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The role and regulation of FoxI1e in Xenopus ectoderm formation

by Mir, Adnan

Abstract (Summary)
The segregation of the vertebrate embryo into three primary germ layers is one of the earliest developmental decisions. In Xenopus, the endoderm is specified by a vegetally localized transcription factor, VegT, and releases nodal signals that instruct the adjacent marginal zone of the blastula to become mesoderm. However, little is known about how the ectoderm becomes specified. In this study, we show that the Forkhead-box protein FoxI1e is required at the blastula stage for normal formation of the two early derivatives of the ectoderm, the central nervous system and epidermis. FoxI1e is also required to maintain the regional identity of the animal cells of the blastula, the precursors of ectodermal structures. We have also studied the control of FoxI1e expression. In situ hybridization for FoxI1e shows a mosaic expression pattern at the blastula stage, with expressing cells interspersed with non-expressing cells. It is expressed in a wave initiated on the dorsal side of the animal hemisphere, and extends across to the ventral side by the mid-gastrula stage, confined to the inner layers of cells in the animal cap, and expressed in a mosaic fashion throughout. Finally, we show that this pattern of expression is controlled by both short and long range signals. Notch signaling controls both the mosaic, and dorsal/ventral progression in expression. Notch signaling is controlled, in turn, by the vegetally localized TGF? ligand Vg1. FoxI1e expression is also regulated by nodal signaling downstream of VegT. Canonical Wnt signaling contributes only to late changes in the FoxI1e expression pattern. Overall, these results provide an initial framework for the activation of ectoderm formation in the Xenopus embryo, and provide new insights into the roles of vegetally localized mRNAs in controlling zygotic genes expressed in the animal hemisphere by long range signaling.
Bibliographical Information:

Advisor:

School:University of Cincinnati

School Location:USA - Ohio

Source Type:Master's Thesis

Keywords:development xenopus laevis ectoderm foxi1e notch signaling tgf? vegt

ISBN:

Date of Publication:01/01/2007

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