title: Regionalization of the tail-tip epidermis requires inductive influence from vegetal cells and FGF signaling in the development of an ascidian, Halocynthia roretzi.
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.
authors.affiliation: Department of Biological Science, Graduate School of Science and Engineering, Tokyo Metropolitan University, Tokyo, Japan.
authors.forename: Naohito
authors.initials: N
authors.lastname: Takatori
authors.forename: Shuichi
authors.initials: S
authors.lastname: Wada
authors.forename: Hidetoshi
authors.initials: H
authors.lastname: Saiga
mesh_terms: D000818:Animals; D004817:Epidermis / Q000196:embryology* / Q000378:metabolism; D005346:Fibroblast Growth Factors / Q000378:metabolism*; D005786:Gene Expression Regulation; D015398:Signal Transduction; D013623:Tail / Q000166:cytology* / Q000196:embryology; D014561:Urochordata / Q000196:embryology*
chemical_list: D005346:Fibroblast Growth Factors