Mechanisms of epithelial tube development, orientation and integrity - Project Summary Epithelia are sheets of polarized cells that that transport fluids, cells, and gasses. These tubes are the building blocks of organs, glands and embryonic endoderm. To understand the biology of epithelial tubes, we need to define the often organize into tubes, specialized tissues mechanisms that control epithelial patterning and integrity. However, because of the great variety of epithelial tubes across animals, we must expand our investigation into new model organisms so that we can determine the fundamental and shared mechanisms of tube development. we have recently established the larva of the sea star Patiria miniata as an innovative model that leverages while To address this challenge and uncover general mechanisms, the experimental advantages of a small invertebrate sharing a close phylogenetic position to vertebrates. Taking advantage of the first genetic tools (CRISPR Cas9) and long-term live imaging methods that we established for sea stars, our proposal will address three fundamental questions of epithelia biology. First, how is the orientation and shape of epithelial tubes controlled? Our recent work found that the Wnt pathway regulates tissue orientation through the Frizzled 1/2/7 receptor and uncovered a new role for Dishevelled in controlling lumen shape, but the mechanisms activated by these effectors remain unknown. Second, what molecular mechanisms keep tube cells in an epithelial state? In our preliminary data we found that tube cells that are blocked in G1 of the cell cycle undergo epithelial to mesenchymal transition (EMT) and leave behind a disrupted basal lamina, damaging tissue integrity. We will leverage these methods that precisely induce EMT to investigate whether there are external cues or cell intrinsic factors that trigger EMT from a tube, a pathological process that is poorly understood. Third, how does the gene regulatory network that defines epithelial cell lineages change over time, from the initial tube to a more complex structure? Our recent work has shown that the FGFR induces expression of the transcriptional factor Six1/2, that in turn regulates branching points, thus defining a first node in the GRN. But how the GRN integrates information from all the genes expressed by different cells, and what are the basic cell-types that are conserved in evolution to build a solid tube has not been defined yet. Major key gaps remain in our understanding of the integration of signaling pathways, cell cycle and gene networks that guide epithelial tube morphogenesis. The tools we developed, the advantage of a novel experimental system and the multipronged approach we will undertake in these projects uniquely position us to address these gaps. Our results will improve our understanding of the conserved mechanisms of tube morphogenesis and may provide insights on a broad range of epithelial diseases in humans , including congenital disorders, tissue fibrosis, organ malfunctions and cancer.
