Primary structure and developmental expression of Bufo arenarum cellular nucleic acid-binding protein: changes in subcellular localization during early embryogenesis

CNBP acts as a key transcriptional regulator of sustained expression of interleukin-6

The transcription of inflammatory genes is an essential step in host defense activation. Here, we show that cellular nucleic acid-binding protein (CNBP) acts as a transcription regulator that is required for activating the innate immune response. We identified specific CNBP-binding motifs present in the promoter region of sustained inflammatory cytokines, thus, directly inducing the expression of target genes. In particular, lipopolysaccharide (LPS) induced cnbp expression through an NF-κB-dependent manner and a positive autoregulatory mechanism, which enables prolonged il-6 gene expression. This event depends strictly on LPS-induced CNBP nuclear translocation through phosphorylation-mediated dimerization. Consequently, cnbp-depleted zebrafish are highly susceptible to Shigella flexneri infection in vivo. Collectively, these observations identify CNBP as a key transcriptional regulator required for activating and maintaining the immune response.

The nucleic acid-binding protein PcCNBP is transcriptionally regulated during the immune response in red swamp crayfish Procambarus clarkii

Gene family encoding cellular nucleic acid binding proteins (CNBP) is well conserved among vertebrates; however, there is limited knowledge in lower organisms. In this study, a CNBP homolog from the red swamp crayfish Procambarus clarkii was characterised. The full-length cDNA of PcCNBP was of 1257 bp with a 5'-untranslated region (UTR) of 63 bp and a 3'-UTR of 331 bp with a poly (A) tail, and an open-reading frame (ORF) of 864 bp encoding a polypeptide of 287 amino acids with the predicted molecular weight of about 33 kDa. The predicted protein possesses 7 tandem repeats of 14 amino acids containing the CCHC zinc finger consensus sequence, two RGG-rich single-stranded RNA-binding domain and a nuclear localization signal, strongly suggesting that PcCNBP was a homolog of vertebrate CNBP. The PcCNBP transcript was constitutively expressed in all tested tissues of unchallenged crayfish, including hepatopancreas, gill, eyestalk, haemocytes, intestine, stomach and cuticle with highest expression in haemocytes, intestine, gills and hepatopancreas. The mRNA expression of PcCNBP in haemocytes was modulated at transcriptional level by different immune challenges, suggesting its involvement in the immune response of P. clarkii during both bacteria and viruses infection.

Novel high-performance purification protocol of recombinant CNBP suitable for biochemical and biophysical characterization

Cellular nucleic acid binding protein (CNBP) is a highly conserved multi-zinc knuckle protein that enhances c-MYC expression, is related to certain human muscular diseases and is required for proper rostral head development. CNBP binds to single-stranded DNA (ssDNA) and RNA and acts as nucleic acid chaperone. Despite the advances made concerning CNBP biological roles, a full knowledge about the structure-function relationship has not yet been achieved, likely due to difficulty in obtaining pure and tag-free CNBP. Here, we report a fast, simple, reproducible, and high-performance expression and purification protocol that provides recombinant tag-free CNBP from Escherichia coli cultures. We determined that tag-free CNBP binds its molecular targets with higher affinity than tagged-CNBP. Furthermore, fluorescence spectroscopy revealed the presence of a unique and conserved tryptophan, which is exposed to the solvent and involved, directly or indirectly, in nucleic acid binding. Size-exclusion HPLC revealed that CNBP forms homodimers independently of nucleic acid binding and coexist with monomers as non-interconvertible forms or in slow equilibrium. Circular dichroism spectroscopy showed that CNBP has a secondary structure dominated by random-coil and β-sheet coincident with the sequence-predicted repetitive zinc knuckles motifs, which folding is required for CNBP structural stability and biochemical activity. CNBP structural stability increased in the presence of single-stranded nucleic acid targets similar to other unstructured nucleic acid chaperones. Altogether, data suggest that CNBP is a flexible protein with interspersed structured zinc knuckles, and acquires a more rigid structure upon nucleic acid binding.

Isolation and nucleotide sequence analysis of the of Rhinella arenarum β-catenin: an mRNA and protein expression study during the larval stages of the digestive tract development

β-catenin interacts with several proteins mediating key biological processes, such as cadherin-mediated cell-cell adhesion as well as signal transduction. This work was done to establish the molecular basis and regulation of the formation pattern of cadherin/β-catenin-mediated adherens junctions, using an animal model of unknown gene sequence, the toad Rhinella arenarum. A Rhinella arenarum β-catenin homolog was isolated from larval tissue, their sequence compared and analyzed with those of eight other vertebrates using bioinformatics tools. The mRNA and protein expression levels of β-catenin were determined during the development of Rhinella arenarum digestive tract both by Reverse Transcriptase-Polymerase Chain Reaction (RT-PCR) and immunohistochemistry-morphometry respectively. Using Xenopus laevis frog specific primers, a fragment 539 bp of Rhinella arenarum toad β-catenin cDNA was obtained and sequenced. The resulting putative sequence of 177 amino acids showed high similarity at the amino acid level (97%) when compared to other six vertebrates (Xenopus laevis, Xenopus tropicalis, Mus musculus, Rattus norvegicus, Bos taurus and Homo sapiens), with sequences and structural domains characteristic of catenins. Subsequently, using primers specifically designed for Rhinella arenarum nucleotide sequence, β-catenin-mRNA increasing levels were found during the Rhinella arenarum metamorphosis. Finally, increasing β-catenin protein expression during development has confirmed the specificity the detection of Rhinella arenarum β-catenin. Summarizing, we have isolated and sequenced a β-catenin-homologue sequence from the Rhinella arenarum toad, which is highly conserved between species, and following we have detected β-catenin mRNA and protein levels during their digestive tract development.

Deciphering the cellular and molecular roles of cellular nucleic acid binding protein during cranial neural crest development

Cellular nucleic acid binding protein (Cnbp) is a highly conserved single-stranded nucleic acid binding protein required for rostral head development. The use of a morpholino that inhibits Cnbp mRNA translation previously revealed a role of Cnbp in balancing neural crest cell apoptosis and proliferation in the developing zebrafish. Here, we report the use of another morpholino that specifically modifies the splicing of Cnbp pre-mRNA resulting in a reduction of full-length mRNA levels along with the generation of a novel transcript coding for an isoform that may act as dominant negative proteins. The use of this morpholino resulted in more severe phenotypes that enabled us to demonstrate that Cnbp loss-of-function adversely affects the formation and survival of craniofacial cartilaginous structures not only controlling the ratio of cell proliferation and apoptosis but also defining skeletogenic neural crest cell fate.

CNBP: a multifunctional nucleic acid chaperone involved in cell death and proliferation control

Cellular nucleic acid binding protein (CNBP) has been implicated in vertebrate craniofacial development and in myotonic dystrophy type 2 (DM2) and sporadic inclusion body myositis (sIBM) human diseases. In these seemingly unrelated biological processes, CNBP appears to be involved in controlling cell death and proliferation rates. Low levels of CNBP may reduce rate of global protein synthesis, thereby reducing proliferation and increasing apoptosis. Conversely, CNBP might affect transcription of genes required for cell proliferation. Experimental evidences gathered so far make it difficult to ascertain or rule out any of these possibilities. Moreover, both possibilities may not be mutually exclusive. CNBP is a small and strikingly conserved single-stranded nucleic acid binding protein that is able to bind DNA as well as RNA. CNBP has a broad spectrum of targets, ranging from regulatory sites in gene promoters to translational regulatory elements in mRNA untranslated regions. Biochemical experiments have recently shed light on the possible mechanism of action for CNBP, which may act as a nucleic acid chaperone catalyzing the rearrangement of G-rich nucleic acid secondary structures likely relevant for transcriptional and/or translational gene regulation. This review focuses on the involvement of CNBP in vertebrate craniofacial development and human DM2 and sIBM diseases, as well as on the biochemical and structural features of CNBP and its cellular and molecular mechanism of action.

Vitellogenesis in Bufo arenarum: identification, characterization and immunolocalization of high molecular mass lipovitellin during oogenesis

Vitellogenin (Vtg), a large lipoglycophosphoprotein, is the most important precursor of the yolk proteins, and the major source of nutrients for the developing embryo in oviparous species. After its uptake by the oocytes, Vtg is converted into lipovitellins (high and light) and phosvitin, which are deposited into crystalline yolk platelets. We describe here the presence of two high molecular mass lipovitellin isoforms in Bufo arenarum mature oocytes with masses of 113 and 100 kDa, respectively. The amino acid sequence analysis of p113 and p100 peptides showed a high sequence homology between both polypeptides and the complete reported sequences of Xenopus laevis vitellogenin. Using specific antibodies, we determined that the Vtg uptake begins early during oogenesis, at the previtellogenic stage, and continues until oocytes have reached their mature status. In addition, we found that large endocytic vesicles mediate Vtg uptake in stage I oocytes, and that the size of the endocytic vesicles declines with oogenesis progression. In terms of the Vtg protein trafficking, we detected the Vtg precursor (190 kDa) in the liver of estradiol-injected females. Finally, we propose a subclassification of B. arenarum stage II oocytes into three physiologically and morphologically distinct periods (early, mid and late).

Dissecting CNBP, a zinc-finger protein required for neural crest development, in its structural and functional domains

Cellular nucleic-acid-binding protein (CNBP) plays an essential role in forebrain and craniofacial development by controlling cell proliferation and survival to mediate neural crest expansion. CNBP binds to single-stranded nucleic acids and displays nucleic acid chaperone activity in vitro. The CNBP family shows a conserved modular organization of seven Zn knuckles and an arginine-glycine-glycine (RGG) box between the first and second Zn knuckles. The participation of these structural motifs in CNBP biochemical activities has still not been addressed. Here, we describe the generation of CNBP mutants that dissect the protein into regions with structurally and functionally distinct properties. Mutagenesis approaches were followed to generate: (i) an amino acid replacement that disrupted the fifth Zn knuckle; (ii) N-terminal deletions that removed the first Zn knuckle and the RGG box, or the RGG box alone; and (iii) a C-terminal deletion that eliminated the three last Zn knuckles. Mutant proteins were overexpressed in Escherichia coli, purified, and used to analyze their biochemical features in vitro, or overexpressed in Xenopus laevis embryos to study their function in vivo during neural crest cell development. We found that the Zn knuckles are required, but not individually essential, for CNBP biochemical activities, whereas the RGG box is essential for RNA-protein binding and nucleic acid chaperone activity. Removal of the RGG box allowed CNBP to preserve a weak single-stranded-DNA-binding capability. A mutant mimicking the natural N-terminal proteolytic CNBP form behaved as the RGG-deleted mutant. By gain-of-function and loss-of-function experiments in Xenopus embryos, we confirmed the participation of CNBP in neural crest development, and we demonstrated that the CNBP mutants lacking the N-terminal region or the RGG box alone may act as dominant negatives in vivo. Based on these data, we speculate about the existence of a specific proteolytic mechanism for the regulation of CNBP biochemical activities during neural crest development.

Cellular nucleic acid binding protein binds G-rich single-stranded nucleic acids and may function as a nucleic acid chaperone

Cellular nucleic acid binding protein (CNBP) is a small single-stranded nucleic acid binding protein made of seven Zn knuckles and an Arg-Gly rich box. CNBP is strikingly conserved among vertebrates and was reported to play broad-spectrum functions in eukaryotic cells biology. Neither its biological function nor its mechanisms of action were elucidated yet. The main goal of this work was to gain further insights into the CNBP biochemical and molecular features. We studied Bufo arenarum CNBP (bCNBP) binding to single-stranded nucleic acid probes representing the main reported CNBP putative targets. We report that, although bCNBP is able to bind RNA and single-stranded DNA (ssDNA) probes in vitro, it binds RNA as a preformed dimer whereas both monomer and dimer are able to bind to ssDNA. A systematic analysis of variant probes shows that the preferred bCNBP targets contain unpaired guanosine-rich stretches. These data expand the knowledge about CNBP binding stoichiometry and begins to dissect the main features of CNBP nucleic acid targets. Besides, we show that bCNBP presents a highly disordered predicted structure and promotes the annealing and melting of nucleic acids in vitro. These features are typical of proteins that function as nucleic acid chaperones. Based on these data, we propose that CNBP may function as a nucleic acid chaperone through binding, remodeling, and stabilizing nucleic acids secondary structures. This novel CNBP biochemical activity broadens the field of study about its biological function and may be the basis to understand the diverse ways in which CNBP controls gene expression.

CNBP mediates neural crest cell expansion by controlling cell proliferation and cell survival during rostral head development

Striking conservation in various organisms suggests that cellular nucleic acid binding protein (CNBP) plays a fundamental biological role across different species. Recently, it was reported that CNBP is required for forebrain formation during chick and mouse embryogenesis. In this study, we have used the zebrafish model system to expand and contextualize the basic understanding of the molecular mechanisms of CNBP activity during vertebrate head development. We show that zebrafish cnbp is expressed in the anterior CNS in a similar fashion as has been observed in early chick and mouse embryos. Using antisense morpholino oligonucleotide knockdown assays, we show that CNBP depletion causes forebrain truncation while trunk development appears normal. A substantial reduction in cell proliferation and an increase in cell death were observed in the anterior regions of cnbp morphant embryos, mainly within the cnbp expression territory. In situ hybridization assays show that CNBP depletion does not affect CNS patterning while it does cause depletion of neural crest derivatives. Our data suggest an essential role for CNBP in mediating neural crest expansion by controlling proliferation and cell survival rather than via a cell fate switch during rostral head development. This possible role of CNBP may not only explain the craniofacial anomalies observed in zebrafish but also those reported for mice and chicken and, moreover, demonstrates that CNBP plays an essential and conserved role during vertebrate head development.

Differential display analysis of gene expression in female-to-male sex-reversing gonads of the frog Rana rugosa

Sex steroids play pivotal roles in gonadal differentiation in many species of vertebrates. The sex can be reversed from female to male by testosterone in the Japanese wrinkled frog Rana rugosa, but it is still unclear what genes are up- or down-regulated during the XX sex-reversal in this species. To search the genes for the female-to-male sex-reversal, we employed differential display and 5'/3'-RACE. Consequently, we isolated from the gonads at day 8 after testosterone injection 24 different cDNA fragments showing a testosterone treatment-related change and then obtained three full-length cDNAs, which we termed Zfp64, Zfp112, and Rrp54. The former two cDNAs encoded different proteins with zinc-finger domains, whereas the latter cDNA encoded an unknown protein. Transcripts of the three genes were hardly detectable in the sex-reversing gonads at day 24 after the injection; at this time few growing oocytes were observed in the sex-reversing gonad. Besides, in situ hybridization analysis showed positive signals of the three genes in the cytoplasm of growing oocytes of an ovary when testosterone was injected into a tadpole. Thus, the decrease in expression of these three genes was probably due to the disappearance of growing oocytes and not to their direct involvement in the testis formation. To find the key-gene for testis formation, it will be necessary to analyze, by the differential display method, more genes showing a change in expression pattern during sex reversal.

In vitro embryonic developmental phosphorylation of the cellular nucleic acid binding protein by cAMP-dependent protein kinase, and its relevance for biochemical activities

The zinc-finger cellular nucleic acid binding protein (CNBP) is a strikingly conserved single-stranded nucleic acid binding protein essential for normal forebrain formation during mouse and chick embryogenesis. CNBP cDNAs from a number of vertebrates have been cloned and analysed. CNBP is mainly conformed by seven retroviral Cys-Cys-His-Cys zinc-knuckles and a glycine/arginine rich region box. CNBP amino acid sequences show a putative Pro-Glu-Ser-Thr site of proteolysis and several putative phosphorylation sites. In this study, we analysed CNBP phosphorylation by embryonic kinases and its consequences on CNBP biochemical activities. We report that CNBP is differentially phosphorylated by Danio rerio embryonic extracts. In vitro CNBP phosphorylation is basal and constant at early embryonic developmental stages, it begins to increase after mid-blastula transition stage reaching the highest level at 48 hours postfertilization stage, and decreases thereafter to basal levels at 5 days postfertilization. The cAMP-dependent protein kinase (PKA) was identified as responsible for phosphorylation on the unique CNBP conserved putative phosphorylation site. Site-directed mutagenesis replacing the PKA phospho-acceptor amino acid residue impairs CNBP phosphorylation, suggesting that phosphorylation may not only exist in D. rerio but also in other vertebrates. CNBP phosphorylation does not change single-stranded nucleic acid binding capability. Instead, it promotes in vitro the annealing of complementary oligonucleotides representing the CT element (CCCTCCCC) from the human cellular myelocytomatosis oncogene (c-myc) promoter, an element responsible for c-myc enhancer transcription. Our results suggest that phosphorylation might be a conserved post-translational modification that allows CNBP to perform a fine tune expression regulation of a group of target genes, including c-myc, during vertebrate embryogenesis.

Characterization and biological properties of L-HGP, a glycoprotein from the amphibian oviduct with acrosome-stabilizing effects

BACKGROUND INFORMATION

The role of the jelly coat that surrounds the amphibian oocytes has been widely discussed, but is poorly understood. The presence of the jelly coat is essential for fertilization. However, the structure and function of the molecules that comprise the jelly coat have not been thoroughly documented. L-HGP (low-molecular-mass highly glycosylated protein) is a highly glycosylated protein that is present in the jelly coat of the toad, Bufo arenarum, oocytes and diffuses to the surrounding media. L-HGP, when purified from egg water, protects the sperm acrosome from breakdown induced by hypotonic solutions.

RESULTS

L-HGP is an acidic glycoprotein, formed by two different subunits, linked by disulphide bonds. We raised polyclonal antibodies in rabbits against the deglycosylated protein. We determined that L-HGP is secreted along the oviduct, being hence present in all the jelly layers. The molecular mass of L-HGP is higher in the most cephalic region of the oviduct. The lower-M(r) L-HGP isoform, produced in the caudal regions of the oviduct, presents an acrosome-protecting property. L-HGP is produced by secretory cells in the oviduct and is deposited on the cilia at the oviduct lumen.

CONCLUSIONS

Biochemical characterization of L-HGP has been carried out. It is synthesized by secretory cells in the oviduct and, when secreted, is deposited over the ciliated surface of the cells. The lower-M(r) isoform, secreted by the caudal region of the oviduct, protects acrosome integrity. This isoform diffuses into the medium. The role of the higher-M(r) L-HGP isoform in fertilization remains unknown.

Expression pattern and developmental behaviour of cellular nucleic acid-binding protein (CNBP) during folliculogenesis and oogenesis in fish

In vertebrates, folliculogeneis establishes an intricate system for somatic cell-oocyte interaction, and ultimately leads to the acquisition of their respective competences. Although the formation process and corresponding interactions are strikingly similar in diverse organisms, knowledge of genes and signaling pathways involved in follicle formation is very incomplete and the underlying molecular mechanisms remain enigmatic. CNBP has been identified for more than ten years, and the highest level of CNBP transcripts has been observed in adult zebrafish ovary, but little is known about its functional significance during folliculogeneis and oogenesis. In this study, we clone CNBP cDNA from gibel carp (Carassius auratus gibelio), and demonstrate its predominant expression in gibel carp ovary and testis not only by RT-PCR but also by Western blot. Its full-length cDNA is 1402 bp, and has an ORF of 489 nt for encoding a peptide of 163 aa. And its complete amino acid sequence shared 68.5%-96.8% identity with CNBPs from other vertebrates. Based on the expression characterization, we further analyze its expression pattern and developmental behaviour during folliculogeneis and oogenesis. Following these studies, we reveal an unexpected discovery that the CagCNBP is associated with follicular cells and oocytes, and significant distribution changes have occurred in degenerating and regenerating follicles. More interestingly, the CagCNBP is more highly expressed in some clusters of interconnected cells within ovarian cysts, no matter whether the cell clusters are formed from the original primordial germ cells or from the newly formed cells from follicular cells that invaded into the atretic oocytes. It is the first time to reveal CNBP relevance to folliculogeneis and oogenesis. Moreover, a similar stage-specific and cell-specific expression pattern has also been observed in the gibel carp testis. Therefore, further studies on CNBP expression pattern and developmental behaviour will be of significance for understanding functional roles of CNBP during gametogenesis.

Identification of mushroom body miniature, a zinc-finger protein implicated in brain development of Drosophila

The mushroom bodies are bilaterally arranged structures in the protocerebrum of Drosophila and most other insect species. Mutants with altered mushroom body structure have been instrumental not only in establishing their role in distinct behavioral functions but also in identifying the molecular pathways that control mushroom body development. The mushroom body miniature(1) (mbm(1)) mutation results in grossly reduced mushroom bodies and odor learning deficits in females. With a survey of genomic rescue constructs, we have pinpointed mbm(1) to a single transcription unit and identified a single nucleotide exchange in the 5' untranslated region of the corresponding transcript resulting in a reduced expression of the protein. The most obvious feature of the Mbm protein is a pair of C(2)HC zinc fingers, implicating a function of the protein in binding nucleic acids. Immunohistochemical analysis shows that expression of the Mbm protein is not restricted to the mushroom bodies. BrdUrd labeling experiments indicate a function of Mbm in neuronal precursor cell proliferation.

Zebrafish cellular nucleic acid-binding protein: gene structure and developmental behaviour

Here we analyse the structural organisation and expression of the zebrafish cellular nucleic acid-binding protein (zCNBP) gene and protein. The gene is organised in five exons and four introns. A noteworthy feature of the gene is the absence of a predicted promoter region. The coding region encodes a 163-amino acid polypeptide with the highly conserved general structural organisation of seven CCHC Zn knuckle domains and an RGG box between the first and the second Zn knuckles. Although theoretical alternative splicing is possible, only one form of zCNBP is actually detected. This form is able to bind to single-stranded DNA and RNA probes in vitro. The analysis of zCNBP developmental expression shows a high amount of CNBP-mRNA in ovary and during the first developmental stages. CNBP-mRNA levels decrease while early development progresses until the midblastula transition (MBT) stage and increases again thereafter. The protein is localised in the cytoplasm of blastomeres whereas it is mainly nuclear in developmental stages after the MBT. These findings suggest that CNBP is a strikingly conserved single-stranded nucleic acid-binding protein which might interact with maternal mRNA during its storage in the embryo cell cytoplasm. It becomes nuclear once MBT takes place possibly in order to modulate zygotic transcription and/or to associate with newly synthesised transcripts.

Human cellular nucleic acid-binding protein Zn2+ fingers support replication of human immunodeficiency virus type 1 when they are substituted in the nucleocapsid protein

A family of cellular nucleic acid binding proteins (CNBPs) contains seven Zn(2+) fingers that have many of the structural characteristics found in retroviral nucleocapsid (NC) Zn(2+) fingers. The sequence of the NH(2)-terminal NC Zn(2+) finger of the pNL4-3 clone of human immunodeficiency virus type 1 (HIV-1) was replaced individually with sequences from each of the seven fingers from human CNBP. Six of the mutants were normal with respect to protein composition and processing, full-length genomic RNA content, and infectivity. One of the mutants, containing the fifth CNBP Zn(2+) finger (CNBP-5) packaged reduced levels of genomic RNA and was defective in infectivity. There appear to be defects in reverse transcription in the CNBP-5 infections. Models of Zn(2+) fingers were constructed by using computational methods based on available structural data, and atom-atom interactions were determined by the hydropathic orthogonal dynamic analysis of the protein method. Defects in the CNBP-5 mutant could possibly be explained, in part, by restrictions of a set of required atom-atom interactions in the CNBP-5 Zn(2+) finger compared to mutant and wild-type Zn(2+) fingers in NC that support replication. The present study shows that six of seven of the Zn(2+) fingers from the CNBP protein can be used as substitutes for the Zn(2+) finger in the NH(2)-terminal position of HIV-1 NC. This has obvious implications in antiviral therapeutics and DNA vaccines employing NC Zn(2+) finger mutants.

Molecular cloning, developmental expression, promoter analysis and functional characterization of the mouse CNBP gene

Striking conservation in various organisms suggests that cellular nucleic acid-binding protein (CNBP) plays a fundamental biological role across different species. However, the regulated expression and physiological properties of the CNBP gene are unknown. In this study, we report the molecular cloning, promoter characterization, developmental expression and functional analysis of the mouse CNBP gene. The gene contains five exons and is localized to chromosome 6 in the region corresponding to band 6 D1-D2. Primer extension assay indicates that the transcription start site is located 230 bp upstream of the initiator Met codon. Our promoter analysis indicates that strong transcription enhancer and silencer regions lie within the 1.6 kb proximal region of the promoter and the upstream -3.0 to -1.6 kb region, respectively. The promoter activity is 10 fold higher in embryonic carcinoma cells than that in fibroblast, as determined by CAT assay. Consistent with its function as a transcription factor, CNBP protein is located in the nucleus of cells. During mouse embryogenesis, CNBP is expressed in the anterior region of the early embryo and in the limb, tail and craniofacial region. Overexpression of CNBP strongly stimulates cell proliferation and increases c-myc promoter activity. Our finds suggest that CNBP may play an important role in cell proliferation and tissue patterning during anterior-posterior axis, craniofacial and limb development by targeting c-Myc.