Single molecule tracking raw data: SOX18 and its dominant-negative mutant SOX18RaOp

Few genetically dominant mutations involved in human disease have been
fully explained at the molecular level. In cases where the mutant gene
encodes a transcription factor, the dominant-negative mode of action of
the mutant protein is particularly poorly understood. Here, we studied the
genome-wide mechanism underlying a dominant-negative form of the SOX18
transcription factor (SOX18RaOp) responsible for both the classical mouse
mutant Ragged Opossum and the human genetic disorder
Hypotrichosis-Lymphedema-Telangiectasia-Renal Syndrome. Combining three
single-molecule imaging assays in living cells together with genomics and
proteomics analysis, we found that SOX18RaOp disrupts the system through
an accumulation of molecular interferences which impair several functional
properties of the wild-type SOX18 protein, including its target gene
selection process. The dominant-negative effect is further amplified by
poisoning the interactome of its wild-type counterpart, which perturbs
regulatory nodes such as SOX7 and MEF2C. Our findings explain in
unprecedented detail the multi-layered process that underpins the
molecular aetiology of dominant-negative transcription factor function.