Transcriptional programming of social hierarchy

In this issue of Neuron, Choi and colleagues1 uncover the direct role of the transcription factor Pou3f1 in regulating dominance hierarchy in mice. Pou3f1 accomplishes this role via its action in specific prefrontal projection neurons that regulate behaviors associated with low social status.

Zfp296 knockout enhances chromatin accessibility and induces a unique state of pluripotency in embryonic stem cells

The Zfp296 gene encodes a zinc finger-type protein. Its expression is high in mouse embryonic stem cells (ESCs) but rapidly decreases following differentiation. Zfp296-knockout (KO) ESCs grew as flat colonies, which were reverted to rounded colonies by exogenous expression of Zfp296. KO ESCs could not form teratomas when transplanted into mice but could efficiently contribute to germline-competent chimeric mice following blastocyst injection. Transcriptome analysis revealed that Zfp296 deficiency up- and down-regulates a distinct group of genes, among which Dppa3, Otx2, and Pou3f1 were markedly downregulated. Chromatin immunoprecipitation sequencing demonstrated that ZFP296 binding is predominantly seen in the vicinity of the transcription start sites (TSSs) of a number of genes, and ZFP296 was suggested to negatively regulate transcription. Consistently, chromatin accessibility assay clearly showed that ZFP296 binding reduces the accessibility of the TSS regions of target genes. Zfp296-KO ESCs showed increased histone H3K9 di- and trimethylation. Co-immunoprecipitation analyses revealed interaction of ZFP296 with G9a and GLP. These results show that ZFP296 plays essential roles in maintaining the global epigenetic state of ESCs through multiple mechanisms including activation of Dppa3, attenuation of chromatin accessibility, and repression of H3K9 methylation, but that Zfp296-KO ESCs retain a unique state of pluripotency while lacking the teratoma-forming ability.

The class III POU domain protein Brn-1 can fully replace the related Oct-6 during schwann cell development and myelination

For differentiation, Schwann cells rely on the class III POU domain transcription factor Oct-6, which is expressed transiently when Schwann cells have established a one-to-one relation with axons but have not yet started to myelinate. Loss of Oct-6 leads to a transient arrest in this promyelinating stage and a delay in myelination. Although the closely related POU domain protein Brn-2 is coexpressed with Oct-6 in Schwann cells, its loss has only mild consequences. Combined loss of both POU domain proteins, in contrast, dramatically increases the myelination delay, raising the question of how related POU domain proteins compare to each other in their activities. Here, we have replaced Oct-6 expression in the mouse with expression of the class III POU domain protein Brn-1. Although this protein is not normally expressed in Schwann cells, Brn-1 was capable of fully replacing Oct-6. Brn-1 efficiently induced Krox-20 expression as a prerequisite for myelination. Onset and extent of myelination were also indistinguishable from that of the wild type in mice that carried only Brn-1 instead of Oct-6 alleles. Similar to Oct-6, Brn-1 down-regulated its own expression at later stages of myelination. Thus, class III POU domain proteins can fully replace each other in Schwann cell development.

The remyelinating potential and in vitro differentiation of MOG-expressing oligodendrocyte precursors isolated from the adult rat CNS

There is a long-standing controversy as to whether oligodendrocytes may be capable of cell division and thus contribute to remyelination. We recently published evidence that a subpopulation of myelin oligodendrocyte glycoprotein (MOG)-expressing cells in the adult rat spinal cord co-expressed molecules previously considered to be restricted to oligodendrocyte progenitors [G. Li et al. (2002) Brain Pathol., 12, 463-471]. To further investigate the properties of MOG-expressing cells, anti-MOG-immunosorted cells were grown in culture and transplanted into acute demyelinating lesions. The immunosorting protocol yielded a cell preparation in which over 98% of the viable cells showed anti-MOG- and O1-immunoreactivity; 12-15% of the anti-MOG-immunosorted cells co-expressed platelet-derived growth factor alpha receptor (PDGFRalpha) or the A2B5-epitope. When cultured in serum-free medium containing EGF and FGF-2, 15-18% of the anti-MOG-immunosorted cells lost anti-MOG- and O1-immunoreactivity and underwent cell division. On removal of these growth factors, cells differentiated into oligodendrocytes, or astrocytes and Schwann cells when the differentiation medium contained BMPs. Transplantation of anti-MOG-immunosorted cells into areas of acute demyelination immediately after isolation resulted in the generation of remyelinating oligodendrocytes and Schwann cells. Our studies indicate that the adult rat CNS contains a significant number of oligodendrocyte precursors that express MOG and galactocerebroside, molecules previously considered restricted to mature oligodendrocytes. This may explain why myelin-bearing oligodendrocytes were considered capable of generating remyelinating cells. Our study also provides evidence that the adult oligodendrocyte progenitor can be considered as a source of the Schwann cells that remyelinate demyelinated CNS axons following concurrent destruction of oligodendrocytes and astrocytes.

Fez1 is layer-specifically expressed in the adult mouse neocortex

The mammalian cerebral neocortex occupies the largest area of the cerebral cortex and is cytoarchitectually composed of six layers (I-VI). Recent molecular analysis has begun to reveal the existence of various developmental programs, including the genetic regulation of arealization of the neocortex. Although an increasing number of molecular determinants of the developmental stages of the neocortex have been identified, no genes specifically expressed in the adult neocortex have been identified to date. By global screening using microarrays, combined with systematic in situ hybridization, we identified a zinc-finger type transcription factor, Fez1, which is expressed predominantly in the mouse adult neocortex. No other genes in the neocortex have been shown to date to have their expression with such high specificity. Using two-color in situ hybridization, we show that Fez1 is mainly expressed in cortical layers V and VI, not in gamma-aminobutyric acid neurons but in pyramidal neurons, the projection neurons of the cerebral cortex. Immunohistochemistry also shows that Fez1 is expressed in deep layers of the neocortex. Fez1 will be invaluable not only for the molecular understanding of corticogenesis but also for understanding the physiological functions of the adult neocortex, as well as for the use of its promoter in gene-manipulated animals and in conditional expression systems.

A role for schwann cells in the neuroregenerative effects of a non-immunosuppressive fk506 derivative, jnj460

FK506 and its non-immunosuppressive derivatives represent a class of pharmacological agents referred to as immunophilin ligands that have been reported to promote neuroregeneration and survival in several experimental models; however their cellular and molecular mechanisms of action have not been well established. Here we characterize a new immunophilin ligand that interacts with both FK506 binding protein 12 (FKBP12) and FKBP52, and demonstrate that JNJ460 induces neurite outgrowth from freshly explanted dorsal root ganglia (DRG) in a Schwann cell-dependent manner. Purified cultures of neurons fail to respond to these drugs, but cultures containing Schwann cells and neurons respond with neurite outgrowth, as do neurons grown in conditioned medium from JNJ460-treated Schwann cells. Using microarray analysis and a transcription reporter assay, we show that JNJ460 induces a series of transcriptional changes that occur in a temporal cascade. Among the Schwann cell-expressed genes upregulated following JNJ460 treatment is the POU transcription factor SCIP, which has been shown to regulate Schwann cell gene transcription and differentiation. JNJ460 potentiated transforming growth factor beta (TGF-beta)-induced transcriptional activation and SCIP induction in Schwann cells, by altering the interaction between FKBP12 and the TGF-beta type I receptor, TbetaR1. Finally, to test whether JNJ460 enhances neurite regeneration in vivo, we treated animals with JNJ460 for 30 days following mechanical transection of the sciatic nerve and demonstrated myelin and axonal hypertrophy at the ultrastructural level. Collectively, these data suggest that Schwann cells play an important role in the biological effects of immunophilin ligands by affecting neuron-glial signaling during regeneration.

SUMMARY

The cellular and molecular mechanisms responsible for the regenerative effects of immunophilin ligands are not well understood. Here we show that the neuritogenic effects of JNJ460 in a DRG model depend on interactions between neurons and Schwann cells. Treatment of purified Schwann cells with JNJ460 alters Schwann cell gene expression, and promotes the generation of factors that act on neurons. These data indicate that Schwann cells play an important role in the actions of immunophilin ligands.

Structure of the hepatocyte nuclear factor 6alpha and its interaction with DNA

Hepatocyte nuclear factor 6 (HNF-6) belongs to the family of One Cut transcription factors (also known as OC-1) and is essential for the development of the mouse pancreas, gall bladder, and the interhepatic bile ducts. HNF-6 binds to DNA as a monomer utilizing a single cut domain and a divergent homeodomain motif located at its C terminus. Here, we have used NMR methods to determine the solution structures of the 162 amino acid residue DNA-binding domain of the HNF-6alpha protein. The resulting overall structure of HNF-6alpha has two different distinct domains: the Cut domain and the Homeodomain connected by a long flexible linker. Our NMR structure shows that the Cut domain folds into a topology homologous to the POU DNA-binding domain, even though the sequences of these two protein families do not show homology. The DNA contact sequence of the HNF-6alpha was mapped with chemical shift perturbation methods. Our data also show that a proposed CREB-binding protein histone acetyltransferase protein-recruiting sequence, LSDLL, forms a helix and is involved in the hydrophobic core of the Cut domain. The structure implies that this sequence has to undergo structural changes when it interacts with CREB-binding protein.

The nuclear orphan receptor COUP-TFI is important for differentiation of oligodendrocytes

We report here that a member of the nuclear hormone receptor superfamily, chicken ovalbumin upstream promoter-transcription factor 1 (COUP-TFI), plays a critical role in glial cell development and subsequent central nervous system myelination. We demonstrate that COUP-TF1 is expressed in cells of oligodendrocyte lineage. Furthermore, we demonstrate that COUP-TFI null mutant mice exhibit delayed axon myelination and increased dysmyelination in the central nervous system. Using in vitro differentiation assays, we show that these myelination defects are due to delays in oligodendrocyte differentiation. Finally, in situ hybridization and transfection analysis suggests that COUP-TFI acts as an upstream regulator of SCIP/Oct-6/Tst-1, a transcription factor involved in axon myelination. Taken together, these results suggest that COUP-TFI is an important regulator of oligodendrocyte differentiation.

Cyclic AMP and tumor necrosis factor-alpha regulate CXCR4 gene expression in Schwann cells

Rat peripheral nerve Schwann cells have been shown to express the alpha-chemokine receptor CXCR4 as well as the corresponding ligand stromal cell-derived factor-1 (SDF-1). We have investigated gene regulatory mechanisms acting on the expression of CXCR4 in cultured rat Schwann cells and found that receptor expression at transcript- and protein levels is directly dependent on intracellular cyclic AMP. Such increased levels of CXCR4 expression were found to be efficiently reversed by the action of tumor necrosis factor-alpha (TNFalpha). We also provide evidence that the POU box transcription factor Oct-6/SCIP is involved in the control of CXCR4 transcription. Finally, we could demonstrate that CXCR4 activation by SDF-1alpha increases the number of dying Schwann cells, indicating that this receptor/ligand interaction is modulating cell survival. Our data, therefore, suggest that in the Schwann cell lineage signal transduction cascades controlled by the activation of TNF- and CXCR4 receptors are functionally coupled.

Oct-6 transcription factor

A variety of neurological disorders may have their origin during development of the central nervous system. Defects consistent with abnormal brain development have been reported in schizophrenia. These include faulty neuronal migration,altered spatial neuronal distribution, and the absence of significant gliosis. These abnormalities in the adult are allocated to developmental processes and thus indicate a developmental basis for schizophrenia. Our way toward understanding schizophrenia pathology has been to consider the genes that regulate normal brain development. One such family of genes is the POU family of homeobox transcription factors. This chapter reviews POU domain proteins, focusing on the POU III domain gene, Oct-6, along with its potential relevance to schizophrenia.

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.

The POU proteins Brn-2 and Oct-6 share important functions in Schwann cell development

The genetic hierarchy that controls myelination of peripheral nerves by Schwann cells includes the POU domain Oct-6/Scip/Tst-1and the zinc-finger Krox-20/Egr2 transcription factors. These pivotal transcription factors act to control the onset of myelination during development and tissue regeneration in adults following damage. In this report we demonstrate the involvement of a third transcription factor, the POU domain factor Brn-2. We show that Schwann cells express Brn-2 in a developmental profile similar to that of Oct-6 and that Brn-2 gene activation does not depend on Oct-6. Overexpression of Brn-2 in Oct-6-deficient Schwann cells, under control of the Oct-6 Schwann cell enhancer (SCE), results in partial rescue of the developmental delay phenotype, whereas compound disruption of both Brn-2 and Oct-6 results in a much more severe phenotype. Together these data strongly indicate that Brn-2 function largely overlaps with that of Oct-6 in driving the transition from promyelinating to myelinating Schwann cells.

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.

The embryonic Octamer factor 3/4 displays distinct DNA binding specificity from those of other Octamer factors

The Oct-3/4 is a transcriptional factor expressed rather specifically in inner cell mass and embryonic ectoderm during early embryogenesis in mammals. During the course of characterizing the regulatory element of embryonic transcriptional coactivator UTF1 which is one of the downstream genes of Oct-3/4, we have found that Oct-3/4, but not other Octamer factors, shows unique DNA binding specificity, being able to bind to variant Octamer sequence (5'-ACTAGCAT-3') present in UTF1 regulatory element. Here, we have determined the DNA binding property of Oct-3/4 in a systematic manner using all possible one point mutants of Octamer sequence as well as completely random sequences. These analyses led to the identification of nine distinct nucleotide sequences including the one (5'-ACTAGCAT-3') present in UTF1 regulatory element which serves rather as specific binding site for the Oct-3/4. Moreover, we show that, at least, one of the newly identified sequences, 5'-ATCAGCAT-3', exhibits a transcriptional stimulating activity equivalent to that of the variant Octamer sequence present in the UTF1 regulatory region in embryonic stem cells in a pluripotent-state specific manner.

Oct6, a transcription factor controlling myelination, is a marker for active nerve regeneration in peripheral neuropathies

Three transcription factors, Krox20 (EGR2), Oct6 (SCIP/Tst1) and Sox10, are considered necessary for transition from the nonmyelinating to the myelinating stage of Schwann cell development. We immunohistochemically studied Oct6 expression in peripheral nerve specimens from 25 patients with various diseases including Charcot-Marie-Tooth disease type 1A (CMT1A). Oct6 was present in cytoplasm of Schwann cells associated with normal-appearing myelinated nerve fibers, but not in nuclei. Expression was seen in nuclei of Schwann cells in the early phase of acute axonal degeneration; nuclear expression peaked at the regenerative stage. Schwann cells forming "onion bulbs" expressed Oct6 in chronic inflammatory demyelinating polyneuropathy (CIDP), but showed minimal expression in CMT1A, reflecting their proliferative activity in CIDP. Nerves showing chronic axonal loss had no expression. Oct6, then, may be a marker for dedifferentiation of adult Schwann cells and active nerve regeneration.

Hippocampal heterotopia with molecular and electrophysiological properties of neocortical neurons

Cortical malformations resulting from aberrant brain development can be associated with mental retardation, dyslexia, and intractable forms of epilepsy. Despite emerging interest in the pathology and etiology of cortical malformations, little is known about the phenotype of cells within these lesions. In utero exposure to the DNA methylating agent methylazoxymethanol acetate (MAM) during a critical stage in neurodevelopment results in animals with distinct clusters of displaced neurons in hippocampus, i.e. nodular heterotopia. Here we examined the molecular and electrophysiological properties of cells within hippocampal heterotopia using rats exposed to MAM during gestation. Molecular analysis revealed that heterotopic cells do not express mRNA markers normally found in hippocampal pyramidal cells or dentate granule cells (SCIP, Math-2, Prox-1, neuropilin-2). In contrast, Id-2 mRNA, normally abundant in Layer II-III supragranular neocortical neurons but not in CA1 pyramidal neurons, was prominently expressed in hippocampal heterotopia. Current-clamp analysis of the firing properties of heterotopic neurons revealed a striking similarity with supragranular cortical neurons. In particular, both cells were characterized by small hyperpolarizing 'sag' potentials, high input resistance values, slow spike-train afterhyperpolarizations, and the absence of a depolarizing afterpotential. Normotopic CA1 pyramidal neurons (e.g. pyramidal cells with normal lamination adjacent to a heterotopia) in the MAM brain exhibited molecular and electrophysiological properties that were nearly identical to those of age-matched CA1 pyramidal neurons from control rats. We conclude that neuronal heterotopiae in the hippocampus of MAM-exposed rats are comprised of neurons with a Layer II-III supragranular cortex phenotype. The MAM model, therefore, may serve as a useful tool in examination of the factors influencing aberrant brain development and epilepsy.

Identification of genes that are downregulated in the absence of the POU domain transcription factor pou3f1 (Oct-6, Tst-1, SCIP) in sciatic nerve

Despite the importance of myelinating Schwann cells in health and disease, little is known about the genetic mechanisms underlying their development. The POU domain transcription factor pou3f1 (Tst-1, SCIP, Oct-6) is required for the normal differentiation of myelinating Schwann cells, but its precise role requires identification of the genes that it regulates. Here we report the isolation of six genes whose expression is reduced in the absence of pou3f1. Only one of these genes, the fatty acid transport protein P2, was known previously to be expressed in Schwann cells. The LIM domain proteins cysteine-rich protein-1 (CRP1) and CRP2 are expressed in sciatic nerve and induced by forskolin in cultured Schwann cells, but only CRP2 requires pou3f1 for normal expression. pou3f1 appears to require the claw paw gene product for activation of at least some of its downstream effector genes. Expression of the novel Schwann cell genes after nerve injury suggests that they are myelin related. One of the genes, tramdorin1, encodes a novel amino acid transport protein that is localized to paranodes and incisures. Our results suggest that pou3f1 functions to activate gene expression in the differentiation of myelinating Schwann cells.

A cell type-specific allele of the POU gene Oct-6 reveals Schwann cell autonomous function in nerve development and regeneration

While an important role for the POU domain transcription factor Oct-6 in the developing peripheral nerve has been well established, studies into its exact role in nerve development and regeneration have been hampered by the high mortality rate of newborn Oct-6 mutant animals. In this study we have generated a Schwann cell-specific Oct-6 allele through deletion of the Schwann cell-specific enhancer element (SCE) in the Oct-6 locus. Analysis of mice homozygous for this allele (deltaSCE allele) reveals that rate-limiting levels of Oct-6 in Schwann cells are dependent on the SCE and that this element does not contribute to Oct-6 regulation in other cell types. We demonstrate a Schwann cell autonomous function for Oct-6 during nerve development as well as in regenerating nerve. Additionally, we show that Krox-20, an important regulatory target of Oct-6 in Schwann cells, is activated, with delayed kinetics, through an Oct-6-independent mechanism in these mice.

Expression of the POU-domain transcription factors SCIP/Oct-6 and Brn-2 is associated with Schwann cell but not oligodendrocyte remyelination of the CNS

The class III POU-domain transcription factor SCIP/Oct-6 is expressed by promyelinating Schwann cells and, in tissue culture, by oligodendrocyte progenitors (OPs), but is down-regulated in both cells types as they differentiate. Although the expression of SCIP/Oct-6 has been examined in peripheral nerve remyelination, its expression in CNS remyelination has not been addressed. Using a toxin model of demyelination, in which the demyelinated axons are remyelinated in an age-dependent manner by both oligodendrocytes and Schwann cells, we have compared the expression of SCIP/Oct-6 mRNA with that of an OP marker (PDGF-alphaR), a marker of myelinating oligodendrocytes (PLP), and markers of myelinating Schwann cells (P(0) and Krox-20) by in situ hybridization. We have found that the expression of SCIP/Oct-6 mRNA precedes that of P(0) and Krox-20 mRNA expression, but bears little correlation with the expression profiles of either PDGF-alphaR or PLP mRNA. Moreover, there is a spatial correlation between the expression SCIP/Oct-6 mRNA and that of P(0) but not of PDGF-alphaR. These results indicate that SCIP/Oct-6 expression following CNS demyelination is associated with Schwann cell and not oligodendrocyte remyelination. We have also shown that another POU-domain transcription factor, Brn-2, is expressed during CNS remyelination, but that like SCIP/Oct-6, it too has an expression profile indicating that it is associated with the Schwann cell component of remyelination. In addition, we show that Brn-2 expression in Schwann cells is not restricted to CNS remyelination but is also expressed in a similar manner to SCIP/Oct-6 during Schwann cell myelination of neonatal peripheral nerves and regenerating transected adult nerve and in cultured Schwann cells following induction of elevated cAMP levels.

Identification of Sox-2 regulatory region which is under the control of Oct-3/4-Sox-2 complex

Sox-2 is a transcriptional cofactor expressed in embryonic stem (ES) cells as well as in neuronal cells. It has been demonstrated that Sox-2 plays an important role in supporting gene expression in ES cells, especially by forming a complex with embryonic Octamer factor, Oct-3/4. Here, we have analyzed the regulatory regions of the Sox-2 gene and identified two enhancers which stimulate transcription in ES cells as well as in embryonal carcinoma cells. These regulatory regions, which we termed Sox regulatory regions (SRR) 1 and 2, exert their function specifically when cells are in an undifferentiated state. Interestingly, like the regulatory elements of FGF-4 and UTF1 genes, combinatorial action of Octamer and Sox-2 binding sites support the SRR2 activity. However, biochemical analyses reveal that, due to the unique sequence and/or its organization, the SRR2 bears distinct characteristics from those of FGF-4 and UTF1 regulatory elements. That is, unlike the FGF-4 gene enhancer, the SRR2 precludes the binding of the Oct-1-Sox-2 complex. The difference between the SRR2 and UTF1 regulatory element is in the ability of SRR2 to recruit the Oct-6-Sox-2 complex as well as the Oct-3/4-Sox-2 complex. Co-transfection analyses confirm that both complexes are able to stimulate transcription through the SRR2 element.

Expression of Oct-6, a POU III domain transcription factor, in schizophrenia

OBJECTIVE

Oct-6, a POU-III domain transcription factor, is expressed in embryonic stem cells and Schwann cells and in neuronal subpopulations during early mammalian development, but its relevance to disorders of cerebral development in humans is untested. This study evaluated the expression of Oct-6 in schizophrenia, a disorder that has been linked with neurodevelopmental abnormalities.

METHOD

Immunohistochemistry was used to examine Oct-6 expression in the temporal lobe in postmortem tissue from 10 subjects with schizophrenia and 10 matched comparison subjects. Western blot analysis was used to study Oct-6 expression in the frontal and temporal cortex in tissue from an additional three schizophrenic and three matched comparison subjects and in the frontal lobe only in tissue from an additional 10 schizophrenic and 10 matched comparison subjects.

RESULTS

Extensive Oct-6 immunoreactivity was present in the temporal lobe in all 10 schizophrenic subjects, while very little or no expression was found in the comparison subjects. In schizophrenic subjects, Oct-6 immunoreactivity was found in a subset of cells in the pyramidal cell layer of the hippocampus and in the granule cell layer of the dentate gyrus. Oct-6 staining was predominantly localized in the cytoplasm. Western blot analysis confirmed the presence of Oct-6 in the frontal and temporal cortex in schizophrenic subjects but not in comparison subjects.

CONCLUSIONS

The presence of Oct-6 expression in the schizophrenic subjects but not in the comparison subjects suggests that Oct-6 may provide a marker for the neuropathology associated with schizophrenia. Further, it may provide a clue to the neurodevelopmental basis of the disease and could be a reliable means to examine the developmental brain abnormalities described in this disorder.

Immunohistochemistry study of human vestibular nerve schwannoma differentiation

Differentiation of primary human vestibular nerve schwannomas (VS) caused by mutations of the NF2 gene was evaluated by examining the expression patterns of genes that are specifically expressed in different stages of Schwann cell lineage. In schwannoma cells that are not in contact with an axon, the expression levels of the major myelin sheath proteins, such as protein zero glycoprotein (P0), myelin basic protein (MBP), and peripheral myelin protein 22 (PMP22), were greatly reduced. However, high expression levels of nerve growth factor receptor (NGFR), neural cell adhesion molecule (N-CAM), and cell adhesion molecule L1 (L1) were observed. In addition, expression of transcription factors Krox20, Krox24, and SCIP/Oct6 was also detected in the tumor cells. These results suggest that loss of the NF2 gene was responsible for the transformation of the Schwann cells into a neoplastic stage that has a similar genetic profile to the pro-myelinating stage. Finally, the primary human vestibular schwannoma cells failed to be regulated and redifferentiated by a regenerating axon, when the human tumors were transplanted into sciatic nerve of nude rat. These results suggest that the NF2 gene might be involved in the differentiation of Schwann cells.

TGFbeta1 modulates the phenotype of Schwann cells at the transcriptional level

We have examined the effects of transforming growth factor beta1 (TGFbeta1) on gene expression in cultured rat Schwann cells (SCs). TGFbeta1 decreased the steady-state mRNA levels of several genes that are expressed by myelinating SCs but had varied effects on the mRNA levels of NCAM, L1, GAP-43, and p75-genes that are expressed by denervated and nonmyelinating SCs. TGFbeta1 antagonized the effects of forskolin on the mRNA levels of the transcription factors Oct-6/tst-1/SCIP and Krox20. Transcriptional run-off analysis demonstrated that the effects of TGFbeta1 on gene expression occur at least in part at the level of transcription. Thus, TGFbeta1 suppresses the expression of genes that characterize the different phenotypes of SCs, and these changes occur at least in part at a transcriptional level.

Early activation of transcription factor expression in Schwann cells by progesterone

Progesterone (PROG) promotes the myelination of sciatic nerves during regeneration after cryolesion. But, little is known about the molecular mechanisms by which the hormone exerts its effects. This could be initiated by the regulation of transcription factor expression in Schwann cells, which produce the myelin sheaths in the peripheral nervous system. We investigated by RT-PCR whether PROG activated expression of transcription factors: Egr-1 (Krox-24) Egr-2 (Krox-20), Egr-3, c-jun, jun B, jun D, c-Fos, Fos B, Fra-1, Fra-2, CREB, ATF 4, SCIP and Sox-10 in cultured Schwann cells. PROG triggered a quick (visible as soon as 15 min), strong (6 to 18-fold) and transient (1-2 h) stimulation of Egr-1, Egr-2, Egr-3 and Fos B genes expression. Expression of other genes remained unaffected by PROG treatment. The same expression pattern was obtained in the MSC 80 line (mouse Schwann cells), but not in the NIH-3T3 and CHO lines. Estradiol and testosterone induced different patterns of transcription factor gene activation in Schwann cells. Serum stimulated all genes activated by PROG in addition c-fos, fra-1 and fra-2. The PROG effects were blocked by Actinomycin D and by RU 486. This suggests that the activation of these genes occurs at the transcriptional level via the interaction of the hormone with its cognate receptor. Thus, PROG can regulate Schwann cell functions and differentiation by transiently activating specific transcription factors.

SCIP/Oct-6, Krox-20, and desert hedgehog mRNA expression during CNS remyelination by transplanted olfactory ensheathing cells

Olfactory ensheathing cells (OECs), although having a separate developmental origin to Schwann cells, are able to generate myelin sheaths following transplantation into areas of CNS demyelination that are remarkably similar to those made by Schwann cells. The transcriptional control of Schwann cell myelination has been well documented, in particular the role of SCIP/Oct-6 and Krox-20. It is not known, however, whether these transcription factors are also expressed when OECs assume a myelinating phenotype. In this study, we addressed this question by using a transplantation approach to generate myelinating OECs and then examined the expression of SCIP/Oct-6 and Krox-20 mRNA by in situ hybridization using oligonucleotide probes. We also examined the expression of desert hedgehog (Dhh), a Schwann cell-derived signaling molecule that is responsible for regulating the development of the connective tissue elements in peripheral nerve, which bear similarities to the morphologies adopted by nonmyelinating transplanted cells. Our results indicate that both Krox-20 and Dhh mRNA are strongly expressed by transplanted OECs, with SCIP mRNA present at much lower levels. The expression of Krox-20 relative to the expression of P0 mRNA by the transplanted OECs is consistent with its playing a similar role in OEC myelination to that in Schwann cell myelination, while the expression of Dhh suggests a possible mechanism for the diverse morphologies that cells adopt following OEC transplantation into the damaged CNS. Taken together, our results provide further evidence for the close similarity of OECs and Schwann cells and suggest that, despite their separate origins, the manner in which they generate a peripheral-type myelin sheath involves similar regulatory mechanisms.

SpL201: a conditionally immortalized Schwann cell precursor line that generates myelin

Dramatic progress has been made over recent years toward the elucidation of the mechanisms regulating lineage determination and cell survival in the developing peripheral nervous system. However, our understanding of Schwann cell development is limited. This is partly due to the difficulties in culturing primary Schwann cell precursor cells, the earliest developmental stage of the Schwann cell lineage defined to date. Both the inability to maintain cultured Schwann cell precursor cells in an undifferentiated state and the technical difficulties involved in their isolation have hampered progress. We have conditionally immortalized rat Schwann cell precursor cells using a retrovirally encoded EGFR/neu fusion protein to circumvent these problems and to generate a source of homogeneous cells. The resulting SpL201 cell line expresses p75 and nestin, two proteins expressed by neural crest-derived cells, as well as peripheral myelin protein 22, protein zero, and Oct-6 as markers of the Schwann cell lineage. When cultured in EGF-containing medium, the SpL201 cells proliferate and maintain an undifferentiated, Schwann cell precursor cell-like state. The cell line is dependent on EGF for survival but can differentiate into early Schwann cell-like cells in response to exogenous factors. Like primary rat Schwann cells, SpL201 cells upregulate Oct-6 and myelin gene expression in response to forskolin treatment. Furthermore, the SpL201 cell line can form myelin in the presence of axons in vitro and is capable of extensively remyelinating a CNS white matter lesion in vivo. Thus, this cell line provides a valuable and unique tool to study the Schwann cell lineage, including differentiation from the Schwann cell precursor cell stage through to myelination.

The POU domain factor Skin-1a represses the keratin 14 promoter independent of DNA binding. A possible role for interactions between Skn-1a and CREB-binding protein/p300

The genes encoding keratin 5 and 14 are highly expressed in the basal cell layer keratinocytes of the epidermis, but both genes are silenced when keratinocytes move into the suprabasal compartment. The POU homeodomain factors Skn-1a and Tst-1, which are expressed in epidermis, may play a role in the suprabasal repression of the keratin 5 and 14 genes because keratin 14 mRNA expression persists in suprabasal cells in Skn-1/Tst-1 double knockout mice. In transfection experiments, both Skn-1a and Tst-1 repress the keratin 14 promoter, with the POU domain being sufficient for repression. The region of the keratin 14 gene sufficient and required for repression by Skn-1a is a 100-base pair sequence lacking POU-binding sites adjacent to the transcription start site. DNA-binding defective mutants of Skn-1a and Tst-1 are as effective at mediating repression as the wild type proteins, suggesting that protein-protein interactions rather than direct DNA binding are important for repression. We also show that CREB-binding protein (CBP)/p300 co-activators are strong activators of keratin 14 gene expression, acting through sequences close to the keratin 14 promoter. Further, CBP interacts directly with the POU domain of Skn-1a, and increasing concentrations of CBP can overcome Skn-1a-mediated repression, suggesting that POU domain factors may repress keratin 14 gene expression by interfering with the activity of co-activators such as CBP/p300.

The POU gene Brn-5 is induced by neuregulin and is restricted to myelinating Schwann cells

The POU family of transcription factors plays a vital role in controlling cell-fate determination and the timing of cellular events in a number of tissues, including the nervous system. One such POU protein, SCIP, is expressed by Schwann cells in a tightly delimited developmental window termed promyelination. In the PNS, promyelination is functionally defined as the period following Schwann cell exit from the cell-cycle, but prior to the onset of myelination. Previous transgenic and gene ablation studies have shown that SCIP is a myelin-competence factor in the Schwann cell, where it is required for entry into, and the subsequent maintenance of promyelination. To further understand the molecular biology of the promyelination-to-myelination transition in the Schwann cell, we have undertaken a series of DDRTPCR studies to identify genes that are expressed during this phenotypic flux. Through these studies we have identified another POU gene, Brn-5, the expression of which has not previously been appreciated in the Schwann cell. Here we show that the developmental expression patterns of Brn-5 and SCIP are inverse, with Brn-5 stably expressed in the adult myelinating Schwann cell, but virtually absent during promyelination. Further, we show that the induction of the two genes is independent, with SCIP induction requiring activation of adenyl cyclase, whereas Brn-5 induction requires only GGF2. In addition, the induction of Brn-5 is exquisitely sensitive to neuregulin concentration, with higher levels inhibiting its expression. Following nerve injury, when GGF2 levels are elevated in the distal nerve, Brn-5 expression disappears, and SCIP is reexpressed.

Synergism with the coactivator OBF-1 (OCA-B, BOB-1) is mediated by a specific POU dimer configuration

POU domain proteins contain a bipartite DNA binding domain divided by a flexible linker that enables them to adopt various monomer configurations on DNA. The versatility of POU protein operation is additionally conferred at the dimerization level. The POU dimer formed on the PORE (ATTTGAAATGCAAAT) can recruit the transcriptional coactivator OBF-1, whereas POU dimers formed on the consensus MORE (ATGCATATGCAT) or on MOREs from immunoglobulin heavy chain promoters (AT[G/A][C/A]ATATGCAA) fail to interact. An interaction with OBF-1 is precluded since the same Oct-1 residues that form the MORE dimerization interface are also used for OBF-1/Oct-1 interactions on the PORE. Our findings provide a paradigm of how specific POU dimer assemblies can differentially recruit a coregulatory activity with distinct transcriptional readouts.

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.

A distal Schwann cell-specific enhancer mediates axonal regulation of the Oct-6 transcription factor during peripheral nerve development and regeneration

The POU domain transcription factor Oct-6 is a major regulator of Schwann cell differentiation and myelination. During nerve development and regeneration, expression of Oct-6 is under the control of axonal signals. Identification of the cis-acting elements necessary for Oct-6 gene regulation is an important step in deciphering the complex signalling between Schwann cells and axons governing myelination. Here we show that a fragment distal to the Oct-6 gene, containing two DNase I-hypersensitive sites, acts as the Oct-6 Schwann cell-specific enhancer (SCE). The SCE is sufficient to drive spatially and temporally correct expression, during both normal peripheral nerve development and regeneration. We further demonstrate that a tagged version of Oct-6, driven by the SCE, rescues the peripheral nerve phenotype of Oct-6-deficient mice. Thus, our isolation and characterization of the Oct-6 SCE provides the first description of a cis-acting genetic element that responds to converging signalling pathways to drive myelination in the peripheral nervous system.

Complex interactions between epidermal POU domain and activator protein 1 transcription factors regulate the expression of the profilaggrin gene in normal human epidermal keratinocytes

The human profilaggrin gene is expressed in the granular layer during the late stages of the epidermal differentiation. The proximal promoter region of the gene confers high levels of keratinocyte-specific transcription via interactions with c-Jun/c-Fos heterodimers. Here we provide evidence for another level of complexity in the regulation of the profilaggrin promoter activity. The POU domain proteins Oct1, Skn1a/i, and Oct6, which are abundantly expressed in the epidermal cells, act to both stimulate and repress transcription in a general and a cell type-specific mode. While binding to specific recognition elements within the promoter region, they exert their effects by either stimulating or antagonizing the c-Jun-dependent activity of the promoter. The response of the promoter to forced expression of the POU domain proteins reflects the effect of these transcription factors on the endogenous profilaggrin mRNA synthesis and suggests that the latter requires a fine balance in the amounts and the activities of the individual activator protein 1 and POU domain proteins.

Transcriptional control of the neuronal nicotinic acetylcholine receptor gene cluster by the beta43' enhancer, Sp1, SCIP and ETS transcription factors

Receptors assembled from the products of a neuronal beta4alpha3alpha5 NAChR gene cluster depend on these genes being coordinately regulated in particular populations of neurons. Little is known, however, about the transcriptional mechanisms that are likely to underlie their co-expression in correct neuronal cell types. We have identified several regulatory elements and transcription factors that influence transcription of the alpha3 and beta4 genes. The promoters of these genes appear to contain a common cis element that binds Sp1 transcription factors. They can be activated by the POU-domain factor SCIP and activation does not require SCIP binding sites. Between these two promoters is a cell type specific enhancer called beta43'. This enhancer has little activity in non-neuronal cells and is preferentially active in particular populations of central neurons. The clustered genes are potential targets of ETS factors as the ETS domain factor, Pet-1 can activate beta43'-dependent transcription. The neuron-selective properties of beta43' and its location suggest that it is a component of the cis regulatory information required to control expression of the beta4 and alpha3 genes in specific populations of neurons.

The Ets domain transcription factor Erm distinguishes rat satellite glia from Schwann cells and is regulated in satellite cells by neuregulin signaling

Distinct glial cell types of the vertebrate peripheral nervous system (PNS) are derived from the neural crest. Here we show that the expression of the Ets domain transcription factor Erm distinguishes satellite glia from Schwann cells beginning early in rat PNS development. In developing dorsal root ganglia (DRG), Erm is present both in presumptive satellite glia and in neurons. In contrast, Erm is not detectable at any developmental stage in Schwann cells in peripheral nerves. In addition, Erm is downregulated in DRG-derived glia adopting Schwann cell traits in culture. Thus, Erm is the first described transcription factor expressed in satellite glia but not in Schwann cells. In culture, the Neuregulin1 (NRG1) isoform GGF2 maintains Erm expression in presumptive satellite cells and reinduces Erm expression in DRG-derived glia but not in Schwann cells from sciatic nerve. These data demonstrate that there are intrinsic differences between these glial subtypes in their response to NRG1 signaling. In neural crest cultures, Erm-positive progenitor cells give rise to two distinct glial subtypes: Erm-positive, Oct-6-negative satellite glia in response to GGF2, and Erm-negative, Oct-6-positive Schwann cells in the presence of serum and the adenylate cyclase activator forskolin. Thus, Erm-positive neural crest-derived progenitor cells and presumptive satellite glia are able to acquire Schwann cell features. Given the in vivo expression of Erm in peripheral ganglia, we suggest that ganglionic Erm-positive cells may be precursors of Schwann cells.

Transcriptional regulation of the POU gene Oct-6 in Schwann cells

Genetic evidence suggests that the POU transcription factor Oct-6 plays a pivotal role as an intracellular regulator of Schwann cell differentiation. In the absence of Oct-6 function Schwann cells are generated in appropriate numbers and these cells differentiate normally up to the promyelin stage at which they transiently arrest. During peripheral nerve development Oct-6 expression is initiated in Schwann cell precursors and is strongly upregulated in promyelin cells. Oct-6 expression is subsequently extinguished in terminally differentiating Schwann cells. Thus, identification and characterisation of the DNA elements involved in this stage specific regulation may lead us to the signaling cascade and the axon-derived signals that drive Schwann cell differentiation and initiate myelination. Here we present experiments that aim at identifying such regulatory sequences.

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.

Sublytic terminal complement complexes decrease P0 Gene expression in Schwann cells

Complement cascade activation on peripheral nerve myelin can cause myelin destruction. Although terminal complement complexes (TCCs) are transiently detected on Schwann cells (SchCs) during inflammatory neuropathy, SchCs appear resistant to complement-mediated lysis, and little is known about the functional consequences of sublytic TCC deposition on SchCs. We studied the effects of sublytic complement in modulating myelin gene expression at the posttranscriptional and transcriptional levels. Cultured SchCs, stimulated to express protein zero (P0), were treated with sensitizing antibody (Ab) and normal human serum (NHS) complement. P0 mRNA content decreased by 71% during 12 h. In the presence of actinomycin D, P0 mRNA levels declined 50% following incubation with Ab plus 10% NHS over 6 h, compared with control levels, suggesting enhanced P0 mRNA degradation. The decreases, in part, reflected TCC formation because C7 reconstitution of Ab plus C7-depleted human serum (C7dHS) or TCCs assembled from purified components down-regulated P0 mRNA 53 and 55% over that of Ab plus C7dHS or heat-activated components, respectively. Expression of a P0 promoter/luciferase reporter construct transiently transfected into SchCs was reduced 70% by sublytic TCCs at 6 h, demonstrating that P0 gene transcription was also inhibited. c-jun mRNA was up-regulated within 30 min by sublytic TCCs, before the reduction in P0 mRNA expression. Our data suggest that sublytic complement activation on SchCs may contribute to peripheral nerve demyelination by decreasing expression of genes important in myelin formation and compaction.

Ebf1 controls early cell differentiation in the embryonic striatum

Ebf1/Olf-1 belongs to a small multigene family encoding closely related helix-loop-helix transcription factors, which have been proposed to play a role in neuronal differentiation. Here we show that Ebf1 controls cell differentiation in the murine embryonic striatum, where it is the only gene of the family to be expressed. Ebf1 targeted disruption affects postmitotic cells that leave the subventricular zone (SVZ) en route to the mantle: they appear to be unable to downregulate genes normally restricted to the SVZ or to activate some mantle-specific genes. These downstream genes encode a variety of regulatory proteins including transcription factors and proteins involved in retinoid signalling as well as adhesion/guidance molecules. These early defects in the SVZ/mantle transition are followed by an increase in cell death, a dramatic reduction in size of the postnatal striatum and defects in navigation and fasciculation of thalamocortical fibres travelling through the striatum. Our data therefore show that Ebf1 plays an essential role in the acquisition of mantle cell molecular identity in the developing striatum and provide information on the genetic hierarchies that govern neuronal differentiation in the ventral telencephalon.

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.

Regulation of myelin-specific gene expression. Relevance to CMT1

Schwann cells, the myelinating cells of the peripheral nervous system, are derived from the neural crest. Once neural crest cells are committed to the Schwann cell fate, they can take on one of two phenotypes to become myelinating or nonmyelinating Schwann cells, a decision that is determined by interactions with axons. The critical step in the differentiation of myelinating Schwann cells is the establishment of a one-to-one relationship with axons, the so-called "promyelinating" stage of Schwann cell development. The transition from the promyelinating to the myelinating stage of development is then accompanied by a number of significant changes in the pattern of gene expression, including the activation of a set of genes encoding myelin structural proteins and lipid biosynthetic enzymes, and the inactivation of a set of genes expressed only in immature or nonmyelinating Schwann cells. These changes are regulated mainly at the transcriptional level and also require continuous interaction between Schwann cells and their axons. Two transcription factors, Krox 20 (EGR2) and Oct 6 (SCIP/Tst1), are necessary for the transition from the promyelinating to the myelinating stage of Schwann cell development. Krox 20, expressed in myelinating but not promyelinating Schwann cells, is absolutely required for this transition, and myelination cannot occur in its absence. Oct 6, expressed mainly in promyelinating Schwann cells and then down-regulated before myelination, is necessary for the correct timing of this transition, since myelination is delayed in its absence. Neither Krox 20 nor Oct 6, however, is required for the initial activation of myelin gene expression. Although the mechanisms of Krox 20 and Oct 6 action during myelination are not known, mutation in Krox 20 has been shown to cause CMT1, further implicating this protein in the pathogenesis of this disease. Identifying the molecular mechanisms of Krox 20 and Oct 6 action will thus be important both for understanding myelination and for designing future treatments for CMT1. Point mutlations in the genes encoding the myelin proteins PMP22 and P0 cause CMT1A without a gene duplication and CMT1B, respectively. Although the clinical and pathological phenotypes of CMT1A and CMT1B are similar, their molecular pathogenesis is quite different. Point mutations in PMP22 alter the trafficking of the protein, so that it accumulates in the endoplasmic reticulum (ER) and intermediate compartment (IC). Mutant PMP22 also sequesters its normal counterpart in the ER, further reducing the amount of PMP22 available for myelin synthesis at the membrane, and accounting, at least in part, for its severe effect on myelination. Mutant PMP22 probably also activates an ER-to-nucleus signal transduction pathway associated with misfolded proteins, which may account for the decrease of myelin gene expression in Schwann cells in Trembler mutant mice. In contrast, absence of expression of the homotypic adhesion molecule, P0, in mice in which the gene has been inactivated, produces a unique pattern of Schwann cell gene expression, demonstrating that P0 plays a regulatory as well as a structural role in myelination. Whether this role is direct, through a P0-mediated adhesion pathway, or indirect, through adhesion pathways mediated by cadherins or integrins, however, remains to be determined. The molecular mechanisms underlying dysmyelination in CMT1 are thus complex, with pleitropic effects on Schwann cell physiology that are determined both by the type of mutation and the protein mutated. Identifying these molecular mechanisms, however, are important both for understanding myelination and for designing future treatments for CMT1. Although demyelination is the hallmark of CMT1, the clinical signs and symptoms of this disease are probably produced by axonal degeneration, not demyelination. (ABSTRACT TRUNCATED)

Patterning events and specification signals in the developing hippocampus

The mouse hippocampus is an attractive model system in which to study patterning of a cortical structure. Ongoing studies indicate that hippocampal areas or fields are specified many days before birth -- possibly involving signals from within the cortical mantle. Although the hippocampal CA fields are distinguished by cytoarchitecture only after birth, molecular differences between fields appear by late gestation. Moreover, these embryonic fields are already specified to develop additional features that characterize the mature fields. The basic division of the hippocampus into fields may be specified still earlier. Thus, if medial cortical neuroepithelium is isolated in vitro early in hippocampal neurogenesis, it can autonomously generate features of a patterned hippocampus. In vivo, the spatial progression of initial field differentiation suggests that signals regulating growth and patterning could arise from sources close to the hippocampal poles. Observations of mouse mutants indicate that the cortical hem, an embryonic structure close to one pole of the hippocampus, is a source of such regulatory signals.

Increased intracellular calcium alters myelin gene expression in the N20.1 oligodendroglial cell line

Regulation of intracellular Ca(2+) (Ca(i)) plays a central role in cell survival, proliferation, and differentiation. We previously reported that immature oligodendroglia (OLs) are less susceptible than mature OLs to cell death following increases in Ca(i) (Benjamins and Nedelkoska [1995] Neurochem. Res. 21:471-479). The N20.1 murine OL cell line provides a model of an intermediate stage of OL maturation in which to study responses to Ca(i) increases with regard to viability, as well as the expression of mRNAs for myelin basic protein (MBP), proteolipid protein (PLP), DM-20, SCIP, and the immediate early genes ZIF268, c-fos, and c-jun. Cells were treated with the calcium ionophore A23187 or thapsigargin for 1, 3, and 18 hr. A23187 at 1.0 microM had no significant effect on cell detachment or death, whereas thapsigargin at 1.0 microM slightly increased both. With both agents, SCIP, MBP, and PLP mRNA levels were unaffected by 3 hr, but markedly reduced after 18 hours. DM-20 mRNA levels remained unchanged at both time points. With both agents, ZIF268, c-fos, and c-jun mRNA levels were unaffected after 1 hr; c-jun mRNA levels showed a significant increase after 3 hr of thapsigargin treatment. Thus, in N20.1 cells, increased calcium affects the IEG c-jun first, SCIP is coordinately decreased with MBP and PLP mRNAs at a later time point, and DM-20 message is under different regulation than PLP. J. Neurosci. Res. 57:633-642.

The J domain of papovaviral large tumor antigen is required for synergistic interaction with the POU-domain protein Tst-1/Oct6/SCIP

Large T antigens from polyomaviruses are multifunctional proteins with roles in transcriptional regulation, viral DNA replication, and cellular transformation. They have been shown to enhance the activity of various cellular transcription factors. In the case of the POU protein Tst-1/Oct6/SCIP, this enhancement involves a direct physical interaction between the POU domain of the transcription factor and the amino-terminal region of large T antigen. Here we have analyzed the structural requirements for synergistic interaction between the two proteins in greater detail. Tst-1/Oct6/SCIP and the related POU protein Brn-1 were both capable of direct physical interaction with large T antigen. Nevertheless, only Tst-1/Oct6/SCIP functioned synergistically with large T antigen. This differential behavior was due to differences in the amino-terminal regions of the proteins, as evident from chimeras between Tst-1/Oct6/SCIP and Brn-1. Synergy was specifically observed for constructs containing the amino-terminal region of Tst-1/Oct6/SCIP. Large T antigen, on the other hand, functioned synergistically with Tst-1/Oct6/SCIP only when the integrity of its J-domain-containing amino terminus was maintained. Mutations that disrupted the J domain concomitantly abolished the ability to enhance the function of Tst-1/Oct6/SCIP. The J domain of T antigen was also responsible for the physical interaction with Tst-1/Oct6/SCIP and could be replaced in this property by other J domains. Intriguingly, a heterologous J domain from a human DnaJ protein partially substituted for the amino terminus of T antigen even with regard to the synergistic enhancement of Tst-1/Oct6/SCIP function. Given the general role of J domains, we propose chaperone activity as the underlying mechanism for synergy between Tst-1/Oct6/SCIP and large T antigens.

Krox-20 controls SCIP expression, cell cycle exit and susceptibility to apoptosis in developing myelinating Schwann cells

The transcription factors Krox-20 and SCIP each play important roles in the differentiation of Schwann cells. However, the genes encoding these two proteins exhibit distinct time courses of expression and yield distinct cellular phenotypes upon mutation. SCIP is expressed prior to the initial appearance of Krox-20, and is transient in both the myelinating and non-myelinating Schwann cell lineages; while in contrast, Krox-20 appears approximately 24 hours after SCIP and then only within the myelinating lineage, where its expression is stably maintained into adulthood. Similarly, differentiation of SCIP−/− Schwann cells appears to transiently stall at the promyelinating stage that precedes myelination, whereas Krox-20(−/−) cells are, by morphological criteria, arrested at this stage. These observations led us to examine SCIP regulation and Schwann cell phenotype in Krox-20 mouse mutants. We find that in Krox-20(−/−) Schwann cells, SCIP expression is converted from transient to sustained. We further observe that both Schwann cell proliferation and apoptosis, which are normal features of SCIP+ cells, are also markedly increased late in postnatal development in Krox-20 mutants relative to wild type, and that the levels of cell division and apoptosis are balanced to yield a stable number of Schwann cells within peripheral nerves. These data demonstrate that the loss of Krox-20 in myelinating Schwann cells arrests differentiation at the promyelinating stage, as assessed by SCIP expression, mitotic activity and susceptibility to apoptosis.

Promyelinating Schwann cells express Tst-1/SCIP/Oct-6

Tst-1/SCIP/Oct-6, a POU domain transcription factor, is transiently expressed by developing Schwann cells and is required for their normal development into a myelinating phenotype. In tst-1/scip/oct-6-null sciatic nerves, Schwann cells are transiently arrested at the "promyelinating" stage, when they have a one-to-one relationship with an axon but before they have elaborated a myelin sheath. To determine when Schwann cells express Tst-1/SCIP/Oct-6, we examined beta-galactosidase (beta-gal) expression in heterozygous tst-1/scip/oct-6 mice, in which one copy of the tst-1/scip/oct-6 gene has been replaced with the LacZ gene. beta-Gal expression from the LacZ gene seems to parallel Tst-1/SCIP/Oct-6 expression from the endogenous tst-1/scip/oct-6 gene in developing and regenerating sciatic nerves. Furthermore, electron microscopic examination of 5bromo-4-chloro-3-indolyl-beta-D-galactopyranoside- (X-gal) and halogenated indolyl-beta-D-galactoside- (Bluo-gal) stained nerves showed that promyelinating Schwann cells express the highest levels of beta-gal, both in developing and in regenerating nerves. Thus, the expression of beta-gal, a surrogate marker of Tst-1/SCIP/Oct-6, peaks at the same stage of Schwann cell development at which development is arrested in tst-1/scip/oct-6-null mice, indicating that Tst-1/SCIP/Oct-6 has a critical role in promyelinating Schwann cells.

Comparison of sequence and function of the Oct-6 genes in zebrafish, chicken and mouse

To examine the role of the Oct-6 gene in Schwann cell differentiation we have cloned and characterized the chicken and zebrafish homologues of the mouse Oct-6 gene. While highly homologous in the Pit1-Oct1/2-Unc86 (POU) domain, sequence similarities are limited outside this domain. Both genes are intronless and both proteins lack the amino acid repeats that are a characteristic feature of the mammalian Oct-6 proteins. However as in mammals, the aminoterminal parts of the chicken and zebrafish Oct-6 proteins are essential for transactivation of octamer containing promoters. By immunohistochemistry we have found that the chicken Oct-6 protein is expressed in late embryonic ensheathing Schwann cells of the sciatic nerve and is rapidly downregulated when myelination proceeds. This expression profile in glial cells is identical to that in the mouse and rat. Furthermore the zebrafish Oct-6 homolog is expressed in the posterior lateral nerve at a time when it contains actively myelinating Schwann cells. Thus despite extensive primary sequence divergence among the vertebrate Oct-6 proteins, the expression of the chicken and zebrafish Oct-6 proteins is consistent with the notion that Oct-6 functions as a 'competence factor' in promyelin cells to execute the myelination program.

Role of Oct-6 in Schwann cell differentiation

Research into the POU transcription factor Oct-6 has been the focus of much current attention, in particular its role in Schwann cell development and differentiation. Based on published data and data presented here, we propose a model for Oct-6 function at two distinct stages of Schwann cell maturation. First, Oct-6 function is required in promyelin cells for their timely differentiation into myelinating cells. Second, Oct-6 functions during myelination and is required for the proper downregulation of its own gene. While the first function of Oct-6 is firmly established, the second function is still highly hypothetical. Experiments to establish a distinct role for Oct-6 in late Schwann cell differentiation are discussed.

The GnRH promoter: target of transcription factors, hormones, and signaling pathways

Gonadotropin-releasing hormone (GnRH) is essential for normal reproductive maturation and function. We present a review of the known mechanisms of hypothalamic GnRH transcriptional control through the conserved GnRH promoter. Understanding this promoter region will allow us to comprehend better the complexities of the hypothalamic pituitary-gonadal axis.

Accelerated nerve regeneration mediated by Schwann cells expressing a mutant form of the POU protein SCIP

After injury, the peripheral nervous system (PNS) is capable of full regeneration and recovery of function. Many molecular events that are the hallmarks of the regenerating PNS are recapitulations of developmental processes. The expression of one such molecule, the POU transcription factor suppressed cAMP-inducible POU protein (SCIP), is required for the establishment of normal nerves and is reexpressed during regeneration. Here we describe markedly accelerated regeneration and hypertrophy of both myelin and axons in transgenic mice that express an amino-terminal deletion of the SCIP molecule. This mutant SCIP molecule retains the POU-specific and POU homeodomain moieties, which allow for both DNA binding and some protein-protein interaction. We demonstrate that the transgene indirectly effects dramatic axonal changes. This is the first demonstration of a genetically controlled acceleration of neural regeneration.

Rex-1, a gene encoding a transcription factor expressed in the early embryo, is regulated via Oct-3/4 and Oct-6 binding to an octamer site and a novel protein, Rox-1, binding to an adjacent site

The Rex-1 (Zfp-42) gene, which encodes an acidic zinc finger protein, is expressed at high levels in embryonic stem (ES) and F9 teratocarcinoma cells. Prior analysis identified an octamer motif in the Rex-1 promoter which is required for promoter activity in undifferentiated F9 cells and is involved in retinoic acid (RA)-associated reduction in expression. We show here that the Oct-3/4 transcription factor, but not Oct-1, can either activate or repress the Rex-1 promoter, depending on the cellular environment. Rex-1 repression is enhanced by E1A. The protein domain required for Oct-3/4 activation was mapped to amino acids 1 to 35, whereas the domain required for Oct-3/4 repression was mapped to amino acids 61 to 126, suggesting that the molecular mechanisms underlying transcriptional activation and repression differ. Like Oct-3/4, Oct-6 can also lower the expression of the Rex-1 promoter via the octamer site, and the amino-terminal portion of Oct-6 mediates this repression. In addition to the octamer motif, a novel positive regulatory element, located immediately 5' of the octamer motif, was identified in the Rex-1 promoter. Mutations in this element greatly reduce Rex-1 promoter activity in F9 cells. High levels of a binding protein(s), designated Rox-1, recognize this novel DNA element in F9 cells, and this binding activity is reduced following RA treatment. Taken together, these results indicate that the Rex-1 promoter is regulated by specific octamer family members in early embryonic cells and that a novel element also contributes to Rex-1 expression.