The homeodomain protein Arix promotes protein kinase A-dependent activation of the dopamine beta-hydroxylase promoter through multiple elements and interaction with the coactivator cAMP-response element-binding protein-binding protein

Marine thermal fluctuation induced gluconeogenesis by the transcriptional regulation of CgCREBL2 in Pacific oysters

Marine thermal fluctuation profoundly influences energy metabolism, physiology, and survival of marine life. In the present study, short-term and long-term high-temperature stresses were found to affect gluconeogenesis by inhibiting PEPCK activity in the Pacific oyster (Crassostrea gigas), which is a globally distributed species that encounters significant marine thermal fluctuations in intertidal zones worldwide. CgCREBL2, a key molecule in the regulation of gluconeogenesis, plays a critical role in the transcriptional regulation of PEPCK in gluconeogenesis against high-temperature stress. CgCREBL2 was able to increase the transcription of CgPEPCK by either binding the promoter of CgPEPCK gene or activating CgPGC-1α and CgHNF-4α after short-term (6 h) high-temperature stress, while only by binding CgPEPCK after long-term (60 h) high-temperature stress. These findings will further our understanding of the effect of marine thermal fluctuation on energy metabolism on marine organisms.

Lack of zinc finger protein 521 upregulates dopamine β-hydroxylase expression in the mouse brain, leading to abnormal behavior

AIM

Previously, we reported that mice deficient in most of the Zfp521 coding region (Zfp521^Δ/Δ mice) displayed abnormal behaviors, including hyperlocomotion and lower anxiety. In this study, we aimed to elucidate the involvement and mechanisms of monoamine variation.

MAIN METHODS

First, we compared the levels of dopamine (DA), noradrenaline (NA), and serotonin in the brains of Zfp521^Δ/Δ and Zfp521^+/+ mice using enzyme-linked immunosorbent assay. Next, we elucidated the mechanisms using quantitative PCR and Western Blotting. Additionally, we administered inhibitory drug to the mice and performed behavioral tests.

KEY FINDINGS

Our results showed that the DA level decreased and the NA level increased in Zfp521^Δ/Δ mice. We found that ZFP521 suppresses the expression of dopamine β-hydroxylase (DBH), which converts DA into NA. We also demonstrated that paired homeodomain transcription factor 2 and early growth response protein-1, which are the transcription factors for Dbh, were involved in the upregulation of Dbh by ZFP521. The administration of nepicastat, a specific inhibitor of DBH, attenuated the abnormal behaviors of Zfp521^Δ/Δ mice.

SIGNIFICANCE

These results suggest that the lack of ZFP521 upregulates the expression of DBH, which leads to a decrease in the DA level and an increase in the NA level in the brain, resulting in abnormal behaviors.

Choices choices: regulation of precursor differentiation during enteric nervous system development

Background The enteric nervous system (ENS) is the largest subdivision of the peripheral nervous system and forms a complex circuit of neurons and glia that controls the function of the gastrointestinal (GI) tract. Within this circuit, there are multiple subtypes of neurons and glia. Appropriate differentiation of these various cell subtypes is vital for normal ENS and GI function. Studies of the pediatric disorder Hirschprung's Disease (HSCR) have provided a number of important insights into the mechanisms and molecules involved in ENS development; however, there are numerous other GI disorders that potentially may result from defects in development/differentiation of only a subset of ENS neurons or glia. Purpose Our understanding of the mechanisms and molecules involved in enteric nervous system differentiation is far from complete. Critically, it remains unclear at what point the fates of enteric neural crest cells (ENCCs) become committed to a specific subtype cell fate and how these cell fate choices are made. We will review our current understanding of ENS differentiation and highlight key questions that need to be addressed to gain a more complete understanding of this biological process.

Phox2b influences the development of a caudal dopaminergic subset

The developing mesodiencephalic dopaminergic (mdDA) neuronal field can be subdivided into several molecularly distinct domains that arise due to spatiotemporally distinct origins of the neurons and distinct transcriptional pathways controlling these neuronal subsets. Two large anatomically and functionally different subdomains are formed that eventually give rise to the SNc and VTA, but more subsets exist which require detailed characterization in order to better understand the development of the functionally different mdDA subsets, and subset-specific vulnerability. In this study, we aimed to characterize the role of transcription factor Phox2b in the development of mdDA neurons. We provide evidence that Phox2b is co-expressed with TH in a dorsal-caudal subset of neurons in the mdDA neuronal field during embryonic development. Moreover, Phox2b transcripts were identified in FAC-sorted Pitx3 positive neurons. Subsequent analysis of Phox2b mutant embryos revealed that in the absence of Phox2b, a decrease of TH expression occurred specifically in the midbrain neuronal subset that normally co-expresses Phox2b with TH. Our data suggest that Phox2b is, next to the known role in the development of the oculomotor complex, involved in the development of a specific caudal mdDA neuronal subset.

Transcription factor Phox2 upregulates expression of norepinephrine transporter and dopamine β-hydroxylase in adult rat brains

Degeneration of the noradrenergic locus coeruleus (LC) in aging and neurodegenerative diseases is well documented. Slowing or reversing this effect may have therapeutic implications. Phox2a and Phox2b are homeodomain transcriptional factors that function as determinants of the noradrenergic phenotype during embryogenesis. In the present study, recombinant lentiviral eGFP-Phox2a and -Phox2b (vPhox2a and vPhox2b) were constructed to study the effects of Phox2a/2b over-expression on dopamine β-hydroxylase (DBH) and norepinephrine transporter (NET) levels in central noradrenergic neurons. Microinjection of vPhox2 into the LC of adult rats significantly increased Phox2 mRNA levels in the LC region. Over-expression of either Phox2a or Phox2b in the LC was paralleled by significant increases in mRNA and protein levels of DBH and NET in the LC. Similar increases in DBH and NET protein levels were observed in the hippocampus following vPhox2 microinjection. In the frontal cortex, only NET protein levels were significantly increased by vPhox2 microinjection. Over-expression of Phox2 genes resulted in a significant increase in BrdU-positive cells in the hippocampal dentate gyrus. The present study demonstrates an upregulatory effect of Phox2a and Phox2b on the expression of DBH and NET in noradrenergic neurons of rat brains, an effect not previously shown in adult animals. Phox2 genes may play an important role in maintaining the function of the noradrenergic neurons after birth, and regulation of Phox2 gene expression may have therapeutic utility in aging or disorders involving degeneration of noradrenergic neurons.

Interaction of Hand2 and E2a is important for transcription of Phox2b in sympathetic nervous system neuron differentiation

Transcription factors play a crucial role in the development of various tissues. In particular, the transcription factors of the basic helix-loop-helix (bHLH) family are crucial regulators of neurodifferentiation. Previous studies suggested that the bHLH transcription factor Hand2 is essential for sympathetic nervous system neuron differentiation in vivo, but the molecular mechanisms involved have not been well elucidated. It is important for understanding their mode of action in cellular differentiation to clarify how these bHLH factors regulate distinct transcriptional targets in a temporally and spatially controlled manner. Recent reports on ES cell differentiation suggested that its molecular mechanism mimics that of in vivo neurogenesis. However, the diverse nature of ES cell populations has prevented efficient analysis. To address this issue, we previously established a cell line in P19 embryonal carcinoma (EC) cells. Efficient sympathetic nervous system (SNS) neuron differentiation is induced in the cell line. Using this cell line, we succeeded in showing that the interaction of bHLH transcription factor Hand2 with E2a is required for transcription of Phox2b, which is essential for autonomic nervous system neuron development, and this binding activates this expression in SNS differentiation. Moreover, we also demonstrated that Hes5 regulated the transcription of Phox2b as a negative regulator and it inhibited the SNS differentiation. These findings have enabled us to determine the novel regulatory mechanism of Phox2b in SNS differentiation.

Varied mechanisms of oestradiol-mediated regulation of dopamine β-hydroxylase transcription

Experiments performed in vivo and in cell culture have demonstrated that oestradiol induces dopamine β-hydroxylase (DBH) gene transcription. In the present study, we examined oestrogen-responsive elements of the rat DBH gene promoter aiming to characterise the mechanisms of oestradiol-induced DBH transcription. Various mutations and deletions of DBH promoter reporter constructs were tested for responsiveness to 17β-oestradiol (E(2) ). Mutation of the half palindromic oestrogen response element (ERE) at position -759 reduced the response to E(2) in PC12 cells co-transfected with oestrogen receptor (ER) α, indicating a functional role for this motif. In cells co-transfected with ERβ, mutations at the -759 site were unresponsive to E(2) . To characterise the additional E(2) responsive elements, mediated by ERα, the DBH promoter was truncated to the proximal 249 or 200 nucleotides upstream of the transcription start site. Despite either truncation, 10 nm E(2) still elicited an approximately two-fold induction of DBH promoter activity. Mutation of a possible ERE-like sequence at -59 had no effect. The lack of a functional ERE in the proximal region of the rat DBH promoter despite E(2) -mediated DBH promoter activity, suggests regulation by a nonclassical mechanism, such as a membrane-initiated signalling pathway. Moreover, the induction of DBH promoter activity and the rise in DBH mRNA levels were observed within hours. To determine whether membrane-initiated E(2) signalling is involved in rat DBH gene transcription, a membrane impermeable E(2) conjugate, β-oestradiol-6-(O-carboxy-methyl) oxime-bovine serum albumin (E(2) BSA), was used. Incubation with E(2) -BSA induced luciferase activity and elicited a significant rise in DBH mRNA levels in the ERα transfected cells. The findings indicate two different mechanisms whereby DBH transcription is regulated by E(2) in the presence of ERα. The results implicate both genomic and membrane-initiated mechanisms, mediated by ERα, in E(2) -induced DBH gene transcription.

Time-dependent activation of Phox2a by the cyclic AMP pathway modulates onset and duration of p27Kip1 transcription

In noradrenergic progenitors, Phox2a mediates cell cycle exit and neuronal differentiation by inducing p27(Kip1) transcription in response to activation of the cyclic AMP (cAMP) pathway. The mechanism of cAMP-mediated activation of Phox2a is unknown. We identified a cluster of phosphoserine-proline sites in Phox2a by mass spectrometry. Ser206 appeared to be the most prominent phosphorylation site. A phospho-Ser206 Phox2a antibody detected dephosphorylation of Phox2a that was dependent on activation of the cAMP pathway, which occurred prior to neuronal differentiation of noradrenergic CAD cells. Employing serine-to-alanine and serine-to-aspartic acid Phox2a substitution mutants expressed in inducible CAD cell lines, we demonstrated that the transcriptional activity of Phox2a is regulated by two sequential cAMP-dependent events: first, cAMP signaling promotes dephosphorylation of Phox2a in at least one site, Ser206, thereby allowing Phox2a to bind DNA and initiate p27(Kip1) transcription; second, following dephosphorylation of the phosphoserine cluster (Ser202 and Ser208), Phox2a becomes phosphorylated by protein kinase A (PKA) on Ser153, which prevents association of Phox2a with DNA and terminates p27(Kip1) transcription. This represents a novel mechanism by which the same stimulus, cAMP signaling, first activates Phox2a by dephosphorylation of Ser206 and then, after a built-in delay, inactivates Phox2a via PKA-dependent phosphorylation of Ser153, thereby modulating onset and duration of p27(Kip1) transcription.

Effects of transcription factors Phox2 on expression of norepinephrine transporter and dopamine beta-hydroxylase in SK-N-BE(2)C cells

Phox2a and Phox2b are two homeodomain proteins that control the differentiation of noradrenergic neurons during embryogenesis. In the present study, we examined the possible effect of Phox2a/2b on the in vitro expression of the norepinephrine transporter (NET) and dopamine beta-hydroxylase (DBH), two important markers of the noradrenergic system. SK-N-BE(2)C cells were transfected with cDNAs or short hairpin RNAs specific to the human Phox2a and Phox2b genes. Transfection of 0.1 to 5 mug of cDNAs of Phox2a or Phox2b significantly increased mRNA and protein levels of NET and DBH in a concentration-dependent manner. As a consequence of the enhanced expression of NET after transfection, there was a parallel increase in the uptake of [(3)H]norepinephrine. Co-transfection of Phox2a and Phox2b did not further increase the expression of noradrenergic markers when compared with transfection of either Phox2a or Phox2b alone. Transfection of shRNAs specific to Phox2a or Phox2b genes significantly reduced mRNA and protein levels of NET and DBH after shutdown of endogenous Phox2, which was accompanied by a decreased [(3)H]norepinephrine uptake. Furthermore, there was an additive effect after cotransfection with both shRNAs specific to Phox2a or Phox2b genes on NET mRNA levels. Finally, the reduced DBH expression caused by the shRNA specific to Phox2a could be reversed by transfection with Phox2b cDNA and vice versa. The present findings verify the determinant role of Phox2a and Phox2b on the expression and function of NET and DBH in vitro. Further clarifying the regulatory role of these two transcription factors on key proteins of the noradrenergic system may open a new avenue for therapeutics of aging-caused dysfunction of the noradrenergic system.

Catecholaminergic systems in stress: structural and molecular genetic approaches

Stressful stimuli evoke complex endocrine, autonomic, and behavioral responses that are extremely variable and specific depending on the type and nature of the stressors. We first provide a short overview of physiology, biochemistry, and molecular genetics of sympatho-adrenomedullary, sympatho-neural, and brain catecholaminergic systems. Important processes of catecholamine biosynthesis, storage, release, secretion, uptake, reuptake, degradation, and transporters in acutely or chronically stressed organisms are described. We emphasize the structural variability of catecholamine systems and the molecular genetics of enzymes involved in biosynthesis and degradation of catecholamines and transporters. Characterization of enzyme gene promoters, transcriptional and posttranscriptional mechanisms, transcription factors, gene expression and protein translation, as well as different phases of stress-activated transcription and quantitative determination of mRNA levels in stressed organisms are discussed. Data from catecholamine enzyme gene knockout mice are shown. Interaction of catecholaminergic systems with other neurotransmitter and hormonal systems are discussed. We describe the effects of homotypic and heterotypic stressors, adaptation and maladaptation of the organism, and the specificity of stressors (physical, emotional, metabolic, etc.) on activation of catecholaminergic systems at all levels from plasma catecholamines to gene expression of catecholamine enzymes. We also discuss cross-adaptation and the effect of novel heterotypic stressors on organisms adapted to long-term monotypic stressors. The extra-adrenal nonneuronal adrenergic system is described. Stress-related central neuronal regulatory circuits and central organization of responses to various stressors are presented with selected examples of regulatory molecular mechanisms. Data summarized here indicate that catecholaminergic systems are activated in different ways following exposure to distinct stressful stimuli.

Transcription factor GATA-3 regulates the transcriptional activity of dopamine beta-hydroxylase by interacting with Sp1 and AP4

GATA-3 is a zinc finger transcription factor that is expressed in T cell lineages as well as in the nervous system during development. In this study, we report that forced expression of GATA-3 resulted in an increased number of dopamine beta-hydroxylase (DBH)-expressing neurons in primary neural crest stem cell (NCSC) culture, suggesting that the DBH gene may be a downstream target gene of GATA-3. GATA-3 robustly transactivates the promoter function of the noradrenaline (NA)-synthesizing DBH gene, via two specific upstream promoter domains; one at -62 to -32 bp and the other at -891 to -853 bp. Surprisingly, none of these domains contain GATA-3 binding sites but encompass binding motifs for transcription factors Sp1 and AP4, respectively. Protein-protein interaction analyses both in vitro and in vivo and chromatin immunoprecipitation (ChIP) assays showed that GATA-3 effects its transcriptional regulatory function through physical interactions with these transcription factors.

Trim11 increases expression of dopamine beta-hydroxylase gene by interacting with Phox2b

The homeodomain transcription factor Phox2b is one of the key determinants involved in the development of noradrenergic (NA) neurons in both the central nervous system (CNS) and the peripheral nervous system (PNS). Using yeast two-hybrid screening, we isolated a Phox2b interacting protein, Trim11, which belongs to TRIM (Tripartite motif) or RBCC proteins family, and contains a RING domain, B-boxes, a coiled-coil domain, and the B30.2/SPRY domain. Protein-protein interaction assays showed that Phox2b was able to physically interact with Trim11. The B30.2/SPRY domain of Trim11 was required for the interaction with Phox2b. Expression of Phox2b and Trim11 was detected in the sympathetic ganglia (SG) of mouse embryos. Forced expression of Trim11 with Phox2b further increased mRNA levels of dopamine beta-hydroxylase (DBH) gene in primary avian neural crest stem cell (NCSC) culture. This study suggests a potential role for Trim11 in the specification of NA phenotype by interaction with Phox2b.

Regulation of rat dopamine beta-hydroxylase gene transcription by early growth response gene 1 (Egr1)

Egr1, a transcription factor rapidly induced by various stimuli including stress, can elevate transcription of genes for the catecholamine biosynthetic enzymes TH and PNMT. To examine if Egr1 also regulates dopamine beta-hydroxylase (DBH) gene expression, PC12 cells were transfected with expression vector for full length or truncated inactive Egr1 and various DBH promoter-driven luciferase constructs. While Egr1 elevated TH promoter activity, DBH promoter activity was reduced. The reduction occurred as early as 4 h and reached maximal inhibition 16-40 h after transfection. Egr1 also reduced the expression of endogenous DBH mRNA and the induction of DBH promoter activity by cAMP. These effects were not observed with truncated Egr1 lacking the DNA binding domain. The first 247, but not 200, nucleotides of DBH promoter are sufficient for this suppression. Several putative Egr1 motifs were identified, and mutagenesis showed that the motif at -227/-224 is required. Binding of Egr1 to this region of the DBH promoter was verified by chromatin immunoprecipitation and electrophoretic mobility shift assays. This study demonstrates that DBH promoter contains at least one functional Egr1 motif; and indicates, for the first time, that Egr1 can play an inhibitory role in regulation of DBH gene transcription.

Transcription Factor PHOX2A Regulates the Human α3 Nicotinic Receptor Subunit Gene Promoter

PHOX2A is a paired-like homeodomain transcription factor that participates in specifying the autonomic nervous system. It is also involved in the transcriptional control of the noradrenergic neurotransmitter phenotype as it regulates the gene expression of tyrosine hydroxylase and dopamine-beta-hydroxylase. The results of this study show that the human orthologue of PHOX2A is also capable of regulating the transcription of the human alpha3 nicotinic acetylcholine receptor gene, which encodes the ligand-binding subunit of the ganglionic type nicotinic receptor. In particular, we demonstrated by chromatin immunoprecipitation and DNA pulldown assays that PHOX2A assembles on the SacI-NcoI region of alpha3 promoter and, by co-transfection experiments, that it exerts its transcriptional effects by acting through the 60-bp minimal promoter. PHOX2A does not seem to bind to DNA directly, and its DNA binding domain seems to be partially dispensable for the regulation of alpha3 gene transcription. However, as suggested by the findings of our co-immunoprecipitation assays, it may establish direct or indirect protein-protein interactions with Sp1, thus regulating the expression of alpha3 through a DNA-independent mechanism. As the alpha3 subunit is expressed in every terminally differentiated ganglionic cell, this is the first example of a "pan-autonomic" gene whose expression is regulated by PHOX2 proteins.

Perspectives on integration of cell extrinsic and cell intrinsic pathways of signaling required for differentiation of noradrenergic sympathetic ganglion neurons

This review presents an analysis of current research aimed at deciphering the interplay of cell extrinsic and intrinsic signals required for specification and differentiation of noradrenergic sympathetic ganglion neurons. The development of noradrenergic sympathetic ganglion neurons depends upon expression of a core set of DNA regulatory molecules, including the Phox2 homeodomain proteins and the basic helix-loop-helix proteins, HAND2 and MASH1 whose expression is dependent upon cell extrinsic cues. Both bone morphogenetic protein(s) and cAMP have an integral role in the specification/differentiation of noradrenergic sympathetic ganglion neurons but how signaling downstream of these molecules is integrated and identification of their particular functions is just beginning to be elucidated. Data currently available suggests a model with BMP providing both instructive and permissive cues in a pathway integrated by cAMP and MAPK by activation of both canonical and non-canonical intracellular signaling cascades.

ERK1/2 is a negative regulator of homeodomain protein Arix/Phox2a

The homeodomain protein Arix/Phox2a plays a role in the development and maintenance of the noradrenergic cell type by regulating the transcription of genes involved in the biosynthesis and metabolism of noradrenaline. Previous work has shown that Arix/Phox2a is a phosphoprotein, and the phosphorylated form of Arix/Phox2a exhibits poorer DNA-binding activity than does the dephosphorylated form. Here, we demonstrate that Arix/Phox2a is phosphorylated by extracellular signal-related kinase (ERK)1/2 at two sites within the N-terminal transactivation domain. The phosphorylation level of Arix in cultured SH-SY5Y neuroblastoma cells is reduced when cells are treated with the mitogen activated protein kinase kinase 1 (MEK1) inhibitor UO126. Treatment of sympathetic neurons with the MEK1 inhibitor, PD98059, results in an elevation of mRNAs encoding noradrenergic proteins, dopamine beta-hydroxylase (DBH) and norepinephrine transporter (NET), but not tyrosine hydroyxlase (TH). Treatment of neuroblastoma cultures with PD98059 increases the interaction of Arix with DBH and NET genes, but not the TH gene. Together, these results suggest that phosphorylation of Arix by ERK1/2 inhibits its ability to interact with target genes, and that both specificity of expression and modulation by external stimuli are monitored through the same transcription factor.

BMP4 supports noradrenergic differentiation by a PKA-dependent mechanism

Differentiation of neural crest-derived noradrenergic neurons depends upon signaling mediated downstream of BMP binding to cognate receptors and involving cAMP. Compiled data from many groups suggest that neurogenesis and cell type-specific noradrenergic marker gene regulation is coordinated through the expression and function of the basic helix-loop-helix DNA binding protein HAND2 and the homeodomain DNA binding protein Phox2a. However, information detailing how BMP-mediated signaling and signaling through cAMP are coordinated has been lacking. We now provide compelling data suggesting that differentiation of noradrenergic sympathetic ganglion neurons depends upon both canonical and non-canonical pathways of BMP-mediated signaling. The non-canonical pathway involves the activation of protein kinase A (PKA) independent of cAMP. This is a novel mechanism in neural crest-derived cells and is necessary to support neurogenesis as well as aspects of DBH promoter regulation involving HAND2 phosphorylation and dimerization. The expression of transcripts encoding HAND2 and Phox2a is regulated via canonical BMP signaling and thus affects both neurogenesis and cell type-specific gene expression. Interestingly, cAMP- and MapK-mediated signaling modulate specific target sites in both the canonical and non-canonical BMP pathways. Activity of MapK is required for HAND2 transcription and thus affects neurogenesis. Signaling affected by cAMP is necessary for the transcription of Phox2a as well as regulation of DBH promoter transactivation by Phox2a and HAND2. We suggest a comprehensive model that shows how BMP- and cAMP-mediated intracellular signaling integrate neurogenesis and cell type-specific noradrenergic marker gene expression and function.

Mechanisms and perspectives on differentiation of autonomic neurons

Neurons share many features in common but are distinguished by expression of phenotypic characteristics that define their specific function, location, or connectivity. One aspect of neuronal fate determination that has been extensively studied is that of neurotransmitter choice. The generation of diversity of neuronal subtypes within the developing nervous system involves integration of extrinsic and intrinsic instructive cues resulting in the expression of a core set of regulatory molecules. This review focuses on mechanisms of growth and transcription factor regulation in the generation of peripheral neural crest-derived neurons. Although the specification and differentiation of noradrenergic neurons are the focus, I have tried to integrate these into a larger picture providing a general roadmap for development of autonomic neurons. There is a core of DNA binding proteins required for the development of sympathetic, parasympathetic, and enteric neurons, including Phox2 and MASH1, whose specificity is regulated by the recruitment of additional transcriptional regulators in a subtype-specific manner. For noradrenergic neurons, the basic helix-loop-helix DNA binding protein HAND2 (dHAND) appears to serve this function. The studies reviewed here support the notion that neurotransmitter identity is closely linked to other aspects of neurogenesis and reveal a molecular mechanism to coordinate expression of pan-neuronal genes with cell type-specific genes.

Molecular cloning and characterization of the promoter region of the human Phox2b gene

The closely related homeodomain transcription factors, Phox2a and Phox2b, are restrictively expressed in central and peripheral noradrenergic (NA) neurons in an overlapping but distinct manner, and critically regulate the differentiation and neurotransmitter identity of NA neurons. The structure and function of the human Phox2a (hPhox2a) promoter has recently been reported. Towards the long-term goal of delineating the regulatory cascade of NA neuron differentiation, we isolated a human Phox2b (hPhox2b) genomic clone encompassing approximately 7.8 kb of the 5' upstream promoter region, the entire exon-intron structure and 4.5 kb of the 3' flanking region. Two transcription start sites are identified to reside 115 and 110 nucleotides upstream of the start codon, based on both primer extension and 5'-rapid amplification of the cDNA ends analyses. In addition, transient transfection assays indicate that 1.1 kb or longer upstream sequences of the hPhox2b gene may confer cell type-specific gene expression in certain, but not all cell lines. The promoter activity of the hPhox2b gene is modestly transactivated by forced co-expression of Phox2b and the hPhox2b gene promoter contains a high-affinity binding site at -320 to -295 bp. This study provides a frame to further elucidate the molecular mechanisms underlying the regulation of Phox2a and Phox2b gene expression and its relation to NA differentiation.

Classification and surgical management of patients with familial and sporadic forms of congenital fibrosis of the extraocular muscles

PURPOSE

To outline the clinical features and surgical treatment of patients with familial and sporadic (simplex) forms of congenital fibrosis of extraocular muscles (CFEOM) from 2 countries, and to classify them according to phenotype and mode of inheritance.

DESIGN

Observational and experimental study.

METHODS

Twenty-eight affected individuals from 20 families with familial or sporadic CFEOM underwent assessment of ocular motility, visual acuity, slit-lamp biomicroscopy, tonometry, and ophthalmoscopy. Seventeen patients had a variety of eye muscle procedures and ptosis repair.

RESULTS

There were 1 Iranian family with autosomal dominant CFEOM, 4 Iranian families with autosomal recessive disease, and 15 simplex cases with various CFEOM phenotypes. Two simplex patients had unilateral disease. All other cases were bilateral. Inferior rectus recession improved hypotropia and Bell's phenomenon in the patients with infraducted eyes and chin elevation. Horizontal muscle recession, sometimes combined with opposite muscle resection, corrected horizontal strabismus satisfactorily in most cases. Ptosis was repaired by frontalis sling and/or levator resection.

CONCLUSION

Definite recessive CFEOM was present only in Iranian patients. American patients had the classic phenotype of dominant CFEOM, which was also observed in some of the Iranian patients. The surgical management of patients with CFEOM is challenging. Correction of vertical and horizontal strabismus was addressed using large muscle recessions. Ptosis repair should aim at placing the lid level 1 to 2 mm above the pupil in the primary position to avoid exposure keratopathy.

Effects of positively selected sequence variations in human and Macaca fascicularis beta-defensins 2 on antimicrobial activity

The evolution of orthologous genes coding for beta-defensin 2 (BD2) in primates has been subject to positive selection during the divergence of the platyrrhines from the catarrhines and of the Cercopithecidae from the Hylobatidae, great apes, and humans. Three peptides have been selected for a functional analysis of the effects of sequence variations on the direct antimicrobial activity: human BD2 (hBD2), Macaca fascicularis BD2 (mfaBD2), and a variant of the human peptide lacking Asp(4), (-D)hBD2, which is characteristic only of the human/great ape peptides. hBD2 and mfaBD2 showed a significant difference in specificity, the former being more active towards Escherichia coli and the later towards Staphylococcus aureus and Candida albicans. Asp(4) in the human peptide appears to be important, as (-D)hBD2 was less structured and had a markedly lower antimicrobial activity. The evolution of beta-defensin 2 in primates may thus have been driven, at least in part, by different environmental pressures so as to modulate antimicrobial activity.

Interaction of Mash1 and Phox2b in sympathetic neuron development

The transcription factors Mash1 and Phox2b are both essential for sympathetic neuron development. To understand in more detail their function and interaction, Phox2b and Mash1 were ectopically expressed in vivo, in peripheral nerve precursors. Here, we demonstrate that the Phox2b-induced generation of ectopic noradrenergic neurons in chick peripheral nerve involves the induction of Cash1, the chick homolog of Mash1. All Phox2-induced neurons coexpress the noradrenergic marker genes TH and DBH. Conversely, Mash1 induces neuronal differentiation characterized by the expression of generic neuronal genes SCG10, Hu and NF160; however, only a subpopulation of these neurons also displays an autonomic, noradrenergic phenotype. This context-dependent action of Mash1 implicates autonomic codeterminants, required for noradrenergic differentiation in response to Mash1. In contrast, Phox2b coordinates generic and noradrenergic gene expression, recruiting Mash1/Cash1, which may have a major function in the control of pan-neuronal gene expression during noradrenergic neuron development.

ARIX gene polymorphisms in patients with congenital superior oblique muscle palsy

AIM

To identify ARIX gene polymorphisms in patients with congenital superior oblique muscle palsy and to find the relation between the ARIX gene and congenital superior oblique muscle palsy.

METHODS

The three exons of the ARIX gene were sequenced by genomic DNA amplification with polymerase chain reaction (PCR) and direct sequencing in 15 patients with superior oblique muscle palsy (13 with congenital and two with acquired palsy) and 54 normal individuals. PCR products cloned into plasmids were also sequenced. A family with father and a daughter each having congenital superior oblique muscle palsy was also involved in this study.

RESULTS

Four patients with congenital superior oblique muscle palsy carried heterozygous nucleotide changes in the ARIX gene. One patient with the absence of the superior oblique muscle had T7C in the 5'-UTR of the exon 1 and C-44A in the promoter region, both of which were located on the same strand. Another unrelated patient with congenital superior oblique muscle palsy had C76G in the 5'-UTR of the exon 1 and C-9A in the promoter region on the same strand. G153A in the 5'-UTR of exon 1 was found in common in two affected members of a family with congenital superior oblique muscle palsy. This G153A in the 5'-UTR of exon 1 was also present in four unrelated normal individuals. No other heterozygous nucleotide changes were found in normal individuals.

CONCLUSIONS

The nucleotide change (G153A) in the 5'-UTR of exon 1 co-segregated with congenital superior oblique muscle palsy in one family. Four other nucleotide changes in the exon 1 or the promoter region were found only in patients with congenital superior oblique muscle palsy. These nucleotide polymorphisms may be one of the risk factors for the development of congenital superior oblique muscle palsy.

HAND2 synergistically enhances transcription of dopamine-beta-hydroxylase in the presence of Phox2a

Noradrenergic neuronal identity and differentiation are controlled by cascades of transcription factors acting downstream of BMP4, including the basic helix-loop-helix DNA binding protein HAND2 and the homeodomain factor Phox2a. Dopamine-beta-hydroxylase (DBH) is the penultimate enzyme required for synthesis of norepinephrine and is thus a noradrenergic cell type-specific marker. We have examined the interaction of HAND2 and Phox2a at the DBH promoter. Using transient transfection of P19 or NT-2 cells, HAND2 is shown to synergistically enhance Phox2a-driven transcriptional activity at the DBH promoter, an effect that is enhanced by cAMP. While mutation of the Phox2a homeodomain binding sites HD1, HD2, and HD3 results in the loss of HAND2/Phox2a transactivation of DBH, it is the interaction of HAND2/Phox2a at the CRE/AP1-HD1/2 domains in the DBH enhancer that are required for synergistic activation by HAND2. We find that HAND2 functions as a transcriptional activator without directly binding to E-box sequences in the DBH promoter, suggesting that HAND2-mediated DBH activity occurs by protein-protein interactions with other transcriptional regulators. Although we were unable to detect interaction of HAND2 and Phox2a in IP/Western blots, HAND2 synergistic activation of DBH is blocked by E1A, suggesting that HAND2 interacts with CBP (cAMP response element binding protein) in this transcriptional complex. In the presence of the putative HAND2 dimerization partner, E12, synergistic activation of DBH transcription is titrated away, suggesting that HAND2 does not functionally dimerize with E12 in the DBH transcription complex. Our data suggest that HAND2 regulates cell type-specific expression of norepinephrine in concert with Phox2a by a novel mechanism.

The interaction between dHAND and Arix at the dopamine beta-hydroxylase promoter region is independent of direct dHAND binding to DNA

Dopamine beta-hydroxylase (DBH) catalyzes the production of norepinephrine, and its expression defines the noradrenergic phenotype. Transcription factors dHAND, a basic helix-loop-helix protein, and Arix/Phox2a, a homeoprotein, have been demonstrated to play a role in the differentiation and maintenance of catecholaminergic neurons. Three Arix regulatory sites have been identified in the DBH promoter proximal region, but there is no such evidence for dHAND. Cotransfection with a DBH promoter-luciferase reporter construct plus dHAND or dHAND-E12 expression plasmids did not alter luciferase activity, whereas transfection with Arix resulted in a 2.5-fold stimulation of luciferase activity. However, a 5.5-fold increase was observed when Arix and dHAND were combined, and an 8-fold level of expression was observed when Arix was transfected with a dHAND mutant lacking the basic DNA-binding domain. When the homeodomain sites in the DBH promoter proximal region were mutated, all activity was lost, demonstrating dependence upon Arix-DNA interaction for transcriptional activation. In electrophoretic mobility shift assays, the addition of dHAND decreased the amount of Arix needed to elicit a mobility shift with the DBH homeodomain sites, and the dHAND basic mutant potentiated Arix binding in a manner similar to wild-type dHAND. The dHAND-Arix complex was dissociated upon the addition of an unlabeled competitor containing a homeodomain, but not upon the addition of a competitor containing E-boxes. Arix coprecipitated with antisera directed against recombinant dHAND, demonstrating direct protein-protein interactions. These results indicate that the activation of the DBH promoter by Arix is potentiated by dHAND via a mechanism independent of a direct interaction of dHAND with DNA.

Cytokine suppression of dopamine-beta-hydroxylase by extracellular signal-regulated kinase-dependent and -independent pathways

Cholinergic differentiation factors (CDFs) suppress noradrenergic properties and induce cholinergic properties in sympathetic neurons. The CDFs leukemia inhibitory factor (LIF) and ciliary neurotrophic factor (CNTF) bind to a LIFR.gp130 receptor complex to activate Jak/signal transducers and activators of transcription and Ras/mitogen-activated protein kinases signaling pathways. Little is known about how these differentiation factors suppress noradrenergic properties. We used sympathetic neurons and SK-N-BE(2)M17 neuroblastoma cells to investigate CDF down-regulation of the norepinephrine synthetic enzyme dopamine-beta-hydroxylase (DBH). LIF and CNTF activated extracellular signal-regulated kinases (ERKs) 1 and 2 but not p38 or Jun N-terminal kinases in both cell types. Preventing ERK activation with PD98059 blocked CNTF suppression of DBH protein in sympathetic neurons but did not prevent the loss of DBH mRNA. CNTF decreased transcription of a DBH promoter-luciferase reporter construct in SK-N-BE(2)M17 cells, and this was also ERK-independent. Cytokine inhibition of DBH promoter activity did not require a silencer element but was prevented by overexpression of the transcriptional activator Phox2a. Inhibiting ERK activation increased basal DBH transcription in SK-N-BE(2)M17 cells, and DBH mRNA in sympathetic neurons. Transfection of Phox2a into PD98059-treated M17 cells resulted in a synergistic increase in DBH promoter activity compared with Phox2a or PD98059 alone. These data suggest that CDFs down-regulate DBH protein via an ERK-dependent pathway but inhibit DBH gene expression through an ERK-independent pathway. They further suggest that ERK activity inhibits basal DBH gene expression.

Molecular control of ciliary neuron development: BMPs and downstream transcriptional control in the parasympathetic lineage

The generation of noradrenergic sympathetic neurons is controlled by BMPs and the downstream transcription factors Mash1, Phox2b, Phox2a and dHand. We examined the role of these signals in developing cholinergic parasympathetic neurons. The expression of Mash1 (Cash1), Phox2b and Phox2a in the chick ciliary ganglion is followed by the sequential expression of panneuronal, noradrenergic and cholinergic marker genes. BMPs are expressed at the site where ciliary ganglia form and are essential and sufficient for ciliary neuron development. Unlike sympathetic neurons, ciliary neurons do not express dHand; noradrenergic gene expression is eventually lost but can be maintained by ectopic dHand expression. Together, these results demonstrate a common BMP dependence of sympathetic neurons and parasympathetic ciliary neurons and implicate dHand in the maintenance of noradrenergic gene expression in the autonomic nervous system.

Phox2 genes - from patterning to connectivity

In the developing brain, many transcription factors are expressed in complex patterns and dynamics, and drive the differentiation of many classes of neurons. How does the spatio-temporal landscape of transcription factor expression map onto the bewildering variety of neuronal types, and, for each of them, the variety of developmental stages they go through? In other words, what is the logic in the transcriptional control of neuronal differentiation? Here, we review what recent work on the two neuronal-type-specific transcription factors Phox2a and Phox2b has contributed to our understanding of this broad question.

Specification of catecholaminergic and serotonergic neurons

The specification of neurotransmitter phenotype is an important aspect of neuronal fate determination. Substantial progress has been made in uncovering key extracellular signals and transcriptional regulators that control the mode of neurotransmission in several model systems, among which catecholaminergic and serotonergic neurons feature prominently. Here, we review our current knowledge of the regulatory circuits that direct neurotransmitter choice, and discuss the development of well-studied types of catecholaminergic and serotonergic neurons. One emerging concept is that different types of neuron use a similar core programme to control shared modes of neurotransmission, but recruit different factors that are specific for each neuronal type. Another is that most factors that specify neurotransmitter identity also control other features of the neuronal phenotype.

The paired-like homeodomain protein, Arix, mediates protein kinase A-stimulated dopamine beta-hydroxylase gene transcription through its phosphorylation status

The homeodomain transcription factor Arix/Phox2a plays a critical role in the specification of noradrenergic neurons by inducing the expression of dopamine beta-hydroxylase (DBH), the terminal enzyme for noradrenaline biosynthesis. In reporter assays, Arix together with activation of cAMP-dependent protein kinase (PKA) potentiates DBH gene transcription. We have evaluated whether post-translational modification of Arix regulates PKA-mediated DBH gene transcription. We found that Arix is constitutively phosphorylated in vivo at the basal level and that the phosphorylation level is substantially decreased upon stimulation of the PKA pathway. The change in the Arix phosphorylation state coincides with DNA binding activity of Arix. Treatment of cells with forskolin results in a robust enhancement of the DNA binding of Arix, which is reversed by treatment with serine/threonine and tyrosine phosphatase inhibitors. Consistent with the DNA binding activity of Arix, treatment of cultured cells with phosphatase inhibitors diminishes transcriptional activation with Arix plus forskolin. Amino acid analysis demonstrates the presence of phosphoserine within Arix. The results collectively suggest that dephosphorylation of Arix is a necessary event to fully activate PKA-mediated DBH transcription. Thus, the present study demonstrates that Arix can integrate extrinsic signals through post-translational modification, regulating DBH gene transcription in response to activation of the PKA pathway.

Applications of molecular genetics to the understanding of congenital ocular motility disorders

The congenital fibrosis syndromes (CFS), including congenital fibrosis of the extraocular muscles (CFEOM) and Duane syndrome (DS), are rare congenital strabismus syndromes that present with nonprogressive restrictive ophthalmoplegia with or without ptosis. Although historically believed to result from primary extraocular muscle (EOM) fibrosis, our laboratory's work is based on the hypothesis that these disorders result from distinct, but analogous, developmental defects of the oculomotor (nIII), trochlear (nIV), and abducens (nVI) nuclei. We have defined three inherited CFEOM phenotypes (CFEOM1-3) and have mapped each phenotype to a distinct genetic locus (FEOM1-3). Individuals with CFEOM1 are born with bilateral ptosis and both eyes fixed in a downward position with absent upgaze and aberrant horizontal gaze. This disorder maps to the FEOM1 locus on chromosome 12cen.(1,2) Neuropathology studies of CFEOM1 reveal the absence of the superior division of oculomotor nerve and its corresponding alpha motor neurons in the midbrain, with abnormalities of target EOMs.(3) These neuropathology findings parallel those previously identified in Duane syndrome, in which there is an absence of nVI and the abducens nerve.(4,5) Individuals with CFEOM2 are born with bilateral ptosis and exotropia. This atypical form of CFEOM maps to the FEOM2 locus on chromosome 11q13 and results from mutations in ARIX (PHOX2A).(6,7) ARIX encodes a homeodomain transcription factor protein previously shown to be required for nIII/nIV development in mouse and zebrafish.(8,9) Together, these findings support the hypothesis that the congenital fibrosis syndromes result from parallel defects in nIII, nIV, and nVI nuclear development. Functional studies of the CFEOM genes should provide additional insight into the unique features of the extraocular lower motor neuron axis in health and disease. (For full (refs. 1-9), see reference list of the main paper.)

A direct role of the homeodomain proteins Phox2a/2b in noradrenaline neurotransmitter identity determination

Development of noraderenergic (NA) neurons in the vertebrate brain is dependent on the homeodomain proteins Phox2a and 2b. Here, we show that Phox2a directly controls the NA identity by activating NA-synthesizing dopamine beta-hydroxylase (DBH ) gene. Single point mutations in the homeodomain of Phox2a resulted in a failure to transactivate the DBH promoter in vitro and resulted in the loss of NA neurons in vivo. In addition, injection of Phox2a-specific antisense oligonucleotide induced the loss of NA neurons in developing zebrafish. Phox2a and 2b activate the DBH promoter and bind to three domains (PBD1-3). PBD1 is composed of two overlapping sites with which monomers of Phox2a can interact. In contrast, PBD2 and 3 interact with the dimeric form of Phox2a. Mutations in three or four, but not one or two, of the binding sites completely abolished activation of the DBH promoter by Phox2a or 2b, while the conversion of PBD3 to a consensus motif (ATTA) improved the DBH promoter activity by > 10-fold. Taken together, these findings establish that Phox2a and 2b control the development of NA neurons in part by directly transactivating DBH transcription through interactions with four binding sites clustered in the proximal promoter.

Structural and functional characterization of the 5' upstream promoter of the human Phox2a gene: possible direct transactivation by transcription factor Phox2b

The specification of neurotransmitter identity is a critical step in neural development. Recent progresses have indicated that the closely related homeodomain factors Phox2a and 2b are essential for development of noradrenergic (NA) neuron differentiation, and may directly determine the neurotransmitter identity. With a long-term goal of understanding the regulatory cascade of NA phenotype determination, we isolated and characterized a hPhox2a genomic clone encompassing approximately 7.5 kb of the 5' upstream promoter region, the entire exon-intron structure, and approximately 4 kb of the 3' flanking region. Using mRNAs isolated from the Phox2a-expressing human cell line, both primer extension and 5'-rapid amplification of cDNA ends analyses identified a single transcription start site that resides 172 nucleotides upstream of the start codon. The transcription start site was preceded by a TATA-like sequence motif and transcripts from this site contained an additional G residue at the 5' position, supporting the authenticity of this site as the transcriptional start site of hPhox2a. We assembled hPhox2a-luciferase reporter constructs containing different lengths of the 5' upstream sequences. Transient transfection assays of these reporter constructs in both hPhox2a-positive and -negative cell lines show that 1.3-kb or longer upstream sequences of the hPhox2a gene may confer NA cell-specific reporter gene expression. Furthermore, cotransfection assays in the Phox2a-negative HeLa cell line show that forced expression of Phox2b, but not that of Phox2a or MASH1, significantly transactivates the transcriptional activity of hPhox2a. This study will provide a frame to further delineate the regulatory cascade of NA neuron differentiation.

Homozygous mutations in ARIX(PHOX2A) result in congenital fibrosis of the extraocular muscles type 2

Isolated strabismus affects 1-5% of the general population. Most forms of strabismus are multifactorial in origin; although there is probably an inherited component, the genetics of these disorders remain unclear. The congenital fibrosis syndromes (CFS) represent a subset of monogenic isolated strabismic disorders that are characterized by restrictive ophthalmoplegia, and include congenital fibrosis of the extraocular muscles (CFEOM) and Duane syndrome (DURS). Neuropathologic studies indicate that these disorders may result from the maldevelopment of the oculomotor (nIII), trochlear (nIV) and abducens (nVI) cranial nerve nuclei. To date, five CFS loci have been mapped (FEOM1, FEOM2, FEOM3, DURS1 and DURS2), but no genes have been identified. Here, we report three mutations in ARIX (also known as PHOX2A) in four CFEOM2 pedigrees. ARIX encodes a homeodomain transcription factor protein previously shown to be required for nIII/nIV development in mouse and zebrafish. Two of the mutations are predicted to disrupt splicing, whereas the third alters an amino acid within the conserved brachyury-like domain. These findings confirm the hypothesis that CFEOM2 results from the abnormal development of nIII/nIV (ref. 7) and emphasize a critical role for ARIX in the development of these midbrain motor nuclei.

Two signal transduction pathways involved in the catecholaminergic differentiation of avian neural crest-derived cells in vitro

Molecules derived from the neural tube and found in chick embryo extract (CEE) and bone morphogenetic proteins (BMP) support the differentiation of neural crest-derived catecholaminergic (CA) neurons. We now report that intracellular signaling resulting in the activation of Map kinase (MapK) or translocation of Smad1 mediate the differentiation of CA neurons in response to CEE or BMP 4, respectively. The differentiation of CA neurons was significantly reduced by inhibiting MapK using PD98059 or by pan-specific blockade of tyrosine kinases using Herbimycin A. In the presence of BMP 4 and inhibitors of MapK signaling, differentiation of CA neurons was only moderately reduced. Independent of MapK, BMP 4 induced translocation of Smad1 from the cytosol to the nucleus and induced transcription of dHAND, a DNA binding protein required for the differentiation of CA neurons. The data suggest that CEE-derived factors and BMP4 support the differentiation of CA neurons via independent signaling pathways.

Pitx3 activates mouse tyrosine hydroxylase promoter via a high-affinity binding site

Tyrosine hydroxylase (TH) is the rate-limiting enzyme of dopamine and (nor)adrenaline biosynthesis. Regulation of its gene expression is complex and different regulatory mechanisms appear to be operative in various neuronal lineages. Pitx3, a homeodomain-containing transcription factor, has been cloned from neuronal tissues and, in the CNS, mouse Pitx3 is exclusively expressed in midbrain dopaminergic (MesDA) neurons from embryonic day 11 (E11). TH appears in these neurons at E11.5, consistent with a putative role of Pitx3 in TH transcription. We show that Pitx3 activates the TH promoter through direct interaction with a single high-affinity binding site within the promoter and that this site is sufficient for Pitx3 responsiveness. In contrast, we did not observe an effect of Nurr1, an orphan nuclear receptor essential for normal development of MesDA neurons, on TH promoter activity. Pitx3 activation of TH promoter activity appears to be cell-dependent suggesting that Pitx3 action may be modulated by other(s) regulatory mechanism(s) and factor(s).

Solution structure of the TAZ2 (CH3) domain of the transcriptional adaptor protein CBP

The TAZ2 (CH3) domain of the transcriptional adapter protein CBP has been implicated in direct functional interactions with numerous cellular transcription factors and viral oncoproteins. The solution structure of the TAZ2 domain of murine CBP has been determined by nuclear magnetic resonance (NMR). The protein adopts a novel helical fold stabilized by three zinc ions, each of which is bound to one histidine and three cysteine ligands in HCCC-type motifs. Each zinc-binding site is formed from the carboxy terminus of an alpha-helix, a short loop, and the amino terminus of the next alpha-helix. A peptide derived from the N-terminal transactivation domain of p53 binds specifically to one face of the TAZ2 domain. The close similarities between the TAZ2 and TAZ1 (CH1 domain of CBP/p300) sequences suggest that both domains will adopt similar three-dimensional structures.

Paired-like homeodomain proteins Phox2a/Arix and Phox2b/NBPhox have similar genetic organization and independently regulate dopamine beta-hydroxylase gene transcription

The homeodomain transcription factors Arix/Phox2a and NBPhox/Phox2b play a role in the specification of the noradrenergic phenotype of central and peripheral neurons. To better understand the functions of these two factors, we have compared the genetic organization, chromosomal location, and transcriptional regulatory properties of Arix and NBPhox. The gene structure is very similar, with each gene containing three exons and two introns, extending a total of approximately 5 kb. Arix and NBPhox are unlinked in human and mouse genomes. NBPhox is located on human Chromosome 4p12 and mouse Chromosome 5, while Arix is located on human Chromosome 11q13 and mouse Chromosome 7. Both proteins bind to three sites in the promoter proximal region of the rat dopamine beta-hydroxylase gene (DBH). In vitro, Arix and NBPhox form DNA-independent multimers and exhibit cooperative binding to the DB1 regulatory element, which contains two homeodomain recognition sites. Both proteins regulate transcription from the rat DBH promoter, and transcription is synergistically increased in the presence of the protein kinase A catalytic subunit (PKA) plus either Arix or NBPhox. The transcription factors exhibit similar concentration-dependent efficacies, and when they are coexpressed, transcription is stimulated to a value approximately equal to that seen with either factor alone. The N-terminal segment of Arix is essential for transcriptional regulatory activity, and this region bears 50% identity with NBPhox, suggesting a similar mechanism of transcriptional activation of the DBH gene. We conclude from this study that Arix and NBPhox exhibit indistinguishable and independent transcriptional regulatory properties on the DBH promoter.