TGF-beta related genes in development

Association of TGF-β2 Gene Polymorphism with Growth Rate in Local Chickens

Iraqi native chickens have tasty meat and eggs; however, they are characterized by low production efficiency. In fact, phenotypic traits, such as growth rate, are influenced by genes and environmental factors. During health and disease, a variety of cellular processes such as proliferation, differentiation, motility, adhesion, migration, apoptosis, and immune response regulate the TGF-β genes. The enhancement in body weight can be reached through mass selection, whereas feed conversion ratio (FCR) is relatively more difficult to improve. This means, selecting for body weight has been submitted as an effective way of indirectly improving feed conversion ratio. Therefore, the present study attempts to identify associations between productive traits and polymorphism of TGF-β2 gene in local Iraqi chicken. Seventy-five male birds were used in this study. The restriction enzyme RsaI has been used to detect the target region (284 bp) in the TGF-β2 gene. A single nucleotide polymorphism (SNP) was identified at the position 62 in the exon 1 region of TGF-β2 by using PCR-RFLP and DNA sequencing technique. The genotypic frequencies were 46.7, 40, and 13.3% for CC and TC and TT genotypes, respectively. While the allele frequency of C and T were 0.67 and 0.33%, respectively. Generally, during the last period of rearing the best significant (P<0.05) improve in the body weight, weight gain and FCR were recorded in the TT genotype of the TGF-β2 gene. In conclusion, a functional sequence in the genome could be attributed to the mutation. Therefore, genotype of the TGF-β2 gene could be exploited to select the best individual as a parent to the next generations for improving of growth rate in

Modeling congenital disease and inborn errors of development in Drosophila melanogaster

Fly models that faithfully recapitulate various aspects of human disease and human health-related biology are being used for research into disease diagnosis and prevention. Established and new genetic strategies in Drosophila have yielded numerous substantial successes in modeling congenital disorders or inborn errors of human development, as well as neurodegenerative disease and cancer. Moreover, although our ability to generate sequence datasets continues to outpace our ability to analyze these datasets, the development of high-throughput analysis platforms in Drosophila has provided access through the bottleneck in the identification of disease gene candidates. In this Review, we describe both the traditional and newer methods that are facilitating the incorporation of Drosophila into the human disease discovery process, with a focus on the models that have enhanced our understanding of human developmental disorders and congenital disease. Enviable features of the Drosophila experimental system, which make it particularly useful in facilitating the much anticipated move from genotype to phenotype (understanding and predicting phenotypes directly from the primary DNA sequence), include its genetic tractability, the low cost for high-throughput discovery, and a genome and underlying biology that are highly evolutionarily conserved. In embracing the fly in the human disease-gene discovery process, we can expect to speed up and reduce the cost of this process, allowing experimental scales that are not feasible and/or would be too costly in higher eukaryotes.

Requirement of Smad4-mediated signaling in odontoblast differentiation and dentin matrix formation

Dentin is the major part of tooth and formed by odontoblasts. Under the influence of the inner enamel epithelium, odontoblasts differentiate from ectomesenchymal cells of the dental papilla and secrete pre-dentin which then undergo mineralization into dentin. Transforming growth factor-beta (TGF-β)/bone morphogenetic protein (BMP) signaling is essential for dentinogenesis; however, the precise molecular mechanisms remain unclear. To understand the role of TGF-β/BMP signaling in odontoblast differentiation and dentin formation, we generated mice with conditional ablation of Smad4, a key intracellular mediator of TGF-β/BMP signaling, using Osr2 or OC-Cre mice. Here we found the molars of Osr2^CreSmad4 mutant mice exhibited impaired odontoblast differentiation, and normal dentin was replaced by ectopic bone-like structure. In Osr2^CreSmad4 mutant mice, cell polarity of odontoblast was lost, and the thickness of crown dentin was decreased in later stage compared to wild type. Moreover, the root dentin was also impaired and showed ectopic bone-like structure similar to Osr2^CreSmad4 mutant mice. Taken together, our results suggest that Smad4-dependent TGF-β/BMP signaling plays a critical role in odontoblast differentiation and dentin formation during tooth development.

Soluble factors derived from human amniotic epithelial cells suppress collagen production in human hepatic stellate cells

BACKGROUND

Intravenous infusion of human amniotic epithelial cells (hAECs) has been shown to ameliorate hepatic fibrosis in murine models. Hepatic stellate cells (HSCs) are the principal collagen-secreting cells in the liver. The aim of this study was to investigate whether factors secreted by hAECs and present in hAEC-conditioned medium (CM) have anti-fibrotic effects on activated human HSCs.

METHODS

Human AECs were isolated from the placenta and cultured. Human hepatic stellate cells were exposed to hAEC CM to determine potential anti-fibrotic effects.

RESULTS

HSCs treated for 48 h with hAEC CM displayed a significant reduction in the expression of the myofibroblast markers α-smooth muscle actin and platelet-derived growth factor. Expression of the pro-fibrotic cytokine transforming growth factor-β1 (TGF-β1) and intracellular collagen were reduced by 45% and 46%, respectively. Human AEC CM induced HSC apoptosis in 11.8% of treated cells and reduced HSC proliferation. Soluble human leukocyte antigen-G1, a hAEC-derived factor, significantly decreased TGF-β1 and collagen production in activated HSCs, although the effect on collagen production was less than that of hAEC CM. The reduction in collagen and TGF-B1 could not be attributed to PGE2, relaxin, IL-10, TGF-B3, FasL or TRAIL.

CONCLUSIONS

Human AEC CM treatment suppresses markers of activation, proliferation and fibrosis in human HSCs as well as inducing apoptosis and reducing proliferation. Human AEC CM treatment may be effective in ameliorating liver fibrosis and warrants further study.

GDF5 regulates TGFß-dependent angiogenesis in breast carcinoma MCF-7 cells: in vitro and in vivo control by anti-TGFß peptides

BACKGROUND

TGFß overproduction in cancer cells is one of the main characteristics of late tumor progression being implicated in metastasis, tumor growth, angiogenesis and immune response. We investigated the therapeutic efficacy of anti-TGFß peptides in the control of angiogenesis elicited by conditional over-expression of TGFß.

METHODS

We have inserted in human MCF7 mammary-cancer cells a mutated TGFß gene in a tetracycline-repressible vector to obtain conditional expression of mature TGFß upon transient transfection, evaluated the signaling pathways involved in TGFß-dependent endothelial cells activation and the efficacy of anti-TGFß peptides in the control of MCF7-TGFß-dependent angiogenesis.

RESULTS

TGFß over-expression induced in MCF7 several markers of the epithelial-to-mesenchymal transition. Conditioned-medium of TGFß-transfected MCF7 stimulated angiogenesis in vivo and in vitro by subsequent activation of SMAD2/3 and SMAD1/5 signaling in endothelial cells, as well as SMAD4 nuclear translocation, resulting in over-expression of the pro-angiogenic growth and differentiation factor-5 (GDF5). Inhibition or silencing of GDF5 in TGFß-stimulated EC resulted in impairment of GDF5 expression and of TGFß-dependent urokinase-plasminogen activator receptor (uPAR) overproduction, leading to angiogenesis impairment. Two different TGFß antagonist peptides inhibited all the angiogenesis-related properties elicited in EC by exogenous and conditionally-expressed TGFß in vivo and in vitro, including SMAD1/5 phosphorylation, SMAD4 nuclear translocation, GDF5 and uPAR overexpression. Antagonist peptides and anti-GDF5 antibodies efficiently inhibited in vitro and in vivo angiogenesis.

CONCLUSIONS

TGFß produced by breast cancer cells induces in endothelial cells expression of GDF5, which in turn stimulates angiogenesis both in vitro and in vivo. Angiogenesis activation is rapid and the involved mechanism is totally opposed to the old and controversial dogma about the AKL5/ALK1 balance. The GDF-dependent pro-angiogenic effects of TGFß are controlled by anti-TGFß peptides and anti-GDF5 antibodies, providing a basis to develop targeted clinical studies.

A TGFbeta-responsive gene signature is associated with a subset of diffuse scleroderma with increased disease severity

Systemic sclerosis is a complex disease with widespread skin fibrosis and variable visceral organ involvement. Since transforming growth factor-beta (TGFbeta) has been implicated in driving fibrosis in systemic sclerosis, a mechanism-derived gene expression signature was used to assay TGFbeta-responsive gene expression in the skin of patients with systemic sclerosis (SSc). Primary dermal fibroblasts from patients with diffuse SSc (dSSc) and healthy controls were treated with TGFbeta, and the genome-wide gene expression was measured on DNA microarrays over a time course of 24 hours. Eight hundred and ninety-four probes representing 674 uniquely annotated genes were identified as TGFbeta responsive. Expression of the TGFbeta-responsive signature was examined in skin biopsies from 17 dSSc, seven limited SSc (lSSc), three morphea patients, and six healthy controls. The TGFbeta-responsive signature was expressed in 10 out of 17 dSSc skin biopsies, but was not found in lSSc, morphea, or healthy control biopsies. Expression of dSSC the TGFbeta-responsive signature stratifies patients into two major groups, one of which corresponds to the "diffuse-proliferation" intrinsic subset that showed higher modified Rodnan skin score and a higher likelihood of scleroderma lung disease. The TGFbeta-responsive signature is found in only a subset of dSSc patients who could be targeted by specific therapies.

Bone morphogenetic protein 4 expressed in esophagitis induces a columnar phenotype in esophageal squamous cells

BACKGROUND & AIMS

Barrett's esophagus (BE) is a metaplastic condition in which normal squamous esophageal epithelium is replaced by columnar epithelium. It is proposed that one of the possible mechanisms is dedifferentiation of squamous epithelium into columnar epithelium. The pathophysiology through which this metaplasia occurs is unknown. A recent study by serial analysis of gene expression showed that bone morphogenetic protein 4 (BMP-4) is uniquely expressed in BE. In this study, the role of the BMP pathway in the metaplastic transformation of normal squamous cells into columnar cells was examined.

METHODS

Tissues from patients with esophagitis and BE and in an esophagitis-BE rat model were examined for the activation of the BMP pathway. Short-term cultures of primary normal squamous esophageal cells were treated with BMP-4, and cell biological changes were examined by Western blot analysis, immunohistochemistry, and microarrays.

RESULTS

In both human and rat tissues, the BMP pathway proved to be activated in esophagitis and BE. Upon incubation of squamous cell cultures with BMP-4, the cytokeratin expression pattern showed a shift that was consistent with columnar epithelium. Involvement of the BMP pathway was suggested by up-regulation of Phosphorylated-Smad 1/5/8 (P-Smad 1/5/8) that was effectively blocked by Noggin, a BMP antagonist. Comparison of the gene expression profiles of squamous cells, BMP-4-treated squamous cells, and BE cells showed a significant shift in the profile of the BMP-4-treated squamous cells toward that of the cultured BE cells.

CONCLUSIONS

These results suggest that the BMP pathway could play a role in the transformation of normal esophageal squamous cells into columnar cells.

Bone morphogenetic protein-2/4 signalling pathway components are expressed in the human thymus and inhibit early T-cell development

T-cell differentiation is driven by a complex network of signals mainly derived from the thymic epithelium. In this study we demonstrate in the human thymus that cortical epithelial cells produce bone morphogenetic protein 2 (BMP2) and BMP4 and that both thymocytes and thymic epithelium express all the molecular machinery required for a response to these proteins. BMP receptors, BMPRIA and BMPRII, are mainly expressed by cortical thymocytes while BMPRIB is expressed in the majority of the human thymocytes. Some thymic epithelial cells from cortical and medullary areas express BMP receptors, being also cell targets for in vivo BMP2/4 signalling. The treatment with BMP4 of chimeric human-mouse fetal thymic organ cultures seeded with CD34+ human thymic progenitors results in reduced cell recovery and inhibition of the differentiation of human thymocytes from CD4- CD8- to CD4+ CD8+ cell stages. These results support a role for BMP2/4 signalling in human T-cell differentiation.

BMP type I receptor ALK2 is essential for proper patterning at late gastrulation during mouse embryogenesis

Bone morphogenetic proteins (BMPs) have multiple functions during vertebrate development. Previously, it was shown that BMP type I receptor ALK2 (also known as ACVRI, ActRI, or ActRIA) was important for normal mouse gastrulation by deleting exon 4 or exon 5 of Alk2. Recently, flanking exon 7 by loxP sites generated a conditional allele for Alk2. To assess whether the deletion of exon 7 causes functional null of ALK2, and does not produce a dominant negative form or a partially functional form of ALK2, we performed a comparative analysis between Alk2 homozygous mutant embryos with an exon 5 deletion (Alk2(Delta5/Delta5)) and embryos with an exon 7 deletion (Alk2(Delta7/Delta7)). Both Alk2(Delta5/Delta5) and Alk2(Delta7/Delta7) mutants showed identical morphological gastrulation defects. Histological examinations and molecular marker analyses revealed identical abnormal gastrulation phenotypes in Alk2(Delta5/Delta5) and Alk2(Delta7/Delta7) mutants. Although Fgf8 was expressed in the primitive streak of Alk2(Delta5/Delta5) and Alk2(Delta7/Delta7) mutants, Brachyury, Wnt3a, and Tbx6 were dramatically downregulated in Alk2(Delta5/Delta5) and Alk2(Delta7/Delta7) mutants. These results indicate that deletion of exon 7 for Alk2 leads to a functionally null mutation in vivo, and Alk2 is crucial for sustaining the proper gastrulation events in early mouse embryogenesis.

Effects of growth factors on testicular morphogenesis

Since the discovery of the sex-determining gene Sry in 1990, research effort has focused on the events downstream of its expression. A range of different experimental approaches including gene expression, knocking-out and knocking-in genes of interest, and cell and tissue culture techniques have been applied, highlighting the importance of growth factors at all stages of testicular morphogenesis. Migration of primordial germ cells and the mesonephric precursors of peritubular myoid cells and endothelial cells to the gonad is under growth factor control. Proliferation of both germ cells and somatic cells within the gonadal primordium is also controlled by cytokines as is the interaction of Sertoli cells (with each other and with the extracellular matrix) to form testicular cords. Several growth factors/growth factor families (e.g., platelet-derived growth factor, fibroblast growth factor family, TGFbeta family, and neurotrophins) have emerged as key players, exerting an influence at different time points and steps in organogenesis. Although most evidence has emerged in the mouse, comparative studies are important in elucidating the variety, potential, and evolution of control mechanisms.

Transforming growth factor beta inhibits proliferation of somatic cells without influencing germ cell number in the chicken embryonic ovary

The gonadal development of chicken embryo is regulated by hormones and growth factors. Transforming growth factor beta (TGF-beta) isoforms may play a critical role in the regulation of growth in chicken gonads. We have investigated the effect of the TGF-beta isoforms on the number of germ and somatic cells in the ovary of the chicken embryo. Ovaries were obtained from chicken embryos at 9 days of incubation. They were organ-cultured for 72 h in groups treated with TGF-beta1, TGF-beta2, soluble betaglycan, TGF-beta1 plus soluble betaglycan, or TGF-beta2 plus soluble betaglycan, and untreated (control). TGF-beta1 and TGF-beta2 diminished the somatic cell number in the ovary of the chicken embryo at this age by inhibiting the proliferation of the somatic cells without increasing apoptosis. On the other hand, TGF-beta1 and TGF-beta2 did not affect the number of germ cells in the cultured ovary. The capacity of TGF-beta1 and TGF-beta2 to diminish the number of somatic cells in the ovary was blocked with soluble betaglycan, a natural TGF-beta antagonist. However, changes in the location of germ cells within the ovary suggested that TGF-beta promoted the migration of the germ cells from the ovarian cortex to the medulla. Thus, TGF-beta affects germ and somatic cells in the ovary of the 9-day-old chicken embryo and inhibits the proliferation of somatic cells.

Inactivation of ELF/TGF-beta signaling in human gastrointestinal cancer

TGF-beta/Smads regulate a wide variety of biological responses through transcriptional regulation of target genes. ELF, a beta-spectrin, plays a key role in the transmission of TGF-beta-mediated transcriptional response through Smads. ELF was originally identified as a key protein involved in endodermal stem/progenitor cells committed to foregut lineage. Also, as a major dynamic adaptor and scaffolding protein, ELF is important for the generation of functionally distinct membranes, protein sorting and the development of polarized differentiated epithelial cells. Disruption of elf results in the loss of Smad3/Smad4 activation and, therefore, a disruption of the TGF-beta pathway. These observations led us to pursue the function of ELF in gastrointestinal (GI) epithelial cell-cell adhesion and tumor suppression. Here, we show a significant loss of ELF and reduced Smad4 expression in human gastric cancer tissue samples. Also, of the six human gastric cancer cell lines examined, three show deficient ELF expression. Furthermore, we demonstrate the rescue of E-cadherin-dependent homophilic cell-cell adhesion by ectopic expression of full-length elf. Our results suggest that ELF has an essential role in tumor suppression in GI cancers.

Molecular characterization of conditionally immortalized cell lines derived from mouse early embryonic inner ear

Inner ear sensory hair cells (HCs), supporting cells (SCs), and sensory neurons (SNs) are hypothesized to develop from common progenitors in the early embryonic otocyst. Because little is known about the molecular signals that control this lineage specification, we derived a model system of early otic development: conditionally immortalized otocyst (IMO) cell lines from the embryonic day 9.5 Immortomouse. This age is the earliest stage at which the otocyst can easily be separated from surrounding mesenchymal, nervous system, and epithelial cells. At 9.5 days post coitum, there are still pluripotent cells in the otocyst, allowing for the eventual identification of both SN and HC precursors--and possibly an elusive inner ear stem cell. Cell lines derived from primitive precursor cells can also be used as blank canvases for transfections of genes that can affect lineage decisions as the cells differentiate. It is important, therefore, to characterize the "baseline state" of these cell lines in as much detail as possible. We characterized seven representative "precursor-like" IMO cell populations and the uncloned IMO cells, before cell sorting, at the molecular level by polymerase chain reaction (PCR) and immunocytochemistry (IHC), and one line (IMO-2B1) in detail by real-time quantitative PCR and IHC. Many of the phenotypic markers characteristic of differentiated HCs or SCs were detected in IMO-2B1 proliferating cells, as well as during differentiation for up to 30 days in culture. These IMO cell lines represent a unique model system for studying early stages of inner ear development and determining the consequences of affecting key molecular events in their differentiation.

BMP2 initiates chondrogenic lineage development of adult human mesenchymal stem cells in high-density culture

Human bone marrow-derived mesenchymal stem cells (MSCs) have been shown to differentiate into distinct mesenchymal tissues including bone and cartilage. The capacity of MSCs to replicate undifferentiated and to mature into cartilaginous tissues suggests these cells as an attractive cell source for cartilage tissue engineering. Here we show that the stimulation of human bone marrow-derived MSCs with recombinant bone morphogenetic protein-2 (BMP2) results in chondrogenic lineage development under serum-free conditions. Histological staining of proteoglycan with Alcian blue and immunohistochemical staining of cartilage-specific type II collagen revealed the deposition of typical cartilage extracellular matrix components. Semi-quantitative real-time gene expression analysis of characteristic chondrocytic matrix genes, such as cartilage link protein, cartilage oligomeric matrix protein, aggrecan, and types I, II, and IX collagen, confirmed the induction of the chondrocytic phenotype in high-density culture upon stimulation with BMP2 and transforming growth factor-beta3 (TGFbeta3). Histologic staining of mineralized extracellular matrix with von Kossa, immunostaining of type X collagen (typical for hypertrophic chondrocytes), and gene expression analysis of osteocalcin and adipocyte-specific fatty acid binding protein (aP2) further documented that BMP2 induced chondrogenic lineage development and not osteogenesis and/or adipogenesis in human MSCs. These results suggest BMP2 as a promising candidate for tissue engineering approaches regenerating articular cartilage on the basis of mesenchymal progenitors from bone marrow.

Loss of the Smad3 expression increases susceptibility to tumorigenicity in human gastric cancer

Loss of the tumor suppressive effect of transforming growth factor-beta (TGF-beta) has been commonly found at later stages in carcinogenic progression. Although the genes encoding TGF-beta receptors and Smads have been found genetically altered in certain human cancers, no mutation in Smad3 has been observed. Therefore, suppression of Smad3 expression may mediate key oncogenic properties of TGF-beta. First, we observed that 37.5% of human gastric cancer tissues showed low to undetectable levels of Smad3 and that in nine human gastric cancer cell lines examined, two showed deficient Smad3 expression. Introduction of Smad3 into human gastric cancer cells that did not express Smad3, restored TGF-beta responsiveness: induction of p21 and p15 gene expression, and growth inhibition in response to TGF-beta. Furthermore, these Smad3-expressing cells showed markedly decreased and delayed tumorigenicity in vivo. These findings suggest that Smad3 expression may have a critical role in tumor suppression in the early stages of gastric carcinogenesis.

Patterning the peripheral retina of the fly: decoding a gradient

The peripheral regions of the fly eye show a number of specializations. First, immediately interior to the circumscribing head capsule and completely encircling the rest of the eye lies a thick band of pigment cells (pigment rim; PR). Second, in the dorsal periphery of the eye directly interior to the PR lie the dorsal rim (DR) ommatidia that are specialized polarized light detectors. The equivalent position in the ventral eye is occupied by standard ommatidia. Third, ommatidia characteristically project mechanosensory hairs above their lenses, but in the most peripheral rows (including the DR) the ommatidia are bald. Wingless secreted from the head capsule appears to organize all these peripheral specializations. Higher Wg levels induce PR, intermediate levels induce DR, and lower levels induce baldness. The predisposition of dorsal cells to generate DR ommatidia appears to be endowed by the exclusive dorsal expression of Iroquois genes.

Chicken quantitative trait loci for growth and body composition associated with transforming growth factor-beta genes

Transforming growth factor-beta (TGF-beta) belongs to a large family of multifunctional growth factors that regulate a broad spectrum of biological activities involved in morphogenesis, development, and differentiation. The current study was designed to investigate the effects of TGF-beta genes on chicken growth and body composition traits. The Iowa Growth and Composition Resource Population was established by crossing broiler sires with dams from two unrelated highly inbred lines (Leghorn and Fayoumi). The F1 birds were intercrossed, within dam line, to produce two related F2 populations. Body weight and body composition traits were measured in the F2 population. Primers for TGF-beta2, TGF-beta3, and TGF-beta4 were designed from database chicken sequence. Polymorphisms between parental lines were detected by DNA sequencing, and PCR-RFLP methods were then developed to screen the F2 population. The TGF-beta2 polymorphisms between broiler and Leghorn and the TGF-beta4 polymorphism between broiler and Fayoumi were associated with traits of skeletal integrity, such as tibia length, bone mineral content, bone mineral density, and the percentage of each measure to BW. The TGF-beta3 polymorphism between broilers and Leghorns was associated with traits of growth and body composition, such as BW, average daily gain, weight of breast muscle, abdominal fat pad and spleen, as well as the percentage of these organ weights to BW, and the percentage of shank weight and length to BW. The current research supports the broad effects of TGF-beta genes on growth and development of chickens.

Testosterone is a potential augmentor of antioxidant-induced apoptosis in human prostate cancer cells

We have investigated the effect of antioxidant-induced apoptosis in human prostate cancer cell lines that is augmented by testosterone (T). In this study, DU-145 (androgen unresponsive), ALVA-101 (partially androgen responsive), and LNCaP (androgen responsive) were grown in tissue culture with RPMI 1640 medium, 5-10% fetal bovine serum (FBS), antibiotics and 5% CO2. Treatment with 2.5-20 microg/ml of PDTC significantly (P < 0.05, n = 6) lowered cell growth in all three cells 2-60% following treatment for 1-7 days. T (10(-12) M) alone enhances cell growth in androgen responsive cells. In contrast, the combination of PDTC and T significantly (P < 0.05, n = 6) augmented the PDTC induction of apoptosis in the androgen responsive cells, (ALVA-101 and LNCaP), but not in the androgen unresponsive cells (DU-145). PDTC reduced the nuclear NF-KB, as determined with an electrophoretic mobility shift assay (EMSA), to 50% of the control in LNCaP cells, 65% in ALVA-101 cells and 45% in DU-145 cells, but the combination of PDTC and T was not more potent than PDTC alone in any of the cell lines. PDTC suppressed both the AR mRNA and protein expression and reversed the stimulatory effect of T on androgen receptor (AR) protein synthesis in LNCaP and AVLA-101 cells. In conclusion, PDTC is a potent growth inhibitor and an inducer of apoptosis in human prostate cancer cells by reducing nuclear NF-kappaB and AR protein expression. PDTCs suppression of AR synthesis and nuclear NF-kappaB in response to T may contribute to its enhancement of apoptosis observed with T and PDTC compared to PDTC alone.

Targeted disruption of the Tab1 gene causes embryonic lethality and defects in cardiovascular and lung morphogenesis

The transforming growth factor-beta (TGF-beta) superfamily consists of a group of secreted signaling molecules that perform important roles in the regulation of cell growth and differentiation. TGF-beta activated kinase-1 binding protein-1 (TAB1) was identified as a molecule that activates TGF-beta activated kinase-1 (TAK1). Recent studies have revealed that the TAB1-TAK1 interaction plays an important role in signal transduction in vitro, but little is known about the role of these molecules in vivo. To investigate the role of TAB1 during development, we cloned the murine Tab1 gene and disrupted it by homologous recombination. Homozygous Tab1 mutant mice died, exhibiting a bloated appearance with extensive edema and hemorrhage at the late stages of gestation. By histological examinations, it was revealed that mutant embryos exhibited cardiovascular and lung dysmorphogenesis. Tab1 mutant embryonic fibroblast cells displayed drastically reduced TAK1 kinase activities and decreased sensitivity to TGF-beta stimulation. These results indicate a possibility that TAB1 plays an important role in mammalian embryogenesis and is required for TAK1 activation in TGF-beta signaling.

Genetic analysis of the mammalian transforming growth factor-beta superfamily

Members of the TGF-beta superfamily, which includes TGF-betas, growth differentiation factors, bone morphogenetic proteins, activins, inhibins, and glial cell line-derived neurotrophic factor, are synthesized as prepropeptide precursors and then processed and secreted as homodimers or heterodimers. Most ligands of the family signal through transmembrane serine/threonine kinase receptors and SMAD proteins to regulate cellular functions. Many studies have reported the characterization of knockout and knock-in transgenic mice as well as humans or other mammals with naturally occurring genetic mutations in superfamily members or their regulatory proteins. These investigations have revealed that TGF-beta superfamily ligands, receptors, SMADs, and upstream and downstream regulators function in diverse developmental and physiological pathways. This review attempts to collate and integrate the extensive body of in vivo mammalian studies produced over the last decade.

Bone morphogenetic protein 2/4 signaling regulates early thymocyte differentiation

Bone morphogenetic protein (BMP)2 and BMP4 are involved in the development of many tissues. In this study, we show that BMP2/4 signaling is involved in thymocyte development. Our data suggest that termination of BMP2/4 signaling is necessary for differentiation of CD44(+)CD25(-)CD4(-)CD8(-) double negative (DN) cells along the T cell lineage. BMP2 and BMP4 are produced by the thymic stroma and the requisite BMP receptor molecules (BMPR-1A, BMPR-1B, BMPR-II), and signal transduction molecules (Smad-1, -5, -8, and -4) are expressed by DN thymocytes. BMP4 inhibits thymocyte proliferation, enhances thymocyte survival, and arrests thymocyte differentiation at the CD44(+)CD25(-) DN stage, before T cell lineage commitment. Neutralization of endogenous BMP2 and BMP4 by treatment with the antagonist Noggin promotes and accelerates thymocyte differentiation, increasing the expression of CD2 and the proportion of CD44(-)CD25(-) DN cells and CD4(+)CD8(+) double-positive cells. Our study suggests that the BMP2/4 pathway may function in thymic homeostasis by regulating T cell lineage commitment and differentiation.

Inhibition of nuclear factor κB induces apoptosis following treatment with tumor necrosis factor α and an antioxidant in human prostate cancer cells

Transforming growth factor beta-1 (TGFbeta-1) and tumor necrosis factor alpha (TNF-alpha), an activator of nuclear factor kappa B (NF-kappaB), modulate apoptosis and/or cell growth. This study was designed to investigate the activity of NF-kappaB and its regulation of inhibitor of apoptosis gene (c-IAP2) in two human prostate cancer cell lines, DU-145 (which is androgen unresponsive) and ALVA-101 (which is moderately androgen responsive). These cells were treated with and without various concentrations of a strong antioxidant, pyrrolidinedithiocarbamate (PDTC), and TNF-alpha at various time intervals. Following treatments, cell growth and apoptosis were determined by ELISA techniques. NF-kappaB activity was determined by electrophoretic mobility shift assay (EMSA), and c-IAP2 mRNA production was determined with Northern blot analysis. PDTC treatment significantly reduced cell growth up to 80% in both DU-145 and ALVA-101 cells. TNF-alpha and lower but not higher doses of PDTC combined demonstrated an additive inhibition of cell growth in both cell lines. Active NF-kappaB and c-IAP2 was blocked significantly following PDTC treatments, whereas treatments with TNF-alpha alone showed increased NF-kappaB activity and c-IAP2. However, when both PDTC and TNF-alpha were combined, nuclear presence of NF-kappaB and c-IAP2 were reduced significantly (P < 0.05) to levels observed with PDTC alone. In conclusion, the antioxidant, PDTC, appears to initiate apoptosis by blocking cytoplasmic NF-kappaB translocation to the nucleus where it normally activates the production of apoptosis-inhibitory proteins like c-IAP2. Both TNF-alpha and PDTC alone cause apoptosis and reduce cell growth, but their combined effects are additive in reducing cell growth of DU-145 and ALVA-101 human prostate cancer cells.

Activation of bone morphogenetic protein/Smad signaling in bronchial epithelial cells during airway inflammation

Bone morphogenetic proteins (BMPs) are pleiotropic secreted proteins, structurally related to transforming growth factor (TGF)-beta and activins. BMPs play pivotal roles in the regulation of embryonic lung development and branching of airways and have recently been considered to influence inflammatory processes in adults due to their chemotactic activity on fibroblasts, myocytes, and inflammatory cells. In this study, we have investigated the possible involvement of BMPs in a model of experimental allergic-airway inflammation in situ using antibodies that detect activated Smad proteins, and have monitored the modulation of BMP ligands during the inflammatory response. Inflamed bronchial epithelial cells and a few scattered alveolar cells expressed levels of phosphorylated Smad1 (pSmad1/5), indicative of active BMP/Smad signaling. This was in contrast to healthy epithelium, which was devoid of immunoreactivity. A mechanistic explanation for increased pSmad1/5 staining during inflammation was provided by the upregulated expression of all the BMP type I receptors, i.e., activin receptor-like kinase (ALK)2, ALK3, and ALK6, in the inflamed bronchial epithelial cells. Furthermore, the mRNA and protein profiles for BMP ligands were significantly altered during airway inflammation with induction of BMP2, BMP4, and BMP6, and downregulation of BMP5 and BMP7. Collectively, our data demonstrate for the first time active BMP/Smad signaling during airway inflammation in bronchial epithelial cells and thus raise the possibility that BMPs could play a determining role in respiratory pathophysiology.

Jab1 antagonizes TGF-beta signaling by inducing Smad4 degradation

Tumor suppressor Smad4 is the common signaling effector in the transforming growth factor beta (TGF-beta) superfamily. Phosphorylated regulatory Smads (R-Smads) interact with Smad4, and the complex translocates into the nucleus to regulate gene transcription. Proper TGF-beta signaling requires precise control of Smad functions. Smurfs have been shown to mediate the degradation of R-Smads but not the common-partner Smad4. We report a novel mechanism of Smad4 degradation. Jab1 interacts directly with Smad4 and induces its ubiquitylation for degradation. Jab1 was initially identified as a co-activator of c-Jun, and it also induces degradation of cell cycle inhibitor p27 and tumor suppressor p53. Ectopic expression of Jab1 decreased endogenous Smad4 steady-state levels. The 26S proteasome inhibitors lactacystin and MG132 reduced the degradation rate of Smad4 protein. Examination of the effects of JAB1-induced Smad4 degradation indicates that Jab1 inhibited TGF-beta-induced gene transcription. Our data suggest that Jab1 antagonizes TGF-beta function by inducing degradation of Smad4 through a distinct degradation pathway.

Identification of new bone morphogenetic protein-related members in invertebrates

Although believed to be widely distributed among the animal kingdom, transforming growth factor-beta (TGF-beta) superfamily members have mainly been characterized in vertebrate and in invertebrate model organisms such as Drosophila and C. elegans. To characterize such new factors in invertebrates, a PCR screen was performed on genomic DNA from different animal phyla, using degenerate primers deduced from consensus sequences of known members of the TGF-beta superfamily. Four new members were identified from a cnidaria, an echinoderm and from two classes of molluscs. These new proteins exhibit a high degree of identity with human bone morphogenetic proteins (BMP2/4). Sequence comparisons suggest an early origin and an evolutionary conservation of the molecular conformation. However, their possible involvement in distinct regulatory pathways is discussed.

TGF-beta1 regulates the expression of multiple max-interacting transcription factors in Balb/MK cells: implications for understanding the mechanism of action of TGF-beta1

Appropriate transforming growth factor-beta1 (TGF-beta1) signaling is required to preserve homeostasis of diverse tissues during development. At the cellular level, one function of TGF-beta1 that is critical for preserving homeostasis is the ability to arrest cell growth. TGF-beta1 arrests growth by blocking the function of the c-myc proto-oncogene. c-myc function is determined by the level of c-myc expression relative to other Max-interacting transcription factors, and TGF-beta1 has been shown to inhibit c-myc expression by inhibiting c-myc transcription. However, whether TGF-beta1 might also increase the expression of a Max-interacting factor that blocks myc function by competing with myc for Max binding is not known. Therefore, we determined the effect of TGF-beta1 on the expression of Max-interacting transcription factors in Balb/MK cells. We found unexpectedly that Balb/MK cells express both N-myc and c-myc. The pattern of N-myc expression during the cell cycle differs from that of c-myc, indicating that mRNA accumulation is controlled by mechanisms specific to each gene. TGF-beta1 rapidly inhibits N-myc mRNA expression; thus N-myc is a novel target of TGF-beta1 in Balb/MK cells. More importantly, we found that TGF-beta1 induces the expression of the putative tumor suppressor genes Mad4 and Mxi1 in both the Balb/MK and Mv1Lu cell lines. Mad4 and Mxi1 are novel targets of TGF-beta1, known to inhibit cell growth by antagonizing the interaction of Myc with Max. Thus, our results suggest that the induction of Mad4 and Mxi1 may function in tandem with the inhibition of N-myc and c-myc to mediate the growth inhibitory function of TGF-beta1.

Gonadal development in mammals at the cellular and molecular levels

In mammals, although sex is determined chromosomally, gonads in both sexes begin development as similar structures. Until recently it was widely held that female development constituted a "default" pathway of development, which would occur in the absence of a testis-determining gene. This master gene on the Y chromosome, SRY in the human and Sry in the mouse, is thought to act in a cell-autonomous fashion to determine that cells in the gonadal somatic population develop as pre-Sertoli cells. Triggering of somatic cell differentiation along the Sertoli cell pathway is therefore a key event; it was thought that further steps in gonadal differentiation would follow in a developmental cascade. In the absence of Sertoli cells, the lack of anti-Mullerian hormone would allow development of the female Mullerian duct and absence of Leydig cells would prevent maintenance of the Wolffian duct. Recent findings that female signals not only maintain the Mullerian duct and repress the Wolffian duct but also suppress the development of Leydig cells and maintain meiotic germ cells, together with the finding that an X-linked gene is required for ovarian development and must be silenced in the male, have shown that the female default pathway model is an oversimplification. Morphological steps in gonadal differentiation can be correlated with emerging evidence of molecular mechanisms; growth factors, cell adhesion, and signaling molecules interact together, often acting within short time windows via reciprocal control relationships.

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

The eight mammalian Smad proteins mediate cellular signaling from members of the transforming growth factor-beta (TGF-beta), bone morphogenetic protein (BMP), and activin families. Smads 1, 5, and 8 transmit signals from BMPs, while Smads 2 and 3 transmit signals from TGF-betas and activin. Smad 4 is a common mediator of both pathways, while Smads 6 and 7 inhibit signaling. Signal transduction involves translocation of Smad complexes to the nucleus and subsequent gene activation. Little is known about the expression of endogenous Smad proteins during development. We identified commercially available Smad antibodies that specifically recognize a unique Smad protein and are suitable for immunohistochemistry. Here we compare the localization of Smads 1, 2, 3, 4, 5, and 6 in tissues of the 15-day gestation mouse embryo. Immunoreactive Smad proteins are seen in many tissues with differences in the localization being dependent upon the cell type. All tissues express Smad 4 and at least one each of the BMP-specific and TGF-beta-specific Smads, while expression of Smad 6 is more restricted. Differences are observed in the nuclear versus cytoplasmic localization among the Smads in different cell types or tissues, suggesting selective activation of Smads during this stage of development.

Mesendoderm induction and reversal of left-right pattern by mouse Gdf1, a Vg1-related gene

TGFbeta signals play important roles in establishing the body axes and germ layers in the vertebrate embryo. Vg1 is a TGFbeta-related gene that, due to its maternal expression and vegetal localization in Xenopus, has received close examination as a potential regulator of development in Xenopus, zebrafish, and chick. However, a mammalian Vg1 ortholog has not been identified. To isolate mammalian Vg1 we screened a mouse expression library with a Vg1-specific monoclonal antibody and identified a single cross-reactive clone encoding mouse Gdf1. Gdf1 is expressed uniformly throughout the embryonic region at 5.5-6.5 days postcoitum and later in the node, midbrain, spinal cord, paraxial mesoderm, lateral plate mesoderm, and limb bud. When expressed in Xenopus embryos, native GDF1 is not processed, similar to Vg1. In contrast, a chimeric protein containing the prodomain of Xenopus BMP2 fused to the GDF1 mature domain is efficiently processed and signals via Smad2 to induce mesendoderm and axial duplication. Finally, right-sided expression of chimeric GDF1, but not native GDF1, reverses laterality and results in right-sided Xnr1 expression and reversal of intestinal and heart looping. Therefore, GDF1 can regulate left-right patterning, consistent with the Gdf1 loss-of-function analysis in the mouse (C. T. Rankin, T. Bunton, A. M. Lawler, and S. J. Lee, 2000, Nature Genet. 24, 262-265) and a proposed role for Vg1 in Xenopus. Our results establish that Gdf1 is posttranslationally regulated, that mature GDF1 activates a Smad2-dependent signaling pathway, and that mature GDF1 is sufficient to reverse the left-right axis. Moreover, these findings demonstrate that GDF1 and Vg1 are equivalent in biochemical and functional assays, suggesting that Gdf1 provides a Vg1-like function in the mammalian embryo.

Smad7 selectively interferes with different pathways of activin signaling and inhibits erythroid leukemia cell differentiation

Smad family proteins are essential for transforming growth factor β (TGF-β) signal mediation downstream of a heteromeric complex of the type I and type II receptor serine/threonine kinases. A distant family member, Smad7, is expressed in most mammalian tissues and cells and prevents TGF-β signaling. In this study, we examined the physiologic role of Smad7 in mediating the effects of activin, a member of the TGF-β superfamily of peptides that functions in a number of processes, including blood-cell development. We report here that Smad7 expression is specifically absent in particular hematopoietic cells that respond to activin by differentiating into the erythroid lineage and that ectopic production of Smad7 causes mouse erythroid leukemia (F5-5) cells to become resistant to activin induction of erythroid differentiation. When coexpressed with type I activin receptor ActR-I or ActR-IB in concert with type II receptor ActR-II, Smad7 efficiently reduced an early transcriptional response mediated by ActR-I but had only a minimal effect on the response mediated by ActR-IB. In the presence of Smad7, overexpression of an activated form of ActR-IB, but not of an activated form of ActR-I, induced F5-5 cells to differentiate. These results suggest that Smad7 selectively interferes with the ActR-I pathway in activin signal transduction. The findings also indicate the existence of a novel activity of Smad7 that inhibits erythroid differentiation by blocking intracellular signaling of activin.

Smad7 selectively interferes with different pathways of activin signaling and inhibits erythroid leukemia cell differentiation

Smad family proteins are essential for transforming growth factor β (TGF-β) signal mediation downstream of a heteromeric complex of the type I and type II receptor serine/threonine kinases. A distant family member, Smad7, is expressed in most mammalian tissues and cells and prevents TGF-β signaling. In this study, we examined the physiologic role of Smad7 in mediating the effects of activin, a member of the TGF-β superfamily of peptides that functions in a number of processes, including blood-cell development. We report here that Smad7 expression is specifically absent in particular hematopoietic cells that respond to activin by differentiating into the erythroid lineage and that ectopic production of Smad7 causes mouse erythroid leukemia (F5-5) cells to become resistant to activin induction of erythroid differentiation. When coexpressed with type I activin receptor ActR-I or ActR-IB in concert with type II receptor ActR-II, Smad7 efficiently reduced an early transcriptional response mediated by ActR-I but had only a minimal effect on the response mediated by ActR-IB. In the presence of Smad7, overexpression of an activated form of ActR-IB, but not of an activated form of ActR-I, induced F5-5 cells to differentiate. These results suggest that Smad7 selectively interferes with the ActR-I pathway in activin signal transduction. The findings also indicate the existence of a novel activity of Smad7 that inhibits erythroid differentiation by blocking intracellular signaling of activin.

Presence and roles of calcium gradients along the dorsal-ventral axis in Drosophila embryos

Dorsal-ventral specification of the Drosophila embryo is mediated by signaling pathways which have been very well described in genetic terms. However, little is known about the physiology of Drosophila development. By imaging patterns of free cytosolic calcium in Drosophila embryos, we found that several calcium gradients are generated along the dorsal-ventral axis. The most pronounced gradient is formed during stage 5, in which calcium levels are high dorsally. Manipulation of the stage 5 calcium gradient affects specification of the amnioserosa, the dorsal-most region of the embryo. We further show that this calcium gradient is inhibited in pipe, Toll, and dorsal mutants, but is unaltered in decapentaplegic (dpp) or punt mutants, suggesting that the stage 5 calcium gradient is formed by a suppression of ventral calcium concentrations. We conclude that calcium plays a role in specification of the dorsal embryonic region.

Crystal structure of a transcriptionally active Smad4 fragment

BACKGROUND

Smad4 functions as a common mediator of transforming growth factor beta (TGF-beta) signaling by forming complexes with the phosphorylated state of pathway-restricted SMAD proteins that act in specific signaling pathways to activate transcription. SMAD proteins comprise two domains, the MH1 and MH2 domain, separated by a linker region. The transcriptional activity and synergistic effect of Smad4 require a stretch of proline-rich sequence, the SMAD-activation domain (SAD), located N-terminal of the MH2 domain. To understand how the SAD contributes to Smad4 function, the crystal structure of a fragment including the SAD and MH2 domain (S4AF) was determined.

RESULTS

The structure of the S4AF trimer reveals novel features important for Smad4 function. A Smad4-specific sequence insertion within the MH2 domain interacts with the C-terminal tail to form a structural extension from the core. This extension (the TOWER) contains a solvent-accessible glutamine-rich helix. The SAD reinforces the TOWER and the structural core through interactions; two residues involved in these interactions are targets of tumorigenic mutation. The solvent-accessible proline residues of the SAD are located on the same face as the glutamine-rich helix of the TOWER, forming a potential transcription activation surface. A tandem sulfate-ion-binding site was identified within the subunit interface, which may interact with the phosphorylated C-terminal sequence of pathway-restricted SMAD proteins.

CONCLUSIONS

The structure suggests that the SAD provides transcriptional capability by reinforcing the structural core and coordinating with the TOWER to present the proline-rich and glutamine-rich surfaces for interaction with transcription partners. The sulfate-ion-binding sites are potential 'receptors' for the phosphorylated sequence of pathway-restricted SMAD proteins in forming a heteromeric complex. The structure thus provides a new model that can be tested using biochemical and cellular approaches.

Multiple roles for activin-like kinase-2 signaling during mouse embryogenesis

The members of the transforming growth factor-beta (TGF-beta) superfamily are secreted proteins that interact with cell-surface receptors to elicit signals that regulate a variety of biological processes during vertebrate embryogenesis. Alk2, also known as ActRIA, Tsk7L, and SKR1, encodes a type I TGF-beta family receptor for activins and BMP-7. Initially, Alk2 transcripts are detected in the visceral endoderm of gastrula stage mouse embryos, suggesting a signaling role in extraembryonic tissues during development. To study the role of Alk2 during mammalian development, Alk2 mutant mice were generated. After embryonic day 9.5 (E9.5), no homozygous mutants were recovered from heterozygote matings. Homozygous mutants with morphological defects were first detected at E7.0 and were smaller than controls. Morphological and molecular examination demonstrated that Alk2 mutant embryos formed a primitive streak, although abnormally thickened, and were arrested in their development around the late streak stage. These gastrulation defects were rescued in chimeric embryos generated by injection of Alk2 mutant embryonic stem (ES) cells into wild-type blastocysts. This rescue of gastrulation defects was also observed in chimeric embryos generated by aggregation of Alk2 homozygous mutant ES cells with tetraploid wild-type embryos. However, at E9.5, these embryos that were completely ES-derived also had defects. In contrast, chimeric embryos generated by injection of wild-type ES cells into Alk2 mutant blastocysts did not show rescue of the gastrulation defects. These results suggest that signaling through this type I receptor is essential in extraembryonic tissues at the time of gastrulation for normal mesoderm formation and also suggest that subsequent Alk2 signaling is essential for normal development after gastrulation.

Transforming growth factor beta-1 and beta-2 and type II receptor functional regulation of ALVA-101 human prostate cancer cells

Transforming growth factor beta-1 (TGFbeta-1) causes apoptosis of many epithelial cells, including the prostate, but other secondary effects of TGFbeta-1 may be important in carcinogenesis. In a human prostate cancer cell line (ALVA-101), we determined the effects of TGFbeta-1 and TGFbeta type I and II receptor antibody on cell proliferation and TGFbeta-1 receptor binding. TGFbeta-1 and -2 and TGFbeta type II receptor mRNA expression levels were determined by polymerase chain reaction (PCR) and Northern blot analysis. A dose-responsive suppression (0.03 to 10 ng/mL) was observed for cells treated with TGFbeta-1 from 3 to 7 days (P < .01). Untreated cells had 1.1 x 10(3) (n = 3) TGFbeta receptors per cell, with a Kd of 0.20 nmol/L (n = 3) as determined by Scatchard analysis; treatment for 3 days with TGFbeta-1 (1 ng/mL) reduced the receptor number (0.9 x 10(3)) and the Kd (0.12 nmol/L). Antibodies to TGFbeta type I and II receptor stimulated proliferation with or without added TGFbeta-1 (50% +/- 5% above control, P < .01, n = 6). TGFbeta-1 and -2 and TGFbeta type II receptor mRNA expression was observed in untreated cells. In cells treated with TGFbeta-1, TGFbeta-1 mRNA was not affected by treatment, but expression levels of the TGFbeta type II receptor and TGFbeta-2 mRNA were moderately suppressed after 72 hours of treatment. Control cells actively produced TGFbeta-1 as measured by radioimmunoassay. The active and inactive forms of TGFbeta-1 were approximately equal, but TGFbeta-2 was secreted in smaller quantities than TGFbeta-1 and the inactive form of TGFbeta-2 predominated, with very small amounts of the active form. Our results suggest that the human prostate cancer cell line ALVA-101 retains negative control of proliferation in response to TGFbeta-1. Inhibition of endogenous TGFbeta action by antibodies to its receptor enhances the growth of ALVA-101 human prostate cancer cells, suggesting that endogenous TGFbeta exerts an inhibitory control on their growth and cellular function.

Dcdc42 acts in TGF-beta signaling during Drosophila morphogenesis: distinct roles for the Drac1/JNK and Dcdc42/TGF-beta cascades in cytoskeletal regulation

During Drosophila embryogenesis the two halves of the lateral epidermis migrate dorsally over a surface of flattened cells, the amnioserosa, and meet at the dorsal midline in order to form the continuous sheet of the larval epidermis. During this process of epithelial migration, known as dorsal closure, signaling from a Jun-amino-terminal-kinase cascade causes the production of the secreted transforming-growth-factor-beta-like ligand, Decapentaplegic. Binding of Decapentaplegic to the putative transforming-growth-factor-beta-like receptors Thickveins and Punt activates a transforming-growth-factor-beta-like pathway that is also required for dorsal closure. Mutations in genes involved in either the Jun-amino-terminal-kinase cascade or the transforming-growth-factor-beta-like signaling pathway can disrupt dorsal closure. Our findings show that although these pathways are linked they are not equivalent in function. Signaling by the Jun-amino-terminal-kinase cascade may be initiated by the small Ras-like GTPase Drac1 and acts to assemble the cytoskeleton and specify the identity of the first row of cells of the epidermis prior to the onset of dorsal closure. Signaling in the transforming-growth-factor-beta-like pathway is mediated by Dcdc42, and acts during the closure process to control the mechanics of the migration process, most likely via its putative effector kinase DPAK.

Strain dependency of TGFbeta1 function during embryogenesis

There is incomplete penetrance to Tgfb1 knockout phenotypes. About 50% of Tgfb1 homozygous mutant (Tgfb1-/-) and 25% of Tgfb1 heterozygous (Tgfb1+/-) embryos die during embryogenesis. In a mixed NIH/Ola x C57BL/6J/Ola x 129 background partial embryonic lethality of the Tgfb1-/-embryos occurs due to defective yolk sac vasculopoiesis and/or hematopoiesis. We show here that on a predominantly CF-1 genetic background, lack of TGFbeta1 causes a pre-morula lethality in about 50% of the null embryos. This partial lethality is not reversed by transfer of Tgfb1-/- embryos to Tgfb1-/+ hosts. The extent of embryonic lethality in Tgfb1-/- embryos ranges in a background dependent manner from 20% to 100%. Based on these and other studies it is clear that TGFbeta1 acts at two distinct phases of embryogenesis: pre-implantation development and yolk sac vasculogenesis/hematopoiesis. The susceptibility for the pre-implantation lethality depends on a small number of genetic modifiers since a small number of backcrosses onto the high susceptibility strain C57BL/6 leads to complete penetrance of the lethality.

decapentaplegic is required for arrest in G1 phase during Drosophila eye development

During eye development in Drosophila, cell cycle progression is coordinated with differentiation. Prior to differentiation, cells arrest in G1 phase anterior to and within the morphogenetic furrow. We show that Decapentaplegic (Dpp), a TGF-β family member, is required to establish this G1 arrest, since Dpp-unresponsive cells located in the anterior half of the morphogenetic furrow show ectopic S phases and ectopic expression of the cell cycle regulators Cyclins A, E and B. Conversely, ubiquitous over-expression of Dpp in the eye imaginal disc transiently inhibits S phase without affecting Cyclin E or Cyclin A abundance. This Dpp-mediated inhibition of S phase occurs independently of the Cyclin A inhibitor Roughex and of the expression of Dacapo, a Cyclin E-Cdk2 inhibitor. Furthermore, Dpp-signaling genes interact genetically with a hypomorphic cyclin E allele. Taken together our results suggest that Dpp acts to induce G1 arrest in the anterior part of the morphogenetic furrow by a novel inhibitory mechanism. In addition, our results provide evidence for a Dpp-independent mechanism that acts in the posterior part of the morphogenetic furrow to maintain G1 arrest.

Mathematical modelling of juxtacrine cell signalling

Juxtacrine signalling is emerging as an important means of cellular communication, in which signalling molecules anchored in the cell membrane bind to and activate receptors on the surface of immediately neighbouring cells. We develop a mathematical model to describe this process, consisting of a coupled system of ordinary differential equations, with one identical set of equations for each cell. We use a generic representation of ligand-receptor binding, and assume that binding exerts a positive feedback on the secretion of new receptors and ligand. By linearising the model equations about a homogeneous equilibrium, we categorize the range and extent of signal patterns as a function of parameters. We show in particular that the signal decay rate depends crucially on the form of the feedback functions, and can be made arbitrarily small by appropriate choice of feedback, for any set of kinetic parameters. As a specific example, we consider the application of our model to juxtacrine signalling by TGF alpha in response to epidermal wounding. We demonstrate that all the predictions of our linear analysis are confirmed in numerical simulations of the non-linear system, and discuss the implications for the healing response.

Development of the avian iris and ciliary body: the role of activin and follistatin in coordination of the smooth-to-striated muscle transition

Although general principles have been established in the regulation of vetebrate organogenesis, the specific molecules responsible for such signaling are just being identified. We have studied differentiation in the avian iris and ciliary body which undergoes a transition from smooth to striated muscle. Using heterochronic cocultures, we have found that striated muscle differentiation in pretransition (E8) cells is induced by midtransition (E11) cells through a secreted and soluble activity. In addition, contact-mediated mechanisms among pretransition cells prevented precocious striated muscle differentiation. We have tested the role of activin and its antagonist follistatin, as candidate regulators of this muscle transition. Activin induced smooth muscle differentiation while repressing striated muscle development. Conversely, follistatin promoted the emergence of striated muscle, while inhibiting smooth muscle differentiation. Significantly, secreted follistatin activity was found to increase during the smooth-to-striated muscle transition. Moreover, the striated muscle inducing activity from midtransition iris and ciliary body cell conditioned medium was depleted with an activin-affinity column which binds follistatin. These results suggest that activin and follistatin coordinate differentiation in the avian iris and ciliary body.

Gene expression of growth and differentiation factors-5, -6, and -7 in developing bovine tooth at the root forming stage

Growth and differentiation factors (GDF)-5, -6, and -7 are members of the bone morphogenetic protein (BMP) family. Previous studies suggest their importance in bone development and in tendon/ligament morphogenesis. The cells of the dental attachment apparatus, cementum, periodontal ligament, and alveolar bone proper are derived from the dental follicle proper. In this study, we investigated the expression of GDF-5, -6, and -7 genes in tissues of the bovine incisor tooth germ at the root forming stage. The results demonstrate distinct expression of GDFs in both the dental follicle and the odontoblast layer. While GDF-5 and -6 mRNAs were expressed in both the dental follicle and the odontoblast layer, GDF-7 mRNA expression was detected only in the dental follicle. These results indicate that GDFs, expressed in the bovine tooth germ including the dental follicle, may be potent regulatory molecules in the development of the dental attachment apparatus.

The tumor suppressor gene Smad4/Dpc4 is required for gastrulation and later for anterior development of the mouse embryo

Mutations in the SMAD4/DPC4 tumor suppressor gene, a key signal transducer in most TGFbeta-related pathways, are involved in 50% of pancreatic cancers. Homozygous Smad4 mutant mice die before day 7.5 of embryogenesis. Mutant embryos have reduced size, fail to gastrulate or express a mesodermal marker, and show abnormal visceral endoderm development. Growth retardation of the Smad4-deficient embryos results from reduced cell proliferation rather than increased apoptosis. Aggregation of mutant Smad4 ES cells with wild-type tetraploid morulae rescues the gastrulation defect. These results indicate that Smad4 is initially required for the differentiation of the visceral endoderm and that the gastrulation defect in the epiblast is secondary and non-cell autonomous. Rescued embryos show severe anterior truncations, indicating a second important role for Smad4 in anterior patterning during embryogenesis.

Functional analysis of an ascidian homologue of vertebrate Bmp-2/Bmp-4 suggests its role in the inhibition of neural fate specification

The ascidian tadpole larva is thought to be close to a prototype of the ancestral chordate. The vertebrate body plan is established by a series of inductive cellular interactions, whereas ascidians show a highly determinate mode of development. Recent studies however, suggest some roles of cell-cell interaction during ascidian embryogenesis. To elucidate the signaling molecules responsible for the cellular interaction, we isolated HrBMPb, an ascidian homologue of the vertebrate bone morphogenetic protein (BMP) gene, from Halocynthia roretzi. The amino acid sequence of HrBMPb closely resembled those of vertebrate BMP-2 and BMP-4 and of Drosophila Decapentaplegic (DPP). In addition to the sequence similarity, HrBMPb overexpression induced the ventralization of Xenopus embryos, suggesting functional conservation. The zygotic expression of HrBMPb was first detected around gastrulation. HrBMPb expression was maintained in some cells at the lateral edges of the neural plate through gastrulation to neurulation, although that in the presumptive muscle cells was downregulated. HrBMPb was not expressed in the presumptive epidermis during gastrulation. When HrBMPb mRNA was injected into fertilized Halocynthia eggs, cells that normally give rise to the neural tissue differentiated into epidermis, causing a loss of anterior neural tissue in the larva. In addition, HrBMPb might function synergistically with HrBMPa, an ascidian homologue of BMPs-5 to 8. However, HrBMPb overexpression did not affect differentiation of the notochord and muscle cells. These results suggest that HrBMPb functions as a neural inhibitor and as an epidermal inducer but not as a ventralizing agent in ascidian development.