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Sphingosine 1-phosphate (S1P) is a major bioactive lipid mediator in the vascular and immune system. Here, we have shown that inhibition of S1P signaling prevents blood-brain barrier (BBB) dysfunction after ischemia both in vitro and in vivo. In the in vitro BBB models, oxygen-glucose deprivation and reoxygenation (OGD/R) enhanced the expression of an S1P synthesizing enzyme (Sphk1) and S1P transporters (Abca1, Spns2), increasing S1P in culture media. Inhibitors of Sphk1 (SKI-II) or Abca1 (probucol) attenuated the decrease in transendothelial electrical resistance and the increase in permeability caused by OGD/R. In the middle cerebral artery occlusion and reperfusion (MCAO/R) model of mice, probucol administration after MCAO operation reduced the infarction area and vascular leakage, preserving the integrity of tight junction proteins. Furthermore, MCAO/R caused activation of STAT3, a downstream mediator of S1P signaling, which was suppressed by postoperative probucol administration. Accordingly, S1P activated STAT3, both in cultured vascular endothelial cells and pericytes, and STAT3 signaling inhibitor (Stattic) protected BBB dysfunction in OGD/R-treated in vitro BBB models. These results suggest that inhibition of S1P signaling is a strategy to treat BBB impairment after cerebral ischemia and highlight the potential alternative use of probucol, a classical anti-hyperlipidemic drug, for emergency treatment of stroke.

Culture models of the blood-brain barrier (BBB) are important research tools. Their role in the preclinical phase of drug development to estimate the permeability for potential neuropharmaceuticals is especially relevant. Since species differences in BBB transport systems exist, primate models are considered as predictive for drug transport to brain in humans. Based on our previous expertise we have developed and characterized a non-human primate co-culture BBB model using primary cultures of monkey brain endothelial cells, rat brain pericytes, and rat astrocytes. Monkey brain endothelial cells in the presence of both pericytes and astrocytes (EPA model) expressed enhanced barrier properties and increased levels of tight junction proteins occludin, claudin-5, and ZO-1. Co-culture conditions also elevated the expression of key BBB influx and efflux transporters, including glucose transporter-1, MFSD2A, ABCB1, and ABCG2. The correlation between the endothelial permeability coefficients of 10 well known drugs was higher (R2 = 0.8788) when the monkey and rat BBB culture models were compared than when the monkey culture model was compared to mouse in vivo data (R2 = 0.6619), hinting at transporter differences. The applicability of the new non-human primate model in drug discovery has been proven in several studies.

LRFN2 encodes a synaptic adhesion-like molecule that physically interacts with N-methyl-D-aspartate (NMDA) receptor 1 and its scaffold proteins. Previous studies in humans and mice have demonstrated its genetic association with neurodevelopmental disorders such as learning deficiency and autism. In this study, we showed that Lrfn2-deficient (KO) mice exhibit abnormalities of erythropoietic systems due to altered NMDA receptor function. In mature Lrfn2 KO male mice, peripheral blood tests showed multilineage abnormalities, including normocytic erythrocythemia, and reduced platelet volume. Colony forming unit assay using bone marrow cells revealed decreases in the counts of erythrocyte progenitors (CFU-E) as well as granulocytes and monocyte progenitors (CFU-GM). Whole bone marrow cell staining showed that serum erythropoietin (EPO) level was decreased and EPO receptor-like immunoreactivity was increased. Flow cytometry analysis of bone marrow cells revealed increased early erythroblast count and increased transferrin receptor expression in late erythroblasts. Further, we found that late erythroblasts in Lrfn2 KO exhibited defective NMDA receptor-mediated calcium influx, which was inhibited by the NMDA receptor antagonist MK801. These results indicate that Lrfn2 has biphasic roles in hematopoiesis and is associated with the functional integrity of NMDA receptors in hematopoietic cells. Furthermore, taken together with previous studies that showed the involvement of NMDA receptors in hematopoiesis, the results of this study indicate that Lrfn2 may regulate erythropoiesis through its regulatory activity on NMDA receptors., PLoS ONE, 16(1), art.no.245624; 2021

Zic3 encodes a zinc finger protein essential for the development of meso-ectodermal tissues. In mammals, Zic3 has important roles in the development of neural tube, axial skeletons, left-right body axis, and in maintaining pluripotency of ES cells. Here we characterized cis-regulatory elements required for Zic3 expression. Enhancer activities of human-chicken-conserved noncoding sequences around Zic1 and Zic3 were screened using chick whole-embryo electroporation. We identified enhancers for meso-ectodermal tissues. Among them, a mesodermal enhancer (Zic3-ME) in distant 3′ flanking showed robust enhancement of reporter gene expression in the mesodermal tissue of chicken and mouse embryos, and was required for mesodermal Zic3 expression in mice. Zic3-ME minimal core region is included in the DNase hypersensitive region of ES cells, mesoderm, and neural progenitors, and was bound by T (Brachyury), Eomes, Lef1, Nanog, Oct4, and Zic2. Zic3-ME is derived from an ancestral sequence shared with a sequence encoding a mitochondrial enzyme. These results indicate that Zic3-ME is an integrated cis-regulatory element essential for the proper expression of Zic3 in vertebrates, serving as a hub for a gene regulatory network including Zic3.

Zic family genes encode C2H2-type zinc finger proteins that act as critical toolkit proteins in the metazoan body plan establishment. In this study, we searched evolutionarily conserved domains (CDs) among 121 Zic protein sequences from 22 animal phyla and 40 classes, and addressed their evolutionary significance. The collected sequences included those from poriferans and orthonectids. We discovered seven new CDs, CD0-CD6, (in order from the N- to C-terminus) using the most conserved Zic protein sequences from Deuterostomia (Hemichordata and Cephalochordata), Lophotrochozoa (Cephalopoda and Brachiopoda), and Ecdysozoa (Chelicerata and Priapulida). Subsequently, we analyzed the evolutionary history of Zic CDs including the known CDs (ZOC, ZFD, ZFNC, and ZFCC). All Zic CDs are predicted to have existed in a bilaterian ancestor. During evolution, they have degenerated in a taxa-selective manner with significant correlations among CDs. The N terminal CD (CD0) was largely lost, but was observed in Brachiopoda, Priapulida, Hemichordata, Echinodermata, and Cephalochordata, and the C terminal CD (CD6) was highly conserved in conserved-type-Zic possessing taxa, but was truncated in vertebrate Zic gene paralogues (Zic1/2/3), generating a vertebrate-specific C-terminus critical for transcriptional regulation. ZOC was preferentially conserved in insects and in an anthozoan paralogue, and it was bound to the homeodomain transcription factor Msx in a phylogenetically conserved manner. Accordingly, the extent of divergence of Msx and Zic CDs from their respective bilaterian ancestors is strongly correlated. These results suggest that coordinated divergence among the toolkit CDs and among toolkit proteins is involved in the divergence of metazoan body plans.

Zic genes are strongly expressed in the cerebellum. This feature leads to their initial identification and their name "zic," as the abbreviation of "zinc finger protein of the cerebellum." Zic gene function in cerebellar development has been investigated mainly in mice. However, association of heterozygous loss of ZIC1 and ZIC4 with Dandy-Walker malformation, a structural birth defect of the human cerebellum, highlights the clinical relevance of these studies. Two proposed mechanisms for Zic-mediated cerebellar developmental control have been documented: regulation of neuronal progenitor proliferation-differentiation and the patterning of the cerebellar primordium. Clinical studies have also revealed that ZIC1 gain of function mutations contribute to coronal craniosynostosis, a rare skull malformation. The molecular pathways contributing to these phenotypes are not fully explored; however, embryonic interactions with sonic hedgehog signaling, retinoic acid signaling, and TGFβ signaling have been described during mouse cerebellar development. Further, Zic1/2 target a multitude of genes associated with cerebellar granule cell maturation during postnatal mouse cerebellar development.

Proper functions of Zic proteins are essential for animals in health and disease. Here, we summarize our current understanding of the molecular properties and functions of the Zic family across animal species and paralog subtypes. Zics are basic proteins with some posttranslational modifications and can move to the cell nucleus via importin- and CRM1-based nucleocytoplasmic shuttling mechanisms. Degradation is mediated by the ubiquitin proteasome system. Many Zic proteins are capable of binding to two types of target DNA sequences (CTGCTG-core-type and GC-stretch-type). Recent chromatin immunoprecipitation assays showed that CTGCTG-core-type target sequences are enriched in enhancers. Nonetheless, the DNA binding is not always required for transcriptional regulation by Zic proteins. On the other hand, Zic proteins bind many proteins including transcription factors (Gli1-3, Tcf1 or Tcf4, Smad2 or Smad3, Oct4, Pax3, Cdx, and SRF), chromatin-remodeling factors (NuRD and NURF), and other nuclear enzymes (DNA-PK, PARP1, and RNA helicase A). Zic family-mediated gene expression control involves both their actions near the transcription start site and those affecting the global gene expression via binding to enhancers. Although Zic proteins perform essential functions in transcriptional regulation of Oct4 and Nanog expression via their promoters, recent genome-wide analyses of the Zic-binding sites and their downstream targets indicate that Zic proteins are associated with distant regulatory elements and are the critical enhancer-priming nuclear regulators in organismal development. Chromatin-remodeling complexes such as NuRD and NURF that interact with Zic proteins have been shown to participate in Zic-mediated enhancer regulation.

Zic family proteins have been investigated in various biomedical studies. Here we summarize the contact points between Zic proteins and recent medical research. The topics cover a wide range, reflecting the pleiotropic roles of these proteins in early embryogenesis and organogenesis. Zic1, Zic2, and Zic3 proteins play important roles in the development of axial and limb bones, and of muscles, among the derivatives of the notochord and somites. Zic1 is involved in bone's response to mechanical stress, and it also serves as a marker specific for brown adipocytes. Zic1, Zic2, Zic3, and Zic5 proteins are required for the development of neural crest derivatives, including the meningeal membrane and facial bones, and deficiency of these proteins causes cortical lamination defects resembling those in type II lissencephaly. In vascular systems, Zic3 is associated not only with normal cardiovascular development, failure of which causes congenital heart anomalies, but also controls maturation of the blood-brain barrier. Zic1 is also expressed in the brain pericytes possessing stem cell properties that control the blood-brain barrier activity and capillary hemodynamic responses. The possible involvement of Zic proteins in neuropsychiatric disorders has been indicated by the analyses of mutant mice behaviors. Zic1 and Zic3 mutant mice show hypotonia and decreased locomotor activities. Zic2 hypomorphic mutant mice exhibit schizophrenia-related behavioral abnormalities such as cognitive dysfunction and impaired sensorimotor gating and social behaviors, and ZIC2 mutations found in schizophrenia patients included a severely functionally defective one. Based on these facts, the application of Zic protein activities in translational medicine might be considered.

Zic family genes encode five C2H2-type zinc finger domain-containing proteins that have many roles in animal development and maintenance. Recent phylogenetic analyses showed that Zic family genes are distributed in metazoans (multicellular animals), except Porifera (sponges) and Ctenophora (comb jellies). The sequence comparisons revealed that the zinc finger domains were absolutely conserved among the Zic family genes. Zic zinc finger domains are similar to, but distinct from those of the Gli, Glis, and Nkl gene family, and these zinc finger protein families are proposed to have been derived from a common ancestor gene. The Gli-Glis-Nkl-Zic superfamily and some other eukaryotic zinc finger proteins share a tandem CWCH2 (tCWCH2) motif, a hallmark for inter-zinc finger interaction between two adjacent C2H2 zinc fingers. In Zic family proteins, there exist additional evolutionally conserved domains known as ZOC and ZFNC, both of which may have appeared before cnidarian-bilaterian divergence. Comparison of the exon-intron boundaries in the Zic zinc finger domains revealed an intron (A-intron) that was absolutely conserved in bilaterians (metazoans with bilateral symmetry) and a placozoan (a simple nonparasitic metazoan). In vertebrates, there are five to seven Zic paralogs among which Zic1, Zic2, and Zic3 are generated through a tandem gene duplication and carboxy-terminal truncation in a vertebrate common ancestor, sharing a conserved carboxy-terminal sequence. Several hypotheses have been proposed to explain the Zic family phylogeny, including their origin, unique features in the first and second zinc finger motif, evolution of the nuclear localization signal, significance of the animal taxa-selective degeneration, gene multiplication in the vertebrate lineage, and involvement in the evolutionary alteration of the animal body plan.

One of the causal genes for holoprosencephaly (HPE) is ZIC2 (HPE5). It belongs to the zinc finger protein of the cerebellum (Zic) family of genes that share a C2H2-type zinc finger domain, similar to the GLI family of genes. In order to clarify the role of Zic2 in gene regulation, we searched for its direct target genes using chromatin immunoprecipitation (ChIP). We identified TGIF1 (HPE4), another holoprosencephaly-causative gene in humans. We identified Zic2-binding sites (ZBS) on the 5′ flanking region of Tgif1 by in vitro DNA binding assays. ZBS were essential for Zic2-dependent transcriptional activation in reporter gene assays. Zic2 showed a higher affinity to ZBS than GLI-binding sequences. Zic2-binding to the cis-regulatory element near the Tgif1 promoter may be involved in the mechanism underlying forebrain development and incidences of HPE.

Zic family proteins have been investigated in various biomedical studies. Here we summarize the contact points between Zic proteins and recent medical research. The topics cover a wide range, reflecting the pleiotropic roles of these proteins in early embryogenesis and organogenesis. Zic1, Zic2, and Zic3 proteins play important roles in the development of axial and limb bones, and of muscles, among the derivatives of the notochord and somites. Zic1 is involved in bone’s response to mechanical stress, and it also serves as a marker specific for brown adipocytes. Zic1, Zic2, Zic3, and Zic5 proteins are required for the development of neural crest derivatives, including the meningeal membrane and facial bones, and deficiency of these proteins causes cortical lamination defects resembling those in type II lissencephaly. In vascular systems, Zic3 is associated not only with normal cardiovascular development, failure of which causes congenital heart anomalies, but also controls maturation of the blood-brain barrier. Zic1 is also expressed in the brain pericytes possessing stem cell properties that control the blood-brain barrier activity and capillary hemodynamic responses. The possible involvement of Zic proteins in neuropsychiatric disorders has been indicated by the analyses of mutant mice behaviors. Zic1 and Zic3 mutant mice show hypotonia and decreased locomotor activities. Zic2 hypomorphic mutant mice exhibit schizophrenia-related behavioral abnormalities such as cognitive dysfunction and impaired sensorimotor gating and social behaviors, and ZIC2 mutations found in schizophrenia patients included a severely functionally defective one. Based on these facts, the application of Zic protein activities in translational medicine might be considered.

Lophotrochozoa is a sister taxon of Ecdysozoa in the Protostomia that includes mollusks, annelids, brachiopods, and platyhelminths. Recent studies have clarified the structure, expression, and roles of lophotrochozoan Zic family genes. Zic genes in oligochaete annelid Tubifex tubifex (freshwater sludge worm) and polychaete annelid Capitella teleta (bristle worm) are commonly expressed in a subset of developing brain and mesoderm derivatives. The latter includes the naive mesoderm and the associated chaetal sacs in each body segment, although the segmentation processes differ between the two species. Furthermore, in brachiopod Terebratalia transversa (lamp shell), Zic is expressed in the anterior ectodermal domains and mesodermal derivatives, including those associated with the chaetal sacs. This result suggests the common involvement of Zic genes in the development of chaetae, a lophotrochozoan novelty acquired in the course of evolution. In addition, the highly simplified lophotrochozoan Dicyema acuticephalum (dicyemid mesozoan, a cephalopod endoparasite), which lost its gut, nervous system, and muscles during evolution, expresses its Zic genes in hermaphroditic gonads, highlighting the role of Zic genes in germ cell development. The role of Zic in head regeneration was revealed in studies on platyhelminth Schmidtea mediterranea (freshwater planarian). Planarian Zic expression was induced in a subpopulation of neoblasts that includes adult pluripotent stem cells. It is needed for head regeneration and production of an anterior signaling center. Suppression of Wnt-β-catenin signaling underlies Zic-mediated head regeneration, reminiscent of Wnt-β-catenin suppression by vertebrate Zic genes. Taken together, studies on the lophotrochozoan Zic genes are essential to understanding not only the roles of these genes in body plan evolution but also the molecular mechanism underlying adult stem cell regulation.

Proper functions of Zic proteins are essential for animals in health and disease. Here, we summarize our current understanding of the molecular properties and functions of the Zic family across animal species and paralog subtypes. Zics are basic proteins with some posttranslational modifications and can move to the cell nucleus via importin- and CRM1-based nucleocytoplasmic shuttling mechanisms. Degradation is mediated by the ubiquitin proteasome system. Many Zic proteins are capable of binding to two types of target DNA sequences (CTGCTG-core-type and GC-stretch-type). Recent chromatin immunoprecipitation assays showed that CTGCTG-core-type target sequences are enriched in enhancers. Nonetheless, the DNA binding is not always required for transcriptional regulation by Zic proteins. On the other hand, Zic proteins bind many proteins including transcription factors (Gli1–3, Tcf1 or Tcf4, Smad2 or Smad3, Oct4, Pax3, Cdx, and SRF), chromatin-remodeling factors (NuRD and NURF), and other nuclear enzymes (DNA-PK, PARP1, and RNA helicase A). Zic family–mediated gene expression control involves both their actions near the transcription start site and those affecting the global gene expression via binding to enhancers. Although Zic proteins perform essential functions in transcriptional regulation of Oct4 and Nanog expression via their promoters, recent genome-wide analyses of the Zic-binding sites and their downstream targets indicate that Zic proteins are associated with distant regulatory elements and are the critical enhancer-priming nuclear regulators in organismal development. Chromatin-remodeling complexes such as NuRD and NURF that interact with Zic proteins have been shown to participate in Zic-mediated enhancer regulation.

Monoamine oxidase A (MAO-A), the catabolic enzyme of norepinephrine and serotonin, plays a critical role in emotional and social behavior. However, the control and impact of endogenous MAO-A levels in the brain remains unknown. Here we show that the RING finger-type E3 ubiquitin ligase Rines/RNF180 regulates brain MAO-A subset, monoamine levels, and emotional behavior. Rines interacted with MAO-A and promoted its ubiquitination and degradation. Rines knock-out mice displayed impaired stress responses, enhanced anxiety, and affiliative behavior. Norepinephrine and serotonin levels were altered in the locus ceruleus, prefrontal cortex, and amygdala in either stressed or resting conditions, and MAO-A enzymatic activity was enhanced in the locus ceruleus in Rines knock-out mice. Treatment of Rines knock-out mice with MAO inhibitors showed genotype-specific effects on some of the abnormal affective behaviors. These results indicated that the control of emotional behavior by Rines is partly due to the regulation of MAO-A levels. These findings verify that Rines is a critical regulator of the monoaminergic system and emotional behavior and identify a promising candidate drug target for treating diseases associated with emotion.

Advances in mouse neural circuit genetics, brain atlases, and behavioral assays provide a powerful system for modeling the genetic basis of cognition and psychiatric disease. However, a critical limitation of this approach is how to achieve concordance of mouse neurobiology with the ultimate goal of understanding the human brain. Previously, the common marmoset has shown promise as a genetic model system toward the linking of mouse and human studies. However, the advent of marmoset transgenic approaches will require an understanding of developmental principles in marmoset compared to mouse. In this study, we used gene expression analysis in marmoset brain to pose a series of fundamental questions on cortical development and evolution for direct comparison to existing mouse brain atlas expression data. Most genes showed reliable conservation of expression between marmoset and mouse. However, certain markers had strikingly divergent expression patterns. The lateral geniculate nucleus and pulvinar in the thalamus showed diversification of genetic organization between marmoset and mouse, suggesting they share some similarity. In contrast, gene expression patterns in early visual cortical areas showed marmoset-specific expression. In prefrontal cortex, some markers labeled architectonic areas and layers distinct between mouse and marmoset. Core hippocampus was conserved, while afferent areas showed divergence. Together, these results indicate that existing cortical areas are genetically conserved between marmoset and mouse, while differences in areal parcellation, afferent diversification, and layer complexity are associated with specific genes. Collectively, we propose that gene expression patterns in marmoset brain reveal important clues to the principles underlying the molecular evolution of cortical and cognitive expansion.

Balanced development of excitatory and inhibitory synapses is required for normal brain function, and an imbalance in this development may underlie the pathogenesis of many neuropsychiatric disorders. Compared with the many identified trans-synaptic adhesion complexes that organize excitatory synapses, little is known about the organizers that are specific for inhibitory synapses. We found that Slit and NTRK-like family member 3 (Slitrk3) actS as a postsynaptic adhesion molecule that selectively regulates inhibitory synapse development via trans-interaction with axonal tyrosine phosphatase receptor PTPδ. When expressed in fibroblasts, Slitrk3 triggered only inhibitory presynaptic differentiation in contacting axons of co-cultured rat hippocampal neurons. Recombinant Slitrk3 preferentially localized to inhibitory postsynaptic sites. Slitrk3-deficient mice exhibited decreases in inhibitory, but not excitatory, synapse number and function in hippocampal CA1 neurons and exhibited increased seizure susceptibility and spontaneous epileptiform activity. Slitrk3 required trans-interaction with axonal PTPδ to induce inhibitory presynaptic differentiation. These results identify Slitrk3-PTPδ as an inhibitory-specific trans-synaptic organizing complex that is required for normal functional GABAergic synapse development.

Zic3 controls neuroectodermal differentiation and left–right patterning in Xenopus laevis embryos. Here we demonstrate that Zic3 can suppress Wnt/β-catenin signaling and control development of the notochord and Spemann's organizer. When we overexpressed Zic3 by injecting its RNA into the dorsal marginal zone of 2-cell-stage embryos, the embryos lost mesodermal dorsal midline structures and showed reduced expression of organizer markers (Siamois and Goosecoid) and a notochord marker (Xnot). Co-injection of Siamois RNA partially rescued the reduction of Xnot expression caused by Zic3 overexpression. Because the expression of Siamois in the organizer region is controlled by Wnt/β-catenin signaling, we subsequently examined the functional interaction between Zic3 and Wnt signaling. Co-injection of Xenopus Zic RNAs and β-catenin RNA with a reporter responsive to the Wnt/β-catenin cascade indicated that Zic1, Zic2, Zic3, Zic4, and Zic5 can all suppress β-catenin-mediated transcriptional activation. In addition, co-injection of Zic3 RNA inhibited the secondary axis formation caused by ventral-side injection of β-catenin RNA in Xenopus embryos. Zic3-mediated Wnt/β-catenin signal suppression required the nuclear localization of Zic3, and involved the reduction of β-catenin nuclear transport and enhancement of β-catenin degradation. Furthermore, Zic3 co-precipitated with Tcf1 (a β-catenin co-factor) and XIC (I-mfa domain containing factor required for dorsoanterior development). The findings in this report produce a novel system for fine-tuning of Wnt/β-catenin signaling.

Disruptions in ZIC3 cause heterotaxy, a congenital anomaly of the left-right axis. ZIC3 encodes a nuclear protein with a zinc finger (ZF) domain that contains five tandem C2H2 ZF motifs. Missense mutations in the first ZF motif (ZF1) result in defective nuclear localization, which may underlie the pathogenesis of heterotaxy. Here we revealed the structural and functional basis of the nuclear localization signal (NLS) of ZIC3 and investigated its relationship to the defect caused by ZF1 mutation. The ZIC3 NLS was located in the ZF2 and ZF3 regions, rather than ZF1. Several basic residues interspersed throughout these regions were responsible for the nuclear localization, but R320, K337 and R350 were particularly important. NMR structure analysis revealed that ZF1-4 had a similar structure to GLI ZF, and the basic side chains of the NLS clustered together in two regions on the protein surface, similar to classical bipartite NLSs. Among the residues for the ZF1 mutations, C253 and H286 were positioned for the metal chelation, whereas W255 was positioned in the hydrophobic core formed by ZF1 and ZF2. Tryptophan 255 was a highly conserved inter-finger connector and formed part of a structural motif (tandem CXW-C-H-H) that is shared with GLI, Glis and some fungal ZF proteins. Furthermore, we found that knockdown of Karyopherin alpha1/alpha6 impaired ZIC3 nuclear localization, and physical interactions between the NLS and the nuclear import adapter proteins were disturbed by mutations in the NLS but not by W255G. These results indicate that ZIC3 is imported into the cell nucleus by the Karyopherin (Importin) system and that the impaired nuclear localization by the ZF1 mutation is not due to a direct influence on the NLS.

Upstream stimulatory factors (USF) 1 and 2 are members of the basic helix–loop–helix leucine zipper transcription factor family. They are considered to play critical roles in cell-cycle regulation and chromatin remodeling. Their gene expression patterns are considered ubiquitous but have not been fully investigated in terms of embryogenesis. We examined the expression of the genes encoding USF1 and USF2 in Xenopus laevis during embryonic development. Expression of both genes was first detected as maternal transcripts and was observed continuously throughout development. However, in situ hybridization analysis revealed that the two genes were expressed differentially. In the late blastula, both genes were expressed in the blastocoel roof and marginal zone. At the gastrula stage, USF2 was strongly expressed in the sensorial layer of the ectoderm and in the mesoderm, whereas USF1 expression was hardly detectable. From the neurula stage onward, expression of both genes was markedly enhanced in the neural tissues, neural crest, eye and otic vesicle. However, spatial expression of the genes within the neural tube differed in that the strongest USF1 signals were observed in the lateral region of the basal plate and the strongest USF2 ones in the dorsal region of the neural tube. Expression of the two genes occurred in different mesoderm derivatives at the tailbud stage (USF1, somite; USF2, pronephros and lateral plate mesoderm of the tail region). USF1 was expressed in the notochord of the early neurula, but was lost at the stage.

Msx (/msh) family genes encode homeodomain (HD) proteins that control ontogeny in many animal species. We compared the structures of Msx genes from a wide range of Metazoa (Porifera, Cnidaria, Nematoda, Arthropoda, Tardigrada, Platyhelminthes, Mollusca, Brachiopoda, Annelida, Echiura, Echinodermata, Hemichordata, and Chordata) to gain an understanding of the role of these genes in phylogeny. Exon-intron boundary analysis suggested that the position of the intron located N-terminally to the HDs was widely conserved in all the genes examined, including those of cnidarians. Amino acid (aa) sequence comparison revealed 3 new evolutionarily conserved domains, as well as very strong conservation of the HDs. Two of the three domains were associated with Groucho-like protein binding in both a vertebrate and a cnidarian Msx homolog, suggesting that the interaction between Groucho-like proteins and Msx proteins was established in eumetazoan ancestors. Pairwise comparison among the collected HDs and their C-flanking aa sequences revealed that the degree of sequence conservation varied depending on the animal taxa from which the sequences were derived. Highly conserved Msx genes were identified in the Vertebrata, Cephalochordata, Hemichordata, Echinodermata, Mollusca, Brachiopoda, and Anthozoa. The wide distribution of the conserved sequences in the animal phylogenetic tree suggested that metazoan ancestors had already acquired a set of conserved domains of the current Msx family genes. Interestingly, although strongly conserved sequences were recovered from the Vertebrata, Cephalochordata, and Anthozoa, the sequences from the Urochordata and Hydrozoa showed weak conservation. Because the Vertebrata-Cephalochordata-Urochordata and Anthozoa-Hydrozoa represent sister groups in the Chordata and Cnidaria, respectively, Msx sequence diversification may have occurred differentially in the course of evolution. We speculate that selective loss of the conserved domains in Msx family proteins contributed to the diversification of animal body organization.

We studied a series of 42 cases of transposition of the great arteries (TGA), a complex heart defect (CHD) that is two times more prevalent in males than in females. A mutation in the X chromosome at the ZIC3 gene was found in two affected siblings (one male, one female) and their unaffected mother. A second factor, skewed X-inactivation pattern explained the discrepancy between the daughter/mother phenotype. In this family, the missense mutation (p.W255G) was found in the first zinc finger of ZIC3, a domain that is relatively specific to each of the five human ZIC genes. It was tested further along with two other mutations of this domain (p.C253S and p.H286R). In transfected 3T3 cells, mutants p.W255G and p.H286R expressed lower protein levels, and an increased protein degradation (p.W255G only). Moreover, mutants p.C253S and p.W255G had a decreased transcription activation of the TK-luciferase reporter gene. Nuclear translocation of the three ZIC3 mutants varied considerably depending on the experimental models. Finally, p.W255G and p.H286R showed diminished activities for both left-right axis disturbance and neural crest induction in Xenopus embryos. These results suggest that mutations in the first zinc finger of ZIC3 mildly affect several functions of the protein.

Opalin is a transmembrane protein detected specifically in mammalian oligodendrocytes. Opalin homologs are found only in mammals and not in the genome sequences of other animal classes. We first determined the nucleotide sequences of Opalin orthologs and their flanking regions derived from four prosimians, a group of primitive primates. A global comparison revealed that an evolutionarily conserved region exists in the first intron of Opalin. When the conserved domain was assayed for its enhancer activity in transgenic mice, oligodendrocyte-directed expression was observed. In an oligodendroglial cell line, Oli-neu, the conserved domain showed oligodendrocyte-directed expression. The conserved domain is composed of eight subdomains, some of which contain binding sites for Myt1 and cAMP-response element binding protein (CREB). Deletion analysis and cotransfection experiments revealed that the subdomains have critical roles in Opalin gene expression. Over-expression of Myt1, treatment of the cell with leukemia inhibitory factor (LIF), and cAMP analog (CREB activator) enhanced the expression of endogenous Opalin in Oli-neu cells and activated the oligodendrocyte enhancer. These results suggest that LIF, cAMP signaling cascades and Myt1 play significant roles in the differentiation of oligodendrocytes through their action on the Opalin oligodendrocyte enhancer.

The Zic family of zinc finger proteins is essential for animal development, as demonstrated by the holoprosencephaly caused by mammalian Zic2 mutation. To determine the molecular mechanism of Zic-mediated developmental control, we characterized two types of high molecular weight complexes, including Zic2. Complex I was composed of DNA-dependent protein kinase catalytic subunit (DNA-PKcs), Ku70/80, and poly(ADP-ribose) polymerase; complex II contained Ku70/80 and RNA helicase A; all the components interacted directly with Zic2 protein. Immunoprecipitation, subnuclear localization, and in vitro phosphorylation analyses revealed that the DNA-PKcs in complex I played an essential role in the assembly of complex II. Stepwise exchange from complex I to complex II depended on phosphorylation of Zic2 by DNA-PK and poly-(ADP-ribose) polymerase. Phosphorylated Zic2 protein made a stable complex with RNA helicase A, and complex II could interact with RNA polymerase II. Phosphorylation-dependent transformation of Zic2-containing molecular complexes may occur in transcriptional regulation.

We compared the expression and function of Xenopus Zic4 with those of the other four Xenopus laevis Zic family members (Zic1, Zic2, Zic3, and Zic5). Zic4 expression was detected mainly in the neural plate border, dorsal neural tube, and somites, and was similar to that of Zic1, which is adjacent to Zic4 on the same chromosome. Injection of wild-type or mutant Zic4 RNA caused the induction of neural crest marker gene expression, hyperplastic neural tissue, and ectopic pigment cell formation, indicating that Zic4 can induce neural and neural crest tissue, as can other Xenopus Zic genes. Deletion analysis showed that the zinc-finger domain is critical for many Zic4 functions, but the C-terminal region is differently involved in induction of two neural crest markers, Slug and Sox10. The protein function as determined by the animal cap explant assay was similar to that of Zic5, but different from those of Zic1, Zic2, and Zic3, suggesting that Xenopus Zic genes can be divided into two groups based on function. These results indicate that the five Xenopus Zic genes cooperatively regulate both neural and neural crest development, despite significantly diverged expression profiles and functions.

The Zic-family proteins control various developmental processes. Previous studies have shown that Zic1, Zic2, and Zic3 can act as transcriptional regulators, and that their functions are repressed by I-mfa, which has been identified as a repressor for basic helix–loop–helix-type transcriptional factors. Here, we investigated the molecular properties of the Zic4 and Zic5 proteins. Zic4/Zic5 showed DNA-binding activity to the Gli-binding sequence, similar to Zic1/Zic2/Zic3 proteins. However, Zic4/Zic5 did not exhibit any significant transcriptional activation ability nor they bind to I-mfa differently from Zic1/Zic2/Zic3. The nuclear localization of Zic4/Zic5 was not affected by the presence of the I-mfa protein, whereas the Zic1/Zic2/Zic3 proteins were translocated to the cytoplasmic compartment in the presence of I-mfa. The difference may be attributable to the dissimilarity of the N-terminal region between the Zic1/Zic2/Zic3 and Zic4/Zic5 proteins, since the binding of the Zic1/Zic2/Zic3 proteins to I-mfa occurs through their N-terminal regions.

Zinc finger proteins belonging to the Zic family control several developmental processes such as patterning of the axial skeleton. Here we mapped the transcriptional regulatory domains in Zic2 protein and identified a protein which specifically binds to one of them. In the mapping experiments, an amino-terminal region was identified as transcriptional regulatory domains. A search for proteins binding to the amino terminal domain of Zic2 revealed that inhibitor of MyoD family (I-mfa) protein, which has been identified as a repressor of myogenic helix-loop-helix class transcription factors, can physically interact with the amino terminal domain. When Zic1-3 and I-mfa proteins were co-expressed in cultured cells, nuclear import of the Zic proteins was inhibited. Consequently, I-mfa inhibited transcriptional activation by the Zic proteins in cultured cells. These results suggest that the physical and functional interaction between Zic and I-mfa proteins can play a role in the vertebrate development.