Stochastic Epidemic Models inference and diagnosis with Poisson Random Measure Data Augmentation.

We present a new Bayesian inference method for compartmental models that takes into account the intrinsic stochasticity of the process. We show how to formulate a SIR-type Markov jump process as the solution of a stochastic differential equation with respect to a Poisson Random Measure (PRM), and how to simulate the process trajectory deterministically from a parameter value and a PRM realization. This forms the basis of our Data Augmented MCMC, which consists of augmenting parameter space with the unobserved PRM value. The resulting simple Metropolis-Hastings sampler acts as an efficient simulation-based inference method, that can easily be transferred from model to model. Compared with a recent Data Augmentation method based on Gibbs sampling of individual infection histories, PRM-augmented MCMC scales much better with epidemic size and is far more flexible. It is also found to be competitive with Particle MCMC for moderate epidemics when using approximate simulations. PRM-augmented MCMC also yields a posteriori estimates of the PRM, that represent process stochasticity, and which can be used to validate the model. A pattern of deviation from the PRM prior distribution will indicate that the model underfits the data and help to understand the cause. We illustrate this by fitting a non-seasonal model to some simulated seasonal case count data. Applied to the Zika epidemic of 2013 in French Polynesia, our approach shows that a simple SEIR model cannot correctly reproduce both the initial sharp increase in the number of cases as well as the final proportion of seropositive. PRM augmentation thus provides a coherent story for Stochastic Epidemic Model inference, where explicitly inferring process stochasticity helps with model validation.

The reality of Neandertal symbolic behavior at the Grotte du Renne, Arcy-sur-Cure, France.

BACKGROUND: The question of whether symbolically mediated behavior is exclusive to modern humans or shared with anatomically archaic populations such as the Neandertals is hotly debated. At the Grotte du Renne, Arcy-sur-Cure, France, the Châtelperronian levels contain Neandertal remains and large numbers of personal ornaments, decorated bone tools and colorants, but it has been suggested that this association reflects intrusion of the symbolic artifacts from the overlying Protoaurignacian and/or of the Neandertal remains from the underlying Mousterian. METHODOLOGY/PRINCIPAL FINDINGS: We tested these hypotheses against the horizontal and vertical distributions of the various categories of diagnostic finds and statistically assessed the probability that the Châtelperronian levels are of mixed composition. Our results reject that the associations result from large or small scale, localized or generalized post-depositional displacement, and they imply that incomplete sample decontamination is the parsimonious explanation for the stratigraphic anomalies seen in the radiocarbon dating of the sequence. CONCLUSIONS/SIGNIFICANCE: The symbolic artifacts in the Châtelperronian of the Grotte du Renne are indeed Neandertal material culture.

A perfusion-independent role of blood vessels in determining branching stereotypy of lung airways.

Blood vessels have been shown to play perfusion-independent roles in organogenesis. Here, we examined whether blood vessels determine branching stereotypy of the mouse lung airways in which coordinated branching of epithelial and vascular tubes culminates in their co-alignment. Using different ablative strategies to eliminate the lung vasculature, both in vivo and in lung explants, we show that proximity to the vasculature is indeed essential for patterning airway branching. Remarkably, although epithelial branching per se proceeded at a nearly normal rate, branching stereotypy was dramatically perturbed following vascular ablation. Specifically, branching events requiring a rotation to change the branching plane were selectively affected. This was evidenced by either the complete absence or the shallow angle of their projections, with both events contributing to an overall flat lung morphology. Vascular ablation also led to a high frequency of ectopic branching. Regain of vascularization fully rescued arrested airway branching and restored normal lung size and its three-dimensional architecture. This role of the vasculature is independent of perfusion, flow or blood-borne substances. Inhibition of normal branching resulting from vascular loss could be explained in part by perturbing the unique spatial expression pattern of the key branching mediator FGF10 and by misregulated expression of the branching regulators Shh and sprouty2. Together, these findings uncovered a novel role of the vasculature in organogenesis, namely, determining stereotypy of epithelial branching morphogenesis.

FGF10 controls the patterning of the tracheal cartilage rings via Shh.

During embryonic development, appropriate dorsoventral patterning of the trachea leads to the formation of periodic cartilage rings from the ventral mesenchyme and continuous smooth muscle from the dorsal mesenchyme. In this work, we have investigated the role of two crucial morphogens, fibroblast growth factor 10 and sonic hedgehog, in the formation of periodically alternating cartilaginous and non-cartilaginous domains in the ventral mesenchyme. Using a combination of gain- and loss-of-function approaches for FGF10 and SHH, we demonstrate that precise spatio-temporal patterns and appropriate levels of expression of these two signaling molecules in the ventral area are crucial between embryonic day 11.5 and 13.5 for the proper patterning of the cartilage rings. We conclude that the expression level of FGF10 in the mesenchyme has to be within a critical range to allow for periodic expression of Shh in the ventral epithelium, and consequently for the correct patterning of the cartilage rings. We propose that disturbed balances of Fgf10 and Shh may explain a subset of human tracheomalacia without tracheo-esophageal fistula or tracheal atresia.

Mouse embryonic lung culture, a system to evaluate the molecular mechanisms of branching.

Lung primordial specification as well as branching morphogenesis, and the formation of various pulmonary cell lineages requires a specific interaction of the lung endoderm with its surrounding mesenchyme and mesothelium. Lung mesenchyme has been shown to be the source of inductive signals for lung branching morphogenesis. Epithelial-mesenchymal-mesothelial interactions are also critical to embryonic lung morphogenesis. Early embryonic lung organ culture is a very useful system to study epithelial-mesenchymal interactions. Both epithelial and mesenchymal morphogenesis proceeds under specific conditions that can be readily manipulated in this system (in the absence of maternal influence and blood flow). More importantly this technique can be readily done in a serumless, chemically defined culture media. Gain and loss of function can be achieved using expressed proteins, recombinant viral vectors and/or analysis of transgenic mouse strains, antisense RNA, as well as RNA interference gene knockdown.

Chemical genetics screen for enhancers of rapamycin identifies a specific inhibitor of an SCF family E3 ubiquitin ligase.

The target of rapamycin (TOR) plays a central role in eukaryotic cell growth control. With prevalent hyperactivation of the mammalian TOR (mTOR) pathway in human cancers, strategies to enhance TOR pathway inhibition are needed. We used a yeast-based screen to identify small-molecule enhancers of rapamycin (SMERs) and discovered an inhibitor (SMER3) of the Skp1-Cullin-F-box (SCF)(Met30) ubiquitin ligase, a member of the SCF E3-ligase family, which regulates diverse cellular processes including transcription, cell-cycle control and immune response. We show here that SMER3 inhibits SCF(Met30) in vivo and in vitro, but not the closely related SCF(Cdc4). Furthermore, we demonstrate that SMER3 diminishes binding of the F-box subunit Met30 to the SCF core complex in vivo and show evidence for SMER3 directly binding to Met30. Our results show that there is no fundamental barrier to obtaining specific inhibitors to modulate function of individual SCF complexes.

Explant culture of mouse embryonic whole lung, isolated epithelium, or mesenchyme under chemically defined conditions as a system to evaluate the molecular mechanism of branching morphogenesis and cellular differentiation.

Lung primordial specification as well as branching morphogenesis, and the formation of various pulmonary cell lineages, requires a specific interaction of the lung endoderm with its surrounding mesenchyme and mesothelium. Lung mesenchyme has been shown to be the source of inductive signals for lung branching morphogenesis. Epithelial-mesenchymal-mesothelial interactions are also critical to embryonic lung morphogenesis. Early embryonic lung organ culture is a very useful system to study epithelial-mesenchymal interactions. Both epithelial and mesenchymal morphogenesis proceed under specific conditions that can be readily manipulated in this system (in the absence of maternal influence and blood flow). More importantly this technique can be readily done in a serumless, chemically defined culture media. Gain and loss of function can be achieved using expressed proteins, recombinant viral vectors, and/or analysis of transgenic mouse strains, antisense RNA, as well as RNA interference gene knockdown. Additionally, to further study epithelial-mesenchymal interactions, the relative roles of epithelium versus mesenchyme signaling can also be determined using tissue recombination (e.g., epithelial and mesenchymal separation) and microbead studies.

Induction of fibroblast growth factor 10 (FGF10) in the ileal crypt epithelium after massive small bowel resection suggests a role for FGF10 in gut adaptation.

We have previously reported that fibroblast growth factor 10 (FGF10) is crucial for the survival and proliferation of progenitor cells during embryonic gastrointestinal development. We sought to characterize the potential role of FGF10 signaling in the adaptive response following small bowel resection. Adult wild-type and Fgf10(LacZ) mice underwent 50% small bowel resection (SBR) or sham operation. Tissues were harvested 24 or 48 hr after surgery for histology, immunohistochemistry, and in situ hybridization. After SBR, Fgf10 expression was demonstrated in the epithelium at the base of the crypts. Moreover, there was a statistically significant increase in proliferating cells and goblet cells after SBR. In vitro studies using rat intestinal epithelial crypt (IEC-6) cells exposed to medium with or without recombinant FGF10 showed increased proliferation and phosphorylation of Raf and AKT with the addition of FGF10. Our results suggest that FGF10 may play a therapeutic role in diseases involving intestinal failure.

Regulation of mouse lung development by the extracellular calcium-sensing receptor, CaR.

Postnatal lung function is critically dependent upon optimal embryonic lung development. As the free ionized plasma calcium concentration ([Ca(2+)](o)) of the fetus is higher than that of the adult, the process of lung development occurs in a hypercalcaemic environment. In the adult, [Ca(2+)](o) is monitored by the G-protein coupled, extracellular calcium-sensing receptor (CaR), but neither its ontogeny nor its potential role in lung development are known. Here, we demonstrate that CaR is expressed in the mouse lung epithelium, and that its expression is developmentally regulated, with a peak of expression at embryonic day 12.5 (E12.5) and a subsequent decrease by E18, after which the receptor is absent. Experiments carried out using the lung explant culture model in vitro show that lung branching morphogenesis is sensitive to [Ca(2+)](o), being maximal at physiological adult [Ca(2+)](o) (i.e. 1.0-1.3 mM) and lowest at the higher, fetal (i.e. 1.7 mM) [Ca(2+)](o). Administration of the specific CaR positive allosteric modulator, the calcimimetic R-568, mimics the suppressive effects of high [Ca(2+)](o) on branching morphogenesis while both phospholipase C and PI3 kinase inhibition reverse these effects. CaR activation suppresses cell proliferation while it enhances intracellular calcium signalling, lung distension and fluid secretion. Conditions which are restrictive either to branching or to secretion can be rescued by manipulating [Ca(2+)](o) in the culture medium. In conclusion, fetal Ca(2+)(o), acting through a developmentally regulated CaR, is an important extrinsic factor that modulates the intrinsic lung developmental programme. Our observations support a novel role for the CaR in preventing hyperplastic lung disease in utero.

Tracheal occlusion increases the rate of epithelial branching of embryonic mouse lung via the FGF10-FGFR2b-Sprouty2 pathway.

Tracheal occlusion during lung development accelerates growth in response to increased intraluminal pressure. In order to investigate the role of internal pressure on murine early lung development, we cauterized the tip of the trachea, to occlude it, and thus to increase internal pressure. This method allowed us to evaluate the effect of tracheal occlusion on the first few branch generations and on gene expression. We observed that the elevation of internal pressure induced more than a doubling in branching, associated with increased proliferation, while branch elongation speed increased 3-fold. Analysis by RT-PCR showed that Fgf10, Vegf, Sprouty2 and Shh mRNA expressions were affected by the change of intraluminal pressure after 48h of culture, suggesting mechanotransduction via internal pressure of these key developmental genes. Tracheal occlusion did not increase the number of branches of Fgfr2b-/- mice lungs nor of wild type lungs cultured with Fgfr2b antisense RNA. Tracheal occlusion of Fgf10(LacZ/-) hypomorphic lungs led to the formation of fewer branches than in wild type. We conclude that internal pressure regulates the FGF10-FGFR2b-Sprouty2 pathway and thus the speed of the branching process. Therefore pressure levels, fixed both by epithelial secretion and boundary conditions, can control or modulate the branching process via FGF10-FGFR2b-Sprouty2.

Fgf10 dosage is critical for the amplification of epithelial cell progenitors and for the formation of multiple mesenchymal lineages during lung development.

The key role played by Fgf10 during early lung development is clearly illustrated in Fgf10 knockout mice, which exhibit lung agenesis. However, Fgf10 is continuously expressed throughout lung development suggesting extended as well as additional roles for FGF10 at later stages of lung organogenesis. We previously reported that the enhancer trap Mlcv1v-nLacZ-24 transgenic mouse strain functions as a reporter for Fgf10 expression and displays decreased endogenous Fgf10 expression. In this paper, we have generated an allelic series to determine the impact of Fgf10 dosage on lung development. We report that 80% of the newborn Fgf10 hypomorphic mice die within 24 h of birth due to respiratory failure. These mutant mouse lungs display severe hypoplasia, dilation of the distal airways and large hemorrhagic areas. Epithelial differentiation and proliferation studies indicate a specific decrease in TTF1 and SP-B expressing cells correlating with reduced epithelial cell proliferation and associated with a decrease in activation of the canonical Wnt signaling in the epithelium. Analysis of vascular development shows a reduction in PECAM expression at E14.5, which is associated with a simplification of the vascular tree at E18.5. We also show a decrease in alpha-SMA expression in the respiratory airway suggesting defective smooth muscle cell formation. At the molecular level, these defects are associated with decrease in Vegfa and Pdgfa expression likely resulting from the decrease of the epithelial/mesenchymal ratio in the Fgf10 hypomorphic lungs. Thus, our results indicate that FGF10 plays a pivotal role in maintaining epithelial progenitor cell proliferation as well as coordinating alveolar smooth muscle cell formation and vascular development.

Fibroblast growth factor 10 is required for survival and proliferation but not differentiation of intestinal epithelial progenitor cells during murine colon development.

Epithelial-mesenchymal interactions that govern the development of the colon from the primitive gastrointestinal tract are still unclear. In this study, we determine the temporal-spatial expression pattern of Fibroblast growth factor 10 (Fgf10), a key developmental gene, in the colon at different developmental stages. We found that Fgf10 is expressed in the mesenchyme of the distal colon, while its main receptor Fgfr2-IIIb is expressed throughout the entire intestinal epithelium. We demonstrate that Fgf10 inactivation leads to decreased proliferation and increased cell apoptosis in the colonic epithelium at E10.5, therefore resulting in distal colonic atresia. Using newly described Fgf10 hypomorphic mice, we show that high levels of FGF10 are dispensable for the differentiation of the colonic epithelium. Our work unravels for the first time the pivotal role of FGF10 in the survival and proliferation of the colonic epithelium, biological activities which are essential for colonic crypt formation.

Differential role of FGF9 on epithelium and mesenchyme in mouse embryonic lung.

Mesothelial Fibroblast Growth Factor 9 (Fgf9) has been demonstrated by inactivation studies in mouse to be critical for the proliferation of the mesenchyme. We now show that Fgf9 is also expressed at significant levels in the distal epithelium from the mid-pseudoglandular stages. Using mesenchymal-free lung endoderm culture, we show that FGF9 triggers the proliferation of the distal epithelium leading to the formation of a cyst-like structure. On embryonic Fgfr2b-/- lungs, FGF9 induces proliferation of the mesenchyme but fails to trigger a similar effect on the epithelium, therefore involving the FGFR2b receptor in the proliferative response of the epithelium to FGF9. While FGF9 inhibits the differentiation of the mesenchyme, the epithelium appears to differentiate normally. At the molecular level, FGF9 up-regulates Fgf10 expression in the mesenchyme likely via increased expression of Tbx4 and 5 and controls the transcription of Hedgehog targets Ptc and Gli-1 in a Hedgehog-independent manner. We also show that FGF9 inhibits the activation of the canonical Wnt pathway in the epithelium by increasing Dkk1 expression, a canonical Wnt antagonist. Our work shows for the first time that FGF9 acts on the epithelium involving FGFR2b to control its proliferation but not its differentiation and contributes to the regulation of canonical Wnt signaling in the epithelium.

The fibroblast growth factor pathway serves a regulatory role in proliferation and apoptosis in the pathogenesis of intestinal atresia.

BACKGROUND/PURPOSE: Intestinal atresia occurs in 1:5000 live births and is a neonatal challenge. Fibroblast growth factor receptor 2b (Fgfr2b) is a critical developmental regulator of proliferation and apoptosis in multiple organ systems including the gastrointestinal tract (GIT). Fgfr2b invalidation results in an autosomal recessive intestinal atresia phenotype. This study evaluates the role of Fgfr2b signaling in regulating proliferation and apoptosis in the pathogenesis of intestinal atresia. METHODS: Wild-type and Fgfr2b-/- embryos were harvested from timed pregnant mice. The GIT was harvested using standard techniques. Terminal deoxynucleotidyl transferase biotin-dUTP nick end labeling) was used to evaluate apoptosis and bromodeoxyuridine to assess proliferation by standard protocols. Photomicrographs were compared (Institutional Animal Care and Use Committee-approved protocol 32-02). RESULTS: Wild-type and mutant GIT demonstrate that deletion of the Fgfr2b gene results in inhibition of epithelial proliferation and increased apoptosis. Inhibited proliferation and increased apoptosis are specific to those tissues of normal Fgfr2b expression, corresponding to the site of intestinal atresia. CONCLUSIONS: The absence of embryonic GIT Fgfr2b expression results in decreased proliferation and increased apoptosis resulting in GIT atresia. The regulation of proliferation and apoptosis in intestinal cells as a genetically based cause of intestinal atresia represents a novel consideration in the pathogenesis of intestinal atresia.

VEGF-A signaling through Flk-1 is a critical facilitator of early embryonic lung epithelial to endothelial crosstalk and branching morphogenesis.

Vascular endothelial growth factor-A (VEGF-A) signaling directs both vasculogenesis and angiogenesis. However, the role of VEGF-A ligand signaling in the regulation of epithelial-mesenchymal interactions during early mouse lung morphogenesis remains incompletely characterized. Fetal liver kinase-1 (Flk-1) is a VEGF cognate receptor (VEGF-R2) expressed in the embryonic lung mesenchyme. VEGF-A, expressed in the epithelium, is a high affinity ligand for Flk-1. We have used both gain and loss of function approaches to investigate the role of this VEGF-A signaling pathway during lung morphogenesis. Herein, we demonstrate that exogenous VEGF 164, one of the 3 isoforms generated by alternative splicing of the Vegf-A gene, stimulates mouse embryonic lung branching morphogenesis in culture and increases the index of proliferation in both epithelium and mesenchyme. In addition, it induces differential gene and protein expression among several key lung morphogenetic genes, including up-regulation of BMP-4 and Sp-c expression as well as an increase in Flk-1-positive mesenchymal cells. Conversely, embryonic lung culture with an antisense oligodeoxynucleotide (ODN) to the Flk-1 receptor led to reduced epithelial branching, decreased epithelial and mesenchymal proliferation index as well as downregulating BMP-4 expression. These results demonstrate that the VEGF pathway is involved in driving epithelial to endothelial crosstalk in embryonic mouse lung morphogenesis.

A novel function for the protein tyrosine phosphatase Shp2 during lung branching morphogenesis.

Branching morphogenesis of many organs, including the embryonic lung, is a dynamic process in which growth factor mediated tyrosine kinase receptor activation is required, but must be tightly regulated to direct ramifications of the terminal branches. However, the specific regulators that modulate growth factor signaling downstream of the tyrosine kinase receptor remain to be determined. Herein, we demonstrate for the first time an important function for the intracellular protein tyrosine phosphatase Shp2 in directing embryonic lung epithelial morphogenesis. We show that Shp2 is specifically expressed in embryonic lung epithelial buds, and that loss of function by the suppression of Shp2 mRNA expression results in a 53% reduction in branching morphogenesis. Furthermore, by intra-tracheal microinjection of a catalytically inactive adenoviral Shp2 construct, we provide direct evidence that the catalytic activity of Shp2 is required for proper embryonic lung branch formation. We demonstrate that Shp2 activity is required for FGF10 induced endodermal budding. Furthermore, a loss of Shp2 catalytic activity in the embryonic lung was associated with a reduction in ERK phosphorylation and epithelial cell proliferation. However, epithelial cell differentiation was not affected. Our results show that the protein tyrosine phosphatase Shp2 plays an essential role in modulating growth factor mediated tyrosine kinase receptor activation in early embryonic lung branching morphogenesis.

Molecular mechanisms of early lung specification and branching morphogenesis.

The "hard wiring" encoded within the genome that determines the emergence of the laryngotracheal groove and subsequently early lung branching morphogenesis is mediated by finely regulated, interactive growth factor signaling mechanisms that determine the automaticity of branching, interbranch length, stereotypy of branching, left-right asymmetry, and finally gas diffusion surface area. The extracellular matrix is an important regulator as well as a target for growth factor signaling in lung branching morphogenesis and alveolarization. Coordination not only of epithelial but also endothelial branching morphogenesis determines bronchial branching and the eventual alveolar-capillary interface. Improved prospects for lung protection, repair, regeneration, and engineering will depend on more detailed understanding of these processes. Herein, we concisely review the functionally integrated morphogenetic signaling network comprising the critical bone morphogenetic protein, fibroblast growth factor, Sonic hedgehog, transforming growth factor-beta, vascular endothelial growth factor, and Wnt signaling pathways that specify and drive early embryonic lung morphogenesis.

Fibroblast growth factor-10 serves a regulatory role in duodenal development.

PURPOSE: Duodenal obstruction occurs in 1 of 6000 live births and requires urgent surgical intervention. Duodenal atresia previously has been ascribed to a developmental failure of luminal recanalization; however, the cause of duodenal atresia remains incompletely understood. Although familial intestinal atresias have been described and syndromic associations are known, no specific genetic link has been established. Fibroblast growth factor-10 (Fgf10) is a known regulatory molecule relevant to mesenchymal-epithelial interactions, and mice deficient in Fgf10 demonstrate congenital anomalies in several organ systems including the gastrointestinal tract. The authors hypothesized that Fgf10 could serve a regulatory role in establishing normal duodenal development. METHODS: Wild-type mice with beta-galactosidase under the control of the Fgf10 promoter were harvested from timed-pregnancy mothers. The expression of Fgf10 in the duodenum during development was evaluated by developing the embryos in X-Gal solution. Wild-type and mutant Fgf10(-/-) embryos were harvested from timed-pregnancy mothers at 18.5 days postconception (near term) and were analyzed for duodenal morphology (Institutional Animal Care and Use Committee-approved protocol 32-02). Photomicrographs were reviewed. RESULTS: Fibroblast growth factor-10 is active in the duodenum at a late stage of development. The Fgf10(-/-) mutants demonstrate duodenal atresia with a variable phenotype similar to clinical findings. The duodenum fails to develop luminal continuity and has proximal dilation. The phenotype occurs in an autosomal recessive pattern with incomplete penetrance (38%). CONCLUSIONS: Fibroblast growth factor-10 serves as a regulator in normal duodenal growth and development. Its deletion leads to duodenal atresia and challenges traditionally accepted theories of pathogenesis. This novel, genetically mediated duodenal malformation reflects an animal model that will allow further evaluation of the pathogenesis of this surgically correctable disease. By studying the mechanism of Fgf10 function in foregut development, the authors hope to better understand these anomalies and to explore possible therapeutic alternatives.

Colonic atresia without mesenteric vascular occlusion. The role of the fibroblast growth factor 10 signaling pathway.

BACKGROUND/PURPOSE: Colonic atresia occurs in 1:20,000 live births, offering a neonatal surgical challenge. Prenatal expression of fibroblast growth factor 10 (Fgf10), acting through fibroblast growth factor receptor 2b (Fgfr2b), is critical to the normal development of the colon. Invalidation of the Fgf10 pathway results in colonic atresia, inherited in an autosomal recessive pattern. Classically, disturbance of the mesenteric vasculature has been thought to cause many forms of intestinal atresia. The purpose of this study was to evaluate the role of vascular occlusion in the pathogenesis of colonic atresia. METHODS: Wild type (Wt), Fgf10(-/-), and Fgfr2b(-/-) mutant mouse embryos were harvested from timed pregnant mothers. Immediately following harvest, filtered India ink was infused via intracardiac microinjection. The gastrointestinal tract was dissected, and photomicrographs of the mesenteric arterial anatomy were taken at key developmental time points. RESULTS: Photomicrographs after India ink microinjections demonstrate normal, patent mesenteric cascades to the atretic colon at the time points corresponding to the failure of colonic development in the Fgf10(-/-) and Fgfr2b(-/-) mutants. The mesenteric arterial anatomy of the colon demonstrates no difference between the Wt and mutant colonic atresia. CONCLUSIONS: The absence of embryonic expression of Fgf10 or its receptor Fgfr2b results in colonic atresia in mice. India ink microinjection is a direct measure of mesenteric arterial patency. Colonic atresia in the Fgf10(-/-) and Fgfr2b(-/-) mutants occurs despite normal mesenteric vascular development. Thus the atresia is not the result of a mesenteric vascular occlusion. The patent colonic mesentery of the Fgf10(-/-) and Fgfr2b(-/-) mutants challenges an accepted pathogenesis of intestinal atresia. Although colonic atresia can occur as a result of vascular occlusion, new evidence exists to suggest that a genetic mechanism may play a role in the pathogenesis of this disease.

Dickkopf-1 (DKK1) reveals that fibronectin is a major target of Wnt signaling in branching morphogenesis of the mouse embryonic lung.

Members of the Dickkopf (Dkk) family of secreted proteins are potent inhibitors of Wnt/beta-catenin signaling. In this study we show that Dkk1, -2, and -3 are expressed distally in the epithelium, while Kremen1, the needed co-receptor, is expressed throughout the epithelium of the developing lung. Using TOPGAL mice [DasGupta, R., Fuchs, E., 1999. Multiple roles for activated LEF/TCF transcription complexes during hair follicle development and differentiation. Development 126, 4557-4568] to monitor the Wnt pathway, we show that canonical Wnt signaling is dynamic in the developing lung and is active throughout the epithelium and in the proximal smooth muscle cells (SMC) until E12.5. However, from E13.5 onwards, TOPGAL activity is absent in the SMC and is markedly reduced in the distal epithelium coinciding with the onset of Dkk-1 expression in the distal epithelium. To determine the role of Wnt signaling in early lung development, E11.5 organ cultures were treated with recombinant DKK1. Treated lungs display impaired branching, characterized by failed cleft formation and enlarged terminal buds, and show decreased alpha-smooth muscle actin (alpha-SMA) expression as well as defects in the formation of the pulmonary vasculature. These defects coincide with a pattern of decreased fibronectin (FN) deposition. DKK1-induced morphogenetic defects can be mimicked by inhibition of FN and overcome by addition of exogenous FN, suggesting an involvement of FN in Wnt-regulated morphogenetic processes.