Morphogenetic Protein Signaling Pathway Research Articles

Membrane proteome functional characterization of breast cancer-initiating cells subjected to bone morphogenetic protein signaling inhibition by dorsomorphin

In this study, A17 cells, which are an invasive mesenchymal cell line with cancer stem cell properties, were exploited for the study of the role of bone morphogenetic protein pathways in cancer-initiating cells employing a proteomics-based approach. A17 cells were treated with the bone morphogenetic protein signaling inhibitor dorsomorphin for 3 days. After that, subcellular fractionation of cell samples was performed and the membrane fraction analyzed by shotgun proteomics. The extracted membrane proteins were enzymatically digested and the resulting peptide mixture was analyzed by nano liquid chromatography coupled to tandem mass spectrometry and relative label-free quantitation. Protein profiles of A17 membrane fractions before and after dorsomorphin treatment were compared, and further mined by Gene Ontology search. The protein profile of untreated A17 samples correlated with the mesenchymal phenotype, whereas changes were observed in dorsomorphin-treated samples, further supporting a mesenchymal to epithelial transition upon bone morphogenetic protein signaling pathway inhibition and the importance of this pathway in breast cancer cell malignancy.

SMAD Signaling Is Required for Structural Integrity of the Female Reproductive Tract and Uterine Function During Early Pregnancy in Mice.

Pregnancy is a complex physiological process tightly controlled by the interplay among hormones, morphogens, transcription factors, and signaling pathways. Although recent studies using genetically engineered mouse models have revealed that ligands and receptors of transforming growth factor beta (TGFbeta) and bone morphogenetic protein (BMP) signaling pathways are essential for multiple reproductive events during pregnancy, the functional role of SMAD transcription factors, which serve as the canonical signaling platform for the TGFbeta/BMP pathways, in the oviduct and uterus is undefined. Here, we used a mouse model containing triple conditional deletion of the BMP receptor signaling Smads (Smad1 and Smad5) and Smad4, the central mediator of both TGFbeta and BMP signaling, to investigate the role of the SMADs in reproductive tract structure and function in cells from the Amhr2 lineage. Unlike the respective single- or double-knockouts, female Smad1flox/flox Smad5flox/flox Smad4flox/flox Amhr2cre/+conditional knockout (i.e., Smad1/5/4-Amhr2-cre KO) mice are sterile. We discovered that Smad1/5/4-Amhr2-cre KO females have malformed oviducts that subsequently develop oviductal diverticuli. These oviducts showed dysregulation of multiple genes essential for oviduct and smooth muscle development. In addition, uteri from Smad1/5/4-Amhr2-cre KO females exhibit multiple defects in stroma, epithelium, and smooth muscle layers and fail to assemble a closed uterine lumen upon embryo implantation, with defective uterine decidualization that led to pregnancy loss at early to mid-gestation. Taken together, our study uncovers a new role for the SMAD transcription factors in maintaining the structural and functional integrity of oviduct and uterus, required for establishment and maintenance of pregnancy.

Bosentan reverses the hypoxia-induced downregulation of the bone morphogenetic protein signaling in pulmonary artery smooth muscle cells

AimsPulmonary hypertension (PH) is a common complication of chronic hypoxic lung diseases. Bone morphogenetic protein (BMP) and endothelin-1 signaling pathways have been shown to be altered in hypoxic PH and to play crucial roles in the associated pulmonary artery remodeling. We, therefore, aimed to study the potential link between hypoxia and the alteration of BMP and endothelin-1 signaling observed in pulmonary artery smooth muscle cells (PA-SMCs) in hypoxic PH. Materials and MethodsHuman PA-SMCs were treated with hypoxia-mimetic agent cobalt chloride (CoCl2; 100μM), with or without pretreatment with a dual endothelin receptor antagonist bosentan (10μM). Expressions of preproendothelin-1 (PPET1), BMP type 2 receptor (BMPR-2), and one BMP signaling target gene, the inhibitor of DNA binding 1 (ID1) were evaluated by real time quantitative polymerase chain reaction. BMP2-treated PA-SMCs were assessed for Smad1/5/8 signaling activation by Western Blotting. Key findingsTreatment of PA-SMCs with CoCl2 increased PPET1 gene expression, while it did not alter expressions of endothelin converting enzyme, endothelin receptor type A or type B. Hypoxia-mimetic agent CoCl2 decreased the expressions of BMPR-2 and ID1 maximally after 3- and 6-hour treatment respectively, while CoCl2 treatment progressively increased noggin expression. Bosentan pretreatment restored expressions of BMPR-2 and ID1, as well as the activation (by phosphorylation) of Smad1/5/8 signaling induced by BMP2. SignificanceHypoxia induces the downregulation of the BMP signaling in PA-SMCs, at least, partly through the endothelin system. In hypoxic PH, increased endothelin-1 production might therefore contribute to the altered BMP signaling and subsequent PA-SMC hyperplasia.

Loss of BMP signaling through BMPR1A in osteoblasts leads to greater collagen cross-link maturation and material-level mechanical properties in mouse femoral trabecular compartments

Bone morphogenetic protein (BMP) signaling pathways play critical roles in skeletal development and new bone formation. Our previous study, however, showed a negative impact of BMP signaling on bone mass because of the osteoblast-specific loss of a BMP receptor (i.e. BMPR1A) showing increased trabecular bone volume and mineral density in mice. Here, we investigated the bone quality and biomechanical properties of the higher bone mass associated with BMPR1A deficiency using the osteoblast-specific Bmpr1a conditional knockout (cKO) mouse model. Collagen biochemical analysis revealed greater levels of the mature cross-link pyridinoline in the cKO bones, in parallel with upregulation of collagen modifying enzymes. Raman spectroscopy distinguished increases in the mature to immature cross-link ratio and mineral to matrix ratio in the trabecular compartments of cKO femora, but not in the cortical compartments. The mineral crystallinity was unchanged in the cKO in either the trabecular or cortical compartments. Further, we tested the intrinsic material properties by nanoindentation and found significantly higher hardness and elastic modulus in the cKO trabecular compartments, but not in the cortical compartments. Four point bending tests of cortical compartments showed lower structural biomechanical properties (i.e. strength and stiffness) in the cKO bones due to the smaller cortical areas. However, there were no significant differences in biomechanical performance at the material level, which was consistent with the nanoindentation test results on the cortical compartment. These studies emphasize the pivotal role of BMPR1A in the determination of bone quality and mechanical integrity under physiological conditions, with different impact on femoral cortical and trabecular compartments.

Inflammation in arthritis induces expression of BMP3, an inhibitor of bone formation

Objectives: Inflammation in diseases such as rheumatoid arthritis (RA) stimulates osteoclast-mediated articular bone erosion and inhibits osteoblast-mediated bone formation, leading to a net loss of bone. Pro-inflammatory cytokines and antagonists of the Wnt signalling pathway have been implicated in the inhibition of osteoblast differentiation and activity in RA, contributing to the erosive process and impairing erosion healing. Importantly, osteoblast differentiation and function are also regulated by the osteogenic bone morphogenetic protein (BMP) signalling pathway, which is antagonized by BMP3. We therefore examined the potential role of BMP3 in inflammatory arthritis.Method: Two murine models of RA, K/BxN serum transfer arthritis (STA) and antigen-induced arthritis (AIA), were used to establish the temporal expression of BMP3 and the cellular sources of BMP3 mRNA and protein in inflammatory arthritis. To determine the effects of inflammation on the expression of BMP3 in osteoblasts, murine calvarial osteoblasts were treated with pro-inflammatory cytokines and BMP3 expression was assessed.Results: In both murine models of RA, BMP3 mRNA and protein are highly expressed by osteoblasts lining inflammation–bone interfaces late in the course of arthritis. Synovial tissues are not a significant source of BMP3. BMP3 expression is induced in osteocalcin-expressing osteoblasts in vitro following stimulation by tumour necrosis factor (TNF).Conclusions: These data implicate BMP3 as a novel factor that may act locally to contribute to the erosive process and inhibit the repair of articular bone in RA through inhibition of osteoblast differentiation and function.

The molecular basis of craniofacial placode development.

The sensory organs of the vertebrate head originate from simple ectodermal structures known as cranial placodes. All cranial placodes derive from a common domain adjacent to the neural plate, the preplacodal region, which is induced at the border of neural and non-neural ectoderm during gastrulation. Induction and specification of the preplacodal region is regulated by the fibroblast growth factor, bone morphogenetic protein, WNT, and retinoic acid signaling pathways, and characterized by expression of the EYA and SIX family of transcriptional regulators. Once the preplacodal region is specified, different combinations of local signaling molecules and placode-specific transcription factors, including competence factors, promote the induction of individual cranial placodes along the neural axis of the head region. In this review, we summarize the steps of cranial placode development and discuss the roles of the main signaling molecules and transcription factors that regulate these steps during placode induction, specification, and development. For further resources related to this article, please visit the WIREs website.

Mechanical Forces Reshape Differentiation Cues That Guide Cardiomyogenesis.

Soluble morphogen gradients have long been studied in the context of heart specification and patterning. However, recent data have begun to challenge the notion that long-standing in vivo observations are driven solely by these gradients alone. Evidence from multiple biological models, from stem cells to ex vivo biophysical assays, now supports a role for mechanical forces in not only modulating cell behavior but also inducing it de novo in a process termed mechanotransduction. Structural proteins that connect the cell to its niche, for example, integrins and cadherins, and that couple to other growth factor receptors, either directly or indirectly, seem to mediate these changes, although specific mechanistic details are still being elucidated. In this review, we summarize how the wingless (Wnt), transforming growth factor-β, and bone morphogenetic protein signaling pathways affect cardiomyogenesis and then highlight the interplay between each pathway and mechanical forces. In addition, we will outline the role of integrins and cadherins during cardiac development. For each, we will describe how the interplay could change multiple processes during cardiomyogenesis, including the specification of undifferentiated cells, the establishment of heart patterns to accomplish tube and chamber formation, or the maturation of myocytes in the fully formed heart.

Titanium With Nanotopography Induces Osteoblast Differentiation by Regulating Endogenous Bone Morphogenetic Protein Expression and Signaling Pathway.

We aimed at evaluating the effect of titanium (Ti) with nanotopography (Nano) on the endogenous expression of BMP-2 and BMP-4 and the relevance of this process to the nanotopography-induced osteoblast differentiation. MC3T3-E1 cells were grown on Nano and machined (Machined) Ti surfaces and the endogenous BMP-2/4 expression and the effect of BMP receptor BMPR1A silencing in both osteoblast differentiation and expression of genes related to TGF-β/BMP signaling were evaluated. Nano supported higher BMP-2 gene and protein expression and upregulated the osteoblast differentiation compared with Machined Ti surface. The BMPR1A silencing inhibited the osteogenic potential induced by Nano Ti surface as indicated by reduced alkaline phosphatase (ALP), osteocalcin and RUNX2 gene expression, RUNX2 protein expression and ALP activity. In addition, the expression of genes related to TGF-β/BMP signaling was deeply affected by BMPR1A-silenced cells grown on Nano Ti surface. In conclusion, we have demonstrated for the first time that nanotopography induces osteoblast differentiation, at least in part, by upregulating the endogenous production of BMP-2 and modulating BMP signaling pathway. J. Cell. Biochem. 117: 1718-1726, 2016. © 2015 Wiley Periodicals, Inc.

S113R mutation in SLC33A1 leads to neurodegeneration and augmented BMP signaling in a mouse model.

ABSTRACTThe S113R mutation (c.339T>G) (MIM #603690.0001) in SLC33A1 (MIM #603690), an ER membrane acetyl-CoA transporter, has been previously identified in individuals with hereditary spastic paraplegia type 42 (SPG42; MIM #612539). SLC33A1 has also been shown to inhibit the bone morphogenetic protein (BMP) signaling pathway in zebrafish. To better understand the function of SLC33A1, we generated and characterized Slc33a1S113R knock-in mice. Homozygous Slc33a1S113R mutant mice were embryonic lethal, whereas heterozygous Slc33a1 mutant mice (Slc33a1wt/mut) exhibited behavioral abnormalities and central neurodegeneration, which is consistent with hereditary spastic paraplegia (HSP) phenotypes. Importantly, we found an upregulation of BMP signaling in the nervous system and mouse embryonic fibroblasts of Slc33a1wt/mut mice. Using a sciatic nerve crush injury model in vivo and dorsal root ganglion (DRG) culture in vitro we showed that injury-induced axonal regeneration in Slc33a1wt/mut mice was accelerated and mediated by upregulated BMP signaling. Exogenous addition of BMP signaling antagonist, noggin, could efficiently alleviate the accelerated injury-induced axonal regrowth. These results indicate that SLC33A1 can negatively regulate BMP signaling in mice, further supporting the notion that upregulation of BMP signaling is a common mechanism of a subset of hereditary spastic paraplegias.

The Chordin Morphogenetic Pathway.

The ancestral Chordin/bone morphogenetic protein (BMP) signaling pathway that establishes dorsal-ventral (D-V) patterning in animal development is one of the best understood morphogenetic gradients, and is established by multiple proteins that interact with each other in the extracellular space-including several BMPs, Chordin, Tolloid, Ont-1, Crossveinless-2, and Sizzled. The D-V gradient is adjusted redundantly by regulating the synthesis of its components, by direct protein-protein interactions between morphogens, and by long-range diffusion. The entire embryo participates in maintaining the D-V BMP gradient, so that for each action in the dorsal side there is a reaction in the ventral side. A gradient of Chordin is formed in the extracellular matrix that separates ectoderm from endomesoderm, called Brachet's cleft in Xenopus. The Chordin/BMP pathway is self-organizing and able to scale pattern in the dorsal half of bisected embryos or in Spemann dorsal lip transplantation experiments.

A Survey of Strategies to Modulate the Bone Morphogenetic Protein Signaling Pathway: Current and Future Perspectives.

Bone morphogenetic proteins (BMPs) constitute the largest subdivision of the TGF-β family of ligands and are unequivocally involved in regulating stem cell behavior. Appropriate regulation of canonical BMP signaling is critical for the development and homeostasis of numerous human organ systems, as aberrations in the BMP pathway or its regulation are increasingly associated with diverse human pathologies. In this review, we provide a wide-perspective on strategies that increase or decrease BMP signaling. We briefly outline the current FDA-approved approaches, highlight emerging next-generation technologies, and postulate prospective avenues for future investigation. We also detail how activating other pathways may indirectly modulate BMP signaling, with a particular emphasis on the relationship between the BMP and Activin/TGF-β pathways.

Hypoxia potentiates the BMP-2 driven COL2A1 stimulation in human articular chondrocytes via p38 MAPK

Since the biological effect of cartilage mediators is generally studied in a non-physiologic environment of 21% O2, we investigated the effects of a chronic hypoxia on the capability of articular chondrocytes to respond to one anabolic stimulation. Human Articular Chondrocytes (HACs) were cultured under hypoxia and stimulated with the chondrogenic growth factor BMP-2. The phenotype of the chondrocytes was studied by RT-PCR, and the cartilage-specific type II collagen production and deposition were also examined by western immunoblot and immunofluorescence. The Bone Morphogenetic protein (BMP) signalling pathway was also analysed. BMP-2 is much more efficient to stimulate the expression of the cartilage-specific gene COL2A1 by HACs when cultured under hypoxia (1%O2) compared to normoxia (21%O2). Analysis of the BMP-activated signalling shows that the Smad pathway is inhibited under hypoxia, whereas p38 MAPK is activated, and is involved in a synergy between hypoxia and BMP signalling, thus contributing to the enhanced anabolic response. Our study shows that hypoxia interplays with a chondrogenic factor and enhances the overall anabolic activity of the HACs. Alternatively to Hypoxia-Inducible Factor (HIF) signalling, and through a cross-talk with the BMP signalling which involves the p38 pathway, hypoxic stimulation markedly increases the capability of chondrocytes to produce the cartilage-specific type II collagen. Therefore our study provides new evidences of the multilayered effects of hypoxia in the anabolic functions of chondrocytes. This understanding may help promoting the anabolic function of articular chondrocytes, and thus improving their manipulation for cell therapy.

Commensal Bacteria-induced Interleukin 1β (IL-1β) Secreted by Macrophages Up-regulates Hepcidin Expression in Hepatocytes by Activating the Bone Morphogenetic Protein Signaling Pathway

The liver hormone hepcidin is the central regulator of systemic iron metabolism. Its increased expression in inflammatory states leads to hypoferremia and anemia. Elucidation of the mechanisms that up-regulate hepcidin during inflammation is essential for developing rational therapies for this anemia. Using mouse models of inflammatory bowel disease, we have shown previously that colitis-associated hepcidin induction is influenced by intestinal microbiota composition. Here we investigate how two commensal bacteria, Bifidobacterium longum and Bacteroides fragilis, representative members of the gut microbiota, affect hepcidin expression. We found that supernatants of a human macrophage cell line infected with either of the bacteria up-regulated hepcidin when added to a human hepatocyte cell line. This activity was abrogated by neutralization of IL-1β. Moreover, purified IL-1β increased hepcidin expression when added to the hepatocyte line or primary human hepatocytes and when injected into mice. IL-1β activated the bone morphogenetic protein (BMP) signaling pathway in hepatocytes and in mouse liver, as indicated by increased phosphorylation of small mothers against decapentaplegic proteins. Activation of BMP signaling correlated with IL-1β-induced expression of BMP2 in human hepatocytes and activin B in mouse liver. Treatment of hepatocytes with two different chemical inhibitors of BMP signaling or with a neutralizing antibody to BMP2 prevented IL-1β-induced up-regulation of hepcidin. Our results clarify how commensal bacteria affect hepcidin expression and reveal a novel connection between IL-1β and activation of BMP signaling. They also suggest that there may be differences between mice and humans with respect to the mechanism by which IL-1β up-regulates hepcidin.

Covering the Cover

Covering the Cover

Mutations in RASA1 and GDF2 identified in patients with clinical features of hereditary hemorrhagic telangiectasia.

Hereditary hemorrhagic telangiectasia (HHT) is an autosomal dominant vascular disorder caused by mutations in ENG, ACVRL1 and SMAD4, which function in regulating the transforming growth factor beta and bone morphogenetic protein signaling pathways. Symptoms of HHT can be present in individuals who test negative for mutations in these three genes indicating other genes may be involved. In this study, we tested for mutations in two genes, RASA1 and GDF2, which were recently reported to be involved in vascular disorders. To determine whether RASA1 and GDF2 have phenotypic overlap with HHT and should be included in diagnostic testing, we developed a next-generation sequencing assay to detect mutations in 93 unrelated individuals who previously tested negative for mutations in ENG, ACVRL1 and SMAD4, but were clinically suspected to have HHT. Pathogenic mutations in RASA1 were identified in two samples (2.15%) and a variant of unknown significance in GDF2 was detected in one sample. All three individuals experienced epistaxis with dermal lesions described in medical records as telangiectases. These results indicate that the inclusion of RASA1 and GDF2 screening in individuals suspected to have HHT will increase the detection rate and aid clinicians in making an accurate diagnosis.

Nanogel-Mediated RNAi Against Runx2 and Osx Inhibits Osteogenic Differentiation in Constitutively Active BMPR1A Osteoblasts.

Trauma-induced heterotopic ossification (HO) and fibrodysplasia ossificans progressiva (FOP) are acquired and genetic variants of pathological bone formation occurring in soft tissues. Conventional treatment modalities target the inflammatory processes preceding bone formation. We investigated the development of a prophylaxis for heterotopic bone formation by addressing the biological basis for HO - dysregulation in the bone morphogenetic protein (BMP) signaling pathway. We previously reported the synthesis of cationic nanogel nanostructured polymers (NSPs) for efficient delivery of short interfering ribonucleic acids (siRNAs) and targeted gene silencing. Results suggested that nanogel:siRNA weight ratios of 1:1 and 5:1 silenced Runx2 and Osx gene expression in primary mouse osteoblasts with a constitutively active (ca) BMP Receptor 1A (BMPR1A) by the Q233D mutation. Repeated RNAi treatments over 14 days significantly inhibited alkaline phosphatase activity in caBMPR1A osteoblasts. Hydroxyapatite (HA) deposition was diminished over 28 days in culture, though complete suppression of HA deposition was not achieved. Outcome data suggested minimal cytotoxicity of nanogel-based RNAi therapeutics, and the multistage disruption of BMP-induced bone formation processes. This RNAi based approach to impeding osteoblastic differentiation and subsequent bone formation may form the basis of a clinical therapy for heterotopic bone formation.

BMPER Promotes Epithelial-Mesenchymal Transition in the Developing Cardiac Cushions.

Formation of the cardiac valves is an essential component of cardiovascular development. Consistent with the role of the bone morphogenetic protein (BMP) signaling pathway in cardiac valve formation, embryos that are deficient for the BMP regulator BMPER (BMP-binding endothelial regulator) display the cardiac valve anomaly mitral valve prolapse. However, how BMPER deficiency leads to this defect is unknown. Based on its expression pattern in the developing cardiac cushions, we hypothesized that BMPER regulates BMP2-mediated signaling, leading to fine-tuned epithelial-mesenchymal transition (EMT) and extracellular matrix deposition. In the BMPER-/- embryo, EMT is dysregulated in the atrioventricular and outflow tract cushions compared with their wild-type counterparts, as indicated by a significant increase of Sox9-positive cells during cushion formation. However, proliferation is not impaired in the developing BMPER-/- valves. In vitro data show that BMPER directly binds BMP2. In cultured endothelial cells, BMPER blocks BMP2-induced Smad activation in a dose-dependent manner. In addition, BMP2 increases the Sox9 protein level, and this increase is inhibited by co-treatment with BMPER. Consistently, in the BMPER-/- embryos, semi-quantitative analysis of Smad activation shows that the canonical BMP pathway is significantly more active in the atrioventricular cushions during EMT. These results indicate that BMPER negatively regulates BMP-induced Smad and Sox9 activity during valve development. Together, these results identify BMPER as a regulator of BMP2-induced cardiac valve development and will contribute to our understanding of valvular defects.

BMP pathway suppression is an early event in inflammation-driven colon neoplasmatogenesis of uPA-deficient mice.

The suppression of the bone morphogenetic protein (BMP) signaling pathway has been recently shown to promote adenoma-to-carcinoma transition in sporadic colon cancer. However, its role in the evolution of early preneoplastic changes to neoplasia remains elusive. In the present study, we aimed to investigate the gene expression levels of multiple extracellular BMP family constituents, including BMP ligands/receptors and inhibitors, during the early stages of inflammation-associated colon carcinogenesis. For that, we used the recently developed urokinase-type plasminogen activator (uPA)-deficient mouse model of colonic polypoidogenesis, in which adenomatous polyps arise several months after the induction of dextran sodium sulfate (DSS) colitis. In DSS-treated wild-type mice, the preneoplastic lesions which did not eventually evolve to adenomas resided in a colitic microenvironment characterized by a balanced upregulation of both BMP ligands, i.e., Bmp4/7 and BMP inhibitors, such as chordin, noggin, and gremlin-1. In the uPA-deficient tumor-promoting inflammatory microenvironment, however, there was a clear evidence for BMP pathway suppression. By contrast to DSS-treated wild-type controls, the inflammation-associated Bmp4 upregulation was abolished, and the BMP signaling suppression was further enhanced by a particularly high increase of gremlin-1 expression. These findings propose that BMP pathway suppression in colon cancer could be associated with very early stages of the preneoplasia-to-neoplasia sequence of events.

Regulatory RNAs controlling vascular (dys)function by affecting TGF-ß family signalling.

Cardiovascular disease (CVD) is a leading cause of morbidity and mortality worldwide. Over the last few years, microRNAs (miRNAs) have emerged as master regulators of gene expression in cardiovascular biology and disease. miRNAs are small endogenous non-coding RNAs that usually bind to 3′ untranslated region (UTR) of their target mRNAs and inhibit mRNA stability or translation of their target genes. miRNAs play a dynamic role in the pathophysiology of many CVDs through their effects on target mRNAs in vascular cells. Recently, numerous miRNAs have been implicated in the regulation of the transforming growth factor-β (TGF-β)/bone morphogenetic protein (BMP) signalling pathway which plays crucial roles in diverse biological processes, and is involved in pathogenesis of many diseases including CVD. This review gives an overview of current literature on the role of miRNAs targeting TGF-β/BMP signalling in vascular cells, including endothelial cells and smooth muscle cells. We also provide insight into how this miRNA-mediated regulation of TGF-β/BMP signalling might be used to harness CVD.

Synergistic interaction between the fibroblast growth factor and bone morphogenetic protein signaling pathways in lens cells.

Fibroblast growth factors (FGFs) play a central role in two processes essential for lens transparency--fiber cell differentiation and gap junction-mediated intercellular communication (GJIC). Using serum-free primary cultures of chick lens epithelial cells (DCDMLs), we investigated how the FGF and bone morphogenetic protein (BMP) signaling pathways positively cooperate to regulate lens development and function. We found that culturing DCDMLs for 6 d with the BMP blocker noggin inhibits the canonical FGF-to-ERK pathway upstream of FRS2 activation and also prevents FGF from stimulating FRS2- and ERK-independent gene expression, indicating that BMP signaling is required at the level of FGF receptors. Other experiments revealed a second type of BMP/FGF interaction by which FGF promotes expression of BMP target genes as well as of BMP4. Together these studies reveal a novel mode of cooperation between the FGF and BMP pathways in which BMP keeps lens cells in an optimally FGF-responsive state and, reciprocally, FGF enhances BMP-mediated gene expression. This interaction provides a mechanistic explanation for why disruption of either FGF or BMP signaling in the lens leads to defects in lens development and function.