BIRTH AND FATE OF PROLIFERATIVE CELLS IN THE INNER NUCLEAR LAYER OF THE MATURE FISH RETINA

In teleost fish, unlike other vertebrates, the retina continues to gro w throughout the animal's life both by stretching of the mature tissue and by the addition of new cells. Following larval development, new r etinal cell birth is known to occur in a rim at the periphery of the m ature retina and in the outer nuclear layer (ONL). We have now found t hat cell birth and proliferation also occurs in the inner nuclear laye r (INL) of the mature fish retina. In rainbow trout (Onchoryncus mykis s), proliferative cells exist in the INL of fish of all ages, at least up to 2 years posthatching. The proliferative cells form clusters in the INL that align in radial columns, reaching from the inner to the o uter plexiform layers. The density of proliferative cell clusters chan ges along the equatorial plane of the retina and is highest near both the nasal and temporal poles. Our data suggest that, after birth, the proliferative cells migrate away from the INL and into the ONL, with a half-time of about 3 days, and their cell bodies can be seen in the o uter plexiform layer. Once they are in the ONL, the proliferative cell s continue to divide and likely give rise to the precursor cells that differentiate into new rod photoreceptors. (C) 1998 Wiley-Liss, Inc.