A Coffin-Siris syndrome-associated mutation modeled in C. elegans affects multiple developmental processes.

Abstract

Coffin-Siris syndrome (CSS) is a rare human genetic disorder that is characterized by developmental delay, fifth digit abnormalities, and craniofacial defects. Heterozygous mutations in two SoxC proteins, SOX4 and SOX11, are associated with this disorder. C. elegans has a single SoxC protein, SEM-2, which is essential for development. In this study, we use C. elegans as a model system to explore the molecular effects of one CSS-associated SOX11 mutation, Y116C, on SoxC protein function in vivo. The equivalent amino acid of SOX11 Y116 is SEM-2 Y160, a residue in the C-terminal tail of the highly conserved DNA-binding domain. Homozygous, but not heterozygous, sem-2[Y160C] animals exhibit a high rate of embryonic and larval lethality, egg-laying defects, reduced brood size, bivulval phenotype and a low penetrance of hermaphrodite tail abnormalities. Additionally, sem-2[Y160C] animals have reduced expression of hlh-8/Twist, whose human counterparts, when mutated, are known to be associated with craniofacial disorders. All the phenotypes observed in sem-2[Y160C] animals resemble SEM-2 loss-of-function phenotypes, suggesting that SOX11[Y116C] is a loss-of-function, recessive mutation that likely causes defects due to haploinsufficiency. Our work suggests that using C. elegans as a model system to analyze the molecular effects of point mutations associated with craniofacial defects has the potential for unraveling the underlying mechanisms.