The PDZ Protein, Dlg-1, is Required for Proper Lens Development in the Mouse Ocular Lens

Abstract

Purpose:: PDZ proteins, such as Dlg-1, are scaffolding molecules that function in cell polarity, proliferation, and adhesion. Our lab has explored the role of PDZ proteins in the lens using transgenic mouse models that express the viral oncoprotein, E6, a pan-dominant repressor of multiple PDZ proteins. These transgenic lenses show increased proliferation, defects in cell adhesion, polarity and differentiation. Though E6 is a powerful tool to understand the global function of PDZ proteins, there is still a need to understand the individual contribution of PDZ proteins in these processes. In this abstract, we address the role of Dlg-1 in lens development by utilizing mice with lens specific deletions of Dlg-1 throughout the lens beginning at the lens vesicle stage (achieved by mating to MLR10cre mice) or specifically in the lens fibers beginning at E12.5 (achieved by mating to MLR39cre mice).

Methods:: Lenses from neonate or P2 Dlg-1^+/+, Dlg-1^f/+;cre , Dlg-1^f/f;cre were embedded in paraffin and oriented longitudinally. Sections were stained for propidium iodide to label nuclei or immunostained for N-cadherin. BrdU incorporation assays were conducted to assess effects on cell cycle regulation. TUNEL analysis was conducted to monitor effects on apoptosis. Cryosections of lenses from these genotypes and developmental stages were stained with phalloidin to label filamentous actin.

Results:: Lenses from the Dlg-1^f/f;MLR10cre mice exhibited a disorganized bow region and inhibition of denucleation. N-cadherin was misorganized, especially in the regions of the posterior and anterior sutures, which correlated with actin disorganization. Increased number of BrdU positive cells was observed throughout the lens epithelium as compared to wildtype. Also, Dlg-1^f/f;MLR10cre showed increased TUNEL positive cells in both the epithelium and fibers. Dlg-1^f/f;MLR39cre recapitulated several Dlg-1^f/f;MLR10cre defects including abnormal organization of nuclei in the bow regions, inhibition of denucleation, failure to form sutures, altered organization of filamentous actin, and TUNEL positive cells in the secondary fibers.

Conclusions:: These data suggest that Dlg-1 may specifically contribute to numerous aspects of lens development including proper cell cycle regulation and the initiation of fiber cell differentiation. Furthermore, these data support a cell autonomous role of Dlg-1 in fiber cell maturation. A possible mechanism through which Dlg-1 affects these processes may be through the proper maintenance of cell adhesion linkages.

Keywords: development • cell adhesions/cell junctions • cytoskeleton