The Wnt signalling pathway is used multiple times throughout the development of an organism. Early in embryonic development this path is known to be involved in the induction of the ectodermally derived neural crest. The Wnt pathway is also thought to function in other ectodermal cell types. How the same signalling pathway can induce different cellular responses within a germ layer is an intriguing question. There are several properties of a cell that can influence its response to an extracellular signal including what intracellular components are poised ready for activation. Whether the Wnt-responsive transcription factor family members have functionally distinct mechanisms of influencing transcription in the ectoderm may account for the ability of the Wnt/beta-catenin signal to achieve induction of multiple cell types. This work examines whether or not two Wnt/beta-catenin responsive transcription factor family members, XLef1 and XTcf3, are functionally distinct proteins and what domains of these transcription factors are attributable to these differences. I utilized the model organism <em>Xenopus laevis</em> to examine how the Wnt/beta-catenin pathway influences the patterning of the ectodermal germ layer. Microinjection of mRNA into the embryos enabled overexpression studies of wildtype and mutant pathway proteins, allowing me to observe the influence of such pathway components. <em>In situ</em> hybridization was carried out to examine the expression domains of genes specific for particular ectodermal domains. The ectoderm is patterned into several domains including the neural plate, neural crest, placode, and cement gland regions. I was able to determine that Wnt inhibition is necessary to allow early neural development. When the pathway is ectopically upregulated in the ectoderm, neural induction is prevented. Differences exist between the ability of XLef1 and XTcf3 to mediate the formation of the neural domain in the ectoderm. These differences are partially attributable to several repressive motifs in XTcf3. Endogenously, these Wnt responsive transcription factors are required for ectodermal development, as depletion of XLef1 or XTcf3 using morpholinos inhibits normal induction of this germ layer. In order to accomplish the multitude of tasks during development, there must be cellular competence differences that enable the same signalling pathway to elicit different consequences. I determined that the presence of different Wnt-responsive transcription factors is partially responsible for these differences.

Last modified

• 05/09/2018

Creator

• Elizabeth Yvette Truesdell

DOI

• https://doi.org/10.21985/N2711D

Subject

• Interdepartmental Biological Sciences Program

Keyword

• Xenopus
• Tcf3
• ectoderm
• Wnt
• neural
• Lef1

Date created

• 2006-12-13

Resource type

• Dissertation

Rights statement

• In Copyright