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David R Mcclay - One of the best experts on this subject based on the ideXlab platform.
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Gastrulation in the sea urchin.
Current Topics in Developmental Biology, 2019Co-Authors: David R Mcclay, Jacob Warner, Megan L. Martik, Esther Miranda, Leslie A. SlotaAbstract:Abstract Gastrulation is arguably the most important evolutionary innovation in the animal kingdom. This process provides the basic embryonic architecture, an inner layer separated from an outer layer, from which all animal forms arise. An extraordinarily simple and elegant process of gastrulation is observed in the sea urchin embryo. The cells participating in sea urchin gastrulation are specified early during cleavage. One outcome of that specification is the expression of transcription factors that control each of the many subsequent morphogenetic changes. The first of these movements is an epithelial-mesenchymal transition (EMT) of skeletogenic mesenchyme cells, then EMT of pigment cell progenitors. Shortly thereafter, invagination of the Archenteron occurs. At the end of Archenteron extension, a second wave of EMT occurs to release immune cells into the blastocoel and primordial germ cells that will home to the coelomic pouches. The Archenteron then remodels to establish the three parts of the gut, and at the anterior end, the gut fuses with the stomodaeum to form the through-gut. As part of the anterior remodeling, mesodermal coelomic pouches bud off the lateral sides of the Archenteron tip. Multiple cell biological processes conduct each of these movements and in some cases the upstream transcription factors controlling this process have been identified. Remarkably, each event seamlessly occurs at the right time to orchestrate formation of the primitive body plan. This review covers progress toward understanding many of the molecular mechanisms underlying this sequence of morphogenetic events.
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New insights from a high-resolution look at gastrulation in the sea urchin, Lytechinus variegatus.
Mechanisms of Development, 2017Co-Authors: Megan L. Martik, David R McclayAbstract:Abstract Background Gastrulation is a complex orchestration of movements by cells that are specified early in development. Until now, classical convergent extension was considered to be the main contributor to sea urchin Archenteron extension, and the relative contributions of cell divisions were unknown. Active migration of cells along the axis of extension was also not considered as a major factor in invagination. Results Cell transplantations plus live imaging were used to examine endoderm cell morphogenesis during gastrulation at high-resolution in the optically clear sea urchin embryo. The invagination sequence was imaged throughout gastrulation. One of the eight macromeres was replaced by a fluorescently labeled macromere at the 32 cell stage. At gastrulation those patches of fluorescent endoderm cell progeny initially about 4 cells wide, released a column of cells about 2 cells wide early in gastrulation and then often this column narrowed to one cell wide by the end of Archenteron lengthening. The primary movement of the column of cells was in the direction of elongation of the Archenteron with the narrowing (convergence) occurring as one of the two cells moved ahead of its neighbor. As the column narrowed, the labeled endoderm cells generally remained as a contiguous population of cells, rarely separated by intrusion of a lateral unlabeled cell. This longitudinal cell migration mechanism was assessed quantitatively and accounted for almost 90% of the elongation process. Much of the extension was the contribution of Veg2 endoderm with a minor contribution late in gastrulation by Veg1 endoderm cells. We also analyzed the contribution of cell divisions to elongation. Endoderm cells in Lytechinus variagatus were determined to go through approximately one cell doubling during gastrulation. That doubling occurs without a net increase in cell mass, but the question remained as to whether oriented divisions might contribute to Archenteron elongation. We learned that indeed there was a biased orientation of cell divisions along the plane of Archenteron elongation, but when the impact of that bias was analyzed quantitatively, it contributed a maximum 15% to the total elongation of the gut. Conclusions The major driver of Archenteron elongation in the sea urchin, Lytechinus variagatus, is directed movement of Veg2 endoderm cells as a narrowing column along the plane of elongation. The narrowing occurs as cells in the column converge as they migrate, so that the combination of migration and the angular convergence provide the major component of the lengthening. A minor contributor to elongation is oriented cell divisions that contribute to the lengthening but no more than about 15%.
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Morphogenesis in sea urchin embryos: linking cellular events to gene regulatory network states.
Wiley Interdisciplinary Reviews-Developmental Biology, 2011Co-Authors: Deirdre C. Lyons, Stacy L. Kaltenbach, David R McclayAbstract:Gastrulation in the sea urchin begins with ingression of the primary mesenchyme cells (PMCs) at the vegetal pole of the embryo. After entering the blastocoel the PMCs migrate, form a syncitium, and synthesize the skeleton of the embryo. Several hours after the PMCs ingress the vegetal plate buckles to initiate invagination of the Archenteron. That morphogenetic process occurs in several steps. The non-skeletogenic cells produce the initial inbending of the vegetal plate. Endoderm cells then rearrange and extend the length of the gut across the blastocoel to a target near the animal pole. Finally, cells that will form part of the midgut and hindgut are added to complete gastrulation. Later, the stomodeum invaginates from the oral ectoderm and fuses with the foregut to complete the Archenteron. In advance of, and during these morphogenetic events an increasingly complex gene regulatory network controls the specification and the cell biological events that conduct the gastrulation movements.
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RhoA regulates initiation of invagination, but not convergent extension, during sea urchin gastrulation.
Developmental Biology, 2006Co-Authors: Wendy S. Beane, Jeffrey M. Gross, David R McclayAbstract:During gastrulation, the Archenteron is formed using cell shape changes, cell rearrangements, filopodial extensions, and convergent extension movements to elongate and shape the nascent gut tube. How these events are coordinated remains unknown, although much has been learned from careful morphological examinations and molecular perturbations. This study reports that RhoA is necessary to trigger Archenteron invagination in the sea urchin embryo. Inhibition of RhoA results in a failure to initiate invagination movements, while constitutively active RhoA induces precocious invagination of the Archenteron, complete with the actin rearrangements and extracellular matrix secretions that normally accompany the onset of invagination. Although RhoA activity has been reported to control convergent extension movements in vertebrate embryos, experiments herein show that RhoA activity does not regulate convergent extension movements during sea urchin gastrulation. Instead, the results support the hypothesis that RhoA serves as a trigger to initiate invagination, and once initiation occurs, RhoA activity is no longer involved in subsequent gastrulation movements.
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The allocation of early blastomeres to the ectoderm and endoderm is variable in the sea urchin embryo
Development, 1997Co-Authors: Catriona Y Logan, David R McclayAbstract:During sea urchin development, a tier-to-tier progression of cell signaling events is thought to segregate the early blastomeres to five different cell lineages by the 60-cell stage (E. H. Davidson, 1989, Development 105, 421–445). For example, the sixth equatorial cleavage produces two tiers of sister cells called ‘veg1′ and ‘veg2,’ which were projected by early studies to be allocated to the ectoderm and endoderm, respectively. Recent in vitro studies have proposed that the segregation of veg1 and veg2 cells to distinct fates involves signaling between the veg1 and veg2 tiers (O. Khaner and F. Wilt, 1991, Development 112, 881–890). However, fate-mapping studies on 60-cell stage embryos have not been performed with modern lineage tracers, and cell interactions between veg1 and veg2 cells have not been shown in vivo. Therefore, as an initial step towards examining how Archenteron precursors are specified, a clonal analysis of veg1 and veg2 cells was performed using the lipophilic dye, DiI(C16), in the sea urchin species, Lytechinus variegatus. Both veg1 and veg2 descendants form Archenteron tissues, revealing that the ectoderm and endoderm are not segregated at the sixth cleavage. Also, this division does not demarcate cell type boundaries within the endoderm, because both veg1 and veg2 descendants make an overlapping range of endodermal cell types. The allocation of veg1 cells to ectoderm and endoderm during cleavage is variable, as revealed by both the failure of veg1 descendants labeled at the eighth equatorial division to segregate predictably to either tissue and the large differences in the numbers of veg1 descendants that contribute to the ectoderm. Furthermore, DiI-labeled mesomeres of 32-cell stage embryos also contribute to the endoderm at a low frequency. These results show that the prospective Archenteron is produced by a larger population of cleavage-stage blastomeres than believed previously. The segregation of veg1 cells to the ectoderm and endoderm occurs relatively late during development and is unpredictable, indicating that later cell position is more important than the early cleavage pattern in determining ectodermal and Archenteron cell fates.
Jeff Hardin - One of the best experts on this subject based on the ideXlab platform.
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cell rearrangement induced by filopodial tension accounts for the late phase of convergent extension in the sea urchin Archenteron
Molecular Biology of the Cell, 2019Co-Authors: Jeff Hardin, Michael WelikyAbstract:: George Oster was a pioneer in using mechanical models to interrogate morphogenesis in animal embryos. Convergent extension is a particularly important morphogenetic process to which George Oster gave significant attention. Late elongation of the sea urchin Archenteron is a classic example of convergent extension in a monolayered tube, which has been proposed to be driven by extrinsic axial tension due to the activity of secondary mesenchyme cells. Using a vertex-based mechanical model, we show that key features of Archenteron elongation can be accounted for by passive cell rearrangement due to applied tension. The model mimics the cell elongation and the Poisson effect (necking) that occur in actual Archenterons. We also show that, as predicted by the model, ablation of secondary mesenchyme cells late in Archenteron elongation does not result in extensive elastic recoil. Moreover, blocking the addition of cells to the base of the Archenteron late in Archenteron elongation leads to excessive cell rearrangement consistent with tension-induced rearrangement of a smaller cohort of cells. Our mechanical simulation suggests that responsive rearrangement can account for key features of Archenteron elongation and provides a useful starting point for designing future experiments to examine the mechanical properties of the Archenteron.
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a homologue of snail is expressed transiently in subsets of mesenchyme cells in the sea urchin embryo and is down regulated in axis deficient embryos
Developmental Dynamics, 2006Co-Authors: Jeff Hardin, Charles A IllingworthAbstract:Vertebrate members of the zinc finger transcription factor family related to Drosophila snail are expressed in neural crest and paraxial mesoderm along the left–right axis of the embryo. As simple deuterostomes, echinoderms are an important sister phylum for the chordates. We have identified populations of patterned, nonskeletogenic mesenchyme in the sea urchin Lytechinus variegatus by their expression of a sea urchin member of the snail family (Lv-snail). Lv-snail mRNA and protein are detectable at the midgastrula stage within the Archenteron. At the late gastrula stage, a contiguous cluster of cells on the left side of the tip of the Archenteron is Lv-snail–positive. At the early prism stage, two small clusters of mesenchyme cells near the presumptive arm buds are also Lv-snail–positive. At the pluteus stage, staining is detectable in isolated mesenchyme cells and the ciliated band. Based on fate mapping of secondary mesenchyme cells (SMCs) and double-label immunostaining, these patterns are consistent with expression of SNAIL by novel subsets of SMCs that are largely distinct from skeletogenic mesenchyme. In radialized embryos lacking normal bilateral symmetry, mesenchymal expression of Lv-SNAIL is abolished. These results suggest that transient expression of Lv-snail may be important for the differentiation of a subset of axially patterned nonskeletogenic mesenchyme cells and suggest conserved functions for snail family members in deuterostome development. Developmental Dynamics 235:3121–3131, 2006. © 2006 Wiley-Liss, Inc.
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Archenteron precursor cells can organize secondary axial structures in the sea urchin embryo
Development, 1997Co-Authors: Helene A Benink, Gregory A Wray, Jeff HardinAbstract:Local cell-cell signals play a crucial role in establishing major tissue territories in early embryos. The sea urchin embryo is a useful model system for studying these interactions in deuterostomes. Previous studies showed that ectopically implanted micromeres from the 16-cell embryo can induce ectopic guts and additional skeletal elements in sea urchin embryos. Using a chimeric embryo approach, we show that implanted Archenteron precursors differentiate autonomously to produce a correctly proportioned and patterned gut. In addition, the ectopically implanted presumptive Archenteron tissue induces ectopic skeletal patterning sites within the ectoderm. The ectopic skeletal elements are bilaterally symmetric, and flank the ectopic Archenteron, in some cases resulting in mirror-image, symmetric skeletal elements. Since the induced patterned ectoderm and supernumerary skeletal elements are derived from the host, the ectopic presumptive Archenteron tissue can act to ‘organize’ ectopic axial structures in the sea urchin embryo. SUMMARY
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4 The Cellular Basis of Sea Urchin Gastrulation
Current Topics in Developmental Biology, 1996Co-Authors: Jeff HardinAbstract:Publisher Summary This chapter discusses the cellular mechanisms of morphogenesis in the sea urchin gastrula. The sea urchin embryo has been historically important system for investigating the cellular basis of gastrulation. Sea urchin embryos can be obtained in large numbers; they develop synchronously, they are optically transparent, and their organization is relatively simple. The simplicity of the organization of the sea urchin embryo makes it an appealing model system for undertaking a cellular analysis of gastrulation. Mechanical interactions are significant during gastrulation. Forces capable of shaping the embryo may be produced by single cells or groups of cells. Understanding the response of other cells to such forces is a part of the analysis of gastrulation. Behaviors exhibited by a cell, may serve multiple functions during gastrulation. A clear example of such multiplicity is the role played by the secondary mesenchyme cells. Their mechanical influence seems to be important for elongating the Archenteron, but they are also required for correct attachment and positioning of the tip of the Archenteron.
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Local cell interactions and the control of gastrulation in the sea urchin embryo
Seminars in Developmental Biology, 1994Co-Authors: Jeff HardinAbstract:Abstract The sea urchin embryo is a good model system for studying the role of mechanical and cell-cell interactions during epithelial invagination, cell rearrangement and mesenchymal patterning in the gastrula. The mechanisms underlying the initial invagination of the Archenteron have been surprisingly elusive; several possible mechanisms are discussed. In contrast to its initial invagination, the cellular basis for the elongation of the Archenteron is better understood: both autonomous epithelial cell rearrangement and further rearrangement driven by secondary mesenchyme cells appear to be involved. Experiments indicate that patterning of freely migrating primary mesenchyme cells and secondary mesenchyme cells residing in the tip of the Archenteron relies to a large extent on information resident in the ectoderm. Interactions between cells in the early embryo and later cell-cell interactions are both required for the establishment of ectodermal pattern information. Surprisingly, in the case of the oral ectoderm the fixation of pattern information does not occur until immediately prior to gastrulation.
John B Morrill - One of the best experts on this subject based on the ideXlab platform.
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Characterization of Involution during Sea Urchin Gastrulation Using Two-Photon Excited Photorelease and Confocal Microscopy.
Microscopy and Microanalysis, 1998Co-Authors: David W. Piston, Robert G Summers, Susan M. Knobel, John B MorrillAbstract:Sea urchin embryos have served as a model system for the investigation of many concepts in developmental biology. Their gastrulation consists of two stages; primary invagination, where part of the epithelium invaginates into the blastocoel, and secondary invagination, where the Archenteron elongates to completely traverse the blastocoel. Primary invagination involves proliferation of cells within the vegetal plate during primary invagination, but until recently, it was assumed that the larval gastrointestinal (GI) tract developed without further involution of epithelial cells. To investigate rigorously the contribution of epithelial cell involution during Archenteron and GI tract development in the sea urchin, Lytechinus variegatus , we developed a new method for cell tracking based on two-photon excited photorelease of caged fluorophores. Single-cell embryos were injected with caged dye and two-photon excitation uncaging was employed to mark small groups of cells throughout gastrulation. Two-photon excitation allowed for noninvasive, three-dimensionally resolved uncaging inside living cells with minimal biological damage. Cellular involution into the Archenteron was observed throughout primary and secondary invagination, and the larval intestine was formed by further involution of cells following secondary invagination, which is inconsistent with the traditional model of sea urchin gastrulation. Further, as two-photon excitation microscopy becomes accessible to many researchers, the novel techniques described here will be broadly applicable to development of other invertebrate and vertebrate embryos.
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cells are added to the Archenteron during and following secondary invagination in the sea urchin lytechinus variegatus
Developmental Biology, 1998Co-Authors: Gabriel G Martins, Robert G Summers, John B MorrillAbstract:In the present investigation, nuclei of endodermal cells, primary and secondary mesenchyme cells (PMCs and SMCs), and small micromere descendants (SMDs) of the sea urchin Lytechinus variegatus were counted and mapped at five developmental stages, ranging from primary invagination to pluteus larva. The Archenteron and its derivatives were measured three dimensionally with STERECON analytical software. For the first time SMC production is included in the kinetic analysis of Archenteron formation. While the Archenteron lumen doubled in length during secondary invagination, the number of Archenteron cells increased by at least 38% (over 50% when SMCs that emigrated from the tip of the Archenteron were included). The volume of the Archenteron epithelial wall plus the volume of 17 new SMCs increased by 40% over the equivalent volumes at the end of primary invagination. Because secondary invagination involves the addition of Archenteron cells and an increase in volume of the Archenteron epithelium, we conclude that secondary invagination is not accomplished simply by the rearrangement and reshaping of the primary Archenteron cells. Both Archenteron cell number and wall volume continued to increase at the same rates from the end of secondary invagination until the 27-h prism stage, although the lumen lengthened more slowly. SMCs were also produced at a constant rate from primary invagination until the prism stage. Because the production of both endodermal and mesodermal cells continues until the late prism stage, we conclude that gastrulation (defined as the establishment of the germ layers) also extends into the late prism stage.
Steven B. Oppenheimer - One of the best experts on this subject based on the ideXlab platform.
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Terminal alpha-d-mannosides are critical during sea urchin gastrulation.
Zygote, 2016Co-Authors: Heghush Aleksanyan, Jing Liang, Stan Metzenberg, Steven B. OppenheimerAbstract:: The sea urchin embryo is a United States National Institutes of Health (NIH) designated model system to study mechanisms that may be involved in human health and disease. In order to examine the importance of high-mannose glycans and polysaccharides in gastrulation, Lytechinus pictus embryos were incubated with Jack bean α-mannosidase (EC 3.2.1.24), an enzyme that cleaves terminal mannose residues that have α1-2-, α1-3-, or α1-6-glycosidic linkages. The enzyme treatment caused a variety of morphological deformations in living embryos, even with α-mannosidase activities as low as 0.06 U/ml. Additionally, formaldehyde-fixed, 48-hour-old L. pictus embryos were microdissected and it was demonstrated that the adhesion of the tip of the Archenteron to the roof of the blastocoel in vitro is abrogated by treatment with α-mannosidase. These results suggest that terminal mannose residues are involved in the adhesion between the Archenteron and blastocoel roof, perhaps through a lectin-like activity that is not sensitive to fixation.
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Involvement of l(-)-rhamnose in sea urchin gastrulation. Part II: α-l-Rhamnosidase.
Zygote, 2015Co-Authors: Jing Liang, Heghush Aleksanyan, Stan Metzenberg, Steven B. OppenheimerAbstract:The sea urchin embryo is recognized as a model system to reveal developmental mechanisms involved in human health and disease. In Part I of this series, six carbohydrates were tested for their effects on gastrulation in embryos of the sea urchin Lytechinus pictus . Only l -rhamnose caused dramatic increases in the numbers of unattached Archenterons and exogastrulated Archenterons in living, swimming embryos. It was found that at 30 h post-fertilization the l -rhamnose had an unusual inverse dose-dependent effect, with low concentrations (1–3 mM) interfering with development and higher concentrations (30 mM) having little to no effect on normal development. In this study, embryos were examined for inhibition of Archenteron development after treatment with α- l -rhamnosidase, an endoglycosidase that removes terminal l -rhamnose sugars from glycans. It was observed that the enzyme had profound effects on gastrulation, an effect that could be suppressed by addition of l -rhamnose as a competitive inhibitor. The involvement of l -rhamnose-containing glycans in sea urchin gastrulation was unexpected, since there are no characterized biosynthetic pathways for rhamnose utilization in animals. It is possible there exists a novel l -rhamnose-containing glycan in sea urchins, or that the enzyme and sugar interfere with the function of rhamnose-binding lectins, which are components of the innate immune system in many vertebrate and invertebrate species.
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A role for polyglucans in a model sea urchin embryo cellular interaction.
Zygote, 2013Co-Authors: Suprita Singh, Stan Metzenberg, Eddie Karabidian, Alexander Kandel, Edward J. Carroll, Steven B. OppenheimerAbstract:: The enzymatic activities of commercially prepared glycosidases were verified by direct chemical assays using defined substrates and fixed and live sea urchin (Lytechinus pictus) embryos to determine if a model cellular interaction of interest to developmental biologists for over a century (interaction of Archenteron tip and roof of the blastocoel) was mediated by glycans. Glycosidases (active and denatured) were incubated with microdissected Archenterons and blastocoel roofs in a direct assay to learn if their enzymatic activities could prevent the normal adhesive interaction. Of the five glycosidases tested only β-amylase (an exoglycosidase) immediately inhibited the interaction at relatively low unit activity. α-Amylase (an endoglycosidase) had no measurable effect, while other glycosidases (α-glucosidase, β-glucosidase, β-galactosidase) only substantially inhibited adhesion after a 12-h incubation. We demonstrated that the five glycosidases were active (not inhibited) in the presence of embryo materials, and that cleaved sugars could be detected directly after incubation of some enzymes with the embryos. The biochemical purity of the enzymes was examined using gel electrophoresis under denaturing conditions, and the absence of contaminating proteases was confirmed using Azocoll™ substrate. As we cannot entirely rule out the presence of minor contaminating enzymatic activities, only inhibitions of adhesion after very short incubations with enzyme were considered significant and biologically relevant. Although glycans in indirect experiments have been implicated in mediating the interaction of the tip of the Archenteron and roof of the blastocoel, to our knowledge, this is the first study that directly implicates polyglucans with terminal 1,4-linked glucose residues in this adhesive event.
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Use of specific glycosidases to probe cellular interactions in the sea urchin embryo
Experimental Cell Research, 2010Co-Authors: Brian Idoni, Stan Metzenberg, Steven B. Oppenheimer, Virginia Hutchins-carroll, Haike Ghazarian, Edward J. CarrollAbstract:Abstract We present an unusual and novel model for initial investigations of a putative role for specifically conformed glycans in cellular interactions. We have used α- and s-amylase and α- and s-glucosidase in dose–response experiments evaluating their effects on Archenteron organization using the NIH designated sea urchin embryo model. In quantitative dose–response experiments, we show that defined activity levels of α-glucosidase and s-amylase inhibited Archenteron organization in living Lytechinus pictus gastrula embryos, whereas all concentrations of s-glucosidase and α-amylase were without substantial effects on development. Product inhibition studies suggested that the enzymes were acting by their specific glycosidase activities and polyacrylamide gel electrophoresis suggested that there was no detectable protease contamination in the active enzyme samples. The results provide evidence for a role of glycans in sea urchin embryo cellular interactions with special reference to the possible structural conformation of these glycans based on the differential activities of the α- and s-glycosidases.
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Exogenous hyalin and sea urchin gastrulation. Part III: Biological activity of hyalin isolated from Lytechinus pictus embryos
Zygote, 2008Co-Authors: Azalia Contreras, Edward J. Carroll, John Vitale, Virginia Hutchins-carroll, Steven B. OppenheimerAbstract:Hyalin is a large glycoprotein, consisting of the hyalin repeat domain and non-repeated regions, and is the major component of the hyaline layer in the early sea urchin embryo of Strongylocentrotus purpuratus . The hyalin repeat domain has been identified in proteins from organisms as diverse as bacteria, sea urchins, worms, flies, mice and humans. While the specific function of hyalin and the hyalin repeat domain is incompletely understood, many studies suggest that it has a functional role in adhesive interactions. In part I of this series, we showed that hyalin isolated from the sea urchin S. purpuratus blocked Archenteron elongation and attachment to the blastocoel roof occurring during gastrulation in S. purpuratus embryos, (Razinia et al ., 2007). The cellular interactions that occur in the sea urchin, recognized by the U.S. National Institutes of Health as a model system, may provide insights into adhesive interactions that occur in human health and disease. In part II of this series, we showed that S. purpuratus hyalin heterospecifically blocked Archenteron–ectoderm interaction in Lytechinus pictus embryos (Alvarez et al ., 2007). In the current study, we have isolated hyalin from the sea urchin L. pictus and demonstrated that L. pictus hyalin homospecifically blocks Archenteron–ectoderm interaction, suggesting a general role for this glycoprotein in mediating a specific set of adhesive interactions. We also found one major difference in hyalin activity in the two sea urchin species involving hyalin influence on gastrulation invagination.
Yoshihiko K Maruyama - One of the best experts on this subject based on the ideXlab platform.
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a starfish homolog of mouse t brain 1 is expressed in the Archenteron of asterina pectinifera embryos possible involvement of two t box genes in starfish gastrulation
Development Growth & Differentiation, 2000Co-Authors: Eiichi Shoguchi, Nori Satoh, Yoshihiko K MaruyamaAbstract:A cDNA clone for a starfish T-box gene (Ap-Tbr) was isolated and characterized. Molecular phylogenetic analysis showed that the Ap-Tbr gene was a member of the T-brain subfamily, which includes mouse T-brain-1 and Xenopus Eomesodermin. Ap-Tbr was expressed as early as in late blastulae, and the transcript was evident in a disc-like region at the vegetal end or the vegetal plate. In early gastrulae, the gene was expressed in the cells of the invaginated Archenteron, from which the majority of mesodermal cells as well as some endodermal cells are derived. The Ap-Tbr expression disappeared by the end of gastrulation, and was not detected in early bipinnaria larvae. This expression pattern of Ap-Tbr suggests its role in an early step of Archenteron invagination, associated with mesoderm and endoderm formation. Furthermore, double staining of late blastulae and early gastrulae with a probe specific for Ap-Tbr and one for ApBra (the starfish Brachyury gene) demonstrated that the regions of Ap-Tbr and ApBra expression at the vegetal/posterior end of the embryo did not overlap, the region with Ap-Tbr expression being encircled by a ring-shaped region of ApBra expression. A gap without expression of the two genes was located between them, and the gap was seen around the blastoporal lip in the early gastrula. These observations suggest implication of the two T-box genes, with different roles, in starfish gastrulation.
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Pattern of Brachyury gene expression in starfish embryos resembles that of hemichordate embryos but not of sea urchin embryos.
Mechanisms of Development, 1999Co-Authors: Eiichi Shoguchi, Noriyuki Satoh, Yoshihiko K MaruyamaAbstract:Abstract Echinoderms, hemichordates and chordates are deuterostomes and share a number of developmental features. The Brachyury gene is responsible for formation of the notochord, the most defining feature of chordates, and thus may be a key to understanding the origin and evolution of the chordates. Previous studies have shown that the ascidian Brachyury ( As-T and Ci-Bra ) is expressed in the notochord and that a sea urchin Brachyury ( HpTa ) is expressed in the secondary mesenchyme founder cells. A recent study by Tagawa et al. (1998) , however, revealed that a hemichordate Brachyury ( PfBra ) is expressed in a novel pattern in an Archenteron invagination region and a stomodaeum invagination region in the gastrula. The present study demonstrated that the expression pattern of Brachyury ( ApBra ) of starfish embryos resembles that of PfBra in hemichordate embryos but not of HpTa in sea urchin embryos. Namely, ApBra is expressed in an Archenteron invagination region and a stomodaeum invagination region.
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Archenteron forming capacity in blastomeres isolated from eight cell stage embryos of the starfish asterina pectinifera
Development Growth & Differentiation, 1990Co-Authors: Yoshihiko K Maruyama, Masaru ShinodaAbstract:Starfish blastomeres are reported to be totipotent up to the 8-cell stage. We reinvestigated the development of blastomeres of 8-cell stage embryos with a regular cubic shape consisting of two tiers of 4 blastomeres. On dissociation of the embryo by disrupting the fertilization membrane at the 8-cell stage, each of the 4 blastomeres of the vegetal hemisphere gave rise to an embryo that gastrulated, whereas blastomeres from the animal hemisphere did not. By injection of a cell lineage tracer into blastomeres of 8-cell stage embryos, we found that only those of the vegetal hemisphere formed cells constituting the Archenteron. Next, we compressed 4-cell stage embryos along the animal-vegetal axis so that all the blastomeres in the 8-cell stage were in a single layer. When these 8 blastomeres were then dissociated, an average of 7 of them developed into gastrulae. By cell lineage analysis, all the blastomeres in single-layered embryos at the 8-cell stage were shown to have the capacity to form cells constituting an Archenteron. Taken together, these findings indicate that the fate to form the Archenteron is specified by a cytoplasmic factor(s) localized at the vegetal hemisphere, and that isolated blastomeres that have inherited this factor develop into gastrulae.
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Archenteron‐Forming Capacity in Blastomeres Isolated from Eight‐Cell Stage Embryos of the Starfish, Asterina pectinifera
Development Growth & Differentiation, 1990Co-Authors: Yoshihiko K Maruyama, Masaru ShinodaAbstract:Starfish blastomeres are reported to be totipotent up to the 8-cell stage. We reinvestigated the development of blastomeres of 8-cell stage embryos with a regular cubic shape consisting of two tiers of 4 blastomeres. On dissociation of the embryo by disrupting the fertilization membrane at the 8-cell stage, each of the 4 blastomeres of the vegetal hemisphere gave rise to an embryo that gastrulated, whereas blastomeres from the animal hemisphere did not. By injection of a cell lineage tracer into blastomeres of 8-cell stage embryos, we found that only those of the vegetal hemisphere formed cells constituting the Archenteron. Next, we compressed 4-cell stage embryos along the animal-vegetal axis so that all the blastomeres in the 8-cell stage were in a single layer. When these 8 blastomeres were then dissociated, an average of 7 of them developed into gastrulae. By cell lineage analysis, all the blastomeres in single-layered embryos at the 8-cell stage were shown to have the capacity to form cells constituting an Archenteron. Taken together, these findings indicate that the fate to form the Archenteron is specified by a cytoplasmic factor(s) localized at the vegetal hemisphere, and that isolated blastomeres that have inherited this factor develop into gastrulae.