Characterizing pathogenic Robinow Syndrome-associated Dishevelled1 variants in Drosophila

Human development is regulated by intricate, and interconnected, signal transduction networks. Given the complexity, deciphering the effects of mutations that give rise to abnormal development can be challenging. Using Drosophila melanogaster can simplify the puzzle of studying human disorders as flies have less genetic redundancy and are significantly easier, cheaper, and faster to raise than vertebrate models. I use Drosophila to characterize three pathogenic Dishevelled1 (DVL1) mutations obtained from patients with Autosomal Dominant Robinow Syndrome (RS), a rare genetic disorder associated with craniofacial abnormalities and shortened stature. Most of the mutations associated with RS affect components of the Planar Cell Polarity (PCP) branch of Wnt signaling. Wnt signaling is critical for embryonic development and homeostasis. The two main pathways, canonical and PCP Wnt signaling, require DVL but there is still much to learn about the latter which mediates cytoskeletal rearrangement events and orients cell polarity within the epithelial plane. Each of the DVL1 variants I study have unique frameshift mutations that replace the highly conserved C-terminus with the same novel peptide sequence of no known homology. I use the Gal4-UAS system to express wildtype human DVL1 and the three DVL1 variants in Drosophila. This design is strategically suited to test for functional differences between mutant and wild-type human proteins in relevant developmental contexts. My research has shown that these DVL1 patient variants cause Wnt signaling imbalances by disrupting the stability of Armadillo (Arm)/β-catenin while ectopically inducing PCP/JNK signaling. Furthermore, I show that the variants activate apoptosis, interfere with core PCP protein localization, and disrupt dorso-ventral cell adhesion during wing development. Additionally, the variants induce several novel phenotypes in wing tissue such as anterior cross vein abnormalities, ectopic bristles, and vein thickening, suggesting novel functions in other conserved signaling pathways. The study of rare genetic diseases provides valuable insights into human gene function. By understanding how conserved signaling pathways are altered by these DVL1 variants, we gain insight into the underlying mechanisms of non-canonical Wnt signaling and more broadly, how development in individuals with RS is altered. This information may guide future therapeutics for RS patients.