Neuroblast of the grasshopper embryo as a new mutagen test system. II. Chromosome breakage induced by in vitro exposure of embryos to the direct-acting mutagens 4NQO, MNNG, adriamycin, and bleomycin.

The dose-response for the induction of acentric chromosome fragments was determined in neuroblasts of the grasshopper embryo (Chortophaga viridifasciata De Geer, Orthoptera: Acrididae) exposed in vitro to four direct-acting chemical known to be mutagenic, clastogenic, and carcinogenic: 4-nitroquinoline-1-oxide (4NQO), N-methyl-N-nitro-N-nitrosoguanidine (MNNG), Adriamycin (ADM), and bleomycin (BLM). After a 1-hr exposure followed by a 3-hr recovery period (untreated cell cycle time is 4 hr), acentric fragments were observed at doses down to 1 microM 4NQO, 1.25 microM MNNG, and 0.125 microM ADM and BLM. After an 8-hr continuous exposure, acentric fragments were induced by 4NQO at a dose as low as 0.125 microM. These low concentrations also reduced the number of dividing cells. No chromosome aberrations or mitotic effects were observed in untreated embryos or in those exposed only to the solvent dimethyl sulfoxide. Because of the short cell cycle and the sensitivity of the neuroblast to the induction of acentric chromosome fragments by chemical clastogens, a minimum of time is needed to perform the test. From a comparison with the prominent clastogen test systems currently used, it is concluded that the grasshopper neuroblast test is the fastest and that it detects some agents that some systems do not. Grasshoppers have a worldwide distribution. If neuroblasts of other species prove to be as sensitive to mutagens as those of Chortophaga, investigators in many countries would have available a eukaryotic mutagen test system that is simple, fast, reproducible, and inexpensive.