Formation of craniofacial structures relies on the correct spatiotemporal formation and migration of neural crest cells. This is frequently disrupted in craniofacial disorders, which accounts for one of the largest groups of birth defects. Two such birth defect syndromes, CHARGE syndrome and Brjeson-Forssman-Lehmann Syndrome (BFLS) have characteristic craniofacial phenotypes that are strikingly contrasting. CHARGE syndrome patients display reduced, dysmorphic facial bones. BFLS patients, in addition to cognitive defects, have characteristic broad faces, thickened calvarium, and excessive skin pigmentation, all indicative of excess neural crest derived structures. CHD7 haploinsufficiency is known to account for 60% of all CHARGE syndrome cases. CHD7 is an ATP-dependent chromatin remodeler, and studies in a wide variety of model organisms demonstrate reduction in neural crest cell formation upon CHD7 loss of function, supporting an evolutionarily conserved and necessary role of CHD7 remodeling activity in neural crest cell formation. We have identified a dual plant homeodomain (PHD) finger protein, PHF6, which physically associates with CHD7 in neural crest and neuroectodermal cells, precursors of developing neural crest cells. Loss-of-function mutations in PHF6 cause BFLS, suggesting that PHF6 loss may be involved in excessive neural crest formation. PHF6 is thought to be involved in transcriptional regulation, as other PHD domain proteins bind modified histone tails and often are able to influence transcription. However, the cellular and molecular activity of PHF6 remains largely unknown. This project will investigate the molecular mechanism by which PHF6 can influence development of the craniofacial structures, and establish a basis upon which we can discover how PHF6 mutation can cause BFLS. This project will also investigate (i) how PHF6 interacts with CHD7, and (ii) what the functional output of this interaction is. Better understanding of the molecular mechanisms by which these two syndromes occur will allow for new understanding of potential therapeutic approaches for these patients, and a better understanding of the etiology of craniofacial disorders as a whole.
Craniofacial disorders are among the most common birth defects, and the mechanisms by which they occur is often not well understood. Findings resulting from this proposal will lead to better understanding of two birth defect syndromes which have characteristic and opposing facial phenotypes, CHARGE syndrome and Brjeson-Forssman-Lehmann Syndrome, two devastating disorders where patients require lifelong care.
