Journal articles: 'Spadetail'

1

Griffin, K. J., S. L. Amacher, C. B. Kimmel, and D. Kimelman. "Molecular identification of spadetail: regulation of zebrafish trunk and tail mesoderm formation by T-box genes." Development 125, no. 17 (September 1, 1998): 3379–88. http://dx.doi.org/10.1242/dev.125.17.3379.

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Inhibition of fibroblast growth factor (FGF) signaling prevents trunk and tail formation in Xenopus and zebrafish embryos. While the T-box transcription factor Brachyury (called No Tail in zebrafish) is a key mediator of FGF signaling in the notochord and tail, the pathways activated by FGF in non-notochordal trunk mesoderm have been uncertain. Previous studies have shown that the spadetail gene is required for non-notochordal trunk mesoderm formation; spadetail mutant embryos have major trunk mesoderm deficiencies, but relatively normal tail and notochord development. We demonstrate here that spadetail encodes a T-box transcription factor with homologues in Xenopus and chick. Spadetail is likely to be a key mediator of FGF signaling in trunk non-notochordal mesoderm, since spadetail expression is regulated by FGF signaling. Trunk and tail development are therefore dependent upon the complementary actions of two T-box genes, spadetail and no tail. We show that the regulatory hierarchy among spadetail, no tail and a third T-box gene, tbx6, are substantially different during trunk and tail mesoderm formation, and propose a genetic model that accounts for the regional phenotypes of spadetail and no tail mutants.

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Amacher, S. L., and C. B. Kimmel. "Promoting notochord fate and repressing muscle development in zebrafish axial mesoderm." Development 125, no. 8 (April 15, 1998): 1397–406. http://dx.doi.org/10.1242/dev.125.8.1397.

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Cell fate decisions in early embryonic cells are controlled by interactions among developmental regulatory genes. Zebrafish floating head mutants lack a notochord; instead, muscle forms under the neural tube. As shown previously, axial mesoderm in floating head mutant gastrulae fails to maintain expression of notochord genes and instead expresses muscle genes. Zebrafish spadetail mutant gastrulae have a nearly opposite phenotype; notochord markers are expressed in a wider domain than in wild-type embryos and muscle marker expression is absent. We examined whether these two phenotypes revealed an antagonistic genetic interaction by constructing the double mutant. Muscle does not form in the spadetail;floating head double mutant midline, indicating that spadetail function is required for floating head mutant axial mesoderm to transfate to muscle. Instead, the midline of spadetail;floating head double mutants is greatly restored compared to that of floating head mutants; the floor plate is almost complete and an anterior notochord develops. In addition, we find that floating head mutant cells can make both anterior and posterior notochord when transplanted into a wild-type host, showing that enviromental signals can override the predisposition of floating head mutant midline cells to make muscle. Taken together, these results suggest that repression of spadetail function by floating head is critical to promote notochord fate and prevent midline muscle development, and that cells can be recruited to the notochord by environmental signals.

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3

Yamamoto, A., S. L. Amacher, S. H. Kim, D. Geissert, C. B. Kimmel, and E. M. De Robertis. "Zebrafish paraxial protocadherin is a downstream target of spadetail involved in morphogenesis of gastrula mesoderm." Development 125, no. 17 (September 1, 1998): 3389–97. http://dx.doi.org/10.1242/dev.125.17.3389.

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Zebrafish paraxial protocadherin (papc) encodes a transmembrane cell adhesion molecule (PAPC) expressed in trunk mesoderm undergoing morphogenesis. Microinjection studies with a dominant-negative secreted construct suggest that papc is required for proper dorsal convergence movements during gastrulation. Genetic studies show that papc is a close downstream target of spadetail, gene encoding a transcription factor required for mesodermal morphogenetic movements. Further, we show that the floating head homeobox gene is required in axial mesoderm to repress the expression of both spadetail and papc, promoting notochord and blocking differentiation of paraxial mesoderm. The PAPC structural cell-surface protein may provide a link between regulatory transcription factors and the actual cell biological behaviors that execute morphogenesis during gastrulation.

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4

Warga, Rachel M., and Christiane Nüsslein-Volhard. "spadetail-Dependent Cell Compaction of the Dorsal Zebrafish Blastula." Developmental Biology 203, no. 1 (November 1998): 116–21. http://dx.doi.org/10.1006/dbio.1998.9022.

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5

Lardelli, Michael. "The evolutionary relationships of zebrafish genes tbx6 , tbx16 / spadetail and mga." Development Genes and Evolution 213, no. 10 (October 1, 2003): 519–22. http://dx.doi.org/10.1007/s00427-003-0348-2.

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6

Row, Richard H., Jean-Léon Maître, Benjamin L. Martin, Petra Stockinger, Carl-Philipp Heisenberg, and David Kimelman. "Completion of the epithelial to mesenchymal transition in zebrafish mesoderm requires Spadetail." Developmental Biology 354, no. 1 (June 2011): 102–10. http://dx.doi.org/10.1016/j.ydbio.2011.03.025.

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7

Griffin, Kevin J. P., and David Kimelman. "One-Eyed Pinhead and Spadetail are essential for heart and somite formation." Nature Cell Biology 4, no. 10 (September 30, 2002): 821–25. http://dx.doi.org/10.1038/ncb862.

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8

Weinberg, E. S., M. L. Allende, C. S. Kelly, A. Abdelhamid, T. Murakami, P. Andermann, O. G. Doerre, D. J. Grunwald, and B. Riggleman. "Developmental regulation of zebrafish MyoD in wild-type, no tail and spadetail embryos." Development 122, no. 1 (January 1, 1996): 271–80. http://dx.doi.org/10.1242/dev.122.1.271.

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We describe the isolation of the zebrafish MyoD gene and its expression in wild-type embryos and in two mutants with altered somite development, no tail (ntl) and spadetail (spt). In the wild-type embryo, MyoD expression first occurs in an early phase, extending from mid-gastrula to just prior to somite formation, in which cells directly adjacent to the axial mesoderm express the gene. In subsequent phases, during the anterior-to-posterior wave of somite formation and maturation, expression occurs within particular regions of each somite. In spt embryos, which lack normal paraxial mesoderm due to incorrect cell migration, early MyoD expression is not observed and transcripts are instead first detected in small groups of trunk cells that will develop into aberrant myotomal-like structures. In ntl embryos, which lack notochords and tails, the early phase of MyoD expression is also absent. However, the later phase of expression within the developing somites appears to occur at the normal time in the ntl mutants, indicating that the presomitogenesis and somitogenesis phases of MyoD expression can be uncoupled. In addition, we demonstrate that the entire paraxial mesoderm of wild-type embryos has the potential to express MyoD when Sonic hedgehog is expressed ubiquitously in the embryo, and that this potential is lost in some of the cells of the paraxial mesoderm lineage in no tail and spadetail embryos. We also show that MyoD expression precedes myogenin expression and follows or is coincident with expression of snaill in some regions that express this gene.

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9

O'Neill, Katelyn, and Chris Thorpe. "BMP signaling and spadetail regulate exit of muscle precursors from the zebrafish tailbud." Developmental Biology 375, no. 2 (March 2013): 117–27. http://dx.doi.org/10.1016/j.ydbio.2012.12.002.

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10

Mueller, Rachel LOCKRIDGE, Cheng Huang, and Robert K. Ho. "Spatio-temporal regulation of Wnt and retinoic acid signaling by tbx16/spadetail during zebrafish mesoderm differentiation." BMC Genomics 11, no. 1 (2010): 492. http://dx.doi.org/10.1186/1471-2164-11-492.

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11

Rohde, Laurel A., Andrew C. Oates, and Robert K. Ho. "A Crucial Interaction between Embryonic Red Blood Cell Progenitors and Paraxial Mesoderm Revealed in spadetail Embryos." Developmental Cell 7, no. 2 (August 2004): 251–62. http://dx.doi.org/10.1016/j.devcel.2004.07.010.

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12

Amacher, Sharon L., Bruce W. Draper, Brian R. Summers, and Charles B. Kimmel. "The zebrafish T-box genesno tailandspadetailare required for development of trunk and tail mesoderm and medial floor plate." Development 129, no. 14 (July 15, 2002): 3311–23. http://dx.doi.org/10.1242/dev.129.14.3311.

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T-box genes encode transcriptional regulators that control many aspects of embryonic development. Here, we demonstrate that the mesodermally expressed zebrafish spadetail (spt)/VegT and no tail (ntl)/Brachyury T-box genes are semi-redundantly and cell-autonomously required for formation of all trunk and tail mesoderm. Despite the lack of posterior mesoderm in spt–;ntl– embryos, dorsal-ventral neural tube patterning is relatively normal, with the notable exception that posterior medial floor plate is completely absent. This contrasts sharply with observations in single mutants, as mutations singly in ntl or spt enhance posterior medial floor plate development. We find that ntl function is required to repress medial floor plate and promote notochord fate in cells of the wild-type notochord domain and that spt and ntl together are required non cell-autonomously for medial floor plate formation, suggesting that an inducing signal present in wild-type mesoderm is lacking in spt–;ntl– embryos.

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13

Thisse, C., B. Thisse, T. F. Schilling, and J. H. Postlethwait. "Structure of the zebrafish snail1 gene and its expression in wild-type, spadetail and no tail mutant embryos." Development 119, no. 4 (December 1, 1993): 1203–15. http://dx.doi.org/10.1242/dev.119.4.1203.

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Mesoderm formation is critical for the establishment of the animal body plan and in Drosophila requires the snail gene. This report concerns the cloning and expression pattern of the structurally similar gene snail1 from zebrafish. In situ hybridization shows that the quantity of snail1 RNA increases at the margin of the blastoderm in cells that involute during gastrulation. As gastrulation begins, snail1 RNA disappears from the dorsal axial mesoderm and becomes restricted to the paraxial mesoderm and the tail bud. snail1 RNA increases in cells that define the posterior border of each somite and then disappears when somitic cells differentiate. Later in development, expression appears in cephalic neural crest derivatives. Many snail1-expressing cells were missing from mutant spadetail embryos and the quantity of snail1 RNA was greatly reduced in mutant no tail embryos. The work presented here suggests that snail1 is involved in morphogenetic events during gastrulation, somitogenesis and development of the cephalic neural crest, and that no tail may act as a positive regulator of snail1.

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14

Ho, Robert K. "Cell movements and cell fate during zebrafish gastrulation." Development 116, Supplement (April 1, 1992): 65–73. http://dx.doi.org/10.1242/dev.116.supplement.65.

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The early lineages of the zebrafish are indeterminate and a single cell labeled before the late blastula period will contribute progeny to a variety of tissues. Therefore, early cell lineages in the zebrafish do not establish future cell fates and early blastomeres must necessarily remain pluripotent. Eventually, after a period of random cell mixing, individual cells do become tissue restricted according to their later position within the blastoderm. The elucidation of a fate map for the zebrafish gastrula (Kimmel et al., 1990), has made it possible to study the processes by which cellular identity is conferred and maintained in the zebrafish. In this chapter, I describe single cell transplantation experiments designed to test for the irreversible restriction or ‘commitment’ of embryonic blastomeres in the zebrafish embryo. These experiments support the hypothesis that cell fate in the vertebrate embryo is determined by cell position. Work on the spadetail mutation will also be reviewed; this mutation causes a subset of mesodermal precursors to mismigrate during gastrulation thereby leading to a change in their eventual cell identity.

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15

Molven, A., C. V. Wright, R. Bremiller, E. M. De Robertis, and C. B. Kimmel. "Expression of a homeobox gene product in normal and mutant zebrafish embryos: evolution of the tetrapod body plan." Development 109, no. 2 (June 1, 1990): 279–88. http://dx.doi.org/10.1242/dev.109.2.279.

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An antibody was used to detect antigens in zebrafish that appear to be homologous to the frog homeodomain-containing protein XlHbox 1. These antigens show a restricted expression in the anteroposterior axis and an anteroposterior gradient in the pectoral fin bud, consistent with the distribution of XlHbox 1 protein in frog and mouse embryos. In the somitic mesoderm, a sharp anterior limit of expression coincides exactly with the boundary between somites 4 and 5, and the protein level fades out posteriorly. A similar, graded expression of the antigen is seen within the series of Rohon-Beard sensory neurons of the CNS. We also immunostained the mutant spt-1 (‘spadetail’), in which the trunk mesoderm is greatly depleted and disorganized in the region of XlHbox 1 expression. The defects stem from misdirected cell movements during gastrulation, but nervertheless, newly recruited cells that partially refill the trunk mesoderm express the antigen within the normal span of the anteroposterior axis. This finding suggests that the mutation does not delete positional information required for activation of the XlHbox 1 gene.

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16

Huang, Chiu-Ju, Val Wilson, Sari Pennings, Calum A. MacRae, and John Mullins. "Sequential effects of spadetail, one-eyed pinhead and no tail on midline convergence of nephric primordia during zebrafish embryogenesis." Developmental Biology 384, no. 2 (December 2013): 290–300. http://dx.doi.org/10.1016/j.ydbio.2013.07.002.

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17

Gourronc, Francoise, Nadira Ahmad, Nicholas Nedza, Timothy Eggleston, and Michael Rebagliati. "Nodal activity around Kupffer's vesicle depends on the T-box transcription factors notail and spadetail and on notch signaling." Developmental Dynamics 236, no. 8 (2007): 2131–46. http://dx.doi.org/10.1002/dvdy.21249.

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18

Hammerschmidt, M., F. Pelegri, M. C. Mullins, D. A. Kane, M. Brand, F. J. van Eeden, M. Furutani-Seiki, et al. "Mutations affecting morphogenesis during gastrulation and tail formation in the zebrafish, Danio rerio." Development 123, no. 1 (December 1, 1996): 143–51. http://dx.doi.org/10.1242/dev.123.1.143.

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We have identified several genes that are required for various morphogenetic processes during gastrulation and tail formation. Two genes are required in the anterior region of the body axis: one eyed pinhead (oep) and dirty nose (dns).oep mutant embryos are defective in prechordal plate formation and the specification of anterior and ventral structures of the central nervous system. In dns mutants, cells of the prechordal plate, such as the prospective hatching gland cells, fail to specify. Two genes are required for convergence and extension movements. In mutant trilobite embryos, extension movements on the dorsal side of the embryo are affected, whereas in the formerly described spadetail mutants, for which two new alleles have been isolated, convergent movements of ventrolateral cells to the dorsal side are blocked. Two genes are required for the development of the posterior end of the body axis. In pipetail mutants, the tailbud fails to move ventrally on the yolk sac after germ ring closure, and the tip of the tail fails to detach from the yolk tube. Mutants in kugelig (kgg) do not form the yolk tube at the posterior side of the yolk sac.

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19

Jesuthasan, S. "Contact inhibition/collapse and pathfinding of neural crest cells in the zebrafish trunk." Development 122, no. 1 (January 1, 1996): 381–89. http://dx.doi.org/10.1242/dev.122.1.381.

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Neural crest cells in the trunk of vertebrate embryos have a choice of pathways after emigrating from the neural tube: they can migrate in either the medial pathway between somites and neural tube, or the lateral pathway between somites and epidermis. In zebrafish embryos, the first cells to migrate all choose the medial pathway. High resolution imaging of cells in living embryos suggests that neural crest cells do so because of repulsion by somites: cells take the medial pathway because the lateral somite surface triggers a paralysis and retraction of protrusions (contact inhibition or collapse) when the medial surface does not. Partial deletion of somites, using the spadetail mutation allows precocious entry into the lateral pathway, but only where somites are absent, supporting the notion that an inhibitory cue on somites delays entry. Growth cones of Rohon-Beard cells enter the lateral pathway before neural crest cells, demonstrating that there is no absolute barrier to migration. These data, in addition to providing a detailed picture of neural crest cells migrating in vivo, suggest that neural crest cells, like neuronal growth cones, are guided by a specific cue that triggers ‘collapse’ of active protrusions.

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20

Oates, Andrew C., Alison Brownlie, Stephen J. Pratt, Danielle V. Irvine, Eric C. Liao, Barry H. Paw, Kristen J. Dorian, et al. "Gene Duplication of Zebrafish JAK2 Homologs Is Accompanied by Divergent Embryonic Expression Patterns: Only jak2a Is Expressed During Erythropoiesis." Blood 94, no. 8 (October 15, 1999): 2622–36. http://dx.doi.org/10.1182/blood.v94.8.2622.420k39_2622_2636.

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Members of the JAK family of protein tyrosine kinase (PTK) proteins are required for the transmission of signals from a variety of cell surface receptors, particularly those of the cytokine receptor family. JAK function has been implicated in hematopoiesis and regulation of the immune system, and recent data suggest that the vertebrate JAK2gene may play a role in leukemia. We have isolated and characterizedjak cDNAs from the zebrafish Danio rerio. The zebrafish genome possesses 2 jak2 genes that occupy paralogous chromosome segments in the zebrafish genome, and these segments conserve syntenic relationships with orthologous genes in mammalian genomes, suggesting an ancient duplication in the zebrafish lineage. The jak2a gene is expressed at high levels in erythroid precursors of primitive and definitive waves and at a lower level in early central nervous system and developing fin buds. jak2b is expressed in the developing lens and nephritic ducts, but not in hematopoietic tissue. The expression of jak2a was examined in hematopoietic mutants and found to be disrupted in clocheand spadetail, suggesting an early role in hematopoiesis. Taken together with recent gene knockout data in the mouse, we suggest that jak2a may be functionally equivalent to mammalianJak2, with a role in early erythropoiesis.

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21

Weber, Gerhard J., Sung E. Choe, Kimberly A. Dooley, Noëlle N. Paffett-Lugassy, Yi Zhou, and Leonard I. Zon. "Mutant-specific gene programs in the zebrafish." Blood 106, no. 2 (July 15, 2005): 521–30. http://dx.doi.org/10.1182/blood-2004-11-4541.

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Abstract Hematopoiesis involves the production of stem cells, followed by the orchestrated differentiation of the blood lineages. Genetic screens in zebrafish have identified mutants with defects that disrupt specific stages of hematopoiesis and vasculogenesis, including the cloche, spadetail (tbx16), moonshine (tif1g), bloodless, and vlad tepes (gata1) mutants. To better characterize the blood program, gene expression profiling was carried out in these mutants and in scl-morphants (sclmo). Distinct gene clusters were demarcated by stage-specific and mutant-specific gene regulation. These were found to correlate with the transcriptional program of hematopoietic progenitor cells, as well as of the erythroid, myeloid, and vascular lineages. Among these, several novel hematopoietic and vascular genes were detected, for instance, the erythroid transcription factors znfl2 and ncoa4. A specific regulation was found for myeloid genes, as they were more strongly expressed in vlt mutants compared with other erythroid mutants. A unique gene expression pattern of up-regulated isoprenoid synthesis genes was found in cloche and sclmo, possibly in migrating cells. In conjunction with the high conservation of vertebrate hematopoiesis, the comparison of transcriptional profiles in zebrafish blood mutants represents a versatile and powerful tool to elucidate the genetic regulation of blood and blood vessel development.

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22

Bisgrove, B. W., J. J. Essner, and H. J. Yost. "Multiple pathways in the midline regulate concordant brain, heart and gut left-right asymmetry." Development 127, no. 16 (August 15, 2000): 3567–79. http://dx.doi.org/10.1242/dev.127.16.3567.

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The embryonic midline in vertebrates has been implicated in left-right development, but the mechanisms by which it regulates left-right asymmetric gene expression and organ morphogenesis are unknown. Zebrafish embryos have three domains of left-right asymmetric gene expression that are useful predictors of organ situs. cyclops (nodal), lefty1 and pitx2 are expressed in the left diencephalon; cyclops, lefty2 and pitx2 are expressed in the left heart field; and cyclops and pitx2 are expressed in the left gut primordium. Distinct alterations of these expression patterns in zebrafish midline mutants identify four phenotypic classes that have different degrees of discordance among the brain, heart and gut. These classes help identify two midline domains and several genetic pathways that regulate left-right development. A cyclops-dependent midline domain, associated with the prechordal plate, regulates brain asymmetry but is dispensable for normal heart and gut left-right development. A second midline domain, associated with the anterior notochord, is dependent on no tail, floating head and momo function and is essential for restricting asymmetric gene expression to the left side. Mutants in spadetail or chordino give discordant gene expression among the brain, heart and gut. one-eyed pinhead and schmalspur are necessary for asymmetric gene expression and may mediate signaling from midline domains to lateral tissues. The different phenotypic classes help clarify the apparent disparity of mechanisms proposed to explain left-right development in different vertebrates.

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23

Essner, J. J., W. W. Branford, J. Zhang, and H. J. Yost. "Mesendoderm and left-right brain, heart and gut development are differentially regulated by pitx2 isoforms." Development 127, no. 5 (March 1, 2000): 1081–93. http://dx.doi.org/10.1242/dev.127.5.1081.

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The pitx2 gene is a member of the bicoid-homeodomain class of transcription factors that has been implicated in the control of left-right asymmetry during organogenesis. Here we demonstrate that in zebrafish there are two pitx2 isoforms, pitx2a and pitx2c, which show distinct expression patterns and have non-overlapping functions during mesendoderm and asymmetric organ development. pitx2c is expressed symmetrically in presumptive mesendoderm during late blastula stages and in the prechordal plate during late gastrulation. pitx2a expression is first detected at bud stage in the anterior prechordal plate. The regulation of early mesendoderm pitx2c expression is dependent on one-eyed pinhead (EGF-CFC-related gene) and spadetail (tbx-transcription factor) and can be induced by ectopic goosecoid expression. Maintenance of pitx2c midline expression is dependent on cyclops (nodal) and schmalspur, but not no tail (brachyury). Ectopic expression of pitx2 isoforms results in distinct morphological and molecular phenotypes, indicating that pitx2a and pitx2c have divergent regulatory functions. Both isoforms downregulate goosecoid on the dorsal side, but in contrast to earlier reports that nodal and lefty are upstream of pitx2, ectopic pitx2c in other regions induces cyclops, lefty2 and goosecoid expression. Asymmetric isoform expression occurs in non-overlapping domains, with pitx2c in left dorsal diencephalon and developing gut and pitx2a in left heart primordium. Targeted asymmetric expression in Xenopus shows that both isoforms can alter left-right development, but pitx2a has a slightly stronger effect on heart laterality. Our results indicate that distinct genetic pathways regulate pitx2a and pitx2c isoform expression, and each isoform regulates different downstream pathways during mesendoderm and asymmetric organ development.

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24

Joly, J. S., C. Joly, S. Schulte-Merker, H. Boulekbache, and H. Condamine. "The ventral and posterior expression of the zebrafish homeobox gene eve1 is perturbed in dorsalized and mutant embryos." Development 119, no. 4 (December 1, 1993): 1261–75. http://dx.doi.org/10.1242/dev.119.4.1261.

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We have identified and characterized zebrafish eve1, a novel member of the Drosophila even-skipped (eve) gene family. eve1 RNAs are expressed initially in late blastulae with a peak during the gastrula stage, at which time expression is confined to ventral and lateral cells of the marginal zone of the zebrafish embryo. Later, eve1 transcripts are located in the most posterior part of the extending tail tip. We show that LiCl, known to dorsalize Xenopus embryos, has the same effect in zebrafish, resulting in embryos with exaggerated dorsoanterior structures. In LiCl-treated embryos, eve1 transcripts are completely absent. eve1 is therefore a marker of ventral and posterior cells. In the light of its ventroposterior expression domain, the localization of eve1 transcripts was analysed in spadetail (spt) and no tail (ntl), two mutants with abnormal caudal development. In sptb140 homozygous mutants, there is an accumulation of cells in the tail region, resulting from inadequate migratory behaviour of precursors to the trunk somites. These cells, in their abnormal environment, express eve1, emphasizing the correlation between ventroposterior position and eve1 expression. In homozygous mutant embryos for the gene ntl (the homologue of mouse Brachyury, originally called Zf-T), posterior structures are missing (M. E. Halpern, C. B. Kimmel, R. K. Ho and C. Walker, 1993; Cell In press). While mutant and wild-type embryos do not differ in their eve1 transcript distribution during gastrulation, eve1 expression is absent in the caudal region of mutant ntl embryos during early somitogenesis, indicating a requirement for ntl in the maintenance of eve1 expression during tail extension. Our findings suggest that eve1 expression is correlated with a ventral and posterior cell fate, and provide first insights into its regulation.

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25

Kalev-Zylinska, Maggie L., Julia A. Horsfield, Maria Vega C. Flores, John H. Postlethwait, Maria R. Vitas, Andrea M. Baas, Philip S. Crosier, and Kathryn E. Crosier. "Runx1 is required for zebrafish blood and vessel development and expression of a human RUNX1-CBF2T1 transgene advances a model for studies of leukemogenesis." Development 129, no. 8 (April 15, 2002): 2015–30. http://dx.doi.org/10.1242/dev.129.8.2015.

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RUNX1/AML1/CBFA2 is essential for definitive hematopoiesis, and chromosomal translocations affecting RUNX1 are frequently involved in human leukemias. Consequently, the normal function of RUNX1 and its involvement in leukemogenesis remain subject to intensive research. To further elucidate the role of RUNX1 in hematopoiesis, we cloned the zebrafish ortholog (runx1) and analyzed its function using this model system. Zebrafish runx1 is expressed in hematopoietic and neuronal cells during early embryogenesis. runx1 expression in the lateral plate mesoderm co-localizes with the hematopoietic transcription factor scl, and expression of runx1 is markedly reduced in the zebrafish mutants spadetail and cloche. Transient expression of runx1 in cloche embryos resulted in partial rescue of the hematopoietic defect. Depletion of Runx1 with antisense morpholino oligonucleotides abrogated the development of both blood and vessels, as demonstrated by loss of circulation, incomplete development of vasculature and the accumulation of immature hematopoietic precursors. The block in definitive hematopoiesis is similar to that observed in Runx1 knockout mice, implying that zebrafish Runx1 has a function equivalent to that in mammals. Our data suggest that zebrafish Runx1 functions in both blood and vessel development at the hemangioblast level, and contributes to both primitive and definitive hematopoiesis. Depletion of Runx1 also caused aberrant axonogenesis and abnormal distribution of Rohon-Beard cells, providing the first functional evidence of a role for vertebrate Runx1 in neuropoiesis.To provide a base for examining the role of Runx1 in leukemogenesis, we investigated the effects of transient expression of a human RUNX1-CBF2T1 transgene [product of the t(8;21) translocation in acute myeloid leukemia] in zebrafish embryos. Expression of RUNX1-CBF2T1 caused disruption of normal hematopoiesis, aberrant circulation, internal hemorrhages and cellular dysplasia. These defects reproduce those observed in Runx1-depleted zebrafish embryos and RUNX1-CBF2T1 knock-in mice. The phenotype obtained with transient expression of RUNX1-CBF2T1 validates the zebrafish as a model system to study t(8;21)-mediated leukemogenesis.

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26

Weidinger, G., U. Wolke, M. Koprunner, M. Klinger, and E. Raz. "Identification of tissues and patterning events required for distinct steps in early migration of zebrafish primordial germ cells." Development 126, no. 23 (December 1, 1999): 5295–307. http://dx.doi.org/10.1242/dev.126.23.5295.

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In many organisms, the primordial germ cells have to migrate from the position where they are specified towards the developing gonad where they generate gametes. Extensive studies of the migration of primordial germ cells in Drosophila, mouse, chick and Xenopus have identified somatic tissues important for this process and demonstrated a role for specific molecules in directing the cells towards their target. In zebrafish, a unique situation is found in that the primordial germ cells, as marked by expression of vasa mRNA, are specified in random positions relative to the future embryonic axis. Hence, the migrating cells have to navigate towards their destination from various starting positions that differ among individual embryos. Here, we present a detailed description of the migration of the primordial germ cells during the first 24 hours of wild-type zebrafish embryonic development. We define six distinct steps of migration bringing the primordial germ cells from their random positions before gastrulation to form two cell clusters on either side of the midline by the end of the first day of development. To obtain information on the origin of the positional cues provided to the germ cells by somatic tissues during their migration, we analyzed the migration pattern in mutants, including spadetail, swirl, chordino, floating head, cloche, knypek and no isthmus. In mutants with defects in axial structures, paraxial mesoderm or dorsoventral patterning, we find that certain steps of the migration process are specifically affected. We show that the paraxial mesoderm is important for providing proper anteroposterior information to the migrating primordial germ cells and that these cells can respond to changes in the global dorsoventral coordinates. In certain mutants, we observe accumulation of ectopic cells in different regions of the embryo. These ectopic cells can retain both morphological and molecular characteristics of primordial germ cells, suggesting that, in zebrafish at the early stages tested, the vasa-expressing cells are committed to the germ cell lineage.

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Journal articles on the topic 'Spadetail'

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