Department of Molecular Medicine
Contact Information: Email: firstname.lastname@example.org; Phone: 607-253-4452
Sponsor: March of Dimes Birth Defects Foundation
Grant Number: 1-FY11-520
Title: The Mechanism of Intestinal Coiling
Annual Direct Cost: $85,342
Project Period: 06/01/2011-05/31/2014
DESCRIPTION (provided by applicant): Intestinal malrotation is a congenital disorder of abnormal intestine morphogenesis that occurs once in approximately 500 live births. While malrotation of the gut predisposes affected infants to the catastrophic condition of midgut volvulus, the origin of this disease and the mechanism of the gut coiling remain entirely unknown. Indeed, despite enormous progress in recent years toward understanding factors that pattern the early embryo, far less has been learned about the downstream cellular mechanisms controlling organ morphogenesis. Here I propose to investigate the molecular and cellular basis by which the counterclockwise direction of the vertebrate intestine is established. We previously have shown that the chirality of midgut coiling is determined by left-right asymmetries in the dorsal mesentery, the structure that connects the primitive gut tube to the body wall. Specifically, the dorsal mesentery of embryonic gut consists of an asymmetric cellular architecture including differential cell behavior and changes in cell shape leading to its mechanical deformation and a resulting leftward tilt of the primitive gut tube. The generation of this initial tilt provides a left-right bias for the subsequent specification of the direction of intestinal coiling. This asymmetric architecture includes condensation of mesenchymal cells specifically on the left side. Moreover, the overlying epithelium on the left exhibits a columnar morphology, in contrast to the cuboidal morphology on the right side of the dorsal mesentery. These properties are instructed by a set of transcription factors: Pitx2 and Islet1 specially express on the left side, and Tbx18 expressed on the right; expression of all these genes is regulated downstream of the secreted left-specific protein Nodal. Following pitx2 misexpression on the ride side of the dorsal mesentery, the mesenchyme condenses and the right epithelium becomes columnar. The misexpression of pitx2 on the right yields a “double-left” phenotype, and results in the loss of the leftward tilt; importantly, the chirality of subsequent gut looping events is randomized. Using laser Capture Microdissection I propose to separate the dorsal mesentery into four functionally distinct cellular compartments: left epithelium, left mesenchyme, right mesenchyme and right epithelium, to identify genes differentially expressed in each mesenteric segment. My research thereafter will be aimed at functional studies to reveal the full repertoire of molecular cellular mechanisms that lead to proper intestinal rotation. This work will increase our understanding of the genetic underpinnings of gut malrotation shedding light on its origin, may ultimately improve diagnosis in neonates, and may also hold lessons relevant to the morphogenesis of the heart and other tubal organs.