THE EFFECT OF LOW TEMPERATURES ON THE SURVIVAL AND DEVELOPMENT OF FROG EMBRYOS IN THE FROG EMBRYO TERATOGENESIS ASSAY - XENOPUS (FETAX)

Abstract

This work assessed the developmental potential of the embryos of the South African Clawed Frog Xenopus laevis at a variety of low temperatures in a standard 96-hour static renewal test system. The purpose was to determine the lowest temperature and the maximum length of time at that temperature to which the embryos could be exposed (exposure times of 3, 24, 48, 72 and 96 hrs.) with minimal mortality and malformation values. Embryonic stage development and metabolic functions are related to and controlled by varying temperature levels and are easily monitored under controlled laboratory conditions. The temperature at which 50% of the tested population could not survive (LT50) and no observable adverse effect level (NOAEL) were calculated in a range-finding study (5°, 10° and 15°C) to determine the narrower temperature range (7°C and 9°C) used in the later definitive study. Nonparametric statistical tests were used to compare results from the five temperature experiments. The lower temperatures of 5°C and 7°C tested produced mortality and malformation results greater than 50% in both categories. Mortality rates of embryos exposed to 9°C were significantly greater than mortality rates of control embryos except for the 3 hr. exposure group. Although the mortality and malformation rates for the control groups at 10°C were greater than values acceptable in a standard FETAX study, a comparison of control and exposed embryos did not show significant differences at most exposure times. However, it is not clear whether the rate of development at 10°C is delayed enough to allow embryos to be shipped or stored. Further research with more control of embryo culture production and testing variables is needed to establish a final protocol and validate test results.