Quantitative analysis of activated caspase-3-positive cells and a circadian cycle of programmed cell death in the adult teleost retina

In adult teleosts, it has been shown that germinal cells proliferate in the marginal retina. Daughter cells also die in this region but the details of their death, presumably by programmed cell death (PCD), are not fully known. In this study, we labeled cells undergoing PCD in the adult goldfish retina by an antibody to activated caspase-3. Most of the activated caspase-3-positive cells (caspase-3+ cells) were found at the primary growth zone in the retinal margin, 80-140 mu m from the circular blood vessel, where their density was 518 +/- 65.3 cells/mm(2) of the retinal surface (mean +/- S.D., n = 3) at midday and 395 +/- 47.4 cells/mm(2) (n = 3) at midnight. Although the local densities of caspase-3+ cells in the primary growth zone in the day and night-time were significantly different, the mean densities of caspase-3+ cells in the retinal margin as a whole remained constant at 185 +/- 29.7 cells/mm(2) (n = 16) during most of the day and night-time. However, immediately after light onset in the morning, the density of caspase-3+ cells in the retinal margin increased by 30%. This transient increase was also seen at the same objective time in goldfish that were kept in the dark for the entire day. Our quantitative study demonstrates that PCD in the marginal retina of the adult goldfish is induced in some parts by a caspase-3-dependent pathway and that it is also regulated by a circadian mechanism. (C) 2008 Elsevier Ireland Ltd. All rights reserved.