Abstract
Purpose: :
To characterize and understand the regulation of lens fiber cell EPPD (ezrin, periplakin, periaxin, desmoyokin) cytoskeletal complexes.
Methods: :
Distribution of the EPPD complex proteins and of Periaxin in particular, was evaluated in developing and postnatal lenses by immunofluorescence, immunogold and immunoblot analyses. To understand the interaction of periaxin with cytoskeletal proteins, periaxin organization was evaluated in Rho and Rac GTPase targeted developing mouse lenses.
Results: :
Periaxin revealed a distinct expression profile in the lens. Firstly, periaxin exhibited a uniquely lens-preferred expression profile relative to various tissues of the eye and brain, and relative to the other EPPD complex proteins assessed in the current study. Secondly, periaxin exhibited a distinct expression profile during lens development, with the expression level increasing dramatically in differentiating lens fibers as the lens posterior vesicle starts differentiating into the lens fibers, together with a concomitant decrease in expression levels in the lens anterior vesicle. Finally, periaxin distribution is predominantly fiber-specific in the neonatal and postnatal lenses, resembling the distribution profile of the MIP-26 protein. Moreover, periaxin exhibits a membrane-specific distribution within lens fibers, being enriched primarily in the detergent (Triton X-100) insoluble fraction. Periaxin co-distributes with actin cytoskeleton and spectrin, and in equatorial lens sections, reveals a distribution similar to that of membrane-bound and cell junctional proteins. Periaxin distribution was disrupted in the Rho GTPase targeted lenses, with no significant changes in Rac1 targeted lenses. Ongoing studies are focused on characterizing the periaxin null mouse lens.
Conclusions: :
Periaxin, a dystroglycan-interacting and PDZ domain protein originally identified in myelinating Schwann cells, exhibits a uniquely lens-preferred expression pattern among the various tissues of the eye. Moreover, periaxin shows a distinct upregulation in the differentiating lens fibers with concomitant downregulation in the lens epithelium in the differentiating lens with preferential localization to the cell membrane and cytoskeletons. These preliminary observations indicate a potentially important role for periaxin in lens fiber cell differentiation,structure and function.
Keywords: cytoskeleton • differentiation • development