Project Summary The overall goal of this project is to expand the knowledge on the genetic basis and molecular mechanisms of Prune Belly Syndrome (PBS), a severe human multi-system congenital urologic anomaly with muscle and connective tissue deficiencies. Hallmark clinical features of PBS include the triad of 1) wrinkled `prune' belly due to hypoplastic or absent abdominal wall skeletal musculature, 2) megacystis secondary to bladder smooth muscle pathology, and 3) bilateral undescended testes. We discovered three gain-of-function missense mutations in the X-linked gene filamin A (FLNA) causing syndromic and isolated PBS. FLNA is an abundant intracellular actin-crosslinking protein that functions as a crucial mechanosensor, transmitting force bidirectionally between actin and integrins as well as binding and regulating other modulatory transmembrane receptors or signaling molecules. FLNA regulates cell shape, adhesion, gene transcription, hypoxic responses, embryonic morphogenesis, and cell contraction. To assess the role of Flna mutations on mouse development and function, we will study our Flna gain-of- function mutant mice that have a highly penetrant PBS-like phenotype when exposed to gestational hypoxia (Aim 1). Using state-of-the-art structural and biochemical techniques, we will characterize mutant FLNA protein structure and the impact on binding partners (Aim 2). As the mouse-derived Flna gain-of-function bladder smooth muscle cells have a dysmorphic, dysfunctional cell phenotype, we will subcellularly and molecularly define their cell form and function when exposed to environmental stress and stimulants (Aim 3). This multidisciplinary expert team with unique scientific expertise and advanced molecular tool sets will unite to identify FLNA-based critical regulatory mechanisms modulating detrusor smooth muscle function and dysfunction leading to PBS. This work may fill an important gap in our understanding of FLNA signaling and yield greater mechanistic understanding of detrusor myogenesis and detrusor underactivity, integrating signaling pathways, creating animal models of PBS, and potentially impacting future management of detrusor underactivity by guiding future rational therapeutic designs.