PROJECT SUMMARY/ABSTRACT Down syndrome (DS) is the most common genetic cause of intellectual disability. For decades, we have known that an extra copy of the 21st chromosome (Hsa21) causes the broad array of physiological and developmental phenotypes associated with DS. However, we are far behind on addressing two critical questions in DS research: 1) Which Hsa21 genes cause phenotypes when overexpressed in DS, and conversely, 2) Which Hsa21 genes might be targeted to improve phenotypes in DS. Researchers using mouse models have discovered the role that a handful of Hsa21 genes play in certain phenotypes when overexpressed, such as Alzheimer’s pathology (APP) and leukemia (GATA1). The vast majority of Hsa21 genes, however, have not been studied in detail due to the impracticality of studying over 200 genes on Hsa21. Studying each of the Hsa21 genes using mouse models is time-consuming and costly. Instead, we propose to systematically study individual Hsa21 gene orthologs using the efficient model Caenorhabditis elegans. Recently, we found that, excluding 48 keratin genes, C. elegans has orthologs for over half of remaining Hsa21 genes, 51 of which are highly-conserved. Through mutant and RNAi analysis of the 51 orthologs, we found that 14 are essential genes and 10 are required for neural and/or muscular function, three of which had not previously been studied. To probe how overexpression (OE) of individual Hsa21 genes contributes to phenotypes relevant to DS, we will carry out complementary aims. For Aim 1, we will systematically test which of the 51 orthologs cause OE phenotypes one-by-one. For Aim 2, using a transgenic worm that carries extra copies of all 51 Hsa21 orthologs, we will systematically test which of the Hsa21 orthologs may be knocked down to reduce OE phenotypes. For OE phenotypes that we are able to suppress by gene knock down, we will also investigate the underlying cellular-molecular mechanistic bases with convenient approaches unique to C. elegans. Our project will leverage cutting-edge transgenic and gene knockdown tools, as well as take advantage of our lab’s expertise in high-throughput quantitative phenotyping. By identifying Hsa21 genes that cause phenotypes when overexpressed in C. elegans, this study will spotlight genes to prioritize for further study using mouse and human stem-cell models of DS. The set of Hsa21 OE strains produced will be shared freely around the world to establish C. elegans as the first mechanistic in vivo model to conveniently study consequences of Hsa21 gene overexpression. Insights gained from this study will highlight novel and uncharacterized molecular pathways as potential therapeutic targets for improving health in those with DS.

People with Down syndrome inherit an extra copy of the 21st chromosome which carries about 200 genes. It remains unclear which of these genes contribute to the wide variety of developmental and physiological phenotypes in DS. The proposed research uses an innovative screening strategy to systematically study the phenotypic consequence of adding and subtracting each of these genes in a powerful animal model.