Morphogenetic Factor Research Articles

組織形成因子Fgf10

組織形成因子Fgf10

Catecholaminergic System of the Medulla Oblongata of the Amur Bitterling (Bony Fishes, Family Cyprinidae)

Catecholaminergic (CA-ergic) systems in the medulla of the Amur bitterling (Rhodeus sericeus) were studied using immunohistochemical labeling of tyrosine hydroxylase (ТН), the main enzyme of catecholamine synthesis. The peculiarities of localization of medullary neurons, morphology of the dendrites, and trajectories of the axon projections in the medulla of the Amur bitterling allow us to differentiate three groups of ТН-positive neurons, namely interfascicular cells, units related to the lobus vagus, and cells localized within the area postrema. Interfascicular medullary neurons form a longitudinal column of multipolar cells with broadly branching dendrites localized on both sides with respect to the midline. Neurons of the second group are smaller than interfascicular cells; their dendrites form branchings within the reticular formation and lobus vagus. On apical parts of the cells of the second group, there are branched processes directed toward the clearance of the cerebral ventricle. The third group consists of bipolar ТН-positive cells; their density of distribution is maximal near the area postrema. Terminal axon fields of medullary CA-ergic neurons in the Amur bitterling are connected with sensory systems of the medulla. In the periventricular region of this cerebral zone, we found phenotypically immature forms of the cells, highly immunopositive processes, and elements of radial glia expressing ТН. We hypothesize that, in fishes, dopamine functions as an inductor of development (morphogenetic factor) and is involved in postembryonal neurogenesis in matrix zones of the brain.

Smurf1 Protein Negatively Regulates Interferon-γ Signaling through Promoting STAT1 Protein Ubiquitination and Degradation

Interferons are important cytokines that mediate antiviral, antiproliferative, antitumor, and immunoregulatory activities. However, uncontrolled IFN signaling may lead to autoimmune diseases. Here we identified Smurf1 as a negative regulator for IFN-γ signaling by targeting STAT1 for ubiquitination and proteasomal degradation. Smurf1 interacted with STAT1 through the WW domains of Smurf1 and the PY motif in STAT1 and catalyzed K48-linked polyubiquitination of STAT1. Interestingly, the Smurf1-mediated ubiquitination and degradation did not require STAT1 tyrosine and serine phosphorylation. Subsequently, overexpression of Smurf1 attenuated IFN-γ-mediated STAT1 activation and antiviral immune responses, whereas knockdown of Smurf1 enhanced IFN-γ-mediated STAT1 activation, expression of STAT1 target genes, and antiviral immune responses. Furthermore, IFN-γ stimulation led to enhanced expression of Smurf1. Therefore, our results demonstrate that Smurf1 is a negative feedback regulator for IFN-γ signaling by targeting STAT1 for ubiquitination and proteasomal degradation.

Ontogenetic changes in the distribution of the vesicular GABA transporter VGAT correlate with the excitation/inhibition shift of GABA action

GABA is the major inhibitory neurotransmitter in the adult CNS and is among others involved in the synchronization of large neuronal networks. During development, GABA acts as a morphogenetic factor and has transient excitatory actions in many brain regions. One distinct protein, the vesicular GABA transporter (VGAT), has been identified accumulating GABA into presynaptic vesicles prior to its exocytotic release. The function of VGAT and its distribution is well defined in the adult, but its contribution to the transient excitatory action at putative GABAergic nerve terminals in the immature brain and its potential roles in putative glutamatergic nerve terminals remain elusive. We have studied VGAT expression in the brain from late embryonic stages through several postnatal stages until adulthood. Quantitative immunoblotting and immunolabeling of tissue sections at the light microscope and the electron microscope levels show an abrupt augmentation in VGAT staining in the cerebral cortex during the first three postnatal weeks, resembling the increase in other proteins involved in GABA synthesis and recycling in the same time frame – such as GAD65, GAD67, GAT1 (Slc6a1) and SN1 (Slc38a3) – and coincides with the synaptogenetic spurt. Dynamic changes in the expression of VGAT are seen in many cellular populations and in several layers in different brain regions. However, mossy fiber terminals (MFT) elude staining for VGAT. We also demonstrate that VGAT+ nerve terminals undergo a developmental reorganization so that from targeting primarily the dendrites of the principal neurons in several brain regions in the immature brain, they target the soma of the same cells in the adult. This shift in the targeted subcellular compartment coincides with the conversion of the chloride gradient across neuronal membranes and suggests that it may be important for the shift of GABA action from excitation to inhibition and for the establishment of the potent synchronization of neuronal networks.

Presence of Ribeiroia ondatrae in the developing anuran limb disrupts retinoic acid levels

The widespread reports of malformed frogs have sparked interest worldwide to try and determine the causes of such malformations. Ribeiroia ondatrae is a digenetic trematode, which has been implicated as one such cause, as this parasite encysts within the developing tadpole hind limb bud and inguinal region causing dramatic limb malformations. Currently, the mechanisms involved in parasite-induced limb deformities remain unclear. We sought to investigate whether the level of retinoic acid (RA), a morphogenetic factor known to play a critical role in limb bud formation, is altered by the presence of R. ondatrae within the infected tadpole. Alteration of RA levels within the limb bud caused by the presence of the parasite may be achieved in three ways. First, metacercariae are actively secreting RA; second, cercariae, upon entering the limb/inguinal region, may release a large amount of RA; finally, the metacercariae may induce either an increase in the synthesis or a decrease in the degradation of the host's endogenous retinoic acid levels. Here, we show through high performance liquid chromatography and mass spectrometry that limb bud tissue of Lithobates sylvaticus, which has been parasitised, contains 70% more RA compared to the unparasitised control. Furthermore, parasites that have encysted within the limb buds appear to contain substantially less RA (56%) than the free swimming cercariae (defined as the infectious stage of the parasite). Taken together, these data illustrate for the first time that encystment of R. ondatrae leads to an increase in RA levels in the tadpole limb bud and may offer insight into the mechanisms involved in parasite-induced limb deformities.

A nodulin/glutamine synthetase-like fusion protein is implicated in the regulation of root morphogenesis and in signalling triggered by flagellin

The nodulin/glutamine synthetase-like protein (NodGS) that we identified proteomically in Arabidopsis thaliana is a fusion protein composed of an N-terminal amidohydrolase domain that shares homology with nodulins and a C-terminal domain of prokaryotic glutamine synthetase type I. The protein is homologous to the FluG protein, a morphogenetic factor in fungi. Although genes encoding NodGS homologues are present in many plant genomes, their products have not yet been characterized. The Arabidopsis NodGS was present in an oligomeric form of ~700-kDa, mainly in the cytosol, and to a lesser extent in the microsomal membrane fraction. The oligomeric NodGS was incorporated into large heterogeneous protein complexes >700 kDa and partially co-immunoprecipitated with γ-tubulin. In situ and in vivo microscopic analyses revealed a NodGS signal in the cytoplasm, with endomembranes, particularly in the perinuclear area. NodGS had no detectable glutamine synthetase activity. Downregulation of NodGS by RNAi resulted in plants with a short main root, reduced meristematic activity and disrupted development of the root cap. Y2H analysis and publicly available microarray data indicated a role for NodGS in biotic stress signalling. We found that flagellin enhanced the expression of the NodGS protein, which was then preferentially localized in the nuclear periphery. Our results point to a role for NodGS in root morphogenesis and microbial elicitation. These data might help in understanding the family of NodGS/FluG-like fusion genes that are widespread in prokaryotes, fungi and plants.

BMP-mediated inhibition of FGF signaling promotes cardiomyocyte differentiation of anterior heart field progenitors

The anterior heart field (AHF) encompasses a niche in which mesoderm-derived cardiac progenitors maintain their multipotent and undifferentiated nature in response to signals from surrounding tissues. Here, we investigate the signaling mechanism that promotes the shift from proliferating cardiac progenitors to differentiating cardiomyocytes in chick embryos. Genomic and systems biology approaches, as well as perturbations of signaling molecules, in vitro and in vivo, reveal tight crosstalk between the bone morphogenetic protein (BMP) and fibroblast growth factor (FGF) signaling pathways within the AHF niche: BMP4 promotes myofibrillar gene expression and cardiomyocyte contraction by blocking FGF signaling. Furthermore, inhibition of the FGF-ERK pathway is both sufficient and necessary for these processes, suggesting that FGF signaling blocks premature differentiation of cardiac progenitors in the AHF. We further revealed that BMP4 induced a set of neural crest-related genes, including MSX1. Overexpression of Msx1 was sufficient to repress FGF gene expression and cell proliferation, thereby promoting cardiomyocyte differentiation. Finally, we show that BMP-induced cardiomyocyte differentiation is diminished following cranial neural crest ablation, underscoring the key roles of these cells in the regulation of AHF cell differentiation. Hence, BMP and FGF signaling pathways act via inter- and intra-regulatory loops in multiple tissues, to coordinate the balance between proliferation and differentiation of cardiac progenitors.

Bone morphogenetic protein and growth differentiation factor cytokine families and their protein antagonists

The BMPs (bone morphogenetic proteins) and the GDFs (growth and differentiation factors) together form a single family of cystine-knot cytokines, sharing the characteristic fold of the TGFbeta (transforming growth factor-beta) superfamily. Besides the ability to induce bone formation, which gave the BMPs their name, the BMP/GDFs display morphogenetic activities in the development of a wide range of tissues. BMP/GDF homo- and hetero-dimers interact with combinations of type I and type II receptor dimers to produce multiple possible signalling complexes, leading to the activation of one of two competing sets of SMAD transcription factors. BMP/GDFs have highly specific and localized functions. These are regulated in a number of ways, including the developmental restriction of BMP/GDF expression and through the secretion of several specific BMP antagonist proteins that bind with high affinity to the cytokines. Curiously, a number of these antagonists are also members of the TGF-beta superfamily. Finally a number of both the BMP/GDFs and their antagonists interact with the heparan sulphate side chains of cell-surface and extracellular-matrix proteoglycans.

Notch and Transforming Growth Factor-β (TGFβ) Signaling Pathways Cooperatively Regulate Vascular Smooth Muscle Cell Differentiation

Notch and transforming growth factor-beta (TGFbeta) play pivotal roles during vascular development and the pathogenesis of vascular disease. The interaction of these two pathways is not fully understood. The present study utilized primary human smooth muscle cells (SMC) to examine molecular cross-talk between TGFbeta1 and Notch signaling on contractile gene expression. Activation of Notch signaling using Notch intracellular domain or Jagged1 ligand induced smooth muscle alpha-actin (SM actin), smooth muscle myosin heavy chain, and calponin1, and the expression of Notch downstream effectors hairy-related transcription factors. Similarly, TGFbeta1 treatment of human aortic smooth muscle cells induced SM actin, calponin1, and smooth muscle protein 22-alpha (SM22alpha) in a dose- and time-dependent manner. Hairy-related transcription factor proteins, which antagonize Notch activity, also suppressed the TGFbeta1-induced increase in SMC markers, suggesting a general mechanism of inhibition. We found that Notch and TGFbeta1 cooperatively activate SMC marker transcripts and protein through parallel signaling axes. Although the intracellular domain of Notch4 interacted with phosphoSmad2/3 in SMC, this interaction was not observed with Notch1 or Notch2. However, we found that CBF1 co-immunoprecipitated with phosphoSmad2/3, suggesting a mechanism to link canonical Notch signaling to phosphoSmad activity. Indeed, the combination of Notch activation and TGFbeta1 treatment led to synergistic activation of a TGFbeta-responsive promoter. This increase corresponded to increased levels of phosphoSmad2/3 interaction at Smad consensus binding sites within the SM actin, calponin1, and SM22alpha promoters. Thus, Notch and TGFbeta coordinately induce a molecular and functional contractile phenotype by co-regulation of Smad activity at SMC promoters.

Cartilage-derived morphogenetic protein growth factor 1-induced rat adipose-derived stem cells in repairing knee joint defect in rabbits

Objective:To repair knee joint defects in rabbits with rat adipose-derived stem cells induced by cartilage-derived morphogenetic protein growth factor 1(CDMP1),so as to assess the feasibility of using heterogeneity cells as the seed cells for cartilage tissue engineering.Methods:The second generation ADSCs were seeded on scaffold,cultured for another two weeks in presence of CDMP1(50 μg/L),and identified by immunohistochemistory method.Bilateral rabbit knee joint defect model was established.The left side defect was embedded with ADSCs-scaffold composite(experimental group);the right side was embedded only with the scaffold(control group).Nine rabbits were killed in each group 8,16,24,and 48 weeks after embedding and the tissues were made into slices for safranine O and haematoxylin eosin staining.Results:In the experimental group the defects were filled with white semi-transparent tissues 8 weeks after embedding,with clear boundary to the surrounding cartilage;16 weeks after embedding,the boundary of defect was further improved but still could be seen;24 weeks after embedding,the repair outcomes were satisfactory,with the newly-generated chondrocytes having a nearly normal morphology(sphere shape,cartilage lacuna),and safranine O and haematoxylin eosin staining results were both positive;and 48 weeks after embedding,the boundary of the repair region could be clearly seen,and the repair effects were not as satisfactory as those of after 24 weeks.In the control group the boundary between the repairing area and the normal circumjacent area was visible at all 4 time points,with clear boundary and granulation tissues;the newly generated cells took a spindle shape and were negative for H-E and safranine O staining.Conclusion:The knee joint defects of rabbits can be satisfactorily repaired by using CDMP1-induced ADSCs seeded on spongy bone scaffold of cattle,which provides a theoretical basis for using heterogeneity cells as the seed cells for cartilage tissue engineering.

Zebrafish (Danio rerio) and the egg size versus egg number trade off: effects of ration size on fecundity are not mediated by orthologues of the Fec gene

Few studies have demonstrated plasticity of egg size within the confines of an egg size-number trade-off in response to trophic conditions in fishes. Moreover, the physiological mechanisms that govern this plasticity are not known. Growth differentiation factor 9 (Gdf9) and bone morphogenetic factor 15 (Bmp15) are oocyte-specific factors implicated in follicular growth and ovulation in mammals. In order to investigate whether expression levels of these genes were correlated with ration-dependent changes in fecundity in fish, zebrafish (Danio rerio) were subjected to four different feeding regimens. Counts of spawned eggs or vitellogenic follicles were used to estimate fecundity, whereas quantitative polymerase chain reaction analyses were performed to determine Gdf9 and Bmp15 mRNA levels in response to changes in ration size. Both relative fecundity and gonadosomatic index increased significantly with increased ration size, whereas egg size and hatching rate decreased significantly. No significant differences in Gdf9 or Bmp15 transcript abundance were evident between feeding regimens, suggesting that these growth factors do not govern fecundity in fish. However, favourable trophic conditions markedly affected follicle or egg size and number, with important implications for downstream egg quality and survival.

The role of growth stop as a morphogenetic factor in Mastomys natalensis (Rodentia: Muridae)

The present study investigated growth patterns under three different environmental conditions in a single population of the rodent Mastomys natalensis (Rodentia, Muridae) in Morogoro, Tanzania. The study aimed to test whether and how post-weaning ontogenetic processes are affected by different environmental conditions. Morogoro is characterized by a bimodal rainfall pattern, with unreliable peaks occurring in November/December of some years and reliable ones in February to May. We recognized three different generation types. In the first one, the α generation, growth occurred during the dry second half of the year in years when the November/December rains were very poor. The second group (β generation) grew under conditions when these rains were abundant. Finally, the γ generation, consisted of animals that were born in the middle of the rainy season in years when there was a continuity between both rainfall peaks. Analyses of size and shape following both Huxley–Jolicoeur and Gould–Mosimann approaches revealed that the three groups differ significantly both in size and shape. In both cases, the importance of the environment in assessing growth trajectories during post-natal ontogenetic processes is apparent. © 2009 The Linnean Society of London, Biological Journal of the Linnean Society, 2009, 97, 791–800.

Mechanical Injury and Cytokines Cause Loss of Cartilage Integrity and Upregulate Proteins Associated with Catabolism, Immunity, Inflammation, and Repair

The objectives of this study were to perform a quantitative comparison of proteins released from cartilage explants in response to treatment with IL-1beta, TNF-alpha, or mechanical compression injury in vitro and to interpret this release in the context of anabolic-catabolic shifts known to occur in cartilage in response to these insults in vitro and their implications in vivo. Bovine calf cartilage explants from 6-12 animals were subjected to injurious compression, TNF-alpha (100 ng/ml), IL-1beta (10 ng/ml), or no treatment and cultured for 5 days in equal volumes of medium. The pooled medium from each of these four conditions was labeled with one of four iTRAQ labels and subjected to nano-2D-LC/MS/MS on a quadrupole time-of-flight instrument. Data were analysed by ProQuant for peptide identification and quantitation. k-means clustering and biological pathways analysis were used to identify proteins that may correlate with known cartilage phenotypic responses to such treatments. IL-1beta and TNF-alpha treatment caused a decrease in the synthesis of collagen subunits (p < 0.05) as well as increased release of aggrecan G2 and G3 domains to the medium (p < 0.05). MMP-1, MMP-3, MMP-9, and MMP-13 were significantly increased by all treatments compared with untreated samples (p < 0.10). Increased release of proteins involved in innate immunity and immune cell recruitment were noted following IL-1beta and TNF-alpha treatment, whereas increased release of intracellular proteins was seen most dramatically with mechanical compression injury. Proteins involved in insulin-like growth factor and TGF-beta superfamily pathway modulation showed changes in pro-anabolic pathways that may represent early repair signals. At the systems level, two principal components were sufficient to describe 97% of the covariance in the data. A strong correlation was noted between the proteins released in response to IL-1beta and TNF-alpha; in contrast, mechanical injury resulted in both similarities and unique differences in the groups of proteins released compared with cytokine treatment.

Examining Modularity via Partial Correlations: A Rejoinder to a Comment by Paul Magwene

We work, as Paul Magwene does, within the general tradition of path models set out nearly a century ago by Sewall Wright. In this approach, when 2 variables each depend linearly on the same cause, the part of their covariance that explanation accounts for is sim ply the product of the 2 path coefficients (regressions on the common cause) times the variance of that cause. Any additional covariance observed is attributed to ad ditional common causes and is conveniently quantified by the partial correlation of the 2 outcome variables con ditional on the first common cause (which is the cor relation between the two residuals from the regression on this cause). A partial correlation thus combines a test for the adequacy of one particularly simple explanation of the covariances among observed variables together with an assessment of the maximum covariance possible that any additional factor, however hypothesized, might contribute. The notion of correlations among residuals extend easily from the case of 3 variables to many. Pearl (2000) is a fine summary of the way in which this sort of logic can be ramified to incorporate fairly sophisticated statistical analyses about alternate causal interpretations of a data set. The first appearance of this elaboration in the con text of morphological integration and modularity was apparently due to Paul Terenrjev in the astoundingly early year of 1933. He investigated partial correlations among measurements on frogs conditioned on 1 mea sure of overall size together with 1 estimated more lo cal morphogenetic factor. Similarly, in Mitteroecker and Bookstein (2007, 2008), we demonstrated interpretation of a pattern of covariances within and between mod ules after partialling out 1, 2, or more common factor estimates.

SHH Pathway and Cerebellar Development

The morphogenetic factor Sonic hedgehog (SHH) has been discovered as one of the masterplayers in cerebellar patterning and was subjected to intensive investigation during the last decade. During early postnatal development, this continuously secreted cholesterol-modified protein drives the expansion of the largest neuronal population of the brain, the granular cells. Moreover, it acts on Bergmann glia differentiation and would potentially affect Purkinje cells homeostasis at adult age. The cerebellar cortex constituted an ideal developmental model to dissect out the upstream mechanisms and downstream targets of this complex pathway. Its deep understanding discloses some of the mechanistic disorders underlying pediatric tumorigenesis, congenital ataxia, and mental retardation. Therapeutical use of its regulators has been consolidated on murine transgenic models and is now considered as a realistic human clinical application. Here, we will review the most recent advances made in the comprehensive understanding of SHH involvement in cerebellar development and pathology.

RodZ, a new player in bacterial cell morphogenesis

RodZ, a new player in bacterial cell morphogenesis

Abstract 5573: Notch Signaling Enhances BMP2-induced Msx2 Gene Expression and Vascular Calcification

Background: Bone morphogenetic protein2 (BMP2) and transcription factor Msx2, known as major regulators of osteoblastic differentiation, have been implicated in the pathogenesis of vascular calcification. Recent evidences indicate that Notch signaling regulates valve calcification and atherosclerosis. In this study, we examined whether Notch signaling effects on BMP2-induced Msx2 gene expression and vascular calcification. Methods and Results: Treatment with either BMP2 or adenovirus expressing Notch intracellular domain (NICD), slightly induced the expression of the Msx2 gene in pluripotent mesenchymal stem cells and human aortic smooth muscle cells. Surprisingly, either NICD overexpression or stimulation by Notch ligands markedly augmented the Msx2 gene expression in the presence of BMP2, as well as other osteogenic genes expression. A knockdown of Msx2 expression using siRNA drastically attenuated synergistic ALP activity induced by BMP2 and NICD. Luciferase assay showed transcription activity of Msx2 promoter, which contains Smad binging elements (SBE) essential for BMP2 responsiveness, was synergistically enhanced by Notch ligands and BMP2 treatment, whereas this synergism was almost completely inhibited in the presence of Notch signaling blocker. Interestingly, DNA affinity precipitation assay revealed that NICD-RBPJK complex bound to Msx2 promoter very adjacently to SBE, which indicates that RBPJK-bound NICD might interact with Smads and this interaction might lead to enhanced BMP2 signaling and Msx2 expression. Correspondingly, OT11 cells, in which RBPJk expression was deficient, did not show increased Msx2 activation in response to BMP2 and Notch signaling. Conclusion: These results suggest that BMP2 and Notch signaling cooperatively promote osteogenic differentiation which may mediate vascular calcification in the development of atherosclerosis.

Multifractal analysis of the species structure of small-mammal communities of the Volga-Ural paleobiocenosis

The late Quaternary evolution of the Volga‐Ural paleobiocenosis has been used as an example to demonstrate the possibility of applying multifractal analysis to the species structure of fossil small-mammal communities. No logical contradictions have been found between the ecological specificities of small-mammal communities, as considered in temporal terms, determined by traditional methods and by means of multifractal formalism. The results have demonstrated that multifractal formalism methodologically based on the self-similarity principle may be regarded as an effective tool of paleoactualism in analysis of paleoecological data. Earlier, we demonstrated [3, 4, 7] that the species structure of biotic communities of modern organisms forming terrestrial and aquatic ecosystems, including zooplankton, zoobenthos, insects, and small mammals, may be satisfactorily described in terms of fractal geometry [9, 11]. The notion of self-similarity as an immanent characteristic of a biocenosis is the methodological basis of the fractal theory of community structure that we are developing. Indeed, biological systems are open, strongly nonequilibrium systems whose existence and evolution are determined by a flow of energy resources from the environment. The resultant systems exhibit spatiotemporal scaling (or self-similarity) within a wide range of parameters. This is one of fundamental types of symmetry of the physical world and a morphogenetic factor of the Universe. All of this applies to biotic communities as well. We have demonstrated that multifractal formalism can be adapted to describe the species structure of recent communities, and the multifractal singularity spectrum of the species structure of a community is an adequate generalize geometric image of the community, which cannot be

Targeting of Bone Morphogenetic Protein Growth Factor Complexes to Fibrillin

Both latent transforming growth factor-beta (TGF-beta)-binding proteins fibrillins are components of microfibril networks, and both interact with members of the TGF-beta family of growth factors. Interactions between latent TGF-beta-binding protein-1 and TGF-beta and between fibrillin-1 and bone morphogenetic protein-7 (BMP-7) are mediated by the prodomain of growth factor complexes. To extend this information, investigations were performed to test whether stable complexes are formed by additional selected TGF-beta family members. Using velocity sedimentation in sucrose gradients as an assay, complex formation was demonstrated for BMP-7 and growth and differentiation factor-8 (GDF-8), which are known to exist in prodomain/growth factor complexes. Comparison of these results with complex formation by BMP-2, BMP-4 (full-length and shortened propeptides), BMP-10, and GDF-5 allowed us to conclude that all, except for BMP-2 and the short BMP-4 propeptides, formed complexes with their growth factors. Using surface plasmon resonance, binding affinities between fibrillin and all propeptides were determined. Binding studies revealed that the N-terminal end of fibrillin-1 serves as a universal high affinity docking site for the propeptides of BMP-2, -4, -7, and -10 and GDF-5, but not GDF-8, and located the BMP/GDF binding site within the N-terminal domain in fibrillin-1. Rotary shadowing electron microscopy of molecules of BMP-7 complex bound to fibrillin-1 confirmed these findings and also showed that prodomain binding targets the growth factor to fibrillin. Immunolocalization of BMP-4 demonstrated fibrillar staining limited to certain tissues, indicating tissue-specific targeting of BMP-4. These data implicate the fibrillin microfibril network in the extracellular control of BMP signaling and demonstrate differences in how prodomains target their growth factors to the extracellular space.

Multifunctional Roles of a Bacteriophage ϕ29 Morphogenetic Factor in Assembly and Infection

Low copy number proteins within macromolecular complexes, such as viruses, can be critical to biological function while comprising a minimal mass fraction of the complex. The Bacillus subtilis double-stranded DNA bacteriophage ϕ29 gene 13 product (gp13), previously undetected in the virion, was identified and localized to the distal tip of the tail knob. Western blots and immuno-electron microscopy detected a few copies of gp13 in ϕ29, DNA-free particles, purified tails, and defective particles produced in suppressor-sensitive ( sus) mutant sus13(330) infections. Particles assembled in the absence of intact gp13 ( sus13(342) and sus13(330)) had the gross morphology of ϕ29 but were not infectious. gp13 has predicted structural homology and sequence similarity to the M23 metalloprotease LytM. Poised at the tip of the ϕ29 tail knob, gp13 may serve as a plug to help restrain the highly pressurized packaged genome. Also, in this position, gp13 may be the first virion protein to contact the cell wall in infection, acting as a pilot protein to depolymerize the cell wall. gp13 may facilitate juxtaposition of the tail knob onto the cytoplasmic membrane and the triggering of genome injection.