Chromosome translocations in T-scripta: The dose-rate effect and in vivo lymphocyte radiation response

Using a whole-chromosome FISH painting probe we previously developed for ch romosome 1 of the yellow-bellied slider turtle (Trachemys scripta), we inve stigated the dose-rate effect for radiation-induced symmetrical translocati ons in T. scripta fibroblasts and lymphocytes. The dose rate below which no reduction in effect per unit dose is observed with further dose protractio n was approximately 23 cGy h(-1). We estimated the whole-genome spontaneous background level of complete, apparently simple symmetrical translocations in T. scripta lymphocytes to be approximately 1.20 x 10(-3)/cell projected from aberrations occurring in chromosome 1. Similar spontaneous background levels reported for humans are some 6- to 25-fold higher, ranging from abo ut 6 x 10(-3) to 3.4 x 10(-2) per cell. This relatively low background leve l for turtles would be a significant advantage for resolution of effects at low doses and dose rates. We also chronically irradiated turtles over a ra nge of doses from 0-8 Gy delivered at approximately 5.5 cCy h(-1) and const ructed a lymphocyte dose-response curve for complete, apparently simple sym metrical translocations suitable for use with animals chronically exposed t o radiation in contaminated environments. The best-fitting calibration curv e (not constrained through the zero dose estimate) was of the form Y-as = c + aD + bD(2), where Y-as was the number of apparently simple symmetrical t ranslocations per cell, D was the dose (Gy), a = (0.0058 +/- 0.0009), b = ( -0.00033 +/- 0.00011), and c = (0.0015 +/- 0.0013). With additional whole-c hromosome probes to improve sensitivity, environmental biodosimetry using s table chromosome translocations could provide a practical and genetically r elevant measurement end point for ecological risk assessments and biomonito ring programs, (C) 2001 by Radiation Research Society.