Functional Characterization of Genetic Variants in Rare Disease Associated with Shoc2 Scaffold

Summary Mutations in the Shoc2 gene result in a developmental disorder called Noonan syndrome with loose anagen hair (NSLH), a condition characterized by craniofacial abnormalities, digestive, cardiac, neurodevelopmental delays, and intellectual disability. These phenotypes can be attributed to alterations in the differentiation or function of neural crest cells. The Shoc2 protein is critical for transmitting the ERK1/2 cascade signals, which is vital in developing many tissues. To regulate ERK1/2 signals, Shoc2 forms an intricate protein complex. Consequently, disruption of Shoc2 function may lead to gene expression alterations during development and defects in cell lineage specification. This application is led by the notion that functional analyses of different Shoc2 mutations present in patients with birth defects will give important insights into the mechanisms by which these pathogenic variants affect cell differentiation and how these alterations lead to the variety of phenotypes observed in NSLH patients. Shoc2 variants found in patients with RASopathy-like symptoms are located in regions of the protein necessary for different aspects of Shoc2 function, including protein-protein binding, intracellular distribution, posttranslational modifications controlling stability or signal transmission that may affect various aspects of how Shoc2 regulates signal specificity and amplitude. Therefore, we hypothesize that variants affecting different Shoc2 functions and, in turn, may affect cell function or differentiation into specific lineages to cause variant-specific phenotypes in NSLH patients. Using variants of unknown significance, which affect single amino acids, we thus propose to examine correlations between patient phenotypes and different aspects of Shoc2 function. We will use a zebrafish vertebrate model carrying patient mutations and biochemical and biophysical approaches to gain insights into the molecular and cellular processes altered by specific Shoc2 variants in neural crest-derived lineages. Results from this work will fill an essential gap in our understanding of the fundamental principles by which alterations of different aspects of signal transmission result in human disease with variable phenotypic outcomes. This work will have a broader impact by elucidating the importance of cell signaling mechanisms in craniofacial morphogenesis.