PURPOSE

The similar lens phenotypes observed in mice with mutations in the genes encoding either Pax6 or AP-2alpha suggested that these transcription factors work together to regulate specific signaling cascades during lens development. In this study we examined the overlapping expression patterns of Pax6 and AP-2alpha in the developing mouse lens and further investigated their potential cooperative roles through the creation of double heterozygote mice.

METHODS

Colocalization of Pax6 and AP-2alpha expression patterns were performed on sections of mouse embryos at embryonic days 9.5, 10.5, 13.5, and 16 as well as on adult sections using immunofluorescence. To test the potential cooperation between these two transcription factors, two mouse strains heterozygous for the genes encoding either Pax6 or AP-2alpha were bred together to produce double heterozygous Pax6(+/lacZ)/AP-2alpha(+/-) mice. Histological examination was then performed on both embryonic and post-natal sections in order to compare double heterozygous Pax6(+/lacZ)/AP-2alpha(+/-) eyes to single heterozygote and wildtype eyes.

RESULTS

Examination of the developmental stages showed distinct colocalization of Pax6 and AP-2alpha protein in the anterior lens epithelium. However, Pax6 expression continued further into the transitional zone of the lens whereas AP-2alpha expression ceased just prior to the region where epithelial cells differentiate into fiber cells. Histological investigation of embryonic and post-natal mutant mouse eyes showed that while single Pax6 heterozygote mice exhibited remnants of a corneal-lenticular adhesion, the lens and cornea were physically separated. In contrast, the Pax6(+/lacZ)/AP-2alpha(+/-) double heterozygotes displayed a distinct lens stalk, which protruded towards the surface of the cornea, creating a direct corneal-lenticular attachment.

CONCLUSIONS

Colocalization of Pax6 and AP-2alpha was mainly observed in the proliferating central lens epithelium, the same region in which the lens stalk phenotype was observed in the double heterozygous Pax6(+/lacZ)/AP-2alpha(+/-) eyes. The more severe phenotype observed in these double heterozygous mice, as compared to the single heterozygotes, suggests that Pax6 and AP-2alpha may work synergistically to control lens development.