Smoothened Is Expressed But Not Required During Lens Development

Abstract

Purpose: : We previously showed that constitutive activation of the Wnt/β-catenin pathway (Catnb^Ex3/Cre^Mlr10) results in abnormal patterns of epithelial proliferation and differentiation in embryonic lens (Martinez et al., 2009, IOVS, 4794-4806). Preliminary expression profiling of these lenses, using Affymetrix arrays, indicated altered expression of Hedgehog signalling pathway components, including Smo, Ptch1, Fused, Sufu, and Gli3 but no change in Gli1 and Gli2. In this study we examined expression of Hh pathway components in wild-type (Wt) and Catnb^Ex3 mutant lenses and investigated the consequences of deleting Smo during lens differentiation.

Methods: : Hh pathway gene expression was examined by RT-PCR, immunofluorescence and quantitative PCR arrays. Smo was deleted in embryonic mouse lenses by crossing Smo^fl/fl mice with LeCre, MLR10 and MLR39 Cre deletor mice. Lens phenotype was investigated by histology, BrdU labelling, TUNEL, immunofluorescence and RT-PCR.

Results: : By RT-PCR, distinct expression of Smo, Ptch1 and Gli3 were detected in both Wt fibres and epithelium; Gli1 and Gli2 were variably detected with Gli1 being weakly detected in epithelium only. By immunofluorescence Ptch1, Smo, Gli2 and Gli3 are expressed in lens from E12.5. Ptch1 and Smo become restricted to the epithelium and equator from E13.5-P21, but Gli2 and Gli3 persist in epithelial and fibre cells. These expression patterns were disrupted in Catnb^Ex3/Cre^Mlr10 lenses, particularly in aberrantly differentiating cells in the fibre compartment; moreover, expression level of Gli3 was reduced in Catnb^Ex3/Cre^Mlr10 lens. Real-time PCR analyses indicated significant down-regulation of Hh pathway components (Smo, Ptch1, Gli1, Gli2 and Gli3) in Catnb^Ex3/Cre^Mlr10 lenses compared to Wt. Conditional deletion of Smo in lens from E12.5 had no observable effects on lens development.

Conclusions: : These data indicate that Hh pathway genes are present in lens and are modulated by Wnt/β-catenin signalling. It is likely that the Hh pathway is normally kept inactive, possibly via Ptch1 and high expression of Gli3 repressor. Smo and Hh signaling is not essential for lens differentiation.

Keywords: growth factors/growth factor receptors • transgenics/knock-outs • development