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E Sage, Q Yan, D Blake, JI Clark; Expression of SPARC in Murine Lens . Invest. Ophthalmol. Vis. Sci. 2002;43(13):3551.
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Purpose: To study the distribution of SPARC (secreted protein acidic and rich in cysteine) in the murine lens. SPARC has been shown to be an essential factor in the development and maintenance of lens transparency in mice because all SPARC-null mice begin to form cataract within 1 month after birth. It is therefore important to identify the localization and cellular expression of SPARC in the murine lens. Method: Immunohistochemistry and immunoblot analyses were conducted on murine lens capsule and on lens cells from E14 to 2 yr; steady-state levels of SPARC mRNA in lens cells were determined by RT-PCR. Results: Lens epithelium produced abundant SPARC as early as E14; the protein remained at high levels up to 2 yr of age. By immunohistochemistry and RT-PCR, the lens fiber cells at the equator were shown to contain SPARC, but not the secondary fibers located inside the bow region. The lens capsule did not contain SPARC. SPARC protein was also identified in the vitreous. Proteolytic cleavage of SPARC was not observed in the lens. Conclusion: SPARC is present mostly in the lens epithelium, where expression is stable up to 2 yr of age. Recently-differentiated secondary lens fibers also synthesized SPARC. These findings implicate SPARC in the maintenance of the functions and activities of lens epithelial cells. The lack of SPARC in the lens capsule predicts that SPARC acts as a regulator of the deposition of other ECM proteins in the lens basement membrane rather than its subserving a structural role in the lens capsule. Supported by F32EY06987 to QY, and EY13180.
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