A 70,000 Mr membrane protein (MP70) has previously been identified as a specific component of lens intercellular junctions. In this paper we use anti-MP70 immunofluorescence microscopy of dissected fibre bundles to study the formation, distribution and dissociation of junctional plaques in the outer cortex region of the sheep lens. Abundant, small junctional plaques are assembled de novo in the broad sides of the elongating fibres near the equatorial lens periphery. In fully elongated, pole-to-pole fibres, junctional plaques are generally larger, and while dispersed on the broad sides of the fibres in the equatorial lens plane, these junctions line up in the middle of the broad and narrow sides of the fibres in the lens polar regions. This precisely defined positioning is independent of junction size and hence cannot solely be explained by the constraints of fibre width. Junctional plaques fragment to smaller sizes and MP70 is cleaved to MP38 in mature, enucleated fibres located in the deeper portions of the lens outer cortex. These results demonstrate a dynamic aspect of lens intercellular junctions and show that they are positioned in a precise fashion, possibly in association with other membrane or cytoskeletal components.

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