Ascidian Wnt-5 gene is involved in the morphogenetic movement of notochord cells

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.

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Early embryonic expression ofFGF4/6/9gene and its role in the induction of mesenchyme and notochord inCiona savignyiembryos

Development ◽

10.1242/dev.129.7.1729 ◽

2002 ◽

Vol 129 (7) ◽

pp. 1729-1738 ◽

Cited By ~ 16

Author(s):

Kaoru S. Imai ◽

Nori Satoh ◽

Yutaka Satou

Keyword(s):

Cell Differentiation ◽

Nuclear Localization ◽

Target Genes ◽

Muscle Cells ◽

Cell Stage ◽

Ciona Savignyi ◽

Mesenchyme Cell ◽

Notochord Cells ◽

Mesenchyme Cells ◽

Endodermal Cells

In early Ciona savignyi embryos, nuclear localization of β-catenin is the first step of endodermal cell specification, and triggers the activation of various target genes. A cDNA for Cs-FGF4/6/9, a gene activated downstream of β-catenin signaling, was isolated and shown to encode an FGF protein with features of both FGF4/6 and FGF9/20. The early embryonic expression of Cs-FGF4/6/9 was transient and the transcript was seen in endodermal cells at the 16- and 32-cell stages, in notochord and muscle cells at the 64-cell stage, and in nerve cord and muscle cells at the 110-cell stage; the gene was then expressed again in cells of the nervous system after neurulation. When the gene function was suppressed with a specific antisense morpholino oligo, the differentiation of mesenchyme cells was completely blocked, and the fate of presumptive mesenchyme cells appeared to change into that of muscle cells. The inhibition of mesenchyme differentiation was abrogated by coinjection of the morpholino oligo and synthetic Cs-FGF4/6/9 mRNA. Downregulation of β-catenin nuclear localization resulted in the absence of mesenchyme cell differentiation due to failure of the formation of signal-producing endodermal cells. Injection of synthetic Cs-FGF4/6/9 mRNA in β-catenin-downregulated embryos evoked mesenchyme cell differentiation. These results strongly suggest that Cs-FGF4/6/9 produced by endodermal cells acts an inductive signal for the differentiation of mesenchyme cells. On the other hand, the role of Cs-FGF4/6/9 in the induction of notochord cells is partial; the initial process of the induction was inhibited by Cs-FGF4/6/9 morpholino oligo, but notochord-specific genes were expressed later to form a partial notochord.

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The expression of nonchordate deuterostome Brachyury genes in the ascidian Ciona embryo can promote the differentiation of extra notochord cells

Mechanisms of Development ◽

10.1016/s0925-4773(00)00395-6 ◽

2000 ◽

Vol 96 (2) ◽

pp. 155-163 ◽

Cited By ~ 19

Author(s):

Gouki Satoh ◽

Yoshito Harada ◽

Nori Satoh

Keyword(s):

Notochord Cells

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Transformed notochordal cells trigger chronic wounds destabilizing the vertebral column and bone homeostasis

10.1101/2020.12.18.423470 ◽

2020 ◽

Author(s):

Paco Lopez-Cuevas ◽

Luke Deane ◽

Yushi Yang ◽

Chrissy L Hammond ◽

Erika Kague

Keyword(s):

Vertebral Column ◽

Wound Response ◽

Transformed Cells ◽

Bone Homeostasis ◽

Mineral Density ◽

Notochordal Cells ◽

Notochord Cells ◽

Ivd Degeneration ◽

The Impact ◽

Sheath Cells

Notochordal cells play a pivotal role in vertebral column patterning, contributing to the formation of the inner architecture of intervertebral discs (IVDs). Their disappearance during development has been associated with reduced repair capacity and IVD degeneration. Notochordal remnants are known to cause chordomas, a highly invasive bone cancer associated with late diagnosis. Understanding the impact of neoplastic cells during development and on the surrounding vertebral column could open avenues for earlier intervention and therapeutics. We investigated the impact of transformed notochord cells in the zebrafish skeleton using a RAS expressing line in the notochord under the control of the Kita promoter, with the advantage of adulthood endurance. Transformed cells caused damage in the notochord and destabilised the sheath layer triggering a wound repair mechanism, with enrolment of sheath cells (col9a2+) and expression of wt1b, similar to induced notochord wounds. Moreover, increased recruitment of neutrophils and macrophages, displaying abnormal behaviour in proximity to the notochord sheath and transformed cells, supported parallels between chordomas, wound and inflammation. Cancerous notochordal cells interfere with differentiation of sheath cells to form chordacentra domains leading to fusions and vertebral clefts during development. Adults displayed IVD irregularities reminiscent of degeneration; reduced bone mineral density, increased osteoclast activity; while disorganised osteoblasts and collagen indicate impaired bone homeostasis. By depleting inflammatory cells, we abrogated chordoma development and rescued the skeletal features of the vertebral column. Therefore, we showed that transformed notochord cells alter the skeleton during life, causing a wound-like phenotype and activating chronic wound response, suggesting parallels between chordoma, wound, IVD degeneration and inflammation, highlighting inflammation as a promising target for future therapeutics.

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FGF signals are involved in the differentiation of notochord cells and mesenchyme cells of the ascidianHalocynthia roretzi

Development ◽

10.1242/dev.128.14.2711 ◽

2001 ◽

Vol 128 (14) ◽

pp. 2711-2721 ◽

Cited By ~ 4

Author(s):

Yoshie Shimauchi ◽

Seiko D. Murakami ◽

Nori Satoh

Keyword(s):

Receptor Gene ◽

Epidermal Cells ◽

Dominant Negative ◽

Tyrosine Kinase Domain ◽

Fgf Receptor ◽

Dominant Negative Form ◽

Notochord Cells ◽

Mesenchyme Cells ◽

Endodermal Cells ◽

Negative Form

Differentiation of notochord cells and mesenchyme cells of the ascidian Halocynthia roretzi requires interactions with neighboring endodermal cells and previous experiments suggest that these interactions require fibroblast growth factor (FGF). In the present study, we examined the role of FGF in these interactions by disrupting signaling using the dominant negative form of the FGF receptor. An FGF receptor gene of H. roretzi (HrFGFR) is expressed both maternally and zygotically. The maternally expressed transcript was ubiquitously distributed in fertilized eggs and in early embryos. Zygotic expression became evident by the neurula stage and transcripts were detected in epidermal cells of the posterior half of embryos. Synthetic mRNA for the dominant negative form of FGFR, in which the intracellular tyrosine kinase domain was deleted, was injected into fertilized eggs to interfere with the possible function of HrFGFR. Injected eggs cleaved and gastrulated the same as the control embryos. Analyses of the expression of differentiation markers in the experimental embryos indicated that the differentiation of epidermal cells, muscle cells and endodermal cells was not affected significantly. However, manipulated embryos showed downregulation of notochord-specific Brachyury expression and failure of notochord cell differentiation, resulting in the development of tailbud embryos with shorted tails. The expression of an actin gene that is normally expressed in mesenchyme cells was also suppressed. These results suggest that FGF signals are involved in differentiation of notochord cells and mesenchyme cells in Halocynthia embryos. Furthermore, the patterning of a neuron-specific tubulin gene expression was disturbed, suggesting that the formation of the nervous system was directly affected by disrupting FGF signals or indirectly affected due to the disruption of normal notochord formation.

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