Terminal renal failure in mice lacking transcription factor AP-2 beta

(Zebra)fishing for nephrogenesis genes

Kidney disease is a devastating condition affecting millions of people worldwide, where over 100,000 patients in the United States alone remain waiting for a lifesaving organ transplant. Concomitant with a surge in personalized medicine, single-gene mutations, and polygenic risk alleles have been brought to the forefront as core causes of a spectrum of renal disorders. With the increasing prevalence of kidney disease, it is imperative to make substantial strides in the field of kidney genetics. Nephrons, the core functional units of the kidney, are epithelial tubules that act as gatekeepers of body homeostasis by absorbing and secreting ions, water, and small molecules to filter the blood. Each nephron contains a series of proximal and distal segments with explicit metabolic functions. The embryonic zebrafish provides an ideal platform to systematically dissect the genetic cues governing kidney development. Here, we review the use of zebrafish to discover nephrogenesis genes.

Crucial role of TFAP2B in the nervous system for regulating NREM sleep

The AP-2 transcription factors are crucial for regulating sleep in both vertebrate and invertebrate animals. In mice, loss of function of the transcription factor AP-2β (TFAP2B) reduces non-rapid eye movement (NREM) sleep. When and where TFAP2B functions, however, is unclear. Here, we used the Cre-loxP system to generate mice in which Tfap2b was specifically deleted in the nervous system during development and mice in which neuronal Tfap2b was specifically deleted postnatally. Both types of mice exhibited reduced NREM sleep, but the nervous system-specific deletion of Tfap2b resulted in more severe sleep phenotypes accompanied by defective light entrainment of the circadian clock and stereotypic jumping behavior. These findings indicate that TFAP2B in postnatal neurons functions at least partly in sleep regulation and imply that TFAP2B also functions either at earlier stages or in additional cell types within the nervous system.

Ap-2β regulates cranial osteogenic potential via the activation of Wnt/β-catenin signaling pathway

The skull is a fundamental bone that protects the development of brain and consists of several bony elements, such as the frontal and parietal bones. Frontal bone exhibited superior in osteogenic potential and regeneration of cranial defects compared to parietal bone. However, how this regional difference is regulated remains largely unknown. In this study, we identified an Ap-2β transcriptional factor with a higher expression in frontal bone, but its molecular function in osteoblasts needs to be elucidated. We found that Ap-2β knockdown in preosteoblasts leads to reduced proliferation, increased cell death and impaired differentiation. Through RNA-seq analysis, we found that Ap-2β influences multiple signaling pathways including the Wnt pathway, and overexpression of Ap-2β showed increased nuclear β-catenin and its target genes expressions in osteoblasts. Pharmacological activation of Wnt/β-catenin signaling using LiCl treatment cannot rescue the reduced luciferase activities of the β-catenin/TCF/LEF reporter in Ap-2β knockdown preosteoblasts. Besides, transient expression of Ap-2β via the lentivirus system could sufficiently rescue the inferior osteogenic potential in parietal osteoblasts, while Ap-2β knockdown in frontal osteoblasts resulted in reduced osteoblast activity, reduced active β-catenin and target genes expressions. Taken together, our data demonstrated that Ap-2β modulates osteoblast proliferation and differentiation through the regulation of Wnt/β-catenin signaling pathway and plays an important role in regulating regional osteogenic potential in frontal and parietal bone.

Genome-Wide Association Analysis Identified Variants Associated with Body Measurement and Reproduction Traits in Shaziling Pigs

With the increasing popularity of genomic sequencing, breeders pay more attention to identifying the crucial molecular markers and quantitative trait loci for improving the body size and reproduction traits that could affect the production efficiency of pig-breeding enterprises. Nevertheless, for the Shaziling pig, a well-known indigenous breed in China, the relationship between phenotypes and their corresponding genetic architecture remains largely unknown. Herein, in the Shaziling population, a total of 190 samples were genotyped using the Geneseek Porcine 50K SNP Chip, obtaining 41857 SNPs for further analysis. For phenotypes, two body measurement traits and four reproduction traits in the first parity from the 190 Shaziling sows were measured and recorded, respectively. Subsequently, a genome-wide association study (GWAS) between the SNPs and the six phenotypes was performed. The correlation between body size and reproduction phenotypes was not statistically significant. A total of 31 SNPs were found to be associated with body length (BL), chest circumference (CC), number of healthy births (NHB), and number of stillborns (NSB). Gene annotation for those candidate SNPs identified 18 functional genes, such as GLP1R, NFYA, NANOG, COX7A2, BMPR1B, FOXP1, SLC29A1, CNTNAP4, and KIT, which exert important roles in skeletal morphogenesis, chondrogenesis, obesity, and embryonic and fetal development. These findings are helpful to better understand the genetic mechanism for body size and reproduction phenotypes, while the phenotype-associated SNPs could be used as the molecular markers for the pig breeding programs.

The regulatory role of AP-2β in monoaminergic neurotransmitter systems: insights on its signalling pathway, linked disorders and theragnostic potential

Monoaminergic neurotransmitter systems play a central role in neuronal function and behaviour. Dysregulation of these systems gives rise to neuropsychiatric and neurodegenerative disorders with high prevalence and societal burden, collectively termed monoamine neurotransmitter disorders (MNDs). Despite extensive research, the transcriptional regulation of monoaminergic neurotransmitter systems is not fully explored. Interestingly, certain drugs that act on these systems have been shown to modulate central levels of the transcription factor AP-2 beta (AP-2β, gene: TFAP2Β). AP-2β regulates multiple key genes within these systems and thereby its levels correlate with monoamine neurotransmitters measures; yet, its signalling pathways are not well understood. Moreover, although dysregulation of TFAP2Β has been associated with MNDs, the underlying mechanisms for these associations remain elusive. In this context, this review addresses AP-2β, considering its basic structural aspects, regulation and signalling pathways in the controlling of monoaminergic neurotransmitter systems, and possible mechanisms underpinning associated MNDS. It also underscores the significance of AP-2β as a potential diagnostic biomarker and its potential and limitations as a therapeutic target for specific MNDs as well as possible pharmaceutical interventions for targeting it. In essence, this review emphasizes the role of AP-2β as a key regulator of the monoaminergic neurotransmitter systems and its importance for understanding the pathogenesis and improving the management of MNDs.

TFAP2B Haploinsufficiency Impacts Gastrointestinal Function and Leads to Pediatric Intestinal Pseudo-obstruction

Background: Pediatric Intestinal Pseudo-obstruction (PIPO) is a congenital enteric disorder characterized by severe gastrointestinal (GI) dysmotility, without mechanical obstruction. Although several genes have been described to cause this disease, most patients do not receive a genetic diagnosis. Here, we aim to identify the genetic cause of PIPO in a patient diagnosed with severe intestinal dysmotility shortly after birth.

Methods: Whole exome sequencing (WES) was performed in the patient and unaffected parents, in a diagnostic setting. After identification of the potential disease-causing variant, its functional consequences were determined in vitro and in vivo. For this, expression constructs with and without the causing variant, were overexpressed in HEK293 cells. To investigate the role of the candidate gene in GI development and function, a zebrafish model was generated where its expression was disrupted using CRISPR/Cas9 editing.

Results: WES analysis identified a de novo heterozygous deletion in TFAP2B (NM_003221.4:c.602-5_606delTCTAGTTCCA), classified as a variant of unknown significance. In vitro studies showed that this deletion affects RNA splicing and results in loss of exon 4, leading to the appearance of a premature stop codon and absence of TFAP2B protein. Disruption of tfap2b in zebrafish led to decreased enteric neuronal numbers and delayed transit time. However, no defects in neuronal differentiation were detected. tfap2b crispants also showed decreased levels of ednrbb mRNA, a downstream target of tfap2b.

Conclusion: We showed that TFAP2B haploinsufficiency leads to reduced neuronal numbers and GI dysmotility, suggesting for the first time, that this gene is involved in PIPO pathogenesis.

Transcription factor Ap2b regulates the mouse autosomal recessive polycystic kidney disease genes, Pkhd1 and Cys1

Transcription factor Ap2b (TFAP2B), an AP-2 family transcription factor, binds to the palindromic consensus DNA sequence, 5'-GCCN_3-5GGC-3'. Mice lacking functional Tfap2b gene die in the perinatal or neonatal period with cystic dilatation of the kidney distal tubules and collecting ducts, a phenotype resembling autosomal recessive polycystic kidney disease (ARPKD). Human ARPKD is caused by mutations in PKHD1, DZIP1L, and CYS1, which are conserved in mammals. In this study, we examined the potential role of TFAP2B as a common regulator of Pkhd1 and Cys1. We determined the transcription start site (TSS) of Cys1 using 5' Rapid Amplification of cDNA Ends (5'RACE); the TSS of Pkhd1 has been previously established. Bioinformatic approaches identified cis-regulatory elements, including two TFAP2B consensus binding sites, in the upstream regulatory regions of both Pkhd1 and Cys1. Based on reporter gene assays performed in mouse renal collecting duct cells (mIMCD-3), TFAP2B activated the Pkhd1 and Cys1 promoters and electromobility shift assay (EMSA) confirmed TFAP2B binding to the in silico identified sites. These results suggest that Tfap2b participates in a renal epithelial cell gene regulatory network that includes Pkhd1 and Cys1. Disruption of this network impairs renal tubular differentiation, causing ductal dilatation that is the hallmark of recessive PKD.

Transcription factor AP-2beta in development, differentiation and tumorigenesis

To date, the AP-2 family of transcription factors comprises five members. Transcription factor AP-2beta (TFAP2B)/AP-2β was first described in 1995. Several studies indicate a critical role of AP-2β in the development of tissues and organs of ectodermal, neuroectodermal and also mesodermal origin. Germline mutation of TFAP2B is known to cause the Char syndrome, an autosomal dominant disorder characterized by facial dysmorphism, patent ductus arteriosus and anatomical abnormalities of the fifth digit. Furthermore, single-nucleotide polymorphisms in TFAP2B were linked to obesity and specific personality traits. In neoplasias, AP-2β was first described in alveolar rhabdomyosarcoma. Immunohistochemical staining of AP-2β is a recommended ancillary test for the histopathological diagnosis of this uncommon childhood malignancy. In neuroblastoma, AP-2β supports noradrenergic differentiation. Recently, the function of AP-2β in breast cancer (BC) has gained interest. AP-2β is associated with the lobular BC subtype. Moreover, AP-2β controls BC cell proliferation and has a prognostic impact in patients with BC. This review provides a comprehensive overview of the current knowledge about AP-2β and its function in organ development, differentiation and tumorigenesis.

Kctd15 regulates nephron segment development by repressing Tfap2a activity

A functional vertebrate kidney relies on structural units called nephrons, which are epithelial tubules with a sequence of segments each expressing a distinct repertoire of solute transporters. The transcriptiona`l codes driving regional specification, solute transporter program activation and terminal differentiation of segment populations remain poorly understood. Here, we demonstrate that the KCTD15 paralogs kctd15a and kctd15b function in concert to restrict distal early (DE)/thick ascending limb (TAL) segment lineage assignment in the developing zebrafish pronephros by repressing Tfap2a activity. During renal ontogeny, expression of these factors colocalized with tfap2a in distal tubule precursors. kctd15a/b loss primed nephron cells to adopt distal fates by driving slc12a1, kcnj1a.1 and stc1 expression. These phenotypes were the result of Tfap2a hyperactivity, where kctd15a/b-deficient embryos exhibited increased abundance of this transcription factor. Interestingly, tfap2a reciprocally promoted kctd15a and kctd15b transcription, unveiling a circuit of autoregulation operating in nephron progenitors. Concomitant kctd15b knockdown with tfap2a overexpression further expanded the DE population. Our study reveals that a transcription factor-repressor feedback module employs tight regulation of Tfap2a and Kctd15 kinetics to control nephron segment fate choice and differentiation during kidney development.

Sleep Architecture in Mice Is Shaped by the Transcription Factor AP-2β

The molecular mechanism regulating sleep largely remains to be elucidated. In humans, families that carry mutations in TFAP2B, which encodes the transcription factor AP-2β, self-reported sleep abnormalities such as short-sleep and parasomnia. Notably, AP-2 transcription factors play essential roles in sleep regulation in the nematode Caenorhabditis elegans and the fruit fly Drosophila melanogaster Thus, AP-2 transcription factors might have a conserved role in sleep regulation across the animal phyla. However, direct evidence supporting the involvement of TFAP2B in mammalian sleep was lacking. In this study, by using the CRISPR/Cas9 technology, we generated two Tfap2b mutant mouse strains, Tfap2bK144 and Tfap2bK145 , each harboring a single-nucleotide mutation within the introns of Tfap2b mimicking the mutations in two human kindreds that self-reported sleep abnormalities. The effects of these mutations were compared with those of a Tfap2b knockout allele (Tfap2b-). The protein expression level of TFAP2B in the embryonic brain was reduced to about half in Tfap2b+/- mice and was further reduced in Tfap2b-/- mice. By contrast, the protein expression level was normal in Tfap2bK145/+ mice but was reduced in Tfap2bK145/K145 mice to a similar extent as Tfap2b-/- mice. Tfap2bK144/+ and Tfap2bK144/K144 showed normal protein expression levels. Tfap2b+/- female mice showed increased wakefulness time and decreased nonrapid eye movement sleep (NREMS) time. By contrast, Tfap2bK145/+ female mice showed an apparently normal amount of sleep but instead exhibited fragmented NREMS, whereas Tfap2bK144/+ male mice showed reduced NREMS time specifically in the dark phase. Finally, in the adult brain, Tfap2b-LacZ expression was detected in the superior colliculus, locus coeruleus, cerebellum, and the nucleus of solitary tract. These findings provide direct evidence that TFAP2B influences NREMS amounts in mice and also show that different mutations in Tfap2b can lead to diverse effects on sleep architecture.

AP-2β/KCTD1 Control Distal Nephron Differentiation and Protect against Renal Fibrosis

The developmental mechanisms that orchestrate differentiation of specific nephron segments are incompletely understood, and the factors that maintain their terminal differentiation after nephrogenesis remain largely unknown. Here, the transcription factor AP-2β is shown to be required for the differentiation of distal tubule precursors into early stage distal convoluted tubules (DCTs) during nephrogenesis. In contrast, its downstream target KCTD1 is essential for terminal differentiation of early stage DCTs into mature DCTs, and impairment of their terminal differentiation owing to lack of KCTD1 leads to a severe salt-losing tubulopathy. Moreover, sustained KCTD1 activity in the adult maintains mature DCTs in this terminally differentiated state and prevents renal fibrosis by repressing β-catenin activity, whereas KCTD1 deficiency leads to severe renal fibrosis. Thus, the AP-2β/KCTD1 axis links a developmental pathway in the nephron to the induction and maintenance of terminal differentiation of DCTs that actively prevents their de-differentiation in the adult and protects against renal fibrosis.

Tfap2a is a novel gatekeeper of nephron differentiation during kidney development

Renal functional units known as nephrons undergo patterning events during development that create a segmental array of cellular compartments with discrete physiological identities. Here, from a forward genetic screen using zebrafish, we report the discovery that transcription factor AP-2 alpha (tfap2a) coordinates a gene regulatory network that activates the terminal differentiation program of distal segments in the pronephros. We found that tfap2a acts downstream of Iroquois homeobox 3b (irx3b), a distal lineage transcription factor, to operate a circuit consisting of tfap2b, irx1a and genes encoding solute transporters that dictate the specialized metabolic functions of distal nephron segments. Interestingly, this regulatory node is distinct from other checkpoints of differentiation, such as polarity establishment and ciliogenesis. Thus, our studies reveal insights into the genetic control of differentiation, where tfap2a is essential for regulating a suite of segment transporter traits at the final tier of zebrafish pronephros ontogeny. These findings have relevance for understanding renal birth defects, as well as efforts to recapitulate nephrogenesis in vivo to facilitate drug discovery and regenerative therapies.

AP-2ε Expression in Developing Retina: Contributing to the Molecular Diversity of Amacrine Cells

AP-2 transcription factors play important roles in the regulation of gene expression during development. Four of the five members of the AP-2 family (AP-2α, AP-2β, AP-2γ and AP-2δ) have previously been shown to be expressed in developing retina. Mouse knockouts have revealed roles for AP-2α, AP-2β and AP-2δ in retinal cell specification and function. Here, we show that the fifth member of the AP-2 family, AP-2ε, is also expressed in amacrine cells in developing mammalian and chicken retina. Our data indicate that there are considerably fewer AP-2ε-positive cells in the developing mouse retina compared to AP-2α, AP-2β and AP-2γ-positive cells, suggesting a specialized role for AP-2ε in a subset of amacrine cells. AP-2ε, which is restricted to the GABAergic amacrine lineage, is most commonly co-expressed with AP-2α and AP-2β, especially at early stages of retinal development. Co-expression of AP-2ε and AP-2γ increases with differentiation. Analysis of previously published Drop-seq data from single retinal cells supports co-expression of multiple AP-2s in the same cell. Since AP-2s bind to their target sequences as either homodimers or heterodimers, our work suggests spatially- and temporally-coordinated roles for combinations of AP-2 transcription factors in amacrine cells during retinal development.

A six-gene expression toolbox for the glands, epithelium and chondrocytes in the mouse nasal cavity

The nose is the central feature of the amniote face. In adults, the nose is a structurally and functionally complex organ that consists of bone, cartilage, glands and ducts. In an ongoing expression screen in our lab, we found several novel markers for specific tissues in the nasal region. Here, using in situ hybridization expression experiments, we report that Alx1, Ap-2β, Crispld1, Eya4, Moxd1, and Penk have tissue specific expression during murine nasal development. At E11.5, we observed that Alx1, Ap-2β, Crispld1, and Eya4 are expressed in the medial and lateral nasal prominences. We found that Moxd1 and Penk are expressed in the lateral nasal prominences. At E15.5, Alx1 is expressed in nasal septum. Ap-2β and Crispld1 are expressed in nasal glands and cartilages. Eya4 is expressed in olfactory epithelium. Intriguingly at E15.5 Moxd1 is expressed in all the nasal cartilage while the expression of Penk is restricted to chondrocytes contributing to the posterior nasal septum. The expression domains reported here suggest that these genes warrant functional studies to determine their role in nasal capsule morphogenesis.

Standardized, systemic phenotypic analysis reveals kidney dysfunction as main alteration of Kctd1 I27N mutant mice

Background

Increased levels of blood plasma urea were used as phenotypic parameter for establishing novel mouse models for kidney diseases on the genetic background of C3H inbred mice in the phenotype-driven Munich ENU mouse mutagenesis project. The phenotypically dominant mutant line HST014 was established and further analyzed.

Methods

Analysis of the causative mutation as well as the standardized, systemic phenotypic analysis of the mutant line was carried out.

Results

The causative mutation was detected in the potassium channel tetramerization domain containing 1 (Kctd1) gene which leads to the amino acid exchange Kctd1^I27N thereby affecting the functional BTB domain of the protein. This line is the first mouse model harboring a Kctd1 mutation. Kctd1^I27N homozygous mutant mice die perinatally. Standardized, systemic phenotypic analysis of Kctd1^I27N heterozygous mutants was carried out in the German Mouse Clinic (GMC). Systematic morphological investigation of the external physical appearance did not detect the specific alterations that are described in KCTD1 mutant human patients affected by the scalp-ear-nipple (SEN) syndrome. The main pathological phenotype of the Kctd1^I27N heterozygous mutant mice consists of kidney dysfunction and secondary effects thereof, without gross additional primary alterations in the other phenotypic parameters analyzed. Genome-wide transcriptome profiling analysis at the age of 4 months revealed about 100 differentially expressed genes (DEGs) in kidneys of Kctd1^I27N heterozygous mutants as compared to wild-type controls.

Conclusions

In summary, the main alteration of the Kctd1^I27N heterozygous mutants consists in kidney dysfunction. Additional analyses in 9–21 week-old heterozygous mutants revealed only few minor effects.

Electronic supplementary material

The online version of this article (doi:10.1186/s12929-017-0365-5) contains supplementary material, which is available to authorized users.

Comparative transcriptomic analysis identifies evolutionarily conserved gene products in the vertebrate renal distal convoluted tubule

Understanding the molecular basis of the complex regulatory networks controlling renal ion transports is of major physiological and clinical importance. In this study, we aimed to identify evolutionarily conserved critical players in the function of the renal distal convoluted tubule (DCT) by a comparative transcriptomic approach. We generated a transgenic zebrafish line with expression of the red fluorescent mCherry protein under the control of the zebrafish DCT-specific promoter of the thiazide-sensitive NaCl cotransporter (NCC). The mCherry expression was then used to isolate from the zebrafish mesonephric kidneys the distal late (DL) segments, the equivalent of the mammalian DCT, for subsequent RNA-seq analysis. We next compared this zebrafish DL transcriptome to the previously established mouse DCT transcriptome and identified a subset of gene products significantly enriched in both the teleost DL and the mammalian DCT, including SLCs and nuclear transcription factors. Surprisingly, several of the previously described regulators of NCC (e.g., SPAK, KLHL3, ppp1r1a) in the mouse were not found enriched in the zebrafish DL. Nevertheless, the zebrafish DL expressed enriched levels of related homologues. Functional knockdown of one of these genes, ppp1r1b, reduced the phosphorylation of NCC in the zebrafish pronephros, similar to what was seen previously in knockout mice for its homologue, Ppp1r1a. The present work is the first report on global gene expression profiling in a specific nephron portion of the zebrafish kidney, an increasingly used model system for kidney research. Our study suggests that comparative analysis of gene expression between phylogenetically distant species may be an effective approach to identify novel regulators of renal function.

The kidney transcriptome and proteome defined by transcriptomics and antibody-based profiling

To understand renal functions and disease, it is important to define the molecular constituents of the various compartments of the kidney. Here, we used comparative transcriptomic analysis of all major organs and tissues in the human body, in combination with kidney tissue micro array based immunohistochemistry, to generate a comprehensive description of the kidney-specific transcriptome and proteome. A special emphasis was placed on the identification of genes and proteins that were elevated in specific kidney subcompartments. Our analysis identified close to 400 genes that had elevated expression in the kidney, as compared to the other analysed tissues, and these were further subdivided, depending on expression levels, into tissue enriched, group enriched or tissue enhanced. Immunohistochemistry allowed us to identify proteins with distinct localisation to the glomeruli (n = 11), proximal tubules (n = 120), distal tubules (n = 9) or collecting ducts (n = 8). Among the identified kidney elevated transcripts, we found several proteins not previously characterised or identified as elevated in kidney. This description of the kidney specific transcriptome and proteome provides a resource for basic and clinical research to facilitate studies to understand kidney biology and disease.

Dlx1 and Rgs5 in the ductus arteriosus: vessel-specific genes identified by transcriptional profiling of laser-capture microdissected endothelial and smooth muscle cells

Closure of the ductus arteriosus (DA) is a crucial step in the transition from fetal to postnatal life. Patent DA is one of the most common cardiovascular anomalies in children with significant clinical consequences especially in premature infants. We aimed to identify genes that specify the DA in the fetus and differentiate it from the aorta. Comparative microarray analysis of laser-captured microdissected endothelial (ECs) and vascular smooth muscle cells (SMCs) from the DA and aorta of fetal rats (embryonic day 18 and 21) identified vessel-specific transcriptional profiles. We found a strong age-dependency of gene expression. Among the genes that were upregulated in the DA the regulator of the G-protein coupled receptor 5 (Rgs5) and the transcription factor distal-less homeobox 1 (Dlx1) exhibited the highest and most significant level of differential expression. The aorta showed a significant preferential expression of the Purkinje cell protein 4 (Pcp4) gene. The results of the microarray analysis were validated by real-time quantitative PCR and immunohistochemistry. Our study confirms vessel-specific transcriptional profiles in ECs and SMCs of rat DA and aorta. Rgs5 and Dlx1 represent novel molecular targets for the regulation of DA maturation and closure.

CDK inhibitors R-roscovitine and S-CR8 effectively block renal and hepatic cystogenesis in an orthologous model of ADPKD

Autosomal dominant polycystic kidney disease (ADPKD) and other forms of PKD are associated with dysregulated cell cycle and proliferation. Although no effective therapy for the treatment of PKD is currently available, possible mechanism-based approaches are beginning to emerge. A therapeutic intervention targeting aberrant cilia-cell cycle connection using CDK-inhibitor R-roscovitine showed effective arrest of PKD in jck and cpk models that are not orthologous to human ADPKD. To evaluate whether CDK inhibition approach will translate into efficacy in an orthologous model of ADPKD, we tested R-roscovitine and its derivative S-CR8 in a model with a conditionally inactivated Pkd1 gene (Pkd1 cKO). Similar to ADPKD, Pkd1 cKO mice developed renal and hepatic cysts. Treatment of Pkd1 cKO mice with R-roscovitine and its more potent and selective analog S-CR8 significantly reduced renal and hepatic cystogenesis and attenuated kidney function decline. Mechanism of action studies demonstrated effective blockade of cell cycle and proliferation and reduction of apoptosis. Together, these data validate CDK inhibition as a novel and effective approach for the treatment of ADPKD.

Familial nonsyndromic patent ductus arteriosus caused by mutations in TFAP2B

Patent ductus arteriosus (PDA) is a common congenital heart disease that develops soon after birth when the arterial duct does not remodel. Mutations in TFAP2B, which encodes a neural crest-derived transcription factor, can cause Char syndrome, characterized by PDA, facial dysmorphism, and skeletal abnormalities of the hand. The TFAP2B mutations result in a great amount of phenotypic variability, and a novel TFAP2B mutation has been found in patients with nonsyndromic PDA. Therefore, this study investigated whether TFAP2B mutations can cause familial nonsyndromic PDA. Clinical data and peripheral blood specimens were collected from two kindreds (A and B) and from a cohort of 100 unrelated subjects with PDA. Kindred A spanned three generations, in which 5 of the 16 individuals had PDA, and kindred B spanned three generations, in which 2 of the 13 individuals had PDA. The study enrolled 100 unrelated healthy individuals as control subjects. Polymerase chain reaction (PCR) was used to amplify seven exons and flanking introns of the TFAP2B gene. A few exons of the TFAP2B gene were amplified using reverse transcription polymerase chain reaction (RT-PCR), and direct forward and reverse sequencing of the PCR products was performed. The acquired sequences were aligned with those in GenBank by using a basic local alignment search tool (BLAST). The following two types of mutations were identified in TFAP2B: c.601+5G>A and c.435_438delCCGG. The mutation c.601+5G>A was detected in the affected members of kindred A. Nested PCR showed a splice junction in intron 3 and a 61-bp deletion in exon 3. The mutation c.435_438delCCGG, found in the affected members of kindred B, was caused by a four-base deletion in exon 2, which in turn caused a frame shift that resulted in the formation of a premature stop codon, p.Arg145Argfsx45. None of these mutations was detected in the unaffected members of the kindred or in the control group. Furthermore, two novel single-nucleotide polymorphisms (SNPs), c.1-34G>A and c.539+62G>C, were detected in the introns. The variant c.1-34G>A was identified 34 bp upstream of the transcription initiation site in the TFAP2B gene. Significant differences in the prevalence of the alleles G and A were observed in the control subjects and PDA patients (Z = -2.513, P = 0.012). The study identified that another variant was c.539+62G>C but that the frequency of this variant was similar between the control subjects and the PDA patients (Z = -0.332, P = 0.74). The TFAP2B mutations may be associated with isolated nonsyndromic, hereditary PDA in Chinese families. The authors propose that a TFAP2B mutation should be considered a risk factor for isolated PDA. However, the detailed genetic mechanism underlying nonsyndromic the PDA-causing TFAP2B mutation is yet to be elucidated.

AP-2δ is a crucial transcriptional regulator of the posterior midbrain

Ap-2 transcription factors comprise a family of 5 closely related sequence-specific DNA binding proteins that play pivotal and non-redundant roles in embryonic organogenesis. To investigate the function of Ap-2δ, wδe analyzed its expression during embryogenesis and generated Ap-2δ-deficient mice. In line with the specific expression pattern of Ap-2δ in the mesencephalic tectum and the dorsal midbrain, Ap-2δ-deficient mice failed to maintain the colliculus inferior, a derivative of the dorsal midbrain, as a consequence of increased apoptotic cell death. To identify specific Ap-2δ target genes in cells of the developing dorsal midbrain, we performed whole genome analysis of cDNA expression levels. This approach identified a set of 12 putative target genes being expressed in the developing midbrain, including the transcription factors Pitx2, Mef2c, Bhlhb4 and Pou4f3. Using chromatin immunoprecipitation (CHIP) we showed that some of these genes are direct targets of Ap-2δ. Consistently, we demonstrate that Ap-2δ occupies and activates the Pou4f3 and Bhlhb4 promoters. In addition, known Pou4f3 target genes were downregulated in the posterior midbrain of Ap-2δ-deficient mice. Despite the absence of a central part of the auditory pathway, the presence of neuronal responses to sounds in the neocortex of Ap-2δ-deficient mice indicates that auditory information from the brainstem still reaches the neocortex. In summary, our data define Ap-2δ as an important transcription factor, specifying gene expression patterns required for the development of the posterior midbrain.

A heart-hand syndrome gene: Tfap2b plays a critical role in the development and remodeling of mouse ductus arteriosus and limb patterning

BACKGROUND

Patent ductus arteriosus (PDA) is one of the most common forms of congenital heart disease. Mutations in transcription factor TFAP2B cause Char syndrome, a human disorder characterized by PDA, facial dysmorphysm and hand anomalies. Animal research data are needed to understand the mechanisms. The aim of our study was to elucidate the pathogenesis of Char syndrome at the molecular level.

METHODOLOGY/PRINCIPAL FINDINGS

Gene expression of Tfap2b during mouse development was studied, and newborns of Tfap2b-deficient mice were examined to identify phenotypes. Gel shift assays had been carried out to search for Tfap2 downstream genes. Promoters of candidate genes were cloned into a reporter construct and used to demonstrate their regulation by Tfap2b in cell transfection. In situ hybridizations showed that the murine transcription factor Tfap2b was expressed during the entire development of mouse ductus arteriosus. Histological examination of ductus arteriosus from Tfap2b knockout mice 6 hours after birth revealed that they were not closed. Consequently, the lungs of Tfap2b(-/-) mice demonstrated progressive congestion of the pulmonary capillaries, which was postulated to result secondarily from PDA. In addition, Tfap2b was expressed in the limb buds, particularly in the posterior limb field during development. Lack of Tfap2b resulted in bilateral postaxial accessory digits. Further study indicated that expressions of bone morphogenetic protein (Bmp) genes, which are reported to be involved in the limb patterning and ductal development, were altered in limb buds of Tfap2b-deficient embryos, due to direct control of Bmp2 and Bmp4 promoter activity by Tfap2b.

CONCLUSIONS/SIGNIFICANCE

Tfap2b plays important roles in the development of mouse ductus arteriosus and limb patterning. Loss of Tfap2b results in altered Bmp expression that may cause the heart-limb defects observed in Tfap2b mouse mutants and Char syndrome patients. The Tfap2b knockout mouse may add to the very limited available animal models of PDA.

Aberrant expressions of AP-2α splice variants in pancreatic cancer

OBJECTIVES

The present study was conducted to evaluate the expression and function of AP-2α isoforms in pancreatic ductal adenocarcinoma.

METHODS

The expression of AP-2α was evaluated at the RNA level by reverse transcription-polymerase chain reaction and at the protein level by Western blotting and immunofluorescence. Its function as a transcription factor was evaluated in transient transfection experiments: DNA binding properties by electromobility shift assay and transactivation capabilities by luciferase assay.

RESULTS

Multiple alternative splicing events of AP-2α messenger occurred in all human pancreatic cancer cell lines, including a novel isoform, termed variant 6, which was not present in HeLa cells. At the protein level, except for 1 cell line, all pancreatic cancer cell lines expressed high nuclear levels of AP-2α. We also showed that AP-2α expressed by the pancreatic cancer cell lines could bind its cognate recognition site and activate transcription. However, variant 6, although not able to activate transcription, did not act in a dominant negative manner when cotransfected with the full-length protein.

CONCLUSIONS

Multiple isoforms of AP-2α are highly expressed in pancreatic cancer cell lines including a new isoform, AP-2α variant 6, which seems to be pancreatic cancer specific and is deprived of transcriptional activity.

Microarray analysis of gene expression patterns in human proximal tubule cells over a short and long time course of cadmium exposure

Numerous studies showed that renal proximal tubules cells are the cell type critically affected by chronic exposure to cadmium (Cd(2+)). The aim of the present study was to apply global gene expression technology and a human renal epithelial cell culture model (HPT) to determine whether time of exposure to Cd(2+) exerts a major influence on the resulting pattern of global gene expression. HPT cells were exposed to Cd(2+) for a short, 1-d, period of exposure (9, 27, and 45 μM) versus a longer, 13-d, period (4.5, 9, and 27 μM), with the hypothesis being that the stress response of the cells would be more active during the short time of exposure. The results showed that the differential expression of genes was very extensive for HPT cells exposed to Cd(2+) for 1 d, with more than 1848 genes displaying alterations compared to control and with the major categories of genes being involved in stress responses; cell death; checkpoint arrest, DNA repair, and the cell cycle; inflammatory responses; and cell adhesion, motion and differentiation. In contrast, HPT cells exposed to Cd(2+) for 13 d showed 923 genes to be differentially expressed, with a marked reduction in the number of differentially expressed stress response genes and a significant increase in the number of genes involved in development and differentiation. There were 387 differentially expressed genes common to both times of exposure. Data suggest that unless one is actively seeking to study the acute stress response, global gene expression technology should not be applied within an early time course of toxicant exposure.

Roles of AP-2 transcription factors in the regulation of cartilage and skeletal development

During embryogenesis, most of the mammalian skeletal system is preformed as cartilaginous structures that ossify later. The different stages of cartilage and skeletal development are well described, and several molecular factors are known to influence the events of this enchondral ossification, especially transcription factors. Members of the AP-2 family of transcription factors play important roles in several cellular processes, such as apoptosis, migration and differentiation. Studies with knockout mice demonstrate that a main function of AP-2s is the suppression of terminal differentiation during embryonic development. Additionally, the specific role of these molecules as regulators during chondrogenesis has been characterized. This review gives an overview of AP-2s, and discusses the recent findings on the AP-2 family, in particular AP-2alpha, AP-2beta, and AP-2epsilon, as regulators of cartilage and skeletal development.

Transcriptional regulation during development of the ductus arteriosus

The ductus arteriosus is a specialized blood vessel containing highly differentiated and contractile vascular smooth muscle, derived largely from neural crest cells, that is essential for fetal life but typically closes after birth. Impaired development of the ductus arteriosus or disruption of signaling pathways that initiate postnatal closure can result in persistent patency of the ductus arteriosus, the third most common congenital heart defect. We found that Tfap2beta, a transcription factor associated with patent ductus arteriosus in humans, was uniquely expressed in mouse ductal smooth muscle. Endothelin-1 and the hypoxia-induced transcription factor, Hif2alpha were also highly enriched in ductal smooth muscle at embryonic day 13.5 and were dependent on Tfap2beta for their expression in this domain. Hif2alpha functioned as a negative regulator of Tfap2beta-induced transcription by disrupting protein-DNA interactions, suggesting a negative feedback loop regulating Tfap2beta activity. Our data indicate that Tfap2beta, Et-1, and Hif2alpha act in a transcriptional network during ductal smooth muscle development and that disruption of this pathway may contribute to patent ductus arteriosus by affecting the development of smooth muscle within the ductus arteriosus.

Polycystic kidney diseases: from molecular discoveries to targeted therapeutic strategies

Polycystic kidney diseases (PKDs) represent a large group of progressive renal disorders characterized by the development of renal cysts leading to end-stage renal disease. Enormous strides have been made in understanding the pathogenesis of PKDs and the development of new therapies. Studies of autosomal dominant and recessive polycystic kidney diseases converge on molecular mechanisms of cystogenesis, including ciliary abnormalities and intracellular calcium dysregulation, ultimately leading to increased proliferation, apoptosis and dedifferentiation. Here we review the pathobiology of PKD, highlighting recent progress in elucidating common molecular pathways of cystogenesis. We discuss available models and challenges for therapeutic discovery as well as summarize the results from preclinical experimental treatments targeting key disease-specific pathways.

Comparative expression profiling identifies an in vivo target gene signature with TFAP2B as a mediator of the survival function of PAX3/FKHR

The chromosomal translocation t(2;13), characteristic for the aggressive childhood cancer alveolar rhabdomyosarcoma (aRMS), generates the chimeric transcription factor PAX3/FKHR with a well known oncogenic role. However, the molecular mechanisms mediating essential pathophysiological functions remain poorly defined. Here, we used comparative expression profiling of PAX3/FKHR silencing in vitro and PAX3/FKHR-specific gene signatures in vivo to identify physiologically important target genes. Hereby, 51 activated genes, both novel and known, were identified. We also found repression of skeletal muscle-specific genes suggesting that PAX3/FKHR blocks further differentiation of aRMS cells. Importantly, TFAP2B was validated as direct target gene mediating the anti-apoptotic function of PAX3/FKHR. Hence, we developed a pathophysiologically relevant transcriptional profile of PAX3/FKHR and identified a critical target gene for aRMS development.

Activator protein-2 in carcinogenesis with a special reference to breast cancer-A mini review

Activator protein-2 (AP-2) transcription factors are involved in the regulation of cell proliferation, differentiation, apoptosis and carcinogenesis. AP-2alpha has been suggested to function as a tumor suppressor in many cancers and AP-2gamma to be a marker of testicular and germ cell malignancies. At least 3 of the 5 AP-2 family members identified to date, AP-2alpha, AP-2beta and AP-2gamma, are known to be expressed in breast tissue and thought to coordinate the growth and development of the breast via regulation of several breast-related genes such as human epidermal growth factor receptor-2 (HER2) and estrogen receptor (ER). The function of AP-2alpha seems to be tumor suppressive in breast tissue, whereas the role of the other AP-2 family members is less well known. In this review, we summarize the current knowledge of AP-2 in carcinogenesis, especially in breast cancer.

Glomerulocystic kidney disease in mice with a targeted inactivation of Wwtr1

Wwtr1 is a widely expressed 14-3-3-binding protein that regulates the activity of several transcription factors involved in development and disease. To elucidate the physiological role of Wwtr1, we generated Wwtr1-/- mice by homologous recombination. Surprisingly, although Wwtr1 is known to regulate the activity of Cbfa1, a transcription factor important for bone development, Wwtr1-/- mice show only minor skeletal defects. However, Wwtr1-/- animals present with renal cysts that lead to end-stage renal disease. Cysts predominantly originate from the dilation of Bowman's spaces and atrophy of glomerular tufts, reminiscent of glomerulocystic kidney disease in humans. A smaller fraction of cysts is derived from tubules, in particular the collecting duct (CD). The corticomedullary accumulation of cysts also shows similarities with nephronophthisis. Cells lining the cysts carry fewer and shorter cilia and the expression of several genes associated with glomerulocystic kidney disease (Ofd1 and Tsc1) or encoding proteins involved in cilia structure and/or function (Tg737, Kif3a, and Dctn5) is decreased in Wwtr1-/- kidneys. The loss of cilia integrity and the down-regulation of Dctn5, Kif3a, Pkhd1 and Ofd1 mRNA expression can be recapitulated in a renal CD epithelial cell line, mIMCD3, by reducing Wwtr1 protein levels using siRNA. Thus, Wwtr1 is critical for the integrity of renal cilia and its absence in mice leads to the development of renal cysts, indicating that Wwtr1 may represent a candidate gene for polycystic kidney disease in humans.

The AP-2 family of transcription factors

AP-2 transcription factors are involved in cell-type-specific stimulation of proliferation and the suppression of terminal differentiation during embryonic development. Members of the family are found in mammals (with five different proteins in human and mice), frogs and fish, as well as protochordates, insects and nematodes.

The AP-2 family of transcription factors consists of five different proteins in humans and mice: AP-2α, AP-2β, AP-2γ, AP-2δ and AP-2ε. Frogs and fish have known orthologs of some but not all of these proteins, and homologs of the family are also found in protochordates, insects and nematodes. The proteins have a characteristic helix-span-helix motif at the carboxyl terminus, which, together with a central basic region, mediates dimerization and DNA binding. The amino terminus contains the transactivation domain. AP-2 proteins are first expressed in primitive ectoderm of invertebrates and vertebrates; in vertebrates, they are also expressed in the emerging neural-crest cells, and AP-2α^-/- animals have impairments in neural-crest-derived facial structures. AP-2β is indispensable for kidney development and AP-2γ is necessary for the formation of trophectoderm cells shortly after implantation; AP-2α and AP-2γ levels are elevated in human mammary carcinoma and seminoma. The general functions of the family appear to be the cell-type-specific stimulation of proliferation and the suppression of terminal differentiation during embryonic development.

A mouse model for cystic biliary dysgenesis in autosomal recessive polycystic kidney disease (ARPKD)

Autosomal recessive polycystic kidney disease (ARPKD) is an important cause of liver- and renal-related morbidity and mortality in childhood. Recently, PKHD1, the gene encoding the transmembrane protein polyductin, was shown to be mutated in ARPKD patients. We here describe the first mouse strain, generated by targeted mutation of Pkhd1. Due to exon skipping, Pkhd1ex40 mice express a modified Pkhd1 transcript and develop severe malformations of intrahepatic bile ducts. Cholangiocytes maintain a proliferative phenotype and continuously synthesize TGF-beta1. Subsequently, mesenchymal cells within the hepatic portal tracts continue to synthesize collagen, resulting in progressive portal fibrosis and portal hypertension. Fibrosis did not involve the hepatic lobules, and we did not observe any pathological changes in morphology or function of hepatocytes. Surprisingly and in contrast to human ARPKD individuals, Pkhd1ex40 mice develop morphologically and functionally normal kidneys. In conclusion,our data indicate that subsequent to formation of the embryonic ductal plate, dysgenesis of terminally differentiated bile ducts occurs in response to the Pkhd1ex40 mutation. The role of polyductin in liver and kidney may be functionally divergent, because protein domains essential for bile duct development do not affect nephrogenesis in our mouse model.

Do cyclooxygenase-2 knockout mice have primary hyperparathyroidism?

The absence of cyclooxygenase-2 (COX-2) activity in vitro reduces differentiation of both bone-forming and bone-resorbing cells. To examine the balance of COX-2 effects on bone in vivo, we studied COX-2 knockout (KO) and wild-type (WT) mice. After weaning, KO mice died 4 times faster than WT mice, consistent with reports of progressive renal failure in KO mice. Among KO mice killed at 4 months of age, some had renal failure with marked secondary hyperparathyroidism, but others appeared healthy. On the assumption that renal failure was not inevitable in COX-2 KO mice and that phenotypic differences might increase with age, we studied KO mice surviving to 10 months of age with serum creatinine levels similar to those of WT mice. In 10-month-old male KO mice, serum calcium and PTH, but not phosphorus, levels were increased compared with those in WT mice. 1,25-Dihydroxyvitamin D(3) levels were markedly elevated in KO mice. Skeletal analysis showed small nonsignificant decreases in cortical bone density by BMD and either an increase (distal femur, by microcomputed tomography) or no difference (distal femur, by static histomorphometry) in trabecular bone density in KO mice. There was a trend toward increased percent osteoblastic and osteoclastic surfaces, and on dynamic histomorphometry, the rates of trabecular bone formation and mineral apposition were increased in KO mice relative to WT mice. Similar trends were observed for most parameters in 10-month-old female COX-2 KO mice. However, rates of trabecular bone formation and mineral apposition were increased in 10-month-old WT females compared with males and did not increase further in female KO mice. These data suggest that COX-2 KO mice with intact renal function have primary hyperparathyroidism, and that effects of increased PTH and 1,25-dihydroxyvitamin D(3) to increase bone turnover may compensate for the absence of COX-2.

Identification and embryonic expression of a new AP-2 transcription factor, AP-2 epsilon

AP-2 proteins comprise a family of highly related transcription factors, which are expressed during mouse embryogenesis in a variety of ectodermal, neuroectodermal, and mesenchymal tissues. AP-2 transcription factors were shown to be involved in morphogenesis of craniofacial, urogenital, neural crest-derived, and placental tissues. By means of a partial cDNA fragment identified during an expressed sequence tag search for AP-2 genes, we identified a fifth, previously unknown AP-2-related gene, AP-2 epsilon. AP-2 epsilon encodes an open reading frame of 434 amino acids, which reveals the typical modular structure of AP-2 transcription factors with highly conserved C-terminal DNA binding and dimerization domains. Although the N-terminally localized activation domain is less homologous, position and identity of amino acids essential for transcriptional transactivation are conserved. Reverse transcriptase-polymerase chain reaction analyses of murine embryos revealed AP-2 epsilon expression from gestational stage embryonic day 7.5 throughout all later embryonic stages until birth. Whole-mount in situ hybridization using a specific AP-2 epsilon cDNA fragment demonstrated that during embryogenesis, expression of AP-2 epsilon is mainly restricted to neural tissue, especially the midbrain, hindbrain, and olfactory bulb. This expression pattern was confirmed by immunohistochemistry with an AP-2 epsilon-specific antiserum. By using this antiserum, we could further localize AP-2 epsilon expression in a hypothalamic nucleus and the neuroepithelium of the vomeronasal organ, suggesting an important function of AP-2 epsilon for the development of the olfactory system.

Aberrant polycystin-1 expression results in modification of activator protein-1 activity, whereas Wnt signaling remains unaffected

Polycystin-1, the polycystic kidney disease 1 gene product, has been implicated in several signaling complexes that are known to regulate essential cellular functions. We investigated the role of polycystin-1 in Wnt signaling and activator protein-1 (AP-1) activation. To this aim, a membrane-targeted construct encoding the conserved C-terminal region of mouse polycystin-1 reported to mediate signal transduction activity was expressed in human embryonic and renal epithelial cells. To ensure specificity and minimal cotransfection effects, we focused our study on the endogenous proteins that actually transduce the signals, beta-catenin and T-cell factor/lymphoid-enhancing factor for Wnt signaling and (phosphorylated) c-Jun, ATF2, and c-Fos for AP-1. Our data indicate that the C-terminal region of polycystin-1 activates AP-1 by inducing phosphorylation and expression of at least c-Jun and ATF2, whereas c-Fos was not affected. Under our experimental conditions, polycystin-1 did not modulate Wnt signaling. AP-1 activity was aberrant in human autosomal dominant polycystic kidney disease (ADPKD) renal cystic epithelial cells and in renal epithelial cells expressing transgenic full-length polycystin-1, resulting in decreased Jun-ATF and increased Jun-Fos activity, whereas Wnt signaling remained unaffected. Since our data indicate that aberrant polycystin-1 expression results in altered AP-1 activity, polycystin-1 may be required for adequate AP-1 activity.