The vertebrate digestive tract develops left-right asymmetric loops and chiral rotations that are essential for normal physiological function. Perturbations of these fascinating anatomical features underlie the development of life-threatening congenital defects. In the early embryo, the initial determination of "left" versus "right" is manifest as unique left-right asymmetric gene expression patterns, including the left-limited expression of the transcription factor, Pitx2, which is required for normal asymmetric organ morphogenesis. However, the mechanism by which this molecular asymmetry then engenders morphological asymmetries within developing organs remains poorly understood. Preliminary data indicate that the endoderm cell rearrangements that drive tissue elongation and epithelial morphogenesis in the Xenopus primitive gut tube (PGT) are governed by Wnt/Planar Cell Polarity (Wnt/PCP) signaling, and are modulated by Pitx2 expression. The objective of this proposal is to determine the individual and combined roles of Pitx2 and Wnt/PCP signaling in regulating endoderm cell shape, adhesion and/or rearrangement during the development of left-right asymmetric anatomy in the digestive tract. Loss- and gain-of-function strategies will be employed, including the use of novel photoactivatable reagents that have been developed for side-, stage-, and tissue-specific spatiotemporal modulation of Wnt-PCP and Pitx2 expression in the Xenopus gut tube.
Specific Aim 1 is to determine whether Wnt-PCP signaling regulates cell shape, adhesion and rearrangement in the endoderm during gut morphogenesis.
Aim 2 is to determine whether asymmetric Pitx2 expression controls these parameters on the left side of the gut tube.
Aim 3 is to determine whether the function of Pitx2 in asymmetric gut morphogenesis is mediated by Wnt-PCP signaling. Successful completion of the proposed research will provide unique insight into the unsolved mechanisms of asymmetric organ morphogenesis, by linking left-right asymmetric gene expression patterns to key mechanisms of asymmetric organ development.
The proposed work will illuminate the currently unknown etiology of common digestive organ birth defects, such as intestinal malrotation, narrowing or occlusion of the digestive tract, and congenital short bowel. The results of this research will also have significant, broad implications for the interrelationship of Pitx2 and Wnt signaling in the morphogenesis of multiple symmetric and asymmetric organs, and in the epithelial-mesenchymal transitions that drive development, maintain gut epithelial homeostasis, and underlie metastatic progression in tumors of the digestive and other epithelia.
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