Ultrastructure and acid phosphatase activity in hereditary cataracts of deer mice

Lenses of cataract-webbed (cw) Peromyscus maniculatus were examined by electron microscopy and compared to age-matched normal deer mouse lenses. Precataractous lenses of offspring of cw/cw matings were examined and compared to early cataract development in the opposite eye of the same animal. The earliest ultrastructural change leading to disturbance of lens transparency was cell fusion and formation of fiber cell syncytia in the posterior subcapsular region. Fiber cells lost their regular hexagonal packing. Small osmiophilic densities on the plasma membrane coincided with many of the sites of cell confluency. Larger osmiophilic whorls were usually localized in ball-and-socket interlocking junctions after the opacity spread. Epithelial cells from the nasal ventral equator migrated to the posterior pole. Later when underlying cortical fibers ruptured, the migrated cells phagocytized lens proteins and incorporated them in acid-phosphatase positive lysosomes. Fiber cells 3 to 20 layers deep in the cortex of normal and cataractous lenses had acid phosphatase reaction product coating the plasma membrane; the possible significance of this finding is discussed. We postulate that this hereditary cataract results from a defect in turnover and control of plasma membrane components.