Protein expression patterns for ubiquitous and tissue specific calpains in the developing mouse lens

Calcium activated proteases (calpains) have been implicated in the processing of lens crystallins during lens maturation and cataract formation. Ubiquitous type calpain 2 and calpain 10 and lens specific Lp82 and Lp85 protein distribution were determined using immunohistochemistry and immunoblotting in embryonic and post-natal mouse eyes. Calpain 2 was first expressed late in embryonic development and localized to the lens epithelium and transition zone. Lp82 was expressed at E9·5 in the lens placode, head ectoderm, and throughout the fiber cells during embryonic lens maturation. Lp82 co-localized at sites of crystallin modification in the juvenile lens. In the adult lens, Lp82 protein was maintained in cortical fibers but could not be detected in the lens nucleus. Lp85, the slightly larger splice variant of Lp82, was first observed at E9·5 and throughout early embryonic lens development. Abundant localization of this enzyme was observed in the cell nuclei of lens epithelium, elongating fibers, and undifferentiated mesoderm. Robust peri-nuclear localization of calpain 10 was observed in the head ectoderm, lens placode, and optic vesicle during early eye induction. Further, calpain 10 protein was maintained in the lens epithelium of pre- and post-natal lens. These data support the hypothesis that Lp82 in rodent lens has an important role in crystallin proteolysis during normal lens maturation. In contrast, calpain 2, Lp85, and calpain 10 may have roles in cell signaling pathways.