Critical functions for ocular gap junctions have been elucidated by the discovery of cataract causing mutations in human lens connexin genes. Since the lens is an avascular cyst, gap junction channels allow cells in the interior of the organ to gain access to metabolites absorbed at the surface from the aqueous humor. This metabolite exchange maintains the precise intracellular ionic conditions necessary to prevent precipitation of the crystallins and subsequent cataract formation. This idea is further supported by the observation that mice with targeted deletions of lens connexins also develop cataracts, thus providing animal models for the human pathology. One of the most difficult remaining challenges is to uncover the mechanisms whereby connexin gene disruption leads to pathological changes and vision loss. The long term goal of this application is to precisely define which cellular functions require gap junctional communication and to understand how the diversity in gap junctional structural proteins influences intercellular communication in ocular tissues. Experiments are outlined which are designed to explore why the elimination of connexin diversity, but not intercellular communication, leads to microphthalmia and cataracts in connexin50 (Cx50) knockout mice. In a second specific aim, experiments are designed to utilize transgenic technology to eliminate multiple connexins in the lens, so that lens development and function in the absence of gap junctional communication pathways can be studied. In a third aim, the generation of 'knock-in' animals where one connexin has been replaced by another is proposed to discriminate whether phenotypes result simply from differential decreases in the absolute numbers of intercellular channels in the different knockout models, rather than a loss of connexin diversity. In a final aim, Connexin diversity in the retina will be explored by functionally analyzing an entirely new class of connexin genes that are preferentially expressed in retinal neurons.
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