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Stimulation of Lens Cell Differentiation by Gap Junction Protein Connexin 45.6

From the Department of Biochemistry, University of Texas Health Science Center San Antonio, San Antonio, Texas.

PURPOSE. The present study was undertaken to explore the roles gap junctions play in lens epithelial cell differentiation.

METHODS. Recombinant retroviruses expressing three chick lens connexins (Cx)—Cx43, Cx45.6, and Cx56—were prepared and used to infect isolated chick lens primary cultures. The expression and distribution of proteins was determined using immunoblots and confocal immunofluorescence microscopy. Intercellular couplings were assessed by single cell microinjection and scrape-loading dye transfer, and cell proliferation was evaluated by [³H]thymidine labeling.

RESULTS. Of the three lens connexins, only the cultures overexpressing exogenous Cx45.6 displayed the advancement of lens epithelial–fiber cell differentiation. The lentoids, a unique morphologic structure that is an indicative of lens fiber formation, were formed earlier in Cx45.6 overexpressed cultures; however, the rate of lens cell proliferation was not affected. The expression of the lens differentiation marker proteins, major intrinsic protein (MIP) and -crystallin, was also increased in Cx45.6-overexpressing cells. The cells overexpressing Cx45.6 displayed similar levels of intercellular couplings as did the controls. Moreover, exogenously expressed connexins were mostly colocalized with their endogenous counterparts and the overexpression of Cx45.6 had no impact on the expression of endogenous Cx43 and Cx56.

CONCLUSIONS. These results suggest that Cx45.6 plays an important role in stimulating lens cell differentiation and fiber formation, which is different from the other lens connexins, Cx43 and Cx56. This stimulatory effect is independent of gap junction–mediated intercellular communication and lens cell proliferation.

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