Abstract
Purpose: :
Mutations in FOXC1, a member of the fox family of transcription factors, cause Axenfeld–Rieger Syndrome (ARS) in humans. ARS is a congenital disorder affecting development of the eye, teeth and abdomen. The eye phenotype is an anterior segment dysgenesis, with about half of the patients developing glaucoma. FoxC1 knockout in mice cause congenital hydrocephalus, eye defects and skeletal abnormalities. In zebrafish, foxC1 is duplicated and the two genes are called foxC1.1 and foxC1.2. Because zebrafish have many experimental advantages for assessing complex genetic interactions and gene function during development, we have examined the expression and loss–of–function phenotypes for foxC1.1 and foxC1.2 in this model organism.
Methods: :
In Situ hybridization was used to determine the expression patterns of foxC1.1 and foxC1.2 during zebrafish ocular development. Anti–sense morpholino oligonucleotides which block translation were used to knock–down activity of foxC1 genes independently and together. Following knock–down, phenotype analysis was conducted using histology and cell markers. Time–lapse confocal microscopy was used to investigate neural crest cell migration to the periocular mesenchyme and hyaloid vascular phenotypes in the foxC1 morphants.
Results: :
Within the head region, foxC1.1 and foxC1.2 are expressed in the developing brain, branchial arches, periocular mesenchyme, and hyaloid vasculature in a manner similar to mammals. Loss–of–function analysis indicated that foxC1.1, but not foxC1.2 showed developmental defects. Phenotypes included hydrocephaly, small eye, and vascular and skeletal defects. Vascular defects involved central nervous system hemorrhaging and dysmorphogenesis of the hyaloid vessels. Time–lapse studies showed that neural crest cells migrated normally to periocular regions, although cellular differentiation of these cells was disrupted. Currently we are investigating the regulation of putative FoxC1 target genes using the zebrafish model.
Conclusions: :
By examining expression patterns and loss–of–function phenotypes, we have found that FoxC1 plays a similar role in the development of zebrafish as compared to mammals. These findings demonstrate the utility of the zebrafish in mechanistic studies of this human disease causing gene.
Keywords: proteins encoded by disease genes • gene/expression • transcription factors