Linking cell forces to organ-scale morphogenesis of the small intestine

PROJECT SUMMARY / ABSTRACT The lengthy small intestine is organized into compact loops within the confines of the body cavity in order to achieve sufficient nutrient-absorbing surface area. Abnormal looping results in congenital gastrointestinal disorders, such as midgut volvulus, which are often debilitating or lethal. During development, these loops form by buckling, a common morphogenetic mechanism by which a tissue bends outward in response to compressive mechanical forces. Elongation of the initially straight gut tube against the constraint of its attached membranous mesentery results in compressive forces that buckle the tube into stereotyped loops. Loop morphology can be predicted from experimental measurement of a handful of physical parameters, including mesentery stiffness. In response to increasing stretch by the elongating gut tube, the mesentery is initially compliant before stiffening and resisting further extension, thereby forcing the tube to buckle. This dependence of stiffness on stretch is known as constitutive nonlinearity, a property well characterized in adult tissues but largely overlooked in development, where its biological determinants are poorly understood. Here, we propose to elucidate key biological bases of mesentery constitutive nonlinearity during small intestine looping. Preliminary data collected by the applicant strongly implicates cell contractility in tuning the stiffening transition of chick mesentery, with disruption of contractility surprisingly resulting in diminished mesentery compliance prior to unchanged stiffening. Together with prior work showing similar changes upon inhibition of bone morphogenic protein (BMP) activity, we hypothesize that BMP signaling induces cell contractility to tune mesentery pre-stiffening compliance (Aim 1) and that extracellular matrix (ECM) compaction by these contracting cells sets the stiffening transition (Aim 2). Experimental examination of this hypothesis will shed light on the mechanics of proper intestinal development by integrating molecular control of cell behavior and matrix organization with organ-scale looping, which will yield important insight into the etiology of gastrointestinal birth defects arising from improper looping. In completing these Aims, the applicant will receive training in experimental techniques spanning developmental biology and bioengineering, including chick embryology, molecular biology, immunochemistry, and soft tissue mechanics. The applicant will participate in cross-department seminars, attend and present at engineering and development conferences, and receive mentorship from the sponsor, co-sponsor, and advisory committee, who contribute a diverse range of expertise. The applicant will also train in responsible conduct of research, oral and written communication, mentorship, and many other career skills. This training will prepare the applicant for postdoctoral research in academia studying the origins of physiological disorders for regenerative applications.