The Experts below are selected from a list of 264 Experts worldwide ranked by ideXlab platform
Ray Keller - One of the best experts on this subject based on the ideXlab platform.
-
the rhogef protein plekhg5 regulates apical constriction of bottle cells during gastrulation
Development, 2018Co-Authors: Ivan K Popov, Paul Skoglund, Ray Keller, Chenbei ChangAbstract:ABSTRACT Apical constriction regulates epithelial morphogenesis during embryonic development, but how this process is controlled is not understood completely. Here, we identify a Rho guanine nucleotide exchange factor (GEF) gene plekhg5 as an essential regulator of apical constriction of bottle cells during Xenopus gastrulation. plekhg5 is expressed in the Blastopore lip and its expression is sufficient to induce ectopic bottle cells in epithelia of different germ layers in a Rho-dependent manner. This activity is not shared by arhgef3, which encodes another organizer-specific RhoGEF. Plekhg5 protein is localized in the apical cell cortex via its pleckstrin homology domain, and the GEF activity enhances its apical recruitment. Plekhg5 induces apical actomyosin accumulation and cell elongation. Knockdown of plekhg5 inhibits activin-induced bottle cell formation and endogenous Blastopore lip formation in gastrulating frog embryos. Apical accumulation of actomyosin, apical constriction and bottle cell formation fail to occur in these embryos. Taken together, our data indicate that transcriptional regulation of plekhg5 expression at the Blastopore lip determines bottle cell morphology via local polarized activation of Rho by Plekhg5, which stimulates apical actomyosin activity to induce apical constriction.
-
Large, long range tensile forces drive convergence during Xenopus Blastopore closure and body axis elongation
eLife, 2018Co-Authors: David R. Shook, Eric M Kasprowicz, Lance A. Davidson, Ray KellerAbstract:Indirect evidence suggests that Blastopore closure during gastrulation of anamniotes, including amphibians such as Xenopus laevis, depends on circumblastoporal convergence forces generated by the marginal zone (MZ), but direct evidence is lacking. We show that explanted MZs generate tensile convergence forces up to 1.5 μN during gastrulation and over 4 μN thereafter. These forces are generated by convergent thickening (CT) until the midgastrula and increasingly by convergent extension (CE) thereafter. Explants from ventralized embryos, which lack tissues expressing CE but close their Blastopores, produce up to 2 μN of tensile force, showing that CT alone generates forces sufficient to close the Blastopore. Uniaxial tensile stress relaxation assays show stiffening of mesodermal and ectodermal tissues around the onset of neurulation, potentially enhancing long-range transmission of convergence forces. These results illuminate the mechanobiology of early vertebrate morphogenic mechanisms, aid interpretation of phenotypes, and give insight into the evolution of Blastopore closure mechanisms.
-
Early development of Ensatina eschscholtzii: an amphibian with a large, yolky egg
EvoDevo, 2010Co-Authors: Andres Collazo, Ray KellerAbstract:Background Comparative analyses between amphibians, concentrating on the cellular mechanisms of morphogenesis, reveal a large variability in the early developmental processes that were thought to be conserved during evolution. Increased egg size is one factor that could have a strong effect on early developmental processes such as cleavage pattern and gastrulation. Salamanders of the family Plethodontidae are particularly appropriate for such comparative studies because the species have eggs of varying size, including very large yolky eggs. Results In this paper, we describe for the first time the early development (from fertilization through neurulation) of the plethodontid salamander Ensatina eschscholtzii . This species has one of the largest eggs known for an amphibian, with a mean ± SD diameter of 6 ± 0.43 mm (range 5.3-6.9; n = 17 eggs). Cleavage is meroblastic until approximately the 16-cell stage (fourth or fifth cleavage). At the beginning of gastrulation, the blastocoel roof is one cell thick, and the dorsal lip of the Blastopore forms below the equator of the embryo. The ventral lip of the Blastopore forms closer to the vegetal pole, and relatively little involution occurs during gastrulation. Cell migration is visible through the transparent blastocoel roof of the gastrula. At the end of gastrulation, a small archenteron spreading dorsally from the Blastopore represents the relatively small and superficial area of the egg where early embryonic axis formation occurs. The resulting pattern is similar to the embryonic disk described for one species of anuran. Conclusions Comparisons with the early development of other species of amphibians suggest that an evolutionary increase in egg size can result in predictable changes in the patterns and rate of early development, but mainly within an evolutionary lineage.
-
Epithelial type, ingression, Blastopore architecture and the evolution of chordate mesoderm morphogenesis.
Journal of experimental zoology. Part B Molecular and developmental evolution, 2008Co-Authors: David R. Shook, Ray KellerAbstract:Chordate embryos show an evolutionary trend in the mechanisms they use to internalize presumptive mesoderm, relying predominantly on invagination in the basal chordates, varying combinations of involution and ingression in the anamniote vertebrates and reptiles, and predominantly on ingression in birds and mammals. This trend is associated with variations in epithelial type and changes in embryonic architecture as well as variations in the type of Blastopore formed by an embryo. We also note the surprising conservation of the involution, during gastrulation, of at least a subset of the notochordal cells throughout the chordates, and suggest that this indicates a constraint on morphogenic evolution based on a functional linkage between architecture and patterning. Finally, we propose a model for the evolutionary transitions from gastrulation through a urodele amphibian-type Blastopore to gastrulation through a primitive streak, as in chick or mouse.
-
Dynamic determinations: patterning the cell behaviours that close the amphibian Blastopore
Philosophical transactions of the Royal Society of London. Series B Biological sciences, 2008Co-Authors: Ray Keller, David R. ShookAbstract:We review the dynamic patterns of cell behaviours in the marginal zone of amphibians with a focus on how the progressive nature and the geometry of these behaviours drive Blastopore closure. Mediolateral cell intercalation behaviour and epithelial–mesenchymal transition are used in different combinations in several species of amphibian to generate a conserved pattern of circumblastoporal hoop stresses. Although these cell behaviours are quite different and involve different germ layers and tissue organization, they are expressed in similar patterns. They are expressed progressively along presumptive lateral–medial and anterior–posterior axes of the body plan in highly ordered geometries of functional significance in the context of the biomechanics of Blastopore closure, thereby accounting for the production of similar patterns of circumblastoporal forces. It is not the nature of the cell behaviour alone, but the context, the biomechanical connectivity and spatial and temporal pattern of its expression that determine specificity of morphogenic output during gastrulation and Blastopore closure. Understanding the patterning of these dynamic features of cell behaviour is important and will require analysis of signalling at much greater spatial and temporal resolution than that has been typical in the analysis of patterning tissue differentiation.
David R. Shook - One of the best experts on this subject based on the ideXlab platform.
-
Large, long range tensile forces drive convergence during Xenopus Blastopore closure and body axis elongation
eLife, 2018Co-Authors: David R. Shook, Eric M Kasprowicz, Lance A. Davidson, Ray KellerAbstract:Indirect evidence suggests that Blastopore closure during gastrulation of anamniotes, including amphibians such as Xenopus laevis, depends on circumblastoporal convergence forces generated by the marginal zone (MZ), but direct evidence is lacking. We show that explanted MZs generate tensile convergence forces up to 1.5 μN during gastrulation and over 4 μN thereafter. These forces are generated by convergent thickening (CT) until the midgastrula and increasingly by convergent extension (CE) thereafter. Explants from ventralized embryos, which lack tissues expressing CE but close their Blastopores, produce up to 2 μN of tensile force, showing that CT alone generates forces sufficient to close the Blastopore. Uniaxial tensile stress relaxation assays show stiffening of mesodermal and ectodermal tissues around the onset of neurulation, potentially enhancing long-range transmission of convergence forces. These results illuminate the mechanobiology of early vertebrate morphogenic mechanisms, aid interpretation of phenotypes, and give insight into the evolution of Blastopore closure mechanisms.
-
Movie 5
2016Co-Authors: Carol A. Hurney, David R. Shook, Sharon K. Babcock, Teresa M. Pelletier, Stephen D. Turner, John Maturo, Salimah Cogbill, Michael C. Snow, Kristie KinchAbstract:A later view showing Blastopore formation at stage 10 and the large amount of contraction that occurs in the vegetal endoderm. Blastopore formation starts about 4 hours elapsed time (frame 25) and continues to the end of the movie (about 13.7 hours). Both here and in movie 4, vegetal endoderm contraction appears to end as Blastopore formation is complete. 10 minutes per frame, 15 fps. Scale bar is 1 mm
-
Movie 9
2016Co-Authors: Carol A. Hurney, David R. Shook, Sharon K. Babcock, Teresa M. Pelletier, Stephen D. Turner, John Maturo, Salimah Cogbill, Michael C. Snow, Kristie KinchAbstract:Shows posterior view from stage 12 to stage 18. 30.5 hours elapsed time. Shows posterior neural tube closure, and the enclosure of the Blastopore within it. 8 min per frame, 15 frames per second. Scale bar is 1 mm
-
Movie 7
2016Co-Authors: Carol A. Hurney, David R. Shook, Sharon K. Babcock, Teresa M. Pelletier, Stephen D. Turner, John Maturo, Salimah Cogbill, Michael C. Snow, Kristie KinchAbstract:Shows gastrulation from late stage 11 through neurulation from a posterior view (74 hours elapsed time). Shows inversion of the Blastopore and it’s enclosure at the posterior end of the neural folds. 10 minutes per frame, 15 fps. Scale bar is 1 mm
-
Confocal Stack 2
2016Co-Authors: Carol A. Hurney, David R. Shook, Sharon K. Babcock, Teresa M. Pelletier, Stephen D. Turner, John Maturo, Salimah Cogbill, Michael C. Snow, Kristie KinchAbstract:The lateral Blastopore lip, from the parasagittally fractured face to lateral. Animal to the upper right, vegetal to the lower left. Shows that the tissue involuting around the lip is 2-3 cell layers thick, interdigitated, with no discrete epithelial layer. Confocal slices are 7 μm apart
Jonathan Q. Henry - One of the best experts on this subject based on the ideXlab platform.
-
deployment of regulatory genes during gastrulation and germ layer specification in a model spiralian mollusc crepidula
Developmental Dynamics, 2015Co-Authors: Kimberly J. Perry, Deirdre C. Lyons, Marta Truchadogarcia, Antje H L Fischer, Lily W Helfrich, Kimberly B Johansson, Julie C Diamond, Cristina Grande, Jonathan Q. HenryAbstract:Background: During gastrulation, endoderm and mesoderm are specified from a bipotential precursor (endomesoderm) that is argued to be homologous across bilaterians. Spiralians also generate mesoderm from ectodermal precursors (ectomesoderm), which arises near the Blastopore. While a conserved gene regulatory network controls specification of endomesoderm in deuterostomes and ecdysozoans, little is known about genes controlling specification or behavior of either source of spiralian mesoderm or the digestive tract. Results: Using the mollusc Crepidula, we examined conserved regulatory factors and compared their expression to fate maps to score expression in the germ layers, Blastopore lip, and digestive tract. Many genes were expressed in both ecto- and endomesoderm, but only five were expressed in ectomesoderm exclusively. The latter may contribute to epithelial-to-mesenchymal transition seen in ectomesoderm. Conclusions: We present the first comparison of genes expressed during spiralian gastrulation in the context of high-resolution fate maps. We found variation of genes expressed in the Blastopore lip, mouth, and cells that will form the anus. Shared expression of many genes in both mesodermal sources suggests that components of the conserved endomesoderm program were either co-opted for ectomesoderm formation or that ecto- and endomesoderm are derived from a common mesodermal precursor that became subdivided into distinct domains during evolution. Developmental Dynamics 244:1215–1248, 2015. © 2015 Wiley Periodicals, Inc.
-
Spiralian gastrulation: germ layer formation, morphogenesis, and fate of the Blastopore in the slipper snail Crepidula fornicata
EvoDevo, 2015Co-Authors: Deirdre C. Lyons, Kimberly J. Perry, Jonathan Q. HenryAbstract:Background Gastrulation is a critical step in bilaterian development, directly linked to the segregation of germ layers, establishment of axes, and emergence of the through-gut. Theories about the evolution of gastrulation often concern the fate of the Blastopore (site of endomesoderm internalization), which varies widely in a major branch of bilaterians, the Spiralia. In this group, the Blastopore has been said to become the mouth, the anus, both, or neither. Different developmental explanations for this variation exist, yet no modern lineage tracing study has ever correlated the position of cells surrounding the Blastopore with their contribution to tissues of the mouth, foregut, and anus in a spiralian. This is the first study to do so, using the gastropod Crepidula fornicata.
Lance A. Davidson - One of the best experts on this subject based on the ideXlab platform.
-
Large, long range tensile forces drive convergence during Xenopus Blastopore closure and body axis elongation
eLife, 2018Co-Authors: David R. Shook, Eric M Kasprowicz, Lance A. Davidson, Ray KellerAbstract:Indirect evidence suggests that Blastopore closure during gastrulation of anamniotes, including amphibians such as Xenopus laevis, depends on circumblastoporal convergence forces generated by the marginal zone (MZ), but direct evidence is lacking. We show that explanted MZs generate tensile convergence forces up to 1.5 μN during gastrulation and over 4 μN thereafter. These forces are generated by convergent thickening (CT) until the midgastrula and increasingly by convergent extension (CE) thereafter. Explants from ventralized embryos, which lack tissues expressing CE but close their Blastopores, produce up to 2 μN of tensile force, showing that CT alone generates forces sufficient to close the Blastopore. Uniaxial tensile stress relaxation assays show stiffening of mesodermal and ectodermal tissues around the onset of neurulation, potentially enhancing long-range transmission of convergence forces. These results illuminate the mechanobiology of early vertebrate morphogenic mechanisms, aid interpretation of phenotypes, and give insight into the evolution of Blastopore closure mechanisms.
-
Mechanics of Blastopore closure during amphibian gastrulation
Developmental biology, 2014Co-Authors: Rafey Feroze, Joseph H. Shawky, Michelangelo Von Dassow, Lance A. DavidsonAbstract:Abstract Blastopore closure in the amphibian embryo involves large scale tissue reorganization driven by physical forces. These forces are tuned to generate sustained Blastopore closure throughout the course of gastrulation. We describe the mechanics of Blastopore closure at multiple scales and in different regions around the Blastopore by characterizing large scale tissue deformations, cell level shape change and subcellular F-actin organization and by measuring tissue force production and structural stiffness of the Blastopore during gastrulation. We find that the embryo generates a ramping magnitude of force until it reaches a peak force on the order of 0.5 μN. During this time course, the embryo also stiffens 1.5 fold. Strain rate mapping of the dorsal, ventral and lateral epithelial cells proximal to the Blastopore reveals changing patterns of strain rate throughout closure. Cells dorsal to the Blastopore, which are fated to become neural plate ectoderm, are polarized and have straight boundaries. In contrast, cells lateral and ventral to the Blastopore are less polarized and have tortuous cell boundaries. The F-actin network is organized differently in each region with the highest percentage of alignment occurring in the lateral region. Interestingly F-actin was consistently oriented toward the Blastopore lip in dorsal and lateral cells, but oriented parallel to the lip in ventral regions. Cell shape and F-actin alignment analyses reveal different local mechanical environments in regions around the Blastopore, which was reflected by the strain rate maps.
Horst Grunz - One of the best experts on this subject based on the ideXlab platform.
-
The Dorsalization of Spermann's Organizer Takes Place during Gastrulation in Xenopus laevis Embryos. (Spemann's organizer/dorsal mesoderm/neural induction/suramin/inhibition of notochord formation)
Development Growth and Differentiation, 1993Co-Authors: Horst GrunzAbstract:Suramin, a polyanionic compound, which is thought to inhibit the binding of growth factors to their receptors, prevents the differentiation of the dorsal Blastopore lip of early gastrulae into dorsal mesodermal structures as notochord and somites. Suramin treated Blastopore lips form ventral mesodermal structures, mainly heart structures. Several cases showed rythmic contractions (“beating hearts”). Of special interest is the fact that Blastopore lips isolated from middle gastrulae followed by suramin treatment differentiate in about 50% of the cases brain structures without the presence of notochord. These data suggest that suramin prevents the differentiation of the dorsal Blastopore lip into notochord up to the early middle gastrula stage but no longer the formation of head mesoderm, which is the prequisite for the induction of archencephalic brain structures. Treated chordamesoderm with overlaying ectoderm from late gastrulae will differentiate as untreated controls, namely into dorsal axial structures like notochord, somites and brain structures. The results indicate that primarily a more general or ventral mesodermal signal is transferred from the dorsal vegetal blastomeres (Nieuwkoop center) to the dorsal marginal zone. The dorsalization, which enables the Blastopore lip to differentiate into head mesoderm and notochord and in turn to acquire neuralizing activity, takes place during the early steps of gastrulation.
-
Suramin changes the fate of Spemann's organizer and prevents neural induction in Xenopus laevis.
Mechanisms of development, 1992Co-Authors: Horst GrunzAbstract:Suramin, a polyanionic compound, which has previously shown to dissociate platelet derived growth factor (PDGF) from its receptor, prevents the differentiation of neural (brain) structures of recombinants of dorsal Blastopore lip (Spemann's organizer) and competent neuroectoderm. Furthermore, the suramin treatment changes the prospective differentiation pattern of isolated Blastopore lip. While untreated dorsal Blastopore lip will differentiate into dorsal mesodermal structures (notochord and somites), suramin treated dorsal Blastopore lip will form ventral mesoderm structures, especially heart structures. The results are discussed in the context of the current opinion about the mode of action of different growth factor superfamilies.