Canonical Bone Morphogenetic Protein Signaling Research Articles

Myo/Nog cell regulation of bone morphogenetic protein signaling in the blastocyst is essential for normal morphogenesis and striated muscle lineage specification

Cells that express MyoD mRNA, the G8 antigen and the bone morphogenetic protein (BMP) inhibitor noggin (Nog) are present in the epiblast before gastrulation. Ablation of “Myo/Nog” cells in the blastocyst results in an expansion of canonical BMP signaling and prevents the expression of noggin and follistatin before and after the onset of gastrulation. Once eliminated in the epiblast, they are neither replaced nor compensated for as development progresses. Older embryos lacking Myo/Nog cells exhibit severe axial malformations. Although Wnts and Sonic hedgehog are expressed in ablated embryos, skeletal muscle progenitors expressing Pax3 are missing in the somites. Pax3+ cells do emerge adjacent to Wnt3a+ cells in vitro; however, few undergo skeletal myogenesis. Ablation of Myo/Nog cells also results in ectopically placed cardiac progenitors and cardiomyocytes in the somites. Reintroduction of Myo/Nog cells into the epiblast of ablated embryos restores normal patterns of BMP signaling, morphogenesis and skeletal myogenesis, and inhibits the expression of cardiac markers in the somites. This study demonstrates that Myo/Nog cells are essential regulators of BMP signaling in the early epiblast and are indispensable for normal morphogenesis and striated muscle lineage specification.

Noncanonical BMP Signaling Regulates Cyclooxygenase-2 Transcription

Activation of p38 MAPK has been shown to be relevant for a number of bone morphogenetic protein (BMP) physiological effects. We report here the involvement of noncanonical phosphorylated mothers against decapentaplegic (Smad) signaling in the transcriptional induction of Cox2 (Ptgs2) by BMP-2 in mesenchymal cells and organotypic calvarial cultures. We demonstrate that different regulatory elements are required for regulation of Cox2 expression by BMP-2: Runt-related transcription factor-2 and cAMP response element sites are essential, whereas a GC-rich Smad binding element is important for full responsiveness. Efficient transcriptional activation requires cooperation between transcription factors because mutation of any element results in a strong decrease of BMP-2 responsiveness. BMP-2 activation of p38 leads to increased recruitment of activating transcription factor-2, Runx2, Smad, and coactivators such as p300 at the responsive sites in the Cox2 proximal promoter. We demonstrate, by either pharmacological or genetic analysis, that maximal BMP-2 effects on Cox2 and JunB expression require the function of p38 and its downstream effector mitogen/stress-activated kinase 1. Altogether our results strongly suggest that cooperative effects between canonical and noncanonical BMP signaling allow the fine-tuning of BMP transcriptional responses on specific target genes.

Dynamic analysis of BMP‐responsive smad activity in live zebrafish embryos

Bone morphogenetic proteins (BMPs) are critical players in development and disease, regulating such diverse processes as dorsoventral patterning, palate formation, and ossification. These ligands are classically considered to signal via BMP receptor-specific Smad proteins 1, 5, and 8. To determine the spatiotemporal pattern of Smad1/5/8 activity and thus canonical BMP signaling in the developing zebrafish embryo, we generated a transgenic line expressing EGFP under the control of a BMP-responsive element. EGFP is expressed in many established BMP signaling domains and is responsive to alterations in BMP type I receptor activity and smad1 and smad5 expression. This transgenic Smad1/5/8 reporter line will be useful for determining ligand and receptor requirements for specific domains of BMP activity, as well as for genetic and pharmacological screens aimed at identifying enhancers or suppressors of canonical BMP signaling.

The canonical BMP signaling pathway is involved in human monocyte‐derived dendritic cell maturation

Bone morphogenetic proteins (BMPs), members of the transforming growth factor-β superfamily, are multifunctional polypeptides regulating a broad spectrum of functions in embryonic and adult tissues. Recent reports have demonstrated that BMPs regulate the survival, proliferation and differentiation of several cell types in the immune system. In this study, we investigate the effects of BMP signaling activation on the capacity of human dendritic cells (DCs) to stimulate immune responses. Human DCs express type I and type II BMP receptors (BMPRIA, BMPRIB, type IA activin receptor, BMPRII) and BMP signal transduction molecules (Smad1, 5, and 8, as well as Smad4). On BMP stimulation, Id1-3 (inhibitor of differentiation 1-3/DNA binding) mRNA expression is upregulated and this effect can be blocked with the inhibitor dorsomorphin, showing that the canonical BMP signal transduction pathway is functionally active in DCs. BMP signaling activation promotes the phenotypic maturation of human DCs by increasing the expression of co-stimulatory molecules and also CD83, programmed cell death ligand 1 (PD-L1) and PD-L2, and stimulates cytokine secretion, mainly interleukin-8 and tumor necrosis factor-α. Accordingly, BMP-treated DCs exhibit an enhanced T-cell stimulatory capacity. BMP signaling also enhances the survival of human DCs increasing the Bcl-2/Bax ratio. Finally, the expression of Runx transcription factors is increased in mature DCs, and the mRNA levels of Runx1-3 are upregulated in response to BMP stimulation, indicating that Runx transcription factor family may mediate the effects of BMP signaling in human DC maturation.

The Canonical BMP Signaling Pathway Plays a Crucial Part in Stimulation of Dentin Sialophosphoprotein Expression by BMP-2

Dentin sialophosphoprotein (DSPP), a typical dentin-specific protein, is mainly expressed in the dentin extracellular matrix and plays a role in dentin mineralization. BMP-2 provides a strong signal for differentiation and mineralization of odontoblasts and osteoblasts. Previously, BMP-2 treatment is reported to stimulate Dspp expression in the MD10-F2 pre-odontoblast cells through activation of the heterotrimeric transcription factor Y (NF-Y). The canonical BMP signaling pathway is known to contribute greatly to biomineralization, however, it is not known whether it is involved in Dspp expression. Here, we investigated this question. Activation of the canonical BMP-2 signaling pathway in MDPC-23, preodontoblast cell, by overexpression of constitutively active Smad1/5 or downstream transcription factors Dlx5 and Runx2 stimulated Dspp expression. Conversely, knockdown of each element with siRNA significantly blocked the BMP-2-induced Dspp expression. To test whether these transcription factors downstream of BMP-2 are directly involved in regulating Dspp, we analyzed the mouse Dspp promoter. There are 5 well conserved homeodomain binding elements, H1 to H5, in Dspp proximal promoter regions (-791 to +54). A serial deletion of H1 and H2 greatly changed basal promoter activity and responsiveness to Dlx5 or Msx2. However, further deletions did not change the responsiveness to Dlx5 or Msx2. H1 and H2 sites can be suggested as specific response elements of Dlx5 and Msx2, respectively, based on their promoter activity modulation. Thus, the canonical BMP-2 signaling pathway plays a crucial part in the regulation of Dspp expression through the action of Smads, Dlx5, Runx2, and Msx2.

Canonical BMP signaling is dispensable for hematopoietic stem cell function in both adult and fetal liver hematopoiesis, but essential to preserve colon architecture

AbstractNumerous publications have described the importance of bone morphogenetic protein (BMP) signaling in the specification of hematopoietic tissue in developing embryos. Here we investigate the full role of canonical BMP signaling in both adult and fetal liver hematopoiesis using conditional knockout strategies because conventional disruption of components of the BMP signaling pathway result in early death of the embryo. By targeting both Smad1 and Smad5, we have generated a double-knockout mouse with complete disruption of canonical BMP signaling. Interestingly, concurrent deletion of Smad1 and Smad5 results in death because of extrahematopoietic pathologic changes in the colon. However, Smad1/Smad5-deficient bone marrow cells can compete normally with wild-type cells and display unaffected self-renewal and differentiation capacity when transplanted into lethally irradiated recipients. Moreover, although BMP receptor expression is increased in fetal liver, fetal liver cells deficient in both Smad1 and Smad5 remain competent to long-term reconstitute lethally irradiated recipients in a multilineage manner. In conclusion, canonical BMP signaling is not required to maintain either adult or fetal liver hematopoiesis, despite its crucial role in the initial patterning of hematopoiesis in early embryonic development.

Finding partners: How BMPs select their targets

The bone morphogenetic protein (BMP) signaling pathway is a conserved and evolutionarily ancient regulatory module affecting a large variety of cellular behaviors. The evolutionary flexibility in using BMP responses presumably arose by co-option of a canonical BMP signaling cascade to regulate the transcription of diverse batteries of target genes. This begs the question of how seemingly interchangeable BMP signaling components elicit widely different outputs in different cell types, an important issue in the context of understanding how BMP signaling integrates with gene regulatory networks to control development. Because a molecular understanding of how BMP signaling activates different batteries of target genes is an essential prerequisite to comprehending the roles of BMPs in regulating cellular responses, here we review the current knowledge of how BMP-regulated target genes are selected by the signal transduction machinery. We highlight recent studies suggesting the evolutionary conservation of BMP target gene regulation signaling by Schnurri family zinc finger proteins. Developmental Dynamics 238:1321-1331, 2009. (c) 2009 Wiley-Liss, Inc.

Activation of the BMP Canonical Signaling Pathway in Human Optic Nerve Head Tissue and Isolated Optic Nerve Head Astrocytes and Lamina Cribrosa Cells

Bone morphogenetic proteins (BMPs) are members of the transforming growth factor (TGF)-beta superfamily that controls multiple functions in a variety of cells. We have previously shown that human optic nerve head (ONH) astrocytes and lamina cribrosa (LC) cells express BMP and BMP receptor mRNA and proteins. The purpose of the present study was to determine whether human ONH tissues express the canonical BMP signaling pathway and whether ONH cells secrete BMP-4 and respond to exogenous BMP-4 through this pathway. Well-characterized human ONH astrocytes (N = 2) and LC cells (N = 3) were treated with exogenous BMP-4 (20 ng/mL) for various times. Western immunoblot analysis was used to detect secreted BMP-4 in serum-free conditioned media of ONH cells and in human ONH tissues (N = 4) and Smad proteins in total cell lysate of ONH cells and tissues. Intracellular colocalization of p-R-Smad1 with Co-Smad4 and localization of inhibitory Smads (e.g., I-Smad6 and I-Smad7) were studied through immunocytochemistry. In addition, coimmunoprecipitation was used to verify the interaction of p-R-Smad1 with Co-Smad4. ONH astrocytes and LC cells secrete BMP-4 and synthesize R-Smad1, R-Smad5, I-Smad6, I-Smad7, and Co-Smad4 proteins. Exposure to BMP-4 for either 10 or 60 minutes resulted in increased p-R-Smad1 and p-R-Smad1/5/8 protein levels that declined after 12 hours of treatment. Immunocytochemistry and coimmunoprecipitation studies revealed that p-R-Smad1/5/8 and Co-Smad4 interact and colocalize in the nucleus. BMP-4 treatment resulted in increased coprecipitation of p-R-Smad1/5/ 8 and Co-Smad4. I-Smad6 and I-Smad7 are localized in the nucleus and cytoplasm of ONH astrocytes and LC cells. Proteins for BMP-4, p-R-Smad1/5/8, R-Smad1, R-Smad5, R-Smad8, and Co-Smad4 are present in human ONH tissues. In addition, phosphorylated Smad1 and Smad5 colocalize with Smad4 in the nuclei of ONH tissues. These results indicate that BMP-4 and Smad signaling proteins are present in human ONH tissues, isolated ONH astrocytes, and LC cells. In addition, exogenous BMP-4 treatment of ONH astrocytes and LC cells results in downstream signaling through the canonical Smad pathway. Thus, cells within the human ONH may respond to locally released BMP through paracrine or autocrine mechanisms.

Developmental pattern of expression of BMP receptors and Smads and activation of Smad1 and Smad5 by BMP9 in mouse basal forebrain

Basal forebrain cholinergic neurons play critical roles in the organization of brain cortical structures and in processes such as learning and memory. We have previously shown that bone morphogenetic protein (BMP) 9, a member of the transforming growth factor (TGF) β superfamily of cytokines, is a differentiating factor for cholinergic central nervous system neurons. However, whereas the basic signal transduction pathways for most known members of the TGF-β superfamily have been well characterized in brain and other organs, nothing is known about the signal transduction pathway of BMP9 in the brain. Here, we describe the pattern of expression of BMP receptors, including Bmpr-Ia, Bmpr-Ib, Bmpr-II, Actr-I. Actr-Ib, Actr-II and Actr-IIb, Alk-1, and Smad proteins (Smads 1–5 and Smad8) in the septal region of the basal forebrain during mouse development. Using cultured basal forebrain cells derived from embryonic day (E) 14 mice, we show that BMP9 causes phosphorylation of Smad1 and Smad5, formation of a complex of Smad4 with Samd1 and/or Smad5, and translocation of these proteins into the nucleus. These data show that BMP9 activates the canonical BMP signaling pathway and suggest that this could be one of the mechanisms responsible for the induction of the cholinergic phenotype by BMP9 in the basal forebrain.