Journal of Cell Science, Vol 89, Issue 2 263-272, Copyright © 1988 by Company of Biologists

JOURNAL ARTICLES

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

JD Chen and FH Yew
Department of Zoology, National Taiwan University, Taipei, Republic of China.

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).