Mechanical forces and their molecular control during epithelial folding in Drosophila

• Applicant: Professor Dr. Christian Dahmann
• Subject Area: Developmental Biology
• Term: since 2019
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 428986026

The shaping of tissues is crucial for establishing functional organs during animal development. One fundamental shape change of epithelial tissues is folding. Epithelial folding is important, e.g. during embryonic gastrulation, neural tube, eye, gut and brain development. Defects in epithelial folding can give rise to human disease. Epithelial folding can be subdivided into two steps: First, the position within the tissue where the fold will be formed is specified through genetic networks often involving extracellular signaling molecules. Second, in response to the extracellular signaling molecules, the specified cells modulate their mechanical forces resulting in their deformation and the subsequent folding of the tissue. However, how the signaling pathways connect to the intracellular machinery that alters mechanical forces remains poorly understood. The Drosophila wing disc, the precursor of the adult wing, is a single cell-layered epithelium that serves as a well-established model system to study signaling pathways and tissue morphogenesis. During larval stages, the initially flat wing disc forms three stereotypic folds. We previously showed that one fold, the Hinge/Pouch fold, is generated through an increase in mechanical tension along lateral cell faces, which is mediated by pulsed actomyosin contractions. We also showed that a second fold, the Hinge/Hinge fold, forms through a local release of basal mechanical tension mediated by a decrease in extracellular matrix density. Recently, we identified the conserved Wingless and Hedgehog signals as upstream cues for positioning and inducing the Hinge/Hinge and Hinge/Pouch fold, respectively. In this project, we aim to identify downstream targets of these two signaling pathways that control actomyosin contractions and extracellular matrix density. We have established laser capture microdissection to sample cells specifically from the fold regions and controls. We will next use RNA sequencing and bioinformatics analysis to identify genes exclusively expressed in the Hinge/Hinge or Hinge/Pouch fold. We will then functionally characterize these candidate genes and test whether and how they influence actomyosin contractions or the extracelullar matrix. In a complementary approach, to identify additional molecules involved in fold formation, we will perform a RNA interference screen using an assay for fold formation that we recently established and validated. We expect that this project will gain novel insights into the molecular connections between signaling pathways and their downstream cellular processes during epithelial morphogenesis.

• DFG Programme: Research Grants