Biomedical subjects

Andrew C Oates

Publications and source records attributed to Andrew C Oates.

9 recordsLinked to original sources

PubMed2006

Coordination of symmetric cyclic gene expression during somitogenesis by Suppressor of Hairless involves regulation of retinoic acid catabolism.

Vertebrate embryos faithfully produce bilaterally symmetric somites that give rise to repetitive body structures such as vertebrae and skeletal muscle. Body segmentation is regulated by a cyclic gene expression system, containing the Delta-Notch pathway and targets, which generates bilaterally symmetric oscillations across the Pre-Somitic Mesoderm (PSM). The position of the forming somite boundary is controlled by interaction of this oscillator with a determination front comprised of opposing gradients of FGF and retinoic acid (RA) signalling. Disruption of RA production leads to asymmetries in cyclic gene expression, but the link between RA and the oscillator is unknown. In somitogenesis, Notch signalling activates target genes through the transcription factor Suppressor of Hairless (Su(H)). Here, we report that two Su(H) genes coordinate bilaterally symmetric positioning of somite boundaries in the zebrafish embryo. Combined Su(H) gene knockdown caused defects in visceral left/right asymmetry, neurogenic lateral inhibition, and symmetrical failure of the segmentation oscillator. However, by selectively down-regulating Su(H)2 or Su(H)1 function using specific antisense morpholinos, we observed asymmetric defects in anterior or posterior somite boundaries, respectively. These morphological abnormalities were reflected by underlying asymmetric cyclic gene expression waves in the presomitic mesoderm, indicating a key role for Su(H) in coordinating the left-right symmetry of this process. Strikingly, expression of the RA-degrading enzyme cyp26a1 in the tailbud was controlled by Su(H) activity, and morpholino knockdown of cyp26a1 alone caused asymmetric cyclic dlc expression, suggesting that excess RA in the tailbud may contribute to the cyclic asymmetries. Indeed, exogenous RA was sufficient to generate asymmetric expression of all cyclic genes. Our observations indicate that one element of the Notch signalling pathway, Su(H), is required for control of RA metabolism in the tailbud and that this regulation is involved in bilateral symmetry of cyclic gene expression and somitogenesis.

Amino Acid Sequence↗

PubMed2006

Analysis and visualization of cell movement in the developing zebrafish brain.

Detailed reconstruction of the spatiotemporal history of embryonic cells is key to understanding tissue formation processes but is often complicated by the large number of cells involved, particularly so in vertebrates. Through a combination of high-resolution time-lapse lineage tracing and antibody staining, we have analyzed the movement of mesencephalic and metencephalic cell populations in the early zebrafish embryo. To facilitate the analysis of our cell tracking data, we have created TracePilot, a software tool that allows interactive manipulation and visualization of tracking data. We demonstrate its utility by showing novel visualizations of cell movement in the developing zebrafish brain. TracePilot (http://www.mpi-cbg.de/tracepilot) is Java-based, available free of charge, and has a program structure that allows the incorporation of additional analysis tools.

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PubMed2005

Generation of segment polarity in the paraxial mesoderm of the zebrafish through a T-box-dependent inductive event.

The first morphological sign of vertebrate postcranial body segmentation is the sequential production from posterior paraxial mesoderm of blocks of cells termed somites. Each of these embryonic structures is polarized along the anterior/posterior axis, a subdivision first distinguished by marker gene expression restricted to rostral or caudal territories of forming somites. To better understand the generation of segment polarity in vertebrates, we have studied the zebrafish mutant fused somites (fss), because its paraxial mesoderm lacks segment polarity. Previously examined markers of caudal half-segment identity are widely expressed, whereas markers of rostral identity are either missing or dramatically down-regulated, suggesting that the paraxial mesoderm of the fss mutant embryo is profoundly caudalized. These findings gave rise to a model for the formation of segment polarity in the zebrafish in which caudal is the default identity for paraxial mesoderm, upon which is patterned rostral identity in an fss-dependent manner. In contrast to this scheme, the caudal marker gene ephrinA1 was recently shown to be down-regulated in fss embryos. We now show that notch5, another caudal identity marker and a component of the Delta/Notch signaling system, is not expressed in the paraxial mesoderm of early segmentation stage fss embryos. We use cell transplantation to create genetic mosaics between fss and wild-type embryos in order to assay the requirement for fss function in notch5 expression. In contrast to the expression of rostral markers, which have a cell-autonomous requirement for fss, expression of notch5 is induced in fss cells at short range by nearby wild-type cells, indicating a cell-non-autonomous requirement for fss function in this process. These new data suggest that segment polarity is created in a three-step process in which cells that have assumed a rostral identity must subsequently communicate with their partially caudalized neighbors in order to induce the fully caudalized state.

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PubMed2005

Cooperative function of deltaC and her7 in anterior segment formation.

Segmentation of paraxial mesoderm in vertebrates is regulated by a genetic oscillator that manifests as a series of wavelike or cyclic gene expression domains in the embryo. In zebrafish, this oscillator involves members of the Delta/Notch intercellular signaling pathway, and its down-stream targets, the Her family of transcriptional repressors. Loss of function of any one of the genes of this system, such as her7, gives rise to segmentation defects in the posterior trunk and tail, concomitant with a disruption of cyclic expression domains, indicating that the oscillator is required for posterior segmentation. Control of segmentation in the anterior trunk, and its relationship to that of the posterior is, however, not yet well understood. A combined loss of the cyclic Her genes her1 and her7 disrupts segmentation of both anterior and posterior paraxial mesoderm, indicating that her genes function redundantly in anterior segmentation. To test whether this anterior redundancy is specific to the her gene family, or alternatively is a more global feature of the segmentation oscillator, we looked at anterior segmentation after morpholino knock down of the cyclic cell-surface Notch ligand deltaC (dlc), either alone or in combination with her7, or other Delta/Notch pathway genes. We find that dlc is required for coherence of wavelike expression domains of cyclic genes her1 and her7 and maintenance of their expression levels, as well as for cyclic transcription of dlc itself, confirming that dlc is a component of the segmentation oscillator. Dose dependent, posteriorly-restricted segmentation defects were seen in the dlc knock down, and in combination with the deltaD or notch1a mutants. However, combined reduction of function of dlc and her7 results in defective segmentation of both anterior and posterior paraxial mesoderm, and a failure of cyclic expression domains to initiate, similar to loss of both her genes. Thus, anterior segmentation requires the functions of both her and delta family members in a parallel manner, suggesting that the segmentation oscillator operates in paraxial mesoderm along the entire vertebrate axis.

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PubMed2004

Zebrafish gcm2 is required for gill filament budding from pharyngeal ectoderm.

The pharyngeal arches give rise to multiple organs critical for diverse processes, including the thymus, thyroid and parathyroids. Several molecular regulators of thymus and thyroid organogenesis are strikingly conserved between mammals and zebrafish. However, land animals have parathyroids whereas fish have gills. The murine transcription factor Glial cells missing 2 (Gcm2) is expressed specifically in the parathyroid primordium in the endodermal epithelium of the third pharyngeal pouch, and in both mice and humans is required for normal development of parathyroid glands. The molecular regulation of fish gill organogenesis remains to be described. We report the expression of gcm2 in the zebrafish pharyngeal epithelium and a requirement for Hox group 3 paralogs for gcm2 expression. Strikingly, zebrafish gcm2 is expressed in the ectodermal portion of the pharyngeal epithelium and is required for the development of the gill filament buds, precursors of fish-specific gill filaments. This study identifies yet another role for a GCM gene in embryonic development and indicates a role for gcm2 during the evolution of divergent pharyngeal morphologies.

Amino Acid Sequence↗

PubMed2004

A crucial interaction between embryonic red blood cell progenitors and paraxial mesoderm revealed in spadetail embryos.

Zebrafish embryonic red blood cells (RBCs) develop in trunk intermediate mesoderm (IM), and early macrophages develop in the head, suggesting that local microenvironmental cues regulate differentiation of these two blood lineages. spadetail (spt) mutant embryos, which lack trunk paraxial mesoderm (PM) due to a cell-autonomous defect in tbx16, fail to produce embryonic RBCs but retain head macrophage development. In spt mutants, initial hematopoietic gene expression is absent in trunk IM, although endothelial and pronephric expression is retained, suggesting that early blood progenitor development is specifically disrupted. Using cell transplantation, we reveal that spt is required cell autonomously for early hematopoietic gene expression in trunk IM. Further, we uncover an interaction between embryonic trunk PM and blood progenitors that is essential for RBC development. Importantly, our data identify a hematopoietic microenvironment that allows embryonic RBC production in the zebrafish.

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PubMed2003

Characterization of embryonic globin genes of the zebrafish.

Hemoglobin switching is a complex process by which distinct globin chains are produced during stages of development. In an effort to characterize the process of hemoglobin switching in the zebrafish model system, we have isolated and characterized several embryonic globin genes. The embryonic and adult globin genes are found in clusters in a head-to-head configuration. One cluster of embryonic and adult genes is localized to linkage group 3, whereas another embryonic cluster is localized on linkage group 12. Several embryonic globin genes demonstrate an erythroid-specific pattern of expression early during embryogenesis and later are downregulated as definitive hematopoiesis occurs. We utilized electrospray mass spectroscopy to correlate globin genes and protein expression in developing embryonic red cells. The mutation, zinfandel, has a hypochromic microcytic anemia as an embryo, but later recovers in adulthood. The zinfandel gene maps to linkage group 3 near the major globin gene locus, strongly suggesting that zinfandel represents an embryonic globin defect. Our studies are the first to systematically evaluate the embryonic globins in the zebrafish and will ultimately be useful in evaluating zebrafish mutants with defects in hemoglobin production and switching.

Amino Acid Sequence↗

PubMed2002

Zebrafish SPI-1 (PU.1) marks a site of myeloid development independent of primitive erythropoiesis: implications for axial patterning.

The mammalian transcription factor SPI-1 (synonyms: SPI1, PU.1, or Sfpi1) plays a critical role in myeloid development. To examine early myeloid commitment in the zebrafish embryo, we isolated a gene from zebrafish that is a SPI-1 orthologue on the basis of homology and phylogenetic considerations. The zebrafish spi1 (pu1) gene was first expressed at 12 h postfertilization in rostral lateral plate mesoderm (LPM), anatomically isolated from erythroid development in caudal lateral plate mesoderm. Fate-mapping traced rostral LPM cells from the region of initial spi1 expression to a myeloid fate. spi1 expression was lost in the bloodless mutant cloche, but rostral spi1 expression and myeloid development were preserved in the mutant spadetail, despite its complete erythropoietic failure. This dissociation of myeloid and erythroid development was further explored in studies of embryos overexpressing BMP-4, or chordin, in bmp-deficient swirl and snailhouse mutants, and chordin-deficient chordino mutants. These studies demonstrate that, in zebrafish, spi1 marks a rostral population of LPM cells committed to a myeloid fate anatomically separated from and developmentally independent of erythroid commitment in the caudal LPM. Such complete anatomical and developmental dissociation of two hematopoietic lineages adds an interesting complexity to the understanding of vertebrate hematopoietic development and presents significant implications for the mechanisms regulating axial patterning.

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PubMed2002

Hairy/E(spl)-related (Her) genes are central components of the segmentation oscillator and display redundancy with the Delta/Notch signaling pathway in the formation of anterior segmental boundaries in the zebrafish.

We have examined the expression of a Hairy/E(spl)-related (Her) gene, her7, in the zebrafish and show that its expression in the PSM cycles similarly to her1 and deltaC. A decrease in her7 function generated by antisense oligonucleotides disrupts somite formation in the posterior trunk and tail, and disrupts the dynamic expression domains of her1 and deltaC, suggesting that her7 plays a role in coordinating the oscillations of neighboring cells in the presomitic mesoderm. This phenotype is reminiscent of zebrafish segmentation mutants with lesions in genes of the Delta/Notch signaling pathway, which also show a disruption of cyclic her7 expression. The interaction of HER genes with the Delta/Notch signaling system was investigated by introducing a loss of her7 function into mutant backgrounds. This leads to segmental defects more anterior than in either condition alone. Combining a decrease of her7 function with reduction of her1 function results in an enhanced phenotype that affects all the anterior segments, indicating that Her functions in the anterior segments are also partially redundant. In these animals, gene expression does not cycle at any time, suggesting that a complete loss of oscillator function had been achieved. Consistent with this, combining a reduction of her7 and her1 function with a Delta/Notch mutant genotype does not worsen the phenotype further. Thus, our results identify members of the Her family of transcription factors that together behave as a central component of the oscillator, and not as an output. This indicates, therefore, that the function of the segmentation oscillator is restricted to the positioning of segmental boundaries. Furthermore, our data suggest that redundancy between Her genes and genes of the Delta/Notch pathway is in part responsible for the robust formation of anterior somites in vertebrates.

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