The Tlx-2 homeobox gene is a downstream target of BMP signalling and is required for mouse mesoderm development

A Comprehensive Review Exploring the Role of Bone Morphogenetic Proteins [BMP]: Biological Mechanisms

Bone morphogenetic proteins (BMPs) belong to the TGF-β family. They perform diverse roles in development, osteogenesis, and vasculogenesis. BMPs have crucial functions in embryonic development and regulate the specialization of various cell types. The dysregulation of BMP activity at various stages in signal transduction is associated with a diverse range of human diseases. It is not surprising that BMPs also have a role in tumor formation and control the progression of cancer through different phases. Nevertheless, their specific roles remain ambiguous and the findings regarding this have been inconsistent. The objective of this review is to highlight the important functions of BMP ligands, receptors, and signaling mediators and the subsequent effects on final cellular responses resulting from these signaling modalities. This review elucidates the dysregulation of BMPs identified in various cancer types, which serves as a predictive sign for favorable results in cancer therapy. Alterations in the BMP pathway can represent a crucial milestone in the genetic and molecular mechanisms that facilitate cancer formation. This review has shown that alterations in certain components of the BMP pathway are evident in various tumor forms, including breast, gastric, colorectal, and myeloma cancer. This review reinforces the conclusion that BMPs exert both beneficial and detrimental effects on cancer biology. Collectively, these findings indicate that BMPs serve multiple functions in cancer; therefore, directing therapeutic efforts to focus on BMP may be a highly effective method for treating several cancers.

The covariance environment defines cellular niches for spatial inference

A key challenge of analyzing data from high-resolution spatial profiling technologies is to suitably represent the features of cellular neighborhoods or niches. Here we introduce the covariance environment (COVET), a representation that leverages the gene-gene covariate structure across cells in the niche to capture the multivariate nature of cellular interactions within it. We define a principled optimal transport-based distance metric between COVET niches that scales to millions of cells. Using COVET to encode spatial context, we developed environmental variational inference (ENVI), a conditional variational autoencoder that jointly embeds spatial and single-cell RNA sequencing data into a latent space. ENVI includes two decoders: one to impute gene expression across the spatial modality and a second to project spatial information onto single-cell data. ENVI can confer spatial context to genomics data from single dissociated cells and outperforms alternatives for imputing gene expression on diverse spatial datasets.

The covariance environment defines cellular niches for spatial inference

The tsunami of new multiplexed spatial profiling technologies has opened a range of computational challenges focused on leveraging these powerful data for biological discovery. A key challenge underlying computation is a suitable representation for features of cellular niches. Here, we develop the covariance environment (COVET), a representation that can capture the rich, continuous multivariate nature of cellular niches by capturing the gene-gene covariate structure across cells in the niche, which can reflect the cell-cell communication between them. We define a principled optimal transport-based distance metric between COVET niches and develop a computationally efficient approximation to this metric that can scale to millions of cells. Using COVET to encode spatial context, we develop environmental variational inference (ENVI), a conditional variational autoencoder that jointly embeds spatial and single-cell RNA-seq data into a latent space. Two distinct decoders either impute gene expression across spatial modality, or project spatial information onto dissociated single-cell data. We show that ENVI is not only superior in the imputation of gene expression but is also able to infer spatial context to disassociated single-cell genomics data.

[Mullerian inhibiting substance type II receptor as a potential target for antineoplastic therapy]

The review considers properties of the type II anti-Mullerian hormone receptor (mullerian inhibiting substance receptor type II, MISRII), a transmembrane sensor with its own serine/threonine protein kinase activity, triggering apoptosis of the Mullerian ducts in mammalian embryogenesis and providing formation of the male type reproductive system. According to recent data, MISRII overexpression in the postnatal period is found in cells of a number of ovarian, mammary gland, and prostate tumors, and anti-Mullerian hormone (AMH) has a pro-apoptotic effect on MISRII-positive tumor cells. This fact makes MISRII a potential target for targeted anti-cancer therapy. Treatment based on targeting MISRII seems to be a much more effective alternative to the traditional one and will significantly reduce the drug dose. However, the mechanism of MISRII-AMH interaction is still poorly understood, so the development of new anticancer drugs is complicated. The review analyzes MISRII molecular structure and expression levels in various tissues and cell lines, as well as current understanding of the AMH binding mechanisms and data on the possibility of using MISRII as a target for the action of AMH-based antineoplastic drugs.

Prostaglandin E2 Is Required for BMP4-Induced Mesoderm Differentiation of Human Embryonic Stem Cells

The accurate control of early cell fate specification during differentiation of human embryonic stem cells (hESCs) is critical for acquiring pure therapeutic cell populations of interest. Bone morphogenetic protein 4 (BMP4) is a key mesoderm inducer from ESCs. However, the molecular mechanism of the mesodermal cell fate decision induced by BMP4 remains unclear. Here, we demonstrate the requirement of a bioactive lipid, prostaglandin E₂ (PGE₂), for the mesoderm specification from hESCs by BMP4 induction. We show that BMP4 directly regulates the expression of the key enzyme for PGE₂ synthesis, COX-1, and promotes PGE₂ production. More importantly, in the absence of BMP4, forced COX-1 expression or PGE₂ treatment is sufficient to initiate mesoderm specification of hESCs by activation of EP2-PKA signaling and modulation of nuclear translocation of β-catenin. Together, our findings provide insights into the critical role of BMP regulation of PGE₂ synthesis and its downstream signaling in initiating mesoderm commitment of hESCs.

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COX-1 and PGE₂ played pivotal roles in the mesoderm specification of hESCs

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Specific inhibition of COX-1 suppressed mesoderm differentiation of hESCs

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BMP4 directly upregulated the transcription of the COX-1

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PGE₂ stimulated differentiation mainly via the EP2-PKA-GSK3β/β-catenin signaling pathway

BMP-6 inhibits the metastasis of MDA-MB-231 breast cancer cells by regulating MMP-1 expression

Bone morphogenetic protein-6 (BMP-6) is a multifunctional molecule with distinct abilities in embryogenesis and organogenesis. In the present study, our results showed that the rate of BMP-6-negative expression was 30.56% in breast cancer tissues, but was 9.58% in normal tissues by immunohistochemical staining. This implied that BMP-6 expression is absent in breast cancer tissues and may suppress breast cancer metastasis. In addition, stable overexpression of BMP-6 in MDA-MB‑231 cells was established to analyze the metastatic ability. The Boyden chamber assay showed that BMP-6 inhibited the migration and invasion of MDA-MB-231 cells. Moreover, real-time PCR analysis showed that BMP-6 markedly downregulated matrix metalloproteinase-1 (MMP-1) expression at both the mRNA and protein levels in the MDA-MB‑231 cells. Importantly, the results of luciferase and CHIP assays revealed that BMP-6 inhibited MMP-1 promoter activity through the AP-1 response element. In MDA-MB-231 cells treated with BMP-6, a significant decrease in the recruitment of AP-1 components, c-Jun/c-Fos, to the endogenous MMP-1 promoter was noted. We also demonstrated that BMP-6 inhibited the invasion of MDA-MB-231 cells, and this effect was significantly attenuated by overexpression of MMP-1. In contrast, MMP-1 knockdown by RNA interference or MMP-1 inhibitor exhibited an opposite effect. These observations suggest a novel role of BMP-6 in the inhibition of breast cancer metastasis by regulating secretion of MMPs in the tumor microenvironment.

LENS: web-based lens for enrichment and network studies of human proteins

Background

Network analysis is a common approach for the study of genetic view of diseases and biological pathways. Typically, when a set of genes are identified to be of interest in relation to a disease, say through a genome wide association study (GWAS) or a different gene expression study, these genes are typically analyzed in the context of their protein-protein interaction (PPI) networks. Further analysis is carried out to compute the enrichment of known pathways and disease-associations in the network. Having tools for such analysis at the fingertips of biologists without the requirement for computer programming or curation of data would accelerate the characterization of genes of interest. Currently available tools do not integrate network and enrichment analysis and their visualizations, and most of them present results in formats not most conducive to human cognition.

Results

We developed the tool Lens for Enrichment and Network Studies of human proteins (LENS) that performs network and pathway and diseases enrichment analyses on genes of interest to users. The tool creates a visualization of the network, provides easy to read statistics on network connectivity, and displays Venn diagrams with statistical significance values of the network's association with drugs, diseases, pathways, and GWASs. We used the tool to analyze gene sets related to craniofacial development, autism, and schizophrenia.

Conclusion

LENS is a web-based tool that does not require and download or plugins to use. The tool is free and does not require login for use, and is available at http://severus.dbmi.pitt.edu/LENS.

miR-148a is Associated with Obesity and Modulates Adipocyte Differentiation of Mesenchymal Stem Cells through Wnt Signaling

Obesity results from numerous, interacting genetic, behavioral, and physiological factors. Adipogenesis is partially regulated by several adipocyte-selective microRNAs (miRNAs) and transcription factors that regulate proliferation and differentiation of human adipose-derived mesenchymal stem cells (hMSCs-Ad). In this study, we examined the roles of adipocyte-selective miRNAs in the differentiation of hMSCs-Ad to adipocytes. Results showed that the levels of miR-148a, miR-26b, miR-30, and miR-199a increased in differentiating hMSCs-Ad. Among these miRNAs, miR-148a exhibited significant effects on increasing PPRE luciferase activity (it represents PPAR-dependent transcription, a major factor in adipogenesis) than others. Furthermore, miR-148a expression levels increased in adipose tissues from obese people and mice fed high-fat diet. miR-148a acted by suppressing its target gene, Wnt1, an endogenous inhibitor of adipogenesis. Ectopic expression of miR-148a accelerated differentiation and partially rescued Wnt1-mediated inhibition of adipogenesis. Knockdown of miR-148a also inhibited adipogenesis. Analysis of the upstream region of miR-148a locus identified a 3 kb region containing a functional cAMP-response element-binding protein (CREB) required for miR-148a expression in hMSCs-Ad. The results suggest that miR-148a is a biomarker of obesity in human subjects and mouse model, which represents a CREB-modulated miRNA that acts to repress Wnt1, thereby promoting adipocyte differentiation.

Regulation of neuropeptide Y Y1 receptor expression by bone morphogenetic protein 2 in C2C12 myoblasts

The neuropeptide Y (NPY) system is known as one of the major neural signaling pathways. NPY, produced by peripheral tissues including osteoblasts, is known to bind to the Y1 receptor. Recently, osteoblast-specific Y1 receptor knockout mice were developed and were found to have a high bone mass phenotype, indicating a role for the NPY-Y1 receptor axis as a regulator of bone homeostasis. However, regulation of Y1 receptor expression during osteoblastic differentiation remains unexplored. In the present study, we examined the role of bone morphogenetic protein (BMP) 2 signaling in regulating Y1 receptor expression. In C2C12 cells, expression of Y1 receptor mRNA was induced by BMP2. This induction was also observed after co-transfection with Smad1 and Smad4, the intracellular signaling molecules of the BMP2 signaling pathway. In a transfection assay, Smad1/4 up-regulated transcriptional activity through interaction with the Y1 receptor gene promoter. Following transfection of MC3T3-E1 cells with siRNA for the Y1 receptor, the expression of alkaline phosphatase, osteocalcin, Runx2 and osterix were increased. These results show that BMP2 signaling regulates Y1 receptor gene expression, and raises the possibility that NPY acts in osteoblasts via an autocrine mechanism.

The mammalian germline as a pluripotency cycle

Naive pluripotency refers to the capacity of single cells in regulative embryos to engender all somatic and germline cell types. Only germ cells - conventionally considered to be unipotent - can naturally re-acquire pluripotency, by cycling through fertilisation. Furthermore, primordial germ cells express, and appear to be functionally dependent upon, transcription factors that characterise the pluripotent state. We hypothesise that germ cells require pluripotency factors to control a de-restricted epigenome. Consequently, they harbour latent potential, as manifested in teratocarcinogenesis or direct conversion into pluripotent stem cells in vitro. Thus, we suggest that there exists an unbroken cycle of pluripotency, naive in the early epiblast and latent in the germline, that is sustained by a shared transcription factor network.

The zinc finger transcription factor Ovol2 acts downstream of the bone morphogenetic protein pathway to regulate the cell fate decision between neuroectoderm and mesendoderm

During early embryonic development, bone morphogenetic protein (BMP) signaling is essential for neural/non-neural cell fate decisions. BMP signaling inhibits precocious neural differentiation and allows for proper differentiation of mesoderm, endoderm, and epidermis. However, the mechanisms underlying the BMP pathway-mediated cell fate decision remain largely unknown. Here, we show that the expression of Ovol2, which encodes an evolutionarily conserved zinc finger transcription factor, is down-regulated during neural differentiation of mouse embryonic stem cells. Knockdown of Ovol2 in embryonic stem cells facilitates neural conversion and inhibits mesendodermal differentiation, whereas Ovol2 overexpression gives rise to the opposite phenotype. Moreover, Ovol2 knockdown partially rescues the neural inhibition and mesendodermal induction by BMP4. Mechanistic studies further show that BMP4 directly regulates Ovol2 expression through the binding of Smad1/5/8 to the second intron of the Ovol2 gene. In the chick embryo, cOvol2 expression is specifically excluded from neural territory and is up-regulated by BMP4. In addition, ectopic expression of cOvol2 in the prospective neural plate represses the expression of the definitive neural plate marker cSox2. Taken together, these results indicate that Ovol2 acts downstream of the BMP pathway in the cell fate decision between neuroectoderm and mesendoderm to ensure proper germ layer development.

A critical role for endoglin in the emergence of blood during embryonic development

Much remains unknown about the signals that induce early mesoderm to initiate hematopoietic differentiation. Here, we show that endoglin (Eng), a receptor for the TGFβ superfamily, identifies all cells with hematopoietic fate in the early embryo. These arise in an Eng(+)Flk1(+) mesodermal precursor population at embryonic day 7.5 (E7.5), a cell fraction also endowed with endothelial potential. In Eng-knockout embryos, hematopoietic colony activity and numbers of CD71(+)Ter119(+) erythroid progenitors were severely reduced. This coincided with severely reduced expression of embryonic globin and key bone morphogenic protein (BMP) target genes, including the hematopoietic regulators Scl, Gata1, Gata2, and Msx-1. To interrogate molecular pathways active in the earliest hematopoietic progenitors, we applied transcriptional profiling to sorted cells from E7.5 embryos. Eng(+)Flk-1(+) progenitors coexpressed TGFβ and BMP receptors and target genes. Furthermore, Eng(+)Flk-1(+) cells presented high levels of phospho-SMAD1/5, indicating active TGFβ and/or BMP signaling. Remarkably, under hematopoietic serum-free culture conditions, hematopoietic outgrowth of Eng-expressing cells was dependent on the TGFβ superfamily ligands BMP4, BMP2, or TGF-β1. These data demonstrate that the E(+)F(+) fraction at E7.5 represents mesodermal cells competent to respond to TGFβ1, BMP4, or BMP2, shaping their hematopoietic development, and that Eng acts as a critical regulator in this process by modulating TGF/BMP signaling.

Genome-wide identification of microRNA targets in human ES cells reveals a role for miR-302 in modulating BMP response

MicroRNAs are important regulators in many cellular processes, including stem cell self-renewal. Recent studies demonstrated their function as pluripotency factors with the capacity for somatic cell reprogramming. However, their role in human embryonic stem (ES) cells (hESCs) remains poorly understood, partially due to the lack of genome-wide strategies to identify their targets. Here, we performed comprehensive microRNA profiling in hESCs and in purified neural and mesenchymal derivatives. Using a combination of AGO cross-linking and microRNA perturbation experiments, together with computational prediction, we identified the targets of the miR-302/367 cluster, the most abundant microRNAs in hESCs. Functional studies identified novel roles of miR-302/367 in maintaining pluripotency and regulating hESC differentiation. We show that in addition to its role in TGF-β signaling, miR-302/367 promotes bone morphogenetic protein (BMP) signaling by targeting BMP inhibitors TOB2, DAZAP2, and SLAIN1. This study broadens our understanding of microRNA function in hESCs and is a valuable resource for future studies in this area.

BMP-6 inhibits MMP-9 expression by regulating heme oxygenase-1 in MCF-7 breast cancer cells

PURPOSE

BMP-6, which belongs to the TGF-β superfamily, is a multifunctional molecule with distinct abilities in embryogenesis and organogenesis. Our recent research has implied that BMP-6 may suppress breast cancer metastasis. In the present study, we extended to elucidate the molecular mechanism by which BMP-6 exerts its anti-tumorigenic effect.

METHODS

The Boyden chamber assay was used to examine the ability of BMP-6 and HO-1 in MCF-7 malignant progress. RT-PCR, western blot, luciferase assay, and quantitative CHIP were used to determine the potential mechanism and signaling pathways by which BMP-6 and HO-1 function as anti-metastatic factors in MCF-7 cells.

RESULTS

The Boyden chamber assay showed that BMP-6 inhibited the migration and invasion of MCF-7 cells, which effect was significantly deprived by knockdown of HO-1. We further demonstrated that BMP-6 treatment resulted in an activation of HO-1 transcription through the recruitment of Smad1/5 to the Smad-responsive element on its promoter. In addition, BMP-6-induced up-regulation of HO-1 exhibited an inhibitory effect on MMP-9 secretion in a paracrine action in MCF-7 cells. Overexpression of BMP-6 and HO-1 synergistically suppressed MMP-9 transcription, which effect was specifically mediated via the MAPK/p38/AP-1 signaling. However, blockade of HO-1 using ZnPPIX totally abolished BMP-6-regulated MMP-9 activation in MCF-7 cells.

CONCLUSIONS

These observations suggest a novel role of BMP-6/HO-1 cascade to relieve breast cancer metastasis by regulating the secretion of growth factors in tumor microenvironment.

Conservation of gene linkage in dispersed vertebrate NK homeobox clusters

Nk homeobox genes are important regulators of many different developmental processes including muscle, heart, central nervous system and sensory organ development. They are thought to have arisen as part of the ANTP megacluster, which also gave rise to Hox and ParaHox genes, and at least some NK genes remain tightly linked in all animals examined so far. The protostome-deuterostome ancestor probably contained a cluster of nine Nk genes: (Msx)-(Nk4/tinman)-(Nk3/bagpipe)-(Lbx/ladybird)-(Tlx/c15)-(Nk7)-(Nk6/hgtx)-(Nk1/slouch)-(Nk5/Hmx). Of these genes, only NKX2.6-NKX3.1, LBX1-TLX1 and LBX2-TLX2 remain tightly linked in humans. However, it is currently unclear whether this is unique to the human genome as we do not know which of these Nk genes are clustered in other vertebrates. This makes it difficult to assess whether the remaining linkages are due to selective pressures or because chance rearrangements have "missed" certain genes. In this paper, we identify all of the paralogs of these ancestrally clustered NK genes in several distinct vertebrates. We demonstrate that tight linkages of Lbx1-Tlx1, Lbx2-Tlx2 and Nkx3.1-Nkx2.6 have been widely maintained in both the ray-finned and lobe-finned fish lineages. Moreover, the recently duplicated Hmx2-Hmx3 genes are also tightly linked. Finally, we show that Lbx1-Tlx1 and Hmx2-Hmx3 are flanked by highly conserved noncoding elements, suggesting that shared regulatory regions may have resulted in evolutionary pressure to maintain these linkages. Consistent with this, these pairs of genes have overlapping expression domains. In contrast, Lbx2-Tlx2 and Nkx3.1-Nkx2.6, which do not seem to be coexpressed, are also not associated with conserved noncoding sequences, suggesting that an alternative mechanism may be responsible for the continued clustering of these genes.

BMP-6 inhibits microRNA-21 expression in breast cancer through repressing deltaEF1 and AP-1

MicroRNAs (miRNAs), which are small noncoding RNA molecules, play important roles in the post-transcriptional regulation process. The microRNA-21 gene (miR-21) has been reported to be highly expressed in various solid tumors, including breast cancer. Bone morphogenetic protein-6 (BMP-6) has been identified as an inhibitor of breast cancer epithelial-mesenchymal transition (EMT) through rescuing E-cadherin expression. We initiated experiments to identify the relationships between miR-21 and BMP-6 in breast cancer progression. Real-time PCR analysis showed that miR-21 expression was very high in MDA-MB-231 cells that expressed little BMP-6. A reverse correlation between BMP-6 and miR-21 was also determined in breast cancer tissue samples. Moreover, BMP-6 inhibited miR-21 transcription in MDA-MB-231 cells. In order to investigate how BMP-6 inhibited the miR-21 promoter (miPPR-21), we constructed a series of miPPR-21 reporters. Luciferase assay results indicated that BMP-6 inhibited miPPR-21 activity through the E2-box and AP-1-binding sites. We also demonstrated that both deltaEF1 and TPA induced miR-21 expression. Using site-directed mutation and CHIP assay, we found that deltaEF1 induced miPPR-21 activity by binding to the E2-box on miPPR-21. Moreover, TPA triggered miPPR-21 activity through the AP-1 binding sites. BMP-6 treatment significantly reduced the binding of these factors to miPPR-21 by decreasing the expression of deltaEF1 and c-Fos/c-Jun. We also demonstrated that BMP-6-induced downregulation of miR-21 modified the activity of PDCD4 3'UTR and inhibited MDA-MB-231 cell invasion. deltaEF1 overexpression and TPA induction blocked this inhibitory effect of BMP-6. In conclusion, BMP-6-induced inhibition of miR-21 suggests that BMP-6 may function as an anti-metastasis factor by a mechanism involving transcriptional repression of miR-21 in breast cancer.

Statins decrease dendritic arborization in rat sympathetic neurons by blocking RhoA activation

Clinical and experimental evidence suggest that statins decrease sympathetic activity, but whether peripheral mechanisms involving direct actions on post-ganglionic sympathetic neurons contribute to this effect is not known. Because tonic activity of these neurons is directly correlated with the size of their dendritic arbor, we tested the hypothesis that statins decrease dendritic arborization in sympathetic neurons. Oral administration of atorvastatin (20 mg/kg/day for 7 days) significantly reduced dendritic arborization in vivo in sympathetic ganglia of adult male rats. In cultured sympathetic neurons, statins caused dendrite retraction and reversibly blocked bone morphogenetic protein-induced dendritic growth without altering cell survival or axonal growth. Supplementation with mevalonate or isoprenoids, but not cholesterol, attenuated the inhibitory effects of statins on dendritic growth, whereas specific inhibition of isoprenoid synthesis mimicked these statin effects. Statins blocked RhoA translocation to the membrane, an event that requires isoprenylation, and constitutively active RhoA reversed statin effects on dendrites. These observations that statins decrease dendritic arborization in sympathetic neurons by blocking RhoA activation suggest a novel mechanism by which statins decrease sympathetic activity and protect against cardiovascular and cerebrovascular disease.

Bone morphogenetic protein 2 induces pulmonary angiogenesis via Wnt-beta-catenin and Wnt-RhoA-Rac1 pathways

Mutations in bone morphogenetic protein (BMP) receptor II (BMPRII) are associated with pulmonary artery endothelial cell (PAEC) apoptosis and the loss of small vessels seen in idiopathic pulmonary arterial hypertension. Given the low penetrance of BMPRII mutations, abnormalities in other converging signaling pathways may be necessary for disease development. We hypothesized that BMPRII supports normal PAEC function by recruiting Wingless (Wnt) signaling pathways to promote proliferation, survival, and motility. In this study, we report that BMP-2, via BMPRII-mediated inhibition of GSK3-beta, induces beta-catenin (beta-C) accumulation and transcriptional activity necessary for PAEC survival and proliferation. At the same time, BMP-2 mediates phosphorylated Smad1 (pSmad1) or, with loss of BMPRII, pSmad3-dependent recruitment of Disheveled (Dvl) to promote RhoA-Rac1 signaling necessary for motility. Finally, using an angiogenesis assay in severe combined immunodeficient mice, we demonstrate that both beta-C- and Dvl-mediated RhoA-Rac1 activation are necessary for vascular growth in vivo. These findings suggest that the recruitment of both canonical and noncanonical Wnt pathways is required in BMP-2-mediated angiogenesis.

Molecular basis for skeletal variation: insights from developmental genetic studies in mice

Skeletal variations are common in humans, and potentially are caused by genetic as well as environmental factors. We here review molecular principles in skeletal development to develop a knowledge base of possible alterations that could explain variations in skeletal element number, shape or size. Environmental agents that induce variations, such as teratogens, likely interact with the molecular pathways that regulate skeletal development.

Protective effect of bone morphogenetic protein-6 on neurons from H2O2 injury

Bone morphogenetic protein-6 (BMP6) is a member of the TGF-beta superfamily. Expression of BMP6 and its receptors are increased when brain tissues of adult rats are injured, suggesting that BMP6 may have a neuroprotective function in the physiologic response to neurological damage. This research investigates the molecular mechanisms supporting a neuroprotective effect of BMP6 in neural cells traumatized by H(2)O(2). We demonstrate that presence of BMP6 either before or after H(2)O(2)-induced injury protects the cultured primary cortical cells from apoptosis. However, molecular mechanisms mediating the protective effects of either pre- or post-treatment with BMP6 are different. Cells pre-treated with BMP6 have attenuated MAPK activity induced by H(2)O(2), whereas the MAPK activity in cells post-treated with BMP6 remains unchanged. Further, pharmacological inhibitors of MAPKs, PD98059 and SB203580, block the protective effect of BMP6 in the cells pre-treated with BMP6 but not in the cells post-treated with BMP6. The protective effect of post-treatment with BMP6 appears to be mediated through regulation of p53 and Bax molecules, evidenced by decreased mRNA levels after BMP6 treatment. Taken together, these data suggest BMP6 protect cortical cells against oxidation stress induced by H(2)O(2) via two different mechanisms, where (1) pre-treatment with BMP6 acts through MAPK pathway and (2) post-treatment with BMP6 works by down-regulating p53 and Bax.

Cytosolic signaling protein Ecsit also localizes to mitochondria where it interacts with chaperone NDUFAF1 and functions in complex I assembly

Ecsit is a cytosolic adaptor protein essential for inflammatory response and embryonic development via the Toll-like and BMP (bone morphogenetic protein) signal transduction pathways, respectively. Here, we demonstrate a mitochondrial function for Ecsit (an evolutionary conserved signaling intermediate in Toll pathways) in the assembly of mitochondrial complex I (NADH:ubiquinone oxidoreductase). An N-terminal targeting signal directs Ecsit to mitochondria, where it interacts with assembly chaperone NDUFAF1 in 500- to 850-kDa complexes as demonstrated by affinity purification and vice versa RNA interference (RNAi) knockdowns. In addition, Ecsit knockdown results in severely impaired complex I assembly and disturbed mitochondrial function. These findings support a function for Ecsit in the assembly or stability of mitochondrial complex I, possibly linking assembly of oxidative phosphorylation complexes to inflammatory response and embryonic development.

Ancient connection between NKL genes and the mesoderm? Insights from Tlx expression in a ctenophore

In recent years, evo-devo studies on non-bilaterian metazoans have improved our understanding of the early evolution of animal body plans. In particular, works on cnidarians suggested that contrary to classical views, the mesoderm originated far before the emergence of the Bilateria. In this context, a synthesis of genomic and functional data concerning the Antennapedia (Antp) superclass of homeobox genes suggested that early in animal evolution, each of the three germ layers was under the control of one cluster of Antp genes. In particular, the patterning and differentiation of the mesoderm was under the control of the NKL cluster. The ctenophores stand as a key taxon with respect to such issues because unlike other non-bilaterian phyla, their intermediate germ layer satisfies the strict embryological definition of a mesoderm. For that reason, we investigated the only known member of the NKL group in Ctenophora, a gene previously isolated from Pleurobrachia and attributed to the Tlx family. In our analysis of the NKL group, this ctenophore gene branches as the sister-group of bilaterian Tlx genes, but without statistical support. The expression pattern of this gene was revealed by in situ hybridisation in the adult ctenophore. The expression territories of PpiTlx are predominantly ectodermal, in two distinct types of ciliated epidermal cells and in one category of gland cells. We also identified a probable endodermal site of expression. Because we failed to detect any mesodermal expression, the results do not provide support to the hypothesis of an ancient functional association between the NKL group and the mesoderm.

Characterization of dSnoN and its relationship to Decapentaplegic signaling in Drosophila

Vertebrate members of the ski/snoN family of proto-oncogenes antagonize TGFbeta and BMP signaling in a variety of experimental situations. This activity of Ski/SnoN proteins is related to their ability to interact with Smads, the proteins acting as key mediators of the transcriptional response to the TGFbeta superfamily members. However, despite extensive efforts to identify the physiological roles of the Ski/SnoN proteins, it is not yet clear whether they participate in regulating Activin and/or BMP signaling during normal development. It is therefore crucial to examine their roles in vivo mostly because of the large number of known Ski/SnoN-interacting proteins and the association between the up-regulation of these genes and cancer progression. Here we characterize the Drosophila homolog to vertebrate ski and snoN genes. The Drosophila dSnoN protein retains the ability of its vertebrate counterparts to antagonize BMP signaling in vivo and in cultured cells. dSnoN does not interfere with Mad phosphorylation but it interacts genetically with Mad, Medea and dSmad2. Mutations in either the Smad2-3 or Smad4 putative binding sites of dSnoN prevent the antagonism of dSnoN towards Dpp signaling, although homozygous flies for these mutations or for a genetic deficiency of the locus are viable and have wings of normal size and pattern.

The TLX2 homeobox gene is a transcriptional target of PHOX2B in neural-crest-derived cells

The TLX2 (HOX11L1, Ncx, Enx) and PHOX2B genes encode transcription factors crucial in the development of neural-crest-derived cells, leading to ANS (autonomic nervous system) specific neuronal lineages. Moreover, they share a similar expression pattern and are both involved in downstream steps of BMP (bone morphogenetic protein) signalling. In an attempt to reconstruct the gene network sustaining the correct development of the ANS, we have undertaken an in vitro experimental strategy to identify direct upstream regulators of the TLX2 gene. After characterizing a sequence displaying enhancer property in its 5' flanking region, we confirmed the functional link between the human PHOX2B and TLX2 genes. Transient transfections and electrophoretic-mobility-shift assays suggested that PHOX2B is able to bind the cell-specific element in the 5' regulatory region of the TLX2 gene, determining its transactivation in neuroblastoma cells. Such interaction was also confirmed in vivo by means of chromatin immunoprecipitation assay and, in addition, up-regulation of endogenous TLX2 mRNA level was demonstrated following PHOX2B over-expression, by quantitative real-time PCR. Finally, PHOX2B proteins carrying mutations responsible for CCHS (congenital central hypoventilation syndrome) development showed a severe impairment in activating TLX2 expression, both in vitro and in vivo. Taken together, these results support the PHOX2B-TLX2 promoter interaction, suggesting a physiological role in the transcription-factor cascade underlying the differentiation of neuronal lineages of the ANS during human embryogenesis.

Localization of Brachyury (T) in embryonic and extraembryonic tissues during mouse gastrulation

T-box gene family members have important roles during murine embryogenesis, gastrulation, and organogenesis. Although relatively little is known about how T-box genes are regulated, published gene expression studies have revealed dynamic and specific patterns in both embryonic and extraembryonic tissues of the mouse conceptus. Mutant alleles of the T-box gene Brachyury (T) have identified roles in formation of mesoderm and its derivatives, such as somites and the allantois. However, given the cell autonomous nature of T gene activity and conflicting results of gene expression studies, it has been difficult to attribute a primary function to T in normal allantoic development. We report localization of T protein by sectional immunohistochemistry in both embryonic and extraembryonic tissues during mouse gastrulation, emphasizing T localization within the allantois. T was detected in all previously reported sites within the conceptus, including the primitive streak and its derivatives, nascent embryonic mesoderm, the node and notochord, as well as notochord-associated endoderm and posterior neurectoderm. In addition, we have clarified T within the allantois, where it was first detected in the proximal midline of the late allantoic bud (approximately 7.5 days postcoitum, dpc) and persisted within an expanded midline domain until 6-somite pairs (s; approximately 8.5 dpc). Lastly, we have discovered several novel T sites, including the developing heart, visceral endoderm, extraembryonic ectoderm, and its derivative, chorionic ectoderm. Together, these data provide a unified picture of T in the mammalian conceptus, and demonstrate T's presence in unrelated cell types and tissues in highly dynamic spatiotemporal patterns in both embryonic and extraembryonic tissues.

Mutual regulation of follicle-stimulating hormone signaling and bone morphogenetic protein system in human granulosa cells

Bone morphogenetic proteins (BMPs) play critical roles in folliculogenesis by modulating the actions of follicle-stimulating hormone (FSH) in the ovary. However, the effects of FSH on the BMP system remain unknown. Here, we have investigated the effects of FSH on BMP signaling using the human granulosa-like tumor cell line KGN. KGN cells express BMP type I and type II receptors and the BMP signaling molecules SMADs. FSH administration upregulated BMP type IA (BMPR1A) and IB (BMPR1B) receptors, activin type II receptor (ACVR2), and BMP type II receptor (BMPR2). FSH also augmented SMAD1 and SMAD5 expression, and conversely, FSH suppressed the expression of the inhibitory SMADs, SMAD6 and SMAD7. Bioassays revealed that FSH enhances BMP-induced SMAD1/5/8 phosphorylation and cellular DNA synthesis induced by BMP6 and BMP7. Since overexpression of BMPR1A and BMPR1B, but not SMADs, significantly enhanced the BMP responses, these type I receptors were revealed to be limiting factors for BMP signaling in KGN cells. BMPs significantly suppressed progesterone synthesis induced by forskolin and dibutyryl-cAMP (BtcAMP) but had no effect on estradiol induced by the same factors. KGN cAMP levels induced by forskolin were not altered by BMPs, suggesting that BMPs regulate steroidogenesis at a level downstream of cAMP synthesis in KGN cells. In this regard, BMPs specifically reduced the STAR transcription, whereas the levels of CYP11A, HSD3B2, and CYP19 stimulated by forskolin as well as BtcAMP were not altered. Collectively, the two major factors, FSH-cAMP pathway and BMP system, are reciprocally and functionally linked. Given that BMPs downregulate FSH receptors in KGN cells, this interaction may contribute to fine-tuning of the mutual sensitivity toward BMP ligands and FSH.

Smad transcription factors

Smad transcription factors lie at the core of one of the most versatile cytokine signaling pathways in metazoan biology-the transforming growth factor-beta (TGFbeta) pathway. Recent progress has shed light into the processes of Smad activation and deactivation, nucleocytoplasmic dynamics, and assembly of transcriptional complexes. A rich repertoire of regulatory devices exerts control over each step of the Smad pathway. This knowledge is enabling work on more complex questions about the organization, integration, and modulation of Smad-dependent transcriptional programs. We are beginning to uncover self-enabled gene response cascades, graded Smad response mechanisms, and Smad-dependent synexpression groups. Our growing understanding of TGFbeta signaling through the Smad pathway provides general principles for how animal cells translate complex inputs into concrete behavior.

Transcriptional regulation of the homeobox gene Mixl1 by TGF-beta and FoxH1

Mixl1 is a paired-type homeodomain protein that plays a crucial role in morphogenesis and endoderm differentiation in the murine embryo. To understand how Mixl1 directs embryogenesis, we studied the regulation of Mixl1 expression at a transcriptional level. In HepG2 cells, a genomic fragment encompassing the Mixl1 promoter conferred strong TGF-beta-induced transcription that was dependent on the presence of the DNA-binding protein FoxH1. Further analysis of the Mixl1 promoter identified a proximal response element (PRE) containing SMAD- and FoxH1-binding sites required for TGF-beta responsiveness. The PRE was also responsive to signalling by Nodal, a TGF-beta ligand required for normal embryonic patterning. These results demonstrate for the first time a functional role for TGF-beta ligands in regulation of mammalian Mixl1, identify FoxH1 as an essential transcriptional co-activator, and implicate Nodal as the embryonic regulator of Mixl1 in mesendoderm morphogenesis.

Induction of ectopic olfactory structures and bone morphogenetic protein inhibition by Rossy, a group XII secreted phospholipase A2

The secreted phospholipases A(2) (sPLA(2)s) comprise a family of small secreted proteins with the ability to catalyze the generation of bioactive lipids through glycophospholipid hydrolysis. Recently, a large number of receptor proteins and extracellular binding partners for the sPLA(2)s have been identified, suggesting that these secreted factors might exert a subset of their broad spectrum of biological activities independently of their enzymatic activity. Here, we describe an activity for the sPLA(2) group XII (sPLA(2)-gXII) gene during Xenopus laevis early development. In the ectoderm, sPLA(2)-gXII acts as a neural inducer by blocking bone morphogenetic protein (BMP) signaling. Gain of function in embryos leads to ectopic neurogenesis and to the specification of ectopic olfactory sensory structures, including olfactory bulb and sensory epithelia. This activity is conserved in the Drosophila melanogaster, Xenopus, and mammalian orthologs and appears to be independent of the lipid hydrolytic activity. Because of its effect on olfactory neurogenesis, we have renamed this gene Rossy, in homage to the Spanish actress Rossy de Palma. We present evidence that Rossy/sPLA(2)-gXII can inhibit the transcriptional activation of BMP direct-target gene reporters in Xenopus and mouse P19 embryonic carcinoma cells through the loss of DNA-binding activity of activated Smad1/4 complexes. Collectively, these data represent the first evidence for signaling cross talk between a secreted phospholipase A(2) and the BMP/transforming growth factor beta pathways and identify Rossy/sPLA(2)-gXII as the only factor thus far described which is sufficient to induce anterior sensory neural structures during vertebrate development.

Bone morphogenic protein (Smad)-mediated repression of proopiomelanocortin transcription by interference with Pitx/Tpit activity

The signaling molecules bone morphogenic protein (BMP) 4 and 2 have been implicated in early organogenesis and cell differentiation of the pituitary. However, the use of different experimental paradigms has led to conflicting interpretations with regard to the action of these factors on differentiation of corticotroph cells and on expression of the proopiomelanocortin (POMC) gene. We have now directly assessed the action of BMP signaling on POMC expression and found that BMP4 represses POMC mRNA levels and promoter activity. This repression appears to be dependent on the classical BMP signaling pathway that involves the activin-like kinase 3/6 receptors and the Smad1/4 transcription factors. The repression is reversed by overexpression of the inhibitory Smads, Smad6 or Smad7. Collectively, the evidence suggests that autocrine BMP signaling may be acting upon AtT-20 cells to set the level of POMC expression. Upon BMP4 stimulation, activated phospho-Smad1 is recruited to the POMC promoter, where it apparently acts through interactions with the Pitx and Tpit transcription factors. It is postulated that these interactions interfere with the transcriptional activity of Pitx and/or Tpit, thus resulting in transcriptional repression.

Hox11L1 expression by precursors of enteric smooth muscle: an alternative explanation for megacecum in HOX11L1-/- mice

Previous studies have focused on expression of Hox11L1 in enteric neurons as the explanation for intestinal and urinary bladder dysmotility observed in mice that do not have the transcription factor. However, Hox11L1 is also expressed transiently in endo-, meso-, and ectodermal cells of the most caudal embryo during gastrulation. We sought to more fully characterize the fates of these cells because they might help explain the pathogenesis of lethal pseudo-obstruction in Hox11L1-null mice. The Cre recombinase cDNA was introduced into the Hox11L1 locus, and expression of the "knock-in" allele was used to activate the Rosa26R, beta-galactosidase reporter gene in cells with ongoing Hox11L1 transcription and their descendants. During gastrulation, Rosa26R activation was observed in progenitors of caudal somatic and visceral cells, including enteric smooth muscle. Expression in enteric neural precursors appeared much later. Analysis of endogenous Hox11L1 mRNA in aneuronal segments of large intestine that were grafted under the renal capsule indicated that the early activation of Hox11L1 in visceral mesoderm was transient and ceased before colonization of the large intestine by neural progenitors. Mice homozygous for the Cre allele died shortly after weaning, with cecal and proximal colonic distention but without overt anatomic defects that might represent maldevelopment of the visceral mesoderm. Our findings expand the range of possible functions of Hox11L1 to include activation of an as yet unknown developmental program in visceral smooth muscle and allow the possibility that intestinal dysmotility in Hox11L1-null animals may not be a primary neural disorder.

An atlas of differential gene expression during early Xenopus embryogenesis

We have carried out a large-scale, semi-automated whole-mount in situ hybridization screen of 8369 cDNA clones in Xenopus laevis embryos. We confirm that differential gene expression is prevalent during embryogenesis since 24% of the clones are expressed non-ubiquitously and 8% are organ or cell type specific marker genes. Sequence analysis and clustering yielded 723 unique genes displaying a differential expression pattern. Of these, 18% were already described in Xenopus, 47% have homologs and 35% are lacking significant sequence similarity in databases. Many of them encode known developmental regulators. We classified 363 of the 723 genes for which a Gene Ontology annotation for molecular function could be attributed and found 'DNA binding' and 'enzyme' the most represented terms. The most common protein domains encoded in these embryonic, differentially expressed genes are the homeobox and RNA Recognition Motif (RRM). Fifty-nine putative orthologs of human disease genes, and 254 organ or cell specific marker genes were identified. Markers were found for nasal placode and archenteron roof, organs for which a specific marker was previously unavailable. Markers were also found for novel subdomains of various other organs. The tissues for which most markers were found are muscle and epidermis. Expression of cell cycle regulators fell in two classes, containing proliferation-promoting and anti-proliferative genes, respectively. We identified 66 new members of the BMP4, chromatin, endoplasmic reticulum, and karyopherin synexpression groups, thus providing a first glimpse of their probable cellular roles. Cluster analysis of tissues to measure tissue relatedness yielded some unorthodox affinities besides expectable lineage relationships. In conclusion, this study represents an atlas of gene expression patterns, which reveals embryonic regionalization, provides novel marker genes, and makes predictions about the functional role of unknown genes.

Human retroviral gag- and gag-pol-like proteins interact with the transforming growth factor-beta receptor activin receptor-like kinase 1

Mutations in activin receptor-like kinase 1 (ALK1), a transforming growth factor (TGF)-beta type I receptor, lead to the vascular disorder hereditary hemorrhagic telangiectasia caused by abnormal vascular remodeling. The underlying molecular cause of this disease is not well understood. Identifying binding partners for ALK1 will help to understand its cellular function. Using the two-hybrid system, we identified an ALK1-binding protein encoded by an ancient retroviral/retrotransposon element integrated as a single copy gene known as PEG10 on human chromosome 7q21. PEG10 contains two overlapping reading frames from which two proteins, PEG10-RF1 and PEG10-RF1/2, are translated by a typical retroviral -1 ribosomal frameshift mechanism. Reverse transcription-PCR and Northern blot analysis showed a broad range of PEG10 expression in different tissues and cell types, i.e. human placenta, brain, kidney, endothelial cells, lymphoblasts, and HepG2 and HEK293 cells. However, endogenous PEG10-RF1 and PEG10-RF1/2 proteins were only detected in HepG2 and HEK293 cells. PEG10-RF1, which is the major PEG10 protein product, represents a gag-like protein, and PEG10-RF1/2 represents a gag-pol-like protein. PEG10-RF1 also interacts with different members of TGF-beta superfamily type I and II receptors. PEG10-RF1 binding to ALK1 is mediated by a 200-amino acid domain with no recognized motif. PEG10-RF1 inhibits ALK1 as well as ALK5 signaling. Co-expression of ALK1 and PEG10-RF1 in different cell types induced morphological changes reminiscent of neuronal cells or sprouting cells. This is the first report of a human retroviral-like protein interacting with members of the TGF-beta receptor family.

Characterization of the bone morphogenetic protein (BMP) system in human pulmonary arterial smooth muscle cells isolated from a sporadic case of primary pulmonary hypertension: roles of BMP type IB receptor (activin receptor-like kinase-6) in the mitotic action

The functional involvement of bone morphogenetic protein (BMP) system in primary pulmonary hypertension (PPH) remains unclear. Here we demonstrate a crucial role of the BMP type IB receptor, activin receptor-like kinase (ALK)-6 for pulmonary arterial smooth muscle cell (pphPASMC) mitosis isolated from a sporadic PPH patient bearing no mutations in BMPR2 gene. A striking increase in the levels of ALK-6 mRNA was revealed in pphPASMC compared with control PASMCs, in which ALK-6 transcripts were hardly detectable. BMP-2 and -7 stimulated the mitosis of pphPASMCs, which was opposite to their suppressive effects on the mitosis of the control PASMCs. BMP-4 and -6 and activin inhibited pphPASMC mitosis, whereas these did not affect control PASMCs. The presence of BMP signaling machinery in pphPASMCs was elucidated based on the analysis on Id-1 transcription and Smad-reporter genes. Overexpression of a dominant-negative ALK-6 construct revealed that ALK-6 plays a key role in the mitosis as well as intracellular BMP signaling of pphPASMCs. Gene silencing of ALK-6 using small interfering RNA also reduced DNA synthesis as well as Id-1 transcription in pphPASMCs regardless of BMP-2 stimulation. Although Id-1 response was not stimulated by BMP-2 in control PASMCs, the gene delivery of wild-type ALK-6 caused significant increase in the Id-1 transcripts in response to BMP-2. Additionally, inhibitors of ERK and p38 MAPK pathways suppressed pphPASMC mitosis induced by BMP-2, implying that the mitotic action is in part MAPK dependent. Thus, the BMP system is strongly involved in pphPASMC mitosis through ALK-6, which possibly leads to activation of Smad and MAPK, resulting in the progression of vascular remodeling of pulmonary arteries in PPH.

Novel action of activin and bone morphogenetic protein in regulating aldosterone production by human adrenocortical cells

We have uncovered a functional bone morphogenetic protein (BMP) and activin system complete with ligands (BMP-6 and activin betaA/betaB), receptors (activin receptor-like kinase receptors 2, 3, and 4; activin type-II receptor; and BMP type-II receptor), and the binding protein follistatin in the human adrenocortical cell line H295R. Administration of activin and BMP-6 to cultures of H295R cells caused concentration-responsive increases in aldosterone production. The mRNA levels of steroidogenic acute regulatory protein or P450 steroid side-chain cleavage enzyme, the rate-limiting steps of adrenocortical steroidogenesis, were enhanced by activin and BMP-6. Activin and BMP-6 also activated the transcription of steroidogenic acute regulatory protein as well as the late-step steriodogenic enzyme CYP11B2. Activin enhanced ACTH-, forskolin-, or dibutyryl-cAMP- but not angiotensin II (Ang II)-induced aldosterone production, whereas BMP-6 specifically augmented Ang II-induced aldosterone production. Activin and ACTH but not BMP-6 increased cAMP production. Follistatin, which inhibits activin actions by binding, suppressed basal and ACTH-induced aldosterone secretion but failed to affect the Ang II-induced aldosterone level. Furthermore, MAPK signaling appeared to be involved in aldosterone production induced by Ang II and BMP-6 because an inhibitor of MAPK activation, U0126, reduced the level of aldosterone synthesis stimulated by Ang II and BMP-6 but not activin. In addition, Ang II reduced the expression levels of BMP-6 but increased that of activin betaB, whereas ACTH had no effect on these levels. Collectively, the present data suggest that activin acts to regulate adrenal aldosterone synthesis predominantly by modulating the ACTH-cAMP-protein kinase A signaling cascade, whereas BMP-6 works primarily by modulating the Ang II-MAPK cascade in human adrenal cortex in an autocrine/paracrine fashion.

Poly(ADP-ribose) polymerase 1 interacts with OAZ and regulates BMP-target genes

OAZ is a multi zinc finger protein which interacts with several distinct nuclear proteins including Olf-1/EBF, Smad1, and Smad4 and regulates transcription of various genes. Here we show that poly(ADP-ribose) polymerase 1 (Parp1) forms a complex with OAZ and positively regulates BMP-target genes, Xenopus Vent-2 and mouse Smad6 genes. Both wild type and the mutant forms of Parp1, which is deficient in poly(ADP-ribose) polymerase activity, constitutively interact with OAZ; however, the mutant Parp1 did not activate transcription. These results suggest that poly(ADP-ribose) polymerase activity is essential for the transcriptional activation of Vent-2 and Smad6. These results suggest that Parp1 serves as a transcriptional coactivator of OAZ in BMP-dependent gene regulation.

Components of the anti-Müllerian hormone signaling pathway in gonads

Anti-Müllerian hormone (AMH) is a member of the Transforming Growth Factor-beta (TGF-beta) family implicated in the regression of Müllerian ducts in male fetuses and in the development and function of gonads of both sexes. Members of the TGF-beta family signal through two types of serine/threonine kinase receptors called type I and type II, and two types of Smad proteins, receptor-regulated Smad (R-Smad) and common Smad, Smad4. Components of the AMH signaling pathway have been identified in gonads and gonadal cell lines. The AMH type II receptor is highly specific. In contrast, the identity of the AMH type I receptor is not clear; three type I receptors of Bone Morphogenetic Proteins (BMPs), Alk2, Alk3 and Alk6 may transduce AMH signals, but none of them has all the characteristics of an AMH type I receptor. AMH activates BMP-specific R-Smads and reporter genes.

Molecules mimicking Smad1 interacting with Hox stimulate bone formation

Bone morphogenetic proteins (BMPs) induce osteoblast differentiation and bone formation. Smads, a group of functionally and structurally related intracellular effectors, mediate signaling initiated by BMPs and regulate cell definite commitment. Previously, we showed that Smad1 activates osteopontin and osteoprotegerin gene expression by dislodging Hoxc-8 from its DNA binding sites. A domain of Smad1, termed Smad1C, was characterized as interacting with Hoxc-8 and then crippling its DNA-binding ability. Ectopic expression of Smad1C is able to bypass BMP signaling in the induction of osteoblast differentiation and bone formation in vitro. To test the function of Smad1C on osteogenesis in vivo, we generated transgenic mice in which Smad1C expression was induced with doxycycline and localized in bone by using a tetracycline-inducible expression system (Tet-on) modified with a bone-specific gene promoter, type I collagen alpha1. The mice expressing Smad1C showed increased skeletal bone mineral density compared with their littermates. Bone histomorphometric analysis of mouse tibiae showed that Smad1C significantly increases trabecular bone area and length of trabecular surface covered with osteoid and up-regulates bone marker gene (OPN, Cbfa1, Col I alpha1, BSP, ALP) expression in vivo. Moreover, stromal cells isolated from mice expressing Smad1C displayed a higher potential for differentiating into osteoblasts than the other mice. These results indicate that Smad1C mimics BMPs in the induction of osteogenesis in vivo. Most important, using a high throughput screening assay based on mimicking Smad1C's displacement of Hoxc-8 binding to DNA, we identified chemical entities that exhibit bone anabolic activity in cell and bone organ cultures, suggesting the possibility that the compounds may be used as bone anabolic agents to treat bone pathologies.

Ecsit is required for Bmp signaling and mesoderm formation during mouse embryogenesis

Bone morphogenetic proteins (Bmps) are members of the transforming growth factor beta (TGFbeta) superfamily that play critical roles during mouse embryogenesis. Signaling by Bmp receptors is mediated mainly by Smad proteins. In this study, we show that a targeted null mutation of Ecsit, encoding a signaling intermediate of the Toll pathway, leads to reduced cell proliferation, altered epiblast patterning, impairment of mesoderm formation, and embryonic lethality at embryonic day 7.5 (E7.5), phenotypes that mimic the Bmp receptor type1a (Bmpr1a) null mutant. In addition, specific Bmp target gene expression is abolished in the absence of Ecsit. Biochemical analysis demonstrates that Ecsit associates constitutively with Smad4 and associates with Smad1 in a Bmp-inducible manner. Together with Smad1 and Smad4, Ecsit binds to the promoter of specific Bmp target genes. Finally, knock-down of Ecsit with Ecsit-specific short hairpin RNA inhibits both Bmp and Toll signaling. Therefore, these results show that Ecsit functions as an essential component in two important signal transduction pathways and establishes a novel role for Ecsit as a cofactor for Smad proteins in the Bmp signaling pathway.

Genetic background modifies intestinal pseudo-obstruction and the expression of a reporter gene in Hox11L1-/- mice

BACKGROUND & AIMS

The transcription factor Hox11L1 is expressed by enteric neurons. Two groups mutated murine Hox11L1, and reported lethal intestinal pseudo-obstruction and colonic hyperganglionosis in many, but not all, homozygous null mutants. We investigated the regulation of Hox11L1 and factors that influence the penetrance of pseudo-obstruction in Hox11L1-null mice.

METHODS

Expression of beta-galactosidase (lacZ), under control of putative Hox11L1 regulatory sequences, was assessed in transgenic mice wild-type, heterozygous, and null for native Hox11L1. Transgene expression and signs of pseudo-obstruction were compared in null mice with different genetic backgrounds.

RESULTS

In enteric neurons and other parts of the nervous system, the transgene was expressed in a pattern consistent with native Hox11L1. Enteric beta-galactosidase activity initiated in the proximal small intestine and spread cranially and caudally in a subset of postmitotic enteric neurons. Hox11L1-lacZ transgene expression persisted in Hox11L1-null animals, suggesting that Hox11L1 is not required cell autonomously for neuronal survival. Genetic background dramatically affected the phenotypes of Hox11L1-null animals, with complete penetrance of severe proximal colonic distention on a predominantly C57BL/6J (B6) background and very low penetrance of dysmotility on a 129SvJ (129) background. Coincidently, Hox11L1-lacZ expression by most enteric neurons, but not CNS neurons, was lost on a 129 background.

CONCLUSIONS

Cis-acting, 5' regulatory elements are sufficient to regulate site-specific expression of Hox11L1 in vivo. Expression of the transgene by enteric neurons and penetrance of pseudo-obstruction in Hox11L1-null animals are influenced by one or more modifier genes, counterparts of which may play a similar role in human disease.

GATA- and Smad1-dependent enhancers in the Smad7 gene differentially interpret bone morphogenetic protein concentrations

Smad7, an inhibitor of transforming growth factor beta superfamily signaling, is induced by bone morphogenetic protein (BMP) in an inhibitory feedback loop. Here, we identify multiple BMP response elements (BREs) in the Smad7 gene and demonstrate that they function differentially to interpret BMP signals in a cell type-specific manner. Two BREs (BRE-1 and -2) reside in the promoter region. One of these contains several conserved Smad1 and Smad4 binding sites that cooperate to mediate BMP-dependent induction, most likely in the absence of DNA binding partners. The third BRE (I-BRE) resides in the first intron and contains GATA factor binding sites. GATA-1, -5, or -6 is required for strong activation of I-BRE, and we show that they assemble with Smad1 on the I-BRE in living cells. Activation of the I-BRE is mediated by a specific region in GATA-5 and -6 but does not require direct physical interaction with Smad1. Comparison of I-BRE to BRE-1 showed that I-BRE is more responsive to low BMP concentrations. Moreover, analysis by chromatin immunoprecipitation experiments demonstrates that the endogenous I-BRE is occupied more robustly by endogenous Smad1 than is BRE-1. This correlates with regulation of the Smad7 gene, which is induced at lower BMP concentrations in GATA-expressing cell lines compared to non-GATA-expressing lines. These data thus define how cooperative and noncooperative Smad-dependent transcriptional regulation can function to interpret different BMP concentrations.

Bone morphogenetic protein 2 induces placental growth factor in mesenchymal stem cells

Bone-forming osteoblasts differentiate from pluripotent mesenchymal stem cells (MSCs) in a multistage process that can be modeled in vitro using MSCs isolated from adult human trabecular bone or bone marrow. To identify new genes involved in osteoblast differentiation, we have performed large-scale gene expression profiling using high-density cDNA microarrays in primary human MSCs treated with the known osteogenic agent bone morphogenetic protein 2 (BMP-2). The vascular endothelial growth factor (VEGF) family member placental growth factor (PlGF) was found as an early regulated gene whose induction was already detected after 2 h treatment with BMP-2. Tissue distribution analysis of PlGF mRNA expression using microarrays revealed a very restricted expression of PlGF only in BMP-2-treated MSCs and in placenta as expected. Ribonuclease protection assay (RPA) confirmed the induction of PlGF and showed preferential expression of the PlGF-1 isoform over PLGF-2 in MSCs and MG63 cells. BMP-2 stimulated PlGF expression in MG63 cells with an EC50 of about 50 ng/ml and mRNA levels peaked between 24 and 32 h after stimulation. Furthermore, induction of PlGF by BMP-2 appeared specific, as other osteogenic agents including vitamin D3, transforming growth factor beta, and basic fibroblast growth factor were inactive. BMP-2 stimulated PlGF secretion from MG63 and MSC cells, but PlGF had no effect on MSC proliferation and osteoblastic differentiation. Based on the known function of PlGF in the recruitment of endothelial and hematopoietic stem cells, these results suggest a paracrine role for MSC-derived PlGF in the angiogenesis and hematopoiesis that accompany BMP-2-induced bone formation.

New intracellular components of bone morphogenetic protein/Smad signaling cascades

Bone morphogenetic proteins (BMPs) regulate many processes in the embryo, including cell type specification, patterning, apoptosis, and epithelial-mesenchymal interaction. They also act in soft and hard tissues in adult life. Their signals are transduced from the plasma membrane to the nucleus through a limited number of Smad proteins. The list of Smad-interacting proteins is however growing and it is clear that these partners determine the outcome of the signal. We summarize the present status in BMP/Smad signaling, with emphasis on recently identified Smad partners and how these proteins may cooperate in the regulation of the expression of BMP target genes.

Mastoid obliteration by BMP-2/collagen composites: an experimental study using tissue engineering

PURPOSE

Several materials have been used in the application of mastoid cavity obliteration during surgery for cholesteatoma; however, nothing has won universal acceptance. Through the advancement of tissue engineering, bone morphogenetic protein-2 (BMP-2)/collagen composites have been elucidated as inducers of heterogenic bone formation. This study was performed to investigate whether these composites are potentially obliteration materials for use in the mastoid cavity by using an animal experimental study.

MATERIALS AND METHODS

The composites were implanted in the rat mastoid to investigate whether new bone would be tissue engineered in the mastoid and, if so, whether the newly formed bone was stable. The composites were examined histologically over a 24-week period.

RESULTS

The composites implanted in the rat mastoid were able to tissue engineer new bone, and the newly formed bone was stable as assessed histologically, with almost normal bone structure, that was not resorbed during the 24-week period. Adverse immunological reactions were not found during our observation.

CONCLUSIONS

Bone that was tissue engineered by the BMP-2/collagen composites was stable as assessed by histological examination and persisted in the rat mastoid. The present study shows that the composites have the potential to become real materials for use in mastoid obliteration.

BMP pathways are involved in otic capsule formation and epithelial-mesenchymal signaling in the developing chicken inner ear

The vertebrate inner ear consists of a complex labyrinth of epithelial cells that is surrounded by a bony capsule. The molecular mechanisms coordinating the development of the membranous and bony labyrinths are largely unknown. Previously, using avian retrovirus encoding Noggin (RCAS-Noggin) or beads soaked with Noggin protein, we have shown that bone morphogenetic proteins (BMPs) are important for the development of the otic epithelium in the chicken inner ear. Here, using two additional recombinant avian retroviruses, dominant negative and constitutively active forms of BMP receptors IB (BMPRIB), we show that BMPs, possibly acting through BMPRIB, are important for otic capsule formation. We also show that Bmp2 is strongly expressed in the prospective semicircular canals starting from the canal outpouch stage, suggesting that BMP2 plays an important role in canal formation. In addition, by correlating expression patterns of Bmps, their receptors, and localization of phosphorylated R-Smad (phospho R-Smad) immunoreactivity, an indicator of BMP activation, we show that BMPs emanating from the otic epithelium influence chondrogenesis of the otic capsule including the cartilage surrounding the semicircular canals.

Identification of mZnf8, a mouse Krüppel-like transcriptional repressor, as a novel nuclear interaction partner of Smad1

To identify novel genes that play critical roles in mediating bone morphogenetic protein (BMP) signal pathways, we performed a yeast two-hybrid screen using Smad1 as bait. A novel mouse Krüppel-type zinc finger protein, mZnf8, was isolated. Interactions between mZnf8 and Smad proteins were further analyzed with various in vitro and in vivo approaches, including mammalian two-hybrid, in vitro glutathione S-transferase pulldown, and copurification assays. Results from functional analysis indicate that mZnf8 is a nuclear transcriptional repressor. Overexpression of mZnf8 represses activity of BMP and transforming growth factor beta (TGF-beta) reporters. Silencing the expression of endogenous mZnf8 with an RNA interference approach caused a significant increase in the expression of one BMP reporter. These results suggest that mZnf8 negatively regulates the TGF-beta/BMP signaling pathway in vivo. Transcription of mZnf8 is ubiquitous in mouse embryos, but high levels are specifically observed in adult mouse testes, with the same cell- and stage-specific transcription pattern as Smad1. Our data support the hypothesis that mZnf8 plays critical roles in mediating BMP signaling during spermatogenesis.

A high-throughput induction gene trap approach defines C4ST as a target of BMP signaling

Here we describe a novel gene trap protocol to screen for target genes that are regulated during inductive events in undifferentiated and differentiated mouse embryonic stem cells. This approach integrates several features that allows in vitro screening of large numbers of gene trap clones prior to generating lines of mutant mice. Moreover, targets of spatially and temporally restricted signaling pathways can be analyzed by screening undifferentiated ES cells versus ES cells differentiated into embryoid bodies. We employed this protocol to screen 1920 gene trap lines to identify targets and mediators of signaling through three growth factors of the TGFbeta superfamily--BMP2, activin and nodal. We identified two genes that are induced by BMP2 in a differentiation-dependent manner. One of the genes encodes for Chondroitin-4-sulfotransferase and displays a highly specific temporal and spatial expression pattern during mouse embryogenesis. These results demonstrate the feasibility of a high-throughput gene trap approach as a means to identify mediators and targets of multiple growth factor signaling pathways that function during different stages of development.