Canonical Wnt signaling functions in second cardiac lineage and anterior pituitary development : a dissertation /

Bibliographic Details
Main Author:	Ai, Di
Format:	Thesis Book
Language:	English
Published:	[College Station, Tex.] : [Texas A&M Health Science Center], [2007]
Subjects:	Wnt Proteins. Organogenesis > physiology. Disease Models, Animal. Major Medical Sciences.

Description
Abstract:	ABSTRACT: Organogenesis is controlled by families of secreted signaling molecules and modulated by the complement of tissue-restricted transcription factors and coregulators present in each cell. Wnt/[beta]-catenin pathway, also called canonical Wnt signaling, is the best characterized Wnt signaling pathway. It is involved in diversified developmental processes and adult homeostasis, including cell fate determination, proliferation, differentiation and migration. In the absence of Wnt ligand, [beta]-catenin was phosphorylated by APC/Axin/GSK-3[beta] complex and degraded in the cytoplasm. In the presence of Wnt ligand, activated Dvl inhibits GSK-3[beta] and [beta]-catenin gets stabilized and translocates into nuclei. In the nuclei, [beta]-catenin binds to transcription factors of LEF/TCF family, which bind to the regulatory element of downstream target genes for transcriptions. Wnt/[beta]-catenin-Pitx2 pathway has been identified to mediate cell type specific proliferation in outflow tract neural crest and pituitary during development. TCF/LEF regulatory element in Pitx2 promoter was found to be functional by ChIP assay and LiCl (mimics Wnt pathway activation) treated embryos showed increased Pitx2 expression in outflow tract and pituitary tissue. ChIP assay also identified the binding of Pitx2 to promoter region of G1 phase growth control genes CyclinD2 in C2C12 (myoblast cell) and [alpha]-T3-1 (pituitary cell line) cells by dismissing HDAC1 and increased histone H3/H4 acetylation and recruitment of DNA Polymerase II were observed. But the Wnt/[beta]-catenin pathway function in second cardiac lineage progenitor cells is still elusive. To answer this question, we used transgenic line Mef2c AHF(cre) to conditionally inactivate [beta]-catenin and stabilize [beta]-catenin in the second cardiac lineage using two different conditional [beta]-catenin mutant alleles. Right ventricle hypoplasia was observed in both [beta]-catenin mutants. Wnt/[beta]-catenin pathway downstream target CyclinD2 is dramatically decreased in the proximal outflow tract in [beta]-catenin(f/f) mutant. Bmp4 is downregulated in pharyngeal arch mesoderm and outflow tract myocardium in [beta]-catenin f/f mutant and upregulated in stabilized [beta]-catenin mutant, suggesting Bmp4 could be regulated by Wnt pathway in the second cardiac lineage. Our findings reveal that Wnt signaling promotes second lineage precursor growth and provide insight into regenerative medicine to treat congenital and acquired heart disease. The finding that Wnt signaling regulates Pitx2a in pituitary development through a TCF/LEF regularly element in Pitx2a promoter raised another interesting question: Can Wnt signaling regulates Pitx2 through other TCF/LEF regularly elements in Pitx2 pituitary enhancer? We used transgenic approaches and mapped a minimal regulatory element in the downstream region of Pitx2, which is essential and sufficient to drive Pitx2c expression in the Rathke's pouch (the primordia of anterior and intermediate lobe of pituitary) and one TCF/LEF binding site was proved to be functional by both in vivo and in vitro experiments, suggesting that Wnt signaling could regulate different Pitx2 isoform through different TCF/LEF binding site during organogenesis. One functional NF-1 binding sites was found close to TCF/LEF binding site and probably plays role of chromatin remodeling to facilitate the access of TCF/LEF protein. Identification of cis- and trans- regulatory elements of Pitx2 will provide insight into the molecular mechanisms that establish oral ectoderm and its derivatives formation, like teeth and rugae.
Item Description:	Vita. "Major Subject: Medical Sciences". "Submitted to the Office of Research and Graduate Studies The Texas A&M Health Science Center in partial fulfillment of the requirements for the degree of Doctor of Philosophy May 2007." Approved as to style and content by: James F. Martin, Richard H. Finnell, Richard R. Behringer, Mingyao Liu, Robert Tsai, Robert J. Schwartz.
Physical Description:	xiii, 162 leaves : illustrations ; 28 cm.
Bibliography:	Includes bibliographical references (leaves 115-137).