Regulation of Growth and Morphogenesis

Project Summary Our research investigates molecular mechanisms through which mechanical forces are regulated and perceived, how biochemical and biomechanical signals are integrated, and how they act together to modulate growth and shape during developmental, physiological, and pathological processes. Planned investigations build on our discovery of a process that links cytoskeletal tension at adherens junctions to regulation of Hippo signaling and tissue growth. This occurs through tension-dependent recruitment of an Ajuba family LIM protein (Jub in Drosophila) to a-catenin. Jub then recruits and inhibits the key Hippo pathway kinase, Warts, which leads to increased activity of the Hippo pathway transcription factor Yorkie (Yki). We will investigate molecular mechanisms mediating this regulation, extending our recent discovery of recruitment of Warts into phase-separated condensates with Jub and of a Jub-promoted phosphorylation of the Warts N-terminus. Our research will test hypotheses regarding how these activities contribute to inhibition of Warts and their relevance to regenerative and oncogenic stimuli that activate Yki and its mammalian homologues. Our research on Hippo signaling will also extend our discovery that it modulates Drosophila glial cell proliferation, focusing on how Hippo signaling is regulated in the glial cells that form the blood-brain barrier in Drosophila. Our research will also investigate how the cytoskeleton is regulated to drive morphogenetic processes. Spectrins are membrane cytoskeletal proteins that influence cell shape and Hippo signaling. We discovered that the Drosophila βH-Spectrin Karst (βH-Spec) can compete with myosin for binding to F-actin to influence cytoskeletal tension. This raises fundamental questions that we will address regarding how and where spectrin and myosin functions are integrated to modulate cell shape and behavior, including how the apically localized βH-Spec and myosin compete and cooperate to influence normal development and physiology, how the localization of βH-Spec and myosin are coordinated, and whether the laterally localized β-Spectrin similarly competes with myosin for F-actin binding to modulate morphogenesis. We will also extend understanding of Notch signaling functions by investigating how Notch regulates the cytoskeleton to create the dorsal-ventral compartment boundary of the Drosophila wing disc. Our studies investigate highly conserved proteins and signaling networks, and they are relevant to understanding normal development and physiology, as formation of organs of characteristic and reproducible size and shape is essential for organ function, and the symptoms of many congenital syndromes stem from defects in organ growth or morphogenesis. Moreover, dysregulation of growth control is associated with tumorigenesis, and a detailed understanding of organ growth, morphogenesis, and repair is required to create functional organs from stem cells, which is a key goal of regenerative medicine.