Development of Two Functional Assays to Study SIX3 mutations in Holoprosencephaly (HPE).

SABINA DOMENE; NAOKI NAKAYA; KENIA EL-JAICK; ERICH ROESSLER; FELICITAS LACBAWAN; STANISLAV TOMAREV; BEN FELDMAN; MAXIMILIAN MUENKE

Princeton, New Jersey, USA

Congreso; Mid-Atlantic Regional Developmental Biology Meeting; 2007

Society for Developmental Biology

Holoprosencephaly (HPE) is the most common structural anomaly of human brain development, with a prevalence of ~1 in 250 conceptuses and ~1 in 16,000 at birth. Mutations in at least eight different genes have been identified in human HPE patients. SIX3 is a transcription factor involved in midline forebrain and eye formation during early development. It has an important role in defining and maintaining anterior brain identity. It consists of two highly conserved domains: a SIX domain needed for interaction with other proteins and a DNA-binding homeodomain. SIX3 interacts with groucho corepressor proteins through two eh 1-related motifs located within the SIX domain. This interaction not only mediates regulation of transcriptional expression of other genes involved in early development, but is also needed for its autorepression control at the level of its own promoter. A total of 18 SIX3 mutations have been previously reported in patients with HPE, and our lab has recently identified an additional 28 mutations through dHPLC screening (46 in total). These are located throughout the entire gene and include 32 missense, 5 nonsense, 8 frameshift mutations and 1 in frame deletion.  Due to the absence of functional data regarding these HPE mutations, our lab is exploring several ways to test them. The approaches involve zebrafish as a model organism and include an overexpression and a rescue assay, as well as marker changes using in situ hybridization. With these assays we hope to be able to functionally characterize these SIX3 mutations in order to increase our understanding of the pathogenesis of HPE.