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Salvador Martinez - One of the best experts on this subject based on the ideXlab platform.
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Molecular mechanisms controlling brain development: an overview of neuroepithelial secondary organizers.
The International journal of developmental biology, 2010Co-Authors: Claudia Vieira, Ana Pombero, Raquel Garcia-lopez, L. Gimeno, Diego Echevarria, Salvador MartinezAbstract:The vertebrate Central Nervous System (CNS) originates from the embryonic dorsal ectoderm. Differentiation of the neural epithelium from the ectoderm and the formation of the neural plate constitute the first phase of a complex process called neurulation which culminates in the formation of the neural tube, the anlage of the CNS in sauropsids and mammals (for review see Smith and Schoenwolf, 1997; Colas and Schoenwolf, 2001). At neural plate and neural tube stages, local signaling centers in the neuroepithelium, known as secondary organizers, refine the antero-posterior specification of different neural territories (for review see Echevarria et al., 2003; Stern et al.,2006; Woltering and Durston, 2008). In this review, we will describe the principle aspects of CNS development in birds and mammals, starting from early stages of embryogenesis (gastrulation and neurulation) and culminating with the formation of a variety of different regions which contribute to the structural complexity of the brain (regionalization and morphogenesis). We will pay special attention to the cellular and molecular mechanisms involved in neural tube regionalization and the key role played by localized secondary organizers in the patterning of neural primordia.
Ursula C. Dräger - One of the best experts on this subject based on the ideXlab platform.
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Retinoic Acid Synthesizing Enzymes in the Embryonic and Adult Vertebrate
Advances in experimental medicine and biology, 1995Co-Authors: Peter Mccaffery, Ursula C. DrägerAbstract:The oxidation of retinaldehyde to retinoic acid (RA) provides the retinoid form of highest potency for a variety of cellular systems. RA has been implicated in many processes, such as growth and differentiation of epithelia in the adult organism (De Luca 1991), and determination of the antero-posterior axis for the limb bud (Eichele and Thaller 1987; Tickle et al. 1982) and the entire body of the vertebrate embryo (Durston et al. 1989; Hogan, Thaller, and Eichele 1992). In addition, RA is thought to promote neuronal survival, differentiation and neurite outgrowth (Haskell et al. 1987; Quinn and De Boni 1991; Wuarin, Sidell, and De Vellis 1990). RA exerts its effects by binding to specific nuclear receptors that regulate transcription. The diversity in RA actions is commonly attributed to differences in local expression patterns of different receptors and cytoplasmic binding proteins that modify the availability of intracellular RA (Giguere 1994). In addition, however, retinoid metabolism may contribute significantly to local diversity in RA actions. Retinoid metabolism includes the processes of precursor circulation and cellular uptake mediated by binding proteins, the reversible oxidation of retinol to retinaldehyde, the irreversible oxidation of retinaldehyde to RA, and RA degradation. Here we focus on the enzymes that mediate the oxidation of retinaldehyde to RA.
Claudia Vieira - One of the best experts on this subject based on the ideXlab platform.
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Molecular mechanisms controlling brain development: an overview of neuroepithelial secondary organizers.
The International journal of developmental biology, 2010Co-Authors: Claudia Vieira, Ana Pombero, Raquel Garcia-lopez, L. Gimeno, Diego Echevarria, Salvador MartinezAbstract:The vertebrate Central Nervous System (CNS) originates from the embryonic dorsal ectoderm. Differentiation of the neural epithelium from the ectoderm and the formation of the neural plate constitute the first phase of a complex process called neurulation which culminates in the formation of the neural tube, the anlage of the CNS in sauropsids and mammals (for review see Smith and Schoenwolf, 1997; Colas and Schoenwolf, 2001). At neural plate and neural tube stages, local signaling centers in the neuroepithelium, known as secondary organizers, refine the antero-posterior specification of different neural territories (for review see Echevarria et al., 2003; Stern et al.,2006; Woltering and Durston, 2008). In this review, we will describe the principle aspects of CNS development in birds and mammals, starting from early stages of embryogenesis (gastrulation and neurulation) and culminating with the formation of a variety of different regions which contribute to the structural complexity of the brain (regionalization and morphogenesis). We will pay special attention to the cellular and molecular mechanisms involved in neural tube regionalization and the key role played by localized secondary organizers in the patterning of neural primordia.
Gregory M. Colon Semenza - One of the best experts on this subject based on the ideXlab platform.
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Politics of Restoration Sport
2016Co-Authors: Gregory M. Colon SemenzaAbstract:The raising of Maypoles throughout England in the spring of 1660 signified more than the return of monarchy; the Maypoles also symbolized the rejection of Interregnum ordinances that had rendered unlawful the traditional pastimes of the people. The ascension of Charles II and the subsequent proliferation of activities that were officially condemned by Interregnum leadersas well as the king's patronage of and participation in such activities-assured the representational volatility of sport in polemics and literature. In Samnson Agonistes, Milton's use of the term "sport" to signify activities involving "sword-players, and every sort / Of gymnic artists, wrestlers, riders, [and] runners" deviates from the biblical account of Samson's trials: such sports are neither mentioned nor implied in Judges, which offers "sport" as a term betokening "jest."' Milton's decision to widen the biblical definition of sport should be understood as a key component of his allegorical critique of Restoration monarchy and culture. According to Christopher Durston, one of the "prime targets of the puritan reformers" during the Interregnum was the traditional festive calendar, along with the sports, games, and pastimes of the English people.2 The battles waged between royalists and parliamentarians in the 1630s-over the legality and morality of the Sabbath day sports endorsed by Charles I in the 1633 reissuance of his father's Book of Sports-ended abruptly with the victory of the New Model Army in the Civil War. The official burnings of the Book of Sports in 1643 were followed by legisla
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Samson Agonistes and the Politics of Restoration Sport
SEL Studies in English Literature 1500-1900, 2002Co-Authors: Gregory M. Colon SemenzaAbstract:The raising of Maypoles throughout England in the spring of 1660 signified more than the return of monarchy; the Maypoles also symbolized the rejection of Interregnum ordinances that had rendered unlawful the traditional pastimes of the people. The ascension of Charles II and the subsequent proliferation of activities that were officially condemned by Interregnum leadersas well as the king's patronage of and participation in such activities-assured the representational volatility of sport in polemics and literature. In Samnson Agonistes, Milton's use of the term "sport" to signify activities involving "sword-players, and every sort / Of gymnic artists, wrestlers, riders, [and] runners" deviates from the biblical account of Samson's trials: such sports are neither mentioned nor implied in Judges, which offers "sport" as a term betokening "jest."' Milton's decision to widen the biblical definition of sport should be understood as a key component of his allegorical critique of Restoration monarchy and culture. According to Christopher Durston, one of the "prime targets of the puritan reformers" during the Interregnum was the traditional festive calendar, along with the sports, games, and pastimes of the English people.2 The battles waged between royalists and parliamentarians in the 1630s-over the legality and morality of the Sabbath day sports endorsed by Charles I in the 1633 reissuance of his father's Book of Sports-ended abruptly with the victory of the New Model Army in the Civil War. The official burnings of the Book of Sports in 1643 were followed by legisla-
Antony J. Durston - One of the best experts on this subject based on the ideXlab platform.
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Time, space and the vertebrate body axis
Seminars in cell & developmental biology, 2015Co-Authors: Antony J. DurstonAbstract:Anterior-posterior (A-P) patterning of the vertebrate main body axis regulated by timing. Anterior structures are specified early, posterior late. (1) Timing involves timed decision points as emphasised by the Wnt studies of Sokol and colleagues. It also involves complex timers, where large parts of the axis are patterned sequentially by a common upstream mechanism (articles by Durston et al., Mullins et al., Oates et al.,). (2) A gastrula BMP-anti BMP dependent time-space translation (TST) mechanism was demonstrated for the trunk section of the axis (Durston). (3) Thisses' studies emphasise the importance of BMP-anti BMP and the organiser inducing factor nodal for A-P patterning. (4) Meinhardt's interesting studies on the organiser and A-P patterning are reviewed in relation to TST. (5) Mullins' investigations show that anti-BMP dependent TST starts earlier (at the blastula stage) and extends further anteriorly (to the anterior head). Sive's studies imply it may extend further still to the "extreme anterior domain" (EAD). (6) The somitogenesis timer (clock) is presented. Stern's and Oates' findings are discussed. (7) Relations between somitogenesis and axial TST are discussed. (8) Relations of classical axial patterning pathways to TST decision points and somitogenesis are inventarised. In conclusion, all of these findings point to an integral BMP-anti BMP dependent A-P TST mechanism, running from cement gland in the EAD, Six3 and the anterior tip of the forebrain at blastula stages to Hox13 and the tip of the tail by the mid neurula stage. TST acts via sequential timed transitions between ventral (unstable, timed) and dorsal (stabilised) states. In the trunk-tail, the timer is thought to be Hox temporal collinearity and TST depends on Hox function. In the head, TST is under investigation. The somitogenesis clock is upstream of the TST timer, providing precision in the posterior part of the axis at least. Classical A-P signalling pathways: retinoids, FGFs and Wnts, change behaviour at functional decision points on the axis.
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Intracellular acidification of gastrula ectoderm is important for posterior axial development in Xenopus
Development (Cambridge England), 1995Co-Authors: D. R. Gutknecht, Cees H. Koster, Leon G.j. Tertoolen, S. W. De Laat, Antony J. DurstonAbstract:There is evidence suggesting that pHi elevation can induce differentiation to cement gland, an extremely anterior structure, during the early development of Xenopus laevis (Picard, J. J. (1975) J. Embryol. exp. Morphol. 33, 957–967; Sive, H. L., Hattori, K. and Weintraub, H. (1989) Cell 58, 171–180). We wanted to investigate whether axial development or neural induction are mediated in Xenopus via regulation of pHi. Our interest was stimulated further because certain signal transduction pathways, which are thought to mediate anterior neural induction (Otte, A. P., Van Run, P., Heideveld, M., Van Driel, R. and Durston, A. J. (1989) Cell 58, 641–648; Durston and Otte (1991), Cell-Cell Interactions in Early Development, pp. 109–127), are also known to modify the activity of proton extruders (Mitsuka and Berk (1991) Am. J. Physiol. 260, C562-C569; Wakabayashi, S., Sardet, C., Fafournoux, P., Counillon, L., Meloche, S., Pages, G. and Pouyssegur, J. (1993) Rev. Physiol. Biochem. Pharmacol. Vol. 119, pp. 157–186). We therefore measured pHi in explants of gastrula ectoderm and neurectoderm and identified ion exchangers that regulate pHi in these tissues. The measurements showed that pHi decreases in explants of both neurectoderm and uninduced ectoderm during the time course of gastrulation, this pHi decrease thus fails to correlate with neural induction. One important regulator of this cytoplasmic acidification is the Na+/H+ exchanger. The pHi set point, at which the acid extrusion activity of this alkalizing exchanger is shut off, shifts to more acidic values during the time course of gastrulation, thus permitting cytoplasmic acidification. We found also that preventing cytoplasmic acidification and thereby elevating pHi in late gastrula cells led to the specific suppression of posterior development. Neural induction and anterior development were unaffected by treatments leading either to an elevation of or a decrease in pHi. These findings indicate that the cellular processes mediating anterior development and neural induction are pHi tolerant, while the signals mediating posterior development require a sustained pHi decrease for their action, suggesting that downregulation of pHi is necessary for posterior axial development.
