A Meier-Gorlin Syndrome Mutation in Orc4 Causes Tissue-Specific DNA Replication Defects inDrosophila melanogaster

Abstract

1Meier-Gorlin syndrome is a rare recessive disorder characterized by a number of distinct 2 developmental defects, including primordial dwarfism, small ears, and small or missing 3 patella. Genes encoding members of the origin recognition complex (ORC) and additional 4 proteins essential for DNA replication (CDC6, CDT1, GMNN, CDC45, and MCM5) are 5 mutated in individuals diagnosed with MGS. The primary role of ORC is to license origins 6 during the G1 phase of the cell cycle, but it also plays roles in cilia development, 7 heterochromatin formation, and other cellular processes. Because of its essential role in 8 DNA replication, ORC is required for every cell division during development. Thus, it is 9 unclear how the Meier-Gorlin syndrome mutations in ORC lead to the tissue-specific 10 defects associated with the disease. To address this question, we have used Cas9-11 mediated genome engineering to generate a Drosophila melanogaster model of 12 individuals carrying a mutation in ORC4. Like the people with Meier-Gorlin syndrome, 13 these flies reach adulthood, but have several tissue-specific defects. Genetic analysis 14revealed that this allele is a hypomorph and that mutant females are sterile. We 15 demonstrated that this sterility is caused by a failure in DNA replication. By leveraging the 16 well-studied Drosophila system, we showed that a disease-causing mutation in orc4 17 disrupts DNA replication, and we propose that in individuals with MGS defects arise 18 preferentially in tissues with a high-replication demand. 19 20 4