DYNAMIC EXPRESSION OF NEURAL PLATE BORDER SPECIFERS ESTABLISHES AND MAINTAINS ECTODERMAL DOMAINS IN THE DEVELOPING XENOPUS EMBRYO

Open Access
Author:
Peterson, Meredith C.
Area of Honors:
Biology
Degree:
Bachelor of Science
Document Type:
Thesis
Thesis Supervisors:
  • Allison Virginia Moody, Thesis Supervisor
  • Wendy Hanna Rose, Thesis Supervisor
  • James Harold Marden, Honors Advisor
Keywords:
  • Xenopus
  • ectoderm
  • neural plate border
  • neural crest
  • preplacodal ectoderm
  • lateral neurogenic zone
Abstract:
As gastrulation ends, the newly formed ectoderm of the developing vertebrate embryo is divided into broad domains of neurogenic and non-neurogenic tissues via the well-studied process of neural induction. Interactions between these two domains, along with the long-range inductive signals that establish the main body axes, result in the formation of a lateral neurogenic zone (LNZ) with a mixed developmental fate. The medial region of this domain will give rise to the neural crest, while the lateral and anterior regions will become preplacodal ectoderm. Considerable work has been done to clarify the transcriptional program that specifies these domains, yet the mechanism by which genes expressed in adjacent ectodermal domains pattern the lateral neurogenic zone and its derivatives remains to be elucidated. In this investigation, we use gain-of-function experiments in whole Xenopus embryos to examine the influence of five neural plate border genes upon the specification and maintenance of preplacodal ectoderm and neural crest fates. We demonstrate that overexpression of any of a suite of neural plate border specifiers in the lateral neurogenic zone is sufficient to inhibit expression of the preplacodal ectoderm marker Six1, and that this activity is attenuated as the embryo progresses through neurulation. We also show that within the lateral neurogenic zone, neural plate border genes of the Zic family promote neural crest fate at the expense of preplacodal ectoderm. Together, these results suggest that the dynamic redistribution of neural plate border genes within the lateral neurogenic zone is a critical event in the specification of its two major derivatives. We propose a model in which a small set of ‘lateral neurogenic zone specifiers’ lies upstream of the neural plate border specifiers, and after induction of this latter gene suite, the former withdraw from the LNZ into the epidermis, permitting specification of the preplacodal ectoderm.