Vegetal cell fate specification and anterior neuroectoderm formation by Hroth, the ascidian homologue of orthodenticle/otx

To obtain insights into the mechanisms of gastrulation and neural tube form ation, we studied the function and regulation of expression of Hroth, the a scidian homologue of orthodenticle/otx, during embryogenesis. Microinjectio n of synthetic Hroth mRNA into fertilized eggs led to embryos with an expan ded trunk and a reduced tail. In these embryos, development of notochord an d muscle was effected. Also, Hroth overexpression caused ectopic formation of anterior neuroectoderm, along with suppression of epidermis development, even in the absence of cell-cell interaction. Furthermore, we demonstrated that ectodermal expression of Hroth requires an inductive influence from t he vegetal hemisphere cells. These data suggest roles of Hroth in both spec ification of mesoendodermal cells and anterior neuroectoderm formation. (C) 1999 Elsevier Science Ireland Ltd. All rights reserved.