Heat shock affects cell cycling in the neural plate of cultured rat embryos: a flow cytometric study.

The effects of heat shock on cell cycling in the mammalian neuroectoderm were determined by applying heat shocks to cultured rat embryos at the neural plate stage, as part of a study on the teratogenic effects of heat shock on neural development. The heat shocks had been characterized previously (Walsh et al.: Teratology 36:181-191, 1987) with respect to their effects on the gross morphological development of the rat embryos. The effects on cell cycling were observed in DNA histograms of neural plate cells recorded in a flow cytometer after staining with DAPI. The mild heat shock (42 degrees C for 10 min) arrested cells at entry to S phase. The teratogenic heat shock (43 degrees C for 7.5 min) arrested cells at entry to S phase also but for a longer time and inhibited cycling through S phase. After each arrest, a synchronized peak of cells later entered S phase and progressed through the cycle. The induced-thermotolerance heat shock, which was the mild heat shock followed after an interval by the teratogenic heat shock, showed that pre-treatment with the mild heat shock reduced the magnitude of the response to the teratogenic heat shock. The cell-cycle inhibitor ICRF 159 showed the effects on cycling rates of the heat-shock treatments. The arrest of cells at entry to S phase by heat shock may function to prevent cells entering DNA synthesis under non-optimal conditions. We report estimates of proportions of non-proliferative cells in the neural plate of the rat embryos.