The B-cell and neuronal forms of the octamer-binding protein Oct-2 differ in DNA-binding specificity and functional activity

Association between perinatal methylation of the neuronal differentiation regulator HES1 and later childhood neurocognitive function and behaviour

Background Early life environments induce long-term changes in neurocognitive development and behaviour. In animal models, early environmental cues affect neuropsychological phenotypes via epigenetic processes but, as yet, there is little direct evidence for such mechanisms in humans.

Method We examined the relation between DNA methylation at birth and child neuropsychological outcomes in two culturally diverse populations using a genome-wide methylation analysis and validation by pyrosequencing.

Results Within the UK Southampton Women’s Survey (SWS) we first identified 41 differentially methylated regions of interest (DMROI) at birth associated with child’s full-scale IQ at age 4 years. Associations between HES1 DMROI methylation and later cognitive function were confirmed by pyrosequencing in 175 SWS children. Consistent with these findings, higher HES1 methylation was associated with higher executive memory function in a second independent group of 200 SWS 7-year-olds. Finally, we examined a pathway for this relationship within a Singaporean cohort (n = 108). Here, HES1 DMROI methylation predicted differences in early infant behaviour, known to be associated with academic success. In vitro, methylation of HES1 inhibited ETS transcription factor binding, suggesting a functional role of this site.

Conclusions Thus, our findings suggest that perinatal epigenetic processes mark later neurocognitive function and behaviour, providing support for a role of epigenetic processes in mediating the long-term consequences of early life environment on cognitive development.

Oct2 and Obf1 as Facilitators of B:T Cell Collaboration during a Humoral Immune Response

The Oct2 protein, encoded by the Pou2f2 gene, was originally predicted to act as a DNA binding transcriptional activator of immunoglobulin (Ig) in B lineage cells. This prediction flowed from the earlier observation that an 8-bp sequence, the “octamer motif,” was a highly conserved component of most Ig gene promoters and enhancers, and evidence from over-expression and reporter assays confirmed Oct2-mediated, octamer-dependent gene expression. Complexity was added to the story when Oct1, an independently encoded protein, ubiquitously expressed from the Pou2f1 gene, was characterized and found to bind to the octamer motif with almost identical specificity, and later, when the co-activator Obf1 (OCA-B, Bob.1), encoded by the Pou2af1 gene, was cloned. Obf1 joins Oct2 (and Oct1) on the DNA of a subset of octamer motifs to enhance their transactivation strength. While these proteins variously carried the mantle of determinants of Ig gene expression in B cells for many years, such a role has not been borne out for them by characterization of mice lacking functional copies of the genes, either as single or as compound mutants. Instead, we and others have shown that Oct2 and Obf1 are required for B cells to mature fully in vivo, for B cells to respond to the T cell cytokines IL5 and IL4, and for B cells to produce IL6 normally during a T cell dependent immune response. We show here that Oct2 affects Syk gene expression, thus influencing B cell receptor signaling, and that Oct2 loss blocks Slamf1 expression in vivo as a result of incomplete B cell maturation. Upon IL4 signaling, Stat6 up-regulates Obf1, indirectly via Xbp1, to enable plasma cell differentiation. Thus, Oct2 and Obf1 enable B cells to respond normally to antigen receptor signals, to express surface receptors that mediate physical interaction with T cells, or to produce and respond to cytokines that are critical drivers of B cell and T cell differentiation during a humoral immune response.

Oct-2 transcription factor binding activity and expression up-regulation in rat cerebral ischaemia is associated with a diminution of neuronal damage in vitro

Brain plasticity provides a mechanism to compensate for lesions produced as a result of stroke. The present study aims to identify new transcription factors (TFs) following focal cerebral ischaemia in rat as potential therapeutic targets. A transient focal cerebral ischaemia model was used for TF-binding activity and TF-TF interaction profile analysis. A permanent focal cerebral ischaemia model was used for the transcript gene analysis and for the protein study. The identification of TF variants, mRNA analysis, and protein study was performed using conventional polymerase chain reaction (PCR), qPCR, and Western blot and immunofluorescence, respectively. Rat cortical neurons were transfected with small interfering RNA against the TF in order to study its role. The TF-binding analysis revealed a differential binding activity of the octamer family in ischaemic brain in comparison with the control brain samples both in acute and late phases. In this study, we focused on Oct-2 TF. Five of the six putative Oct-2 transcript variants are expressed in both control and ischaemic rat brain, showing a significant increase in the late phase of ischaemia. Oct-2 protein showed neuronal localisation both in control and ischaemic rat brain cortical slices. Functional studies revealed that Oct-2 interacts with TFs involved in important brain processes (neuronal and vascular development) and basic cellular functions and that Oct-2 knockdown promotes neuronal injury. The present study shows that Oct-2 expression and binding activity increase in the late phase of cerebral ischaemia and finds Oct-2 to be involved in reducing ischaemic-mediated neuronal injury.

Regulation of the Cell Type-specific dentin sialophosphoprotein gene expression in mouse odontoblasts by a novel transcription repressor and an activator CCAAT-binding factor

Dentin sialophosphoprotein (DSPP) is an extracellular matrix protein that is cleaved into dentin sialoprotein (DSP) and dentin phosphoprotein (DPP) with a highly restricted expression pattern in tooth and bone. Mutations of the DSPP gene are associated with dentin genetic diseases. Regulation of tissue-specific DSPP expression has not been described. To define the molecular basis of this cell-specific expression, we characterized the promoter responsible for the cell-specific expression of the DSPP gene in odontoblasts. Within this region, DNase I footprinting and electrophoretic mobility shift assays delineated one element that contains an inverted CCAAT-binding factor site and a protein-DNA binding site using nuclear extracts from odontoblasts. A series of competitive electrophoretic mobility shift assay analyses showed that the protein-DNA binding core sequence, ACCCCCA, is a novel site sufficient for protein binding. These two protein-DNA binding sequences are conserved at the same proximal position in the mouse, rat, and human DSPP gene promoters and are ubiquitously present in the promoters of other tooth/bone genes. Mutations of the CCAAT-binding factor binding site resulted in a 5-fold decrease in promoter activity, whereas abolishment of the novel protein-DNA binding site increased promoter activity by about 4.6-fold. In contrast to DSPP, expression levels of the novel protein were significantly reduced during odontoblastic differentiation and dentin mineralization. The novel protein was shown to have a molecular mass of 72 kDa. This study shows that expression of the cell type-specific DSPP gene is mediated by the combination of inhibitory and activating mechanisms.

All known in vivo functions of the Oct-2 transcription factor require the C-terminal protein domain

Oct-2, a transcription factor expressed in the B lymphocyte lineage and in the developing CNS, functions through of a number of discrete protein domains. These include a DNA-binding POU homeodomain flanked by two transcriptional activation domains. In vitro studies have shown that the C-terminal activation domain, a serine-, threonine- and proline-rich sequence, possesses unique qualities, including the ability to activate transcription from a distance in a B cell-specific manner. In this study, we describe mice in which the endogenous oct-2 gene has been modified through gene targeting to create a mutated allele, oct-2DeltaC, which encodes Oct-2 protein isoforms that lack all sequence C-terminal to the DNA-binding domain. Surprisingly, despite the retention of the DNA-binding domain and the glutamine-rich N-terminal activation domain, the truncated protein(s) encoded by the oct-2DeltaC allele are unable to rescue any of the previously described defects exhibited by oct-2 null mice. Homozygous oct-2DeltaC/DeltaC mice die shortly after birth, and B cell maturation, B-1 cell self renewal, serum Ig levels, and B lymphocyte responses to in vitro stimulation are all reduced or absent, to a degree equivalent to that seen in oct-2 null mice. We conclude that the C-terminal activation domain of Oct-2 is required to mediate the unique and indispensable functions of the Oct-2 transcription factor in vivo.

The Oct-2 POU domain gene in the neuroendocrine brain: a transcriptional regulator of mammalian puberty

POU homeodomain genes are transcriptional regulators that control development of the mammalian forebrain. Although they are mostly active during embryonic life, some of them remain expressed in the postnatal hypothalamus, suggesting their involvement in regulating differentiated functions of the neuroendocrine brain. We show here that Oct-2, a POU domain gene originally described in cells of the immune system, is one of the controlling components of the cell-cell signaling process underlying the hypothalamic regulation of female puberty. Lesions of the anterior hypothalamus cause sexual precocity and recapitulate some of the events leading to the normal initiation of puberty. Prominent among these events is an increased astrocytic expression of the gene encoding transforming growth factor-alpha (TGF alpha), a tropic polypeptide involved in the stimulatory control of LHRH secretion. The present study shows that such lesions result in the rapid and selective increase in Oct-2 transcripts in TGF alpha-containing astrocytes surrounding the lesion site. In both lesion-induced and normal puberty, there is a preferential increase in hypothalamic expression of the Oct-2a and Oct-2c alternatively spliced messenger RNA forms of the Oct-2 gene, with an increase in 2a messenger RNA levels preceding that in 2c and antedating the peripubertal activation of gonadal steroid secretion. Both Oct-2a and 2c trans-activate the TGF alpha gene via recognition motifs contained in the TGF alpha gene promoter. Inhibition of Oct-2 synthesis reduces TGF alpha expression in astroglial cells and delays the initiation of puberty. These results suggest that the Oct-2 gene is one of the upstream components of the glia to neuron signaling process that controls the onset of female puberty in mammals.

POU family transcription factors in the nervous system

The POU (Pit-Oct-Unc) family of transcription factors was originally defined on the basis of a common DNA binding domain in the mammalian factors Pit-1, Oct-1, and Oct-2 as well as the nematode protein Unc-86. Subsequently, a number of other POU family factors have been identified in both vertebrates and invertebrates. Many of these original and subsequently isolated members of the family have been shown to play critical roles in the development and functioning of the nervous system. To exemplify this, studies are described involving the functional characterisation of the Oct-2 factor, one of the original POU factors, and of the Brn-3 factors, which were isolated subsequently and are the mammalian factors most closely related to Unc-86.

Regulation of DNA virus transcription by cellular POU family transcription factors

In the same way as other viral functions, the transcription of viral genes is frequently controlled by cellular regulatory proteins either acting alone or together with virally encoded factors. In this review, I discuss three examples of such regulation in different types of DNA viruses by different members of the POU family of transcription factors, all of which involve viruses which play a role in the aetiology of specific human diseases. These are the glial cell-specific transcription of JC virus which is controlled by the glial cell specific POU factor Tst-1; the regulation of human papillomavirus gene expression in the cervix by positively and negatively acting POU factors and the manner in which the balance between lytic or latent infection with HSV is controlled by positively and negatively acting POU factors which differ in their ability to interact with the virally encoded transactivator VP16. As well as being of interest in themselves, these processes may offer a therapeutic target for controlling the diseases caused by these very different viruses.

Adjacent proline residues in the inhibitory domain of the Oct-2 transcription factor play distinct functional roles

A 40 amino acid region of Oct-2 from amino acids 142 to 181 functions as an active repressor domain capable of inhibiting both basal activity and activation of promoters containing a TATA box, but not of those that contain an initiator element. Based on our observation that the equivalent region of the closely related Oct-1 factor does not act as an inhibitory domain, we have mutated specific residues in the Oct-2 domain in an attempt to probe their importance in repressor domain function. Although mutations of several residues have no or minimal effect, mutation of proline 175 to arginine abolishes the ability to inhibit both basal and activated transcription. In contrast, mutation of proline 174 to arginine confers upon the domain the ability to repress activation of an initiator-containing promoter by acidic activation domains, and also suppresses the effect of the proline 175 mutation. Hence, adjacent proline residues play key roles in the functioning of the inhibitory domain and in limiting its specificity to TATA-box-containing promoters.

POU domain genes are differentially expressed in the early stages after lineage commitment of the PNS-derived stem cell line, RT4-AC

RT4 is a family of cell lines derived from a rat peripheral neurotumor and consists of a multipotential stem cell which spontaneously gives rise to a glial derivative and two neuronal derivatives. To begin to understand the role(s) of transcription factors in neural differentiation, we examined the expression of ten transcription factor genes (MASH1, REST/NRSF, Oct-1, Oct-2, Tst-1/SCIP, Brn-1, Brn-2, Brn-3.0, Brn-4, Brn-5) in the RT4 cell lines. We report here that all of the RT4 cells express REST/NRSF, Oct-1 and Brn-5, but do not express MASH1, Brn-3.0 or Brn-4. Furthermore, Brn-2 and Tst-1/SCIP expression was restricted to the RT4 stem cell line and glial derivative, while Oct-2 was expressed predominantly by the RT4 stem cell line and neuronal derivatives. We propose that the lack of expression of MASH1 (which is expressed relatively early in autonomic neuron differentiation) and Brn-3.0 (which is expressed early in sensory neuron differentiation), in combination with the presence of REST/NRSF (a repressor of neuronal gene expression), in all of the RT4 cell lines, establishes the RT4 system as a unique model for examining very early events in neuronal versus glial cell fate determination.

Comparative analyses of the latency-associated transcript promoters from herpes simplex virus type 1 strains H129, +GC and KOS-63

We have analyzed the activity of a specific portion of the latency-associated transcript (LAT) promoter of three strains of herpes simplex virus type 1 (HSV-1) in neuronal and non-neuronal cell types. Restriction fragments containing the LAT promoter sequences and the 5'-end of the LATs were isolated from HSV-1 strains H129, +GC and KOS-63, sequenced and cloned into a chloramphenicol transferase (CAT) plasmid vector. These vectors were separately assayed for CAT production in human (SknSH) and mouse (C-1300) neuroblastoma cell lines and a human continuous cell line (HeLa). Strain KOS-63 contained a C to T base substitution within the LAT promoter binding factor element upstream of the cAMP response element binding sequence. In replicate experiments, in which the construct DNA was used for transfection, the CAT constructs from strains H129 and +GC functioned equally well in all three cell lines. In contrast, the strain KOS-63 CAT construct functioned significantly better in HeLa cells than in neuroblastoma cell lines and better than the identical CAT constructs from strains H129 and +GC. In addition, the construct from strain KOS-63 functioned less well in the human neuroblastoma cell line than in HeLa or C-1300 neuroblastoma cells. When LAT expression was examined directly in vivo by in situ hybridization, strain KOS-63 produced slightly less LAT RNA than strain H129 within trigeminal ganglionic neurons of latently infected rabbits. However, utilizing competitive gel-shift assays, DNA fragments containing the LAT promoter binding element from all three strains bound equivalent amounts of HeLa cell nuclear proteins. Together, these results suggest that the activity expressed by the strain KOS-63 LAT promoter in vivo and in vitro may relate to positive or negative effects of DNA binding proteins on LAT transcription, and that these effects are cell-type dependent.

The ability of the inhibitory domain of the POU family transcription factor Oct-2 to interfere with promoter activation by different classes of activation domains is dependent upon the nature of the basal promoter elements

The Oct-2 transcription factor contains an inhibitory domain which is able to repress transcription following DNA binding. Here we show that within the neuronally expressed Oct-2.5 form, the inhibitory domain can strongly inhibit activation by transcription factor activation domains which are either composed predominantly of acidic residues or contain the HOB motif, whereas it has a weaker effect or no effect on proline-rich activation domains and on a glutamine-rich domain. In contrast, the isolated inhibitory domain of Oct-2 can efficiently repress all types of activation domains. This effect is observed however, only on TATA box-containing promoters and not on promoters containing an initiator motif. This widespread inhibition of different activation domains and its dependence on the nature of the basal promoter elements indicate that the inhibitory domain is likely to act by contacting a common downstream target of activation domains within the basal transcriptional complex bound at the TATA box rather than quenching specific activation domains by direct interaction. These effects are discussed in terms of the functional role of the inhibitory domain within Oct-2.5 and the mechanism by which it acts.

Activation and repression of gene expression by POU family transcription factors

The POU family transcription factors Oct-2 and Brn-3 utilize different mechanisms to produce a variety of effects on gene expression particularly in the nervous system. In the case of Oct-2, a single gene produces a primary RNA transcript. This transcript then undergoes alternative splicing to yield a variety of different mRNAs encoding Oct-2 isoforms which either activate or repress gene expression. In contrast, three distinct genes encode the closely related Brn-3 factors, Brn-3b, Brn-3b and Brn-3c. Although the proteins encoded by the Brn-3a and Brn-3c genes activate their target genes Brn-3b represses these genes and can also interfere with activation by Brn-3a or c. These finding indicate that diverse mechanisms are used to generate activating or repressing forms of POU family transcription factors.

Specific up-regulation of the POU domain transcription factor Oct-2 following axotomy

Peripheral nerve damage causes a dramatic alteration to the gene expression in primary sensory neurons, changes within the neuronal cell body giving rise to an altered phenotype, adapted for axonal regeneration. Such changes suggest an alteration in activity, or levels, of cellular transcription factors. The POU family transcription factor Oct-2 is known to be induced in sensory neurons by nerve growth factor (NGF) and might therefore be affected by the removal of target-derived NGF following axotomy. Paradoxically, however, the expression of Oct-2 showed a transient increase of two- to three-fold 24 h after axotomy. In contrast, axotomy had no effect on the levels of the Brn-3 sub-family of POU proteins, indicating that this effect was specific for Oct-2.

Nerve growth factor-regulated properties of sensory neurones in Oct-2 null mutant mice

The POU-domain transcription factor Oct-2 is expressed in both B lymphocytes and sensory neurones, where its expression is regulated by nerve growth factor (NGF). In order to define a possible role for Oct-2 in neurotrophin signalling, we examined the expression of an NGF-regulated channel (capsaicin-evoked ion fluxes), neuropeptides (substance P, calcitonin gene-related peptide), structural proteins (neurofilaments and peripherin) and receptors (trks) in dorsal root ganglion neurones derived from perinatal transgenic mice containing a defective Oct-2 structural gene. Northern blots show that central nervous tissue contains a larger than normal (> 10 kb) mRNA transcript corresponding in size to an Oct-2 transcript encoding a defective protein. PCR analysis shows the absence of normal Oct-2 transcripts in dorsal root ganglia. In null mutants, capsaicin sensitivity, and neuropeptide and cytoskeletal protein expression were unaffected by the loss of Oct-2 expression. The number of sensory neurones and the gross morphology of CNS tissues that normally express high levels of Oct-2 were also examined and found to be normal in the null mutant. Heterozygous animals show normal thresholds of sensitivity to noxious heat and normal inflammatory responses. Oct-2 does not therefore play an essential role in the NGF responsiveness of sensory neurones in these animals.

Direct evidence that the POU family transcription factor Oct-2 represses the cellular tyrosine hydroxylase gene in neuronal cells

The POU family transcription factor Oct-2 was originally identified in B lymphocytes but has been shown to be expressed in neuronal cells, although it is absent in most other cell types. Cotransfection of Oct-2 expression vectors into nonneuronal cells with a tyrosine hydroxylase promoter/reporter plasmid suggests that Oct-2 can repress this promoter in this artificial situation. Here we report that reduction of endogenous Oct-2 levels in a neuronal cell line by an antisense approach results in an increase in endogenous tyrosine hydroxylase levels. In contrast, the level of the neuronal marker protein PGP9.5 remains unchanged in the antisense lines whereas that of the neuronal nitric oxide synthase decreases. Hence, the tyrosine hydroxylase gene is a natural target for repression by Oct-2 in neuronal cells. The significance of this effect is discussed in terms of the processes that regulate tyrosine hydroxylase gene expression and the role of Oct-2 in neuronal cells.

The transcriptional regulation of human aldehyde dehydrogenase I gene. The structural and functional analysis of the promoter

Human cytosolic aldehyde dehydrogenase 1 (ALDH1) plays a role in the biosynthesis of retinoic acid that is a modulator for gene expression and cell differentiation. Northern blot analysis showed that liver tissue, pancreas tissue, hepatoma cells, and genital skin fibroblast cells expressed high levels of ALDH1. Sequence analysis showed that the 5'-flanking region contains a number of putative regulatory elements, such as NF-IL6, HNF-5, GATA binding sites, and putative response elements for interleukin-6, phenobarbital and androgen, in addition to a noncanonical TATA box (ATAAA) and a CCAAT box. Functional characterization of the 5'-regulatory region of the human ALDH1 gene was carried out by a fusion to the chloramphenicol acetyltransferase gene. A construct containing 2.6 kilobase pairs of the 5'-flanking region was efficiently expressed in hepatoma Hep3B cells, but not in erythroleukemic K562 cells or in fibroblast LTK- cells, which do not express ALDH1. Within this region, we define a minimal promoter (-91 to +53) that contains positive regulatory elements. The study using site-directed mutagenesis demonstrated that the CCAAT box region is the major cis-acting element involved in basal ALDH1 promoter activity in Hep3B cells. Gel mobility shift assays showed that NF-Y and other octamer factors bound CCAAT box and an octamer motif sequence, but not GATA site existing in the minimal promoter region. Two additional DNA binding activities associated with the minimal promoter were found in the nuclear extract from Hep3B cells, but not from K562 cells. These results offer the possible molecular mechanism of the cell type-specific expression of ALDH1 gene.

Control of vascular cell adhesion molecule-1 gene promoter activity during neural differentiation

Here we demonstrate that vascular cell adhesion molecule-1 (VCAM-1) is expressed in the developing central nervous system on neuroepithelial cells, which are the precursors of neurons and glia. As these cells differentiate, VCAM-1 is restricted to a subset of the glial population. An understanding of mechanisms responsible for this restricted pattern could provide insights into how lineage-specific gene expression is maintained during neural differentiation. As a model of neural differentiation, we turned to the P19 embryonic carcinoma cell line, which in response to retinoic acid will differentiate along a neural pathway. We show that VCAM-1 expression on the differentiating P19 cells resembles that in the central nervous system. Transfection of VCAM-1 gene promoter constructs into P19 cells revealed that the VCAM-1 gene is controlled sequentially by negative and positive elements during differentiation. We present evidence that early during differentiation, POU proteins block VCAM-1 gene activity; however, later in differentiation coincident with the appearance of VCAM-1 the pattern of POU proteins changes and the VCAM-1 gene promoter is activated. This activation is mediated through the NF kappa B/rel complex p50/p65, which forms during P19 cell differentiation.

Nerve growth factor induces the Oct-2 transcription factor in sensory neurons with the kinetics of an immediate-early gene

The Oct-2 transcription factor has a predominantly inhibitory effect on gene expression in neuronal cell lines. This factor and its corresponding mRNA have previously been shown to be elevated in adult rat dorsal root ganglion (DRG) neurons chronically exposed to nerve growth factor (NGF). Here we show that the Oct-2 mRNA is rapidly induced in DRG cells exposed to NGF and that such induction still occurs to a lesser extent in the presence of the protein synthesis inhibitor cycloheximide. These findings characterize Oct-2 as a novel member of the immediate-early class of NGF-induced transcription factors whose previously defined members have a predominantly stimulatory effect on the expression of other genes. Induction of the Oct-2 mRNA was also observed in DRG neurons treated with acidic fibroblast growth factor or epidermal growth factor but not with a range of other growth factors and neurotrophins. The role of the Oct-2 transcription factor in mediating the response of DRG neurons to NGF is discussed.

Regulated splicing of the Oct-2 transcription factor RNA in neuronal cells

The primary RNA transcript derived from the gene encoding the Oct-2 transcription factor is alternatively spliced to yield a number of different mRNAs which encode different isoforms of this protein. The mRNAs encoding two such isoforms Oct-2c and mini Oct-2 were originally detected in neuronal cells. We show here that the mRNAs encoding these forms also occur in other tissues with the proportion of the mini Oct-2 mRNA being much higher in the spleen than in the brain. However, the levels of the mini Oct-2 mRNA increase in neuronal cell lines in response to differentiation-inducing stimuli and decrease upon exposure to growth factors. Hence the splicing of the Oct-2 transcript can be regulated in both a tissue specific manner and in neuronal cells in response to specific stimuli. The significance of this effect is discussed in terms of the differing ability of different forms of Oct-2 to activate or inhibit gene expression.

The inhibitory domain in the Oct-2 transcription factor represses gene activity in a cell type-specific and promoter-independent manner

The Oct-2 transcription factor contains an N-terminal inhibitory domain which can act to inhibit promoter activity when linked to either its corresponding DNA-binding POU domain or the heterologous DNA binding domain of the yeast transcription factor GAL4. This inhibitory effect is independent of the number of DNA binding sites or their context in the target promoter. In contrast the effect is cell type-specific and can be relieved by over-expression of the isolated inhibitory domain in the absence of a DNA binding domain. These results suggest that the inhibitory domain acts by decreasing the activity of the basal transcriptional complex but that it operates indirectly by recruiting a second cell type-specific factor to the promoter which then interacts with the basal complex decreasing its activity.

Down regulation of the octamer binding protein Oct-1 during growth arrest and differentiation of a neuronal cell line

The octamer binding transcription/DNA replication factor Oct-1 is present in virtually all cell types including proliferating cell lines of neuronal origin but is not detectable in mature non-dividing neurons. Cell cycle arrest in G0/G1 and morphological differentiation of a neuronal cell line is accompanied by a decline in the level of Oct-1 DNA binding, although the level of DNA binding by another octamer binding protein, Oct-2 is unaltered. This effect is paralled by a decline in the level of the Oct-1 mRNA in the non-dividing cells. The decrease in Oct-1 levels occurs only with the production of a mature, non-dividing neuronal phenotype and not when the cells are arrested in late G1 and do not undergo morphological differentiation. The potential role of Oct-1 and other octamer binding proteins in gene regulation in neuronal cells and in their differentiation is discussed.

A nonconsensus octamer-recognition sequence (TAATGARAT-motif) identifies a novel DNA binding protein in human Merkel cell carcinoma cell lines

We have established a number of cell lines from Merkel cell carcinoma (MCC) of the skin. In many respects these cell lines resemble those established from small cell lung cancer (SCLC) and it is difficult to differentiate between metastatic MCC and SCLC on morphological or histochemical criteria. Both are thought to be neuroendocrine tumours and may express a number of neuroendocrine markers. SCLC cell lines express the octamer-DNA binding transcription factor brn-2 gene products N-Oct3 and N-Oct5, which are restricted to the neuroectodermal cell lineage. In DNA binding studies using a consensus octamer recognition site we have found that 4 of 8 MCC cell lines examined expressed brn-2 in at least trace amounts compared with 3 SCLC cell lines which all expressed brn-2 proteins at high levels. Moreover, these DNA binding studies were extended by using a high-affinity brn-2 recognition site related to the degenerate octamer TAATGARAT-motif. This identified a novel DNA binding protein in a subset of MCC cell lines. The protein was absent from the three SCLC cell lines, melanoma cells and brain tissue. This binding activity, which we term Merkel cell DNA nuclear (MNF), was shown to be specific by competitive inhibition with oligonucleotide binding sites and was not inhibited by polyclonal antisera against the Oct-1, Oct-2 or Brn-2 proteins. This protein may serve as a unique marker for MCC compared with SCLC cells and may be involved in regulating the Merkel cell phenotype.

Mice lacking Snrpn expression show normal regulation of neuronal alternative splicing events

The SmN protein is closely related to the constitutively expressed RNA splicing protein SmB but is expressed only in brain and heart tissue. Mice which lack expression of SmN die shortly after birth suggesting a critical role for this protein possibly in the regulation of neuronal-specific alternative splicing events. We show here however that the neuronal-specific alternative splicing of the RNAs encoding several different classes of protein proceeds normally in mice lacking SmN expression. The potential role of SmN and the reasons for the lethal effect observed in non-expressing mice are discussed.

Broad binding-site specificity and affinity properties of octamer 1 and brain octamer-binding proteins

The ubiquitous Pit-1-Oct-1-Unc-1 (POU)-domain protein octamer 1 (Oct-1) has been observed to bind specifically to a number of degenerate and dissimilar sequences. We have used antibodies directed against a C-terminal Oct-1 peptide to immunoselect binding sequences for HeLa cell Oct-1 from random-sequence oligonucleotides and we describe the isolation of binding sequences of considerable heterogeneity. Although our consensus alignment indicated a 9-bp TATGCAAAT motif with AT-rich flanking sequences, this binding motif is not immediately obvious in the population of sequences and no clone actually contained this sequence. Screening these Oct-1-binding sequences with a mouse whole-brain extract demonstrated that the neuronal octamer-binding proteins exhibit similar but distinct DNA sequence specificities. Unlike the reported selection of binding sequences for other transcription factors, the dependence of Oct-1-binding affinity upon sequence did not correspond tightly to the degree of conservation at particular positions of the consensus sequence. Our results suggest that either base-specific hydrogen bonding is not the only major determinant of binding affinity and specificity, or that Oct-1 binding to some sequences is mechanistically different from its binding to an octamer. These results exemplify the potential to overlook binding sites for some factors by searching gene sequences with a consensus nucleotide sequence.

In vivo and in vitro expression of octamer binding proteins in human melanoma metastases, brain tissue, and fibroblasts

The pattern of octamer sequence-specific DNA binding proteins expressed in human melanoma was examined in nuclear extracts of seven surgically-isolated tumors, short-term cultures of these tumors, and 25 human melanoma cell lines to determine the in vivo and in vitro distribution of the melanocytic-associated Oct-M1 and Oct-M2 octamer binding activities. In the biopsy tissue and cultured melanoma cells of a metastasis from the cerebellum, two other binding activities (N-Oct-2 and N-Oct-6) in addition to the Oct-M1, Oct-M2 and the generally expressed Oct-1 protein were detected; this profile was consistent with that seen in normal human and mouse brain tissue. Melanoma tissue removed from lymph nodes and cell lines established from them also showed Oct-1, Oct-M1, Oct-M2, and N-Oct-2. N-Oct-2 was distinguished from the comigrating Oct-2A activity by failure to react with Oct-2A-specific antibody. All but one of the 25 melanoma cell lines exhibited Oct-1, Oct-M1, and Oct-M2 and/or N-Oct-2 activity, whereas cultured normal melanocytes expressed only Oct-1 and Oct-M1. In contrast to murine fibroblasts, which express only Oct-1, human fibroblast strains also expressed Oct-2A binding activity, which was confirmed by reactivity with Oct-2A antibody and the presence of Oct-2A mRNA and indicated that Oct-2A has a more general role than that of a lymphoid-specific transcription factor. Overall, the results indicate that expression of neural-specific Oct factors in human melanoma is (1) aberrant compared with normal melanocytes, (2) can be modulated by the surrounding tissue in a brain metastasis, and (3) may be part of the altered program of differentiation accompanying transformation.

The latency-related gene of bovine herpesvirus 1 inhibits the activity of immediate-early transcription unit 1

Bovine herpesvirus 1 (BHV-1) establishes a latent infection in sensory neurons of infected animals. Only one virus-encoded latency-related (LR) gene is expressed during a latent infection. The LR transcript overlaps immediate-early transcription unit 1 (IEtu1) and is anti-sense with respect to IEtu1. The transcriptional start site of the LR RNA was mapped to position 724 of the LR gene, downstream from two putative TATA elements. When LR promoter sequences were deleted from a plasmid containing IEtu1 and the LR gene, the resulting construct trans-activated the HSV-1 thymidine kinase (TK) promoter more efficiently than IEtu1 plus the LR gene. Cotransfection of a plasmid containing the intact LR gene with IEtu1 inhibited the ability of IEtu1 to trans-activate the TK promoter. These results imply that a LR gene product(s) repressed the trans-acting capacity of IEtu1.

Mini-Oct and Oct-2c: two novel, functionally diverse murine Oct-2 gene products are differentially expressed in the CNS

We report that two novel alternatively spliced products of the murine Oct-2 gene encode Mini-Oct (Oct-2d), a protein consisting of almost only the POU domain, and Oct-2c, a protein lacking the last 12 amino acids of Oct-2a. Ectopic expression in HeLa cells shows that Oct-2c is a transactivator, whereas Mini-Oct fails to transactivate if the octamer motif is in a promoter position next to TATA box. Mini-Oct can repress the transcriptional signal generated by endogenous octamer factors in F9 cells. It seems that Mini-Oct has the potential to serve as a transcriptional modulator for genes regulated by different octamer-binding factors. In situ hybridization reveals that Mini-Oct expression follows the general pattern of other known Oct-2 transcripts. However, it is absent from the Purkinje cell layer in the cerebellum of adult mice, and strong expression is observed in the developing nasal neuroepithelium and primary spermatids. Differential expression patterns of the Oct-2 transcripts with different transactivation/repression capacities of the encoded proteins may have a specific role in gene expression in the developing nervous system and in adult brain.