Roles of ß-Catenin in Retinal Development in Mouse

Abstract

Purpose:: ß-catenin (ß-catn) plays a central role in the cononical Wnt/ß-catn signalling pathway, as well as the planar cell polarity and cell-cell adhesion pathways. Wnt/ ß-cat pathway is shown to be important for the maintenance, proliferation and differentiation of the stem/progenitor cells in multiple tissues. Here, we investigate the role(s) of the wnt/ß-catenin pathway in retinal development in mouse.

Methods:: Retina-specific ß-catn conditional knockout (ko) mouse, α-Cre; ß-catn^flox/flox was created by crossing α-Cre mice (Marquardt et al. 2001), with ß-catn^flox mice (Huelsken et al. 2001). Eyes of conditional ko animals and wild type (wt) littermates were harvested at embryonic day (E) 14, E18 and/or postnatal day (P) 1 and P10. Proliferating progenitor cells were assayed by immunohistochemistry (IHC) with anti-PCNA antibody. Apoptosis was evaluated by TUNEL assay.

Results:: 1) The eyes of ß-catn conditional ko mice are significantly smaller than their wt littermates at P1-2 and P8-10; 2) The periphery of the retinas developed multiple rosettes in the ko mice, as early as E14 and progressed along the development. 3) PCNA-positive cells are significantly reduced in the periphery of the ko retina at both E14 (69.31+/-1.06 % in ko, 77.76+/-1.64 % in wt; n=4) and E18 (62.96+/-1.48 % in ko, 72.20+/-0.61 % in wt, n= 3); 4) The number of TUNEL positive cells is significant increased in the ß-catn ko retina when compared with wt littermates at P1 (145+/-23.68 in ko, 5.75+/-1.9/half section of retina in wt; n=4), although no significant difference at E14; 5) All mature retinal cell types exist in spite of inactivation of ß-catn.

Conclusions:: 1) Inactivation of ß-catn results in reduced proliferation of retinal progenitor cells and increased cell death in the ko retina; 2) inactivation of ß-catn disrupts the normal cell-cell adhesion and the laminar organization of the retina. This disorganization may have resulted in the failure of differentiating retinal neurons in making proper projections and synaptic connections and led to increased apoptosis in developing retinas at later developmental stage; 3) Inactivation of ß-catn may have no effect on the cell fate determination of the retinal progenitor cells.

Keywords: retinal development • transgenics/knock-outs • cell survival