NONUNIFORM DISTRIBUTION OF CELL-PROLIFERATION IN THE ADULT TELEOST RETINA

Teleost fish continue to grow throughout life, and their eyes enlarge correspondingly. Within the eye, the retina grows by stretching existi ng tissue and adding new cells. Cell addition occurs in two ways: Firs t, all cell types except rod photoreceptors are added circumferentiall y at the edge of the eye where the retina meets the iris; second, rod photoreceptors are generated from a population of rod progenitor cells which divide throughout the outer nuclear layer (ONL). To determine t he spatial distribution of rod progenitor cells across the teleost ret ina, we labeled dividing cells with an antibody to proliferating cell nuclear antigen (PCNA) throughout a 24 h period. We found a significan tly higher density of dividing rod precursor cells at the nasal and te mporal margins than in the central retina throughout the 24 h cycle. A t night, the density of dividing cells is significantly greater at the nasal pole of the eye. The difference between cell division at the ce nter and the margin was reduced at night when the density of cell divi sion in the central retina increased significantly. Taken together, th ese data suggest that the eye grows asymmetrically, with more cells ad ded at the nasal pole. Possible developmental causes and functional co nsequences of the reported distribution of cell divisions in time and location are presented.