Foxe3 is required for morphogenesis and differentiation of the anterior segment of the eye and is sensitive to Pax6 gene dosage

Abstract

The dysgenetic lens (dyl) mouse mutant has mutations in Foxe3, which inactivate DNA binding by the encoded forkhead transcription factor. Here we confirm, by targeted inactivation, that Foxe3 mutations are responsible for the dyl phenotype, which include loss of lens epithelium; a small, cataractic lens; and failure of the lens to detach from the surface ectoderm. In contrast to a recent report of targeted Foxe3, we found no phenotypic difference between dyl and Foxe3(-/-) mutants when congenic strains were compared, and thus nothing that argues against Foxe3(dyl) being a null allele. In addition to the lens, most tissues of the anterior segment-iris, cornea, ciliary body and trabecular meshwork-are malformed or show differentiation defects. Many of these abnormalities, such as irido-corneal and irido-lenticular adherences, are present in a less severe form in mice heterozygous for the Foxe3 mutation, in spite of these having an intact lens epithelium. Early Foxe3 expression is highly sensitive to a halved Pax6 gene dosage and there is a striking phenotypic similarity between Pax6 and Foxe3 mutants. We therefore propose that many of the ocular malformations associated with Pax6 haploinsufficiency are consequences of a reduced expression of Foxe3.

Pitx3 directly regulates Foxe3 during early lens development

“…Chromatin from mid-brain tissue of the same embryos was also precipitated with the Pitx3 antibody; it was used as a negative control to test the specificity of the assay, since Pitx3 and Foxe3 are not co-expressed in this area of the developing brain (Blixt et al, 2007, Medina-Martinez, 2012. PCR amplification in ChIP samples with Pitx3 antibody in comparison to the control antibody (goat-IgG) demonstrated a direct interaction of Pitx3 with the Foxe3 regulatory region in vivo (Fig.…”

“…All animals analyzed in this study; C57BL/6J wild-type, ak and Foxe3-/- (Blixt et al, 2007), were kept in the mouse facility of the Helmholtz Center Munich. Breeding and treatment of the animals were performed according to the German law for animal protection and institutional regulations.…”

Foxe view of lens development and disease

“…However, it is difficult to make a generalization, as the data on congenital primary aphakia are based on only one family. In addition, the direct comparison of human and mouse diseases is not a trivial task, as the phenotype of a disease in mice sometimes varies according to the genetic background of the strain (Blixt et al, 2006).…”

Eye-specific expression of an ancestral jellyfish PaxB gene interferes with Pax6 function despite its conserved Pax6/Pax2 characteristics

“…First, the present findings that the genes acting downstream of Pax6 during lens development encoding Mab2111, FoxE3, Prox1 and crystallins are reduced, while expression of Six3, Meis1 and Meis2, all genes upstream of Pax6, are unaffected in the lenses of the PaxB transgenic mice. Second, targeted disruption of FoxE3, whose expression critically depends on Pax6 (Blixt et al, 2007) results in lens defects resembling the phenotype of PaxB transgenic mice (Blixt et al, 2000;Medina-Martinez et al, 2005). Moreover delayed lens development in PaxB transgenic mice resembled the smaller lens pit or vesicle of Pax6 Sey/+ heterozygote and Pax6 ∆EE/ ∆EE mice (van Raamsdonk and Tilghman, 2000;Dimanlig et al, 2001).…”

“…Moreover, it is known that the early expression of FoxE3 and Mab21l1 is downregulated in Sey mice and therefore dependent on Pax6 gene dosage (Yamada et al, 2003;Blixt et al, 2007).…”