell identity in embryonic, neural, and hematopoietic stem cells.

Intermediate filament protein nestin is expressed in developing kidney and heart and might be regulated by the Wilms' tumor suppressor Wt1

Nestin is an intermediate filament protein originally described in neural stem cells and a variety of progenitor cells. More recently, nestin was detected in rat kidney podocytes. We show here that nestin is expressed in a developmentally regulated pattern in the kidney. Nestin was detected by immunohistochemistry in the condensing mesenchyme surrounding the ureter, in developing glomeruli, in podocytes of the adult kidney, and in a podocyte cell line. Nestin shared a striking overlap in expression with the Wilms' tumor suppressor Wt1. Nestin was significantly upregulated in a cell line with inducible Wt1 expression upon induction of Wt1. Cotransfection experiments in human embryonic kidney cells (HEK293) revealed stimulation of a nestin intron 2 enhancer element up to six-fold by the Wt1(-KTS) splice variant. Nestin expression was significantly reduced in an inducible mouse model of glomerular disease. This model is based on podocyte-specific overexpression of Pax2 and associated with a loss of Wt1 expression. Furthermore, also in the developing heart, nestin was found in an overlapping pattern with Wt1 in the epicardium and the forming coronary vessels. Strikingly, in the hearts of Wt1 knockout mice, nestin was barely detectable compared with the hearts of wild-type embryos. Our results show that nestin is expressed at different stages of kidney and cardiac development and suggest that its expression in these organs might be regulated by the Wilms' tumor suppressor Wt1.

Differential expression of the intermediate filament protein nestin during renal development and its localization in adult podocytes

Nestin, an intermediate filament protein, is widely used as stem cell marker. Nestin has been shown to interact with other cytoskeleton proteins, suggesting a role in regulating cellular cytoskeletal structure. These studies examined renal nestin localization and developmental expression in mice. In developing kidney, anti-nestin antibody revealed strong immunoreactivity in vascular cleft of the S-shaped body and vascular tuft of capillary loop-stage glomerulus. The nestin-positive structures also were labeled by endothelial cell markers FLK1 and CD31 in immature glomeruli. Nestin was not detected in epithelial cells of immature glomeruli. In contrast, in mature glomerular, nestin immunoreactivity was observed only outside laminin-positive glomerular basement membrane, and co-localized with nephrin, consistent with podocyte nestin expression. In adult kidney, podocytes were the only cells that exhibited persistent nestin expression. Nestin was not detected in ureteric bud and its derivatives throughout renal development. Cell lineage studies, using a nestin promoter-driven Cre mouse and a ROSA26 reporter mouse, showed a strong beta-galactosidase activity in intermediate mesoderm in an embryonic day 10 embryo and all of the structures except those that were derived from ureteric bud in embryonic kidney through adult kidney. These studies show that nestin is expressed in progenitors of glomerular endothelial cells and renal progenitors that are derived from metanephric mesenchyme. In the adult kidney, nestin expression is restricted to differentiated podocytes, suggesting that nestin could play an important role in maintaining the structural integrity of the podocytes.

The Sox2 regulatory region 2 functions as a neural stem cell-specific enhancer in the telencephalon

Sox2 is expressed at high levels in neuroepithelial stem cells and persists in neural stem/progenitor cells throughout adulthood. We showed previously that the Sox2 regulatory region 2 (SRR2) drives strong expression in these cells. Here we generated transgenic mouse strains with the beta-geo reporter gene under the control of the SRR2 in order to examine the spatiotemporal function of this regulatory region. We show that the SRR2 functions specifically in neural stem/progenitor cells. However, unlike Nestin 2nd intronic enhancer, the SRR2 shows strong regional specificity functioning only in restricted areas of the telencephalon but not in any other portions of the central nervous system such as the spinal cord. We also show by in vitro clonogenic assay that at least some of these SRR2-functioning cells possess the hallmark properties of neural stem cells. In adult brains, we could detect strong beta-geo expression in the subventricular zone of the lateral ventricle and along the rostral migrating stream where actively dividing cells reside. Chromatin immunoprecipitation assays reveal interactions of POU and Sox factors with SRR2 in neural stem/progenitor cells. Our data also suggest that the specific recruitment of these proteins to the SRR2 in the telencephalon defines the spatiotemporal activity of the enhancer in the developing nervous system.

Hox cofactors in vertebrate development

Hox genes encode homeodomain-containing transcription factors that pattern the body axes of animal embryos. It is well established that the exquisite DNA-binding specificity that allows different Hox proteins to specify distinct structures along the body axis is frequently dependent on interactions with other DNA-binding proteins which act as Hox cofactors. These include the PBC and MEIS classes of TALE (Three Amino acid Loop Extension) homeodomain proteins. The PBC class comprises fly Extradenticle (Exd) and vertebrate Pbx homeoproteins, whereas the MEIS class includes fly Homothorax (Hth) and vertebrate Meis and Prep homeoproteins. Exd was first implicated as a Hox cofactor based on mutant phenotypes in the fly. In vertebrates, PBC and MEIS homeobox proteins play important roles in development and disease. In this review, we describe the evidence that these functions reflect a requirement for Pbx and Meis/Prep proteins as Hox cofactors. However, there is mounting evidence that, like in the fly, Pbx and Meis/Prep proteins function more broadly, and we also discuss how "Hox cofactors" function as partners for other, non-Hox transcription factors during development. Conversely, we review the evidence that Hox proteins have functions that are independent of Pbx and Meis/Prep cofactors and discuss the possibility that other proteins may participate in the DNA-bound Hox complex, contributing to DNA-binding specificity in the absence of, or in addition to, Pbx and Meis/Prep.

The multigene family of fatty acid-binding proteins (FABPs): function, structure and polymorphism

Fatty acid-binding proteins (FABPs) are members of the superfamily of lipid-binding proteins (LBP). So far 9 different FABPs, with tissue-specific distribution, have been identified: L (liver), I (intestinal), H (muscle and heart), A (adipocyte), E (epidermal), Il (ileal), B (brain), M (myelin) and T (testis). The primary role of all the FABP family members is regulation of fatty acid uptake and intracellular transport. The structure of all FABPs is similar - the basic motif characterizing these proteins is beta-barrel, and a single ligand (e.g. a fatty acid, cholesterol, or retinoid) is bound in its internal water-filled cavity. Despite the wide variance in the protein sequence, the gene structure is identical. The FABP genes consist of 4 exons and 3 introns and a few of them are located in the same chromosomal region. For example, A-FABP, E-FABP and M-FABP create a gene cluster. Because of their physiological properties some FABP genes were tested in order to identify mutations altering lipid metabolism. Furthermore, the porcine A-FABP and H-FABP were studied as candidate genes with major effect on fatness traits.

Expression of nestin-green fluorescent protein transgene marks oval cells in the adult liver

Oval cells, which become apparent in the liver after chronic injury, serve as bipotent progenitors for differentiated hepatocytes and cholangiocytes. We found that, in the liver of adult transgenic mice in which expression of green fluorescent protein (GFP) is driven by regulatory elements of the nestin gene, the GFP signal marks a subpopulation of small epithelial cells that meet the criteria for oval cells, including morphology, localization, antigenic profile, and reactivity in response to injury. In the regenerating and developing liver, we also found nestin-GFP-positive cells that express hepatocyte markers; such cells may correspond to transiently appearing differentiating progeny of oval cells. During development, GFP-expressing cells in the liver emerge relatively late, after the appearance of differentiated hepatocytes and cholangiocytes. Our results suggest that nestin-GFP cells in the liver correspond to a specialized cell type whose primary function may be to serve as a reserve for adult liver epithelial cell types.

Second intron of mouse nestin gene directs its expression in pluripotent embryonic carcinoma cells through POU factor binding site

Nestin, an intermediate filament protein, is expressed in the neural stem cells of the developing central nervous system. This tissue-specific expression is driven by the neural stem cell-specific enhancer in the second intron of the nestin gene. In this study, we showed that the mouse nestin gene was expressed in pluripotent embryonic carcinoma (EC) P19 and F9 cells, not in the differentiated cell types. This cell type-specific expression was conferred by the enhancer in the second intron. Mutation of the conserved POU factor-binding site in the enhancer abolished the reporter gene expression in EC cells. Oct4, a Class V POU factor, was found to be coexpressed with nestin in EC cells. Electrophoretic mobility-shift assays and supershift assays showed that a unique protein-DNA complex was formed specifically with nuclear extracts of EC cells, and Oct4 protein was included. Together, these results suggest the functional relevance between the conserved POU factor-binding site and the expression of the nestin gene in pluripotent EC cells.

Astrocytic and neuronal fate of mesenchymal stem cells expressing nestin

Classically, bone marrow mesenchymal stem cells (MSC) differentiate in vivo or in vitro into osteocytes, chondrocytes, fibroblasts and adipocytes. Recently, it was reported by several groups that MSC can also adopt a neural fate in appropriate in vivo or in vitro experimental conditions. However, it is unclear if those cells are really able to differentiate into functional neural cells and in particular into functional neurons. Some observations suggest that a cell fusion process underlies the neural fate adoption by MSC in vivo and first attempts to reproduce in vitro this neural fate decision in MSC cultures were unsuccessful. More recently, however, in several laboratories including ours, differentiation of MSC cultivated from adult rat bone marrow into astrocytes and neuron-like cells was demonstrated. More precisely, we stressed the importance of the expression by MSC of nestin, an intermediate filament protein associated with immaturity in the nervous system, as a pre-requisite to adopting an astrocytic or a neuronal fate in a co-culture paradigm. Using this approach, we have also demonstrated that the MSC-derived neuron-like cells exhibit several electrophysiological key properties classically devoted to neurons, including firing of action potentials. In this review, we will discuss the neurogenic potential of MSC, the factor(s) required for such plasticity, the molecular mechanism(s) underlying this neural plasticity, the importance of the environment of MSC to adopt this neural fate and the therapeutic potential of these observations.

Pluripotent neural crest stem cells in the adult hair follicle

We report the presence of pluripotent neural crest stem cells in the adult mammalian hair follicle. Numerous neural crest cells reside in the outer root sheath from the bulge to the matrix at the base of the follicle. Bulge explants from adult mouse whisker follicles yield migratory neural crest cells, which in clonal culture form colonies consisting of over a thousand cells. Clones contain neurons, smooth muscle cells, rare Schwann cells and melanocytes, demonstrating pluripotency of the clone-forming cell. Targeted differentiation into Schwann cells and chondrocytes was achieved with neuregulin-1 and bone morphogenetic protein-2, respectively. Serial cloning in vitro demonstrated self-renewal capability. Together, the data show that the adult mouse whisker follicle contains pluripotent neural crest stem cells, termed epidermal neural crest cells (eNCSC). eNCSC are promising candidates for diverse cell therapy paradigms because of their high degree of inherent plasticity and due to their easy accessibility in the skin.

Identification of a crucial site for synoviolin expression

Synoviolin is an E3 ubiquitin ligase localized in the endoplasmic reticulum (ER) and serving as ER-associated degradation system. Analysis of transgenic mice suggested that synoviolin gene dosage is implicated in the pathogenesis of arthropathy. Complete deficiency of synoviolin is fatal embryonically. Thus, alternation of Synoviolin could cause breakdown of ER homeostasis and consequently lead to disturbance of cellular homeostasis. Hence, the expression level of Synoviolin appears to be important for its biological role in cellular homeostasis under physiological and pathological conditions. To examine the control of protein level, we performed promoter analysis to determine transcriptional regulation. Here we characterize the role of synoviolin transcription in cellular homeostasis. The Ets binding site (EBS), termed EBS-1, from position -76 to -69 of the proximal promoter, is responsible for synoviolin expression in vivo and in vitro. Interestingly, transfer of EBS-1 decoy into NIH 3T3 cells conferred not only the repression of synoviolin gene expression but also a decrease in cell number. Fluorescence-activated cell sorter analysis using annexin V staining confirmed the induction of apoptosis by EBS-1 decoy and demonstrated recovery of apoptosis by overexpression of Synoviolin. Our results suggest that transcriptional regulation of synoviolin via EBS-1 plays an important role in cellular homeostasis. Our study provides novel insight into the transcriptional regulation for cellular homeostasis.

Brain lipid-binding protein is a direct target of Notch signaling in radial glial cells

Radial glia function during CNS development both as neural progenitors and as a scaffolding supporting neuronal migration. To elucidate pathways involved in these functions, we mapped in vivo the promoter for Blbp, a radial glial gene. We show here that a binding site for the Notch effector CBF1 is essential for all Blbp transcription in radial glia, and that BLBP expression is significantly reduced in the forebrains of mice lacking the Notch1 and Notch3 receptors. These results identify Blbp as the first predominantly CNS-specific Notch target gene and suggest that it mediates some aspects of Notch signaling in radial glia.

Direct visualization of cell movement in the embryonic olfactory bulb using green fluorescent protein transgenic mice: evidence for rapid tangential migration of neural cell precursors

We analyzed motile behavior of neuronal precursor cells in the intact olfactory bulbs (OBs) using transgenic mice expressing GFP under the control of T alpha 1 tubulin promoter. In the olfactory bulbs at the embryonic days 12.5-14.5, a large number of immature neurons expressed GFP in this transgenic line. Embryonic OBs were maintained in an organ culture system and the migratory behavior of GFP-positive cells was analyzed by time-lapse confocal microscopy. We observed rapid tangential movement of GFP-positive cells in the ventral olfactory bulb. In contrast to the typical bipolar morphology of translocating immature neurons within the developing cortex, the motile cells had neither leading nor trailing processes and changed their overall shape frequently. Comparison of the behavior of cells expressing GFP under the control of T alpha 1 tubulin or nestin promoter revealed that rapid motility was specific to cells in the neuronal lineage. The rapid movement was sensitive to an actin perturbing reagent and also dependent on the calcium influx through L-type calcium channels. These results indicate the presence of a specific form of precursor cell migration in the embryonic olfactory bulb.

Different regions of the mouse nestin enhancer may function differentially in nestin expression in an NSC-like cell line and astrocytes

Nestin is a characteristic intermediate filament protein expressed in neural stem cells (NSCs). Evidence has shown that it is also found in reactive astrocytes. Previous studies have demonstrated that the second intron of the human and rat nestin genes harbors the central nervous system (CNS) enhancer and the midbrain enhancer, which regulate nestin expression in different regions of CNS during development. In this study, using an NSC-like cell line C17.2 and primarily cultured astrocytes, we show that both C17.2 cells and astrocytes express nestin. To characterize the nestin enhancer in further detail, we cloned the second intron of the mouse nestin gene, which is homologous to the human and rat counterparts as shown by DNA sequencing. Reporter assay indicated that the full-length nestin enhancer was active in both C17.2 cells and astrocytes, consistent with the immunocytochemistry results. However, in C17.2 cells, the enhancer activity was attributed to the highly conserved 3' part, and the 5' part of the enhancer was suppressive to the transcription activation activity of the full-length enhancer. While in astrocytes, both 3' and 5' parts were able to enhance the reporter gene expression. Our data suggested that different regions of the nestin enhancer might have different functions in C17.2 cells and astrocytes: while the 3' region activates transcription in both cell types, the 5' region suppresses in C17.2 cells but activates in astrocytes nestin expression.

A POU factor binding site upstream of the Chx10 homeobox gene is required for Chx10 expression in subsets of retinal progenitor cells and bipolar cells

Retinal progenitor cells (RPCs) undergo a series of changes over time that affect their competency to produce different cell types at different times in development. The transcriptional machinery that regulates these changes, as well as associated gene expression changes, have not been characterized. An analysis of the regulatory region of the retinal homeodomain transcription factor, Chx10, was carried out using in ovo electroporations in chick and transgenic mice. An RPC enhancer was defined that mediates reporter activity in subsets of RPCs and directs high-level expression in intermediate and late RPCs. Using bioinformatic and biochemical analysis, a key binding site in this enhancer was found and was shown to be bound by the POU domain factors, Brn-2 and Tst-1/SCIP, in retinal extracts. Analysis of the Brn-2 expression pattern shows that it is expressed in intermediate and late RPCs, but not early RPCs, and thus partially overlaps with expression of the reporter activated by the defined Chx10 enhancer. Biochemical analysis also revealed binding of both Chx10 and Brn-2 to an enhancer of the CNS progenitor cell marker, Nestin. Nestin expression in the retina is restricted to intermediate/late RPC subsets, and genetic evidence is presented that demonstrates that Chx10 represses Nestin expression in early RPCs. A bipolar cell enhancer for Chx10 also was defined, and a role for Brn-2 in expression of Chx10 in bipolar cells is predicted. These data identify Brn-2 as a new marker of subsets of RPCs and suggest a mechanism by which a combination of POU factors and Chx10 define RPC gene expression patterns, such as that of Nestin.

Differential expression of duplicated genes for brain-type fatty acid-binding proteins (fabp7a and fabp7b) during early development of the CNS in zebrafish (Danio rerio)

A gene for the zebrafish brain-type fatty acid-binding protein (fabp7b) was identified and its structure defined. The zebrafish fabp7b gene spans 1479 bp and consists of four exons encoding 24, 58, 34 and 16 amino acids, respectively, which is identical to the structure of the fabp7a gene previously described. The complete fabp7b cDNA was isolated by 5' and 3' RACE and its nucleotide sequence determined. The deduced amino acid sequence of FABP7B encoded by the zebrafish fabp7b gene shares 82% identity with that of FABP7A encoded by the zebrafish fabp7a gene. A single transcription start site for the fabp7b gene was mapped by 5' RNA ligase-mediated RACE. Phylogenetic analysis indicated that the duplication of the fabp7 genes occurred in the fish lineage after their divergence from mammals. The zebrafish fabp7b gene was assigned to linkage group 20 by radiation hybrid mapping. Reverse transcription-polymerase chain reaction detected fabp7b transcripts in the same adult tissues as fabp7a transcripts. In the brain, levels of fabp7b transcripts were lower than fabp7a transcripts. Whole-mount in situ hybridization showed that the zebrafish fabp7a transcripts were distributed in the early developing central nervous system. In addition to being expressed in the developing brain and retina, zebrafish fabp7b mRNA was also detected in the swim bladder and pharynx during the embryonic to larval transitory phase.

The adult hair follicle: cradle for pluripotent neural crest stem cells

This review focuses on the recent identification of two novel neural crest-derived cells in the adult mammalian hair follicle, pluripotent stem cells, and Merkel cells. Wnt1-cre/R26R compound transgenic mice, which in the periphery express beta-galactosidase in a neural crest-specific manner, were used to trace neural crest cells. Neural crest cells invade the facial epidermis as early as embryonic day 9.5. Neural crest-derived cells are present along the entire extent of the whisker follicle. This includes the bulge area, an epidermal niche for keratinocyte stem cells, as well as the matrix at the base of the hair follicle. We have determined by in vitro clonal analysis that the bulge area of the adult whisker follicle contains pluripotent neural crest stem cells. In culture, beta-galactosidase-positive cells emigrate from bulge explants, identifying them as neural crest-derived cells. When these cells are resuspended and grown in clonal culture, they give rise to colonies that contain multiple differentiated cell types, including neurons, Schwann cells, smooth muscle cells, pigment cells, chondrocytes, and possibly other types of cells. This result provides evidence for the pluripotentiality of the clone-forming cell. Serial cloning showed that bulge-derived neural crest cells undergo self-renewal, which identifies them as stem cells. Pluripotent neural crest cells are also localized in the back skin hair of adult mice. The bulge area of the whisker follicle is surrounded by numerous Merkel cells, which together with innervating nerve endings form slowly adapting mechanoreceptors that transduce steady skin indentation. Merkel cells express beta-galactosidase in double transgenic mice, which confirms their neural crest origin. Taken together, our data indicate that the epidermis of the adult hair follicle contains pluripotent neural crest stem cells, termed epidermal neural crest stem cells (eNCSCs), and one newly identified neural crest derivative, the Merkel cell. The intrinsic high degree of plasticity of eNCSCs and the fact that they are easily accessible in the skin make them attractive candidates for diverse autologous cell therapy strategies.

Interplay of SOX and POU factors in regulation of the Nestin gene in neural primordial cells

Intermediate-filament Nestin and group B1 SOX transcription factors (SOX1/2/3) are often employed as markers for neural primordium, suggesting their regulatory link. We have identified adjacent and essential SOX and POU factor binding sites in the Nestin neural enhancer. The 30-bp sequence of the enhancer including these sites (Nes30) showed a nervous system-specific and SOX-POU-dependent enhancer activity in multimeric forms in transfection assays and was utilized in assessing the specificity of the synergism; combinations of either group B1 or group C SOX (SOX11) with class III POU proved effective. In embryonic day 13.5 mouse spinal cord, Nestin was expressed in the cells with nuclei in the ventricular and subventricular zones. SOX1/2/3 expression was confined to the nuclei of the ventricular zone; SOX11 localized to the nuclei of both subventricular (high-level expression) and intermediate (low-level expression) zones. Class III POU (Brn2) was expressed at high levels, localizing to the nucleus in the ventricular and subventricular zones; moderate expression was observed in the intermediate zone, distributed in the cytoplasm. These data support the model that synergic interactions between group B1/C SOX and class III POU within the nucleus determine Nestin expression. Evidence also suggests that such interactions are involved in the regulation of neural primordial cells.

Privileged scaffolds for blocking protein-protein interactions: 1,4-disubstituted naphthalene antagonists of transcription factor complex HOX-PBX/DNA

Structure-based-design studies, with the crystal structure of the HOXB1-PBX1/DNA transcription factor complex, were used to identify 1,4-disubstituted naphthalenes as potential antagonists. An initial library of 32 analogs was synthesized, two of which were found to be more potent than the reported activity for a 12 amino acid peptide antagonist. Antagonists were also identified of the related BRN1/DNA and BRN2/DNA transcription factor complexes indicating that a 1,4-disubstituted naphthalene may be a privileged scaffold for preparing screening libraries targeting this family of transcription factor complexes.

Nestin expression is lost in a neural stem cell line through a mechanism involving the proteasome and Notch signalling

Neural stem cells (NSCs) are believed to repair brain damage primarily through cell replacement: i.e., the ability to regenerate lost neurons and glia in a site-specific fashion. The neural stem cell line, MHP36, has been shown to have this capacity, but we have little idea of the molecular mechanisms that control the differentiation of such cells during brain repair. In this study we show that an early event in the differentiation of MHP36 cells, both in vivo and in vitro, is the loss of expression of the intermediate filament protein, nestin. We use a co-culture assay to show that loss of nestin is fast, being detectable after just 1 h and complete in 4 h, and is controlled by proteasome degradation rather than down-regulation of de novo nestin synthesis. We also show that nestin loss is regulated by Notch, and mediated by cell contact.

Conserved POU binding DNA sites in the Sox2 upstream enhancer regulate gene expression in embryonic and neural stem cells

The Sox2 transcription factor is expressed early in the stem cells of the blastocyst inner cell mass and, later, in neural stem cells. We previously identified a Sox2 5'-regulatory region directing transgene expression to the inner cell mass and, later, to neural stem cells and precursors of the forebrain. Here, we identify a core enhancer element able to specify transgene expression in forebrain neural precursors of mouse embryos, and we show that the same core element efficiently activates transcription in inner cell mass-derived embryonic stem (ES) cells. Mutation of POU factor binding sites, able to recognize the neural factors Brn1 and Brn2, shows that these sites contribute to transgene activity in neural cells. The same sites are also essential for activity in ES cells, where they bind different members of the POU family, including Oct4, as shown by gel shift assays and chromatin immunoprecipitation with anti-Oct4 antibodies. Our findings indicate a role for the same POU binding motifs in Sox2 transgene regulation in both ES and neural precursor cells. Oct4 might play a role in the regulation of Sox2 in ES (inner cell mass) cells and, possibly, at the transition between inner cell mass and neural cells, before recruitment of neural POU factors such as Brn1 and Brn2.

Characterization and promoter analysis of the mouse nestin gene

The intermediate filament protein nestin is expressed in the neural stem cells of the developing central nervous system (CNS). Promoter analysis revealed that the minimal promoter of the mouse nestin gene resides in the region -11 to +183 of the 5'-non-coding and upstream flanking region, and that two adjacent Sp1-binding sites are necessary for promoter activity. Electrophoretic mobility-shift assays (EMSA) and supershift assays showed that Sp1 and Sp3 proteins selectively bind to the upstream Sp1 site. These results demonstrate an important functionality of Sp1 and Sp3 in regulating the expression of the mouse nestin gene.

The Sox-2 regulatory regions display their activities in two distinct types of multipotent stem cells

The Sox-2 gene is expressed in embryonic stem (ES) cells and neural stem cells. Two transcription enhancer regions, Sox-2 regulatory region 1 (SRR1) and SRR2, were described previously based on their activities in ES cells. Here, we demonstrate that these regulatory regions also exert their activities in neural stem cells. Moreover, our data reveal that, as in ES cells, both SRR1 and SRR2 show their activities rather specifically in multipotent neural stem or progenitor cells but cease to function in differentiated cells, such as postmitotic neurons. Systematic deletion and mutation analyses showed that the same or at least overlapping DNA elements of SRR2 are involved in its activity in both ES and neural stem or progenitor cells. Thus, SRR2 is the first example of an enhancer in which a single regulatory core sequence is involved in multipotent-state-specific expression in two different stem cells, i.e., ES and neural stem cells.

Transcriptional response to circumscribed cortical brain ischemia: spatiotemporal patterns in ischemic vs. remote non-ischemic cortex

Focal brain infarcts are surrounded by extended perilesional zones that comprise the partially ischemic penumbra but also completely non-ischemic cortex of the remote ipsilateral hemisphere. To delineate the impact of lesion-associated vs. remote processes on transcriptional programming after focal ischemia, we used cDNA array analysis, quantitative real-time polymerase chain reaction and immunohistochemistry in the photothrombosis model of circumscribed cortical ischemia in rats. At an early stage of 4 h after ischemia, gene induction occurred to a similar extent in the ischemic infarct and remote non-ischemic cortex of the ipsilateral hemisphere. Among the genes induced in non-ischemic cortex we found the NGF-inducible genes PC3, VGF and Arc, the transcriptional regulators I kappa B-alpha and Stat3, and the beta-chemokine MIP-1 alpha (CCL3). At 3 days, the spatial pattern of gene expression had changed dramatically with brain fatty acid-binding protein as the only gene significantly induced in non-ischemic ipsilateral cortex. In contrast, numerous genes were exclusively regulated at the lesion site, comprising genes involved in cell cycle regulation, proteolysis, apoptosis, lipid homeostasis and anti-inflammatory counter-regulation. Cortical spreading depression was identified as the main mechanism underlying gene induction in remote non-ischemic cortex. Our data demonstrate a dynamic spatiotemporal pattern of gene induction, which may contribute to delayed progression of damage or, alternatively, mediate neuroprotection, tissue remodeling and functional compensation.

Neural stem and progenitor cells in nestin-GFP transgenic mice

Neural stem cells generate a wide spectrum of cell types in developing and adult nervous systems. These cells are marked by expression of the intermediate filament nestin. We used the regulatory elements of the nestin gene to generate transgenic mice in which neural stem cells of the embryonic and adult brain are marked by the expression of green fluorescent protein (GFP). We used these animals as a reporter line for studying neural stem and progenitor cells in the developing and adult nervous systems. In these nestin-GFP animals, we found that GFP-positive cells reflect the distribution of nestin-positive cells and accurately mark the neurogenic areas of the adult brain. Nestin-GFP cells can be isolated with high purity by using fluorescent-activated cell sorting and can generate multipotential neurospheres. In the adult brain, nestin-GFP cells are approximately 1,400-fold more efficient in generating neurospheres than are GFP-negative cells and, despite their small number, give rise to 70 times more neurospheres than does the GFP-negative population. We characterized the expression of a panel of differentiation markers in GFP-positive cells in the nestin-GFP transgenics and found that these cells can be divided into two groups based on the strength of their GFP signal: GFP-bright cells express glial fibrillary acidic protein (GFAP) but not betaIII-tubulin, whereas GFP-dim cells express betaIII-tubulin but not GFAP. These two classes of cells represent distinct classes of neuronal precursors in the adult mammalian brain, and may reflect different stages of neuronal differentiation. We also found unusual features of nestin-GFP-positive cells in the subgranular cell layer of the dentate gyrus. Together, our results indicate that GFP-positive cells in our transgenic animals accurately represent neural stem and progenitor cells and suggest that these nestin-GFP-expressing cells encompass the majority of the neural stem cells in the adult brain.

The stem-cell menagerie

The numbers, types and locations of stem cells in the nervous system have been the subject of much discussion. This review summarizes data on the types of stem cell present at different stages of development and in the adult brain, and the markers suggested to distinguish between the various possibilities that have been reported. We present evidence that more than one class of stem cell is present in the developing and adult nervous systems, and that it might be possible to distinguish between stem-cell populations and to localize the cell of origin of a particular neurosphere, based on markers that persist in culture and by using universal stem-cell markers prospectively to identify stem cells in vivo.

Functional analysis of chicken Sox2 enhancers highlights an array of diverse regulatory elements that are conserved in mammals

Sox2 expression marks neural and sensory primordia at various stages of development. A 50 kb genomic region of chicken Sox2 was isolated and scanned for enhancer activity utilizing embryo electroporation, resulting in identification of a battery of enhancers. Although Sox2 expression in the early embryonic CNS appears uniform, it is actually pieced together by five separate enhancers with distinct spatio-temporal specificities, including the one activated by the neural induction signals emanating from Hensen's node. Enhancers for Sox2 expression in the lens and nasal/otic placodes and in the neural crest were also determined. These functionally identified Sox2 enhancers exactly correspond to the extragenic sequence blocks conspicuously conserved between chicken and mammals, which are not discernible by sequence comparison among mammals.

Brain lipid binding protein in axon-Schwann cell interactions and peripheral nerve tumorigenesis

Loss of axonal contact characterizes Schwann cells in benign and malignant peripheral nerve sheath tumors (MPNST) from neurofibromatosis type 1 (NF1) patients. Tumor Schwann cells demonstrate NF1 mutations, elevated Ras activity, and aberrant epidermal growth factor receptor (EGFR) expression. Using cDNA microarrays, we found that brain lipid binding protein (BLBP) is elevated in an EGFR-positive subpopulation of Nf1 mutant mouse Schwann cells (Nf1(-/-) TXF) that grows away from axons; BLBP expression was not affected by farnesyltransferase inhibitor, an inhibitor of H-Ras. BLBP was also detected in EGFR-positive cell lines derived from Nf1:p53 double mutant mice and human MPNST. BLBP expression was induced in normal Schwann cells following transfection with EGFR but not H-Ras12V. Furthermore, EGFR-mediated BLBP expression was not inhibited by dominant-negative H-Ras, indicating that BLBP expression is downstream of Ras-independent EGFR signaling. BLBP-blocking antibodies enabled process outgrowth from Nf1(-/-) TXF cells and restored interaction with axons, without affecting cell proliferation or migration. Following injury, BLBP expression was induced in normal sciatic nerves when nonmyelinating Schwann cells remodeled their processes. These data suggest that BLBP, stimulated by Ras-independent pathways, regulates Schwann cell-axon interactions in normal peripheral nerve and peripheral nerve tumors.

Structure, mRNA expression and linkage mapping of the brain-type fatty acid-binding protein gene (FABP7) from zebrafish (Danio rerio)

The brain fatty acid-binding protein (B-FABP) is involved in brain development and adult neurogenesis. We have determined the sequence of the gene encoding the B-FABP in zebrafish. The zebrafish B-FABP gene spans 2370 bp and contains four exons interrupted by three introns. The coding sequence of zebrafish B-FABP gene is identical to its cDNA sequence and the coding capacity of each exon is the same as that for the human and mouse B-FABP genes. A 1249 bp sequence 5' upstream of exon 1 of the zebrafish B-FABP gene was cloned and sequenced. Several brain development/growth-associated transcription factor binding elements, including POU-domain binding elements and the proposed lipogenic-associated transcription factor NF-Y elements, were found within the 5' region of the B-FABP gene. RT-PCR analysis using mRNA extracted from different tissues of adult zebrafish demonstrated that the zebrafish B-FABP mRNA was predominant in brain with lower levels in liver, testis and intestine, but not in ovary, skin, heart, kidney and muscle. Quantitative RT-PCR revealed a similar tissue-specific distribution for zebrafish B-FABP mRNA except that very low levels of B-FABP mRNA, normalized to beta-actin mRNA, were detected in the heart and muscle RNA, but not in liver RNA. Zebrafish B-FABP mRNA was detected by RT-PCR in embryos beyond 12 h postfertilization, suggesting a correlation of zebrafish B-FABP mRNA expression with early brain development. Radiation hybrid mapping assigned the zebrafish B-FABP gene to linkage group 17. Conserved syntenies of the zebrafish B-FABP gene and the human and mouse orthologous B-FABP genes were observed by comparative genomic analysis.

Mutation of a putative nuclear receptor binding site abolishes activity of the nestin midbrain enhancer

Regional differences in gene expression are critical to the proper development of specialized cell types in the nervous system. The ventral midbrain is the prominent source of dopaminergic neurons, which are affected in Parkinson's disease. We have recently identified a gene regulatory element that is specifically active in ventral midbrain neuroepithelium of developing embryos. This 204-bp transcriptional enhancer is conserved within the second intron of mammalian nestin genes and contains a putative binding site for a protein of the nuclear receptor family. Our present study shows, by mutagenesis and reporter gene assay in transgenic mice, that this site is essential for enhancer function in the developing midbrain. The characterization of regulatory sites and transcription factors with specific activity in the ventral midbrain provides insight into the molecular mechanisms by which neural progenitor cells become specified towards particular neuronal differentiation pathways.

Properties of a fetal multipotent neural stem cell (NEP cell)

Multipotent neural stem cells (NSCs) present in the developing neural tube (E10.5, neuroepithelial cells; NEP) were examined for the expression of candidate stem cell markers, and the expression of these markers was compared with later appearing precursor cells (E14.5) that can be distinguished by the expression of embryonic neural cell adhesion molecule (E-NCAM) and A2B5. NEP cells possess gap junctions, express connexins, and appear to lack long cilia. Most candidate markers, including Nestin, Presenilin, Notch, and Numb, were expressed by both NEP cells as well as other cell populations. Fibroblast growth factor receptor 4 (FGFR4), Frizzled 9 (Fz9), and SRY box-containing gene 2 (Sox2) as assessed by immunocytochemistry and in situ hybridization are markers that appear to distinguish NSCs from other precursor cells. Neither Hoechst 33342 nor rhodamine-123 staining, telomerase (Tert) expression, telomerase activity, or breakpoint cluster region protein 1 (Bcrp1) transporter expression could be used to distinguish NEP stem cells from other dividing cells. NEP cells, however, lacked expression of several lineage markers that are expressed by later appearing cells. These included absence of expression of CD44, E-NCAM, A2B5, epidermal growth factor receptor (EGFR), and platelet-derived growth factor receptor-alpha (PDGFR alpha), suggesting that negative selection using cell surface epitopes could be used to isolate stem cell populations from mixed cultures of cells. Using mixed cultures of cells isolated from E14.5 stage embryos, we show that NEP cells can be enriched by depleting differentiating cells that express E-NCAM or A2B5 immunoreactivity. Overall, our results show that a spectrum of markers used in combination can reliably distinguish multipotent NSCs from other precursor cells as well as differentiated cells present in the CNS.

Nestin enhancer requirements for expression in normal and injured adult CNS

The nestin gene is expressed in many CNS stem/progenitor cells, both in the embryo and the adult, and nestin is used commonly as a marker for these cells. In this report we analyze nestin enhancer requirements in the adult CNS, using transgenic mice carrying reporter genes linked to three different nestin enhancer constructs: the genomic rat nestin gene and 5 kb of upstream nestin sequence (NesPlacZ/3), 636 bp of the rat nestin second intron (E/nestin:EGFP), and a corresponding 714 bp region from the human second intron (Nes714tk/lacZ). NesPlacZ/3 and E/nestin:EGFP mice showed reporter gene expression in stem cell-containing regions of brain and spinal cord during normal conditions. NesPlacZ/3 and E/nestin:EGFP mice showed increased expression in spinal cord after injury and NesPlacZ/3 mice displayed elevated expression in the periventricular area of the brain after injury, which was not the case for the E/nestin:EGFP mice. In contrast, no expression in adult CNS in vivo was seen in the Nes714tk/lacZ mice carrying the human enhancer, neither during normal conditions nor after injury. The Nes714 tk/lacZ mice, however, expressed the reporter gene in reactive astrocytes and CNS stem cells cultured ex vivo. Collectively, this suggests a species difference for the nestin enhancer function in adult CNS and that elements outside the second intron enhancer are required for the full injury response in vivo.

Forebrain-specific promoter/enhancer D6 derived from the mouse Dach1 gene controls expression in neural stem cells

Drosophila dachshund is involved in development of eye and limbs and in the development of mushroom bodies, a brain structure required for learning and memory in flies. Its mouse homologue mDach1 is expressed in various embryonic tissues, including limbs, the eye, the dorsal spinal cord and the forebrain. We have isolated a forebrain-specific 2.5-kb enhancer element termed D6 from the mouse mDach1 gene and created D6-LacZ and D6-green fluorescent protein (GFP) reporter gene mouse lines. In embryonic stages, the D6 enhancer activity is first detected at embryonic day 10.5 in scattered cells of the outbuldging cortical vesicles. By embryonic day 12.5, D6 activity expands throughout the developing neocortex and the hippocampus. In the adult mouse brain, D6 enhancer is active in neurons of the cortical plate, in the CA1 layer of the hippocampus and in cells of the subventricular zone and the ventricular ependymal zone. Adult mice also show D6 activity in the olfactory bulb and in the mamillary nucleus. Cultured D6-positive cells, which were derived from embryonic and postnatal brains, show characteristics of neural stem cells. They form primary and secondary neurospheres that differentiate into neurons and astrocytes as examined by cell-specific markers.Our results show that D6 enhancer exerts highly tissue-specific activity in the neurons of the neocortex and hippocampus and in neural stem cells. Moreover, the fluorescence cell sorting of D6-GFP cells from embryonic and postnatal stages allows specific selection of primary neural progenitors and their analysis.

Insulinotropic hormone glucagon-like peptide-1 differentiation of human pancreatic islet-derived progenitor cells into insulin-producing cells

Glucagon-like peptide-1 (GLP-1) is an intestinal incretin hormone, derived from the processing of proglucagon, that exerts insulinotropic actions on insulin-producing pancreatic islet beta-cells. Recently GLP-1 was shown to stimulate the growth and differentiation (neogenesis) of beta-cells and appears to do so by inducing the expression of the homeodomain protein IDX-1 (islet duodenum homeobox-1; also known as PDX-1, pancreatic and duodenal homeobox gene; and as IPF-1, insulin promoter factor), which is required for pancreas development and the expression of beta-cell-specific genes. Earlier we identified multipotential progenitor cells in the islet and ducts of the pancreas, termed nestin-positive islet-derived progenitor cells (NIPs). Here we report the expression of functional GLP-1 receptors on NIPs and that GLP-1 stimulates the differentiation of NIPs into insulin-producing cells. Furthermore, confluent NIP cultures express the proglucagon gene and secrete GLP-1. These findings suggest a model of islet development in which pancreatic progenitor cells express both GLP-1 receptors and proglucagon with the formation of GLP-1. Locally produced GLP-1 may act as an autocrine/paracrine developmental morphogen on receptors on NIPs, resulting in the activation of IDX-1 and the expression of the proinsulin gene conferring a beta-cell phenotype. GLP-1 may be an important morphogen both for the embryonic development of the pancreas and for the neogenesis of beta-cells in the islets of the adult pancreas.

SNPs in the CpG island of NAP1L2: a possible link between DNA methylation and neural tube defects?

Deletion of the murine X-linked Nap1l2 gene causes lethality from midgestation onwards. The affected embryos exhibit neural tube defects (NTDs) closely resembling spina bifida and anencephaly in humans. X-linked familial and spontaneous cases of NTD were analyzed for sequence alterations in the human NAP1L2. No differences were found in the familial cases. However, a number of single nucleotide polymorphisms (SNPs) within the 5' region of NAP1L2 were identified both in cases of spontaneous NTD and in normal controls. Most of these SNPs lead to the replacement of guanidines or cytosines within a CpG island that is conserved between the human and the mouse promoter regions. Demethylation in vitro activates Nap1l2 transcriptional activity, suggesting the importance of the CpG island in regulating the activity of the Nap1l2/NAP1L2 genes, and the potential importance of the polymorphisms in modifying their transcriptional activity. NAP1L2/Nap1l2 expression may therefore depend on the genetic-environmental factors that are frequently associated with NTDs.

Brn-4 transcription factor expression targeted to the early developing mouse pancreas induces ectopic glucagon gene expression in insulin-producing beta cells

The endocrine pancreas is comprised of beta and alpha cells producing the glucostatic hormones insulin and glucagon, respectively, and arises during development by the differentiation of stem/progenitor cells in the foregut programmed by the beta cell lineage-specific homeodomain protein Idx-1. Brain-4 (Brn-4) is expressed in the pancreatic anlaga of the mouse foregut at e10 in the alpha cells and transactivates glucagon gene expression. We expressed Brn-4 in pancreatic precursors or beta cell lineage in transgenic mice by placing it under either Idx-1 or insulin promoter (rat insulin II promoter) control, respectively. Idx-1 expression occurs at developmental day e8.5, and insulin expression occurs at e9.5, respectively. Misexpression of Brn-4 by the Idx-1 promoter results in ectopic expression of the proglucagon gene in insulin-expressing pancreatic beta cells, whereas misexpression by rat insulin II promoter did not. The early developmental expression of Brn-4 appears to be a dominant regulator of the glucagon expressing alpha cell lineage, even in the context of the beta cell lineage.

Androgen receptor interactions with Oct-1 and Brn-1 are physically and functionally distinct

POU domain proteins interact positively or negatively with steroid hormone receptors, depending on the precise array of these and other factors assembled on target gene promoters. Octamer transcription factor 1 (Oct-1), a ubiquitous POU factor, is implicated in androgen induction of the mouse sex-limited protein (Slp) gene based on protein-DNA interaction studies. However, direct evidence for a role of Oct-1 in the hormone response has been difficult to obtain. Brain 1 (Brn-1), another POU factor, is more tissue-specific, expressing in brain and also in kidney, which is a major site of Slp synthesis. We compared the interaction of the androgen receptor (AR) with Oct-1 and Brn-1 to reveal the more likely candidate for regulation of Slp. In transfection, addition of either Oct-1 or Brn-1 reduced AR activation, regardless of the presence of an octamer-like sequence in the enhancer, suggesting interference was indirect. However, when the octamer-like element was changed to a consensus octamer site, Brn-1, but not Oct-1, strongly enhanced androgen activation. This correlated with Brn-l's preference for the consensus octamer sequence in DNA binding assays. Direct interaction of AR with glutathione-S-transferase-(GST)-fused Oct-1 was DNA-dependent, while Brn-l-AR association was not. Chimeric Brn-1 and Oct-1 POU domains demonstrated that the DNA-dependent AR interaction relied on the origin of the POU homeodomain. However, in the context of full-length Brn-1 and Oct-1 chimeric proteins, the POU homedomain was not sufficient to confer the distinct behaviors of these factors in vivo, but instead revealed the importance of an N-terminal transactivation domain in Brn-1. These results demonstrate that functional interaction of Oct-1 and Brn-1 with AR is determined by the precise sequence of the octamer binding site, and by differential interaction of the POU factors with AR and other components of the transcriptional machinery.

Nestin is a neuroepithelial target gene of thyroid transcription factor-1, a homeoprotein required for forebrain organogenesis

Thyroid transcription factor-1 (TTF-1, also known as NKX2.1 and T/EBP), a transcription factor belonging to the NKX-2 family of homeodomain-containing genes, plays an essential role in the organogenesis of the thyroid gland, lung, and ventral forebrain. Nestin is an intermediate filament protein strongly expressed in multipotential neuroepithelial stem cells and rapidly down-regulated during postnatal life. Here we show that stable fibroblastic clones expressing TTF-1 acquire a phenotype reminiscent of neuroepithelial cells in culture and up-regulate the endogenous nestin gene. TTF-1 transactivates in HeLa and NIH3T3 cells a reporter gene driven by a central nervous system-specific enhancer element from the second intron of the rat nestin gene, where it recognizes a DNA-binding site (NestBS) whose sequence resembles a nuclear hormone/cAMP-responsive element very different from canonical TTF-1 binding sites. Nuclear extracts from the head of mouse embryos form a retarded complex with NestBS of the same mobility of the extracts obtained from TTF1-expressing clones, which is either abolished or supershifted in the presence of two different antibodies recognizing the TTF-1 protein. Thus, the neuroepithelial marker nestin is a direct central nervous system-specific target gene of TTF-1, leading to the hypothesis that it might be the effector through which TTF-1 plays its role in the organogenesis of the forebrain.

Sequential actions of BMP receptors control neural precursor cell production and fate

Bone morphogenetic proteins (BMPs) have diverse and sometimes paradoxical effects during embryonic development. To determine the mechanisms underlying BMP actions, we analyzed the expression and function of two BMP receptors, BMPR-IA and BMPR-IB, in neural precursor cells in vitro and in vivo. Neural precursor cells always express Bmpr-1a, but Bmpr-1b is not expressed until embryonic day 9 and is restricted to the dorsal neural tube surrounding the source of BMP ligands. BMPR-IA activation induces (and Sonic hedgehog prevents) expression of Bmpr-1b along with dorsal identity genes in precursor cells and promotes their proliferation. When BMPR-IB is activated, it limits precursor cell numbers by causing mitotic arrest. This results in apoptosis in early gestation embryos and terminal differentiation in mid-gestation embryos. Thus, BMP actions are first inducing (through BMPR-IA) and then terminating (through BMPR-IB), based on the accumulation of BMPR-IB relative to BMPR-IA. We describe a feed-forward mechanism to explain how the sequential actions of these receptors control the production and fate of dorsal precursor cells from neural stem cells.

NF-Y binding is required for transactivation of neuronal aromatic L-amino acid decarboxylase gene promoter by the POU-domain protein Brn-2

We have previously characterized binding sites for the NF-Y transcription factor (-71/-52) and Brn-2 POU-domain protein (-92/-71) in the neuronal promoter of the human aromatic L-amino acid decarboxylase gene [Mol. Brain Res. 56 (1998) 227]. We have now explored the functional role of these binding sites in transfected SK-N-BE neuroblastoma cells. Mutations of the NF-Y site that abolish binding depressed expression of a luciferase reporter gene up to 25-fold. The overexpression of a dominant negative mutant of NF-YA subunit depressed expression by 60%. Promoter activity was increased by the overexpression of Brn-2. Mutations or deletion of the binding site of Brn-2 did not suppress transcriptional activation by overexpressed Brn-2, while promoters defective in NF-Y binding were not transactivated by Brn-2. A GST-pulldown experiment showed that recombinant human Brn-2 protein weakly interacts with recombinant NF-Y outside of DNA. Cooperative binding of recombinant NF-Y and GST--Brn-2 proteins on the neuronal promoter was evidenced by an electrophoretic mobility shift assay. The POU-domain of Brn-2 was sufficient for such interaction. The results thus suggest that the activation of the neuronal promoter of the aromatic L-amino acid decarboxylase gene requires a direct interaction between the ubiquitous NF-Y factor and a cell-specific POU-domain protein. The NF-Y, but not the Brn-2 binding site, is essential for the recruitment of the NF-Y/Brn-2 complex on the promoter.

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.

Developmental mechanisms in the pathogenesis of neurodegenerative diseases

Cellular genes that are mutated in neurodegenerative diseases code for proteins that are expressed throughout neural development. Genetic analysis suggests that these genes are essential for a broad range of normal neurodevelopmental processes. The proteins they code for interact with numerous other cellular proteins that are components of signaling pathways involved in patterning of the neural tube and in regional specification of neuronal subtypes. Further, pathogenetic mutations of these genes can cause progressive, sublethal alterations in the cellular homeostasis of evolving regional neuronal subpopulations, culminating in late-onset cell death. Therefore, as a consequence of the disease mutations, targeted cell populations may retain molecular traces of abnormal interactions with disease-associated proteins by exhibiting changes in a spectrum of normal cellular functions and enhanced vulnerability to a host of environmental stressors. These observations suggest that the normal functions of these disease-associated proteins are to ensure the fidelity and integration of developmental events associated with the progressive elaboration of neuronal subtypes as well as the maintenance of mature neuronal populations during adult life. The ability to identify alterations within vulnerable neuronal precursors present in pre-symptomatic individuals prior to the onset of irrevocable cellular injury may help foster the development of effective therapeutic interventions using evolving pharmacologic, gene and stem cell technologies.

Regulation of brain fatty acid-binding protein expression by differential phosphorylation of nuclear factor I in malignant glioma cell lines

Brain fatty acid-binding protein (B-FABP) is expressed in the radial glial cells of the developing central nervous system as well as in a subset of human malignant glioma cell lines. Most of the malignant glioma lines that express B-FABP also express GFAP, an intermediate filament protein found in mature astrocytes. We are studying the regulation of the B-FABP gene to determine the basis for its differential expression in malignant glioma lines. By DNase I footprinting, we have identified five DNA-binding sites located within 400 base pairs (bp) of the B-FABP transcription start site, including two nuclear factor I (NFI)-binding sites at -35 to -58 bp (footprint 1, fp1) and -237 to -260 bp (fp3), respectively. Competition experiments, supershift experiments with anti-NFI antibody, and methylation interference experiments all indicate that the factor binding to fp1 and fp3 is NFI. By site-directed mutagenesis of both NFI-binding sites, we show that the most proximal NFI site is essential for B-FABP promoter activity in transiently transfected malignant glioma cells. Different band shift patterns are observed with nuclear extracts from B-FABP(+) and B-FABP(-) malignant glioma lines, with the latter generating complexes that migrate more slowly than those obtained with B-FABP(+) extracts. All bands are converted to a faster migrating form with potato acid phosphatase treatment, indicating that NFI is differentially phosphorylated in B-FABP(+) and B-FABP(-) lines. Our results suggest that B-FABP expression in malignant glioma lines is determined by the extent of NFI phosphorylation which, in turn, is controlled by a phosphatase activity specific to B-FABP(+) lines.

Combinatorial roles of the nuclear receptor corepressor in transcription and development

Transcriptional repression plays crucial roles in diverse aspects of metazoan development, implying critical regulatory roles for corepressors such as N-CoR and SMRT. Altered patterns of transcription in tissues and cells derived from N-CoR gene-deleted mice and the resulting block at specific points in CNS, erythrocyte, and thymocyte development indicated that N-CoR was a required component of short-term active repression by nuclear receptors and MAD and of a subset of long-term repression events mediated by REST/NRSF. Unexpectedly, N-CoR and a specific deacetylase were also required for transcriptional activation of one class of retinoic acid response element. Together, these findings suggest that specific combinations of corepressors and histone deacetylases mediate the gene-specific actions of DNA-bound repressors in development of multiple organ systems.