Immunohistochemical expression of Smads 1-6 in the 15-day gestation mouse embryo: signaling by BMPs and TGF-betas

SMAD2 regulates testicular development and testosterone synthesis in Hu sheep

The SMAD protein family plays crucial roles in reproduction as a downstream target genes of the TGFβ signaling pathway. Many studies have focused on the expression change exploration of SMADs during testicular development and investigation of SMAD2 in hormone synthesis regulation. However, little attention has been given to determining the regulatory mechanism of SMADs in sheep testes. In the present study, we first detected SMAD mRNA expression levels in three-month-old (3 M), six-month-old (6 M), nine-month-old (9 M) and two-year-old (2Y) sheep testes. Different SMADs showed various expression patterns. In addition, the subcellular localization of SMAD2 was also analyzed, and Sertoli cells (SCs), Leydig cells (LCs) and spermatogonia presented mainly positive staining. Protein and nucleic acid sequence alignment showed that the SMAD2 gene was extremely homologous between various species. SMAD2 interference RNA was transfected into sheep LCs to examine the cell proliferation and hormone levels. The testosterone level was significantly decreased, and cell proliferation efficiency presented the same trend (P < 0.05). Moreover, SMAD2 downregulation promoted cell apoptosis (P < 0.05) and changed the cell cycle. In total, our results revealed that downregulating the expression of SMAD2 can effectively inhibit testosterone levels by affecting cell proliferation and apoptosis.

SMADS-Mediate Molecular Mechanisms in Sjögren's Syndrome

There is considerable interest in delineating the molecular mechanisms of action of transforming growth factor-β (TGF-β), considered as central player in a plethora of human conditions, including cancer, fibrosis and autoimmune disease. TGF-β elicits its biological effects through membrane bound serine/threonine kinase receptors which transmit their signals via downstream signalling molecules, SMADs, which regulate the transcription of target genes in collaboration with various co-activators and co-repressors. Until now, therapeutic strategy for primary Sjögren’s syndrome (pSS) has been focused on inflammation, but, recently, the involvement of TGF-β/SMADs signalling has been demonstrated in pSS salivary glands (SGs) as mediator of the epithelial-mesenchymal transition (EMT) activation. Although EMT seems to cause pSS SG fibrosis, TGF-β family members have ambiguous effects on the function of pSS SGs. Based on these premises, this review highlights recent advances in unravelling the molecular basis for the multi-faceted functions of TGF-β in pSS that are dictated by orchestrations of SMADs, and describe TGF-β/SMADs value as both disease markers and/or therapeutic target for pSS.

Molecular characterization of two distinct Smads gene and their roles in the response to bacteria change and wound healing from Hyriopsis cumingii

The proteins of Smad family are critical components of the TGF-β superfamily signal pathway. In this paper, we cloned two intracellular mediators of TGF-β signaling, Smad3 and Smad5, from the pearl mussel Hyriopsis cumingii. The full length cDNA of HcSmad3 and HcSmad5 were 2052 bp and 1908 bp and encoded two polypeptides of 418 and 461amino acid residues, respectively. The deduced amino acid of HcSmad3 and HcSmad5 possessed two putative conserved domains, MH1 and MH2, a conserved phosphorylation motif SSXS at the carboxyl-terminal. The two Smad genes were detected muscle, mantle, hepatopancreas and gill, but with a very low level in heamocytes. The transcripts of Smad3 and Smad5 were up-regulated in hemocytes and hepatopancreas after A. hydrophila and PGN stimulation. However, the expression of Smad3 and Smad5 were only up-regulated in hepatopancreas after A. hydrophila stimulation. The transcripts of Smad3 and Smad5 had a slight change in hepatopancreas after PGN stimulation. The transcripts of HcSmad3 showed very little increase and HcSmad5 mRNA significantly up-regulated after wounding.

Sensing relative signal in the Tgf-β/Smad pathway

How signaling pathways function reliably despite cellular variation remains a question in many systems. In the transforming growth factor-β (Tgf-β) pathway, exposure to ligand stimulates nuclear localization of Smad proteins, which then regulate target gene expression. Examining Smad3 dynamics in live reporter cells, we found evidence for fold-change detection. Although the level of nuclear Smad3 varied across cells, the fold change in the level of nuclear Smad3 was a more precise outcome of ligand stimulation. The precision of the fold-change response was observed throughout the signaling duration and across Tgf-β doses, and significantly increased the information transduction capacity of the pathway. Using single-molecule FISH, we further observed that expression of Smad3 target genes (ctgf, snai1, and wnt9a) correlated more strongly with the fold change, rather than the level, of nuclear Smad3. These findings suggest that some target genes sense Smad3 level relative to background, as a strategy for coping with cellular noise.

GATA-dependent transcriptional and epigenetic control of cardiac lineage specification and differentiation

Heart progenitor cells differentiate into various cell types including pacemaker and working cardiomyocytes. Cell-type specific gene expression is achieved by combinatorial interactions between tissue-specific transcription factors (TFs), co-factors, and chromatin remodelers and DNA binding elements in regulatory regions. Dysfunction of these transcriptional networks may result in congenital heart defects. Functional analysis of the regulatory DNA sequences has contributed substantially to the identification of the transcriptional network components and combinatorial interactions regulating the tissue-specific gene programs. GATA TFs have been identified as central players in these networks. In particular, GATA binding elements have emerged as a platform to recruit broadly active histone modification enzymes and cell-type-specific co-factors to drive cell-type-specific gene programs. Here, we discuss the role of GATA factors in cell fate decisions and differentiation in the developing heart.

Smad1 expression in follicular lymphoma

BACKGROUND

Follicular lymphomas present with various immunohistologic patterns. The immunohistochemical markers used in the diagnosis of follicular lymphoma show variable degrees of sensitivity and specificity, and thus, additional germinal center markers are required. Smad1 has been reported to be overexpressed in follicular lymphoma, but little is known regarding the expression patterns of Smad proteins in human lymphoid tissue.

METHODS

In the present study, we performed immunohistochemistry for traditional germinal center markers and for Smad1 in human reactive lymphoid and follicular lymphoma tissues to investigate Smad1's usefulness in the diagnosis of follicular lymphoma.

RESULTS

In the reactive germinal centers, most cells were positive for Smad1. Among the 27 follicular lymphoma cases, 17 of 21 (80%) were Smad1 positive, 17 of 27 (63%) were positive for CD10, and 23 of 27 (85%) were positive for Bcl6. Notably, three cases expressed CD10 only, and one only expressed Bcl6. All these cases were grade 3 tumors and showed follicular and diffuse growth patterns.

CONCLUSIONS

These results indicate that Smad1 is a candidate as a germinal center marker. Furthermore, they suggest that the Smad signaling pathway might be involved in follicular lymphoma.

BMP-FGF signaling axis mediates Wnt-induced epidermal stratification in developing mammalian skin

Epidermal stratification of the mammalian skin requires proliferative basal progenitors to generate intermediate cells that separate from the basal layer and are replaced by post-mitotic cells. Although Wnt signaling has been implicated in this developmental process, the mechanism underlying Wnt-mediated regulation of basal progenitors remains elusive. Here we show that Wnt secreted from proliferative basal cells is not required for their differentiation. However, epidermal production of Wnts is essential for the formation of the spinous layer through modulation of a BMP-FGF signaling cascade in the dermis. The spinous layer defects caused by disruption of Wnt secretion can be restored by transgenically expressed Bmp4. Non-cell autonomous BMP4 promotes activation of FGF7 and FGF10 signaling, leading to an increase in proliferative basal cell population. Our findings identify an essential BMP-FGF signaling axis in the dermis that responds to the epidermal Wnts and feedbacks to regulate basal progenitors during epidermal stratification.

Epidermis, a thin layer of stratified epithelium forming the outmost surface of the skin, provides the crucial function to protect animals from environmental insults, such as bacterial pathogens and water loss. This barrier function is established in embryogenesis, during which single layered epithelial cells differentiate into distinct layers of keratinocytes. Many human genetic diseases are featured with epidermal disruption, affecting at least one in five patients. Skin regeneration and future therapeutics require a thorough understanding of the molecular mechanisms underlying epidermal stratification. Wnt ligands have been implicated in hair follicle induction during skin development and self-renewal of stem cells in the interfollicular epidermis of adult skin; however, little is known about the mechanism of how Wnt signaling controls epidermal stratification during embryogenesis. In this study, by using a genetic mouse model to disrupt Wnt production in skin development, we found that signaling of epidermal Wnt in the dermis initiate mesenchymal responses by activating a Bone Morphogenetic Protein (BMP) and Fibroblast growth factor (FGF) signaling cascade, and this activation is required for feedback regulations in the embryonic epidermis to control stratification. Our findings identify a genetic hierarchy of signaling essential for epidermal-mesenchymal interactions, and promote our understanding of mammalian skin development.

Activin A prevents neuron-like PC12 cell apoptosis after oxygen-glucose deprivation

In this study, PC12 cells were induced to differentiate into neuron-like cells using nerve growth factor, and were subjected to oxygen-glucose deprivation. Cells were treated with 0, 10, 20, 30, 50, 100 ng/mL exogenous Activin A. The 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl tetrazolium bromide assay and Hoechst 33324 staining showed that the survival percentage of PC12 cells significantly decreased and the rate of apoptosis significantly increased after oxygen-glucose deprivation. Exogenous Activin A significantly increased the survival percentage of PC12 cells in a dose-dependent manner. Reverse transcription-PCR results revealed a significant increase in Activin receptor IIA, Smad3 and Smad4 mRNA levels, which are key sites in the Activin A/Smads signaling pathway, in neuron-like cells subjected to oxygen-glucose deprivation, while mRNA expression of the apoptosis-regulation gene caspase-3 decreased. Our experimental findings indicate that exogenous Activin A plays an anti-apoptotic role and protects neurons by means of activating the Activin A/Smads signaling pathway.

GATA-dependent regulatory switches establish atrioventricular canal specificity during heart development

The embryonic vertebrate heart tube develops an atrioventricular canal that divides the atrial and ventricular chambers, forms atrioventricular conduction tissue and organizes valve development. Here we assess the transcriptional mechanism underlying this localized differentiation process. We show that atrioventricular canal-specific enhancers are GATA-binding site-dependent and act as switches that repress gene activity in the chambers. We find that atrioventricular canal-specific gene loci are enriched in H3K27ac, a marker of active enhancers, in atrioventricular canal tissue and depleted in H3K27ac in chamber tissue. In the atrioventricular canal, Gata4 activates the enhancers in synergy with Bmp2/Smad signalling, leading to H3K27 acetylation. In contrast, in chambers, Gata4 cooperates with pan-cardiac Hdac1 and Hdac2 and chamber-specific Hey1 and Hey2, leading to H3K27 deacetylation and repression. We conclude that atrioventricular canal-specific enhancers are platforms integrating cardiac transcription factors, broadly active histone modification enzymes and localized co-factors to drive atrioventricular canal-specific gene activity.

The atrioventricular canal partitions the developing vertebrate heart. Here, the authors show that the cardiac transcription factor Gata4 together with histone modification enzymes and localized co-factors binds atrioventricular canal-specific enhancers, thereby repressing gene activity in the cardiac chambers.

Resolving tumor heterogeneity: genes involved in chordoma cell development identified by low-template analysis of morphologically distinct cells

The classical sacrococcygeal chordoma tumor presents with a typical morphology of lobulated myxoid tumor tissue with cords, strands and nests of tumor cells. The population of cells consists of small non-vacuolated cells, intermediate cells with a wide range of vacuolization and large heavily vacuolated (physaliferous) cells. To date analysis was only performed on bulk tumor mass because of its rare incidence, lack of suited model systems and technical limitations thereby neglecting its heterogeneous composition. We intended to clarify whether the observed cell types are derived from genetically distinct clones or represent different phenotypes. Furthermore, we aimed at elucidating the differences between small non-vacuolated and large physaliferous cells on the genomic and transcriptomic level. Phenotype-specific analyses of small non-vacuolated and large physaliferous cells in two independent chordoma cell lines yielded four candidate genes involved in chordoma cell development. UCHL3, coding for an ubiquitin hydrolase, was found to be over-expressed in the large physaliferous cell phenotype of MUG-Chor1 (18.7-fold) and U-CH1 (3.7-fold) cells. The mannosyltransferase ALG11 (695-fold) and the phosphatase subunit PPP2CB (18.6-fold) were found to be up-regulated in large physaliferous MUG-Chor1 cells showing a similar trend in U-CH1 cells. TMEM144, an orphan 10-transmembrane family receptor, yielded contradictory data as cDNA microarray analysis showed up- but RT-qPCR data down-regulation in large physaliferous MUG-Chor1 cells. Isolation of few but morphologically identical cells allowed us to overcome the limitations of bulk analysis in chordoma research. We identified the different chordoma cell phenotypes to be part of a developmental process and discovered new genes linked to chordoma cell development representing potential targets for further research in chordoma tumor biology.

Progesterone receptor activates Msx2 expression by downregulating TNAP/Akp2 and activating the Bmp pathway in EpH4 mouse mammary epithelial cells

Previously we demonstrated that EpH4 mouse mammary epithelial cells induced the homeobox transcription factor Msx2 either when transfected with the progesterone receptor (PR) or when treated with Bmp2/4. Msx2 upregulation was unaffected by Wnt inhibitors s-FRP or Dkk1, but was inhibited by the Bmp antagonist Noggin. We therefore hypothesized that PR signaling to Msx2 acts through the Bmp receptor pathway. Herein, we confirm that transcripts for Alk2/ActR1A, a non-canonical BmpR Type I, are upregulated in mammary epithelial cells overexpressing PR (EpH4-PR). Increased phosphorylation of Smads 1,5, 8, known substrates for Alk2 and other BmpR Type I proteins, was observed as was their translocation to the nucleus in EpH4-PR cells. Analysis also showed that Tissue Non-Specific Alkaline Phosphatase (TNAP/Akp2) was also found to be downregulated in EpH4-PR cells. When an Akp2 promoter-reporter construct containing a ½PRE site was transfected into EpH4-PR cells, its expression was downregulated. Moreover, siRNA mediated knockdown of Akp2 increased both Alk2 and Msx2 expression. Collectively these data suggest that PR inhibition of Akp2 results in increased Alk2 activity, increased phosphorylation of Smads 1,5,8, and ultimately upregulation of Msx2. These studies imply that re-activation of the Akp2 gene could be helpful in downregulating aberrant Msx2 expression in PR+ breast cancers.

Smad1/Smad5 signaling in limb ectoderm functions redundantly and is required for interdigital programmed cell death

Bone morphogenetic proteins (BMPs) are secreted signals that regulate apical ectodermal ridge (AER) functions and interdigital programmed cell death (PCD) of developing limb. However the identities of the intracellular mediators of these signals are unknown. To investigate the role of Smad proteins in BMP-regulated AER functions in limb development, we inactivated Smad1 and Smad5 selectively in AER and ventral ectoderm of developing limb, using Smad1 or/and Smad5 floxed alleles and an En1(Cre/+) knock-in allele. Single inactivation of either Smad1 or Smad5 did not result in limb abnormalities. However, the Smad1/Smad5 double mutants exhibited syndactyly due to a reduction in interdigital PCD and an increase in interdigital cell proliferation. Cell tracing experiments in the Smad1/Smad5 double mutants showed that ventral ectoderm became thicker and the descendents of ventral En1(Cre/+) expressing ectodermal cells were located at dorsal interdigital regions. At the molecular level, Fgf8 expression was prolonged in the interdigital ectoderm of embryonic day (E) 13 Smad1/Smad5 double mutants, suggesting that the ectopic Fgf8 expression may serve as a survival signal for interdigital epithelial and mesenchymal cells. Our result suggests that Smad1 and Smad5 are required and function redundantly as intracellular mediators for BMP signaling in the AER and ventral ectoderm. Smad1/Smad5 signaling in the AER and ventral ectoderm regulates interdigital tissue regression of developing limb. Our mutants with defects in interdigital PCD could also serve as a valuable model for investigation of PCD regulation machinery.

CD47 regulates the TGF-β signaling pathway in osteoblasts and is distributed in Meckel's cartilage

Previously, CD47 gene expression has been shown to increase during mandible development using a micro array technique. To determine the function of CD47 in osteoblasts, CD47 was silenced using siRNA in vitro. The TGF-β1 and phosphorylated-Smad2 levels and transcription factor genes related to bone metabolism increased dose-dependently with CD47 silencing. Furthermore, we determined the distribution of CD47 in mouse embryonic E13 and E15 in vivo. The CD47-positive cells were localized in Meckel's cartilage and antenatal mandibular bone. These results suggest that TGF-β1 signaling and mandible development might be regulated by CD47.

Control of the bone morphogenetic protein 7 gene in developmental and adult life

The TGFβ superfamily growth factor BMP7 performs essential biological functions in embryonic development and regeneration of injured tissue in the adult. BMP7 activity is regulated at numerous levels in the signaling pathway by the expression of extracellular antagonists, decoy receptors and inhibitory cell signaling components. Additionally, expression of the BMP7 gene is tightly controlled both during embryonic development and adult life. In this review, the current status of work on regulation of BMP7 at the genomic level is discussed. In situ hybridization and reporter gene studies have conclusively defined patterns of BMP7 expression in many tissues. Additionally, both in vivo and cell culture studies have defined some of the mechanistic bases for this regulation. In addition to transcriptional activation mediated by binding of activating transcription factors, there is also strong evidence for repression through recruitment of histone modifying enzymes to specific genetic elements. This review summarizes our current understanding of BMP7 gene regulation in embryonic development and adult tissues.

Smad6 promotes neuronal differentiation in the intermediate zone of the dorsal neural tube by inhibition of the Wnt/beta-catenin pathway

Proliferation of the neural/neuronal progenitor cells (NPCs) at the ventricular zone of the dorsal spinal cord requires the stimuli of Wnt and bone morphogenic protein (BMP). However, how these two signaling pathways are regulated to initiate differentiation in the NPCs as they enter the intermediate zone is not known. Here, we show that Smad6, a negative regulator of BMP signaling, is expressed in the intermediate zone of the chick dorsal spinal cord. Knockdown experiments show that Smad6 is required for promoting NPCs to exit the cell cycle and differentiate into neurons. Although we find that Smad6 inhibits BMP signaling, as expected, we also find that Smad6 unexpectedly inhibits the Wnt/β-catenin pathway. The inhibition of the Wnt/β-catenin pathway by Smad6 is independent of its effect on the BMP pathway. Rather, Smad6 through its N-terminal domain and link region enhances the interaction of C-terminal binding protein with the β-catenin/T cell factor (TCF) complex and the TCF-binding element to inhibit β-catenin-mediated transcriptional activation. Our study provides evidence that transition of NPCs from a proliferative state to a differentiating state is controlled by the dual inhibitory role of Smad6 to both BMP and Wnt signaling at the level of transcription.

Inhibitory Smads differentially regulate cell fate specification and axon dynamics in the dorsal spinal cord

The roof plate resident BMPs have sequential functions in the developing spinal cord, establishing cell fate and orienting axonal trajectories. These activities are, however, restricted to the dI1-dI3 neurons in the most dorsal region of the spinal cord. What limits the extent of the action of the BMPs to these neurons? To address this question, we have examined both the distribution of the inhibitory Smads (I-Smads), Smad6 and Smad7 in the spinal cord and the consequence of ectopically expressing the I-Smads in chicken embryos. Our studies suggest that the I-Smads function in vivo to restrict the action of BMP signaling in the dorsal spinal cord. Moreover, the I-Smads have distinct roles in regulating the diverse activities of the BMPs. Thus, the ectopic expression of Smad7 suppresses the dI1 and dI3 neural fates and concomitantly increases the number of dI4-dI6 spinal neurons. In contrast, Smad6 most potently functions to block dI1 axon outgrowth. Taken together, these experiments suggest that the I-Smads have distinct roles in spatially limiting the response of cells to BMP signaling.

Loss of Smad5 leads to the disassembly of the apical junctional complex and increased susceptibility to experimental colitis

The regulation of intestinal epithelial cell adhesion and migratory properties is often compromised in inflammatory bowel disease (IBD). Despite an increasing interest in bone morphogenetic protein (Bmp) signaling in gut pathologies, little is known of the specific roles played by individual Smads in intestinal epithelial functions. In the present study, we generated a mouse model with deletion of Smad5 transcriptional effector of the Bmp signaling pathway exclusively in the intestinal epithelium. Proliferation, migration, and apical junctional complex (AJC) protein expression were analyzed by immunofluorescence and Western blot. Human intestinal biopsies from control and IBD patients were analyzed for SMAD5 gene transcript expression by quantitative PCR (qPCR). Smad5(ΔIEC) and control mice were subjected to dextran sulfate sodium (DSS)-induced experimental colitis, and their clinical and histological symptoms were assessed. Loss of Smad5 led to intestinal epithelial hypermigration and deregulation of the expression of claudin-1 and claudin-2. E-cadherin was found to be equally expressed but displaced from the AJC to the cytoplasm in Smad5(ΔIEC) mice. Analysis of SMAD5 gene expression in human IBD patient samples revealed a significant downregulation of the gene transcript in Crohn's disease and ulcerative colitis samples. Smad5(ΔIEC) mice exposed to experimental DSS colitis were significantly more susceptible to the disease and had impaired wound healing during the recovery phase. Our results support that Smad5 is partly responsible for mediating Bmp signals in intestinal epithelial cells. In addition, deficiency in epithelial Smad5 leads to the deregulation of cell migration by disassembling the AJC with increasing susceptibility to experimental colitis and impairment in wound healing.

Identification and expression of amphioxus AmphiSmad1/5/8 and AmphiSmad4

Smad family proteins are identified as intracellular signal mediators of the TGF-β superfamily. In this study, we identified two novel members of the Smad family, termed as AmphiSmad1/5/8 and AmphiSmad4, from Chinese amphioxus. Both AmphiSmad1/5/8 and AmphiSmad4 showed a typical domain structure of Smad proteins consisting of conserved MH1 and MH2 domains. Phylogenetic analysis placed AmphiSmad1/5/8 in the Smad1, 5 and 8 subgroup of the R-Smad subfamily, and AmphiSmad4 in the Co-Smad subfamily. The spatial and temporal gene expression patterns of AmphiSmad1/5/8 and AmphiSmad4 showed that they may be involved in the embryonic development of notochord, myotome and alimentary canal, and may help to establish the specification of dorsal-ventral axis of amphioxus. Moreover, AmphiSmad1/5/8 and AmphiSmad4 showed extensive distribution in all adult tissues examined, suggesting that these two genes may play important roles in the morphogenesis of a variety of tissues especially notochord and gonad.

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

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

All-trans-retinoic acid alters Smads expression in embryonic neural tissue of mice

Retinoic acid can cause malformations of the developing nervous system. Smad signaling is involved in embryonic development. The current study investigated all-trans-retinoic acid (ATRA)-induced alteration of Smad expression in the developing neural tubes of mice. Pregnant mice were treated with a single dose of 50 mg/kg ATRA by oral gavage on embryonic day E7. Western immunoblotting was used to examine Smads proteins, particularly phosphorylated (p-) Smad1, total Smad1 and Smad6 in the neural tissue of the embryos on E8-E11 following treatment. Results showed that ATRA treatment significantly increased expression of both p-Smad1 and total Smad1, while Smad6 was decreased in neural tissues of ATRA-exposed embryos in utero from E8 to E11, a critical period for neural tube formation. Data suggest that disruption of Smad signaling may be involved in ATRA-induced neural tube defects.

Altered expression of Smad proteins in T or NK-cell lymphomas

PURPOSE

Smad proteins mediate cellular signaling through the transforming growth factor-beta family (TGF-betas). Smads 2 and 3 transmit signals from TGF-beta, and Smad4 is a common mediator, as well. However, little is known concerning the expression patterns of Smads in lymphoid tissue.

MATERIALS AND METHODS

Immunohistochemistry for Smad3 and Smad4 was performed on paraffin-embedded tissue sections collected from 26 T- or NK-cell lymphomas.

RESULTS

Nearly all cells in germinal centers were positive for Smad3, and more than 50% of paracortical cells were positive for Smad3 in reactive lymphoid tissue. When Smad4 immunostaining was conducted, nearly all the cells in the germinal centers showed diffuse cytoplasmic staining, and most of them exhibited nuclear positivity, as well. In addition, more than 50% of the cells in the paracortex were positive for Smad4. Furthermore, the Smad3 staining pattern was preserved in all malignant lymphomas, but four of these cases (15%) exhibited decreased expression of Smad4. All lymphoblastic lymphomas showed strong positivity in most of tumor cells, but one unspecified peripheral lymphoma, two nasal NK/T cell lymphomas, and one anaplastic large cell lymphoma were negative for Smad4.

CONCLUSIONS

These results suggest that TGF-beta-specific Smads may be actively involved in signal transduction in lymphoid organs and that Smad-mediated TGF-beta signaling pathways are operative in malignant lymphoma. In addition, loss of Smad4 expression might be associated with development of some T-cell lymphomas.

Real time monitoring of BMP Smads transcriptional activity during mouse development

SUMMARY

Bone morphogenetic protein (BMP) signaling is a key pathway in the patterning and development of organisms as diverse as fruit fly and humans. However, the determination of net BMP signaling, paramount to understanding organogenesis, is limited to the analysis of fixed material. We generated a transgenic mouse that reports the transcriptional response of BMP Smad activation by coupling a well established BMP response element (BRE), isolated from the Id1 promoter, to green fluorescent protein (BRE:gfp). We monitored BMP Smad transcriptional activity in fresh and fixed BRE:gfp embryos. GFP expression was observed where expected on the basis of known signaling sites, but also in specific cell populations in which BMP signaling had been implicated but not directly demonstrated. Deletion of Smad5 reduced GFP in vivo as expected. The BRE:gfp transgenic mice are a novel tool, which will facilitate the identification of specific BMP Smad responsive cell types and allow BMP Smad signaling to be monitored in real time, supporting studies in development and disease.

An in vivo reporter of BMP signaling in organogenesis reveals targets in the developing kidney

Background

Bone morphogenetic proteins (BMPs) regulate essential processes during organogenesis, and a functional understanding of these secreted proteins depends on identification of their target cells. In this study, we generate a transgenic reporter for organogenesis studies that we use to define BMP pathway activation in the developing kidney.

Results

Mouse strains reporting on BMP pathway activation were generated by transgenically expressing β-galactosidase under the control of BMP responsive elements from Id1. Reporter expression corresponds well with immunoassays for pathway activation in all organs studied, validating the model. Using these reporters we have generated a detailed map of cellular targets of BMP signaling in the developing kidney. We find that SMAD dependent BMP signaling is active in collecting duct trunks, but not tips. Furthermore, glomerular endothelial cells, and proximal nephron tubules from the renal vesicle stage onward show pathway activation. Surprisingly, little activation is detected in the nephrogenic zone of the kidney, and in organ culture BMP treatment fails to activate SMAD dependent BMP signaling in nephron progenitor cells. In contrast, signaling is efficiently induced in collecting duct tips.

Conclusion

Transgenic reporters driven by control elements from BMP responsive genes such as Id1 offer significant advantages in sensitivity and consistency over immunostaining for studies of BMP pathway activation. They also provide opportunities for analysis of BMP signaling in organ and primary cell cultures subjected to experimental manipulation. Using such a reporter, we made the surprising finding that SMAD dependent BMP signaling is inactive in nephron progenitors, and that these cells are refractory to activation by applied growth factors. Furthermore, we find that the BMP pathway is not normally active in collecting duct tips, but that it can be ectopically activated by BMP treatment, offering a possible explanation for the inhibitory effects of BMP treatment on collecting duct growth and branching.

Immunohistochemical evaluation of phosphorylated SMAD2/SMAD3 and the co-activator P300 in human glomerulonephritis: correlation with renal injury

Background: Smad2 and Smad3 are transcription factors that mediate transforming growth factor beta (TGF-β) signals. Upon their activation, phosphorylated Smad2/Smad3 (pSmad2/Smad3), translocate to the nucleus and associate with co-activators such as p300, regulating the transcription of genes that contribute to the fibrotic processes. Methods: We investigated the immunohistochemical expression of pSmad2/Smad3 and the co-activator p300 in 152 renal biopsy specimens from patients with various types of glomerulonephritides (GNs) and in 15 normal kidney specimens. Patients’ clinical data (serum creatinine level and proteinuria) had been collected. Results: There was a dramatic increase in the expression of pSmad2/3 and p300 in all glomerular cell types in all GNs. pSmad2/3 expression was increased in all tubular segments (except for the proximal tubules in nonproliferative GNs), while p300 expression was significantly increased only in the proximal tubular cells in all GNs. Glomerular and tubular pSmad2/Smad3 and p300 were significantly increased in proliferative GNs (compared to the nonproliferative), particularly in the secondary group. The expression profile of p300 correlated positively with the expression of pSmad2/Smad3 in the diseased glomeruli and proximal tubules. pSmad2/3 and p300 were very often detected in segmental hyperplastic lesions, cellular crescents, microadhesions and segmental or global sclerotic areas. Glomerular and proximal tubular pSmad2/Smad3 was positively correlated with serum creatinine levels, while distal and collecting tubular pSmad2/3 and p300 correlated positively with tubular atrophy. Glomerular and proximal tubular pSmad2/3 expression and glomerular p300 expression correlated positively with lupus nephritis activity. Conclusion: Our results suggest that pSmad2/3-p300 pathway may play a pivotal role in the pathogenesis and progression of human glomerulonephritis.

The role of Smads in skin development

Smads are a group of signaling mediators and antagonists of the transforming growth factor-beta (TGF-beta) superfamily, responding but not limited to signaling from TGF-beta, Activin, and bone morphogenetic proteins (BMPs). As all of these three signaling pathways play important roles in skin development, we have been actively pursuing studies assessing the role of Smads in skin development. Our studies revealed that Smad-4 affects hair follicle differentiation primarily by mediating BMP signaling. Smad-7 significantly affects hair follicle development and differentiation by blocking the TGFbeta/Activin/BMP pathway and by inhibiting WNT/beta-catenin signaling via ubiquitin-mediated beta-catenin degradation. In contrast, other Smads may have redundant or dispensable functions in skin development. Here, we review the work that shows the emergence of Smad functions in skin development via traditional and novel signaling pathways.

Bone morphogenetic protein signaling in the developing kidney: present and future

Bone morphogenetic proteins (BMPs) are members of the transforming growth factor-beta superfamily. A critical role for BMP signaling in the development of the metanephric kidney is supported by a growing number of studies using in vitro assays and in vivo animal models. Here we review current knowledge of BMPs, BMP receptors and regulators of the BMP signaling pathway in the developing kidney. We highlight major gaps in our knowledge of the roles of BMP signaling in the development of the normal and abnormal kidney and identify areas and techniques likely to improve our understanding.

Cloning and expression pattern of a Smad3 homolog from the pearl oyster, Pinctada fucata

Several transforming growth factor beta (TGFbeta) superfamily members have been identified from mollusks. The significant effects of TGFbeta signaling pathways on bone formation in vertebrates give clues to the signal transduction mechanism and how the shell of oysters is formed. However, what kinds of mediators are involved in the molluscan TGFbeta signaling pathways, and how they play their functions in mollusks has not been well explained due to a lack of genomic information and the failure to establish oyster cell lines. That is, if we knew the genome sequence we could search the TGFbeta superfamily members using the blast program (http://www.ncbi.nlm.nih.gov/), and if we established the molluscan cell line, we could transfect the gene of interest to the cell and detect its influence on expression levels of other genes, such as the matrix proteins. Therefore, to investigate whether there are similar TGFbeta pathways in mollusks, many important mediators should be identified. In this paper, we report a cDNA encoding a Smad3 homolog (designated Pf-Smad3) that was isolated from the pearl oyster, Pinctada fucata. Sequence alignment showed that Pf-Smad3 contains a DNA-binding MH1 domain and a Runx2/Cbfa1-binding MH2 domain, and shares an extremely high similarity with Smad3 proteins in vertebrates. However, Smad proteins in Drosophila and Caenorhabditis elegans are very different from other Smad3 proteins. Reverse transcription-polymerase chain reaction results indicated that Pf-Smad3 mRNA was expressed ubiquitously in adult Pin. fucata and was expressed at different levels at different developmental stages. In situ hybridization results showed that Pf-Smad3 mRNA was expressed mainly at the outer epithelial cells of the middle fold and the inner epithelial cells of the outer fold, especially around the gutter. These results suggested that Pf-Smad3 might take part in many physiological processes, including biomineralization, in oysters.

Characterization of an enhancer region of the galanin gene that directs expression to the dorsal root ganglion and confers responsiveness to axotomy

Galanin expression markedly increases in the dorsal root ganglion (DRG) after sciatic nerve axotomy and modulates pain behavior and regeneration of sensory neurons. Here, we describe transgenic mice expressing constructs with varying amounts of sequence upstream of the murine galanin gene marked by LacZ. The 20 kb region upstream of the galanin gene recapitulates the endogenous expression pattern of galanin in the embryonic and adult intact DRG and after axotomy. In contrast, 1.9 kb failed to drive LacZ expression in the intact DRG or after axotomy. However, the addition of an additional 2.7 kb of 5' flanking DNA (4.6 kb construct) restored the expression in the embryonic DRG and in the adult after axotomy. Sequence analysis of this 2.7 kb region revealed unique 18 and 23 bp regions containing overlapping putative Ets-, Stat-, and Smad-binding sites, and adjacent putative Stat- and Smad-binding sites, respectively. Deletion of the 18 and 23 bp regions from the 4.6 kb construct abolished the upregulation of LacZ expression in the DRG after axotomy but did not affect expression in the embryonic or intact adult DRG. Also, a bioinformatic analysis of the upstream regions of a number of other axotomy-responsive genes demonstrated that the close proximity of putative Ets-, Stat-, and Smad-binding sites appears to be a common motif in injury-induced upregulation in gene expression.

Inhibition of Tgf beta signaling by endogenous retinoic acid is essential for primary lung bud induction

Disruption of retinoic acid (RA) signaling during early development results in severe respiratory tract abnormalities, including lung agenesis. Previous studies suggest that this might result from failure to selectively induce fibroblast growth factor 10 (Fgf10) in the prospective lung region of the foregut. Little is known about the RA-dependent pathways present in the foregut that may be crucial for lung formation. By performing global gene expression analysis of RA-deficient foreguts from a genetic [retinaldehyde dehydrogenase 2 (Raldh2)-null] and a pharmacological (BMS493-treated) mouse model, we found upregulation of a large number of Tgfbeta targets. Increased Smad2 phosphorylation further suggested that Tgfbeta signaling was hyperactive in these foreguts when lung agenesis was observed. RA rescue of the lung phenotype was associated with low levels of Smad2 phosphorylation and downregulation of Tgfbeta targets in Raldh2-null foreguts. Interestingly, the lung defect that resulted from RA-deficiency could be reproduced in RA-sufficient foreguts by hyperactivating Tgfbeta signaling with exogenous TGF beta 1. Preventing activation of endogenous Tgfbeta signaling with a pan-specific TGFbeta-blocking antibody allowed bud formation and gene expression in the lung field of both Raldh2-null and BMS493-treated foreguts. Our data support a novel mechanism of RA-Tgfbeta-Fgf10 interactions in the developing foregut, in which endogenous RA controls Tgfbeta activity in the prospective lung field to allow local expression of Fgf10 and induction of lung buds.

Inactivation of Smad5 in endothelial cells and smooth muscle cells demonstrates that Smad5 is required for cardiac homeostasis

Smads are intracellular signaling proteins that transduce signals elicited by members of the transforming growth factor (TGF)-beta superfamily. Smad5 and Smad1 are highly homologous, and they mediate primarily bone morphogenetic protein (Bmp) signals. We used the Cre-loxP system and Sm22-Cre and Tie-1-Cre mice to study the function of Smad5 in the developing blood vessel wall. Analysis of embryos demonstrated that deletion of Smad5 in endothelial or smooth muscle cells resulted in a normal organization of embryonic and extra-embryonic vasculature. Angiogenic assays performed in adult mice revealed that mutant mice display a comparable angiogenic and vascular remodeling response to control mice. In Sm22-Cre; Smad5(fl/-) mice, Smad5 is also deleted in cardiomyocytes. Echocardiographic analysis on those 9-month-old female mice demonstrated larger left ventricle internal diameters and decreased fractional shortening compared with control littermates without signs of cardiac hypertrophy. The decreased cardiac contractility was associated with a decreased performance in a treadmill experiment. In isolated cardiomyocytes, fractional shortening was significantly reduced compared with control cells. These data demonstrate that restricted deletion of Smad5 in the blood vessel wall results in viable mice. However, loss of Smad5 in cardiomyocytes leads to a mild heart defect.

Immunohistochemical evaluation of phosphorylated SMAD2/SMAD3 and the co-activator P300 in human glomerulonephritis: correlation with renal injury

BACKGROUND

Smad2 and Smad3 are transcription factors that mediate transforming growth factor beta (TGF-beta) signals. Upon their activation, phosphorylated Smad2/Smad3 (pSmad2/Smad3), translocate to the nucleus and associate with co-activators such as p300, regulating the transcription of genes that contribute to the fibrotic processes.

METHODS

We investigated the immunohistochemical expression of pSmad2/Smad3 and the co-activator p300 in 152 renal biopsy specimens from patients with various types of glomerulonephritides (GNs) and in 15 normal kidney specimens. Patients' clinical data (serum creatinine levels and proteinuria) had been collected.

RESULTS

There was a dramatic increase in the expression of pSmad2/3 and p300 in all glomerular cell types in all GNs. pSmad2/3 expression was increased in all tubular segments (except for the proximal tubules in nonproliferative GNs), while p300 expression was significantly increased only in the proximal tubular cells in all GNs. Glomerular and tubular pSmad2/Smad3 and p300 were significantly increased in proliferative GNs (compared to the nonproliferative), particularly in the secondary group. The expression profile of p300 correlated positively with the expression of pSmad2/Smad3 in the diseased glomeruli and proximal tubules. pSmad2/3 and p300 were very often detected in segmental hyperplastic lesions, cellular crescents, microadhesions and segmental or global sclerotic areas. Glomerular and proximal tubular pSmad2/Smad3 was positively correlated with serum creatinine levels, while distal and collecting tubular pSmad2/3 and p300 correlated positively with tubular atrophy. Glomerular and proximal tubular pSmad2/3 expression and glomerular p300 expression correlated positively with lupus nephritis activity.

CONCLUSION

Our results suggest that pSmad2/3-p300 pathway may play a pivotal role in the pathogenesis and progression of human glomerulonephritis.

The role of TGF-beta superfamily during T cell development: new insights

Members of the transforming growth factor beta (TGF-beta) superfamily are soluble factors that regulate a variety of functional responses including proliferation, differentiation, apoptosis and cell cycle, among others, depending not only on the cell type and its differentiation state, but also on the milieu of cytokines present. All three members of this superfamily: TGF-betas, bone morphogenetic proteins (BMPs) and Activins, have been shown to be expressed in the thymus suggesting their potential role as regulators of the T lymphocyte differentiation process. Although initial reports described the role of TGF-beta in controlling specific checkpoints during thymocyte development, recent data has provided new evidence on the role of BMPs and Activins in this process. This review provides new insights on the function of members of the TGF-beta superfamily at different stages of thymocyte development.

Smad5 is dispensable for adult murine hematopoiesis

Smad5 is known to transduce intracellular signals from bone morphogenetic proteins (BMPs), which belong to the transforming growth factor-β (TGF-β) superfamily and are involved in the regulation of hematopoiesis. Recent findings suggest that BMP4 stimulates proliferation of human primitive hematopoietic progenitors in vitro, while early progenitors from mice deficient in Smad5 display increased self-renewal capacity in murine embryonic hematopoiesis. Here, we evaluate the role of Smad5 in the regulation of hematopoietic stem cell (HSC) fate decisions in adult mice by using an inducible MxCre-mediated conditional knockout model. Surprisingly, analysis of induced animals revealed unperturbed cell numbers and lineage distribution in peripheral blood (PB), bone marrow (BM), and the spleen. Furthermore, phenotypic characterization of the stem cell compartment revealed normal numbers of primitive lin–Sca-1+c-Kit+ (LSK) cells in Smad5–/– BM. When transplanted in a competitive fashion into lethally irradiated primary and secondary recipients, Smad5-deficient BM cells competed normally with wild-type (wt) cells, were able to provide long-term reconstitution for the hosts, and displayed normal lineage distribution. Taken together, Smad5-deficient HSCs from adult mice show unaltered differentiation, proliferation, and repopulating capacity. Therefore, in contrast to its role in embryonic hematopoiesis, Smad5 is dispensable for hematopoiesis in the adult mouse.

Altered subcellular location of phosphorylated Smads in Alzheimer's disease

A number of growth factors and cytokines, such as transforming growth factor beta 1 (TGF-beta1), is elevated in Alzheimer's disease (AD), giving rise to activated intracellular mitogenic signaling cascades. Activated mitogenic signaling involving the mitogen-activated protein kinases (MAPKs) and other protein kinases might alter the phosphorylation states of structural proteins such as tau, resulting in hyperphosphorylated deposits. Many intracellular signaling proteins are potential targets of misregulated phosphorylation and dephosphorylation. Recently, a crosstalk between MAPKs and Smad proteins, both involved in mediating TGF-beta1 signaling, has been reported. Although TGF-beta1 has previously been shown to be involved in the pathogenesis of AD, the role of Smad proteins has not been investigated. In this study we thus analysed the subcellular distribution of phosphorylated Smad2 and Smad3 in the hippocampus of both normal and AD brains. Here we report on strong nuclear detection of phosphorylated Smad2 and Smad3 in neurons of control brains. In AD brains these phosphorylated proteins were additionally found in cytoplasmic granules in hippocampal neurons, within amyloid plaques and attached to neurofibrillary tangles. Our data suggest a critical role of Smad proteins in the pathogenesis of AD.

Integrin-mediated transforming growth factor-beta activation regulates homeostasis of the pulmonary epithelial-mesenchymal trophic unit

Trophic interactions between pulmonary epithelial and mesenchymal cell types, known as the epithelial-mesenchymal trophic unit (EMTU), are crucial in lung development and lung disease. Transforming growth factor (TGF)-beta is a key factor in mediating these interactions, but it is expressed in a latent form that requires activation to be functional. Using intact fetal tracheal tissue and primary cultures of fetal tracheal epithelial cells and fibroblasts, we demonstrate that a subset of integrins, alpha(v)beta(6) and alpha(v)beta(8), are responsible for almost all of the TGF-beta activation in the EMTU. Both alpha(v)beta(8) and alpha(v)beta(6) contribute to fetal tracheal epithelial activation of TGF-beta, whereas only alpha(v)beta(8) contributes to fetal tracheal fibroblast activation of TGF-beta. Interestingly, fetal tracheal epithelial alpha(v)beta(8)-mediated TGF-beta activation can be enhanced by phorbol esters, likely because of the increased activity of MT1-MMP, an essential co-factor in alpha(v)beta(8)-mediated activation of TGF-beta. Autocrine alpha(v)beta(8)-mediated TGF-beta activation by fetal tracheal fibroblasts results in suppression of both transcription and secretion of hepatocyte growth factor, which is sufficient to affect phosphorylation of the airway epithelial hepatocyte growth factor receptor, c-Met, as well as airway epithelial proliferation in a co-culture model of the EMTU. These findings elucidate the function and complex regulation of integrin-mediated activation of TGF-beta within the EMTU.

Proliferation and cornification during development of the mammalian epidermis

The skin is the largest organ of the body and consists of the underlying dermis and outer epidermis. Proper embryonic development and continual renewal of the adult epidermis are essential to provide an impenetrable barrier against fluid loss and serve as our most important defense against insults from the external environment. During mammalian embryogenesis the epidermis develops from the surface ectoderm, which initially consists of a multipotent single-layer epithelium. Once these epithelial cells receive the appropriate developmental cues, they become committed to stratify, initiate a massive expansion program, and finally embark on a journey of terminal differentiation to produce the morphologically distinct layers of the epidermis. The culmination of this journey is the formation of an impervious cornified envelope via a highly specialized form of programmed cell death, termed "cornification" (reviewed in Candi et al.), which is distinct in many ways from the classic apoptotic pathways. The epidermal developmental program that is first seen in the fetus is recapitulated for the entire life of the organism. The basal layer of adult skin harbors stem cells, which can divide to produce daughter stem cells and transit amplifying (TA) cells that go on to differentiate and cornify (reviewed in Fuchs and Raghavan). In this review we summarize current knowledge about the molecular regulation of proliferation and cornification in the developing mammalian epidermis. We focus on events in the interfollicular epidermis, with special emphasis on transcriptional regulation by p63, Notch, NF-kappaB/IKK, Hox, AP-1, AP-2, and C/EBP factors. We end with a discussion about perturbations in epidermal proliferation and cornification as they pertain to human skin pathologies.

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.

Global Analysis of Smad2/3-Dependent TGF-β Signaling in Living Mice Reveals Prominent Tissue-Specific Responses to Injury

Smad2 and Smad3 (Smad2/3) proteins are key signaling molecules for TGF-beta and some related family members regulating the transcription of several hundred genes. TGF-beta have key roles in development, tissue homeostasis, and the pathogenesis of many human diseases, including cancer, fibrotic disorders, developmental defects, and neurodegeneration. To study the temporal and spatial patterns of Smad2/3-dependent signaling in normal and pathological conditions in the living organism, we engineered transgenic mice with a Smad-responsive luciferase reporter construct (SBE-luc mice). Using bioluminescent imaging, we assessed Smad2/3 signaling activity noninvasively in living mice. At baseline, this activity was highest in brain, intestine, heart, and skin, and correlated with biochemical measurements of reporter activity. Primary astrocytes cultured from SBE-luc mice showed specific activation of the reporter in response to Smad2/3-activating TGF-beta family members. Treatment of mice with the endotoxin LPS resulted in a fast and vigorous, but transient activation of the reporter in the intestine. Although the response was similarly rapid in brain, it remained increased, indicating important but different cellular responses to endotoxin challenge in these organs. Traumatic brain injury with a needle stab resulted in local activation of Smad2/3-dependent genes and a severalfold increase in bioluminescence in living mice. SBE-luc mice can therefore be used to study temporal, tissue-specific activation of Smad2/3-dependent signaling in living mice in normal or pathological conditions as well as for the identification of endogenous or synthetic modulators of this pathway.

Unique and redundant roles of Smad3 in TGF-beta-mediated regulation of long bone development in organ culture

The most well-characterized intracellular signaling molecules for transforming growth factor-beta (TGF-beta) are the Smads. R-Smads interact with and are phosphorylated directly by the TGF-beta type I receptor. Phosphorylated R-Smads can then associate with Smad4, translocate to the nucleus and regulate transcription. Specific R-Smads transduce distinct signals for members of the TGF-beta superfamily. Smad2 and -3 mediate signaling by TGF-beta/activin, whereas Smad1, -5, and -8 mediate bone morphogenetic protein signaling. TGF-beta inhibits proliferation and hypertrophic differentiation in metatarsal organ cultures by a perichondrium-dependent mechanism. To determine the mechanism of TGF-beta signaling in the perichondrium, we tested the hypothesis that TGF-beta-restricted Smad2 and Smad3 regulate chondrocyte proliferation and differentiation in embryonic metatarsal organ cultures. Perichondrium was infected with adenoviruses containing dominant-negative forms of Smad2 (Ad-Smad2-3SA) and Smad3 (Ad-Smad3 Delta C). Proliferation and differentiation were measured in response to treatment with TGF-beta 1. Results were compared with control bones infected with a beta-galactosidase reporter virus (Ad-beta-gal). Infection with Ad-Smad2-3SA completely blocked the effects of TGF-beta 1 on metatarsal development while Ad-Smad3 Delta C only partially blocked TGF-beta 1 effects. To further characterize the role of Smad3 in long bone development, TGF-beta 1 responsiveness in cultures from Smad3(+/+) and Smad3(ex8/ex8) mice were compared. Loss of Smad3 only partially blocked the effects of TGF-beta1 on differentiation. In contrast, the effects of TGF-beta 1 on chondrocyte proliferation were blocked completely. We conclude that Smad2 signaling in the perichondrium can compensate for the loss of Smad3 to regulate inhibition of hypertrophic differentiation; however, Smad3 is required for TGF-beta 1-mediated effects on proliferation.

BMP4 and Madh5 regulate the erythroid response to acute anemia

Acute anemia initiates a systemic response that results in the rapid mobilization and differentiation of erythroid progenitors in the adult spleen. The flexed-tail (f) mutant mice exhibit normal steady-state erythropoiesis but are unable to rapidly respond to acute erythropoietic stress. Here, we show that f/f mutant mice have a mutation in Madh5. Our analysis shows that BMP4/Madh5-dependent signaling, regulated by hypoxia, initiates the differentiation and expansion of erythroid progenitors in the spleen. These findings suggest a new model where stress erythroid progenitors, resident in the spleen, are poised to respond to changes in the microenvironment induced by acute anemia.

BMP signaling in the control of skin development and hair follicle growth

Bone morphogenetic proteins (BMPs), their antagonists, and BMP receptors are involved in controlling a large number of biological functions including cell proliferation, differentiation, cell fate decision, and apoptosis in many different types of cells and tissues during embryonic development and postnatal life. BMPs exert their biological effects via using BMP-Smad and BMP-MAPK intracellular pathways. The magnitude and specificity of BMP signaling are regulated by a large number of modulators operating on several levels (extracellular, cytoplasmic, nuclear). In developing and postnatal skin, BMPs, their receptors, and BMP antagonists show stringent spatio-temporal expressions patterns to achieve proper regulation of cell proliferation and differentiation in the epidermis and in the hair follicle. Genetic studies assert an essential role for BMP signaling in the control of cell differentiation and apoptosis in developing epidermis, as well as in the regulation of key steps of hair follicle development (initiation, cell fate decision, cell lineage differentiation). In postnatal hair follicles, BMP signaling plays an important role in controlling the initiation of the growth phase and is also involved in the regulation of apoptosis-driven hair follicle involution. However, additional efforts are required to fully understand the mechanisms and targets involved in the realization of BMP effects on distinct cell population in the skin and hair follicle. Progress in this area of research will hopefully lead to the development of new therapeutic approaches for using BMPs and BMP antagonists in the treatment of skin and hair growth disorders.

Transforming Growth Factor β–SMAD2 Signaling Regulates Aortic Arch Innervation and Development

Aortic arch interruptions in humans and animal models are mainly caused by aberrant development of the fourth pharyngeal arch artery. Little is known about the maturation of this vessel during normal and abnormal development, which is the subject of this study. Tgfbeta2 knockout mice that present with fourth artery defects have been associated with defective neural crest cell migration. In this study, we concentrated on pharyngeal arch artery development during developmental days 12.5 to 18.5, focusing on neural crest cell migration using a Wnt1-Cre by R26R neural crest cell reporter mouse. Fourth arch artery maturation was studied with antibodies directed against smooth muscle alpha-actin and neural NCAM-1 and RMO-270. For diminished transforming growth factor beta (TGF-beta) signaling, SMAD2 and fibronectin have been analyzed. Neural crest migration and differentiation into smooth muscle cells is unaltered in mutants, regardless of the cardiovascular defect found; however, innervation of the fourth arch artery is affected. Absent staining for nuclear SMAD2, NCAM-1, and RMO-270 in the fourth artery in mutant coincides with severe defects of this segment. Likewise, fibronectin expression is diminished in these cases. From these data we conclude the following: (1) neural crest cell migration is not a common denominator in cardiovascular defects of Tgfbeta2-/- mice; (2) fourth arch artery maturation is a complex process involving innervation; and (3) TGF-beta2 depletion diminishes SMAD2-signaling in the fourth arch artery and coincides with reduced vascular NCAM-1 expression and neural innervation of this artery. We hypothesize that disturbed maturation of the fourth pharyngeal arch artery, and especially abrogated vascular innervation, will result in fourth arch interruptions.

Bone morphogenetic protein and transforming growth factor β inhibitory Smads 6 and 7 are expressed in human adult normal and osteoarthritic cartilage in vivo and are differentially regulated in vitro by interleukin-1β

OBJECTIVE

Bone morphogenetic protein (BMP) and transforming growth factor beta (TGFbeta) are potent anabolic factors in adult articular chondrocytes. In this study, we investigated whether intracellular inhibitors of BMP and TGFbeta signaling, inhibitory Smad6 (I-Smad6) and I-Smad7, are expressed in articular chondrocytes in normal and osteoarthritic (OA) cartilage, and whether their expression shows a correlation with the anabolic activity of OA chondrocytes in vivo and after interleukin-1beta (IL-1beta) stimulation in vitro.

METHODS

RNA isolated directly from normal and OA human knee cartilage as well as from cultured articular chondrocytes was analyzed by (quantitative) polymerase chain reaction technology. Immunolocalization of the I-Smads was performed on tissue sections and compared with the anabolic cellular activity as documented by in situ hybridization experiments for aggrecan and type II collagen.

RESULTS

Both Smad6 and Smad7 were expressed in all samples of normal and OA cartilage. Immunostaining (including confocal microscopy) confirmed the presence of Smad6 and Smad7 in the majority of normal and degenerated articular chondrocytes; localization was mostly cytoplasmic. No correlation between expression of the main anabolic genes and expression of the I-Smads was found. In cultured articular chondrocytes, stimulation with IL-1beta showed up-regulation of Smad7, whereas Smad6 was down-regulated.

CONCLUSION

Both Smad6 and Smad7 are expressed in adult human articular chondrocytes. The primarily cytoplasmic localization suggests permanent activation of the I-Smads in articular cartilage in vivo. No evidence was found that up-regulation or down-regulation of I-Smads in OA cartilage correlates directly with the anabolic (or catabolic) activity of articular chondrocytes. The regulation in chondrocytes of Smad6 and Smad7 expression by IL-1beta suggests a potentially important role of IL-1beta signaling in chondrocytes, via indirect influencing of the BMP/TGFbeta signaling cascade.

Spatio-temporal activation of Smad1 and Smad5 in vivo: monitoring transcriptional activity of Smad proteins

Signaling by bone morphogenetic proteins is essential for a wide variety of developmental processes. Receptor-regulated Smad proteins, Smads 1 and 5, are intracellular mediators of bone morphogenetic protein signaling. Together with Smad4, these proteins translocate to the nucleus and modulate transcription by binding to specific sequences on the promoters of target genes. We sought to map transcriptional Smad1/5 activity in development by generating embryonic stem cell lines carrying a Smad1/5-specific response element derived from the Id1 promoter coupled to beta-galactosidase or luciferase as reporters. Three independent lines (BRE-lac1, BRE-lac2 and BRE-luc) have shown the existence of an autocrine bone morphogenetic protein signaling pathway in mouse embryonic stem cells. Reporter activity was detected in chimeric embryos, suggesting sensitivity to physiological concentrations of bone morphogenetic protein. Reporter activity in embryos from transgenic mouse lines was detected in tissues where an essential role for active bone morphogenetic protein signaling via Smads 1 or 5 had been previously established. We have thus generated, for the first time, an in vivo readout for studying the role of Smad1/5-mediated transcriptional activity in development.

Loss of Smad3 in acute T-cell lymphoblastic leukemia

BACKGROUND

The receptors for transforming growth factor beta (TGF-beta) and their signaling intermediates make up an important tumor-suppressor pathway. The role of one of these intermediates--Smad3--in the pathogenesis of lymphoid neoplasia is unknown.

METHODS

We measured Smad3 messenger RNA (mRNA) and protein in leukemia cells obtained at diagnosis from 19 children with acute leukemia, including 10 with T-cell acute lymphoblastic leukemia (ALL), 7 with pre-B-cell ALL, and 2 with acute nonlymphoblastic leukemia (ANLL). All nine exons of the SMAD3 gene (MADH3) were sequenced. Mice in which one or both alleles of Smad3 were inactivated were used to evaluate the role of Smad3 in the response of normal T cells to TGF-beta and in the susceptibility to spontaneous leukemogenesis in mice in which both alleles of the tumor suppressor p27Kip1 were deleted.

RESULTS

Smad3 protein was absent in T-cell ALL but present in pre-B-cell ALL and ANLL. No mutations were found in the MADH3 gene in T-cell ALL, and Smad3 mRNA was present in T-cell ALL and normal T cells at similar levels. In mice, the loss of one allele for Smad3 impairs the inhibitory effect of TGF-beta on the proliferation of normal T cells and works in tandem with the homozygous inactivation of p27Kip1 to promote T-cell leukemogenesis.

CONCLUSIONS

Loss of Smad3 protein is a specific feature of pediatric T-cell ALL. A reduction in Smad3 expression and the loss of p27Kip1 work synergistically to promote T-cell leukemogenesis in mice.

Generation of a floxed allele of Smad5 for cre-mediated conditional knockout in the mouse

Smad5 is a member of the Smad family of intracellular mediators of BMP signals and in endothelial cells of TGF-beta signals. We and others previously showed that loss of Smad5 in the mouse results in embryonic lethality (between E9.5-E11.5) due to multiple embryonic and extraembryonic defects. To circumvent the early embryonic lethality and to allow tissue- and time-specific Smad5 inactivation, we created a conditional Smad5 allele in the mouse. Floxed Smad5 (Smad5(flE2,Neo/flE2,Neo)) mice were generated in which both exon2 and the Neo-cassette were flanked by loxP sites. Here we demonstrate that embryos with ubiquitous Cre-mediated deletion of Smad5 (Smad5(flDeltaE2/flDeltaE2)) phenocopy the conventional Smad5 knockout mice. Smad5(flE2/flE2) mice are now available and will be a valuable tool to analyze the role of Smad5 beyond its crucial early embryonic function throughout development and postnatal life.

TGF-beta signaling in human skeletal and patterning disorders

Members of the transforming growth factor beta (TGF-beta) family of multifunctional peptides are involved in almost every aspect of development. Model systems, ranging from genetically tractable invertebrates to genetically engineered mice, have been used to determine the mechanisms of TGF-beta signaling in normal development and in pathological situations. Furthermore, mutations in genes for the ligands, receptors, extracellular modulators, and intracellular signaling molecules have been associated with several human disorders. The most common are those associated with the development and maintenance of the skeletal system and axial patterning. This review focuses on the mechanisms of TGF-beta signaling with special emphasis on the molecules involved in human disorders of patterning and skeletal development.

Smad6/Smurf1 overexpression in cartilage delays chondrocyte hypertrophy and causes dwarfism with osteopenia

Biochemical experiments have shown that Smad6 and Smad ubiquitin regulatory factor 1 (Smurf1) block the signal transduction of bone morphogenetic proteins (BMPs). However, their in vivo functions are largely unknown. Here, we generated transgenic mice overexpressing Smad6 in chondrocytes. Smad6 transgenic mice showed postnatal dwarfism with osteopenia and inhibition of Smad1/5/8 phosphorylation in chondrocytes. Endochondral ossification during development in these mice was associated with almost normal chondrocyte proliferation, significantly delayed chondrocyte hypertrophy, and thin trabecular bone. The reduced population of hypertrophic chondrocytes after birth seemed to be related to impaired bone growth and formation. Organ culture of cartilage rudiments showed that chondrocyte hypertrophy induced by BMP2 was inhibited in cartilage prepared from Smad6 transgenic mice. We then generated transgenic mice overexpressing Smurf1 in chondrocytes. Abnormalities were undetectable in Smurf1 transgenic mice. Mating Smad6 and Smurf1 transgenic mice produced double-transgenic pups with more delayed endochondral ossification than Smad6 transgenic mice. These results provided evidence that Smurf1 supports Smad6 function in vivo.