FIGURE 6 - uploaded by Laurent Formery
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Gastrulation stages of Paracentrotus lividus under light microscopy. Developmental stages are as follows: (A) early mesenchyme blastula stage (eMB); (B) late mesenchyme blastula stage (late-MB); (C,D) blastopore formation stage (BF); (E,F) early gastrula stage (EG); (G,H) mid-gastrula stage (mid-G); (I,J) late gastrula stage (LG); (K,L) prism stage (prism). In (A-C,E,G,I,K), the embryos are in lateral view with the animal pole up, and in (K) the ventral side is left. In (D,F,H,J,L), the embryos are in vegetal view with the ventral side up. In (B,C,E,G,I,K), the asterisk marks the animal (or apical) pole domain. In (G,I), red arrows indicate non-skeletogenic mesoderm cells migrating within the blastocoel. ((G) inset) Close-up of the tip of the archenteron of the same embryo as in (G), but at a different focal plane to illustrate non-skeletogenic mesoderm cell ingression. In (H,J,K), the white arrowhead marks the flattening of the ventral ectoderm. In (H,J,L), green arrows highlight the thickened epithelium at the boundary between the vegetal ventral and the vegetal dorsal ectoderm. In (I,J), yellow arrowheads highlight the presence of skeletal elements. In (K), pink arrowheads indicate red-pigmented cells inserted in the aboral ectoderm, and white arrows mark the constriction of the archenteron segregating the esophagus from the stomach. The white dotted lines with the annotation "90 ° " further indicate the right angle between the ventral and the vegetal ectoderm. In (K,L), the sign "#" highlights the position of the stomodeum, and thus where the mouth will form. Scale bar: (A-L) 30 μm; ((G) inset) 10 µm. DC: dorsal chain; lLC: left lateral chain; lVLC: left ventrolateral cluster; rLC: right lateral chain; rVLC: right ventrolateral cluster; VC: ventral chain.
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The sea urchin Paracentrotus lividus has been used as a model system in biology for more than a century. Over the past decades, it has been at the center of a number of studies in cell, developmental, ecological, toxicological, evolutionary, and aquaculture research. Due to this previous work, a significant amount of information is already availabl...
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... P. lividus, as in any other echinoids with micromeres (also called the euechinoids), gastrulation started by the ingression, into the blastocoel, of the descendants of the large micromeres ( Figure 6A). This ingression takes place by an epithelial-tomesenchymal transition and gives rise to the skeletogenic mesoderm (SM) cells (also referred to as the primary mesenchyme cells or PMCs) (Fink and McClay, 1985). ...
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... ingression takes place by an epithelial-tomesenchymal transition and gives rise to the skeletogenic mesoderm (SM) cells (also referred to as the primary mesenchyme cells or PMCs) (Fink and McClay, 1985). Ingression of the SM cells began at the early mesenchyme blastula stage (i.e., at around 14 hpf) ( Figure 6A), and proceeded until the late mesenchyme blastula stage (i.e., at around 17 hpf) ( Figure 6B). During this period, the embryos were characterized by an increasing number of SM cells within the blastocoel (up to 32 cells), which, for the time being, remained in the vicinity of the vegetal plate ( Figures 6A,B). ...
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... ingression takes place by an epithelial-tomesenchymal transition and gives rise to the skeletogenic mesoderm (SM) cells (also referred to as the primary mesenchyme cells or PMCs) (Fink and McClay, 1985). Ingression of the SM cells began at the early mesenchyme blastula stage (i.e., at around 14 hpf) ( Figure 6A), and proceeded until the late mesenchyme blastula stage (i.e., at around 17 hpf) ( Figure 6B). During this period, the embryos were characterized by an increasing number of SM cells within the blastocoel (up to 32 cells), which, for the time being, remained in the vicinity of the vegetal plate ( Figures 6A,B). ...
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... of the SM cells began at the early mesenchyme blastula stage (i.e., at around 14 hpf) ( Figure 6A), and proceeded until the late mesenchyme blastula stage (i.e., at around 17 hpf) ( Figure 6B). During this period, the embryos were characterized by an increasing number of SM cells within the blastocoel (up to 32 cells), which, for the time being, remained in the vicinity of the vegetal plate ( Figures 6A,B). During this period, the embryos further continued to exhibit, at the vegetal pole, a flattened vegetal plate ( Figures 6A,B), which by 17 hpf was only composed of the small micromeres at the center, surrounded by the descendants of the veg2 cells (Ruffins and Ettensohn, 1996;Lyons et al., 2012). ...
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... this period, the embryos were characterized by an increasing number of SM cells within the blastocoel (up to 32 cells), which, for the time being, remained in the vicinity of the vegetal plate ( Figures 6A,B). During this period, the embryos further continued to exhibit, at the vegetal pole, a flattened vegetal plate ( Figures 6A,B), which by 17 hpf was only composed of the small micromeres at the center, surrounded by the descendants of the veg2 cells (Ruffins and Ettensohn, 1996;Lyons et al., 2012). By 17 hpf, the descendants of the veg2 cells were also segregated into two different cell tiers, with two distinct cell fates: an inner cell tier surrounding the small micromeres that will develop into non-skeletogenic mesoderm (NSM) cells (also referred to as the secondary mesenchyme cells or SMCs) and an outer cell tier located at the periphery of the vegetal plate that will develop into endoderm cells (Ruffins and Ettensohn, 1996;Lhomond et al., 2012). ...
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... 17 hpf, the descendants of the veg2 cells were also segregated into two different cell tiers, with two distinct cell fates: an inner cell tier surrounding the small micromeres that will develop into non-skeletogenic mesoderm (NSM) cells (also referred to as the secondary mesenchyme cells or SMCs) and an outer cell tier located at the periphery of the vegetal plate that will develop into endoderm cells (Ruffins and Ettensohn, 1996;Lhomond et al., 2012). In addition, at 17 hpf (i.e., at the late mesenchyme blastula stage), the embryos were also characterized by the presence, at the animal pole, of a patch of elongated cells ( Figure 6B), which will be visible until the end of gastrulation ( Figure 6). These cells delimited the animal (or apical) pole domain, within which the neuroectodermal territory will form (Angerer et al., 2011). ...
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... 17 hpf, the descendants of the veg2 cells were also segregated into two different cell tiers, with two distinct cell fates: an inner cell tier surrounding the small micromeres that will develop into non-skeletogenic mesoderm (NSM) cells (also referred to as the secondary mesenchyme cells or SMCs) and an outer cell tier located at the periphery of the vegetal plate that will develop into endoderm cells (Ruffins and Ettensohn, 1996;Lhomond et al., 2012). In addition, at 17 hpf (i.e., at the late mesenchyme blastula stage), the embryos were also characterized by the presence, at the animal pole, of a patch of elongated cells ( Figure 6B), which will be visible until the end of gastrulation ( Figure 6). These cells delimited the animal (or apical) pole domain, within which the neuroectodermal territory will form (Angerer et al., 2011). ...
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... second main morphogenetic movement observed during P. lividus gastrulation was subsequently the invagination of the archenteron (i.e., the primordium of the digestive tract). Invagination of the archenteron started at around 18 hpf, at the blastopore formation stage ( Figures 6C,D). At this stage, the embryos were characterized by the inward bending of the remaining vegetal plate, which created the first opening of the future digestive tract, the blastopore, which will subsequently develop into the anus. ...
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... the blastocoel, the SM cells concomitantly started migrating, extending filopodia, and attaching and detaching them from the blastocoel wall. By doing so, they progressively adopted a characteristic pattern, forming a ring around the anlage of the archenteron (Figure 6D). At the early gastrula stage (20 hpf), the embryos were characterized by an archenteron that had extended within the blastocoel, reaching the approximate level of a quarter of the blastocoel ( Figure 6E). ...
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... doing so, they progressively adopted a characteristic pattern, forming a ring around the anlage of the archenteron (Figure 6D). At the early gastrula stage (20 hpf), the embryos were characterized by an archenteron that had extended within the blastocoel, reaching the approximate level of a quarter of the blastocoel ( Figure 6E). This extension was likely due to the invagination of additional NSM cells within the blastocoel. ...
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... extension was likely due to the invagination of additional NSM cells within the blastocoel. Meanwhile, some SM cells migrated along the inside of the blastocoel wall, towards the animal pole, thereby constituting two lateral chains, the right and the left lateral chains ( Figure 6E). In addition, and although the embryos were still relatively spherical at this stage, the ring formed by the SM cells, around the anlage of the archenteron, started to display an asymmetric shape, providing the first morphological landmark for the dorsal-ventral axis. ...
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... addition, and although the embryos were still relatively spherical at this stage, the ring formed by the SM cells, around the anlage of the archenteron, started to display an asymmetric shape, providing the first morphological landmark for the dorsal-ventral axis. This ring of SM cells was organized into a short ventral and a long dorsal chain, linked by a right and a left aggregate ( Figure 6F), which are respectively referred to as the right and the left ventrolateral cluster (Peterson and McClay, 2003). ...
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... the mid-gastrula stage (22 hpf), the embryos were characterized by an archenteron length that reached the approximate level of half of the blastocoel ( Figure 6G). The archenteron was now likely composed of all of the NSM cells and most of the endoderm cells. ...
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... archenteron was now likely composed of all of the NSM cells and most of the endoderm cells. Some of the NSM cells, at the tip of the archenteron, started to ingress within the blastocoel ( Figure 6G). These cells were undergoing an epithelial-tomesenchymal transition, extending and projecting thin filopodia to detach from the archenteron (Figure 6G inset). ...
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... of the NSM cells, at the tip of the archenteron, started to ingress within the blastocoel ( Figure 6G). These cells were undergoing an epithelial-tomesenchymal transition, extending and projecting thin filopodia to detach from the archenteron (Figure 6G inset). Within the blastocoel, the SM cells still displayed the same characteristic organization as before: an asymmetric ring around the archenteron and two lateral chains along the blastocoel wall. ...
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... the blastocoel, the SM cells still displayed the same characteristic organization as before: an asymmetric ring around the archenteron and two lateral chains along the blastocoel wall. At this stage, the epithelium constituting the ventral side of the embryo further started to flatten, and the epithelium at the boundary between the vegetal ventral and the vegetal dorsal ectoderm started to thicken ( Figure 6H), marking the future position of the two first larval arms. At the late gastrula stage (24 hpf), the archenteron extended all the way through the blastocoel, up to the blastocoel roof ( Figure 6I). ...
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... this stage, the epithelium constituting the ventral side of the embryo further started to flatten, and the epithelium at the boundary between the vegetal ventral and the vegetal dorsal ectoderm started to thicken ( Figure 6H), marking the future position of the two first larval arms. At the late gastrula stage (24 hpf), the archenteron extended all the way through the blastocoel, up to the blastocoel roof ( Figure 6I). At the tip of the archenteron, more delaminating NSM cells were distinguishable ( Figure 6I). ...
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... the late gastrula stage (24 hpf), the archenteron extended all the way through the blastocoel, up to the blastocoel roof ( Figure 6I). At the tip of the archenteron, more delaminating NSM cells were distinguishable ( Figure 6I). Within the blastocoel, the SM cells still displayed the same organization as before, and, at the level of the ventrolateral clusters, two skeletal pieces became discernable (Figures 6I,J) (for details on skeleton development see the skeletogenesis section below). ...
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... the blastocoel, the SM cells still displayed the same organization as before, and, at the level of the ventrolateral clusters, two skeletal pieces became discernable (Figures 6I,J) (for details on skeleton development see the skeletogenesis section below). At the level of the epithelium, the same features as before were observed, including a flattened ventral ectoderm, thickened areas between the vegetal dorsal and the vegetal ventral ectoderm, and elongated cells constituting the animal pole domain ( Figures 6I,J). ...
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... sea urchin species. The embryo was characterized by a typical triangular ("prism") shape, with a rounded, elongated dorsal ectoderm and a flattened ventral ectoderm ( Figure 6K). The flat ventral ectoderm further formed an almost perfect right angle with the flat vegetal ectoderm ( Figure 6K) and contained a small depression right below the apical pole domain ( Figures 6K,L). ...
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... embryo was characterized by a typical triangular ("prism") shape, with a rounded, elongated dorsal ectoderm and a flattened ventral ectoderm ( Figure 6K). The flat ventral ectoderm further formed an almost perfect right angle with the flat vegetal ectoderm ( Figure 6K) and contained a small depression right below the apical pole domain ( Figures 6K,L). This depression, called the stomodeum, corresponds to the site where the future larval mouth will form (Bergeron et al., 2011). ...
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... embryo was characterized by a typical triangular ("prism") shape, with a rounded, elongated dorsal ectoderm and a flattened ventral ectoderm ( Figure 6K). The flat ventral ectoderm further formed an almost perfect right angle with the flat vegetal ectoderm ( Figure 6K) and contained a small depression right below the apical pole domain ( Figures 6K,L). This depression, called the stomodeum, corresponds to the site where the future larval mouth will form (Bergeron et al., 2011). ...
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... depression, called the stomodeum, corresponds to the site where the future larval mouth will form (Bergeron et al., 2011). The dorsal ectoderm also contained red-pigmented cells ( Figure 6K), which correspond to differentiated NSM cells that are part of the immune system of the embryo and the future larva ( Hibino et al., 2006). Within the blastocoel, the archenteron was also bent toward the stomodeum, and a constriction was distinguishable below its tip ( Figure 6K). ...
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... dorsal ectoderm also contained red-pigmented cells ( Figure 6K), which correspond to differentiated NSM cells that are part of the immune system of the embryo and the future larva ( Hibino et al., 2006). Within the blastocoel, the archenteron was also bent toward the stomodeum, and a constriction was distinguishable below its tip ( Figure 6K). This constriction marked the position of the future cardiac sphincter, which will eventually separate the larval esophagus (above the constriction, close to the stomodeum) from the future larval stomach (below the constriction) ( Annunziata et al., 2014). ...
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... Next, we tested whether See-Star was compatible with two of the most commonly used techniques for visualizing molecules, IHC and ISH. For IHC, we used a cross-reactive commercial anti-acetylated α-tubulin antibody, which allows for visualization of neurons and cilia in a broad range of invertebrate species [14][15][16][17][18][19][20]. We first assayed this antibody in cleared P. miniata post-metamorphic juveniles, defined by bearing only two pairs of secondary tube feet in each ray (2-TF stage) ( Fig. 3A; Fig. S2A). ...
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... In contrast, the first indication of left-right asymmetry in the ancestral developmental mode occurs in the late gastrula (Duboc et al. 2005;Bessodes et al. 2012). Another accelerated patterning event in He involves the early establishment of the imaginal adult rudiment, which begins at about 30 hpf in He (Williams and Anderson 1975;Wray and Raff 1989;Koop et al. 2017) but not until several days post-fertilization in the ancestral condition (Lowe et al. 2002;Formery et al. 2022). ...
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