Project Summary/Abstract During development, tissues are sculpted into organs with precise forms and functions in a process called tissue morphogenesis. Tissue morphogenesis results from cellular forces that are transmitted across the tissue. Improper generation or coordination of forces leads to defects in organ formation, such as spina bifida. Therefore, it is critical to both our understanding of development and human disease to determine the mechanisms that control tissue morphogenesis at the molecular, cellular, and tissue level. Tissue invagination during gastrulation and neural tube closure is driven by apical constriction of epithelial cells. This causes columnar cells to adopt a wedge shape, which promotes folding of the epithelial sheet. We made the surprising discovery that apical constriction during Drosophila gastrulation is driven by pulsed contractions of the actin-myosin cytoskeleton. Contraction pulses have now been observed to promote many different morphogenetic processes, including tissue folding, contraction, and axis elongation. Our work has shown that the dynamic turnover of actomyosin that accompanies pulsing is critical to stably transmit force between cells. Furthermore, mutants in Cofilin, a gene involved in actin turnover, are associated with neural tube defects in mice and humans. The mechanisms that regulate actin turnover and enable forces to be transmitted across a tissue are unknown. We will investigate the mechanisms that enable forces to propagate across a tissue. First, we will determine the spatial and temporal function of actin cytoskeletal genes we have determined are important for force transmission. Second, we will examine how the apical contractile cortex is radially organized, which enables forces to be transmitted across a cell. Third, we will examine the supracellular actomyosin network that drives Drosophila gastrulation and determine how its organization contributes to developmental robustness. The availability of live imaging, quantitative image analysis, genetics (mutants, RNAi), cell biology (drugs), biophysics (laser cutting), and biochemistry makes Drosophila gastrulation a powerful system to address these questions. This multidisciplinary and multiscale approach is essential to understand how dynamic molecular and cellular behaviors collectively result in precise changes in tissue morphology. Members of my lab have backgrounds in cell biology, genetics, physics, and computer science. In addition, we have established collaborations with Mathematicians and experts in Mass Spectrometry to expand our research capabilities. We are poised to make important discoveries regarding forces are passed between cells to drive robust tissue morphogenesis.