Cornelia de Lange Syndrome-associated mutations in Smc1 cause both sister chromatid cohesion and cohesion-independent defects

Abstract

Cornelia de Lange Syndrome is a pervasive developmental disorder characterized by limb truncations, craniofacial abnormalities, and cognitive delays. This syndrome is a member of a class of developmental disorders referred to as cohesinopathies, which result from mutations in the genes encoding subunits or regulators of the cohesin complex. The phenotypic consequences of these mutations may reflect the critical role that cohesin plays in chromosome structure, its ability to tether sister chromatids together during cell cycle progression, or some combination of both. Here we show that a sensitized assay for chromosome loss in budding yeast can be used to assess the impact of Cornelia de Lange syndrome (CdLS)-associated mutations in the core cohesin subunit Smc1 on cohesin function. We find that the CdLS-associated mutations can be grouped into two classes based on their impact on chromosome segregation. One class of mutations includes those that are defective in promoting accurate chromosome segregation, some no better than the null allele. Another class promotes both accurate chromosome cohesion and segregation. Strikingly, the mutations that have no impact chromosome dynamics in this assay are clustered near each other in the context of the folded SMC1 protein suggesting a previously uncharacterized region of functional importance in higher eukaryotes. This analysis illustrates how budding yeast can be used to elucidate mechanisms important in human health and development.