Lack of Gdf11 does not improve anemia or prevent the activity of RAP-536 in a mouse model of β-thalassemia

There is a Blood Commentary on this article in this issue.

Analysis of Cre-mediated genetic deletion of Gdf11 in cardiomyocytes of young mice

Administration of active growth differentiation factor 11 (GDF11) to aged mice can reduce cardiac hypertrophy, and low serum levels of GDF11 measured together with the related protein, myostatin (also known as GDF8), predict future morbidity and mortality in coronary heart patients. Using mice with a loxP-flanked ("floxed") allele of Gdf11 and Myh6-driven expression of Cre recombinase to delete Gdf11 in cardiomyocytes, we tested the hypothesis that cardiac-specific Gdf11 deficiency might lead to cardiac hypertrophy in young adulthood. We observed that targeted deletion of Gdf11 in cardiomyocytes does not cause cardiac hypertrophy but rather leads to left ventricular dilation when compared with control mice carrying only the Myh6-cre or Gdf11-floxed alleles, suggesting a possible etiology for dilated cardiomyopathy. However, the mechanism underlying this finding remains unclear because of multiple confounding effects associated with the selected model. First, whole heart Gdf11 expression did not decrease in Myh6-cre; Gdf11-floxed mice, possibly because of upregulation of Gdf11 in noncardiomyocytes in the heart. Second, we observed Cre-associated toxicity, with lower body weights and increased global fibrosis, in Cre-only control male mice compared with flox-only controls, making it challenging to infer which changes in Myh6-cre;Gdf11-floxed mice were the result of Cre toxicity versus deletion of Gdf11. Third, we observed differential expression of cre mRNA in Cre-only controls compared with the cardiomyocyte-specific knockout mice, also making comparison between these two groups difficult. Thus, targeted Gdf11 deletion in cardiomyocytes may lead to left ventricular dilation without hypertrophy, but alternative animal models are necessary to understand the mechanism for these findings. NEW & NOTEWORTHY We observed that targeted deletion of growth differentiation factor 11 in cardiomyocytes does not cause cardiac hypertrophy but rather leads to left ventricular dilation compared with control mice carrying only the Myh6-cre or growth differentiation factor 11-floxed alleles. However, the mechanism underlying this finding remains unclear because of multiple confounding effects associated with the selected mouse model.

Sclerostin deficiency in humans

Sclerosteosis and van Buchem disease are two rare bone sclerosing dysplasias caused by genetic defects in the synthesis of sclerostin. In this article we review the demographic, clinical, biochemical, radiological, and histological characteristics of patients with sclerosteosis and van Buchem disease that led to a better understanding of the role of sclerostin in bone metabolism in humans and we discuss the relevance of these findings for the development of new therapeutics for the treatment of patients with osteoporosis.

Sost, independent of the non-coding enhancer ECR5, is required for bone mechanoadaptation

Sclerostin (Sost) is a negative regulator of bone formation that acts upon the Wnt signaling pathway. Sost is mechanically regulated at both mRNA and protein level such that loading represses and unloading enhances Sost expression, in osteocytes and in circulation. The non-coding evolutionarily conserved enhancer ECR5 has been previously reported as a transcriptional regulatory element required for modulating Sost expression in osteocytes. Here we explored the mechanisms by which ECR5, or several other putative transcriptional enhancers regulate Sost expression, in response to mechanical stimulation. We found that in vivo ulna loading is equally osteoanabolic in wildtype and Sost^-/- mice, although Sost is required for proper distribution of load-induced bone formation to regions of high strain. Using Luciferase reporters carrying the ECR5 non-coding enhancer and heterologous or homologous hSOST promoters, we found that ECR5 is mechanosensitive in vitro and that ECR5-driven Luciferase activity decreases in osteoblasts exposed to oscillatory fluid flow. Yet, ECR5^-/- mice showed similar magnitude of load-induced bone formation and similar periosteal distribution of bone formation to high-strain regions compared to wildtype mice. Further, we found that in contrast to Sost^-/- mice, which are resistant to disuse-induced bone loss, ECR5^-/- mice lose bone upon unloading to a degree similar to wildtype control mice. ECR5 deletion did not abrogate positive effects of unloading on Sost, suggesting that additional transcriptional regulators and regulatory elements contribute to load-induced regulation of Sost.

[Knockdown of SOST in MDA-MB-231 breast cancer cells increase MG-63 osteoblast-like cell function in co-culture system]

Objective To construct a recombinant adenovirus expressing siRNA targeting human sclerostin (SOST) gene, and test the function of MG-63 cells while co-cultured with MDA-MB-231 cells infected by Ad-siSOST. MethodsAccording to the RNA sequence of SOST gene, two pairs of primers which contained 3 siRNA sequences were designed, and a pB2B plasmid was taken as template to amplify 2 DNA sequences. Both of the 2 DNA sequences were ligated to pAdTrace-OK by Gibson DNA Assembly way. After homologous recombination between recombinant shuttle plasmid and adenovirus vector plasmid, the adenovirus was packaged in HEK-293 cells. PCR and ELISA were used to test the expression of SOST in MDA-MB-231 cells which were infected with Ad-siSOST. In the co-culture system of MG-63 cells and MDA-MB-231 cells infected Ad-siSOST, osteoprotegerin (OPG), osteocalcin (OCN), integrin binding sialoprotein (IBSP) and receptor activator of nuclear factor-κB ligand (RANKL) were tested by quantitative real-time PCR. Results Recombinant shuttle plasmid which contained 3 interfering fragments was constructed successfully, and Ad-siSOST was obtained after homologous recombination and packaging. SOST expression in MDA-MB-231 cells was downregulated significantly after infeceted with Ad-siSOST. The mRNA levels of OPG, OCN, IBSP in MG-63 cells increased significantly, while the level of RANKL mRNA decreased significantly, and all 4 gene expressions were reversed after the infection of Ad-siSOST. Conclusion Knockdown of SOST in MG-63 cells increases osteogenesis and ratio of OPG/RANKL in vitro.

Sostdc1 deficiency accelerates fracture healing by promoting the expansion of periosteal mesenchymal stem cells

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 3days post fracture. Quantitative analysis of mesenchymal stem cell (MSC) and osteoblast populations determined that MSCs express Sostdc1, and that Sostdc1(-/-) 5day calluses harbor >2-fold more MSCs than fractured wildtype controls. Histologically a fraction of Sostdc1-positive cells also expressed nestin and α-smooth muscle actin, suggesting that Sostdc1 marks a population of osteochondral progenitor cells that actively participate in callus formation and bone repair. Elevated numbers of MSCs in D5 calluses resulted in a larger, more vascularized cartilage callus at day 7, and a more rapid turnover of cartilage with significantly more remodeled bone and a thicker cortical shell at 21days post fracture. These data support accelerated or enhanced bone formation/remodeling of the callus in Sostdc1(-/-) mice, suggesting that Sostdc1 may promote and maintain mesenchymal stem cell quiescence in the periosteum.

Interactions between BMP-7 and USAG-1 (uterine sensitization-associated gene-1) regulate supernumerary organ formations

Bone morphogenetic proteins (BMPs) are highly conserved signaling molecules that are part of the transforming growth factor (TGF)-beta superfamily, and function in the patterning and morphogenesis of many organs including development of the dentition. The functions of the BMPs are controlled by certain classes of molecules that are recognized as BMP antagonists that inhibit BMP binding to their cognate receptors. In this study we tested the hypothesis that USAG-1 (uterine sensitization-associated gene-1) suppresses deciduous incisors by inhibition of BMP-7 function. We learned that USAG-1 and BMP-7 were expressed within odontogenic epithelium as well as mesenchyme during the late bud and early cap stages of tooth development. USAG-1 is a BMP antagonist, and also modulates Wnt signaling. USAG-1 abrogation rescued apoptotic elimination of odontogenic mesenchymal cells. BMP signaling in the rudimentary maxillary incisor, assessed by expressions of Msx1 and Dlx2 and the phosphorylation of Smad protein, was significantly enhanced. Using explant culture and subsequent subrenal capsule transplantation of E15 USAG-1 mutant maxillary incisor tooth primordia supplemented with BMP-7 demonstrated in USAG-1+/- as well as USAG-1-/- rescue and supernumerary tooth development. Based upon these results, we conclude that USAG-1 functions as an antagonist of BMP-7 in this model system. These results further suggest that the phenotypes of USAG-1 and BMP-7 mutant mice reported provide opportunities for regenerative medicine and dentistry.

Serum Dickkopf 1 levels in sclerostin deficiency

CONTEXT

Sclerostin and Dickkopf 1 (DKK1) are antagonists of the canonical Wnt signaling pathway, both binding to the same low-density lipoprotein receptor-related protein 5/6 on osteoblasts, thereby inhibiting bone formation. It is not known whether there is an interaction between sclerostin and DKK1.

OBJECTIVE

We examined whether a lack of sclerostin is compensated by increased DKK1 levels.

DESIGN, SETTING, AND PATIENTS

We measured DKK1 levels in serum samples of patients and carriers of sclerosteosis (19 patients, 24 carriers) and van Buchem disease (VBD) (13 patients, 22 carriers) and 25 healthy controls. Sclerosteosis and VBD are caused by deficient sclerostin synthesis and are characterized by increased bone formation and hyperostotic phenotypes.

MAIN OUTCOME MEASURES

DKK1 levels were compared between patients and carriers, and between patients and healthy controls. We also examined associations between levels of DKK1 and the bone turnover markers procollagen type 1 amino-terminal propeptide and carboxy-terminal cross-linking telopeptide.

RESULTS

We found that DKK1 levels were significantly higher in patients with both sclerosteosis (4.28 ng/mL [95% confidence interval (CI), 3.46-5.11 ng/mL]) and VBD (5.28 ng/mL [95% CI, 3.84-6.71 ng/mL]), compared to levels in carriers of the two diseases (sclerosteosis, 2.03 ng/mL [95% CI, 1.78-2.29 ng/mL], P < .001; VBD, 3.47 ng/mL [95% CI, 2.97-3.97 ng/mL], P = 0.017) and to levels in healthy controls (2.77 ng/mL [95% CI, 2.45-3.08 ng/mL]; P = 0.004 and P < .001, respectively). Serum DKK1 levels were positively associated with levels of procollagen type 1 amino-terminal propeptide and carboxy-terminal cross-linking telopeptide in both disorders.

CONCLUSIONS

These results suggest that increased DKK1 levels observed in patients with sclerosteosis and VBD represent an adaptive response to the increased bone formation characterizing these diseases, although these increased levels do not compensate for the lack of sclerostin on bone formation.

Sexual dimorphism in the effect of GDF-6 deficiency on murine tendon

Three members of the growth/differentiation factor (GDF) subfamily of bone morphogenetic proteins (BMPs), GDFs-5, -6, and -7, have demonstrated the potential to augment tendon and ligament repair. To gain further insight into the in vivo role of these molecules, previous studies have characterized intact and healing tendons in mice with functional null mutations in GDF-5 and -7. The primary goal of the present study was to perform a detailed characterization of the intact tendon phenotype in 4- and 16-week-old male and female GDF6-/- mice and their +/+ littermates. The results demonstrate that GDF6 deficiency was associated with an altered tendon phenotype that persisted into adulthood. Among males, GDF6-/- tail tendon fascicles had significantly less collagen and glycosaminoglycan content, and these compositional differences were associated with compromised material properties. The effect of GDF6 deficiency on tendon was sexually dimorphic, however, for among female GDF6-/- mice, neither differences in tendon composition nor in material properties were detected. The tendon phenotype that was observed in males appeared to be stronger in the tail site than in the Achilles tendon site, where some compositional differences were present, but no material property differences were detected. These data support existing in vitro studies, which suggest a potential role for BMP-13 (the human homologue to GDF-6) in tendon matrix modeling and/or remodeling.

Bmp4 is essential for the formation of the vestibular apparatus that detects angular head movements

Angular head movements in vertebrates are detected by the three semicircular canals of the inner ear and their associated sensory tissues, the cristae. Bone morphogenetic protein 4 (Bmp4), a member of the Transforming growth factor family (TGF-β), is conservatively expressed in the developing cristae in several species, including zebrafish, frog, chicken, and mouse. Using mouse models in which Bmp4 is conditionally deleted within the inner ear, as well as chicken models in which Bmp signaling is knocked down specifically in the cristae, we show that Bmp4 is essential for the formation of all three cristae and their associated canals. Our results indicate that Bmp4 does not mediate the formation of sensory hair and supporting cells within the cristae by directly regulating genes required for prosensory development in the inner ear such as Serrate1 (Jagged1 in mouse), Fgf10, and Sox2. Instead, Bmp4 most likely mediates crista formation by regulating Lmo4 and Msx1 in the sensory region and Gata3, p75Ngfr, and Lmo4 in the non-sensory region of the crista, the septum cruciatum. In the canals, Bmp2 and Dlx5 are regulated by Bmp4, either directly or indirectly. Mechanisms involved in the formation of sensory organs of the vertebrate inner ear are thought to be analogous to those regulating sensory bristle formation in Drosophila. Our results suggest that, in comparison to sensory bristles, crista formation within the inner ear requires an additional step of sensory and non-sensory fate specification.

Disruption of the sense of balance is highly debilitating, causing vertigo and nausea. Maintenance of proper balance requires sensory inputs from many body parts, including the inner ears and the eyes. Within the inner ear, the vestibular apparatus plays a key role in the sense of balance and is responsible for detecting head orientation and movements. The portion of the vestibular apparatus that detects angular head movements consists of three fluid-filled, semicircular canals oriented at right angles to each other. At one end of each canal is an enlargement that houses the sensory tissue, crista ampullaris, consisting of sensory hair cells and supporting cells. Bone morphogenetic protein 4 (Bmp4), a secreted signaling molecule, is expressed in these sensory regions during development. However, the lack of Bmp4 in mice affects the formation of not only the sensory regions but also their associated canals. These results demonstrate for the first time that a single gene, Bmp4, is required for the formation of the entire sensory apparatus for detecting angular head movements.

Impaired growth plate function in bmp-6 null mice

Bone morphogenetic protein 6 (BMP-6) is expressed by different skeletal cells including osteoblasts and growth plate chondrocytes, suggesting roles in bone formation and growth regulation. To address these possibilities, we examined whether cancellous and cortical bone parameters, or indices of growth plate function, are altered in bmp-6 null mice as assessed under basal conditions, and following stimulation of bone formation and suppression of growth by estrogen treatment. Ten-week-old female littermate bmp-6 null and wild-type (WT) mice were administered vehicle or E(2) 4, 40, 400 or 4,000 microg/kg/day by daily sc injection for 28 days (6-8 per group). Tibias were removed, and detailed histomorphometric analysis of the proximal metaphysis and growth plates, and tibial diaphysis were performed on longitudinal and transverse sections respectively. Long bone area as measured by DXA was reduced in vehicle-treated bmp-6 null mice compared with WT littermate controls. In addition, vehicle-treated bmp-6 null mice had a reduced cross-sectional area at the tibial mid-diaphysis as assessed by histomorphometry, whereas cancellous bone indices were unaffected. Histomorphometry of the proximal tibial metaphysis demonstrated a defect in bone formation immediately adjacent to the growth plate in bmp-6 null mice compared to WT mice following E(2) treatment. E(2) administration was also associated with a dose-responsive decrease in longitudinal growth rate, and proliferative and hypertrophic zone parameters of the growth plate (p<0.0001). Significantly greater reductions following E(2) treatment were observed in longitudinal growth rate (p<0.01), proliferating and hypertorphic zone widths (p<0.001), and proliferating (p<0.0002) and hypertrophic (p<0.002) cells per column of bmp-6 null mice compared to WT mice. Our observation that long bones are reduced in size compared to wild-type mice primarily through a decrease in cortical cross-sectional area, whilst cancellous bone mass is unaltered, suggests a non-redundant role for BMP-6 in periosteal but not trabecular bone formation. Moreover, growth plate function was reduced in bmp-6 null mice receiving estrogen, leading to an impaired cancellous bone response to estrogen at the highest dose, suggesting that BMP-6 also plays a physiological role in maintaining growth plate function.

Targeted repression of bone morphogenetic protein 7, a novel target of the p53 family, triggers proliferative defect in p53-deficient breast cancer cells

p53 tumor suppressor and its family members, p63 and p73, are known to play a role in the survival of cells exposed to stress signals. As a transcription factor, the p53 family proteins induce a plethora of target genes that mediate their functions in the cell cycle, apoptosis, and other biological activities. However, the mechanism by which the p53 family proteins regulate their cell survival functions is still not clear. Here, we showed that bone morphogenetic protein 7 (BMP7) is a novel target gene regulated by the p53 family and mediates the cell survival function of the basal physiologically relevant level of p53. Specifically, we found that knockdown of BMP7 markedly inhibits the proliferation of p53-deficient, but not p21-knockdown, breast cancer cells compared with the ones with wild-type p53. In addition, we found that inhibitor of differentiation or DNA binding 2 (Id2), a transcription factor implicated for cell survival, is regulated by the BMP7 and p53 pathways. Interestingly, whereas a functional BMP7 or p53 pathway is sufficient to maintain the basal level of Id2 expression, loss of both pathways abrogates Id2 expression. Furthermore, we showed that overexpression of Id2 can restore p53-deficient cells to survive in the absence of BMP7. As a result, we identified a previously unrecognized role for BMP7 in the maintenance of cell survival for p53-deficient cells, at least in part, through Id2. Together, we hypothesize that breast cancer patients with mutant p53 might benefit from targeted repression of BMP7 expression and/or targeted inhibition of the BMP7 pathway.

Abnormal urethra formation in mouse models of split-hand/split-foot malformation type 1 and type 4

Urogenital birth defects are one of the common phenotypes observed in hereditary human disorders. In particular, limb malformations are often associated with urogenital developmental abnormalities, as the case for Hand-foot-genital syndrome displaying similar hypoplasia/agenesis of limbs and external genitalia. Split-hand/split-foot malformation (SHFM) is a syndromic limb disorder affecting the central rays of the autopod with median clefts of the hands and feet, missing central fingers and often fusion of the remaining ones. SHFM type 1 (SHFM1) is linked to genomic deletions or rearrangements, which includes the distal-less-related homeogenes DLX5 and DLX6 as well as DSS1. SHFM type 4 (SHFM4) is associated with mutations in p63, which encodes a p53-related transcription factor. To understand that SHFM is associated with urogenital birth defects, we performed gene expression analysis and gene knockout mouse model analyses. We show here that Dlx5, Dlx6, p63 and Bmp7, one of the p63 downstream candidate genes, are all expressed in the developing urethral plate (UP) and that targeted inactivation of these genes in the mouse results in UP defects leading to abnormal urethra formation. These results suggested that different set of transcription factors and growth factor genes play similar developmental functions during embryonic urethra formation. Human SHFM syndromes display multiple phenotypes with variations in addition to split hand foot limb phenotype. These results suggest that different genes associated with human SHFM could also be involved in the aetiogenesis of hypospadias pointing toward a common molecular origin of these congenital malformations.

Rudiment incisors survive and erupt as supernumerary teeth as a result of USAG-1 abrogation

The term "supernumerary teeth" describes production of more than the normal number of teeth in the primary or permanent dentitions. Their aetiology is not understood. Uterine sensitization associated gene-1 (USAG-1) is a BMP antagonist that plays important roles in the local regulation of BMP signaling by binding and neutralizing BMP activities, and also serves as a modulator of Wnt signaling. We report here that USAG-1 deficient mice have supernumerary teeth. The supernumerary maxillary incisor appears to form as a result of the successive development of the rudimentary upper incisor tooth. We confirmed that the USAG-1 expression is localized to the epithelium and mesenchyme of the rudimentary maxillary incisor tooth organ formation. USAG-1 abrogation rescued apoptotic elimination of odontogenic mesenchymal cells. Based upon these results, we conclude that USAG-1 controls the number of teeth in the maxillary incisor region by regulating apoptosis.

Bmp2 is critical for the murine uterine decidual response

The process of implantation, necessary for all viviparous birth, consists of tightly regulated events, including apposition of the blastocyst, attachment to the uterine lumen, and differentiation of the uterine stroma. In rodents and primates the uterine stroma undergoes a process called decidualization. Decidualization, the process by which the uterine endometrial stroma proliferates and differentiates into large epithelioid decidual cells, is critical to the establishment of fetal-maternal communication and the progression of implantation. The role of bone morphogenetic protein 2 (Bmp2) in regulating the transformation of the uterine stroma during embryo implantation in the mouse was investigated by the conditional ablation of Bmp2 in the uterus using the (PR-cre) mouse. Bmp2 gene ablation was confirmed by real-time PCR analysis in the PR-cre; Bmp2fl/fl (termed Bmp2d/d) uterus. While littermate controls average 0.9 litter of 6.2+/-0.7 pups per month, Bmp2d/d females are completely infertile. Analysis of the infertility indicates that whereas embryo attachment is normal in the Bmp2d/d as in control mice, the uterine stroma is incapable of undergoing the decidual reaction to support further embryonic development. Recombinant human BMP2 can partially rescue the decidual response, suggesting that the observed phenotypes are not due to a developmental consequence of Bmp2 ablation. Microarray analysis demonstrates that ablation of Bmp2 leads to specific gene changes, including disruption of the Wnt signaling pathway, Progesterone receptor (PR) signaling, and the induction of prostaglandin synthase 2 (Ptgs2). Taken together, these data demonstrate that Bmp2 is a critical regulator of gene expression and function in the murine uterus.

Developmental failure of the intra-articular ligaments in mice with absence of growth differentiation factor 5

OBJECTIVE

To show the phenotypic characteristics of the knee joints in brachypodism mice (bp mice), which carry a functional null mutation of the growth differentiation factor 5 (GDF5) gene, we investigated the adult and embryonic bp mice.

METHOD

Radiographic and macroscopic examinations of the knee joint of adult bp mice were performed. A histological examination of the knee joint of bp mice from E12.5 to E18.5 was also performed.

RESULTS

Radiographic and macroscopic examinations of the adult bp mice showed anterior dislocation, hypoplastic condyles, and absence of the intra-articular ligaments. Safranin O staining of knee joints of the embryonic bp mice showed severe hypoplasty of the chondroepiphyses and intra-articular ligaments at E16.5. There was no difference in the number and location of 5-bromo-2'-deoxyuridine (BrdU)-positive cells between wild-type and bp mice through E12.5 to E14.5. A terminal deoxynucleotidyltransferase-mediated dUTP nick-end labeling (TUNEL) study showed excessive cell death of mesenchymal cells of the future knee joint in bp mice at E12.5 and E13.5.

CONCLUSION

bp mice exhibit developmental failure of the condyles and intra-articular ligament of the knee joints.

Zebrafish Bmp4 regulates left-right asymmetry at two distinct developmental time points

Left-right (LR) asymmetry is regulated by early asymmetric signals within the embryo. Even though the role of the bone morphogenetic protein (BMP) pathway in this process has been reported extensively in various model organisms, opposing models for the mechanism by which BMP signaling operates still prevail. Here we show that in zebrafish embryos there are two distinct phases during LR patterning in which BMP signaling is required. Using transgenic lines that ectopically express either noggin3 or bmp2b, we show a requirement for BMP signaling during early segmentation to repress southpaw expression in the right lateral plate mesoderm and regulate both visceral and heart laterality. A second phase was identified during late segmentation, when BMP signaling is required in the left lateral plate mesoderm to regulate left-sided gene expression and heart laterality. Using morpholino knock down experiments, we identified Bmp4 as the ligand responsible for both phases of BMP signaling. In addition, we detected bmp4 expression in Kupffer's vesicle and show that restricted knock down of bmp4 in this structure results in LR patterning defects. The identification of these two distinct and opposing activities of BMP signaling provides new insight into how BMP signaling can regulate LR patterning.

The role of bone morphogenetic protein 4 in inner ear development and function

Bone Morphogenetic Protein 4 (BMP4) is a member of the TGF-beta superfamily and is known to be important for the normal development of many tissues and organs, including the inner ear. Bmp4 homozygous null mice die as embryos, but Bmp4 heterozygous null (Bmp4(+/-)) mice are viable and some adults exhibit a circling phenotype, suggestive of an inner ear defect. To understand the role of BMP4 in inner ear development and function, we have begun to study C57BL/6 Bmp4(+/-) mice. Quantitative testing of the vestibulo-collic reflex, which helps maintain head stability, demonstrated that Bmp4(+/-) mice that exhibit circling behavior have a poor response in the yaw axis, consistent with semicircular canal dysfunction. Although the hair cells of the ampullae were grossly normal, the stereocilia were greatly reduced in number. Auditory brainstem responses showed that Bmp4(+/-) mice have elevated hearing thresholds and immunohistochemical staining demonstrated decreased numbers of neuronal processes in the organ of Corti. Thus Bmp4(+/-) mice have structural and functional deficits in the inner ear.

BMP2 activity, although dispensable for bone formation, is required for the initiation of fracture healing

Adult bones have a notable regenerative capacity. Over 40 years ago, an intrinsic activity capable of initiating this reparative response was found to reside within bone itself, and the term bone morphogenetic protein (BMP) was coined to describe the molecules responsible for it. A family of BMP proteins was subsequently identified, but no individual BMP has been shown to be the initiator of the endogenous bone repair response. Here we demonstrate that BMP2 is a necessary component of the signaling cascade that governs fracture repair. Mice lacking the ability to produce BMP2 in their limb bones have spontaneous fractures that do not resolve with time. In fact, in bones lacking BMP2, the earliest steps of fracture healing seem to be blocked. Although other osteogenic stimuli are still present in the limb skeleton of BMP2-deficient mice, they cannot compensate for the absence of BMP2. Collectively, our results identify BMP2 as an endogenous mediator necessary for fracture repair.

Genetic analysis of the roles of BMP2, BMP4, and BMP7 in limb patterning and skeletogenesis

Bone morphogenetic protein (BMP) family members, including BMP2, BMP4, and BMP7, are expressed throughout limb development. BMPs have been implicated in early limb patterning as well as in the process of skeletogenesis. However, due to complications associated with early embryonic lethality, particularly for Bmp2 and Bmp4, and with functional redundancy among BMP molecules, it has been difficult to decipher the specific roles of these BMP molecules during different stages of limb development. To circumvent these issues, we have constructed a series of mouse strains lacking one or more of these BMPs, using conditional alleles in the case of Bmp2 and Bmp4 to remove them specifically from the limb bud mesenchyme. Contrary to earlier suggestions, our results indicate that BMPs neither act as secondary signals downstream of Sonic Hedghog (SHH) in patterning the anteroposterior axis nor as signals from the interdigital mesenchyme in specifying digit identity. We do find that a threshold level of BMP signaling is required for the onset of chondrogenesis, and hence some chondrogenic condensations fail to form in limbs deficient in both BMP2 and BMP4. However, in the condensations that do form, subsequent chondrogenic differentiation proceeds normally even in the absence of BMP2 and BMP7 or BMP2 and BMP4. In contrast, we find that the loss of both BMP2 and BMP4 results in a severe impairment of osteogenesis.

A group of related signaling molecules called bone morphogenetic proteins (BMPs) are known to play important roles in the formation of the structures such as the limbs. However, because different members of this group often have similar effects on target cells and are produced in overlapping regions of the embryo and hence can be redundant with one another, removal of any single member of the BMP family may not reveal the full extent of the roles they play during development. We have therefore improved on this type of analysis by removing pairs of these factors (BMP2 and BMP4 or BMP2 and BMP7) specifically from the developing limb. Although some have speculated that these signals play an early role in organizing or “patterning” the different tissues of the limb, we find no evidence for such a role. We do find, however, that a minimal amount of BMP signal is required to form cartilage, and hence some cartilaginous elements fail to form in limbs deficient in both BMP2 and BMP4. Moreover, in the absence of these two BMP family members, there is a severe impairment in the development of bone tissue, resulting in severely deformed limbs. This study gives important new insight into the roles of these BMP signals in making skeletal tissues in the embryo.

Eye and neural defects associated with loss of GDF6

Background

In Xenopus the bone morphogenetic protein growth and differentiation factor 6 (GDF6) is expressed at the edge of the neural plate, and within the anterior neural plate including the eye fields. Here we address the role of GDF6 in neural and eye development by morpholino knockdown experiments.

Results

We show that depletion of GDF6 (BMP13) resulted in a reduction in eye size, loss of laminar structure and a reduction in differentiated neural cell types within the retina. This correlated with a reduction in staining for Smad1/5/8 phosphorylation indicating a decrease in GDF6 signalling through loss of phosphorylation of these intracellular mediators of bone morphogenetic protein (BMP) signalling. In addition, the Pax6 expression domain is reduced in size at early optic vesicle stages. Neural cell adhesion molecule (NCAM) is generally reduced in intensity along the neural tube, while in the retina and brain discreet patches of NCAM expression are also lost. GDF6 knock down resulted in an increase in cell death along the neural tube and within the retina as determined by terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL) staining.

Conclusion

Our data demonstrate that GDF6 has an important role in neural differentiation in the eye as well as within the central nervous system, and that GDF6 may act in some way to maintain cell survival within the ectoderm, during the normal waves of programmed cell death.

Bone morphogenetic protein signaling inhibits hair follicle anagen induction by restricting epithelial stem/progenitor cell activation and expansion

Epithelial stem cells (EP-SCs) located in the bulge region of a hair follicle (HF) have the potential to give rise to hair follicle stem/progenitor cells that migrate down to regenerate HFs. Bone morphogenetic protein (BMP) signaling has been shown to regulate the HF cycle by inhibiting anagen induction. Here we show that active BMP signaling functions to prevent EP-SC activation and expansion. Dynamic expression of Noggin, a BMP antagonist, releases EP-SCs from BMP-mediated restriction, leading to EP-SC activation and initiation of the anagen phase. Experimentally induced conditional inactivation of the BMP type IA receptor (Bmpr1a) in EP-SCs leads to overproduction of HF stem/progenitor cells and the eventual formation of matricomas. This genetic manipulation of the BMP signaling pathway also reveals unexpected activation of beta-catenin, a major mediator of Wnt signaling. We propose that BMP activity controls the HF cycle by antagonizing Wnt/beta-catenin activity. This is at least partially achieved by BMP-mediated enhancement of transforming growth factor-beta-regulated epithelial cell-specific phosphatase (PTEN) function. Subsequently, PTEN, through phosphatidyl inositol 3-kinase-Akt, inhibits the activity of beta-catenin, the convergence point of the BMP and Wnt signaling pathways.

Myofibroblast progenitor cells are increased in number in patients with type 1 diabetes and express less bone morphogenetic protein 6: a novel clue to adverse tissue remodelling?

AIMS/HYPOTHESIS

Growth factor imbalance and endothelial progenitor cell dysfunction are well-known elements of the inappropriate response to injury in human and experimental diabetes. We hypothesised that in diabetes the outgrowth of myofibroblast progenitor cells (MFPCs) is also altered and that this relates to aberrant gene expression of growth factors involving members of the TGF-beta/bone morphogenetic protein (BMP) superfamily.

SUBJECTS AND METHODS

MFPCs were cultured from peripheral blood mononuclear cells of patients with type 1 diabetes and control subjects. Microarray analysis, quantitative PCR and ELISA were used to identify differentially regulated TGF-beta/BMP superfamily genes in diabetes- and control-derived MFPC. Possible effects of BMP6 on TGF-beta-induced gene expression were examined in cultured renal fibroblasts (TK173 cells).

RESULTS

Blood from diabetic patients yielded higher numbers of MFPCs than blood from control subjects (1.6-fold increase, p<0.05), involving increased proliferation and decreased apoptosis. BMP6 mRNA and protein were downregulated in MFPCs derived from patients with diabetes (3.9- and 1.8-fold decrease, respectively, p<0.05). Furthermore, an inverse correlation was observed between BMP6 mRNA level and the number of MFPCs in patients with diabetes (r=-0.85, p<0.05). In TK173 cells, BMP6 antagonised the TGF-beta-induced expression of the genes encoding plasminogen activator inhibitor-1 and connective tissue growth factor (70 and 50% reduction, respectively).

CONCLUSIONS/INTERPRETATION

Considering the importance of BMP6 in processes such as angiogenesis and its novel anti-TGF-beta effects, we propose that the excess numbers of BMP6-deficient MFPCs may favour adverse tissue remodelling in patients with diabetes, both numerically and by inappropriate orchestration of their microenvironment.

Bmp2 instructs cardiac progenitors to form the heart-valve-inducing field

A hallmark of heart-valve development is the swelling and deposition of extracellular matrix in the heart-valve region. Only myocardium overlying this region can signal to underlying endothelium and cause it to lose cell-cell contacts, delaminate, and invade the extracellular space abutting myocardium and endocardium to form endocardial cushions (EC) in a process known as epithelial to mesenchymal transformation (EMT). The heart-valve myocardium expresses bone morphogenetic protein-2 (Bmp2) coincident with development of valve mesenchyme. BMPs belong to the transforming growth factor beta superfamily (TGF-beta) and play a wide variety of roles during development. We show that conditional ablation of Bmp2 in cardiac progenitors results in cell fate changes in which the heart-valve region adopts the identity of differentiated chamber myocardium. Moreover, Bmp2-deficient hearts fail to induce production and deposition of matrix at the heart-valve-forming region, resulting in the inability of the endothelium to swell and impairing the development of ECs. Furthermore, in collagen invasion assays, Bmp2 mutant endothelium is incapable of undergoing EMT, and addition of BMP2 protein to mutant heart explants rescues this phenotype. Our results demonstrate that Bmp2 is both necessary and sufficient to specify a field of cardiac progenitor cells as the heart-valve-inducing region amid developing atria and ventricles.

Achilles tendon characterization in GDF-7 deficient mice

Growth/differentiation factors (GDFs) play a significant role in numerous skeletal tissues and processes. Previous work using the brachypod mouse has suggested that GDF-5 affects Achilles tendon composition, ultrastructure, and material behavior, as well as tendon repair. The aim of the present study was to examine the role of a related GDF family member, GDF-7 (BMP-12), in intact tendon by studying the Achilles tendon of genetically engineered knockout mice. Achilles tendons from 16-week-old GDF-7 -/- mice contained 14% less GAG/DNA than did wild type littermates (p = 0.0481), although collagen content was comparable to controls. Quantitative reverse transcriptase-polymerase chain reaction (QRT-PCR) results show that GDF-5 was upregulated two-threefold in response to the absence of GDF-7 protein. GDF-6 was also upregulated in knockouts, but to a lesser extent (twofold, p = 0.0013). On an ultrastructural level, GDF-7 deficient Achilles tendons exhibited a shift towards smaller diameter fibrils which resulted in a small but significant reduction in mean fibril diameter (-8%, p = 0.05). GDF-7 deficiency did not noticeably affect the expression of fibrillar collagens (I, III, V) or tendon proteoglycans (decorin, fibromodulin, lumican, biglycan, versican, aggrecan). Differences in tendon composition and ultrastructure were not biologically significant enough to have a noticeable effect on the structural or material behavior of the tendons. These results demonstrate that GDF-7 deficiency has a subtle effect on the composition and ultrastructure of murine Achilles tendon. The small magnitude of the observed differences may be due to overcompensation by related GDF family members.

Conditional expression of Smad7 in pancreatic beta cells disrupts TGF-beta signaling and induces reversible diabetes mellitus

Identification of signaling pathways that maintain and promote adult pancreatic islet functions will accelerate our understanding of organogenesis and improve strategies for treating diseases like diabetes mellitus. Previous work has implicated transforming growth factor-β (TGF-β) signaling as an important regulator of pancreatic islet development, but has not established whether this signaling pathway is required for essential islet functions in the adult pancreas. Here we describe a conditional system for expressing Smad7, a potent inhibitor of TGF-β signaling, to identify distinct roles for this pathway in adult and embryonic β cells. Smad7 expression in Pdx1⁺ embryonic pancreas cells resulted in striking embryonic β cell hypoplasia and neonatal lethality. Conditional expression of Smad7 in adult Pdx1⁺ cells reduced detectable β cell expression of MafA, menin, and other factors that regulate β cell function. Reduced pancreatic insulin content and hypoinsulinemia produced overt diabetes that was fully reversed upon resumption of islet TGF-β signaling. Thus, our studies reveal that TGF-β signaling is crucial for establishing and maintaining defining features of mature pancreatic β cells.

TGF-β signaling is known to regulate the development of pancreatic β cells; here the authors show that TGF-β is also required for the maintenance of β cell identity in the adult.

Geometric and material contributions to whole bone structural behavior in GDF-7-deficient mice

The growth/differentiation factors (GDFs) are a subfamily of bone morphogenetic proteins (BMPs) known to play a role in a variety of skeletal processes. Previous work using the brachypod mouse demonstrated that mice deficient in GDF-5 have long bones with diminished material properties and ash content compared with control littermates. Our aim was to examine the role of a related GDF family member, GDF-7 (BMP-12), in cortical bone by examining the geometric and material contributions to whole bone structural behavior in GDF-7-deficient mice. Femora from 16-week-old GDF-7 -/- animals had significantly smaller bone cross-sectional geometric parameters (e.g., -20% medial/lateral and anterior/posterior moments of inertia). Despite having smaller bone cross-sections, all structural parameters obtained from four-point bending tests were comparable to those of wild-type bones due to elevated cortical bone material properties (+18% modulus of elasticity, +28% yield strength, and +18% ultimate strength). No significant differences in ash content or collagen content were detected, however. These data suggest that GDF-7 deficiency is associated with elevated cortical bone material properties that compensate for decreased geometric properties, thereby preserving bone structural integrity. The compositional and/or microstructural bases for these altered material properties remain to be determined, however.

Noggin antagonism of BMP4 signaling controls development of the axial skeleton in the mouse

The interaction between bone morphogenetic proteins (BMPs) and their antagonist, Noggin, is critical for normal development. Noggin null mice die at birth with a severely malformed skeleton that is postulated to reflect the activity of unopposed BMP signaling. However, the widespread expression and redundancy of different BMPs have made it difficult to identify a specific role for individual BMPs during mammalian skeletal morphogenesis. Here, we report the effects of modifying Bmp4 dosage on the skeletal development of Noggin mutant mice. The reduction of Bmp4 dosage results in an extensive rescue of the axial skeleton of Noggin mutant embryos. In contrast, the appendicular skeletal phenotype of Noggin mutants was unchanged. Analysis of molecular markers of somite formation and somite patterning suggests that the loss of Noggin results in the formation of small mispatterned somites. Mis-specification and growth retardation rather than cell death most likely account for the subsequent reduction or loss of axial skeletal structures. The severe Noggin phenotype correlates with Bmp4-dependent ectopic expression of Bmp4 in the paraxial mesoderm consistent with Noggin antagonizing an auto-inductive feed-forward mechanism. Thus, specific interactions between Bmp4 and Noggin in the early embryo are critical for establishment and patterning of the somite and subsequent axial skeletal morphogenesis.

Bone mineral density in sclerosteosis; affected individuals and gene carriers

BACKGROUND

Sclerosteosis is an autosomal recessive sclerosing bone disorder due to deficiency of sclerostin, a protein secreted by the osteocytes that inhibits bone formation. In the present study we assessed the effect of variable expression of the genetic defect on bone mineral density (BMD) in patients and carriers of the determinant gene.

METHODS

We studied 25 individuals (seven patients and 18 phenotypically normal heterozygotes). BMD was measured by dual x-ray absorptiometry at the lumbar spine, total hip, and distal forearm, and lateral radiographs of the skull were obtained.

RESULTS

Individuals with sclerosteosis had markedly increased BMD at all skeletal sites (Z-score ranges: lumbar spine, +7.73 to +14.43; total hip, +7.84 to +11.51; forearm, +4.44 to +9.53). In heterozygotes, BMD was above the mean value of healthy age-matched individuals at all skeletal sites and had a wide range of normal and clearly increased values. Skull radiographs showed the typical hyperostotic changes in affected individuals and mild or no changes in heterozygotes.

CONCLUSIONS

Heterozygous carriers of sclerosteosis have BMD values consistently higher than the mean of healthy subjects without any of the bone complications encountered in homozygotes. This finding suggests that the production and/or activity of sclerostin can be titrated in vivo, leading to variable increases in bone mass without any unwanted skeletal effects, a hypothesis of obvious significance for the development of new therapeutics for osteoporosis.

Generation of a Bmp2 conditional null allele

Bone morphogenetic proteins (Bmp's) are known to play many important roles in embryogenesis. In addition, recent data from human genetic studies has revealed that Bmp's also have important functions in maintenance of the adult phenotype and aging. The original Bmp2 germline null allele resulted in lethality at embryonic day 7.0-10.5 due to malformation of the amnion/chorion and cardiac malformations. Because the early embryonic lethality of the Bmp2 germline null allele hinders further investigation into Bmp2 function at later stages, we generated a Bmp2 conditional null allele. Using gene targeting in mouse embryonic stem (ES) cells, we introduced LoxP sites upstream and downstream of Bmp2 exon 3 that encodes the mature peptide. Our results indicate that the Bmp2 conditional null allele is a true conditional null that encodes wildtype activity and reverts to a null allele after cre recombinase-induced recombination.

BMP-14 deficiency inhibits long bone fracture healing: a biochemical, histologic, and radiographic assessment

OBJECTIVES

Bone morphogenetic proteins (BMPs) represent a distinct subset of the transforming growth factor-beta family best known for their role in joint formation and bone growth, and several recent clinical trials have begun to look at their efficacy in the augmentation of fracture healing. The goal of this research is to examine the effect of BMP-14, also known as growth differentiation factor-5 and cartilage- derived morphogenetic protein-1 (GDF-5, CDMP-1) on fracture healing by studying the long bone repair process in mice with a deficiency in this signaling peptide.

METHODS

The animal model used for these studies was the BMP-14 (-/-) brachypodism (bp) mouse. Phenotypically normal heterozygous (+/-) littermates were used as controls. Closed mid shaft femur fractures were created and stabilized with intramedullary fixation in 8-week-old female mice. Forty-eight mice per genotype group were examined. On postoperative days 4, 7, 10, 14, 21, 28, 35, and 42, the mice were killed and the femurs and repair tissue were harvested for analysis. At each time point, the fracture sites were analyzed radiographically, histologically, and biochemically. For all quantitative analyses, the data were normalized and analyzed statistically using a 2-factor ANOVA test.

RESULTS

Biochemically, peak values of normalized proteoglycan content were approximately 3 times less in the mutant fractures early in the time course of healing compared with the controls (P < 0.05). Histologically, BMP-14-deficient fractures exhibited a delay in peak area cell density, callus organization, and bone formation compared with controls. Radiographic analysis demonstrated that the peak callus was 2 weeks delayed and approximately 2 times less in the mutants compared with controls (P < 0.05). Radiographic grading of callus also demonstrated a significant difference after day 14.

CONCLUSIONS

Based on histologic, radiographic, and biochemical analysis, BMP-14-deficient mice display a short-term delay in healing of approximately 1 to 2 weeks. The observed abnormalities seem to be the result of a delay in cellular recruitment and chondrocyte differentiation in the early stages fracture repair in the absence of BMP-14. These results support the hypothesis that BMP-14 deficiency leads to a delay in fracture healing. Further studies are warranted to more closely examine the role of BMP-14 in normal fracture healing and the mechanism by which it works.

BMP4 substitutes for loss of BMP7 during kidney development

Functional inactivation of divergent bone morphogenetic proteins (BMPs) causes discrete disturbances during mouse development. BMP4-deficient embryos display mesodermal patterning defects at early post-implantation stages, whereas loss of BMP7 selectively disrupts kidney and eye morphogenesis. Whether these distinct phenotypes simply reflect differences in expression domains, or alternatively intrinsic differences in the signaling properties of these ligands remains unknown. To address this issue, we created embryos exclusively expressing BMP4 under control of the BMP7 locus. Surprisingly, this novel knock-in allele efficiently rescues kidney development. These results demonstrate unequivocally that these structurally divergent BMP family members, sharing only minimal sequence similarity can function interchangeably to activate all the essential signaling pathways for growth and morphogenesis of the kidney. Thus, we conclude that partially overlapping expression patterns of BMPs serve to modulate strength of BMP signaling rather than create discrete fields of ligands with intrinsically different signaling properties.

Functions for proteinases in the ovulatory process

The ovary is a unique and dynamic organ in respect to rapid and extensive degrees of tissue development and remodeling that are periodically repeated in the female reproductive activity. Ovulation is a directed and sequential process accompanied by broad-spectrum proteolysis and culminates in the follicular rupture to release the matured oocyte. This review will focus on the potential roles of six representative proteinases that are involved in various aspects of ovulatory processes: matrix metalloproteinases (MMPs), plasminogen activator (PA)/plasmin, a disintegrin and metalloproteinase domain with thrombospondin motif (ADAMTS), cathepsin-L, pregnancy-associated plasma protein-A (PAPP-A), and bone morphogenetic protein 1/mammalian Tolloid (BMP-1/mTld). Based on the studies of expression and function, these selected proteinases provide and share diverse functions ranging from cleaving components of the extracellular matrix (ECM) to modulating non-ECM molecules, such as various growth factors and their binding proteins. Consistently, the genetic deletion of each individual gene in mice shows their functional overlap in the reproductive activity.

Direct and indirect roles of CNS dorsal midline cells in choroid plexus epithelia formation

Choroid plexus (CP) produces the cerebrospinal fluid (CSF) of the central nervous system (CNS), but little is known about the mechanisms underlying development of this important tissue. CP forms in the hindbrain (4th ventricle), diencephalon (3rd ventricle) and dorsomedial telencephalon bilaterally (lateral ventricles). All of these sites lie at or near the embryonic dorsal midline (DM), which acts as a CNS patterning center. We therefore examined DM-CP relationships using normal and Gdf7 (Bmp12)transgenic embryos to fate map or ablate DM cells. These studies revealed a Gdf7 fate map that includes most CP epithelial (CPe) cells of the hindbrain and diencephalon. In the telencephalon, Gdf7 cell lineages were found in the small anterior domain of telencephalic CPe (tCPe), but its large posterior domain was devoid of these lineages. Anterior and posterior tCPe domains,which arise within a contiguous field separate from diencephalic CPe, also exhibited different patterns of apoptosis. Despite lacking Gdf7 cell lineages,the posterior tCPe domain failed to form after ablating Gdf7-expressing DM cells at neural tube stages. The tCPe loss was associated with abrogation of high-level bone morphogenetic protein (Bmp) signaling, which is known to be required for tCPe induction. Taken together, these studies demonstrate intimate DM-CPe relationships throughout the CNS and highlight two distinct tCPe domains, including a posterior domain whose genesis depends on DM cells in a non-cell-autonomous fashion.

Glypican-3 modulates inhibitory Bmp2-Smad signaling to control renal development in vivo

Renal branching morphogenesis, defined as growth and branching of the ureteric bud (UB), is a tightly regulated process controlled by growth factor-dependent tissue interactions. Previously, using in vitro models of branching morphogenesis, we demonstrated that BMP2 signals via its intracellular effectors, SMAD1 and SMAD4, to control UB cell proliferation and branching in a manner modulated by Glypican-3 (GPC3), a cell surface heparan sulfate proteoglycan. Here, we used loss-of-function genetic mouse models to investigate the functions of Bmp2 and Gpc3-Bmp2 interactions in vivo. Progressively greater increases in UB cell proliferation were observed in Bmp2+/-, Smad4+/-, and Bmp2+/-; Smad4+/- mice compared to Wt. This increased cell proliferation was accompanied by a significant increase in UB branching in Smad4+/- and Bmp2+/-;Smad4+/- mice compared to Wt. Reduction of Gpc3 gene dosage also increased UB cell proliferation, an effect that was enhanced in Gpc3+/-;Bmp2+/- mice to an extent greater than the sum of that observed in Gpc3+/- and Bmp2+/- mice. Reduction of both Gpc3 and Bmp2 gene dosage enhanced cell proliferation in the metanephric mesenchyme compared to Wt, an effect not observed in either Bmp2+/- or Gpc3+/- mice. Phosphorylation of SMAD1, a measure of SMAD1 activation, was progressively decreased in Gpc3+/- and Gpc3+/-;Bmp2+/- mice compared to Wt, suggesting that Gpc3 stimulates Bmp2-dependent SMAD signaling in vivo. These results demonstrate that BMP2-SMAD signaling, modulated by GPC3, inhibits renal branching morphogenesis in vivo.

Depletion of Bmp2, Bmp4, Bmp7 and Spemann organizer signals induces massive brain formation in Xenopus embryos

To address the patterning function of the Bmp2, Bmp4 and Bmp7 growth factors, we designed antisense morpholino oligomers (MO) that block their activity in Xenopus laevis. Bmp4 knockdown was sufficient to rescue the ventralizing effects caused by loss of Chordin activity. Double Bmp4 and Bmp7 knockdown inhibited tail development. Triple Bmp2/Bmp4/Bmp7 depletion further compromised trunk development but did not eliminate dorsoventral patterning. Unexpectedly, we found that blocking Spemann organizer formation by UV treatment or beta-Catenin depletion caused BMP inhibition to have much more potent effects, abolishing all ventral development and resulting in embryos having radial central nervous system (CNS) structures. Surprisingly, dorsal signaling molecules such as Chordin, Noggin, Xnr6 and Cerberus were not re-expressed in these embryos. We conclude that BMP inhibition is sufficient for neural induction in vivo, and that in the absence of ventral BMPs, Spemann organizer signals are not required for brain formation.

Computer-based detection of neonatal changes to branching morphogenesis reveals different mechanisms of and predicts prostate enlargement in mice haplo-insufficient for bone morphogenetic protein 4

Early changes to branching morphogenesis of the prostate are believed to lead to enlargement of the gland in adult life. However, it has not been possible to demonstrate directly that alterations to branching during the developmental period have a permanent effect on adult prostate size. In order to examine branching morphogenesis in a quantitative manner in neonatal mice, a combination of imaging and computational technology was used to detect and quantify branching using bone morphogenetic protein 4 haplo-insufficient mice that develop enlarged prostate glands in adulthood. Accurate estimates were made of six parameters of branching, including prostate ductal length and volume and number of main ducts, branches, branch points, and tips. The results show that the prostate is significantly larger on day 3, well before the emergence of the phenotype in older animals. The ventral prostate is enlarged because the number of main epithelial ducts is increased; enlargement of the anterior prostate in mutant animals occurs because there are more branches. These lobe-specific mechanisms underlying prostate enlargement indicate the complex nature of gland pathology in mice, rather than a simple increase in weight or volume. This method provides a powerful means to investigate the aetiology of prostate disease in animal models prior to emergence of a phenotype in later life.

The docking protein FRS2alpha is an essential component of multiple fibroblast growth factor responses during early mouse development

The docking protein FRS2alpha is a major mediator of fibroblast growth factor (FGF) signaling. However, the physiological role of FRS2alpha in vivo remains unknown. In this report, we show that Frs2alpha-null mouse embryos have a defect in anterior-posterior (A-P) axis formation and are developmentally retarded, resulting in embryonic lethality by embryonic day 8. We demonstrate that FRS2alpha is essential for the maintenance of self-renewing trophoblast stem (TS) cells in response to FGF4 in the extraembryonic ectoderm (ExE) that gives rise to tissues of the placenta. By analyzing chimeric embryos, we found that FRS2alpha also plays a role in cell movement through the primitive streak during gastrulation. In addition, experiments are presented demonstrating that Bmp4 expression in TS cells is controlled by mitogen-activated protein kinase-dependent FGF4 stimulation. Moreover, both the expression of Bmp4 in ExE and activation of Smad1/5 in epiblasts are reduced in Frs2alpha-null embryos. These experiments underscore the critical role of FRS2alpha in mediating multiple processes during embryonic development and reveal a potential new link between FGF and Bmp4 signaling pathways in early embryogenesis.

Developmental failure of phalanges in the absence of growth/differentiation factor 5

Growth/differentiation factor 5 (GDF5) is a member of the bone morphogenetic protein (BMP) family, which has been implicated in several skeletogenic events including cartilage and bone formation. To study the role of GDF5, we analyzed digit development in brachypodism (bp) mice, which carry functional null mutations of the Gdf5 gene and exhibit a reduction in the length of digit bones and loss of the middle phalanges. In situ detection of apoptosis and whole-mount detection of cell death showed abnormal apoptosis in the developing phalanges of bp mice. In situ hybridization in bp mice showed overexpression of Gdf5 mRNA in the developing phalanges where apoptotic cells were increased. In addition, bp mice exhibited excessive apoptosis in the interdigital regions. The condensed mesenchymal cells were progressively decreased in the developing phalanges and failed to form cartilage models of the middle phalanges. These findings show that excessive apoptosis in the absence of GDF5 results in developmental failure of the phalanges. We conclude that GDF5 is essential for maintenance and growth of the developing phalanges.

Collagen and proteoglycan abnormalities in the GDF-5-deficient mice and molecular changes when treating disk cells with recombinant growth factor

STUDY DESIGN

A magnetic resonance image, histologic, biochemical, and gene expression study was conducted to characterize the effects of growth and development factor-5 (GDF-5) deficiency on the health of the intervertebral disc.

OBJECTIVE

To determine the effect of GDF-5 deficiency on extracellular matrix and gene expression on the intervertebral disc.

SUMMARY OF BACKGROUND DATA

Developmental and degenerative changes in intervertebral disc are not fully understood. Molecular abnormalities and spontaneous mutations that lead to the deficiency in a normal protein have been useful in understanding the function of certain molecules and the role they play in the structure and health of certain tissues. Although the role of GDF-5 in the disc has not been elucidated, this factor may have an important role in the disc as a result of the well-documented effect of GDF-5 in other chondrogenic tissues. METHODS.: Intervertebral discs of 20-week-old GDF-5 (-/-) and (+/+) mice were examined radiographically, histologically, biochemically, and with gene expression studies. Cells isolated from GDF-5-deficient mouse discs were treated with recombinant GDF-5 and gene expression was subsequently analyzed.

RESULTS

GDF-5 (-/-) mice demonstrated significantly lower T2-weighted signal intensity in the central region of their lumbar discs, and disc histology revealed loss of the normal lamellar architecture of the anulus fibrosus and a shrunken, disorganized nucleus pulposus. Biochemical analysis revealed decreased proteoglycan content but no appreciable change in total collagen content of the discs. Significant downregulation of both aggrecan and type II collagen mRNA, without an appreciable change in type I collagen expression, was noted on gene expression studies. Recombinant GDF-5 treatment of disc cells from the GDF-5-deficient mice resulted in a dose-dependent upregulation of the aggrecan and type II collagen genes.

CONCLUSION

The intervertebral disc is markedly affected by GDF-5 deficiency. This relatively simple (single gene) system with a known molecular defect may be useful in studies designed to define the response of the intervertebral disc to treatment with growth factor in vivo.

Altered hypertrophic chondrocyte kinetics in GDF-5 deficient murine tibial growth plates

The growth/differentiation factors (GDFs) are a subgroup of the bone morphogenetic proteins best known for their role in joint formation and chondrogenesis. Mice deficient in one of these signaling proteins, GDF-5, exhibit numerous skeletal abnormalities, including shortened limb bones. The primary aim of this study was determine whether GDF-5 deficiency would alter the growth rate in growth plates from the long bones in mice and, if so, how this is achieved. Stereologic and cell kinetic parameters in proximal tibial growth plates from 5-week-old female GDF-5 -/- mice and control littermates were examined. GDF-5 deficiency resulted in a statistically significant reduction in growth rate (-14%, p=0.03). The effect of genotype on growth rate was associated with an altered hypertrophic phase duration, with hypertrophic cells from GDF-5 deficient mice exhibiting a significantly longer phase duration compared to control littermates (+25%, p=0.006). These data suggest that one way in which GDF-5 might modulate the rate of endochondral bone growth could be by affecting the duration of the hypertrophic phase in growth plate chondrocytes.

Bmp4 signaling is required for outflow-tract septation and branchial-arch artery remodeling

The Bmp4 signaling molecule is expressed in ventral splanchnic and branchial-arch mesoderm and outflow-tract (OFT) myocardium, suggesting a role for Bmp4 in OFT development. Inactivation of Bmp4 in the caudal branchial arch and splanchnic mesoderm and OFT myocardium by using a conditional null allele of Bmp4 and the Nkx2.5cre recombinase allele resulted in abnormal morphogenesis of branchial-arch arteries (BAAs) and defective OFT septation. Expression of aortic-sac myocardial markers was reduced and expression of the sm22LacZ transgene, a smooth-muscle marker, was attenuated in BAAs and conotruncus of Nkx2.5cre; Bmp4 conditional mutants. Moreover, we found tissue-specific functions for Bmp4 in the regulation of cellular proliferation and apoptosis. We also demonstrate a strong genetic interaction between Bmp4 and Bmp7 in OFT development. Our findings uncover a previously uncharacterized function for Bmp4 in vascular remodeling of the BAAs, and they show definitively that Bmp4, in cooperation with Bmp7, has a central role in OFT septation.

Multiple Effects of GDF-5 Deficiency on Skeletal Tissues: Implications for Therapeutic Bioengineering

The growth/differentiation factors (GDFs) are a subfamily of the highly conserved group of bone morphogenetic protein (BMP) signaling molecules known to play a diverse set of roles in the skeletal system. GDFs 5, 6, and 7 in particular have been grouped together on the basis of the high degree of amino acid sequence homology in the C-terminal signaling region of these proteins. The existence of several naturally occurring and engineered mouse models with functional null mutations in these GDFs has led to a variety of investigations into the effects of GDF deficiency on skeletal tissues and processes. The best characterized of these models to date is the GDF-5-deficient brachypod (bp) mouse. In this paper, a comprehensive review of the studies performed on the bp mouse is provided in an effort to elucidate implications for potential therapeutic bioengineering applications using GDF-5. On the basis of the available evidence to date, GDF-5 may hold promise as a possible therapeutic agent for applications involving tendon/ligament repair as well as perhaps intervertebral disk degeneration, cartilage repair, and bone augmentation, although further detailed interventional studies will be required to investigate these potential applications.

Inactivation of mouse Twisted gastrulation reveals its role in promoting Bmp4 activity during forebrain development

Twisted gastrulation (Tsg) is a secreted protein that regulates Bmp signaling in the extracellular space through its direct interaction with Bmp/Dpp and Chordin (Chd)/Short gastrulation (Sog). The ternary complex of Tsg/Chd/Bmp is cleaved by the metalloprotease Tolloid (Tld)/Xolloid (Xld). Studies in Drosophila, Xenopus and zebrafish suggest that Tsg can act both as an anti-Bmp and as a pro-Bmp. We have analyzed Tsgloss-of-function in the mouse. Tsg homozygous mutants are viable but of smaller size and display mild vertebral abnormalities and osteoporosis. We provide evidence that Tsg interacts genetically with Bmp4. When only one copy of Bmp4 is present, a requirement of Tsgfor embryonic development is revealed. Tsg-/-;Bmp4+/- compound mutants die at birth and display holoprosencephaly, first branchial arch and eye defects. The results show that Tsg functions to promote Bmp4 signaling during mouse head development.

GDF-5 deficiency in mice delays Achilles tendon healing

The aim of this study was to examine the role of one of the growth/differentiation factors, GDF-5, in the process of tendon healing. Specifically, we tested the hypothesis that GDF-5 deficiency in mice would result in delayed Achilles tendon repair. Using histologic, biochemical, and ultrastructural analyses, we demonstrate that Achilles tendons from 8-week-old male GDF-5 -/- mice exhibit a short-term delay of 1-2 weeks in the healing process compared to phenotypically normal control littermates. Mutant animals took longer to achieve peak cell density, glycosaminoglycan content, and collagen content in the repair tissue, and the time course of changes in collagen fibril size was also delayed. Revascularization was delayed in the mutant mice by 1 week. GDF-5 deficient Achilles tendons also contained significantly more fat within the repair tissue at all time points examined, and was significantly weaker than control tissue at 5 weeks after surgery, but strength differences were no longer detectable by 12-weeks. Together, these data support the hypothesis that GDF-5 may play an important role in modulating tendon repair, and are consistent with previously posited roles for GDF-5 in cell recruitment, migration/adhesion, differentiation, proliferation, and angiogenesis.

The ventralized ogon mutant phenotype is caused by a mutation in the zebrafish homologue of Sizzled, a secreted Frizzled-related protein

The BMP signaling pathway plays a key role during dorsoventral pattern formation of vertebrate embryos. In zebrafish, all cloned mutants affecting this process are deficient in members of the BMP pathway. In a search for factors differentially expressed in swirl/bmp2b mutants compared with wild type, we isolated zebrafish Sizzled, a member of the secreted Frizzled-related protein family and putative Wnt inhibitor. The knockdown of sizzled using antisense morpholino phenocopied the ventralized mutant ogon (formerly also known as mercedes and short tail). By sequencing and rescue experiments, we demonstrate that ogon encodes sizzled. Overexpression of sizzled, resulting in strongly dorsalized phenotypes, and the expression domains of sizzled in wild type embryos, localized in the ventral side during gastrulation and restricted to the posterior end during segmentation stages, correlate with its role in dorsoventral patterning. The expanded expression domain of sizzled in ogon and chordino together with its downregulation in swirl suggests a BMP2b-dependent negative autoregulation of sizzled. Indicating a novel role for a secreted Frizzled-related protein, we show that, in addition to the BMP pathway, a component of the Wnt signaling pathway is required for dorsoventral pattern formation in zebrafish.

A role for BMP heterodimers in roof plate-mediated repulsion of commissural axons

During spinal cord development, commissural neurons extend their axons ventrally, away from the roof plate. The roof plate is the source of a diffusible repellent that orients commissural axons in vitro and, thus, may regulate the trajectory of commissural axons in vivo. Of three Bmps expressed in the roof plate, BMP7, but not BMP6 or GDF7, mimics the roof plate activity in vitro. We show here that expression of both Bmp7 and Gdf7 by roof plate cells is required for the fidelity of commissural axon growth in vivo. We also demonstrate that BMP7 and GDF7 heterodimerize in vitro and that, under these conditions, GDF7 enhances the axon-orienting activity of BMP7. Our findings suggest that a GDF7:BMP7 heterodimer functions as a roof plate-derived repellent that establishes the initial ventral trajectory of commissural axons.

Disruption of sonic hedgehog signaling alters growth and patterning of lingual taste papillae

Taste buds on the anterior part of the tongue develop in conjunction with epithelial-mesenchymal specializations in the form of gustatory (taste) papillae. Sonic hedgehog (Shh) and Bone Morphogenetic Protein 4 (BMP4) are expressed in developing taste papillae, but the roles of these signaling molecules in specification of taste bud progenitors and in papillary morphogenesis are unclear. We show here that BMP4 is not expressed in the early tongue, but is precisely coexpressed with Shh in papillary placodes, which serve as a signaling center for both gustatory and papillary development. To elucidate the role of Shh, we used an in vitro model of mouse fungiform papillary development to determine the effects of two functional inhibitors of Shh signaling: anti-Shh (5E1) antibody and cyclopamine. Cultured E11.5 tongue explants express Shh and BMP4(LacZ) in a pattern similar to that of intact embryos, localizing to developing papillary placodes after 2 days in culture. Tongues cultured with 5E1 antibody continue to express these genes in papillary patterns but develop more papillae that are larger and closer together than in controls. Tongues cultured with cyclopamine have a dose-dependent expansion of Shh and BMP4(LacZ) expression domains. Both antibody-treated and cyclopamine-treated tongue explants also are smaller than controls. Taken together, these results suggest that, although Shh is not involved in the initial specification of papillary placodes, Shh does play two key roles during pmcry development: (1) as a morphogen that directs cells toward a nonpapillary fate, and (2) as a mitogen, causing expansion of the interplacodal epithelium and underlying mesenchyme.