Using Caenorhabditis elegans as a Model for Mechanistic Insights of Craniofacial Development

Caenorhabditis elegans has served as a powerful model for understanding the molecular and cell biology of clinically important human proteins due to the conservation of genes that are associated with human disorders. It is well established that evolution has conserved critical domains of proteins and their cellular functions even though the phenotypic output for analogous mutations can be distinct among organisms. To that end, the genes that are associated with human craniosynostosis such as TWIST1, TCF12, and FGFR2 have homologs in C. elegans hlh-8, hlh-2, and egl-15, respectively. Whereas mutations in these human genes lead to bone defects in the skull, mutations in the C. elegans genes lead to defects primarily in nonstriated muscles that are responsible for laying eggs and controlling defecation. Even though the phenotypes are distinct in nature, the ability to quantify them in C. elegans can give a sense of the severity to provide a genotype-phenotype correlation. With the advent of CRISPR/Cas-9 genome editing in C. elegans, it is possible to model specific patient mutations that affect conserved amino acids in C. elegans proteins. These mutant strains can then be evaluated for their phenotypes in both homozygous and heterozygous animals. The assays that can be used to measure these phenotypes are described in this chapter.