Meeting Abstract

P2.67  Thursday, Jan. 5  Diurnal Synchronization of the Cell Cycle in Aeolosoma (Annelida) BOWIE, Emily J.*; SMITH, Julian P.S.; Winthrop University; Winthrop University

In many organisms, the cell cycle is at least partly synchronized to a diurnal rhythm. At least two possible hypotheses have emerged to explain this. First, consigning sensitive portions of the cell cycle to periods of low aerobic activity may be one way of protecting the cell’s genetic material. A second hypothesis is that consignment of the sensitive portions of the cell cycle to the scotophase may be a way of reducing light-mediated DNA damage. In order to investigate these hypotheses further, we determined whether the cell cycle in Aeolosoma (a small, transparent annelid common in freshwater habitats) varies diurnally. If so, it might be expected that the stem cells present in Aeolosoma will divide more frequently at night than during the day. Aeolosomareproduces prolifically by asexual fission in culture, and has proven useful in our lab for studying stem cells and the mitotic cycle. Aeolosomawere cultured under a clock-shifted photoperiod of 12L/12D; with artificial noon being around 5:00PM. After the Aeolosomaacclimated to this new diurnal rhythm, they were killed by freezing, which provided a way to preserve any cells undergoing mitoses at the time of death. One group was frozen at relative 3:00AM (dark group) and the second group was frozen at relative 3:00PM (light group). Mitotic cells were labeled with anti-phosH3, the nuclei of the cells were stained with Hoechst 33342, and the cells undergoing mitosis were counted from confocal-laser-scanning microscope stacks. Mitoses were significantly (approximately 77%) higher in the dark group. These results show that the stem cells are more likely to undergo mitosis at night than during the day. Future studies will include more samples at different times to find the time of maximal mitosis, and include the use of EdU labeling to observe S-phase. Support for this research was provided by SC-INBRE II.