Aris Economides - Academia.edu (original) (raw)

Papers by Aris Economides

Research paper thumbnail of Bone Mass Transient Increase in Bone Formation and Conditional Deletion of Gremlin Causes a Developmental Biology: Molecular Basis of Cell and

Gremlin is a glycoprotein that binds bone morphogenetic proteins (BMPs) 2, 4, and 7, antagonizing... more Gremlin is a glycoprotein that binds bone morphogenetic proteins (BMPs) 2, 4, and 7, antagonizing their actions. Gremlin opposes BMP effects on osteoblastic differentiation and function in vitro and in vivo, and its overexpression causes osteopenia. To define the function of gremlin in the skeleton, we generated gremlin 1 (grem1) conditional null mice by mating mice where grem1 was flanked by lox P sequences with mice expressing the Cre recombinase under the control of the osteocalcin promoter. grem1 null male mice displayed increased trabecular bone volume due to enhanced osteoblastic activity, because mineral apposition and bone formation rates were increased. Osteoblast number and bone resorption were not altered. Marrow stromal cells from grem1 conditional null mice expressed higher levels of alkaline phosphatase activity. Gremlin downregulation by RNA interference in ST-2 stromal and MC3T3 osteoblastic cells increased the BMP-2 stimulatory effect on alkaline phosphatase activity, on Smad 1/5/8 phosphorylation, and on the transactivation of the BMP/Smad reporter construct 12؋SBE-Oc-pGL3. Gremlin down-regulation also enhanced osteocalcin and Runx-2 expression, Wnt 3a signaling, and activity in ST-2 cells. In conclusion, deletion of grem1 in the bone microenvironment results in sensitization of BMP signaling and activity and enhanced bone formation in vivo.

Research paper thumbnail of Reactivation of a developmental Bmp2 signaling center is required for therapeutic control of the murine periosteal niche

eLife, 2019

Two decades after signals controlling bone length were discovered, the endogenous ligands determi... more Two decades after signals controlling bone length were discovered, the endogenous ligands determining bone width remain unknown. We show that postnatal establishment of normal bone width in mice, as mediated by bone-forming activity of the periosteum, requires BMP signaling at the innermost layer of the periosteal niche. This developmental signaling center becomes quiescent during adult life. Its reactivation however, is necessary for periosteal growth, enhanced bone strength, and accelerated fracture repair in response to bone-anabolic therapies used in clinical orthopedic settings. Although many BMPs are expressed in bone, periosteal BMP signaling and bone formation require only Bmp2 in the Prx1-Cre lineage. Mechanistically, BMP2 functions downstream of Lrp5/6 pathway to activate a conserved regulatory element upstream of Sp7 via recruitment of Smad1 and Grhl3. Consistent with our findings, human variants of BMP2 and GRHL3 are associated with increased risk of fractures.

Research paper thumbnail of BMP3 Suppresses Osteoblast Differentiation of Bone Marrow Stromal Cells via Interaction with Acvr2b

Molecular Endocrinology, 2012

Enhancing bone morphogenetic protein (BMP) signaling increases bone formation in a variety of set... more Enhancing bone morphogenetic protein (BMP) signaling increases bone formation in a variety of settings that target bone repair. However, the role of BMP in the maintenance of adult bone mass is not well understood. Targeted disruption of BMP3 in mice results in increased trabecular bone formation, whereas transgenic overexpression of BMP3 in skeletal cells leads to spontaneous fracture, consistent with BMP3 having a negative role in bone mass regulation. Here we investigate the importance of BMP3 as a mediator of BMP signaling in the adult skeleton. We find that osteoblasts (OBL) and osteocytes are the source of BMP3 in adult bone. Using in vitro cultures of primary bone marrow stromal cells, we show that overexpression of BMP3 suppresses OBL differentiation, whereas loss of BMP3 increases colony-forming unit fibroblasts and colony-forming unit OBL. The ability of BMP3 to affect OBL differentiation is due to its interaction with activin receptor type 2b (Acvr2b) because knockdown of...

Research paper thumbnail of Bone Morphogenetic Proteins Induce Gremlin, a Protein That Limits Their Activity in Osteoblasts1

Endocrinology, 2000

Bone morphogenetic proteins (BMP) induce the differentiation of cells of the osteoblastic lineage... more Bone morphogenetic proteins (BMP) induce the differentiation of cells of the osteoblastic lineage and enhance the function of the osteoblast. Growth factor activity is regulated by binding proteins, and we previously showed that BMPs induce noggin, a glycoprotein that binds and blocks BMP action. Recently, additional BMP antagonists, such as gremlin, have been described, but there is no information about their expression or function in osteoblasts. We tested for the expression of gremlin and studied its induction by BMPs in cultures of osteoblast-enriched cells from 22-day-old fetal rat calvariae (Ob cells). BMP-2 caused a time-and dose-dependent increase in gremlin messenger RNA and polypeptide levels, as determined by Northern and Western blot analyses. The effects of BMP-2 on gremlin transcripts were independent of new protein synthesis. BMP-2 increased the rate of gremlin transcription as determined by nuclear run-on assays. Fibroblast growth factor-2 and platelet-derived growth factor BB also induced gremlin, but other hormones and growth factors had no effect. Gremlin prevented the stimulatory effects of BMP-2 on DNA, collagen, noncollagen protein synthesis, and alkaline phosphatase activity in Ob cells. In conclusion, BMPs induce gremlin transcription in Ob cells, a mechanism that probably limits BMP action in osteoblasts. (Endocrinology 141: 4558-4563, 2000)

Research paper thumbnail of Skeletal Overexpression of Gremlin Impairs Bone Formation and Causes Osteopenia

Endocrinology, 2005

Skeletal cells synthesize bone morphogenetic proteins (BMPs) and BMP antagonists. Gremlin, a BMP ... more Skeletal cells synthesize bone morphogenetic proteins (BMPs) and BMP antagonists. Gremlin, a BMP antagonist, is expressed in osteoblasts and opposes BMP effects on osteoblastic differentiation and function in vitro. However, its effects in vivo are not known. To investigate the actions of gremlin on bone remodeling in vivo, we generated transgenic mice overexpressing gremlin under the control of the osteocalcin promoter. Gremlin transgenics exhibited bone fractures and reduced bone mineral density by 20-30%, compared with controls. Static and dynamic histomorphometry of femurs revealed that gremlin overexpression caused reduced trabecular bone volume and the appearance of woven bone. Polarized light microscopy revealed disorganized collagen bundles at the endosteal cortical surface. Gremlin transgenic mice displayed a 70% decrease in the number of osteoblasts/trabecular area and reduced mineral apposition and bone formation rates. In vivo bromodeoxyuridine labeling and marrow stromal cell cultures demonstrated an inhibitory effect of gremlin on osteoblastic cell replication, but no change on apoptosis was detected. Marrow stromal cells from gremlin transgenics displayed a reduced response to BMP on phosphorylated mothers against decapentaplegic 1/5/8 phosphorylation and reduced free cytosolic ␤-catenin levels. In conclusion, transgenic mice overexpressing gremlin in the bone microenvironment have decreased osteoblast number and function leading to osteopenia and spontaneous fractures. (Endocrinology 146: 655-665, 2005

Research paper thumbnail of Bone Morphogenetic Proteins, Their Antagonists, and the Skeleton

Endocrine Reviews, 2003

Skeletal homeostasis is determined by systemic hormones and local factors. Bone morphogenetic pro... more Skeletal homeostasis is determined by systemic hormones and local factors. Bone morphogenetic proteins (BMP) are unique because they induce the differentiation of mesenchymal cells toward cells of the osteoblastic lineage and also enhance the differentiated function of the osteoblast. However, the activity of BMPs needs to be tempered by intracellular and extracellular antagonists. BMPs bind to specific receptors and signal by phosphorylating the cytoplasmic proteins mothers against decapentaplegic (Smad) 1 and 5, which form heterodimers with Smad 4, and after nuclear translocation regulate transcription. BMP antagonists can be categorized as pseudoreceptors that compete with signaling receptors, inhibitory Smads that block signaling, intracellular binding proteins that bind Smad 1 and 5, and factors that induce ubiquitination and proteolysis of signaling Smads. In addition, a large number of extracellular proteins that bind BMPs and prevent their binding to signaling receptors have...

Research paper thumbnail of <i>ACVR1</i> <sup> <i>R206H</i> </sup> receptor mutation causes fibrodysplasia ossificans progressiva by imparting responsiveness to activin A

Science Translational Medicine, Sep 2, 2015

Fibrodysplasia ossificans progressiva (FOP) is a rare genetic disorder characterized by episodica... more Fibrodysplasia ossificans progressiva (FOP) is a rare genetic disorder characterized by episodically exuberant heterotopic ossification (HO), whereby skeletal muscle is abnormally converted into misplaced, but histologically normal bone. This HO leads to progressive immobility with catastrophic consequences, including death by asphyxiation. FOP results from mutations in the intracellular domain of the type I BMP (bone morphogenetic protein) receptor ACVR1; the most common mutation alters arginine 206 to histidine (ACVR1 R206H) and has been thought to drive inappropriate bone formation as a result of receptor hyperactivity. We unexpectedly found that this mutation rendered ACVR1 responsive to the activin family of ligands, which generally antagonize BMP signaling through ACVR1 but cannot normally induce bone formation. To test the implications of this finding in vivo, we engineered mice to carry the Acvr1 R206H mutation. Because mice that constitutively express Acvr1[R206H] die perinatally, we generated a genetically humanized conditional-on knock-in model for this mutation. When Acvr1[R206H] expression was induced, mice developed HO resembling that of FOP; HO could also be triggered by activin A

Research paper thumbnail of Saracatinib is an efficacious clinical candidate for fibrodysplasia ossificans progressiva

Currently, no effective therapies exist for fibrodysplasia ossificans progressiva (FOP), a rare c... more Currently, no effective therapies exist for fibrodysplasia ossificans progressiva (FOP), a rare congenital syndrome in which heterotopic bone is formed in soft tissues due to dysregulated activity of the bone morphogenetic protein (BMP) receptor kinase ALK2/ACVR1. From a screen of known biologically active compounds, we identified saracatinib as a potent ALK2 kinase inhibitor. In enzymatic and cell-based assays, saracatinib preferentially inhibited ALK2 compared with other receptors of the BMP/TGFβ signaling pathway, and induced dorsalization in zebrafish embryos consistent with BMP antagonism. We further tested the efficacy of saracatinib using an inducibleACVR1Q207Dtransgenic mouse line, which provides a model of heterotopic ossification, as well as an inducibleACVR1R206Hknock-in, which serves as a genetically and physiologically faithful model of FOP. In both models, saracatinib was well tolerated and potently inhibited the development of heterotopic ossification even when admini...

Research paper thumbnail of Activin A forms a non-signaling complex with ACVR1 and type II Activin/BMP receptors via its finger 2 tip loop

eLife, 2020

Activin A functions in BMP signaling in two ways: it either engages ACVR1B to activate Smad2/3 si... more Activin A functions in BMP signaling in two ways: it either engages ACVR1B to activate Smad2/3 signaling or binds ACVR1 to form a non-signaling complex (NSC). Although the former property has been studied extensively, the roles of the NSC remain unexplored. The genetic disorder fibrodysplasia ossificans progressiva (FOP) provides a unique window into ACVR1/Activin A signaling because in that disease Activin can either signal through FOP-mutant ACVR1 or form NSCs with wild-type ACVR1. To explore the role of the NSC, we generated ‘agonist-only’ Activin A muteins that activate ACVR1B but cannot form the NSC with ACVR1. Using one of these muteins, we demonstrate that failure to form the NSC in FOP results in more severe disease pathology. These results provide the first evidence for a biological role for the NSC in vivo and pave the way for further exploration of the NSC’s physiological role in corresponding knock-in mice.

Research paper thumbnail of The finger 2 tip loop of Activin A is required for the formation of its non-signaling complex with ACVR1 and type II Bone Morphogenetic Protein receptors

Activin A functions in BMP signaling in two ways: it either engages ACVR1B to activate Smad2/3 si... more Activin A functions in BMP signaling in two ways: it either engages ACVR1B to activate Smad2/3 signaling or binds ACVR1 to form a non-signaling complex (NSC). Although the former property has been studied extensively, the roles of the NSC remain unexplored. The genetic disorder fibrodysplasia ossificans progressiva (FOP) provides a unique window into ACVR1/Activin A signaling because in that disease Activin can either signal through FOP-mutant ACVR1 or form NSCs with wild type ACVR1. To explore the role of the NSC, we generated ‘agonist-only’ Activin A muteins that activate ACVR1B but cannot form the NSC with ACVR1. Using one of these muteins we demonstrate that failure to form the NSC in FOP results in more severe disease pathology. These results provide the first evidence for a biological role for the NSC in vivo and pave the way for further exploration of the NSC’s physiological role in corresponding knock-in mice.Impact StatementThe non-signaling complex formed by Activin A and ...

Research paper thumbnail of Conditional Deletion of Sost in MSC-derived lineages Identifies Specific Cell Type Contributions to Bone Mass and B Cell Development

Journal of bone and mineral research : the official journal of the American Society for Bone and Mineral Research, Jan 11, 2018

Sclerostin (Sost) is a negative regulator of bone formation and blocking its function via antibod... more Sclerostin (Sost) is a negative regulator of bone formation and blocking its function via antibodies has shown great therapeutic promise by increasing both bone mass in humans and animal models. Sclerostin deletion in Sost knockout mice (Sost ) causes high bone mass (HBM) similar to Sclerosteosis patients. Sost mice have been shown to display an up to 300% increase in bone volume/total volume (BV/TV), relative to aged matched controls, and it has been postulated that the main source of skeletal Sclerostin is the osteocyte. To understand the cell-type specific contributions to the HBM phenotype described in Sost mice, as well as to address the endocrine and paracrine mode of action of sclerostin, we examined the skeletal phenotypes of conditional Sost loss-of-function (Sost ) mice with specific deletions in (1) the limb mesenchyme (Prx1-Cre; targets osteoprogenitors and their progeny); (2) mid-stage osteoblasts and their progenitors (Col1-Cre); (3) mature osteocytes (Dmp1-Cre) and (4...

Research paper thumbnail of Wnt co-receptors Lrp5 and Lrp6 differentially mediate Wnt3a signaling in osteoblasts

PloS one, 2017

Wnt3a is a major regulator of bone metabolism however, very few of its target genes are known in ... more Wnt3a is a major regulator of bone metabolism however, very few of its target genes are known in bone. Wnt3a preferentially signals through transmembrane receptors Frizzled and co-receptors Lrp5/6 to activate the canonical signaling pathway. Previous studies have shown that the canonical Wnt co-receptors Lrp5 and Lrp6 also play an essential role in normal postnatal bone homeostasis, yet, very little is known about specific contributions by these co-receptors in Wnt3a-dependent signaling. We used high-throughput sequencing technology to identify target genes regulated by Wnt3a in osteoblasts and to elucidate the role of Lrp5 and Lrp6 in mediating Wnt3a signaling. Our study identified 782 genes regulated by Wnt3a in primary calvarial osteoblasts. Wnt3a up-regulated the expression of several key regulators of osteoblast proliferation/ early stages of differentiation while inhibiting genes expressed in later stages of osteoblastogenesis. We also found that Lrp6 is the key mediator of Wn...

Research paper thumbnail of Sostdc1 Deficiency Accelerates Fracture Healing by Promoting the Expansion of Periosteal Mesenchymal Stem Cells

Bone, Jul 18, 2016

Loss of Sostdc1, a growth factor paralogous to Sost, causes the formation of ectopic incisors, fu... more Loss of Sostdc1, a growth factor paralogous to Sost, causes the formation of ectopic incisors, fused molars, abnormal hair follicles, and resistance to kidney disease. Sostdc1 is expressed in the periosteum, a source of osteoblasts, fibroblasts and mesenchymal progenitor cells, which are critically important for fracture repair. Here, we investigated the role of Sostdc1 in bone metabolism and fracture repair. Mice lacking Sostdc1 (Sostdc1(-/-)) had a low bone mass phenotype associated with loss of trabecular bone in both lumbar vertebrae and in the appendicular skeleton. In contrast, Sostdc1(-/-) cortical bone measurements revealed larger bones with higher BMD, suggesting that Sostdc1 exerts differential effects on cortical and trabecular bone. Mid-diaphyseal femoral fractures induced in Sostdc1(-/-) mice showed that the periosteal population normally positive for Sostdc1 rapidly expands during periosteal thickening and these cells migrate into the fracture callus at 3 days post fra...

Research paper thumbnail of Angiogenic sprouting into neural tissue requires Gpr124, an orphan G protein-coupled receptor

Proceedings of the National Academy of Sciences, 2011

The vasculature of the CNS is structurally and functionally distinct from that of other organ sys... more The vasculature of the CNS is structurally and functionally distinct from that of other organ systems and is particularly prone to developmental abnormalities and hemorrhage. Although other embryonic tissues undergo primary vascularization, the developing nervous system is unique in that it is secondarily vascularized by sprouting angiogenesis from a surrounding perineural plexus. This sprouting angiogenesis requires the TGF-β and Wnt pathways because ablation of these pathways results in aberrant sprouting and hemorrhage. We have genetically deleted Gpr124, a member of the large family of long N-terminal group B G protein-coupled receptors, few members of which have identified ligands or well-defined biologic functions in mammals. We show that, in the developing CNS, Gpr124 is specifically expressed in the vasculature and is absolutely required for proper angiogenic sprouting into the developing neural tube. Embryos lacking Gpr124 exhibit vascular defects characterized by delayed v...

Research paper thumbnail of Connective Tissue Growth Factor ( CTGF ) Inactivation Leads to Defects in Islet Cell Lineage Allocation and Cell Proliferation During Embryogenesis

The Journal of Clinical Endocrinology & Metabolism, 2009

The factors necessary for normal pancreatic islet morphogenesis have not been well characterized.... more The factors necessary for normal pancreatic islet morphogenesis have not been well characterized. Here we report that connective tissue growth factor (CTGF) is involved in the establishment of normal islet endocrine cell ratio and architecture. CTGF is a secreted protein known to modulate several growth factor signaling pathways including TGF-␤, BMP, and Wnt. Though its role in pancreatic diseases such as pancreatitis and pancreatic cancer are well documented, a role for CTGF in normal pancreas development and function has heretofore not been examined. Using a lacZ-tagged CTGF allele, we describe for the first time the expression pattern of CTGF in the developing pancreas and the requirement of CTGF for normal islet morphogenesis and embryonic cell proliferation. CTGF is highly expressed in pancreatic ductal epithelium and vascular endothelium, as well as at lower levels in developing insulin ϩ cells, but becomes down-regulated in ␤ cells soon after birth. Pancreata from CTGF null embryos have an increase in glucagon ϩ cells with a concomitant decrease in insulin ϩ cells, and show defects in islet morphogenesis. Loss of CTGF also results in a dramatic decrease in ␤ cell proliferation at late gestation. Unlike CTGF null embryos, CTGF heterozygotes survive past birth and exhibit a range of islet phenotypes, including an intermingling of islet cell types, increased number of glucagon ϩ cells, and ␤ cell hypertrophy.

Research paper thumbnail of Distinct Modes of Inhibition by Sclerostin on Bone Morphogenetic Protein and Wnt Signaling Pathways

Journal of Biological Chemistry, 2010

Sclerostin is expressed by osteocytes and has catabolic effects on bone. It has been shown to ant... more Sclerostin is expressed by osteocytes and has catabolic effects on bone. It has been shown to antagonize bone morphogenetic protein (BMP) and/or Wnt activity, although at present the underlying mechanisms are unclear. Consistent with previous findings, Sclerostin opposed direct Wnt3a-induced but not direct BMP7-induced responses when both ligand and antagonist were provided exogenously to cells. However, we found that when both proteins are expressed in the same cell, sclerostin can antagonize BMP signaling directly by inhibiting BMP7 secretion. Sclerostin interacts with both the BMP7 mature domain and pro-domain, leading to intracellular retention and proteasomal degradation of BMP7. Analysis of sclerostin knockout mice revealed an inhibitory action of sclerostin on Wnt signaling in both osteoblasts and osteocytes in cortical and cancellous bones. BMP7 signaling was predominantly inhibited by sclerostin in osteocytes of the calcaneus and the cortical bone of the tibia. Our results suggest that sclerostin exerts its potent bone catabolic effects by antagonizing Wnt signaling in a paracrine and autocrine manner and antagonizing BMP signaling selectively in the osteocytes that synthesize simultaneously both sclerostin and BMP7 proteins.

Research paper thumbnail of Sost and its paralog Sostdc1 coordinate digit number in a Gli3-dependent manner

Developmental Biology, 2013

WNT signaling is critical in most aspects of skeletal development and homeostasis, and antagonist... more WNT signaling is critical in most aspects of skeletal development and homeostasis, and antagonists of WNT signaling are emerging as key regulatory proteins with great promise as therapeutic agents for bone disorders. Here we show that Sost and its paralog Sostdc1 emerged through ancestral genome duplication and their expression patterns have diverged to delineate nonoverlapping domains in most organ systems including musculoskeletal, cardiovascular, nervous, digestive, reproductive and respiratory. In the developing limb, Sost and Sostdc1 display dynamic expression patterns with Sost being restricted to the distal ectoderm and Sostdc1 to the proximal ectoderm and the mesenchyme. While Sostdc1-/mice lack any obvious limb or skeletal defects, Sost-/mice recapitulate the hand defects described for Sclerosteosis patients. However, elevated WNT signaling in Sost-/-; Sostdc1-/mice causes misregulation of SHH signaling, ectopic activation of Sox9 in the digit 1 field and preaxial polydactyly in a Gli1-and Gli3-dependent manner. In addition, we show that the syndactyly documented in Sclerosteosis is present in both Sost-/and Sost-/-; Sostdc1-/mice, and is driven by misregulation of Fgf8 in the AER, a region lacking Sost and Sostdc1 expression. This study highlights the complexity of WNT signaling in ☆ This is an open-access article distributed under the terms of the Creative Commons Attribution-NonCommercial-No Derivative Works License, which permits non-commercial use, distribution, and reproduction in any medium, provided the original author and source are credited. Open Access under CC BY-NC-ND 3.0 license.

Research paper thumbnail of Follistatin and Noggin Are Excluded from the Zebrafish Organizer

Developmental Biology, 1998

The patterning activity of the Spemann organizer in early amphibian embryos has been characterize... more The patterning activity of the Spemann organizer in early amphibian embryos has been characterized by a number of organizer-specific secreted proteins including Chordin, Noggin, and Follistatin, which all share the same inductive properties. They can neuralize ectoderm and dorsalize ventral mesoderm by blocking the ventralizing signals Bmp2 and Bmp4. In the zebrafish, null mutations in the chordin gene, named chordino, lead to a severe reduction of organizer activity, indicating that Chordino is an essential, but not the only, inductive signal generated by the zebrafish organizer. A second gene required for zebrafish organizer function is mercedes, but the molecular nature of its product is not known as yet. To investigate whether and how Follistatin and Noggin are involved in dorsoventral (D-V) patterning of the zebrafish embryo, we have now isolated and characterized their zebrafish homologues. Overexpression studies demonstrate that both proteins have the same dorsalizing properties as their Xenopus homologues. However, unlike the Xenopus genes, zebrafish follistatin and noggin are not expressed in the organizer region, nor are they linked to the mercedes mutation. Expression of both genes starts at midgastrula stages. While no patterned noggin expression was detectable by in situ hybridization during gastrulation stages, later expression is confined to presumptive cartilage cells in the branchial arches and the neurocranium and to proximal regions of the pectoral fin buds. follistatin transcripts in gastrulating embryos are confined to anterior paraxial regions, which give rise to head mesoderm and the first five somites. The dorsolateral extent of this expression domain is regulated by Bmp2b, Chordino, and Follistatin itself. In addition, transient expression was observed in a subset of cells in the posterior notochord anlage. Later, follistatin is expressed in brain, eyes, and somites. Comparison of the spatiotemporal expression pattern of follistatin and noggin with those of bmp2b and bmp4 and overexpression studies suggest that Noggin and Follistatin may function as Bmp antagonists in later processes of zebrafish development, including late phases of D-V patterning, to refine the early pattern set up by the interaction of Chordino and Bmp2/4. It thus appears that many, but not all, aspects of early dorsoventral patterning are shared among different vertebrate species.

Research paper thumbnail of Cooperative activity of noggin and gremlin 1 in axial skeleton development

Development, 2011

Inductive signals from adjacent tissues initiate differentiation within the somite. In this study... more Inductive signals from adjacent tissues initiate differentiation within the somite. In this study, we used mouse embryos mutant for the BMP antagonists noggin (Nog) and gremlin 1 (Grem1) to characterize the effects of BMP signaling on the specification of the sclerotome. We confirmed reduction of Pax1 and Pax9 expression in Nog mutants, but found that Nog;Grem1 double mutants completely fail to initiate sclerotome development. Furthermore, Nog mutants that also lack one allele of Grem1 exhibit a dramatic reduction in axial skeleton relative to animals mutant for Nog alone. By contrast, Pax3, Myf5 and Lbx1 expression indicates that dermomyotome induction occurs in Nog;Grem1 double mutants. Neither conditional Bmpr1a mutation nor treatment with the BMP type I receptor inhibitor dorsomorphin expands sclerotome marker expression, suggesting that BMP antagonists do not have an instructive function in sclerotome specification. Instead, we hypothesize that Nog- and Grem1-mediated inhibitio...

Research paper thumbnail of Anti-ACVR1 antibodies exacerbate heterotopic ossification in fibrodysplasia ossificans progressiva (FOP) by activating FOP-mutant ACVR1

Journal of Clinical Investigation, Jun 15, 2022

ANE, VI, and SJH are employees of Regeneron Pharmaceuticals and either own or have owned stock in... more ANE, VI, and SJH are employees of Regeneron Pharmaceuticals and either own or have owned stock in Regeneron Pharmaceuticals. KS is an employee of Adimab, LLC, and holds shares in Adimab, LLC. PBY is a cofounder of Keros Therapeutics, which develops therapeutics for hematological and musculoskeletal diseases that target TGF-β signaling pathways and is compensated for work on the company's scientific advisory board and owns equity in the publicly traded company. PBY's interests are reviewed and managed by Brigham and Women's Hospital in accordance with their conflict-of-interest policies.

Research paper thumbnail of Bone Mass Transient Increase in Bone Formation and Conditional Deletion of Gremlin Causes a Developmental Biology: Molecular Basis of Cell and

Gremlin is a glycoprotein that binds bone morphogenetic proteins (BMPs) 2, 4, and 7, antagonizing... more Gremlin is a glycoprotein that binds bone morphogenetic proteins (BMPs) 2, 4, and 7, antagonizing their actions. Gremlin opposes BMP effects on osteoblastic differentiation and function in vitro and in vivo, and its overexpression causes osteopenia. To define the function of gremlin in the skeleton, we generated gremlin 1 (grem1) conditional null mice by mating mice where grem1 was flanked by lox P sequences with mice expressing the Cre recombinase under the control of the osteocalcin promoter. grem1 null male mice displayed increased trabecular bone volume due to enhanced osteoblastic activity, because mineral apposition and bone formation rates were increased. Osteoblast number and bone resorption were not altered. Marrow stromal cells from grem1 conditional null mice expressed higher levels of alkaline phosphatase activity. Gremlin downregulation by RNA interference in ST-2 stromal and MC3T3 osteoblastic cells increased the BMP-2 stimulatory effect on alkaline phosphatase activity, on Smad 1/5/8 phosphorylation, and on the transactivation of the BMP/Smad reporter construct 12؋SBE-Oc-pGL3. Gremlin down-regulation also enhanced osteocalcin and Runx-2 expression, Wnt 3a signaling, and activity in ST-2 cells. In conclusion, deletion of grem1 in the bone microenvironment results in sensitization of BMP signaling and activity and enhanced bone formation in vivo.

Research paper thumbnail of Reactivation of a developmental Bmp2 signaling center is required for therapeutic control of the murine periosteal niche

eLife, 2019

Two decades after signals controlling bone length were discovered, the endogenous ligands determi... more Two decades after signals controlling bone length were discovered, the endogenous ligands determining bone width remain unknown. We show that postnatal establishment of normal bone width in mice, as mediated by bone-forming activity of the periosteum, requires BMP signaling at the innermost layer of the periosteal niche. This developmental signaling center becomes quiescent during adult life. Its reactivation however, is necessary for periosteal growth, enhanced bone strength, and accelerated fracture repair in response to bone-anabolic therapies used in clinical orthopedic settings. Although many BMPs are expressed in bone, periosteal BMP signaling and bone formation require only Bmp2 in the Prx1-Cre lineage. Mechanistically, BMP2 functions downstream of Lrp5/6 pathway to activate a conserved regulatory element upstream of Sp7 via recruitment of Smad1 and Grhl3. Consistent with our findings, human variants of BMP2 and GRHL3 are associated with increased risk of fractures.

Research paper thumbnail of BMP3 Suppresses Osteoblast Differentiation of Bone Marrow Stromal Cells via Interaction with Acvr2b

Molecular Endocrinology, 2012

Enhancing bone morphogenetic protein (BMP) signaling increases bone formation in a variety of set... more Enhancing bone morphogenetic protein (BMP) signaling increases bone formation in a variety of settings that target bone repair. However, the role of BMP in the maintenance of adult bone mass is not well understood. Targeted disruption of BMP3 in mice results in increased trabecular bone formation, whereas transgenic overexpression of BMP3 in skeletal cells leads to spontaneous fracture, consistent with BMP3 having a negative role in bone mass regulation. Here we investigate the importance of BMP3 as a mediator of BMP signaling in the adult skeleton. We find that osteoblasts (OBL) and osteocytes are the source of BMP3 in adult bone. Using in vitro cultures of primary bone marrow stromal cells, we show that overexpression of BMP3 suppresses OBL differentiation, whereas loss of BMP3 increases colony-forming unit fibroblasts and colony-forming unit OBL. The ability of BMP3 to affect OBL differentiation is due to its interaction with activin receptor type 2b (Acvr2b) because knockdown of...

Research paper thumbnail of Bone Morphogenetic Proteins Induce Gremlin, a Protein That Limits Their Activity in Osteoblasts1

Endocrinology, 2000

Bone morphogenetic proteins (BMP) induce the differentiation of cells of the osteoblastic lineage... more Bone morphogenetic proteins (BMP) induce the differentiation of cells of the osteoblastic lineage and enhance the function of the osteoblast. Growth factor activity is regulated by binding proteins, and we previously showed that BMPs induce noggin, a glycoprotein that binds and blocks BMP action. Recently, additional BMP antagonists, such as gremlin, have been described, but there is no information about their expression or function in osteoblasts. We tested for the expression of gremlin and studied its induction by BMPs in cultures of osteoblast-enriched cells from 22-day-old fetal rat calvariae (Ob cells). BMP-2 caused a time-and dose-dependent increase in gremlin messenger RNA and polypeptide levels, as determined by Northern and Western blot analyses. The effects of BMP-2 on gremlin transcripts were independent of new protein synthesis. BMP-2 increased the rate of gremlin transcription as determined by nuclear run-on assays. Fibroblast growth factor-2 and platelet-derived growth factor BB also induced gremlin, but other hormones and growth factors had no effect. Gremlin prevented the stimulatory effects of BMP-2 on DNA, collagen, noncollagen protein synthesis, and alkaline phosphatase activity in Ob cells. In conclusion, BMPs induce gremlin transcription in Ob cells, a mechanism that probably limits BMP action in osteoblasts. (Endocrinology 141: 4558-4563, 2000)

Research paper thumbnail of Skeletal Overexpression of Gremlin Impairs Bone Formation and Causes Osteopenia

Endocrinology, 2005

Skeletal cells synthesize bone morphogenetic proteins (BMPs) and BMP antagonists. Gremlin, a BMP ... more Skeletal cells synthesize bone morphogenetic proteins (BMPs) and BMP antagonists. Gremlin, a BMP antagonist, is expressed in osteoblasts and opposes BMP effects on osteoblastic differentiation and function in vitro. However, its effects in vivo are not known. To investigate the actions of gremlin on bone remodeling in vivo, we generated transgenic mice overexpressing gremlin under the control of the osteocalcin promoter. Gremlin transgenics exhibited bone fractures and reduced bone mineral density by 20-30%, compared with controls. Static and dynamic histomorphometry of femurs revealed that gremlin overexpression caused reduced trabecular bone volume and the appearance of woven bone. Polarized light microscopy revealed disorganized collagen bundles at the endosteal cortical surface. Gremlin transgenic mice displayed a 70% decrease in the number of osteoblasts/trabecular area and reduced mineral apposition and bone formation rates. In vivo bromodeoxyuridine labeling and marrow stromal cell cultures demonstrated an inhibitory effect of gremlin on osteoblastic cell replication, but no change on apoptosis was detected. Marrow stromal cells from gremlin transgenics displayed a reduced response to BMP on phosphorylated mothers against decapentaplegic 1/5/8 phosphorylation and reduced free cytosolic ␤-catenin levels. In conclusion, transgenic mice overexpressing gremlin in the bone microenvironment have decreased osteoblast number and function leading to osteopenia and spontaneous fractures. (Endocrinology 146: 655-665, 2005

Research paper thumbnail of Bone Morphogenetic Proteins, Their Antagonists, and the Skeleton

Endocrine Reviews, 2003

Skeletal homeostasis is determined by systemic hormones and local factors. Bone morphogenetic pro... more Skeletal homeostasis is determined by systemic hormones and local factors. Bone morphogenetic proteins (BMP) are unique because they induce the differentiation of mesenchymal cells toward cells of the osteoblastic lineage and also enhance the differentiated function of the osteoblast. However, the activity of BMPs needs to be tempered by intracellular and extracellular antagonists. BMPs bind to specific receptors and signal by phosphorylating the cytoplasmic proteins mothers against decapentaplegic (Smad) 1 and 5, which form heterodimers with Smad 4, and after nuclear translocation regulate transcription. BMP antagonists can be categorized as pseudoreceptors that compete with signaling receptors, inhibitory Smads that block signaling, intracellular binding proteins that bind Smad 1 and 5, and factors that induce ubiquitination and proteolysis of signaling Smads. In addition, a large number of extracellular proteins that bind BMPs and prevent their binding to signaling receptors have...

Research paper thumbnail of <i>ACVR1</i> <sup> <i>R206H</i> </sup> receptor mutation causes fibrodysplasia ossificans progressiva by imparting responsiveness to activin A

Science Translational Medicine, Sep 2, 2015

Fibrodysplasia ossificans progressiva (FOP) is a rare genetic disorder characterized by episodica... more Fibrodysplasia ossificans progressiva (FOP) is a rare genetic disorder characterized by episodically exuberant heterotopic ossification (HO), whereby skeletal muscle is abnormally converted into misplaced, but histologically normal bone. This HO leads to progressive immobility with catastrophic consequences, including death by asphyxiation. FOP results from mutations in the intracellular domain of the type I BMP (bone morphogenetic protein) receptor ACVR1; the most common mutation alters arginine 206 to histidine (ACVR1 R206H) and has been thought to drive inappropriate bone formation as a result of receptor hyperactivity. We unexpectedly found that this mutation rendered ACVR1 responsive to the activin family of ligands, which generally antagonize BMP signaling through ACVR1 but cannot normally induce bone formation. To test the implications of this finding in vivo, we engineered mice to carry the Acvr1 R206H mutation. Because mice that constitutively express Acvr1[R206H] die perinatally, we generated a genetically humanized conditional-on knock-in model for this mutation. When Acvr1[R206H] expression was induced, mice developed HO resembling that of FOP; HO could also be triggered by activin A

Research paper thumbnail of Saracatinib is an efficacious clinical candidate for fibrodysplasia ossificans progressiva

Currently, no effective therapies exist for fibrodysplasia ossificans progressiva (FOP), a rare c... more Currently, no effective therapies exist for fibrodysplasia ossificans progressiva (FOP), a rare congenital syndrome in which heterotopic bone is formed in soft tissues due to dysregulated activity of the bone morphogenetic protein (BMP) receptor kinase ALK2/ACVR1. From a screen of known biologically active compounds, we identified saracatinib as a potent ALK2 kinase inhibitor. In enzymatic and cell-based assays, saracatinib preferentially inhibited ALK2 compared with other receptors of the BMP/TGFβ signaling pathway, and induced dorsalization in zebrafish embryos consistent with BMP antagonism. We further tested the efficacy of saracatinib using an inducibleACVR1Q207Dtransgenic mouse line, which provides a model of heterotopic ossification, as well as an inducibleACVR1R206Hknock-in, which serves as a genetically and physiologically faithful model of FOP. In both models, saracatinib was well tolerated and potently inhibited the development of heterotopic ossification even when admini...

Research paper thumbnail of Activin A forms a non-signaling complex with ACVR1 and type II Activin/BMP receptors via its finger 2 tip loop

eLife, 2020

Activin A functions in BMP signaling in two ways: it either engages ACVR1B to activate Smad2/3 si... more Activin A functions in BMP signaling in two ways: it either engages ACVR1B to activate Smad2/3 signaling or binds ACVR1 to form a non-signaling complex (NSC). Although the former property has been studied extensively, the roles of the NSC remain unexplored. The genetic disorder fibrodysplasia ossificans progressiva (FOP) provides a unique window into ACVR1/Activin A signaling because in that disease Activin can either signal through FOP-mutant ACVR1 or form NSCs with wild-type ACVR1. To explore the role of the NSC, we generated ‘agonist-only’ Activin A muteins that activate ACVR1B but cannot form the NSC with ACVR1. Using one of these muteins, we demonstrate that failure to form the NSC in FOP results in more severe disease pathology. These results provide the first evidence for a biological role for the NSC in vivo and pave the way for further exploration of the NSC’s physiological role in corresponding knock-in mice.

Research paper thumbnail of The finger 2 tip loop of Activin A is required for the formation of its non-signaling complex with ACVR1 and type II Bone Morphogenetic Protein receptors

Activin A functions in BMP signaling in two ways: it either engages ACVR1B to activate Smad2/3 si... more Activin A functions in BMP signaling in two ways: it either engages ACVR1B to activate Smad2/3 signaling or binds ACVR1 to form a non-signaling complex (NSC). Although the former property has been studied extensively, the roles of the NSC remain unexplored. The genetic disorder fibrodysplasia ossificans progressiva (FOP) provides a unique window into ACVR1/Activin A signaling because in that disease Activin can either signal through FOP-mutant ACVR1 or form NSCs with wild type ACVR1. To explore the role of the NSC, we generated ‘agonist-only’ Activin A muteins that activate ACVR1B but cannot form the NSC with ACVR1. Using one of these muteins we demonstrate that failure to form the NSC in FOP results in more severe disease pathology. These results provide the first evidence for a biological role for the NSC in vivo and pave the way for further exploration of the NSC’s physiological role in corresponding knock-in mice.Impact StatementThe non-signaling complex formed by Activin A and ...

Research paper thumbnail of Conditional Deletion of Sost in MSC-derived lineages Identifies Specific Cell Type Contributions to Bone Mass and B Cell Development

Journal of bone and mineral research : the official journal of the American Society for Bone and Mineral Research, Jan 11, 2018

Sclerostin (Sost) is a negative regulator of bone formation and blocking its function via antibod... more Sclerostin (Sost) is a negative regulator of bone formation and blocking its function via antibodies has shown great therapeutic promise by increasing both bone mass in humans and animal models. Sclerostin deletion in Sost knockout mice (Sost ) causes high bone mass (HBM) similar to Sclerosteosis patients. Sost mice have been shown to display an up to 300% increase in bone volume/total volume (BV/TV), relative to aged matched controls, and it has been postulated that the main source of skeletal Sclerostin is the osteocyte. To understand the cell-type specific contributions to the HBM phenotype described in Sost mice, as well as to address the endocrine and paracrine mode of action of sclerostin, we examined the skeletal phenotypes of conditional Sost loss-of-function (Sost ) mice with specific deletions in (1) the limb mesenchyme (Prx1-Cre; targets osteoprogenitors and their progeny); (2) mid-stage osteoblasts and their progenitors (Col1-Cre); (3) mature osteocytes (Dmp1-Cre) and (4...

Research paper thumbnail of Wnt co-receptors Lrp5 and Lrp6 differentially mediate Wnt3a signaling in osteoblasts

PloS one, 2017

Wnt3a is a major regulator of bone metabolism however, very few of its target genes are known in ... more Wnt3a is a major regulator of bone metabolism however, very few of its target genes are known in bone. Wnt3a preferentially signals through transmembrane receptors Frizzled and co-receptors Lrp5/6 to activate the canonical signaling pathway. Previous studies have shown that the canonical Wnt co-receptors Lrp5 and Lrp6 also play an essential role in normal postnatal bone homeostasis, yet, very little is known about specific contributions by these co-receptors in Wnt3a-dependent signaling. We used high-throughput sequencing technology to identify target genes regulated by Wnt3a in osteoblasts and to elucidate the role of Lrp5 and Lrp6 in mediating Wnt3a signaling. Our study identified 782 genes regulated by Wnt3a in primary calvarial osteoblasts. Wnt3a up-regulated the expression of several key regulators of osteoblast proliferation/ early stages of differentiation while inhibiting genes expressed in later stages of osteoblastogenesis. We also found that Lrp6 is the key mediator of Wn...

Research paper thumbnail of Sostdc1 Deficiency Accelerates Fracture Healing by Promoting the Expansion of Periosteal Mesenchymal Stem Cells

Bone, Jul 18, 2016

Loss of Sostdc1, a growth factor paralogous to Sost, causes the formation of ectopic incisors, fu... more Loss of Sostdc1, a growth factor paralogous to Sost, causes the formation of ectopic incisors, fused molars, abnormal hair follicles, and resistance to kidney disease. Sostdc1 is expressed in the periosteum, a source of osteoblasts, fibroblasts and mesenchymal progenitor cells, which are critically important for fracture repair. Here, we investigated the role of Sostdc1 in bone metabolism and fracture repair. Mice lacking Sostdc1 (Sostdc1(-/-)) had a low bone mass phenotype associated with loss of trabecular bone in both lumbar vertebrae and in the appendicular skeleton. In contrast, Sostdc1(-/-) cortical bone measurements revealed larger bones with higher BMD, suggesting that Sostdc1 exerts differential effects on cortical and trabecular bone. Mid-diaphyseal femoral fractures induced in Sostdc1(-/-) mice showed that the periosteal population normally positive for Sostdc1 rapidly expands during periosteal thickening and these cells migrate into the fracture callus at 3 days post fra...

Research paper thumbnail of Angiogenic sprouting into neural tissue requires Gpr124, an orphan G protein-coupled receptor

Proceedings of the National Academy of Sciences, 2011

The vasculature of the CNS is structurally and functionally distinct from that of other organ sys... more The vasculature of the CNS is structurally and functionally distinct from that of other organ systems and is particularly prone to developmental abnormalities and hemorrhage. Although other embryonic tissues undergo primary vascularization, the developing nervous system is unique in that it is secondarily vascularized by sprouting angiogenesis from a surrounding perineural plexus. This sprouting angiogenesis requires the TGF-β and Wnt pathways because ablation of these pathways results in aberrant sprouting and hemorrhage. We have genetically deleted Gpr124, a member of the large family of long N-terminal group B G protein-coupled receptors, few members of which have identified ligands or well-defined biologic functions in mammals. We show that, in the developing CNS, Gpr124 is specifically expressed in the vasculature and is absolutely required for proper angiogenic sprouting into the developing neural tube. Embryos lacking Gpr124 exhibit vascular defects characterized by delayed v...

Research paper thumbnail of Connective Tissue Growth Factor ( CTGF ) Inactivation Leads to Defects in Islet Cell Lineage Allocation and Cell Proliferation During Embryogenesis

The Journal of Clinical Endocrinology & Metabolism, 2009

The factors necessary for normal pancreatic islet morphogenesis have not been well characterized.... more The factors necessary for normal pancreatic islet morphogenesis have not been well characterized. Here we report that connective tissue growth factor (CTGF) is involved in the establishment of normal islet endocrine cell ratio and architecture. CTGF is a secreted protein known to modulate several growth factor signaling pathways including TGF-␤, BMP, and Wnt. Though its role in pancreatic diseases such as pancreatitis and pancreatic cancer are well documented, a role for CTGF in normal pancreas development and function has heretofore not been examined. Using a lacZ-tagged CTGF allele, we describe for the first time the expression pattern of CTGF in the developing pancreas and the requirement of CTGF for normal islet morphogenesis and embryonic cell proliferation. CTGF is highly expressed in pancreatic ductal epithelium and vascular endothelium, as well as at lower levels in developing insulin ϩ cells, but becomes down-regulated in ␤ cells soon after birth. Pancreata from CTGF null embryos have an increase in glucagon ϩ cells with a concomitant decrease in insulin ϩ cells, and show defects in islet morphogenesis. Loss of CTGF also results in a dramatic decrease in ␤ cell proliferation at late gestation. Unlike CTGF null embryos, CTGF heterozygotes survive past birth and exhibit a range of islet phenotypes, including an intermingling of islet cell types, increased number of glucagon ϩ cells, and ␤ cell hypertrophy.

Research paper thumbnail of Distinct Modes of Inhibition by Sclerostin on Bone Morphogenetic Protein and Wnt Signaling Pathways

Journal of Biological Chemistry, 2010

Sclerostin is expressed by osteocytes and has catabolic effects on bone. It has been shown to ant... more Sclerostin is expressed by osteocytes and has catabolic effects on bone. It has been shown to antagonize bone morphogenetic protein (BMP) and/or Wnt activity, although at present the underlying mechanisms are unclear. Consistent with previous findings, Sclerostin opposed direct Wnt3a-induced but not direct BMP7-induced responses when both ligand and antagonist were provided exogenously to cells. However, we found that when both proteins are expressed in the same cell, sclerostin can antagonize BMP signaling directly by inhibiting BMP7 secretion. Sclerostin interacts with both the BMP7 mature domain and pro-domain, leading to intracellular retention and proteasomal degradation of BMP7. Analysis of sclerostin knockout mice revealed an inhibitory action of sclerostin on Wnt signaling in both osteoblasts and osteocytes in cortical and cancellous bones. BMP7 signaling was predominantly inhibited by sclerostin in osteocytes of the calcaneus and the cortical bone of the tibia. Our results suggest that sclerostin exerts its potent bone catabolic effects by antagonizing Wnt signaling in a paracrine and autocrine manner and antagonizing BMP signaling selectively in the osteocytes that synthesize simultaneously both sclerostin and BMP7 proteins.

Research paper thumbnail of Sost and its paralog Sostdc1 coordinate digit number in a Gli3-dependent manner

Developmental Biology, 2013

WNT signaling is critical in most aspects of skeletal development and homeostasis, and antagonist... more WNT signaling is critical in most aspects of skeletal development and homeostasis, and antagonists of WNT signaling are emerging as key regulatory proteins with great promise as therapeutic agents for bone disorders. Here we show that Sost and its paralog Sostdc1 emerged through ancestral genome duplication and their expression patterns have diverged to delineate nonoverlapping domains in most organ systems including musculoskeletal, cardiovascular, nervous, digestive, reproductive and respiratory. In the developing limb, Sost and Sostdc1 display dynamic expression patterns with Sost being restricted to the distal ectoderm and Sostdc1 to the proximal ectoderm and the mesenchyme. While Sostdc1-/mice lack any obvious limb or skeletal defects, Sost-/mice recapitulate the hand defects described for Sclerosteosis patients. However, elevated WNT signaling in Sost-/-; Sostdc1-/mice causes misregulation of SHH signaling, ectopic activation of Sox9 in the digit 1 field and preaxial polydactyly in a Gli1-and Gli3-dependent manner. In addition, we show that the syndactyly documented in Sclerosteosis is present in both Sost-/and Sost-/-; Sostdc1-/mice, and is driven by misregulation of Fgf8 in the AER, a region lacking Sost and Sostdc1 expression. This study highlights the complexity of WNT signaling in ☆ This is an open-access article distributed under the terms of the Creative Commons Attribution-NonCommercial-No Derivative Works License, which permits non-commercial use, distribution, and reproduction in any medium, provided the original author and source are credited. Open Access under CC BY-NC-ND 3.0 license.

Research paper thumbnail of Follistatin and Noggin Are Excluded from the Zebrafish Organizer

Developmental Biology, 1998

The patterning activity of the Spemann organizer in early amphibian embryos has been characterize... more The patterning activity of the Spemann organizer in early amphibian embryos has been characterized by a number of organizer-specific secreted proteins including Chordin, Noggin, and Follistatin, which all share the same inductive properties. They can neuralize ectoderm and dorsalize ventral mesoderm by blocking the ventralizing signals Bmp2 and Bmp4. In the zebrafish, null mutations in the chordin gene, named chordino, lead to a severe reduction of organizer activity, indicating that Chordino is an essential, but not the only, inductive signal generated by the zebrafish organizer. A second gene required for zebrafish organizer function is mercedes, but the molecular nature of its product is not known as yet. To investigate whether and how Follistatin and Noggin are involved in dorsoventral (D-V) patterning of the zebrafish embryo, we have now isolated and characterized their zebrafish homologues. Overexpression studies demonstrate that both proteins have the same dorsalizing properties as their Xenopus homologues. However, unlike the Xenopus genes, zebrafish follistatin and noggin are not expressed in the organizer region, nor are they linked to the mercedes mutation. Expression of both genes starts at midgastrula stages. While no patterned noggin expression was detectable by in situ hybridization during gastrulation stages, later expression is confined to presumptive cartilage cells in the branchial arches and the neurocranium and to proximal regions of the pectoral fin buds. follistatin transcripts in gastrulating embryos are confined to anterior paraxial regions, which give rise to head mesoderm and the first five somites. The dorsolateral extent of this expression domain is regulated by Bmp2b, Chordino, and Follistatin itself. In addition, transient expression was observed in a subset of cells in the posterior notochord anlage. Later, follistatin is expressed in brain, eyes, and somites. Comparison of the spatiotemporal expression pattern of follistatin and noggin with those of bmp2b and bmp4 and overexpression studies suggest that Noggin and Follistatin may function as Bmp antagonists in later processes of zebrafish development, including late phases of D-V patterning, to refine the early pattern set up by the interaction of Chordino and Bmp2/4. It thus appears that many, but not all, aspects of early dorsoventral patterning are shared among different vertebrate species.

Research paper thumbnail of Cooperative activity of noggin and gremlin 1 in axial skeleton development

Development, 2011

Inductive signals from adjacent tissues initiate differentiation within the somite. In this study... more Inductive signals from adjacent tissues initiate differentiation within the somite. In this study, we used mouse embryos mutant for the BMP antagonists noggin (Nog) and gremlin 1 (Grem1) to characterize the effects of BMP signaling on the specification of the sclerotome. We confirmed reduction of Pax1 and Pax9 expression in Nog mutants, but found that Nog;Grem1 double mutants completely fail to initiate sclerotome development. Furthermore, Nog mutants that also lack one allele of Grem1 exhibit a dramatic reduction in axial skeleton relative to animals mutant for Nog alone. By contrast, Pax3, Myf5 and Lbx1 expression indicates that dermomyotome induction occurs in Nog;Grem1 double mutants. Neither conditional Bmpr1a mutation nor treatment with the BMP type I receptor inhibitor dorsomorphin expands sclerotome marker expression, suggesting that BMP antagonists do not have an instructive function in sclerotome specification. Instead, we hypothesize that Nog- and Grem1-mediated inhibitio...

Research paper thumbnail of Anti-ACVR1 antibodies exacerbate heterotopic ossification in fibrodysplasia ossificans progressiva (FOP) by activating FOP-mutant ACVR1

Journal of Clinical Investigation, Jun 15, 2022

ANE, VI, and SJH are employees of Regeneron Pharmaceuticals and either own or have owned stock in... more ANE, VI, and SJH are employees of Regeneron Pharmaceuticals and either own or have owned stock in Regeneron Pharmaceuticals. KS is an employee of Adimab, LLC, and holds shares in Adimab, LLC. PBY is a cofounder of Keros Therapeutics, which develops therapeutics for hematological and musculoskeletal diseases that target TGF-β signaling pathways and is compensated for work on the company's scientific advisory board and owns equity in the publicly traded company. PBY's interests are reviewed and managed by Brigham and Women's Hospital in accordance with their conflict-of-interest policies.