The Roles of Pax6 in Development of the Ocular Lens

Abstract

Purpose:: The Pax6 transcription factor is essential for the development of the eye as well as the CNS, pancreas and olfactory system. With complete loss of Pax6, eyes fail to develop, while when only one copy of the gene is disrupted, severe ocular abnormalities are observed. In the mouse these abnormalities include microphthalmia, aniridia and cataracts.The proper development of the ocular lens depends on Pax6 activity and normal dosage of expression. Pax6 is detected in the Lens Epithelium cells throughout development. Previously, using the Cre/loxP approach we have demonstrated that Pax6 is required within the surface ectoderm for the formation of the lens placode. In the current study we further explore the role of Pax6 at subsequent stages of lens development, after the lens vesicle has formed.

Methods:: The Cre/loxP conditional knock-out approach was employed to delete the Pax6specifically from the lens subsequent to the lens vesicle stage. Specific Cre expression in the lens was achieved by employing the Mrl10-Cre transgenic mice, in which a Pax6 consensus binding site and the alphaA-crystallin promoter are used to regulate Cre expression.

Results:: A Dramatic change in lens size and morphology was observed in the Pax6^flox/flox;Mrl10-Cre mice. These changes in the lens were further characterized in respect to morphological, cellular and molecular changes.Pax6 was ablated from the Pax6^flox/flox;Mrl10-Cre embryos during mid-gestation. The loss of Pax6 resulted in a number of abnormalities that differed according to the differentiation stage of the mutated lens-cell. Lens epithelial cells that are devoid of Pax6 fail to exit cell-cycle and to differentiate into fiber cells. In addition, Pax6 promotes survival of lens epithelial cells, as mutant animals showed increased levels of apoptosis and a severe decrease in lens size.

Conclusions:: Our findings expose novel roles for Pax6 in regulation of cell cycle exit, for the survival of lens epithelium and for proper differentiation of the lens fibers.

Keywords: development • differentiation • genetics