Unscheduled DNA synthesis assay in mammalian spermatogenic cells: An update

The unscheduled DNA synthesis (UDS) assay measures DNA repair in response t o DNA damage. To date, 59 chemicals plus UV and X rays have been tested for UDS in spermatogenic cells of humans, rabbits, rats, and mice. In vivo, in vitro, and combined in vivo/in vitro procedures have been used. UDS has be en shown to occur in spermatogonia, meiotic spermatocytes, and early sperma tid stages. Fifty-nine percent of the agents tested gave a positive UDS res ponse in one or more germ-cell stages. Results show 95% concordance (positi ve or negative) between different mammalian species. Some well-known genoto xic chemicals, for example, aflatoxin B-1 (AFB(1)), benzo[a] pyrene (B[a]P) , and N-methyl-N'-nitro-Nnitrosoguanidine (MNNG), did not induce significan t levels of UDS. Possible explanations are discussed. Results From the UDS assay were compared with those from the mouse specific-locus mutation (SLM) test to determine correlations between the two assays. Only two chemicals, ethyl- and methyl-nitrosourea (ENU and MNU), have been tested for UDS and SLM induction in spermatogonial stages. Results show full concordance betwe en the two assays. In postspermatogonial stages, 25 chemicals and X rays ha ve been tested for UDS and SLM induction. Seventy-seven percent of these ag ents showed similar results (positive or negative) in these germ-cell stage s. Although the UDS assay cannot replace the SLM test, the strong correlati ons between the two assays suggest the usefulness of the UDS assay as a pre dictor of germ-cell mutations in mammalian systems. Environ. Mol. Mutagen. 36.255-265, 2000. Published 2000 Wiley-Liss, Inc.dagger