Human Molecular Genetics Advance Access originally published online on January 31, 2006
Human Molecular Genetics 2006 15(6):905-919; doi:10.1093/hmg/ddl008
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Functional interactions between FOXC1 and PITX2 underlie the sensitivity to FOXC1 gene dose in Axenfeld–Rieger syndrome and anterior segment dysgenesis
1Department of Ophthalmology and 2Department of Medical Genetics, University of Alberta, Edmonton, Alberta, Canada, T6G 2H7 and 3Department of Ophthalmology and Visual Sciences, University of Michigan, Ann Arbor, MI 48105, USA
* To whom correspondence be addressed. Tel: +1 7804923028; Fax: +1 7804926934; Email: fberry{at}ualberta.ca
Received December 19, 2005; Accepted January 27, 2006
Axenfeld–Rieger ocular dysgenesis is associated with mutations of the human PITX2 and FOXC1 genes, which encode transcription factors of the homeodomain and forkhead types, respectively. We have identified a functional link between FOXC1 and PITX2 which we propose underpins the similar Axenfeld–Rieger phenotype caused by mutations of these genes. FOXC1 and PITX2A physically interact, and this interaction requires crucial functional domains on both proteins: the C-terminal activation domain of FOXC1 and the homeodomain of PITX2. Immunofluorescence further shows PITX2A and FOXC1 to be colocalized within a common nuclear subcompartment. Furthermore, PITX2A can function as a negative regulator of FOXC1 transactivity. This work ties both proteins into a common pathway and offers an explanation of why increased FOXC1 gene dosage produces a phenotype resembling that of PITX2 deletions and mutations. Ocular phenotypes arise despite the deregulated expression of FOXC1-target genes through mutations in FOXC1 or PITX2. Ultimately, PITX2 loss of function mutations have a compound effect: the reduced expression of PITX2-target genes coupled with the extensive activation of FOXC1-regulated targets. Our findings indicate that the functional interaction between FOXC1 and PITX2A underlies the sensitivity to FOXC1 gene dosage in Axenfeld–Rieger syndrome and related anterior segment dysgeneses.
The authors wish it to be known that, in their opinion, the first two authors should be regarded as joint First Authors.
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