Background S ecreted F rizzled r elated p roteins (SFRPs) are extracellular regulators of Wnt sig... more Background S ecreted F rizzled r elated p roteins (SFRPs) are extracellular regulators of Wnt signaling. These proteins contain an N-terminal cysteine rich domain (CRD) highly similar to the CRDs of the Frizzled family of seven-transmembrane proteins that act as Wnt receptors. SFRPs can bind to Wnts and prevent their interaction with the Frizzled receptor. Recently it has been reported that a splice variant of human Frizzled-4 (FZD4S) lacking the transmembrane and the cytoplasmic domains of Frizzled-4 can activate rather than inhibit Wnt-8 activity in Xenopus embryos. This indicates that secreted CRD containing proteins such as Frizzled ecto-domains and SFRPs may not always act as Wnt inhibitors. It is not known how FZD4S can activate Wnt/β-catenin signaling and what biological role this molecule plays in vivo. Results Here we report that the Xenopus frizzled-4 is alternatively spliced to give rise to a putative secreted protein that lacks the seven-transmembrane and the cytoplasmic...
Xenopus frizzled-4S, a splicing variant of Xfz4 is a context-dependent activator and inhibitor of... more Xenopus frizzled-4S, a splicing variant of Xfz4 is a context-dependent activator and inhibitor of Wnt/β-catenin signaling
The International journal of developmental biology, 2001
Seven-transmembrane receptors of the frizzled family can interact with secreted Wnt ligands and t... more Seven-transmembrane receptors of the frizzled family can interact with secreted Wnt ligands and transmit Wnt signals into the cell. Dependent on the ligand receptor combination, distinct Wnt pathways are activated. Xenopus frizzled 7 (Xfz7) and Xwnt-8b as well as Human frizzled 5 (Hfz5) and Xwnt-5a can act synergistically in the activation of Wnt/beta-catenin target genes siamois (Xsia) and nodal related 3 (Xnr3) and in the induction of ectopic axes in Xenopus embryos. In order to characterize the role of different protein domains of Xfz7 in Wnt/beta-catenin signaling, chimeric Xfz7/Hfz5 receptors were generated in which the extracellular (N5-TC7) or the intracellular domains (NT7-C5) between Xfz7 and Hfz5 were exchanged. We present evidence that the extracellular domain of Xfz7 can interact with Xwnt-5a and that the intracellular C-terminus can transmit a Wnt/beta-catenin signal. Despite these abilities, Xfz7 and Xwnt-5a do not act synergistically in the activation of Wnt/beta-cate...
Coronavirus disease 2019 (COVID-19), caused by the severe acute respiratory syndrome coronavirus ... more Coronavirus disease 2019 (COVID-19), caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) virus, has emerged as a global pandemic worldwide. In this study, we used ARTIC primers–based amplicon sequencing to profile 225 SARS-CoV-2 genomes from India. Phylogenetic analysis of 202 high-quality assemblies identified the presence of all the five reported clades 19A, 19B, 20A, 20B, and 20C in the population. The analyses revealed Europe and Southeast Asia as two major routes for introduction of the disease in India followed by local transmission. Interestingly, the19B clade was found to be more prevalent in our sequenced genomes (17%) compared to other genomes reported so far from India. Haplotype network analysis showed evolution of 19A and 19B clades in parallel from predominantly Gujarat state in India, suggesting it to be one of the major routes of disease transmission in India during the months of March and April, whereas 20B and 20C appeared to evolve from 20A....
The host immune responses to Staphylococcus epidermidis, a frequent cause of nosocomial infection... more The host immune responses to Staphylococcus epidermidis, a frequent cause of nosocomial infections, is not well understood. We have established a novel bath immersion model of this infection in zebrafish larvae. Macrophages play a primary role in the host immune response and are involved in clearance of infection in the larvae. S.epidermidis infection activates Tlr-2 signalling pathway by upregulation of tlr-2. There is a marked inflammation characterised by heightened NF-κB signalling and elevation of several pro-inflammatory cytokines. There is rapid upregulation of il-1b and tnf-a transcripts, while increase in il-6 levels is relatively more delayed. IL-6 signalling pathway is further amplified by elevation of IL-6 signal transducer (il-6st) levels, which is negatively-regulated by dre-miR-142-5p. Our studies describe the host immune responses to S.epidermidis infection and identifies a novel role for miR-142-5p – il-6st interaction in modulating this response.
Cell signalling through Frizzled receptors has evolved to considerable complexity within the meta... more Cell signalling through Frizzled receptors has evolved to considerable complexity within the metazoans. The Frizzled-dependent signalling cascade comprises several branches, whose differential activation depends on specific Wnt ligands, Frizzled receptor isoforms and the cellular context. In Xenopus laevis embryos, the canonical beta-catenin pathway contributes to the establishment of the dorsal-ventral axis. A different branch, referred to as the planar cell polarity pathway, is essential for cell polarization during elongation of the axial mesoderm by convergent extension. Here we demonstrate that a third branch of the cascade is independent of Dishevelled function and involves signalling through trimeric G proteins and protein kinase C (PKC). During gastrulation, Frizzled-7 (Fz7)-dependent PKC signalling controls cell-sorting behaviour in the mesoderm. Loss of zygotic Fz7 function results in the inability of involuted anterior mesoderm to separate from the ectoderm, which leads to severe gastrulation defects. This result provides a developmentally relevant in vivo function for the Fz/PKC pathway in vertebrates.
The International journal of developmental biology
The nucleolar protein 4-like (NOL4L) gene is present on chromosome 20 (20q11.21) in humans. Parts... more The nucleolar protein 4-like (NOL4L) gene is present on chromosome 20 (20q11.21) in humans. Parts of this gene have been shown to fuse with RUNX1 and PAX5 in acute myeloid leukemia and acute lymphoblastic leukemia, respectively. The normal function of NOL4L in humans and other organisms is not well understood. The expression patterns and functions of NOL4L homologs during vertebrate development have not been reported. We sought to address these questions by studying the expression pattern of zebrafish nol4l during embryogenesis. Our data show that Znol4l mRNA is expressed in multiple organs in zebrafish embryos. The sites of expression include parts of the brain, spinal cord, pronephros, hematopoietic cells and gut.
FASEB journal : official publication of the Federation of American Societies for Experimental Biology, Jun 3, 2016
C-type lectin family 14, member A (CLEC14A), is a single-pass transmembrane glycoprotein that is ... more C-type lectin family 14, member A (CLEC14A), is a single-pass transmembrane glycoprotein that is overexpressed in tumor endothelial cells, and it promotes sprouting angiogenesis and modulates endothelial function via interactions with extracellular matrix proteins. Here, we show that CLEC14A is cleaved by rhomboid-like protein 2 (RHBDL2), one of 3 catalytic mammalian rhomboid-like (RHBDL) proteases, but that it is not cleaved by RHBDL1 or -3. Site-directed mutagenesis identified the precise site at which RHBDL2 cleaves CLEC14A, and targeted, small interfering RNAs that knockdown endogenous CLEC14A and RHBDL2 in human endothelial cells validated the specificity of CLEC14A shedding by RHBDL2. Loss of endogenous cleaved CLEC14A increased endothelial migration 2-fold, whereas that addition of recombinant cleaved CLEC14A inhibited the sprouting of human and murine endothelial cells 3-fold in several in vitro models. We assessed the in vivo role of cleaved CLEC14A in angiogenesis by using...
Tumor endothelial markers (TEMs) that are highly expressed in human tumor vasculature compared wi... more Tumor endothelial markers (TEMs) that are highly expressed in human tumor vasculature compared with vasculature in normal tissue hold clear therapeutic potential. We report that the C-type lectin CLEC14A is a novel TEM. Immunohistochemical and immunofluorescence staining of tissue arrays has shown that CLEC14A is strongly expressed in tumor vasculature when compared with vessels in normal tissue. CLEC14A overexpression in tumor vessels was seen in a wide range of solid tumor types. Functional studies showed that CLEC14A induces filopodia and facilitates endothelial migration, tube formation and vascular development in zebrafish that is, CLEC14A regulates pro-angiogenic phenotypes. CLE-C14A antisera inhibited cell migration and tube formation, suggesting that anti-CLEC14A antibodies may have anti-angiogenic activity. Finally, in endothelial cultures, expression of CLEC14A increased at low shear stress, and we hypothesize that low shear stress due to poor blood flow in the disorganized tumor vasculature induces expression of CLEC14A on tumor vessels and proangiogenic phenotypes.
The process of angiogenesis requires endothelial cells to undergo profound changes in shape and p... more The process of angiogenesis requires endothelial cells to undergo profound changes in shape and polarity. This must involve remodelling of the endothelial cell cytoskeleton; however, we know little of this process or of the proteins that control it. We used a co-culture assay of angiogenesis to examine the cytoskeleton of endothelial cells actively undergoing angiogenic morphogenesis. We find that elongation of endothelial cells during angiogenesis is accompanied by stabilisation of microtubules and their alignment into parallel arrays directed at the growing tip. In other systems, similar microtubule alignments are mediated by the formin family of cytoskeletal regulators. We screened a library of human formins and indentified the novel formin FMNL3/FRL2 as a critical regulator of endothelial cell elongation during angiogenesis. We show that activated FMNL3 triggers microtubule alignment and that FMNL3 is required for microtubule alignment during angiogenic morphogenesis. FMNL3 is h...
Introduction 3. Developmental morphogenesis 4. Frizzled7 dictates embryonic morphogenesis 4.1. Wn... more Introduction 3. Developmental morphogenesis 4. Frizzled7 dictates embryonic morphogenesis 4.1. Wnt signalling is a highly conserved developmental signalling pathway 4.2. Frizzled7 is an evolutionarily conserved gene in the gut 4.3. Frizzled7 activates different Wnt signalling pathways 4.4. Frizzled7-mediated canonical signalling during development 4.5. Frizzled7-mediated non-canonical signalling during development 5. Frizzled7 in tumour morphogenesis 5.1. Colorectal cancer morphogenesis 5.2. Frizzled7 in colorectal cancer morphogenesis 6. Perspectives 7. Acknowledgement 8. References NEED FIGURES
Background Activation of the Wnt signalling cascade is primarily based on the interplay between W... more Background Activation of the Wnt signalling cascade is primarily based on the interplay between Wnt ligands, their receptors and extracellular modulators. One prominent family of extracellular modulators is represented by the SFRP (secreted Frizzled-related protein) family. These proteins have significant similarity to the extracellular domain of Frizzled receptors, suggesting that they bind Wnt ligands and inhibit signalling. The SFRP-type protein Fz4-v1, a splice variant of the Frizzled-4 receptor found in humans and Xenopus, was shown to augment Wnt/β-catenin signalling, and also interacts with those Wnt ligands that act on β-catenin-independent Wnt pathways. Findings Here we show that Xenopus Fz4-v1 can activate and inhibit the β-catenin-dependent Wnt pathway. Gain-of-function experiments revealed that high Wnt/β-catenin activity is inhibited by low and high concentrations of Fz4-v1. In contrast, signals generated by low amounts of Wnt ligands were enhanced by low concentrations...
We have applied search algorithms to expression databases to identify genes whose expression is r... more We have applied search algorithms to expression databases to identify genes whose expression is restricted to the endothelial cell. Such genes frequently play a critical role in endothelial biology and angiogenesis. Two such genes are the roundabout receptor Robo4 and the ECSCR (endothelial-cell-specific chemotaxis regulator). Endothelial cells express both Robo1 and Robo4, which we have knocked down using siRNA (small interfering RNA) and then studied the effect in a variety of in vitro assays. Both Robo4 and Robo1 knockdown inhibited in vitro tube formation on Matrigel™. Transfection of Robo4 into endothelial cells increased the number of filopodial extensions from the cell, but failed to do so in Robo1-knockdown cells. Separate immunoprecipitation studies showed that Robo1 and Robo4 heterodimerize. We conclude from this and other work that a heteroduplex of Robo1 and Robo4 signals through WASP (Wiskott–Aldrich syndrome protein) and other actin nucleation-promoting factors to incr...
The International Journal of Developmental Biology, 2021
Kidney-related disorders affect millions of people worldwide. A survey of chronic kidney disease ... more Kidney-related disorders affect millions of people worldwide. A survey of chronic kidney disease (CKD) patients showed that the burden of kidney diseases is increasing every year. The global burden of disease (GBD) study 2017 ranked CKD as the 12th leading cause of deaths worldwide. Hence, identification of the causes of kidney diseases, development of accurate diagnostic methods and novel therapeutics is highly relevant. Model organisms that faithfully recapitulate human diseases play important roles in understanding the disease process and provide valuable ground to find their cure. Zebrafish is an excellent model to study the development, pathophysiology and molecular aspects of human kidney diseases. In this review, we summarize various genetic and experimental manipulations that can be carried out in zebrafish to better understand the pathophysiology of human kidney diseases. We suggest that these methods will be helpful in the development of potential therapies to treat kidney...
Background: Activation of the Wnt signalling cascade is primarily based on the interplay between ... more Background: Activation of the Wnt signalling cascade is primarily based on the interplay between Wnt ligands, their receptors and extracellular modulators. One prominent family of extracellular modulators is represented by the SFRP (secreted Frizzled-related protein) family. These proteins have significant similarity to the extracellular domain of Frizzled receptors, suggesting that they bind Wnt ligands and inhibit signalling. The SFRP-type protein Fz4-v1, a splice variant of the Frizzled-4 receptor found in humans and Xenopus, was shown to augment Wnt/β-catenin signalling, and also interacts with those Wnt ligands that act on β-catenin-independent Wnt pathways. Findings: Here we show that Xenopus Fz4-v1 can activate and inhibit the β-catenin-dependent Wnt pathway. Gain-of-function experiments revealed that high Wnt/β-catenin activity is inhibited by low and high concentrations of Fz4-v1. In contrast, signals generated by low amounts of Wnt ligands were enhanced by low concentrations of Fz4-v1 but were repressed by high concentrations. This biphasic activity of Fz4-v1 was not observed in non-canonical Wnt signalling. Fz4-v1 enhanced β-catenin-independent Wnt signalling triggered by either low or high doses of Wnt11. Antisense morpholino-mediated knock-down experiments demonstrated that in early Xenopus embryos Fz4-v1 is required for the migration of cranial neural crest cells and for the development of the dorsal fin. Conclusions: For the first time, we show that a splice variant of the Frizzled-4 receptor modulates Wnt signalling in a dose-dependent, biphasic manner. These results also demonstrate that the cystein-rich domain (CRD), which is shared by Fz4-v1 and SFRPs, is sufficient for the biphasic activity of these secreted Wnt modulators.
Background S ecreted F rizzled r elated p roteins (SFRPs) are extracellular regulators of Wnt sig... more Background S ecreted F rizzled r elated p roteins (SFRPs) are extracellular regulators of Wnt signaling. These proteins contain an N-terminal cysteine rich domain (CRD) highly similar to the CRDs of the Frizzled family of seven-transmembrane proteins that act as Wnt receptors. SFRPs can bind to Wnts and prevent their interaction with the Frizzled receptor. Recently it has been reported that a splice variant of human Frizzled-4 (FZD4S) lacking the transmembrane and the cytoplasmic domains of Frizzled-4 can activate rather than inhibit Wnt-8 activity in Xenopus embryos. This indicates that secreted CRD containing proteins such as Frizzled ecto-domains and SFRPs may not always act as Wnt inhibitors. It is not known how FZD4S can activate Wnt/β-catenin signaling and what biological role this molecule plays in vivo. Results Here we report that the Xenopus frizzled-4 is alternatively spliced to give rise to a putative secreted protein that lacks the seven-transmembrane and the cytoplasmic...
Xenopus frizzled-4S, a splicing variant of Xfz4 is a context-dependent activator and inhibitor of... more Xenopus frizzled-4S, a splicing variant of Xfz4 is a context-dependent activator and inhibitor of Wnt/β-catenin signaling
The International journal of developmental biology, 2001
Seven-transmembrane receptors of the frizzled family can interact with secreted Wnt ligands and t... more Seven-transmembrane receptors of the frizzled family can interact with secreted Wnt ligands and transmit Wnt signals into the cell. Dependent on the ligand receptor combination, distinct Wnt pathways are activated. Xenopus frizzled 7 (Xfz7) and Xwnt-8b as well as Human frizzled 5 (Hfz5) and Xwnt-5a can act synergistically in the activation of Wnt/beta-catenin target genes siamois (Xsia) and nodal related 3 (Xnr3) and in the induction of ectopic axes in Xenopus embryos. In order to characterize the role of different protein domains of Xfz7 in Wnt/beta-catenin signaling, chimeric Xfz7/Hfz5 receptors were generated in which the extracellular (N5-TC7) or the intracellular domains (NT7-C5) between Xfz7 and Hfz5 were exchanged. We present evidence that the extracellular domain of Xfz7 can interact with Xwnt-5a and that the intracellular C-terminus can transmit a Wnt/beta-catenin signal. Despite these abilities, Xfz7 and Xwnt-5a do not act synergistically in the activation of Wnt/beta-cate...
Coronavirus disease 2019 (COVID-19), caused by the severe acute respiratory syndrome coronavirus ... more Coronavirus disease 2019 (COVID-19), caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) virus, has emerged as a global pandemic worldwide. In this study, we used ARTIC primers–based amplicon sequencing to profile 225 SARS-CoV-2 genomes from India. Phylogenetic analysis of 202 high-quality assemblies identified the presence of all the five reported clades 19A, 19B, 20A, 20B, and 20C in the population. The analyses revealed Europe and Southeast Asia as two major routes for introduction of the disease in India followed by local transmission. Interestingly, the19B clade was found to be more prevalent in our sequenced genomes (17%) compared to other genomes reported so far from India. Haplotype network analysis showed evolution of 19A and 19B clades in parallel from predominantly Gujarat state in India, suggesting it to be one of the major routes of disease transmission in India during the months of March and April, whereas 20B and 20C appeared to evolve from 20A....
The host immune responses to Staphylococcus epidermidis, a frequent cause of nosocomial infection... more The host immune responses to Staphylococcus epidermidis, a frequent cause of nosocomial infections, is not well understood. We have established a novel bath immersion model of this infection in zebrafish larvae. Macrophages play a primary role in the host immune response and are involved in clearance of infection in the larvae. S.epidermidis infection activates Tlr-2 signalling pathway by upregulation of tlr-2. There is a marked inflammation characterised by heightened NF-κB signalling and elevation of several pro-inflammatory cytokines. There is rapid upregulation of il-1b and tnf-a transcripts, while increase in il-6 levels is relatively more delayed. IL-6 signalling pathway is further amplified by elevation of IL-6 signal transducer (il-6st) levels, which is negatively-regulated by dre-miR-142-5p. Our studies describe the host immune responses to S.epidermidis infection and identifies a novel role for miR-142-5p – il-6st interaction in modulating this response.
Cell signalling through Frizzled receptors has evolved to considerable complexity within the meta... more Cell signalling through Frizzled receptors has evolved to considerable complexity within the metazoans. The Frizzled-dependent signalling cascade comprises several branches, whose differential activation depends on specific Wnt ligands, Frizzled receptor isoforms and the cellular context. In Xenopus laevis embryos, the canonical beta-catenin pathway contributes to the establishment of the dorsal-ventral axis. A different branch, referred to as the planar cell polarity pathway, is essential for cell polarization during elongation of the axial mesoderm by convergent extension. Here we demonstrate that a third branch of the cascade is independent of Dishevelled function and involves signalling through trimeric G proteins and protein kinase C (PKC). During gastrulation, Frizzled-7 (Fz7)-dependent PKC signalling controls cell-sorting behaviour in the mesoderm. Loss of zygotic Fz7 function results in the inability of involuted anterior mesoderm to separate from the ectoderm, which leads to severe gastrulation defects. This result provides a developmentally relevant in vivo function for the Fz/PKC pathway in vertebrates.
The International journal of developmental biology
The nucleolar protein 4-like (NOL4L) gene is present on chromosome 20 (20q11.21) in humans. Parts... more The nucleolar protein 4-like (NOL4L) gene is present on chromosome 20 (20q11.21) in humans. Parts of this gene have been shown to fuse with RUNX1 and PAX5 in acute myeloid leukemia and acute lymphoblastic leukemia, respectively. The normal function of NOL4L in humans and other organisms is not well understood. The expression patterns and functions of NOL4L homologs during vertebrate development have not been reported. We sought to address these questions by studying the expression pattern of zebrafish nol4l during embryogenesis. Our data show that Znol4l mRNA is expressed in multiple organs in zebrafish embryos. The sites of expression include parts of the brain, spinal cord, pronephros, hematopoietic cells and gut.
FASEB journal : official publication of the Federation of American Societies for Experimental Biology, Jun 3, 2016
C-type lectin family 14, member A (CLEC14A), is a single-pass transmembrane glycoprotein that is ... more C-type lectin family 14, member A (CLEC14A), is a single-pass transmembrane glycoprotein that is overexpressed in tumor endothelial cells, and it promotes sprouting angiogenesis and modulates endothelial function via interactions with extracellular matrix proteins. Here, we show that CLEC14A is cleaved by rhomboid-like protein 2 (RHBDL2), one of 3 catalytic mammalian rhomboid-like (RHBDL) proteases, but that it is not cleaved by RHBDL1 or -3. Site-directed mutagenesis identified the precise site at which RHBDL2 cleaves CLEC14A, and targeted, small interfering RNAs that knockdown endogenous CLEC14A and RHBDL2 in human endothelial cells validated the specificity of CLEC14A shedding by RHBDL2. Loss of endogenous cleaved CLEC14A increased endothelial migration 2-fold, whereas that addition of recombinant cleaved CLEC14A inhibited the sprouting of human and murine endothelial cells 3-fold in several in vitro models. We assessed the in vivo role of cleaved CLEC14A in angiogenesis by using...
Tumor endothelial markers (TEMs) that are highly expressed in human tumor vasculature compared wi... more Tumor endothelial markers (TEMs) that are highly expressed in human tumor vasculature compared with vasculature in normal tissue hold clear therapeutic potential. We report that the C-type lectin CLEC14A is a novel TEM. Immunohistochemical and immunofluorescence staining of tissue arrays has shown that CLEC14A is strongly expressed in tumor vasculature when compared with vessels in normal tissue. CLEC14A overexpression in tumor vessels was seen in a wide range of solid tumor types. Functional studies showed that CLEC14A induces filopodia and facilitates endothelial migration, tube formation and vascular development in zebrafish that is, CLEC14A regulates pro-angiogenic phenotypes. CLE-C14A antisera inhibited cell migration and tube formation, suggesting that anti-CLEC14A antibodies may have anti-angiogenic activity. Finally, in endothelial cultures, expression of CLEC14A increased at low shear stress, and we hypothesize that low shear stress due to poor blood flow in the disorganized tumor vasculature induces expression of CLEC14A on tumor vessels and proangiogenic phenotypes.
The process of angiogenesis requires endothelial cells to undergo profound changes in shape and p... more The process of angiogenesis requires endothelial cells to undergo profound changes in shape and polarity. This must involve remodelling of the endothelial cell cytoskeleton; however, we know little of this process or of the proteins that control it. We used a co-culture assay of angiogenesis to examine the cytoskeleton of endothelial cells actively undergoing angiogenic morphogenesis. We find that elongation of endothelial cells during angiogenesis is accompanied by stabilisation of microtubules and their alignment into parallel arrays directed at the growing tip. In other systems, similar microtubule alignments are mediated by the formin family of cytoskeletal regulators. We screened a library of human formins and indentified the novel formin FMNL3/FRL2 as a critical regulator of endothelial cell elongation during angiogenesis. We show that activated FMNL3 triggers microtubule alignment and that FMNL3 is required for microtubule alignment during angiogenic morphogenesis. FMNL3 is h...
Introduction 3. Developmental morphogenesis 4. Frizzled7 dictates embryonic morphogenesis 4.1. Wn... more Introduction 3. Developmental morphogenesis 4. Frizzled7 dictates embryonic morphogenesis 4.1. Wnt signalling is a highly conserved developmental signalling pathway 4.2. Frizzled7 is an evolutionarily conserved gene in the gut 4.3. Frizzled7 activates different Wnt signalling pathways 4.4. Frizzled7-mediated canonical signalling during development 4.5. Frizzled7-mediated non-canonical signalling during development 5. Frizzled7 in tumour morphogenesis 5.1. Colorectal cancer morphogenesis 5.2. Frizzled7 in colorectal cancer morphogenesis 6. Perspectives 7. Acknowledgement 8. References NEED FIGURES
Background Activation of the Wnt signalling cascade is primarily based on the interplay between W... more Background Activation of the Wnt signalling cascade is primarily based on the interplay between Wnt ligands, their receptors and extracellular modulators. One prominent family of extracellular modulators is represented by the SFRP (secreted Frizzled-related protein) family. These proteins have significant similarity to the extracellular domain of Frizzled receptors, suggesting that they bind Wnt ligands and inhibit signalling. The SFRP-type protein Fz4-v1, a splice variant of the Frizzled-4 receptor found in humans and Xenopus, was shown to augment Wnt/β-catenin signalling, and also interacts with those Wnt ligands that act on β-catenin-independent Wnt pathways. Findings Here we show that Xenopus Fz4-v1 can activate and inhibit the β-catenin-dependent Wnt pathway. Gain-of-function experiments revealed that high Wnt/β-catenin activity is inhibited by low and high concentrations of Fz4-v1. In contrast, signals generated by low amounts of Wnt ligands were enhanced by low concentrations...
We have applied search algorithms to expression databases to identify genes whose expression is r... more We have applied search algorithms to expression databases to identify genes whose expression is restricted to the endothelial cell. Such genes frequently play a critical role in endothelial biology and angiogenesis. Two such genes are the roundabout receptor Robo4 and the ECSCR (endothelial-cell-specific chemotaxis regulator). Endothelial cells express both Robo1 and Robo4, which we have knocked down using siRNA (small interfering RNA) and then studied the effect in a variety of in vitro assays. Both Robo4 and Robo1 knockdown inhibited in vitro tube formation on Matrigel™. Transfection of Robo4 into endothelial cells increased the number of filopodial extensions from the cell, but failed to do so in Robo1-knockdown cells. Separate immunoprecipitation studies showed that Robo1 and Robo4 heterodimerize. We conclude from this and other work that a heteroduplex of Robo1 and Robo4 signals through WASP (Wiskott–Aldrich syndrome protein) and other actin nucleation-promoting factors to incr...
The International Journal of Developmental Biology, 2021
Kidney-related disorders affect millions of people worldwide. A survey of chronic kidney disease ... more Kidney-related disorders affect millions of people worldwide. A survey of chronic kidney disease (CKD) patients showed that the burden of kidney diseases is increasing every year. The global burden of disease (GBD) study 2017 ranked CKD as the 12th leading cause of deaths worldwide. Hence, identification of the causes of kidney diseases, development of accurate diagnostic methods and novel therapeutics is highly relevant. Model organisms that faithfully recapitulate human diseases play important roles in understanding the disease process and provide valuable ground to find their cure. Zebrafish is an excellent model to study the development, pathophysiology and molecular aspects of human kidney diseases. In this review, we summarize various genetic and experimental manipulations that can be carried out in zebrafish to better understand the pathophysiology of human kidney diseases. We suggest that these methods will be helpful in the development of potential therapies to treat kidney...
Background: Activation of the Wnt signalling cascade is primarily based on the interplay between ... more Background: Activation of the Wnt signalling cascade is primarily based on the interplay between Wnt ligands, their receptors and extracellular modulators. One prominent family of extracellular modulators is represented by the SFRP (secreted Frizzled-related protein) family. These proteins have significant similarity to the extracellular domain of Frizzled receptors, suggesting that they bind Wnt ligands and inhibit signalling. The SFRP-type protein Fz4-v1, a splice variant of the Frizzled-4 receptor found in humans and Xenopus, was shown to augment Wnt/β-catenin signalling, and also interacts with those Wnt ligands that act on β-catenin-independent Wnt pathways. Findings: Here we show that Xenopus Fz4-v1 can activate and inhibit the β-catenin-dependent Wnt pathway. Gain-of-function experiments revealed that high Wnt/β-catenin activity is inhibited by low and high concentrations of Fz4-v1. In contrast, signals generated by low amounts of Wnt ligands were enhanced by low concentrations of Fz4-v1 but were repressed by high concentrations. This biphasic activity of Fz4-v1 was not observed in non-canonical Wnt signalling. Fz4-v1 enhanced β-catenin-independent Wnt signalling triggered by either low or high doses of Wnt11. Antisense morpholino-mediated knock-down experiments demonstrated that in early Xenopus embryos Fz4-v1 is required for the migration of cranial neural crest cells and for the development of the dorsal fin. Conclusions: For the first time, we show that a splice variant of the Frizzled-4 receptor modulates Wnt signalling in a dose-dependent, biphasic manner. These results also demonstrate that the cystein-rich domain (CRD), which is shared by Fz4-v1 and SFRPs, is sufficient for the biphasic activity of these secreted Wnt modulators.
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Papers by Rajeeb Swain