CELL-MOVEMENT AND CELL-CYCLE DYNAMICS IN THE RETINA OF THE ADULT TELEOST HAPLOCHROMIS-BURTONI

The authors analyzed the pattern of neurogenesis, the time frame of ce ll movement, and the cell cycle kinetics of a population of stem cells located in the outer nuclear layer in the retina of the adult teleost Haplochromis burtoni. These stem cells continue to give rise to new r od photoreceptors throughout life. The new rods move vitread after the last cell division. The authors investigated events during cell divis ion and cell differentiation by using one marker that labels dividing cells transiently (proliferating cell nuclear antigen) along with anot her marker that labels dividing cells permanently (bromodeoxyuridine). The bulk of cell movement does not occur within 24 hours after S-phas e labeling but is clearly underway 12 hours later, shortly after mitos is. The cell cycle length was estimated to be approximately 25 hours. The distribution of labeled cells at various times after S-phase sugge sts that new rods are generated by asymmetric cell division, that is, one of the daughter cells moves after mitosis and becomes postmitotic, while the other daughter cell remains in place and reenters the cell cycle. The proliferation patterns across the retina suggest that the l ocation of areas of mitotic activity changes over time. The authors hy pothesize that local extracellular factors control the rate of cell di vision in a given area, thereby keeping the overall rod density consta nt. (C) 1997 Wiley-Liss, Inc.