FUNCTIONAL-ANALYSIS OF SOX10 MUTATIONS FOUND IN HUMAN WAARDENBURG-HIRSCHSPRUNG PATIENTS

The Sry-related protein Sox10 is selectively expressed in neural crest cells during early stages of development and in glial cells of the pe ripheral and central nervous systems during late development and in th e adult. Mutation of the Sox10 gene leads to neural crest defects in t he Dominant megacolon mouse mutant and to combined Waardenburg-Hirschs prung syndrome in humans. Here, we have studied the four Sox10 mutatio ns found to date in Waardenburg-Hirschsprung patients both in the cont ext of the rat and the human cDNA. Unlike the rat Sox10 protein, which failed to show transcriptional activity on its own, human Sox10 displ ayed a weak, but reproducible, activity as a transcriptional activator , All mutant Sox10 proteins, including the one that only lacked the 10 6 last amino acids were deficient in this capacity, indicating that th e carboxyl terminus of human Sox10 carries a transactivation domain. W hereas all four mutants failed to transactivate, only two failed to sy nergistically enhance the activity of other transcription factors. Syn ergy required both the ability to bind to DNA and a region in the amin o-terminal part of Sox10, Those mutants that failed to synergize were unable to bind to DNA, Analysis of the naturally occurring Sox10 mutat ions not only helps to dissect Sox10 structure, but also allows limite d predictions on the severity of the disease.