DNA replication and repair of Tilapia cells. II. Effects of temperature on DNA replication and ultraviolet repair in Tilapia ovary cells

Abstract

TO-2 is a fish cell line derived from the Tilapia ovary. It grows over a wide range of temperature (15–34 degrees C). While most fish cells lack DNA excision repair and are hypersensitive to ultraviolet light (u.v.), Tilapia cells are more u.v.-resistant than mammalian cells. In this paper we report the effects of temperature on DNA replication and u.v. repair in TO-2 cells. When the cells were moved from 31 degrees C to the sublethal high temperature of 37 degrees C, the rate of DNA synthesis first decreased to 60%, then speedy recovery soon set in, and after 8 h at 37 degrees C the rate of DNA synthesis overshot the 31 degrees C control level by 180%. When moved to low temperature (18 degrees C) Tilapia cells also showed an initial suppression of DNA synthesis before settling at 30% of the control level. u.v. reduced but could not block DNA synthesis completely. The inhibition was overcome in 3 h at 37, 31 and 25 degrees C, but not at 18 degrees C. Initiation of nascent DNA synthesis was blocked at 4 J m-2 in TO-2 cells compared with less than or equal to 1 J m-2 in mammalian cells. After 9 J m-2 u.v. irradiation, low molecular weight DNA replication intermediates started to accumulate, and they could be chased into high molecular weight DNA with little delay. TO-2 cells showed low levels of u.v.-induced excision repair; but this was prominent compared with other fish cells. The u.v.-induced incision rate has been measured at various temperatures, and the activation energy of incision estimated to be 13 kcal mol-1 (1 cal approximately equal to 4.184 J).