Mouse forkhead (winged helix) gene LUN encodes a transactivator that acts in the lung

De Novo mutation of FOXF1 causes alveolar capillary dysplasia with misalignment of pulmonary veins: A case report

RATIONALE

Alveolar capillary dysplasia with misalignment of the pulmonary veins (ACD/MPV) is a rare congenital malformation in neonates that results in severe respiratory distress and pulmonary hypertension. ACD/MPV is caused by mutations in the FOXF1 gene. Herein, a new case of a girl with ACD/MPV carrying a novel pathogenic variant of FOXF1 was reported.

PATIENT CONCERNS

A 3-month-old Chinese girl was admitted to the hospital presenting a complaint of cyanosis for 10 days and respiratory distress for 2 days. The history of foreign body inhalation was denied.

DIAGNOSES

Blood routine, liver and kidney function, electrolytes, type B natriuretic peptide, electrocardiogram, cardiac computed tomography (CT), and echocardiography were done after admission. Dysplasia of the alveolar and the left upper pulmonary vein was displayed through cardiac CT. Echocardiography showed atrial septal defect, tricuspid valve malformation, and pulmonary hypertension. Sequence analysis of FOXF1 from genomic deoxyribonucleic acid (DNA) revealed that the patient was heterozygous for a novel missense variant (c.418 C>T, p.Pro140Gly). Furthermore, genetic analysis of both parents confirmed the de novo occurrence of the variant. Conservation analysis showed that the locus was highly conserved across species. Then, ACD/MPV was a clinical diagnosis.

INTERVENTIONS

After admission, nasal catheter oxygen inhalation, cefazoxime sodium, furosemide diuretic, milrinone lactate, and Bosentan were given to the patient.

OUTCOMES

After 6 days of hospitalization, the patient's condition did not improved, the parents gave up treatment and discharged. The patient died half a month after discharge.

LESSONS

ACD/MPV is a rare congenital malformation with a poor prognosis. A new de novo mutation of FOXF1 was found in our case. Non-invasive methods such as DNA sequencing and FOXF1 analysis are helpful in the clinical diagnosis of ACD/MPV especially in early infants with respiratory distress and pulmonary hypertension.

Disruption of FOXF2 as a Likely Cause of Absent Uvula in an Egyptian Family

This study investigated the genetic basis of an unusual autosomal dominant phenotype characterized by familial absent uvula, with a short posterior border of the soft palate, abnormal tonsillar pillars, and velopharyngeal insufficiency. Cytogenetic analysis and single-nucleotide polymorphism-based linkage analysis were investigated in a 4-generation family with 8 affected individuals. Whole exome sequencing data were overlaid, and segregation analysis identified a single missense variant, p.Q433P in the FOXF2 transcription factor, that fully segregated with the phenotype. This was found to be in linkage disequilibrium with a small 6p25.3 tandem duplication affecting FOXC1 and GMDS. Notably, the copy number imbalances of this region are commonly associated with pathologies that are not present in this family. Bioinformatic predictions with luciferase reporter studies of the FOXF2 missense variant indicated a negative impact, affecting both protein stability and transcriptional activation. Foxf 2 is expressed in the posterior mouse palate, and knockout animals develop an overt cleft palate. Since mice naturally lack the structural equivalent of the uvula, we demonstrated FOXF2 expression in the developing human uvula. Decipher also records 2 individuals with hypoplastic or bifid uvulae with copy number variants affecting FOXF2. Nevertheless, given cosegregation with the 6p25.3 duplications, we cannot rule out a combined effect of these gains and the missense variant on FOXF2 function, which may account for the rare palate phenotype observed.

Comparative analysis of genes regulated by Dzip1/iguana and hedgehog in zebrafish

BACKGROUND

The zebrafish genetic mutant iguana (igu) has defects in the ciliary basal body protein Dzip1, causing improper cilia formation. Dzip1 also interacts with the downstream transcriptional activators of Hedgehog (Hh), the Gli proteins, and Hh signaling is disrupted in igu mutants. Hh governs a wide range of developmental processes, including stabilizing developing blood vessels to prevent hemorrhage. Using igu mutant embryos and embryos treated with the Hh pathway antagonist cyclopamine, we conducted a microarray to determine genes involved in Hh signaling mediating vascular stability.

RESULTS

We identified 40 genes with significantly altered expression in both igu mutants and cyclopamine-treated embryos. For a subset of these, we used in situ hybridization to determine localization during embryonic development and confirm the expression changes seen on the array.

CONCLUSIONS

Through comparing gene expression changes in a genetic model of vascular instability with a chemical inhibition of Hh signaling, we identified a set of 40 differentially expressed genes with potential roles in vascular stabilization.

Foxf2: a novel locus for anterior segment dysgenesis adjacent to the Foxc1 gene

Anterior segment dysgenesis (ASD) is characterised by an abnormal migration of neural crest cells or an aberrant differentiation of the mesenchymal cells during the formation of the eye's anterior segment. These abnormalities result in multiple tissue defects affecting the iris, cornea and drainage structures of the iridocorneal angle including the ciliary body, trabecular meshwork and Schlemm's canal. In some cases, abnormal ASD development leads to glaucoma, which is usually associated with increased intraocular pressure. Haploinsufficiency through mutation or chromosomal deletion of the human FOXC1 transcription factor gene or duplications of the 6p25 region is associated with a spectrum of ocular abnormalities including ASD. However, mapping data and phenotype analysis of human deletions suggests that an additional locus for this condition may be present in the same chromosomal region as FOXC1. DHPLC screening of ENU mutagenised mouse archival tissue revealed five novel mouse Foxf2 mutations. Re-derivation of one of these (the Foxf2^W174R mouse lineage) resulted in heterozygote mice that exhibited thinning of the iris stroma, hyperplasia of the trabecular meshwork, small or absent Schlemm's canal and a reduction in the iridocorneal angle. Homozygous E18.5 mice showed absence of ciliary body projections, demonstrating a critical role for Foxf2 in the developing eye. These data provide evidence that the Foxf2 gene, separated from Foxc1 by less than 70 kb of genomic sequence (250 kb in human DNA), may explain human abnormalities in some cases of ASD where FOXC1 has been excluded genetically.

The mouse forkhead gene Foxp2 modulates expression of the lung genes

AIMS

Foxp2 is expressed in the lung during mouse development. A monoclonal anti-mouse Foxp2 antibody was created to determine the expression pattern in the developing lung. Next, transcriptional control of two lung genes, CC10 and surfactant protein C (SPC) genes, by Foxp2 was investigated in H441 and A549 cells. Thirdly, expression patterns of Foxp2 and Foxf2 were compared in the developing lung. Finally, Foxp2 expression was determined in the Foxf2-null mice.

MAIN METHODS

Immunohistochemical staining and in situ hybridization were applied to the sections of lungs in the developing embryos.

KEY FINDINGS

Monoclonal anti-Foxp2 antibody demonstrated that Foxp2 was expressed in the bronchial epithelium at E10.5 and its expression became restricted to the distal portion of the elongating bronchiolar epithelium and finally to type II alveolar epithelial cells around birth and in the adult. Foxp2 activated the SPC gene promoter in the presence of Nkx2.1 in A549 cells while it repressed the CC10 gene promoter in H441 cells. Next, the expression domains of the Foxp2 and Foxf2 were found to be exclusive in the lung. Finally, the expression of Foxp2 did not change in the lung of Foxf2-null mice.

SIGNIFICANCE

The Foxp2 protein is expressed in the growing distal edge of airway epithelium. When the bronchiolus elongates, Foxp2 suppresses CC10 expression. When the lung alveolus is formed, Foxp2 modulates the Nkx2.1-mediated SPC expression in type II alveolar cells. Foxp2 and Foxf2 independently play distinct roles in the alveoli and the mesenchyme, respectively.

Effects of cigarette smoke on the activation of oxidative stress-related transcription factors in female A/J mouse lung

Cigarette smoke contains a high concentration of free radicals and induces oxidative stress in the lung and other tissues. Several transcription factors are known to be activated by oxidative stress, including nuclear factor-kappaB (NF-kappaB), activator protein-1 (AP-1), and hypoxia-inducible factor (HIF). Studies were therefore undertaken to examine whether cigarette smoke could activate these transcription factors, as well as other transcription factors that may be important in lung carcinogenesis. Female A/J mice were exposed to cigarette smoke for 2, 5, 10, 15, 20, 42, or 56 d (6 hr/d, 5 d/wk). Cigarette smoke did not increase NF-kappaB activation at any of these times, but NF-kappaB DNA binding activity was lower after 15 d and 56 d of smoke exposure. The DNA binding activity of AP-1 was lower after 10 d and 56 d but was not changed after 42 d of smoke exposure. The DNA binding activity of HIF was quantitatively increased after 42 d of smoke exposure but decreased after 56 d. Whether the activation of other transcription factors in the lung could be altered after exposure to cigarette smoke was subsequently examined. The DNA binding activities of FoxF2, myc-CF1, RORE, and p53 were examined after 10 d of smoke exposure. The DNA binding activities of FoxF2 and p53 were quantitatively increased, but those of myc-CF1 and RORE were unaffected. These studies show that cigarette smoke exposure leads to quantitative increases in DNA binding activities of FoxF2 and p53, while the activations of NF-kappaB, AP-1, and HIF are largely unaffected or reduced.

Antiviral activity of CHO-SS cell-derived human omega interferon and other human interferons against HCV RNA replicons and related viruses

The fully glycosylated human omega interferon produced from CHO-SS cells (glycosylated IFN-omega) has been shown to be well-tolerated in man and to induce a sustained virologic response in patients infected with hepatitis C virus (HCV). We examined the antiviral activity of glycosylated IFN-omega and various human IFNs (IFN-alpha, -beta, -gamma and non-glycosylated bacterial (Escherichia coli) recombinant IFN-omega (non-glycosylated IFN-omega)) against HCV RNA replicons and several viruses related to HCV. Since none of the IFNs displayed cytotoxicity we compared their activities based on the effective concentration of the IFN that inhibited virus growth by 50% (EC50). Glycosylated IFN-omega was found to be the most potent antiviral agent of all the IFNs tested against bovine viral diarrhea virus (BVDV), yellow fever virus and West Nile virus. With HCV RNA replicons, non-glycosylated IFN-omega was comparable in activity to IFN-alpha while glycosylated IFN-omega was markedly more potent, indicating that glycosylation has an important effect on its activity. Drug combination analysis of glycosylated IFN-omega+ribavirin (RBV) in BVDV showed a synergy of antiviral effects similar to IFN-alpha+RBV, as well as a unique antagonism of RBV cytotoxic effects by glycosylated IFN-omega. Transcription factor (TF) profiling indicated that IFN-alpha or glycosylated IFN-omega treatment upregulated the same 17 TFs. IFN-alpha and glycosylated IFN-omega also upregulated 9 and 40 additional unique TFs, respectively. The differences in the expression of these TFs were modest, but statistically significantly different for eight of the TFs that were upregulated exclusively by glycosylated IFN-omega. The activation of these additional TFs by glycosylated IFN-omega might contribute to its high potency.

Hedgehog signaling in the neural crest cells regulates the patterning and growth of facial primordia

Facial abnormalities in human SHH mutants have implicated the Hedgehog (Hh) pathway in craniofacial development, but early defects in mouse Shh mutants have precluded the experimental analysis of this phenotype. Here, we removed Hh-responsiveness specifically in neural crest cells (NCCs), the multipotent cell type that gives rise to much of the skeleton and connective tissue of the head. In these mutants, many of the NCC-derived skeletal and nonskeletal components are missing, but the NCC-derived neuronal cell types are unaffected. Although the initial formation of branchial arches (BAs) is normal, expression of several Fox genes, specific targets of Hh signaling in cranial NCCs, is lost in the mutant. The spatially restricted expression of Fox genes suggests that they may play an important role in BA patterning. Removing Hh signaling in NCCs also leads to increased apoptosis and decreased cell proliferation in the BAs, which results in facial truncation that is evident by embryonic day 11.5 (E11.5). Together, our results demonstrate that Hh signaling in NCCs is essential for normal patterning and growth of the face. Further, our analysis of Shh-Fox gene regulatory interactions leads us to propose that Fox genes mediate the action of Shh in facial development.

Differences in the embryonic expression patterns of mouseFoxf1 and -2 match their distinct mutant phenotypes

Murine genes encoding the forkhead transcription factors Foxf1 and -2 are both expressed in derivatives of the splanchnic mesoderm, i.e., the mesenchyme of organs derived from the primitive gut. In addition, Foxf2 is also expressed in limbs and the central nervous system. Targeted mutagenesis of Foxf1 and -2 suggests that Foxf1 is the more important of the two mammalian FoxF genes with early embryonic lethality of null embryos and a haploinsufficiency phenotype affecting foregut-derived organs. In contrast, the only reported defect in Foxf2 null embryos is cleft palate. To investigate if the differences in mutant phenotype can be attributed to nonoverlapping expression patterns or if distinct functions of the encoded proteins have to be inferred, we analyzed the early embryonic expression of Foxf2 and compared it with that of the better investigated Foxf1. We find that in the early embryo, Foxf1 is completely dominating-in terms of expression-in extraembryonic and lateral plate mesoderm, consistent with the malformations and early lethality of Foxf1 null mutants. Along the developing gut, Foxf1 is highly expressed throughout, whereas Foxf2 expression is concentrated to the posterior part-fitting the foregut haploinsufficiency phenotypes of Foxf1 mutants. Foxf2, on the other hand, is more prominent than Foxf1 in mesenchyme around the oral cavity, as would be predicted from the cleft palate phenotype. The differences in expression pattern also highlight areas where defects should be sought for in the Foxf2 mutant, for example limbs, the posterior gut, genitalia, and derivatives of the neural crest mesenchyme.

Forkhead transcription factor Foxf2 (LUN)-deficient mice exhibit abnormal development of secondary palate

The forkhead genes encode a transcription factor involved in embryogenesis and pattern formation in multicellular organisms. They are mammalian transcriptional regulators that bind DNA as a monomer through their forkhead domain. The Foxf2 (LUN) mRNA is expressed in the mesenchyme directly adjacent to the ectoderm-derived epithelium in the developing tongue and in the mesenchyme adjacent to the endoderm-derived epithelium in the gastrointestinal (GI) tract, lungs, and genitalia. To investigate the developmental role of the Foxf2 gene during embryogenesis, we disrupted the Foxf2 gene and showed that these mutant mice died shortly after birth. Mice lacking the Foxf2 gene were found to develop cleft palate and an abnormal tongue. In addition, we found that the GI tract and the lungs of Foxf2-deficient newborn mice were normal in both morphology and function. These results suggest that the Foxf2 gene plays key roles in palatogenesis by reshaping the growing tongue.

Phenotype discovery by gene expression profiling: mapping of biological processes linked to BMP-2-mediated osteoblast differentiation

Understanding physiological control of osteoblast differentiation necessitates characterization of the regulatory signals that initiate the events directing a cell to lineage commitment and establishing competency for bone formation. The bone morphogenetic protein, BMP-2, a member of the TGFbeta superfamily, induces osteoblast differentiation and functions through the Smad signal transduction pathway during in vivo bone formation. However, the molecular targets of BMP-mediated gene transcription during the process of osteoblast differentiation have not been comprehensively identified. In the present study, BMP-2 responsive factors involved in the early stages of commitment and differentiation to the osteoblast phenotype were analyzed by microarray gene expression profiling in samples ranging from 1 to 24 h following BMP-2 dependent differentiation of C2C12 premyoblasts into the osteogenic lineage. A total of 1,800 genes were responsive to BMP-2 and expression was modulated from 3- to 14-fold for less than 100 genes during the time course. Approximately 50% of these 100 genes are either up- or downregulated. Major events associated with phenotypic changes towards the osteogenic lineage were identified from hierarchical and functional clustering analyses. BMP-2 immediately responsive genes (1-4 h), which exhibited either transient or sustained expression, reflect activation and repression of non-osseous BMP-2 developmental systems. This initial response was followed by waves of expression of nuclear proteins and developmental regulatory factors including inhibitors of DNA binding, Runx2, C/EBP, Zn finger binding proteins, forkhead, and numerous homeobox proteins (e.g., CDP/cut, paired, distaless, Hox) which are expressed at characterized stages during osteoblast differentiation. A sequential profile of genes mediating changes in cell morphology, cell growth, and basement membrane formation is observed as a secondary transient early response (2-8 h). Commitment to the osteogenic phenotype is recognized by 8 h, reflected by downregulation of most myogenic-related genes and induction of a spectrum of signaling proteins and enzymes facilitating synthesis and assembly of an extracellular skeletal environment. These genes included collagens Type I and VI and the small leucine rich repeat family of proteoglycans (e.g., decorin, biglycan, osteomodulin, fibromodulin, and osteoadherin/osteoglycin) that reached peak expression at 24 h. With extracellular matrix development, the bone phenotype was further established from 16 to 24 h by induction of genes for cell adhesion and communication and enzymes that organize the bone ECM. Our microarray analysis resulted in the discovery of a class of genes, initially described in relation to differentiation of astrocytes and oligodendrocytes that are functionally coupled to signals for cellular extensions. They include nexin, neuropilin, latexin, neuroglian, neuron specific gene 1, and Ulip; suggesting novel roles for these genes in the bone microenvironment. This global analysis identified a multistage molecular and cellular cascade that supports BMP-2-mediated osteoblast differentiation.

IKKalpha, IKKbeta, and NEMO/IKKgamma are each required for the NF-kappa B-mediated inflammatory response program

The IKKbeta and NEMO/IKKgamma subunits of the NF-kappaB-activating signalsome complex are known to be essential for activating NF-kappaB by inflammatory and other stress-like stimuli. However, the IKKalpha subunit is believed to be dispensable for the latter responses and instead functions as an in vivo mediator of other novel NF-kappaB-dependent and -independent functions. In contrast to this generally accepted view of IKKalpha's physiological functions, we demonstrate in mouse embryonic fibroblasts (MEFs) that, akin to IKKbeta and NEMO/IKKgamma, IKKalpha is also a global regulator of tumor necrosis factor alpha- and IL-1-responsive IKK signalsome-dependent target genes including many known NF-kappaB targets such as serum amyloid A3, C3, interleukin (IL)-6, IL-11, IL-1 receptor antagonist, vascular endothelial growth factor, Ptx3, beta(2)-microglobulin, IL-1alpha, Mcp-1 and -3, RANTES (regulated on activation normal T cell expressed and secreted), Fas antigen, Jun-B, c-Fos, macrophage colony-stimulating factor, and granulocyte-macrophage colony-stimulating factor. Only a small number of NF-kappaB-dependent target genes were preferentially dependent on IKKalpha or IKKbeta. Constitutive expression of a trans-dominant IkappaBalpha superrepressor (IkappaBalphaSR) in wild type MEFs confirmed that these signalsome-dependent target genes were also dependent on NF-kappaB. A subset of NF-kappaB target genes were IKK-dependent in the absence of exogenous stimuli, suggesting that the signalsome was also required to regulate basal levels of activated NF-kappaB in established MEFs. Overall, a sizable number of novel NF-kappaB/IKK-dependent genes were identified including Secreted Frizzled, cadherin 13, protocadherin 7, CCAAT/enhancer-binding protein-beta and -delta, osteoprotegerin, FOXC2 and FOXF2, BMP-2, p75 neurotrophin receptor, caspase-11, guanylate-binding proteins 1 and 2, ApoJ/clusterin, interferon (alpha and beta) receptor 2, decorin, osteoglycin, epiregulin, proliferins 2 and 3, stromal cell-derived factor, and cathepsins B, F, and Z. SOCS-3, a negative effector of STAT3 signaling, was found to be an NF-kappaB/IKK-induced gene, suggesting that IKK-mediated NF-kappaB activation can coordinately illicit negative effects on STAT signaling.

Wild-type levels of the mouse Forkhead Box f1 gene are essential for lung repair

The Forkhead Box (Fox) family of transcription factors plays important roles in regulating expression of genes involved in cellular proliferation and differentiation. In a previous study, we showed that newborn foxf1(+/-) mice with diminished Foxf1 levels exhibited abnormal formation of pulmonary alveoli and capillaries and died postnatally. Interestingly, surviving newborn foxf1(+/-) mice exhibited increased pulmonary Foxf1 levels and normal adult lung morphology, suggesting that wild-type Foxf1 levels are required for lung development and function. The present study was conducted to determine whether adult foxf1(+/-) mice were able to undergo lung repair similar to that observed in wild-type mice. We demonstrated that adult foxf1(+/-) mice died from severe lung hemorrhage after butylated hydroxytoluene (BHT) lung injury and that this phenotype was associated with a 10-fold decrease in pulmonary Foxf1 expression and increased alveolar endothelial cell apoptosis that disrupted capillary integrity. Furthermore, BHT-induced lung hemorrhage of adult foxf1(+/-) mice was associated with a drastic reduction in expression of the Flk-1, bone morphogenetic protein-4, surfactant protein B, platelet endothelial cell adhesion molecule, and vascular endothelial cadherin genes, whereas the expression of these genes was either transiently diminished or increased in wild-type lungs after BHT injury. Because these proteins are critical for lung morphogenesis and endothelial homeostasis, their decreased mRNA levels are likely contributing to BHT-induced lung hemorrhage in foxf1(+/-) mice. Collectively, our data suggest that sustained expression of Foxf1 is essential for normal lung repair and endothelial cell survival in response to pulmonary cell injury.

GATA6 regulates differentiation of distal lung epithelium

GATA6 is a member of the GATA family of zinc-finger transcriptional regulators and is the only known GATA factor expressed in the distal epithelium of the lung during development. To define the role that GATA6 plays during lung epithelial cell development, we expressed a GATA6-Engrailed dominant-negative fusion protein in the distal lung epithelium of transgenic mice. Transgenic embryos lacked detectable alveolar epithelial type 1 cells in the distal airway epithelium. These embryos also exhibited increased Foxp2 gene expression, suggesting a disruption in late alveolar epithelial differentiation. Alveolar epithelial type 2 cells, which are progenitors of alveolar epithelial type 1 cells, were correctly specified as shown by normal thyroid transcription factor 1 and surfactant protein A gene expression. However, attenuated endogenous surfactant protein C expression indicated that alveolar epithelial type 2 cell differentiation was perturbed in transgenic embryos. The number of proximal airway tubules is also reduced in these embryos, suggesting a role for GATA6 in regulating distal-proximal airway development. Finally, a functional role for GATA factor function in alveolar epithelial type 1 cell gene regulation is supported by the ability of GATA6 to trans-activate the mouse aquaporin-5 promoter. Together, these data implicate GATA6 as an important regulator of distal epithelial cell differentiation and proximal airway development in the mouse.

Transcription factors in mouse lung development and function

Development of the mouse lung initiates on day 9.5 postcoitum from the laryngotracheal groove and involves mesenchymal-epithelial interactions, in particular, those between the splanchnic mesoderm and epithelial cells (derived from foregut endoderm) that induce cellular proliferation, migration, and differentiation, resulting in branching morphogenesis. This developmental process mediates formation of the pulmonary bronchiole tree and integrates a terminal alveolar region with an extensive endothelial capillary bed, which facilitates efficient gas exchange with the circulatory system. The major function of the mesenchymal-epithelial signaling is to potentiate the activity or expression of cell type-specific transcription factors in the developing lung, which, in turn, cooperatively bind to distinct promoter regions and activate target gene expression. In this review, we focus on the role of transcription factors in lung morphogenesis and the maintenance of differentiated gene expression. These lung transcription factors include forkhead box A2 [also known as hepatocyte nuclear factor (HNF)-3beta], HNF-3/forkhead homolog (HFH)-8 [also known as FoxF1 or forkhead-related activator-1], HNF-3/forkhead homolog-4 (also known as FoxJ1), thyroid transcription factor-1 (Nkx2.1), and homeodomain box A5 transcription factors, the zinc finger Gli (mouse homologs of the Drosophila cubitus interruptus) and GATA transcription factors, and the basic helix-loop-helix Pod1 transcription factor. We summarize the phenotypes of transgenic and knockout mouse models, which define important functions of these transcription factors in cellular differentiation and lung branching morphogenesis.

Proximal promoter of the surfactant protein D gene: regulatory roles of AP-1, forkhead box, and GT box binding proteins

Surfactant protein D (SP-D) plays roles in pulmonary host defense and surfactant homeostasis and is increased following lung injury. Because AP-1 proteins regulate cellular responses to diverse environmental stimuli, we hypothesized that the conserved AP-1 motif (at -109) and flanking sequences in the human SP-D promoter contribute to the regulation of SP-D expression. The AP-1 sequence specifically bound to fra-1, junD, and junB in H441 lung adenocarcinoma nuclear extracts. Mutagenesis of the AP-1 motif in a chloramphenicol acetyltransferase reporter construct containing 285 base pairs of upstream sequence nearly abolished promoter activity, and co-transfection of junD significantly increased wild type but not mutant promoter activity. The sequence immediately downstream of the AP-1 element contained a binding site for HNF-3 (FOXA), and simultaneous mutation of this site (fox-d) and an upstream FoxA binding site (-277, fox-u) caused a 4-fold reduction in chloramphenicol acetyltransferase activity. Immediately upstream of the AP-1-binding site, we identified a GT box-containing positive regulatory element. Despite finding regions of limited homology to the thyroid transcription factor 1-binding site, SP-D promoter activity did not require thyroid transcription factor 1. Thus, transcriptional regulation of SP-D gene expression involves complex interactions with ubiquitous and lineage-dependent factors consistent with more generalized roles in innate immunity.

Isolation and localization of type IIb Na/Pi cotransporter in the developing rat lung

Differential display analysis of rat lung at different developmental stages identified a fragment, HG80, which appeared on embryonic day 16.5 and thereafter. A full-length cDNA derived from a cDNA library of newborn rat lung probed with HG80 was the rat counterpart of sodium-dependent phosphate transporter type IIb and was designated rNaPi IIb. In situ hybridization showed that rNaPi IIb was expressed in type II alveolar cells, suggesting a role in the synthesis of surfactant in the alveoli. The time-dependent changes in localization of this gene in the developing lung and its possible use as a type II pneumocyte marker are discussed.

Forkhead transcription factor FoxF2 is expressed in mesodermal tissues involved in epithelio-mesenchymal interactions

The growing family of forkhead transcription factors plays many important roles during embryonic development. In this study we have used in situ hybridization to explore the expression pattern of the forkhead transcription factor gene FoxF2 (FREAC-2, LUN) during mouse and rat embryogenesis, postnatal development, and in adult tissues. We demonstrate that FoxF2 is expressed in the mesenchyme adjacent to the epithelium in alimentary, respiratory, and urinary tracts, similar to FoxF1 (FREAC-1, HFH-8). FoxF2 mRNA was also observed in organs that do not express FoxF1 during embryogenesis, e.g., in the central nervous system, eye, ear, and limb buds. In organs that express both FoxF2 and FoxF1, these transcription factors may have similar functions in epithelio-mesenchymal cross-talk, but the fact that FoxF2 is more widely expressed than FoxF1 suggests that FoxF2 also has an independent role as a developmental regulator.

Genomic structure and embryonic expression of the Xenopus winged helix factors XFD-13/13'

We have isolated the gene, its corresponding cDNA and a closely related cDNA encoding the Xenopus winged helix factors XFD-13' and XFD-13, respectively. XFD-13/13' are regarded as pseudo-alleles and, based upon a comparison of sequences and genomic structures, represent the Xenopus orthologues to mammalian FREAC-1/HFH-8. XFD-13/13' genes are not transcribed during oogenesis, zygotic transcription starts at late gastrula/early neurula and transcripts persist throughout embryogenesis. Expression is found within head derived neural crest cells and the dorsolateral plate (DLP). At later developmental stages, cell populations of the DLP migrate to the ventral region but exclude the most posterior part. Since they are subsequently found to accumulate in vessel like structures, we suggest that these cells represent hematopoietic/endothelial progenitor cells.