A Necessary Requirement for AP–2 in Normal Lens and Retinal Development as Indicated by a Lens–Specific Knockout of AP–2.

Abstract

Abstract: : Purpose: We have made use of a novel mouse strain possessing a conditional knockout of AP–2α in the developing lens which will allow for the determination of a specific role for AP–2α in the developing lens and retina. Methods: A strain of mice exhibiting lens–specific Cre–recombinase expression was crossed with mice possessing an AP–2α gene flanked by two loxP sites. Resultant mutant progeny (Le–AP–α) lacking AP–2α expression in the developing lens were compared with both wild–type and AP–2α null mice for expression patterns of downstream markers in both the developing lens and retina. The Le– AP–2α mutants were also bred onto the AP–2ß null background (Le–AP–α/ AP–2ß^–/–) to determine whether the AP–2α and AP–2ß genes participate together in establishing a threshold required for early lens induction. Results: Embryonic Le– AP–2α mice exhibit a lens stalk similar to the null mutants. However, unlike the AP–2α null mutants that die at birth, we can examine this phenotype into adulthood in the Le– AP–2α mice where we observe a persistent adhesion between the lens and the peripheral cornea. Pax6, PCNA and TUNEL staining appeared relatively normal in the mutant lens versus wild–type littermates. However FoxE3 mRNA expression while detectable appeared abnormal. Unlike the full null mutants, retinal lamination proceeded normally in the Le– AP–2α mutants and markers of retinal cell types were detected, including Brn3b. Le–AP–α/ AP–2ß^–/–mutants exhibit a similar lens phenotype to the Le– AP–2α mutants, however optic cup development was disrupted including partial loss of the RPE with replacement by neural retina. Conclusions: The Le–AP–α mutants exhibit an isolated lens stalk phenotype that will enable us to analyse the expression of potential downstream genes such as FoxE3 or Pitx3, as well as identify and isolate new targets. The fact that the Le–AP–α mutants do not exhibit the retinal defects which are apparent in the AP–2α null mice, suggests a likely intrinsic role for AP–2α in retinogenesis that we are further exploring. The Le–AP–α/ AP–2ß^–/–mice will provide a means for us to further examine the intrinsic and extrinsic role of these two AP–2 genes in lens and eye development.

Keywords: anterior segment • retinal development • gene/expression