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1 May 2007 Regionalization of the Tail-tip Epidermis Requires Inductive Influence from Vegetal Cells and FGF Signaling in the Development of an Ascidian, Halocynthia roretzi
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Abstract

The epidermis of an ascidian larva derived from animal-hemisphere cells is regionalized along the anterior-posterior (AP) axis through inductive signals emanating from vegetal-hemisphere cells in early stages of the development. Previously, we showed by blastomere isolation and ablation experiments that the contact between the animal and vegetal hemispheres until the 32-cell stage is necessary for the proper AP patterning of the epidermis in the tailbud-stage embryo. We here addressed the patterning mechanism of the posteriormost epidermis using a tail-tip epidermis marker, HrTT-1. Employing blastomere isolation and ablation experiments along with knockdown of a master regulator gene for posterior mesoderm, we have demonstrated that presence of the posterior vegetal cells after the 32-cell stage is necessary for the expression of HrTT-1. To explore the timing and nature of the influence of the posterior vegetal cells, we treated the embryos with FGF signaling inhibitors at various developmental stages and found that HrTT-1 expression was lost from embryos treated with the inhibitors from stages earlier than the late neurula stage, just prior to the onset of HrTT-1 expression but not after the initial tailbud stage, at which the expression of HrTT-1 had started. In embryos lacking HrTT-1 expression, the expression domain of Hrcad, which would otherwise be localized anterior to that of HrTT-1, expanded to the tail-tip. These results suggest that FGF signaling from the neurula to initial tailbud stages is necessary for the initiation but not maintenance of HrTT-1 expression in the tail-tip epidermis. The contact with posterior vegetal cells until and after the 32-cell stage may be required for FGF signaling to occur in the posterior tail, which in turn regionalizes the tail-tip epidermal territory.

Naohito Takatori, Shuichi Wada, and Hidetoshi Saiga "Regionalization of the Tail-tip Epidermis Requires Inductive Influence from Vegetal Cells and FGF Signaling in the Development of an Ascidian, Halocynthia roretzi," Zoological Science 24(5), 441-448, (1 May 2007). https://doi.org/10.2108/zsj.24.441
Received: 21 October 2006; Accepted: 1 December 2006; Published: 1 May 2007
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