Graduate Thesis Or Dissertation
 

The influence of ionizing radiation, photoperiod, and environmental temperature on cell proliferation in the intestinal epithelium of the rough-skinned newt (Taricha granulosa)

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  • Kinetics of cell division in the intestinal epithelial proliferative cells (cell nests) of the rough-skinned newt, Taricha granulosa, were studied using tritiated thymidine autoradiography and the mitotic arresting properties of colcemid. Percent labeled mitoses (PLM) curves were drawn from the autoradiographic data from two separate experiments in which the newts were maintained at room temperature (22-23°C). In those experiments, groups of newts were intraperitoneally injected with tritiated thymidine at times ranging between 5 and 58 hours before they were killed. Each newt in both experiments was intraperitoneally injected with colcemid five hours before it was killed. Data from both experiments were very similar and the PLM curves were used to estimate cell cycle phase durations in the cell nests. The DNA synthetic phase was estimated to be 41 hours long and the sum of the G₂ phase duration and one-half the duration of mitosis was approximately seven hours. The duration of the entire cell cycle was considered to be longer than 100 hours and the duration of the G₁ phase longer than 50 hours. Extremely low mitotic indices in the intestinal cell nests of newts maintained at low environmental temperatures (4°C) and in newts which had been exposed to 1000 R X-irradiation precluded attempts to analyze the cell cycles in those animals. Studies were initiated, however, to characterize the effect of environmental temperature, photoperiod, and X-irradiation on the mitotic index of the cell nests. In two separate experiments, groups of newts acclimated to room temperature were killed, five hours after intraperitoneal injection with colcemid, at three-hour intervals over a 24-hour period. A diurnal periodicity in the mitotic activity within the intestinal cell nests was present; peak and nadir mitotic indices occurred in those animals killed in early afternoon hours and in early morning hours, respectively. An environmental temperature of 4°C with a light-dark cycle resulted in diminished mitotic activity in the intestinal cell nests. There was more than a two-fold difference between overall mitotic indices and the mitotic indices at room temperature. With an environmental temperature of 4°C and complete darkness, the overall mitotic index was nearly four-fold less than it was at the same temperature with a light-dark cycle.
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