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Kohji Hotta - One of the best experts on this subject based on the ideXlab platform.
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brachyury downstream Notochord genes and convergent extension in ciona intestinalis embryos
Development Growth & Differentiation, 2007Co-Authors: Kohji Hotta, Shigehiro Yamada, Naoto Ueno, Hiroki TakahashiAbstract:Formation of the chordate body is accomplished by a complex set of morphogenetic movements including convergent extension of Notochord cells. In the ascidian Ciona intestinalis, Brachyury plays a key role in the formation of the Notochord, and more than 30 Bra-downstream Notochord genes have been identified. In the present study, we examined the effects of functional suppression of nine Bra-downstream Notochord genes, which include Ci-PTP, Ci-ACL, Ci-prickle, Ci-netrin, Ci-trop, Ci-Noto3, Ci-ASAK, Ci-ERM and Ci-pellino. When the function of the first two genes (Ci-PTP and Ci-ACL) was suppressed with specific morpholinos, the Notochord cells failed to converge, while functional suppression of Ci-prickle resulted in a failure of intercalation, and therefore the cells in these three types of embryo remained in the mid-dorsal region of the embryo. Functional suppression of the next four genes (Ci-netrin, Ci-trop, Ci-Noto3 and Ci-ASAK) resulted in the partial defect of intercalation, and the Notochord did not consist of a single row. In addition, when the function of the last two genes (Ci-ERM and Ci-pellino) was suppressed, Notochord cells failed to elongate in the embryo, even though convergence/extension took place normally. These results indicate that many Bra-downstream Notochord genes are involved in convergence/extension of the embryo.
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characterization of brachyury downstream Notochord genes in the ciona intestinalis embryo
Developmental Biology, 2000Co-Authors: Kohji Hotta, Hiroki Takahashi, Tomomi Asakura, Banjo Saitoh, Naohito Takatori, Yutaka Satou, Nori SatohAbstract:Abstract The Notochord has two major roles during chordate embryogenesis, as a source of inductive signals for the patterning of neural tube and paraxial mesoderm and as a supportive organ of the larval tail. Despite the recent identification of mutations that affect the Notochord development in vertebrate embryos, little is known about genes that are expressed in the differentiating Notochord itself. In the urochordate ascidian Ciona intestinalis, Brachyury (Ci-Bra) plays a key role in Notochord differentiation. In a previous study, we isolated cDNA clones for nearly 40 potential Ci-Bra target genes that are expressed in Notochord cells (H. Takahashi et al., 1999, Genes Dev. 13, 1519–1523). Here we characterized 20 of them by determining the complete nucleotide sequences of the cDNAs. These genes encode a broad spectrum of divergent proteins associated with Notochord formation and function. Two genes encode ascidian homologs of the Drosophila Prickle LIM domain proteins and another encodes the ERM protein, all 3 of which appear to be involved in the control of cytoskeletal architecture. In addition, genes for netrin, leprecan, cdc45, ATP:citrate lyase, ATP sulfurylase/APS kinase, protein tyrosine phosphatase, β4-galactosyltransferase, fibrinogen-like protein, divergent tropomyosin-like proteins, and Drosophila Pellino-like protein were identified. The observation of the netrin gene expression in the Notochord may provide the first molecular evidence that the ascidian Notochord is a source of signals as in vertebrates. In addition, the present information should be used to identify nonchordate deuterostome tissues homologous to the Notochord as well as genes which are expressed in the Notochord cells of vertebrate embryos.
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characterization of brachyury downstream Notochord genes in the ciona intestinalis embryo
Developmental Biology, 2000Co-Authors: Kohji Hotta, Hiroki Takahashi, Tomomi Asakura, Banjo Saitoh, Naohito Takatori, Yutaka Satou, Nori SatohAbstract:The Notochord has two major roles during chordate embryogenesis, as a source of inductive signals for the patterning of neural tube and paraxial mesoderm and as a supportive organ of the larval tail. Despite the recent identification of mutations that affect the Notochord development in vertebrate embryos, little is known about genes that are expressed in the differentiating Notochord itself. In the urochordate ascidian Ciona intestinalis, Brachyury (Ci-Bra) plays a key role in Notochord differentiation. In a previous study, we isolated cDNA clones for nearly 40 potential Ci-Bra target genes that are expressed in Notochord cells (H. Takahashi et al., 1999, Genes Dev. 13, 1519-1523). Here we characterized 20 of them by determining the complete nucleotide sequences of the cDNAs. These genes encode a broad spectrum of divergent proteins associated with Notochord formation and function. Two genes encode ascidian homologs of the Drosophila Prickle LIM domain proteins and another encodes the ERM protein, all 3 of which appear to be involved in the control of cytoskeletal architecture. In addition, genes for netrin, leprecan, cdc45, ATP:citrate lyase, ATP sulfurylase/APS kinase, protein tyrosine phosphatase, beta4-galactosyltransferase, fibrinogen-like protein, divergent tropomyosin-like proteins, and Drosophila Pellino-like protein were identified. The observation of the netrin gene expression in the Notochord may provide the first molecular evidence that the ascidian Notochord is a source of signals as in vertebrates. In addition, the present information should be used to identify nonchordate deuterostome tissues homologous to the Notochord as well as genes which are expressed in the Notochord cells of vertebrate embryos.
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brachyury downstream Notochord differentiation in the ascidian embryo
Genes & Development, 1999Co-Authors: Hiroki Takahashi, Kohji Hotta, Anna Di Gregorio, Albert Erives, Robert W Zeller, Michael Levine, Nori SatohAbstract:The ascidian tadpole represents the most simplified chordate body plan. It contains a Notochord composed of just 40 cells, but as in vertebrates Brachyury is essential for Notochord differentiation. Here, we show that the misexpression of the Brachyury gene (Ci-Bra) of Ciona intestinalis is sufficient to transform endoderm into Notochord. Subtractive hybridization screens were conducted to identify potential Brachyury target genes that are induced upon Ci-Bra misexpression. Of 501 independent cDNA clones that were surveyed, 38 were specifically expressed in Notochord cells. These potential Ci-Bra downstream genes appear to encode a broad spectrum of divergent proteins associated with Notochord formation.
Nori Satoh - One of the best experts on this subject based on the ideXlab platform.
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Brachyury (T) gene expression and Notochord development in Oikopleura longicauda (Appendicularia, Urochordata).
Development genes and evolution, 2001Co-Authors: Atsuo Nishino, Masaaki Morisawa, Yutaka Satou, Nori SatohAbstract:Appendicularia (Larvacea) is a subgroup of Urochordata (Tunicata) comprised of holoplanktonic organisms that retain their tailed architecture throughout their life history, while other tunicates, including ascidians and doliolids, resorb the tail after metamorphosis. In order to investigate the characteristics of the appendicularian unresorbed Notochord, we isolated a partial genomic clone and a full-length cDNA sequence homologous to the mouse Brachyury (T) gene from the appendicularian Oikopleura longicauda. Brachyury is known to be predominantly expressed in the Notochord cells and plays an important role in their differentiation in other chordates. While phylogenetic analysis robustly supports the orthology of the isolated Brachyury gene, the exon–intron organization found in the genomic clone was distinct from that well-conserved among other T-box genes. In addition to a detailed observation of Notochord development in living specimens, whole-mount double in situ hybridization was carried out using a Brachyury probe along with a muscle actin probe. The Brachyury transcripts were found in the Notochord of the tailbud embryos and persisted into later stages. The present study highlights characteristics of Notochord development in the appendicularian. Furthermore, these results provide basic knowledge for comprehensive understanding of the cellular- and molecular-based mechanisms needed to build the characteristic cytoarchitecture of Notochord that varies among tunicate species.
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characterization of brachyury downstream Notochord genes in the ciona intestinalis embryo
Developmental Biology, 2000Co-Authors: Kohji Hotta, Hiroki Takahashi, Tomomi Asakura, Banjo Saitoh, Naohito Takatori, Yutaka Satou, Nori SatohAbstract:Abstract The Notochord has two major roles during chordate embryogenesis, as a source of inductive signals for the patterning of neural tube and paraxial mesoderm and as a supportive organ of the larval tail. Despite the recent identification of mutations that affect the Notochord development in vertebrate embryos, little is known about genes that are expressed in the differentiating Notochord itself. In the urochordate ascidian Ciona intestinalis, Brachyury (Ci-Bra) plays a key role in Notochord differentiation. In a previous study, we isolated cDNA clones for nearly 40 potential Ci-Bra target genes that are expressed in Notochord cells (H. Takahashi et al., 1999, Genes Dev. 13, 1519–1523). Here we characterized 20 of them by determining the complete nucleotide sequences of the cDNAs. These genes encode a broad spectrum of divergent proteins associated with Notochord formation and function. Two genes encode ascidian homologs of the Drosophila Prickle LIM domain proteins and another encodes the ERM protein, all 3 of which appear to be involved in the control of cytoskeletal architecture. In addition, genes for netrin, leprecan, cdc45, ATP:citrate lyase, ATP sulfurylase/APS kinase, protein tyrosine phosphatase, β4-galactosyltransferase, fibrinogen-like protein, divergent tropomyosin-like proteins, and Drosophila Pellino-like protein were identified. The observation of the netrin gene expression in the Notochord may provide the first molecular evidence that the ascidian Notochord is a source of signals as in vertebrates. In addition, the present information should be used to identify nonchordate deuterostome tissues homologous to the Notochord as well as genes which are expressed in the Notochord cells of vertebrate embryos.
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characterization of brachyury downstream Notochord genes in the ciona intestinalis embryo
Developmental Biology, 2000Co-Authors: Kohji Hotta, Hiroki Takahashi, Tomomi Asakura, Banjo Saitoh, Naohito Takatori, Yutaka Satou, Nori SatohAbstract:The Notochord has two major roles during chordate embryogenesis, as a source of inductive signals for the patterning of neural tube and paraxial mesoderm and as a supportive organ of the larval tail. Despite the recent identification of mutations that affect the Notochord development in vertebrate embryos, little is known about genes that are expressed in the differentiating Notochord itself. In the urochordate ascidian Ciona intestinalis, Brachyury (Ci-Bra) plays a key role in Notochord differentiation. In a previous study, we isolated cDNA clones for nearly 40 potential Ci-Bra target genes that are expressed in Notochord cells (H. Takahashi et al., 1999, Genes Dev. 13, 1519-1523). Here we characterized 20 of them by determining the complete nucleotide sequences of the cDNAs. These genes encode a broad spectrum of divergent proteins associated with Notochord formation and function. Two genes encode ascidian homologs of the Drosophila Prickle LIM domain proteins and another encodes the ERM protein, all 3 of which appear to be involved in the control of cytoskeletal architecture. In addition, genes for netrin, leprecan, cdc45, ATP:citrate lyase, ATP sulfurylase/APS kinase, protein tyrosine phosphatase, beta4-galactosyltransferase, fibrinogen-like protein, divergent tropomyosin-like proteins, and Drosophila Pellino-like protein were identified. The observation of the netrin gene expression in the Notochord may provide the first molecular evidence that the ascidian Notochord is a source of signals as in vertebrates. In addition, the present information should be used to identify nonchordate deuterostome tissues homologous to the Notochord as well as genes which are expressed in the Notochord cells of vertebrate embryos.
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brachyury downstream Notochord differentiation in the ascidian embryo
Genes & Development, 1999Co-Authors: Hiroki Takahashi, Kohji Hotta, Anna Di Gregorio, Albert Erives, Robert W Zeller, Michael Levine, Nori SatohAbstract:The ascidian tadpole represents the most simplified chordate body plan. It contains a Notochord composed of just 40 cells, but as in vertebrates Brachyury is essential for Notochord differentiation. Here, we show that the misexpression of the Brachyury gene (Ci-Bra) of Ciona intestinalis is sufficient to transform endoderm into Notochord. Subtractive hybridization screens were conducted to identify potential Brachyury target genes that are induced upon Ci-Bra misexpression. Of 501 independent cDNA clones that were surveyed, 38 were specifically expressed in Notochord cells. These potential Ci-Bra downstream genes appear to encode a broad spectrum of divergent proteins associated with Notochord formation.
William C Smith - One of the best experts on this subject based on the ideXlab platform.
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tube formation by complex cellular processes in ciona intestinalis Notochord
Developmental Biology, 2009Co-Authors: Bo Dong, Takeo Horie, Elsa Denker, William C Smith, Motoyuki Tsuda, Takehiro Kusakabe, Di JiangAbstract:Abstract In the course of embryogenesis multicellular structures and organs are assembled from constituent cells. One structural component common to many organs is the tube, which consists most simply of a luminal space surrounded by a single layer of epithelial cells. The Notochord of ascidian Ciona forms a tube consisting of only 40 cells, and serves as a hydrostatic “skeleton” essential for swimming. While the early processes of convergent extension in ascidian Notochord development have been extensively studied, the later phases of development, which include lumen formation, have not been well characterized. Here we used molecular markers and confocal imaging to describe tubulogenesis in the developing Ciona Notochord. We found that during tubulogenesis each Notochord cell established de novo apical domains, and underwent a mesenchymal–epithelial transition to become an unusual epithelial cell with two opposing apical domains. Concomitantly, extracellular luminal matrix was produced and deposited between Notochord cells. Subsequently, each Notochord cell simultaneously executed two types of crawling movements bi-directionally along the anterior/posterior axis on the inner surface of Notochordal sheath. Lamellipodia-like protrusions resulted in cell lengthening along the anterior/posterior axis, while the retraction of trailing edges of the same cell led to the merging of the two apical domains. As a result, the Notochord cells acquired endothelial-like shape and formed the wall of the central lumen. Inhibition of actin polymerization prevented the cell movement and tube formation. Ciona Notochord tube formation utilized an assortment of common and fundamental cellular processes including cell shape change, apical membrane biogenesis, cell/cell adhesion remodeling, dynamic cell crawling, and lumen matrix secretion.
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ascidian Notochord morphogenesis
Developmental Dynamics, 2007Co-Authors: Di Jiang, William C SmithAbstract:The development of the Notochord involves a complex set of cellular behaviors. While these morphogenic behaviors are common to all chordates, the ascidian provides a particularly attractive experimental model because of its relative simplicity. In particular, all Notochord morphogenesis in ascidians takes place with only 40 cells, as opposed to the hundreds of cells in vertebrate model systems. Initial steps in ascidian Notochord development convert a monolayer of epithelial-like cells in the pregastrula embryo to a cylindrical rod of single-cell diameter. Convergent extension is responsible for the intercalation of Notochord cells and some degree of Notochord elongation, while a second phase of elongation is observed as the Notochord narrows medially and increases in volume. The mechanism by which the volume of the Notochord increases differs between ascidian species. Some ascidians produce extracellular pockets that will eventually coalesce to form a lumen running the length of the Notochord; whereas others do not. By either mechanism, the resulting Notochord serves as a hydrostatic skeleton allowing for the locomotion of the swimming larva. Several basic cell behaviors, such as cell shape changes, cell rearrangement, establishment of cell polarity, and alteration of extracellular environment, are displayed in the process of Notochord morphogenesis. Modern analysis of ascidian Notochord morphogenesis promises to contribute to our understanding of these fundamental biological processes.
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ascidian prickle regulates both mediolateral and anterior posterior cell polarity of Notochord cells
Current Biology, 2005Co-Authors: Di Jiang, Edwin Munro, William C SmithAbstract:Abstract The ascidian Notochord follows a morphogenetic program that includes convergent extension (C/E) followed by anterior-posterior (A/P) elongation [1–4]. As described here, developing Notochord cells show polarity first in the mediolateral (M/L) axis during C/E, and subsequently in the A/P axis during elongation. Previous embryological studies [3] have shown that contact with neighboring tissues is essential for directing M/L polarity of ascidian Notochord cells. During C/E, the planar cell polarity (PCP) gene products prickle ( pk ) and dishevelled ( dsh ) show M/L polarization. pk and dsh colocalize at the Notochord cell membranes, with the exception of those in contact with neighboring muscle cells. In the mutant aimless ( aim ), which carries a deletion in pk , Notochord morphogenesis is disrupted, and cell polarization is lost. After C/E, there is a dynamic relocalization of PCP proteins in the Notochord cells with dsh localized to the lateral edges of the membrane, and pk and strabismus ( stbm ) at the anterior edges. An A/P polarity is present in the extending Notochord cells and is evident by the position of the nuclei, which in normal embryos are invariably found at the posterior edge of each cell. In the aim mutant, all appearances of A/P polarity in the Notochord are lost.
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Mutations affecting tail and Notochord development in the ascidian Ciona savignyi.
Development (Cambridge England), 1999Co-Authors: Yuki Nakatani, Robert Moody, William C SmithAbstract:Ascidians are among the most distant chordate relatives of the vertebrates. However, ascidians share many features with vertebrates including a Notochord and hollow dorsal nerve cord. A screen for N-ethyl-N-nitrosourea (ENU)-induced mutations affecting early development in the ascidian Ciona savignyi resulted in the isolation of a number of mutants including the complementing Notochord mutants chongmague and chobi. In chongmague embryos the Notochord fails to develop, and the Notochord cells instead adopt a mesenchyme-like fate. The failure of Notochord development in chongmague embryos results in a severe truncation of tail, although development of the tail muscles and caudal nerve tracts appears largely normal. Chobi embryos also have a truncation of the tail stemming from a disruption of the Notochord. However, in chobi embryos the early development of the Notochord appears normal and defects occur later as the Notochord attempts to extend and direct elongation of the tail. We find in chobi tailbud embryos that the Notochord is often bent, with cells clumped together, rather than extended as a column. These results provide new information on the function and development of the ascidian Notochord. In addition, the results demonstrate how the unique features of ascidians can be used in genetic analysis of morphogenesis.
Hiroki Takahashi - One of the best experts on this subject based on the ideXlab platform.
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brachyury downstream Notochord genes and convergent extension in ciona intestinalis embryos
Development Growth & Differentiation, 2007Co-Authors: Kohji Hotta, Shigehiro Yamada, Naoto Ueno, Hiroki TakahashiAbstract:Formation of the chordate body is accomplished by a complex set of morphogenetic movements including convergent extension of Notochord cells. In the ascidian Ciona intestinalis, Brachyury plays a key role in the formation of the Notochord, and more than 30 Bra-downstream Notochord genes have been identified. In the present study, we examined the effects of functional suppression of nine Bra-downstream Notochord genes, which include Ci-PTP, Ci-ACL, Ci-prickle, Ci-netrin, Ci-trop, Ci-Noto3, Ci-ASAK, Ci-ERM and Ci-pellino. When the function of the first two genes (Ci-PTP and Ci-ACL) was suppressed with specific morpholinos, the Notochord cells failed to converge, while functional suppression of Ci-prickle resulted in a failure of intercalation, and therefore the cells in these three types of embryo remained in the mid-dorsal region of the embryo. Functional suppression of the next four genes (Ci-netrin, Ci-trop, Ci-Noto3 and Ci-ASAK) resulted in the partial defect of intercalation, and the Notochord did not consist of a single row. In addition, when the function of the last two genes (Ci-ERM and Ci-pellino) was suppressed, Notochord cells failed to elongate in the embryo, even though convergence/extension took place normally. These results indicate that many Bra-downstream Notochord genes are involved in convergence/extension of the embryo.
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characterization of brachyury downstream Notochord genes in the ciona intestinalis embryo
Developmental Biology, 2000Co-Authors: Kohji Hotta, Hiroki Takahashi, Tomomi Asakura, Banjo Saitoh, Naohito Takatori, Yutaka Satou, Nori SatohAbstract:Abstract The Notochord has two major roles during chordate embryogenesis, as a source of inductive signals for the patterning of neural tube and paraxial mesoderm and as a supportive organ of the larval tail. Despite the recent identification of mutations that affect the Notochord development in vertebrate embryos, little is known about genes that are expressed in the differentiating Notochord itself. In the urochordate ascidian Ciona intestinalis, Brachyury (Ci-Bra) plays a key role in Notochord differentiation. In a previous study, we isolated cDNA clones for nearly 40 potential Ci-Bra target genes that are expressed in Notochord cells (H. Takahashi et al., 1999, Genes Dev. 13, 1519–1523). Here we characterized 20 of them by determining the complete nucleotide sequences of the cDNAs. These genes encode a broad spectrum of divergent proteins associated with Notochord formation and function. Two genes encode ascidian homologs of the Drosophila Prickle LIM domain proteins and another encodes the ERM protein, all 3 of which appear to be involved in the control of cytoskeletal architecture. In addition, genes for netrin, leprecan, cdc45, ATP:citrate lyase, ATP sulfurylase/APS kinase, protein tyrosine phosphatase, β4-galactosyltransferase, fibrinogen-like protein, divergent tropomyosin-like proteins, and Drosophila Pellino-like protein were identified. The observation of the netrin gene expression in the Notochord may provide the first molecular evidence that the ascidian Notochord is a source of signals as in vertebrates. In addition, the present information should be used to identify nonchordate deuterostome tissues homologous to the Notochord as well as genes which are expressed in the Notochord cells of vertebrate embryos.
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characterization of brachyury downstream Notochord genes in the ciona intestinalis embryo
Developmental Biology, 2000Co-Authors: Kohji Hotta, Hiroki Takahashi, Tomomi Asakura, Banjo Saitoh, Naohito Takatori, Yutaka Satou, Nori SatohAbstract:The Notochord has two major roles during chordate embryogenesis, as a source of inductive signals for the patterning of neural tube and paraxial mesoderm and as a supportive organ of the larval tail. Despite the recent identification of mutations that affect the Notochord development in vertebrate embryos, little is known about genes that are expressed in the differentiating Notochord itself. In the urochordate ascidian Ciona intestinalis, Brachyury (Ci-Bra) plays a key role in Notochord differentiation. In a previous study, we isolated cDNA clones for nearly 40 potential Ci-Bra target genes that are expressed in Notochord cells (H. Takahashi et al., 1999, Genes Dev. 13, 1519-1523). Here we characterized 20 of them by determining the complete nucleotide sequences of the cDNAs. These genes encode a broad spectrum of divergent proteins associated with Notochord formation and function. Two genes encode ascidian homologs of the Drosophila Prickle LIM domain proteins and another encodes the ERM protein, all 3 of which appear to be involved in the control of cytoskeletal architecture. In addition, genes for netrin, leprecan, cdc45, ATP:citrate lyase, ATP sulfurylase/APS kinase, protein tyrosine phosphatase, beta4-galactosyltransferase, fibrinogen-like protein, divergent tropomyosin-like proteins, and Drosophila Pellino-like protein were identified. The observation of the netrin gene expression in the Notochord may provide the first molecular evidence that the ascidian Notochord is a source of signals as in vertebrates. In addition, the present information should be used to identify nonchordate deuterostome tissues homologous to the Notochord as well as genes which are expressed in the Notochord cells of vertebrate embryos.
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brachyury downstream Notochord differentiation in the ascidian embryo
Genes & Development, 1999Co-Authors: Hiroki Takahashi, Kohji Hotta, Anna Di Gregorio, Albert Erives, Robert W Zeller, Michael Levine, Nori SatohAbstract:The ascidian tadpole represents the most simplified chordate body plan. It contains a Notochord composed of just 40 cells, but as in vertebrates Brachyury is essential for Notochord differentiation. Here, we show that the misexpression of the Brachyury gene (Ci-Bra) of Ciona intestinalis is sufficient to transform endoderm into Notochord. Subtractive hybridization screens were conducted to identify potential Brachyury target genes that are induced upon Ci-Bra misexpression. Of 501 independent cDNA clones that were surveyed, 38 were specifically expressed in Notochord cells. These potential Ci-Bra downstream genes appear to encode a broad spectrum of divergent proteins associated with Notochord formation.
Marnie E Halpern - One of the best experts on this subject based on the ideXlab platform.
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axial mesoderm and patterning of the zebrafish embryo
Integrative and Comparative Biology, 1997Co-Authors: Marnie E HalpernAbstract:SYNOPSIS. It has long been recognized that the Notochord, a derivative of the gastrula organizer, is important for patterning the vertebrate embryo. Experimental manipulations of amphibian and chick embryos demonstrate the Notochord's influence on neural tube and somite differentiation. Recent studies implicate the Notochord-derived signal Sonic hedgehog. In zebrafish, genetic strategies have enabled the recovery of mutations that disrupt Notochord development. Embryos mutant for floating head or no tail lack differentiated Notochord and, consistent with encoding transcription factors, both genes behave cell autonomously in genetic mosaics: wild-type cells develop into Notochord in mutant embryos, whereas mutant cells fail to contribute to wild-type Notochord. In floating head mutants, axial mesoderm fated to form Notochord respecines to paraxial mesoderm, differentiating into muscle instead. As a result, fused somites develop across the trunk midline. In no tail mutants, mesenchymal cells related by lineage to Notochord are found in the midline, and although trunk somites are bilaterally paired, they lack Engrailed-expressing muscle pioneer cells. In the presence of wild-type Notochord, however, no tail mutant cells can differentiate muscle pioneers, suggesting that induction of muscle pioneers is a normal function of Notochord. Notochord is also involved in induction of floor plate at the ventral midline of the vertebrate neural tube; yet in floating head and no tail mutants, floor plate cells develop in the absence of differentiating Notochord. Expression of sonic hedgehog by newly-forming axial mesoderm at gastrulation may account for floor plate induction prior to Notochord differentiation. Thus, analyses of zebrafish Notochordless mutants suggest a role for both early and late signaling by cells of the Notochord lineage during embryogenesis.
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cell autonomous shift from axial to paraxial mesodermal development in zebrafish floating head mutants
Development, 1995Co-Authors: Marnie E Halpern, Bill Trevarrow, John H Postlethwait, Christine Thisse, Bernard Thisse, B Riggleman, E S Weinberg, Charles B KimmelAbstract:Zebrafish floating head mutant embryos lack Notochord and develop somitic muscle in its place. This may result from incorrect specification of the Notochord domain at gastrulation, or from respecification of Notochord progenitors to form muscle. In genetic mosaics, floating head acts cell autonomously. Transplanted wild-type cells differentiate into Notochord in mutant hosts; however, cells from floating head mutant donors produce muscle rather than Notochord in wild-type hosts. Consistent with respecification, markers of axial mesoderm are initially expressed in floating head mutant gastrulas, but expression does not persist. Axial cells also inappropriately express markers of paraxial mesoderm. Thus, single cells in the mutant midline transiently co-express genes that are normally specific to either axial or paraxial mesoderm. Since floating head mutants produce some floor plate in the ventral neural tube, midline mesoderm may also retain early signaling capabilities. Our results suggest that wild-type floating head provides an essential step in maintaining, rather than initiating, development of Notochord-forming axial mesoderm.
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a homeobox gene essential for zebrafish Notochord development
Nature, 1995Co-Authors: William S Talbot, Marnie E Halpern, Bill Trevarrow, Anna E Melby, Gist H Farr, John H Postlethwait, Trevor Jowett, Charles B KimmelAbstract:The Notochord is a midline mesodermal structure with an essential patterning function in all vertebrate embryos. Zebrafish floating head (flh) mutants lack a Notochord, but develop with prechordal plate and other mesodermal derivatives, indicating that flh functions specifically in Notochord development. We show that floating head is the zebrafish homologue of Xnot, a homeobox gene expressed in the amphibian organizer and Notochord. We propose that flh regulates Notochord precursor cell fate.
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induction of muscle pioneers and floor plate is distinguished by the zebrafish no tail mutation
Cell, 1993Co-Authors: Marnie E Halpern, Charline Walker, Charles B KimmelAbstract:Dorsal mesoderm is thought to provide important signals for axis formation and neural differentiation in vertebrate embryos. We have examined induction and patterning in a zebrafish mutant, no tail, that lacks a derivative of dorsal mesoderm, the Notochord. Despite the absence of a differentiated Notochord, development of the central nervous system including floor plate appears normal, likely owing to the presence of Notochord precursor cells. In contrast, somites are misshapen, and muscle pioneer cells are absent. Wild-type cells transplanted into mutant hosts can autonomously differentiate into Notochord and thereby rescue somitic defects, suggesting that interactions between Notochord and paraxial mesoderm are necessary for proper somite patterning. Thus, cells derived from dorsal mesoderm may have multiple signaling functions during zebrafish embryogenesis.
