A role for Syndecan-4 in neural induction involving ERK- and PKC-dependent pathways

Neural induction: New insight into the default model and an extended four-step model in vertebrate embryos

Neural induction is a process by which naïve ectodermal cells differentiate into neural progenitor cells through the inhibition of BMP signaling, a condition typically considered the "default" state in vertebrate embryos. Studies in vertebrate embryos indicate that active FGF/MAPK signaling reduces BMP signaling to facilitate neural induction. Consequently, I propose that FGF stimulation/BMP inhibition more accurately characterizes the default model. Initially, the neuroectoderm is instructed to differentiate into anterior forebrain tissue, with cranial signals stabilizing this outcome. Subsequently, a gradient of caudalizing signals converts the neuroectodermal cells into posterior midbrain, hindbrain, and spinal cord. Furthermore, at the caudal end of the embryo, neuromesodermal progenitor cells are destined to differentiate into both neural progenitor cells and mesodermal cells, aiding in body extension. In light of these observations, I suggest incorporating an additional step, elongation, into the conventional three-step model of neural induction. This updated model encompasses activation, stabilization, transformation, and elongation.

Heparan sulfate proteoglycans (HSPGs) of the ocular lens

Heparan sulfate proteoglycans (HSPGs) reside in most cells; on their surface, in the pericellular milieu and/or extracellular matrix. In the eye, HSPGs can orchestrate the activity of key signalling molecules found in the ocular environment that promote its development and homeostasis. To date, our understanding of the specific roles played by individual HSPG family members, and the heterogeneity of their associated sulfated HS chains, is in its infancy. The crystalline lens is a relatively simple and well characterised ocular tissue that provides an ideal stage to showcase and model the expression and unique roles of individual HSPGs. Individual HSPG core proteins are differentially localised to eye tissues in a temporal and spatial developmental- and cell-type specific manner, and their loss or functional disruption results in unique phenotypic outcomes for the lens, and other ocular tissues. More recent work has found that different HS sulfation enzymes are also presented in a cell- and tissue-specific manner, and that disruption of these different sulfation patterns affects specific HS-protein interactions. Not surprisingly, these sulfated HS chains have also been reported to be required for lens and eye development, with dysregulation of HS chain structure and function leading to pathogenesis and eye-related phenotypes. In the lens, HSPGs undergo significant and specific changes in expression and function that can drive pathology, or in some cases, promote tissue repair. As master signalling regulators, HSPGs may one day serve as valuable biomarkers, and even as putative targets for the development of novel therapeutics, not only for the eye but for many other systemic pathologies.

Characteristic tetraspanin expression patterns mark various tissues during early Xenopus development

The tetraspanins (Tspans) constitute a family of cell surface proteins with four transmembrane domains. Tspans have been found on the plasma membrane and on exosomes of various organelles. Reports on the function of Tspans during the early development of Xenopus have mainly focused on the expression of uroplakins in gametes. Although the roles of extracellular vesicles (EVs) including exosomes have been actively analyzed in cancer research, the contribution of EVs to early development is not well understood. This is because the diffusivity of EVs is not compatible with a very strict developmental process. In this study, we analyzed members of the Tspan family in early development of Xenopus. Expression was prominent in specific organs such as the notochord, eye, cranial neural crest cells (CNCs), trunk neural crest cells, placodes, and somites. We overexpressed several combinations of Tspans in CNCs in vitro and in vivo. Changing the partner changed the distribution of fluorescent-labeled Tspans. Therefore, it is suggested that expression of multiple Tspans in a particular tissue might produce heterogeneity of intercellular communication, which has not yet been recognized.

Flow-Induced Secretion of Endothelial Heparanase Regulates Cardiac Lipoprotein Lipase and Changes Following Diabetes

Background Lipoprotein lipase (LPL)-derived fatty acid is a major source of energy for cardiac contraction. Synthesized in cardiomyocytes, LPL requires translocation to the vascular lumen for hydrolysis of lipoprotein triglyceride, an action mediated by endothelial cell (EC) release of heparanase. We determined whether flow-mediated biophysical forces can cause ECs to secrete heparanase and thus regulate cardiac metabolism. Methods and Results Isolated hearts were retrogradely perfused. Confluent rat aortic ECs were exposed to laminar flow using an orbital shaker. Cathepsin L activity was determined using gelatin-zymography. Diabetes was induced in rats with streptozotocin. Despite the abundance of enzymatically active heparanase in the heart, it was the enzymatically inactive, latent heparanase that was exceptionally responsive to flow-induced release. EC exposed to orbital rotation exhibited a similar pattern of heparanase secretion, an effect that was reproduced by activation of the mechanosensor, Piezo1. The laminar flow-mediated release of heparanase from EC required activation of both the purinergic receptor and protein kinase D, a kinase that assists in vesicular transport of proteins. Heparanase influenced cardiac metabolism by increasing cardiomyocyte LPL displacement along with subsequent replenishment. The flow-induced heparanase secretion was augmented following diabetes and could explain the increased heparin-releasable pool of LPL at the coronary lumen in these diabetic hearts. Conclusions ECs sense fluid shear-stress and communicate this information to subjacent cardiomyocytes with the help of heparanase. This flow-induced mechanosensing and its dynamic control of cardiac metabolism to generate ATP, using LPL-derived fatty acid, is exquisitely adapted to respond to disease conditions, like diabetes.

Normal Table of Xenopus development: a new graphical resource

Normal tables of development are essential for studies of embryogenesis, serving as an important resource for model organisms, including the frog Xenopus laevis. Xenopus has long been used to study developmental and cell biology, and is an increasingly important model for human birth defects and disease, genomics, proteomics and toxicology. Scientists utilize Nieuwkoop and Faber's classic 'Normal Table of Xenopus laevis (Daudin)' and accompanying illustrations to enable experimental reproducibility and reuse the illustrations in new publications and teaching. However, it is no longer possible to obtain permission for these copyrighted illustrations. We present 133 new, high-quality illustrations of X. laevis development from fertilization to metamorphosis, with additional views that were not available in the original collection. All the images are available on Xenbase, the Xenopus knowledgebase (http://www.xenbase.org/entry/zahn.do), for download and reuse under an attributable, non-commercial creative commons license. Additionally, we have compiled a 'Landmarks Table' of key morphological features and marker gene expression that can be used to distinguish stages quickly and reliably (https://www.xenbase.org/entry/landmarks-table.do). This new open-access resource will facilitate Xenopus research and teaching in the decades to come.

Emerging Role of Mechanical Forces in Cell Fate Acquisition

Mechanical forces are now recognized as key cellular effectors that together with genetic and cellular signals physically shape and pattern tissues and organs during development. Increasing efforts are aimed toward understanding the less explored role of mechanical forces in controlling cell fate decisions in embryonic development. Here we discuss recent examples of how differential forces feedback into cell fate specification and tissue patterning. In particular, we focus on the role of actomyosin-contractile force generation and transduction in affecting tissue morphogenesis and cell fate regulation in the embryo.

Syndecan 4 contributes to osteoclast differentiation induced by RANKL through enhancing autophagy

Periodontitis is a common chronic disease. Osteoclast differentiation contributes to alveolar bone resorption which is a distinct phenomenon during periodontitis. Syndecan 4 (SDC4), a member of the syndecan family, was found to be highly expressed during periodontitis. However, little is known about its role in periodontitis. Herein, we explored the role of SDC4 in osteoclast differentiation. An experimental periodontitis rat model was established by ligating the right first molar. The SDC4 expression in periodontium was detected by western blot and immunofluorescence. Our study demonstrated that SDC4 was highly expressed in the periodontium of periodontitis rats. It was positively transcriptionally regulated by NF-κB. SDC4 silencing abrogated osteoclast differentiation induced by RANKL, while SDC4 overexpression enhanced osteoclast differentiation. Moreover, SDC4 enhanced autophagy induced by RANKL. 3-MA, an autophagy inhibitor, was employed to explore whether SDC4 impacts osteoclast differentiation through activating autophagy. Treatment with 3-MA abolished osteoclast differentiation which was enhanced by SDC4, indicating that SDC4 promotes osteoclast differentiation through activating autophagy. This study reveals that SDC4 may contribute to osteoclast differentiation during periodontitis through activating autophagy. It sheds light on the important role of SDC4 in periodontitis.

Enhanced neurogenesis is involved in neuroprotection provided by rottlerin against trimethyltin-induced delayed apoptotic neuronal damage

AIMS

We here investigated the effect of late- and post-ictal treatment with rottlerin, a polyphenol compound isolated from Mallotus philippinensis, on delayed apoptotic neuronal death induced by trimethyltin (TMT) in mice.

MAIN METHODS

Male C57BL/6N mice received a single injection of TMT (2.4 mg/kg, i.p.), and mice were treated with rottlerin after a peak time (i.e., 2 d post-TMT) of convulsive behaviors and apoptotic cell death (5.0 mg/kg, i.p. at 3 and 4 d after TMT injection). Object location test and tail suspension test were performed at 5 d after TMT injection. In addition, changes in the expression of apoptotic and neurogenic markers in the dentate gyrus were examined.

KEY FINDINGS

Late- and post-ictal treatment with rottlerin suppressed delayed neuronal apoptosis in the dentate gyrus, and attenuated memory impairments (as evaluated by object location test) and depression-like behaviors (as evaluated by tail suspension test) at 5 days after TMT injection in mice. In addition, rottlerin enhanced the expression of Sox2 and DCX, and facilitated p-ERK expression in BrdU-incorporated cells in the dentate gyrus of TMT-treated mice. Rottlerin also increased p-Akt expression, and attenuated the increase in the ratio of pro-apoptotic factors/anti-apoptotic factors, and consequent cytosolic cytochrome c release and caspase-3 cleavage. Rottlerin-mediated action was significantly reversed by SL327, an ERK inhibitor.

SIGNIFICANCE

Our results suggest that late- and post-ictal treatment with rottlerin attenuates TMT-induced delayed neuronal apoptosis in the dentate gyrus of mice via promotion of neurogenesis and inhibition of an on-going apoptotic process through up-regulation of p-ERK.

Syndecan-4 is a Novel Therapeutic Target for Intervertebral Disc Degeneration via Suppressing JNK/p53 Pathway

Syndecan-4 is a member of the polysaccharide syndecan family and plays a vital role in intervertebral disc development. Several studies have demonstrated the positive relationship between syndecan-4 expression and intervertebral disc degeneration. However, the detailed molecular mechanism by which syndecan-4 affects the degeneration of nucleus pulposus cells (NPCs) remains unclear. In this study, cell viability was determined by CCK-8 assay, mRNA level was determined by qPCR, and protein expression was determined by western blot. Molecular interaction was determined by chromatin immunoprecipitation assay. A rabbit intervertebral disc degeneration model was established to test for syndecan in vivo. We found that the morphology and viability of NPCs were not affected by the expression of syndecan-4 in the long term. While the NPC function were affected, which results in the degeneration of intervertebral disc. Syndecan-4 overexpression promoted the degeneration of NPCs. Syndecan-4 also activated the JNK signaling pathway and downstream p53 pathways, and promoted degeneration. Inhibition of the JNK pathway, which down-regulated p53 expression, alleviated the degeneration. In an in vivo study, syndecan-4 siRNA injection stopped the development of rabbit disc degeneration, and even created a reverse effect, in which JNK/p53 played a role. Syndecan-4 may be a novel therapeutic target for intervertebral disc degeneration via suppressing the JNK/p53 pathway.

Age-related difference in protective effect of early post-conditioning on ischemic brain injury: possible involvement of MAP-2/Synaptophysin role

Brain Ischemia/Reperfusion (I/R) injury leads to the failure of the microtubules function and neuronal death. Ischemic post-conditioning is defined as a series of rapid alternating interruptions of blood flow in the first seconds of reperfusion. In the present study, the caspase-3, Microtubule-Associated Protein-2 (MAP-2), Protein Kinase C α (PKCα), c-fos, and synaptophysin were evaluated in the hippocampus of focal I/R post-conditioning model in a time -dependent study in aged and young rats. Adult and aged rats were subjected to right MCAO for 30 min and post-conditioned (10 s) for 3 cycles. Sensory-motor tests were performed, and locomotion and anxiety-like behavior were evaluated. Molecular tests were done by detection kit, RT-PCR, and Western blotting techniques. Ninety-six hours after I/R post-conditioning, neurological signs, locomotion, anxiety-like behavior, and ischemic area were improved in young rats compared to 6 h after I/R post-conditioning (P < 0.001). Caspase-3 activity declined in the hippocampus and cortex of I/R post-conditioned young rats in 96 h after I/R post-conditioning compared with 6 h after I/R post-conditioning (P < 0.001). Also, MAP-2 mRNA, MAP-2 protein level, PKCα, c-fos and synaptophysin protein levels were enhanced during post-conditioning in young rats in 96 h after I/R post-conditioning compared with 6 h after induction of I/R post-conditioning. The results of the present study suggested that, early post-conditioning might be considered as a candidate for therapeutic methods against I/R in the adult animals not aged rats. Moreover, inhibition of cell death in post-conditioned ischemic rats was found to be regulated by some neuroprotective molecules as well as MAP-2 and c-fos in young rats. Graphical abstract Graphical abstract representing the post-conditioning (PC) treatment timeline in adult and old rats.

New SDC function prediction based on protein-protein interaction using bioinformatics tools

The precise roles for SDC have been complex to specify. Assigning and reanalyzing protein and peptide identification to novel protein functions is one of the most important challenges in postgenomic era. Here, we provide SDC molecular description to support, contextualize and reanalyze the corresponding protein-protein interaction (PPI). From SDC-1 data mining, we discuss the potential of bioinformatics tools to predict new biological rules of SDC. Using these methods, we have assembled new possibilities for SDC biology from PPI data, once, the understanding of biology complexity cannot be capture from one simple question.

Multifunctionalization of Cells with a Self-Assembling Molecule to Enhance Cell Engraftment

Cell-based therapy is a promising approach to restoring lost functions to compromised organs. However, the issue of inefficient cell engraftment remains to be resolved. Herein, we take a chemical approach to facilitate cell engraftment by using self-assembling molecules which modify two cellular traits: cell survival and invasiveness. In this system, the self-assembling molecule induces syndecan-4 clusters on the cellular surface, leading to enhanced cell viability. Further integration with Halo-tag technology provided this self-assembly structure with matrix metalloproteinase-2 to functionalize cells with cell-invasion activity. In vivo experiments showed that the pretreated cells were able to survive injection and then penetrate and engraft into the host tissue, demonstrating that the system enhances cell engraftment. Therefore, cell-surface modification via an alliance between self-assembling molecules and ligation technologies may prove to be a promising method for cell engraftment.

Triclosan affects axon formation in the neural development stages of zebrafish embryos (Danio rerio)

Triclosan (TCS) is an organic compound with a wide range of antibiotic activity and has been widely used in items ranging from hygiene products to cosmetics; however, recent studies suggest that it has several adverse effects. In particular, TCS can be passed to both fetus and infants, and while some evidence suggests in vitro neurotoxicity, there are currently few studies concerning the mechanisms of TCS-induced developmental neurotoxicity. Therefore, this study aimed to clarify the effect of TCS on neural development using zebrafish models, by analyzing the morphological changes, the alterations observed in fluorescence using HuC-GFP and Olig2-dsRED transgenic zebrafish models, and neurodevelopmental gene expression. TCS exposure decreased the body length, head size, and eye size in a concentration-dependent manner in zebrafish embryos. It increased apoptosis in the central nervous system (CNS) and particularly affected the structure of the CNS, resulting in decreased synaptic density and shortened axon length. In addition, it significantly up-regulated the expression of genes related to axon extension and synapse formation such as α1-Tubulin and Gap43, while decreasing Gfap and Mbp related to axon guidance, myelination and maintenance. Collectively, these changes indicate that exposure to TCS during neurodevelopment, especially during axonogenesis, is toxic. This is the first study to demonstrate the toxicity of TCS during neurogenesis, and suggests a possible mechanism underlying the neurotoxic effects of TCS in developing vertebrates.

Diverse roles for glycosaminoglycans in neural patterning

The nervous system coordinates the functions of most multicellular organisms and their response to the surrounding environment. Its development involves concerted cellular interactions, including migration, axon guidance, and synapse formation. These processes depend on the molecular constituents and structure of the extracellular matrices (ECM). An essential component of ECMs are proteoglycans, i.e., proteins containing unbranched glycan chains known as glycosaminoglycans (GAGs). A defining characteristic of GAGs is their enormous molecular diversity, created by extensive modifications of the glycans during their biosynthesis. GAGs are widely expressed, and their loss can lead to catastrophic neuronal defects. Despite their importance, we are just beginning to understand the function and mechanisms of GAGs in neuronal development. In this review, we discuss recent evidence suggesting GAGs have specific roles in neuronal patterning and synaptogenesis. We examine the function played by the complex modifications present on GAG glycans and their roles in regulating different aspects of neuronal patterning. Moreover, the review considers the function of proteoglycan core proteins in these processes, stressing their likely role as co-receptors of different signaling pathways in a redundant and context-dependent manner. We conclude by discussing challenges and future directions toward a better understanding of these fascinating molecules during neuronal development. Developmental Dynamics 247:54-74, 2018. © 2017 Wiley Periodicals, Inc.

Regulation of vascular smooth muscle cell calcification by syndecan-4/FGF-2/PKCα signalling and cross-talk with TGFβ

AIMS

Vascular calcification is a major cause of morbidity and mortality. Fibroblast growth factor-2 (FGF-2) plays an instructive role in osteogenesis and bone development, but its role in vascular calcification was unknown. Therefore, we investigated the involvement of FGF-2 in vascular calcification and determined the mechanism by which it regulates this process.

METHODS AND RESULTS

We demonstrate that FGF-2 expression is increased in vascular smooth muscle cells (VSMCs) induced to deposit a mineralized matrix by incubation with β-glycerophosphate. FGF-2 is also localized to sites of calcification within human atherosclerotic plaques. The expression of syndecan-4, a heparan sulfate proteoglycan which regulates FGF-2 signalling, is also increased in mineralizing VSMCs and co-localizes with FGF-2 in human calcified atherosclerotic plaques. Exogenous FGF-2 inhibits VSMC mineralization, and this inhibition is reduced when syndecan-4 expression is knocked-down using siRNA. Biochemical inhibition of FGFR signalling using a pan FGFR inhibitor (BGJ398) or knocking-down syndecan-4 expression in VSMCs using siRNA increases VSMC mineralization. These increases are prevented by inhibiting transforming growth factor-β (TGFβ) signalling with SB431542, suggesting cross-talk between FGF-2 and TGFβ signalling is crucial for the regulation of VSMC mineralization. Syndecan-4 can also regulate FGF-2 signalling directly via protein kinase Cα (PKCα) activation. Biochemical inhibition of PKCα activity using Gö6976, or siRNA-mediated suppression of PKCα expression increases VSMC mineralization; this increase is also prevented with SB431542. Finally, the ability of FGF-2 to inhibit VSMC mineralization is reduced when PKCα expression is knocked-down.

CONCLUSION

This is the first demonstration that syndecan-4 promotes FGF-2 signalling, and in turn, suppresses VSMC mineralization by down-regulating TGFβ signalling. Our discoveries that FGF-2 and syndecan-4 expression is increased in mineralizing VSMCs and that PKCα regulates FGF-2 and TGFβ signalling in VSMCs suggests that the syndecan-4/FGF-2/TGFβ signalling axis could represent a new therapeutic target for vascular calcification.

Neural tube closure: cellular, molecular and biomechanical mechanisms

Neural tube closure has been studied for many decades, across a range of vertebrates, as a paradigm of embryonic morphogenesis. Neurulation is of particular interest in view of the severe congenital malformations - 'neural tube defects' - that result when closure fails. The process of neural tube closure is complex and involves cellular events such as convergent extension, apical constriction and interkinetic nuclear migration, as well as precise molecular control via the non-canonical Wnt/planar cell polarity pathway, Shh/BMP signalling, and the transcription factors Grhl2/3, Pax3, Cdx2 and Zic2. More recently, biomechanical inputs into neural tube morphogenesis have also been identified. Here, we review these cellular, molecular and biomechanical mechanisms involved in neural tube closure, based on studies of various vertebrate species, focusing on the most recent advances in the field.

The Molecular Basis of Radial Intercalation during Tissue Spreading in Early Development

Radial intercalation is a fundamental process responsible for the thinning of multilayered tissues during large-scale morphogenesis; however, its molecular mechanism has remained elusive. Using amphibian epiboly, the thinning and spreading of the animal hemisphere during gastrulation, here we provide evidence that radial intercalation is driven by chemotaxis of cells toward the external layer of the tissue. This role of chemotaxis in tissue spreading and thinning is unlike its typical role associated with large-distance directional movement of cells. We identify the chemoattractant as the complement component C3a, a factor normally linked with the immune system. The mechanism is explored by computational modeling and tested in vivo, ex vivo, and in vitro. This mechanism is robust against fluctuations of chemoattractant levels and expression patterns and explains expansion during epiboly. This study provides insight into the fundamental process of radial intercalation and could be applied to a wide range of morphogenetic events.

Expression profiles of the Gα subunits during Xenopus tropicalis embryonic development

Heterotrimeric G protein signaling plays major roles during different cellular events. However, there is a limited understanding of the molecular mechanisms underlying G protein control during embryogenesis. G proteins are highly conserved and can be grouped into four subfamilies according to sequence homology and function. To further studies on G protein function during embryogenesis, the present analysis identified four Gα subunits representative of the different subfamilies and determined their spatiotemporal expression patterns during Xenopus tropicalis embryogenesis. Each of the Gα subunit transcripts was maternally and zygotically expressed, and, as development progressed, dynamic expression patterns were observed. In the early developmental stages, the Gα subunits were expressed in the animal hemisphere and dorsal marginal zone. While expression was observed at the somite boundaries, in vascular structures, in the eye, and in the otic vesicle during the later stages, expression was mainly found in neural tissues, such as the neural tube and, especially, in the cephalic vesicles, neural crest region, and neural crest-derived structures. Together, these results support the pleiotropism and complexity of G protein subfamily functions in different cellular events. The present study constitutes the most comprehensive description to date of the spatiotemporal expression patterns of Gα subunits during vertebrate development.

Syndecan4 coordinates Wnt/JNK and BMP signaling to regulate foregut progenitor development

Temporally and spatially dynamic Wnt and BMP signals are essential to pattern foregut endoderm progenitors that give rise to the liver, pancreas and lungs, but how these two signaling pathways are coordinated in the extracellular space is unknown. Here we identify the transmembrane heparan sulphate proteoglycan Syndecan-4 (Sdc4), as a key regulator of both non-canonical Wnt and BMP signaling in the Xenopus foregut. Foregut-specific Sdc4 depletion results in a disrupted Fibronectin (Fn1) matrix, reduced cell adhesion, and failure to maintain foregut gene expression ultimately leading to foregut organ hypoplasia. Sdc4 is required to maintain robust Wnt/JNK and BMP/Smad1 signaling in the hhex+ foregut progenitors. Pathway analysis suggests that Sdc4 functionally interacts with Fzd7 to promote Wnt/JNK signaling, which maintains foregut identity and cell adhesion. In addition, the Sdc4 ectodomain is required to support Fn1 matrix assembly, which is essential for the robust BMP signaling that promotes foregut gene expression. This work sheds lights on how the extracellular matrix can coordinate different signaling pathways during organogenesis.

Syndecan-4 modulates the proliferation of neural cells and the formation of CaP axons during zebrafish embryonic neurogenesis

Syndecan-4 (Syn4), a single-pass transmembrane heparin sulphate proteoglycan (HSPG), plays significant role in the formation of focal adhesions and interacts with many growth factors to regulate cell migration and neural induction. Here, we show the new roles of syndecan-4(syn4) in zebrafish embryonic neurogenesis. Syn4 is broadly and dynamically expressed throughout the early stages of embryonic development. Knockdown of syn4 increases the expression of the marker genes of multiple types of neural cells. The increased expression of the marker genes is resulted from excessive proliferation of the neural cells. In addition, disrupting syn4 expression results in truncated and multiple aberrant branching of caudal primary (CaP) axons. Collectively, these data indicate that Syn4 suppresses the cellular proliferation during neurogenesis and is crucial for the formation of CaP axons during zebrafish embryogenesis.

Heparan sulfate proteoglycans: a sugar code for vertebrate development?

Heparan sulfate proteoglycans (HSPGs) have long been implicated in a wide range of cell-cell signaling and cell-matrix interactions, both in vitro and in vivo in invertebrate models. Although many of the genes that encode HSPG core proteins and the biosynthetic enzymes that generate and modify HSPG sugar chains have not yet been analyzed by genetics in vertebrates, recent studies have shown that HSPGs do indeed mediate a wide range of functions in early vertebrate development, for example during left-right patterning and in cardiovascular and neural development. Here, we provide a comprehensive overview of the various roles of HSPGs in these systems and explore the concept of an instructive heparan sulfate sugar code for modulating vertebrate development.

Summary: This Review article examines the role of heparan sulfate proteoglycans in vertebrate development and explores the concept of an instructive 'sugar code' for modulating development.

The serpin PN1 is a feedback regulator of FGF signaling in germ layer and primary axis formation

Germ layer formation and primary axis development rely on Fibroblast growth factors (FGFs). In Xenopus, the secreted serine protease HtrA1 induces mesoderm and posterior trunk/tail structures by facilitating the spread of FGF signals. Here, we show that the serpin Protease nexin-1 (PN1) is transcriptionally activated by FGF signals, suppresses mesoderm and promotes head development in mRNA-injected embryos. An antisense morpholino oligonucleotide against PN1 has the opposite effect and inhibits ectodermal fate. However, ectoderm and anterior head structures can be restored in PN1-depleted embryos when HtrA1 and FGF receptor activities are diminished, indicating that FGF signals negatively regulate their formation. We show that PN1 binds to and inhibits HtrA1, prevents degradation of the proteoglycan Syndecan 4 and restricts paracrine FGF/Erk signaling. Our data suggest that PN1 is a negative-feedback regulator of FGF signaling and has important roles in ectoderm and head development.

Expression and roles of syndecan-4 in dental epithelial cell differentiation

Syndecan-4 (SDC4), a transmembrane heparan sulfate proteoglycan, acts as a signal transducer. It affects the growth and differentiation of a number of tissues and organs. However, the specific mechanisms through which SDC4 regulates the differentiation of dental epithelial cells (amelogenesis) and tooth development remains largely unknown. In the present study, to identify the SDC4-regulated processes in dental epithelial cells, the SDC4 expression pattern was examined in mouse molar and postnatal incisor tooth germs during the late bell stage of development. Small interfering RNA (siRNA) was designed for this study and used to downregulate SDC4 expression in the rat dental epithelial cell line, HAT-7. The results revealed that SDC4 was mainly present in the oral epithelium, the dental epithelial cells of enamel organs in the molars and the cervical loops in the incisors. When the inner enamel epithelial cells gave rise to ameloblasts, however, the loss of SDC4 expression was evident. SDC4 was also expressed in stratum intermedium (SI) cells in the incisors and in dental mesenchymal cells adjacent to the cervical loops in molars (E18) and postnatal incisors. Fibroblast growth factor 10 (FGF10) promoted proliferation and slightly decreased cell differentiation. The knockdown of SDC4 using specific siRNA led to a decrease in cell proliferation and a highly significant increase in amelogenin, ameloblastin, kallikrein 4 and matrix metalloproteinase 20 expression, molecules that are known to participate in the formation of enamel. These effects were attenuated by FGF10, which upregulated SDC4 expression. Taken together, these results suggest that SDC4 participates in amelogenesis, and FGF10 may modulate dental epithelial cell behaviors through the regulation of SDC4 expression.

Wnt-signaling and planar cell polarity genes regulate axon guidance along the anteroposterior axis in C. elegans

During the development of the nervous system, neurons encounter signals that inform their outgrowth and polarization. Understanding how these signals combinatorially function to pattern the nervous system is of considerable interest to developmental neurobiologists. The Wnt ligands and their receptors have been well characterized in polarizing cells during asymmetric cell division. The planar cell polarity (PCP) pathway is also critical for cell polarization in the plane of an epithelium. The core set of PCP genes include members of the conserved Wnt-signaling pathway, such as Frizzled and Disheveled, but also the cadherin-domain protein Flamingo. In Drosophila, the Fat and Dachsous cadherins also function in PCP, but in parallel to the core PCP components. C. elegans also have two Fat-like and one Dachsous-like cadherins, at least one of which, cdh-4, contributes to neural development. In C. elegans Wnt ligands and the conserved PCP genes have been shown to regulate a number of different events, including embryonic cell polarity, vulval morphogenesis, and cell migration. As is also observed in vertebrates, the Wnt and PCP genes appear to function to primarily provide information about the anterior to posterior axis of development. Here, we review the recent work describing how mutations in the Wnt and core PCP genes affect axon guidance and synaptogenesis in C. elegans.

In vivo collective cell migration requires an LPAR2-dependent increase in tissue fluidity

Collective cell migration (CCM) and epithelial-mesenchymal transition (EMT) are common to cancer and morphogenesis, and are often considered to be mutually exclusive in spite of the fact that many cancer and embryonic cells that have gone through EMT still cooperate to migrate collectively. Here we use neural crest (NC) cells to address the question of how cells that have down-regulated cell-cell adhesions can migrate collectively. NC cell dissociation relies on a qualitative and quantitative change of the cadherin repertoire. We found that the level of cell-cell adhesion is precisely regulated by internalization of N-cadherin downstream of lysophosphatidic acid (LPA) receptor 2. Rather than promoting the generation of single, fully mesenchymal cells, this reduction of membrane N-cadherin only triggers a partial mesenchymal phenotype. This intermediate phenotype is characterized by an increase in tissue fluidity akin to a solid-like-to-fluid-like transition. This change of plasticity allows cells to migrate under physical constraints without abolishing cell cooperation required for collectiveness.

Changes in glycosaminoglycan structure on differentiation of human embryonic stem cells towards mesoderm and endoderm lineages

BACKGROUND

Proteoglycans are found on the cell surface and in the extracellular matrix, and serve as prime sites for interaction with signaling molecules. Proteoglycans help regulate pathways that control stem cell fate, and therefore represent an excellent tool to manipulate these pathways. Despite their importance, there is a dearth of data linking glycosaminoglycan structure within proteoglycans with stem cell differentiation.

METHODS

Human embryonic stem cell line WA09 (H9) was differentiated into early mesoderm and endoderm lineages, and the glycosaminoglycanomic changes accompanying these transitions were studied using transcript analysis, immunoblotting, immunofluorescence and disaccharide analysis.

RESULTS

Pluripotent H9 cell lumican had no glycosaminoglycan chains whereas in splanchnic mesoderm lumican was glycosaminoglycanated. H9 cells have primarily non-sulfated heparan sulfate chains. On differentiation towards splanchnic mesoderm and hepatic lineages N-sulfo group content increases. Differences in transcript expression of NDST1, HS6ST2 and HS6ST3, three heparan sulfate biosynthetic enzymes, within splanchnic mesoderm cells compared to H9 cells correlate to changes in glycosaminoglycan structure.

CONCLUSIONS

Differentiation of embryonic stem cells markedly changes the proteoglycanome.

GENERAL SIGNIFICANCE

The glycosaminoglycan biosynthetic pathway is complex and highly regulated, and therefore, understanding the details of this pathway should enable better control with the aim of directing stem cell differentiation.

Par3 controls neural crest migration by promoting microtubule catastrophe during contact inhibition of locomotion

There is growing evidence that contact inhibition of locomotion (CIL) is essential for morphogenesis and its failure is thought to be responsible for cancer invasion; however, the molecular bases of this phenomenon are poorly understood. Here we investigate the role of the polarity protein Par3 in CIL during migration of the neural crest, a highly migratory mesenchymal cell type. In epithelial cells, Par3 is localised to the cell-cell adhesion complex and is important in the definition of apicobasal polarity, but the localisation and function of Par3 in mesenchymal cells are not well characterised. We show in Xenopus and zebrafish that Par3 is localised to the cell-cell contact in neural crest cells and is essential for CIL. We demonstrate that the dynamics of microtubules are different in different parts of the cell, with an increase in microtubule catastrophe at the collision site during CIL. Par3 loss-of-function affects neural crest migration by reducing microtubule catastrophe at the site of cell-cell contact and abrogating CIL. Furthermore, Par3 promotes microtubule catastrophe by inhibiting the Rac-GEF Trio, as double inhibition of Par3 and Trio restores microtubule catastrophe at the cell contact and rescues CIL and neural crest migration. Our results demonstrate a novel role of Par3 during neural crest migration, which is likely to be conserved in other processes that involve CIL such as cancer invasion or cell dispersion.

Biological functions of iduronic acid in chondroitin/dermatan sulfate

The presence of iduronic acid in chondroitin/dermatan sulfate changes the properties of the polysaccharides because it generates a more flexible chain with increased binding potentials. Iduronic acid in chondroitin/dermatan sulfate influences multiple cellular properties, such as migration, proliferation, differentiation, angiogenesis and the regulation of cytokine/growth factor activities. Under pathological conditions such as wound healing, inflammation and cancer, iduronic acid has diverse regulatory functions. Iduronic acid is formed by two epimerases (i.e. dermatan sulfate epimerase 1 and 2) that have different tissue distribution and properties. The role of iduronic acid in chondroitin/dermatan sulfate is highlighted by the vast changes in connective tissue features in patients with a new type of Ehler–Danlos syndrome: adducted thumb-clubfoot syndrome. Future research aims to understand the roles of the two epimerases and their interplay with the sulfotransferases involved in chondroitin sulfate/dermatan sulfate biosynthesis. Furthermore, a better definition of chondroitin/dermatan sulfate functions using different knockout models is needed. In this review, we focus on the two enzymes responsible for iduronic acid formation, as well as the role of iduronic acid in health and disease.

Endothelial heparanase regulates heart metabolism by stimulating lipoprotein lipase secretion from cardiomyocytes

OBJECTIVE

After diabetes mellitus, transfer of lipoprotein lipase (LPL) from cardiomyocytes to the coronary lumen increases, and this requires liberation of LPL from the myocyte surface heparan sulfate proteoglycans with subsequent replenishment of this reservoir. At the lumen, LPL breaks down triglyceride to meet the increased demand of the heart for fatty acid. Here, we examined the contribution of coronary endothelial cells (ECs) toward regulation of cardiomyocyte LPL secretion.

APPROACH AND RESULTS

Bovine coronary artery ECs were exposed to high glucose, and the conditioned medium was used to treat cardiomyocytes. EC-conditioned medium liberated LPL from the myocyte surface, in addition to facilitating its replenishment. This effect was attributed to the increased heparanase content in EC-conditioned medium. Of the 2 forms of heparanase secreted from EC in response to high glucose, active heparanase released LPL from the myocyte surface, whereas latent heparanase stimulated reloading of LPL from an intracellular pool via heparan sulfate proteoglycan-mediated RhoA activation.

CONCLUSIONS

Endothelial heparanase is a participant in facilitating LPL increase at the coronary lumen. These observations provide an insight into the cross-talk between ECs and cardiomyocytes to regulate cardiac metabolism after diabetes mellitus.

Syndecans in cartilage breakdown and synovial inflammation

Syndecans are transmembrane heparan sulphate proteoglycans (HSPGs) that have gained increasing interest as regulators of a variety of tissue responses, including cartilage development and remodelling. These proteoglycans are composed of a core protein to which extracellular glycosaminoglycan (GAG) chains are attached. Through these GAG chains, syndecans can interact with a variety of extracellular matrix molecules and bind to a number of soluble mediators including morphogens, growth factors, chemokines and cytokines. The structure and post-translational modification of syndecan GAG chains seem to differ not only from cell to cell, but also during different stages of cellular differentiation, leading to a complexity of syndecan function that is unique among membrane-bound HSPGs. Unlike other membrane-bound HSPGs, syndecans contain intracellular signalling motifs that can initiate signalling mainly through protein kinase C. This Review summarizes our knowledge of the biology of syndecans and the mechanisms by which binding of molecules to syndecans exert different biological effects, particularly in the joints. On the basis of the structural and functional peculiarities of syndecans, we discuss the regulation of syndecans and their roles in the developing joint as well as during degenerative and inflammatory cartilage remodelling as understood from expression studies and functional analyses involving syndecan-deficient mice.

Proteoglycans in stem cells

The remarkable promise of pluripotent and multipotent stem cells (SCs) imparts tremendous optimism for advancement of regenerative medicine, developmental biology, and drug discovery. Perhaps the greatest challenge is to finely direct, control, and command their differentiation. As those processes are managed on many levels, including genomic, transcriptomic, and epigenomic, examination of all of these components will yield powerful tools for manipulation of SCs. Carbohydrates surround all cells, including SCs as a glycocalyx. Of particular interest is the class of carbohydrates known as proteoglycans (PGs), which are a diverse group of glycoconjugates consisting of core protein with one or more glycosaminoglycan (GAG) chains attached. They are primarily located in the extracellular matrix as well as at cell surfaces, where they are bound or anchored to the membrane through their core proteins. GAG chains are linear, anionic, and highly heterogeneous carbohydrates consisting of repeating disaccharides. PGs facilitate interaction of cells with the extracellular environment by interacting with chemokines, growth factors, and other signaling molecules. Core proteins are involved in many signaling pathways, both individually, as well as through attached proteins via GAG-mediated interactions. These essential and accessible functions make PGs an excellent target for manipulating SCs and guiding their fate. Studying the role of PGs in cell development will yield valuable insight into the mechanism of SC differentiation and suggest approaches toward directing those pathways. Such studies may also help identify valuable markers for distinguishing between various cell populations during differentiation.

Low molecular weight heparin inhibits melanoma cell adhesion and migration through a PKCa/JNK signaling pathway inducing actin cytoskeleton changes

Low molecular weight heparin (LMWH) has significant antimetastatic capabilities and affects cancer progression in humans through, not fully defined mechanisms. Here we evaluated its activity at the intracellular level and how it is correlated with melanoma cell adhesion and migration. LMWH inhibited M5 and A375 melanoma cell adhesion and migration in a dose-dependent manner (p⩽0.01). Treatment of M5 melanoma cells with LMWH caused a marked down regulation of constitutive as well as the FN-induced phosphorylation (p⩽0.01) of protein kinase C alpha (PKCa). This was associated with a profound decrease in the cytoplasmic pPKCa (p⩽0.05) and a simultaneous enhancement of nuclear pPKCa localization (p⩽0.01). A significant decrease in the levels of pJNK (p⩽0.01), which is a downstream effector of PKCa, was also demonstrated in the LMWH-treated cells. Furthermore, LMWH-treated cells had disorganized actin stress fibers correlated to a strong decrease in cell-substratum interface area (p⩽0.05) and altered morphology. The decrease in the activation of PKCa, which is an important regulator of cell motility, was directly correlated to the reduced ability of the LMWH-treated melanoma cells to adhere onto and migrate towards the fibronectin (FN) substrate (p⩽0.01). The lineage activation of PKCa-JNK/p38 and their correlation to M5 cell adhesion was confirmed with the utilization of specific inhibitors. In conclusion, LMWH through the downregulation of pPKCa and redistribution to nuclear region attenuates JNK activation, which in turn induces cytoskeleton changes correlated to M5 cell decreased adhesion/migration. This may provide clues for the pharmacological targeting of melanoma.

Rspo3 binds syndecan 4 and induces Wnt/PCP signaling via clathrin-mediated endocytosis to promote morphogenesis

The R-Spondin (Rspo) family of secreted Wnt modulators is involved in development and disease and holds therapeutic promise as stem cell growth factors. Despite growing biological importance, their mechanism of action is poorly understood. Here, we show that Rspo3 binds syndecan 4 (Sdc4) and that together they activate Wnt/PCP signaling. In Xenopus embryos, Sdc4 and Rspo3 are essential for two Wnt/PCP-driven processes-gastrulation movements and head cartilage morphogenesis. Rspo3/PCP signaling during gastrulation requires Wnt5a and is transduced via Fz7, Dvl, and JNK. Rspo3 functions by inducing Sdc4-dependent, clathrin-mediated endocytosis. We show that this internalization is essential for PCP signal transduction, suggesting that endocytosis of Wnt-receptor complexes is a key mechanism by which R-spondins promote Wnt signaling.

Fibroblast growth factors activate mitogen-activated protein kinase pathways to promote migration in ovine trophoblast cells

Fibroblast growth factors (FGFs) 2 and FGF10 are uterine- and conceptus-derived factors that mediate trophoblast activities in cattle and sheep. To extend our understanding of how FGFs may control peri-implantation development in ruminants, we determined whether FGF2 and FGF10 impact trophoblast cell migration. Transwell inserts containing 8 μm pores were used to examine whether FGF2 or FGF10 supplementation increased oTr1 cell migration. Supplementation with 0.5 ng/ml FGF2 or FGF10 did not affect oTr1 cell migration number, but exposure to 5 or 50 ng/ml FGF2 or FGF10 increased (P<0.05) oTr1 cell migration when compared with controls. The involvement of specific MAP kinase (MAPK) cascades in mediating this FGF response was examined by using pharmacological inhibitors of specific MAPKs. Western blot analysis indicated that FGF2 and FGF10 increased phosphorylation status of MAPKs 1, 3, 8, 9, and 14. Exposure to specific inhibitors blocked FGF induction of each MAPK. Exposure to inhibitors before supplementation with FGF2 or FGF10 prevented FGF induction of cell migration, indicating that each of these signaling molecules was required for FGF effects. A final series of studies examined whether FGF2 and FGF10 also mediated the migration of a bovine trophoblast line (CT1 cell). Increases in migration were detected in each cell line by supplementing 5 or 50 ng/ml FGF2 or FGF10 (P<0.05). In summary, FGF2 and FGF10 regulate migratory activity of ovine trophoblast cells through MAPK-dependent pathways. These outcomes provide further evidence that FGFs function as mediators of peri-implantation conceptus development in cattle and sheep.

Syndecans as cell surface receptors: Unique structure equates with functional diversity

An increasing number of functions for syndecan cell surface heparan sulfate proteoglycans have been proposed over the last decade. Moreover, aberrant syndecan regulation has been found to play a critical role in multiple pathologies, including cancers, as well as wound healing and inflammation. As receptors, they have much in common with other molecules on the cell surface. Syndecans are type I transmembrane molecules with cytoplasmic domains that link to the actin cytoskeleton and can interact with a number of regulators. However, they are also highly complex by virtue of their external glycosaminoglycan chains, especially heparan sulfate. This heterodisperse polysaccharide has the potential to interact with many ligands from diverse protein families. Here, we relate the structural features of syndecans to some of their known functions.

Neuronatin promotes neural lineage in ESCs via Ca(2+) signaling

Neural induction is the first step in the formation of the vertebrate central nervous system. The emerging consensus of the mechanisms underlying neural induction is the combined influences from inhibiting bone morphogenetic protein (BMP) signaling and activating fibroblast growth factor (FGF)/Erk signaling, which act extrinsically via either autocrine or paracrine fashions. However, do intrinsic forces (cues) exist and do they play decisive roles in neural induction? These questions remain to be answered. Here, we have identified a novel neural initiator, neuronatin (Nnat), which acts as an intrinsic factor to promote neural fate in mammals and Xenopus. ESCs lacking this intrinsic factor fail to undergo neural induction despite the inhibition of the BMP pathway. We show that Nnat initiates neural induction in ESCs through increasing intracellular Ca(2+) ([Ca(2+) ](i)) by antagonizing Ca(2+) -ATPase isoform 2 (sarco/endoplasmic reticulum Ca(2+) -ATPase isoform 2) in the endoplasmic reticulum, which in turn increases the phosphorylation of Erk1/2 and inhibits the BMP4 pathway and leads to neural induction in conjunction with FGF/Erk pathway.

Transmembrane signaling proteoglycans

Virtually all metazoan cells contain at least one and usually several types of transmembrane proteoglycans. These are varied in protein structure and type of polysaccharide, but the total number of vertebrate genes encoding transmembrane proteoglycan core proteins is less than 10. Some core proteins, including those of the syndecans, always possess covalently coupled glycosaminoglycans; others do not. Syndecan has a long evolutionary history, as it is present in invertebrates, but many other transmembrane proteoglycans are vertebrate inventions. The variety of proteins and their glycosaminoglycan chains is matched by diverse functions. However, all assume roles as coreceptors, often working alongside high-affinity growth factor receptors or adhesion receptors such as integrins. Other common themes are an ability to signal through their cytoplasmic domains, often to the actin cytoskeleton, and linkage to PDZ protein networks. Many transmembrane proteoglycans associate on the cell surface with metzincin proteases and can be shed by them. Work with model systems in vivo and in vitro reveals roles in growth, adhesion, migration, and metabolism. Furthermore, a wide range of phenotypes for the core proteins has been obtained in mouse knockout experiments. Here some of the latest developments in the field are examined in hopes of stimulating further interest in this fascinating group of molecules.

The extracellular matrix in development and morphogenesis: a dynamic view

The extracellular matrix (ECM) is synthesized and secreted by embryonic cells beginning at the earliest stages of development. Our understanding of ECM composition, structure and function has grown considerably in the last several decades and this knowledge has revealed that the extracellular microenvironment is critically important for cell growth, survival, differentiation and morphogenesis. ECM and the cellular receptors that interact with it mediate both physical linkages with the cytoskeleton and the bidirectional flow of information between the extracellular and intracellular compartments. This review considers the range of cell and tissue functions attributed to ECM molecules and summarizes recent findings specific to key developmental processes. The importance of ECM as a dynamic repository for growth factors is highlighted along with more recent studies implicating the 3-dimensional organization and physical properties of the ECM as it relates to cell signaling and the regulation of morphogenetic cell behaviors. Embryonic cell and tissue generated forces and mechanical signals arising from ECM adhesion represent emerging areas of interest in this field.

The signaling mechanisms of syndecan heparan sulfate proteoglycans

Syndecans are membrane proteins controlling cell proliferation, differentiation, adhesion, and migration. Their extracellular domains bear versatile heparan sulfate chains that provide structural determinants for syndecans to function as coreceptors or activators for molecules like growth factors and constituents of the matrix. Syndecans also signal via their protein cores and their conserved transmembrane and cytoplasmic domains. The direct interactions and signaling cascades they support are becoming better characterized. These interactions are regulated by phosphorylation, induced clustering and shedding of the syndecan extracellular domain. Moreover evidence is emerging that syndecans concentrate in unconventional lipid domains and might govern novel vesicular trafficking pathways. Here we focus on recent findings that refine our understanding of the complex structure-function relationships of these cellular effectors.