Cre–Mediated Deletion of AP–2 in the Developing Retina Reveals Intrinsic Role for AP–2 in Retinogenesis

Abstract

Abstract: : Purpose: We have previously shown that AP–2α has specific roles in development of the lens placode and its derivatives. AP–2α also has a distinct expression pattern in the developing retina and AP–2α null mice exhibit defects in the developing optic cup. In the following study we have created a conditional deletion of AP–2α in the developing retina in order to investigate its specific requirement in retinogenesis. Methods: The Cre–loxP system was used to conditionally delete AP–2α in the developing retina. Mice with the AP–2α gene flanked by two loxP sites were crossed with a transgenic line expressing retina–specific Cre recombinase (Ret–Cre), resulting in Ret–AP–2α mutants. Histology and immunohistochemistry were used to compare the retinal phenotype of adult Ret–AP–2α mutants and their wild–type littermates. These phenotypes were also compared to that of full AP–2α null mice and mice in which AP–2α has been deleted in the lens (Le–AP–2α mutants) in order to discern the intrinsic versus secondary effects of AP–2α deletion on the developing retina. Results: PCR confirmed the specific deletion of the AP–2α gene in the mutant retinas. However some AP–2α expression remained, yet substantially reduced, in the mutant retina. Like wild–type littermates, the Ret–AP–2α mutants exhibited a laminated retina with all layers intact. However, these layers were reduced in thickness, particularly the inner nuclear layer and the optic nerve fiber layer. Interestingly, the Ret–AP–2α mutants did not exhibit the duplicated retina (and lack of retinal pigmented epithelium (rpe)) as observed in the full AP–2α null mice. The duplicated retina phenotype was also absent in the Le–AP–2α mutants and they did not exhibit alterations in retinal layer thickness as observed in the Ret–AP–2α mutants. Conclusions: Comparison of the retinal phenotypes of the different AP–2α mutant models indicates a specific requirement for AP–2α in retinogenesis that can be further explored by detailed analysis of the Ret–AP–2α mutants. The fact that both retinal and lens–specific deletions of AP–2α did not result in the optic cup defects (loss of rpe) observed in the full AP–2α mutants suggests that the loss of AP–2α in other tissues contributing to the developing eye, such as the neural crest, may be responsible for this phenotype.

Keywords: retinal development • transgenics/knock-outs • transcription factors