O6-alkylguanine-DNA alkyltransferase in the chick embryo during development.

In the whole embryo, O6-alkylguanine-DNA alkyltransferase (AT) activity increased until day 9 of development and declined sharply after day 13. AT activity of the liver was greatest between day 12 and day 20 and decreased fast after hatching. In the brain, AT activities reached a maximum at day 17 and 18 and declined sharply after hatching. At two developmental stages with different AT activities (day 10 and day 17) DNA alkylation in the brains was estimated 6, 12, 24 and 48 h after administration of N-methyl-N-nitrosourea in ovo by viscometric measurement of DNA fragmentation. The high AT activities of the chicken embryo brain at the 17th day of development correlated with minor DNA fragmentation following a repair period of 12-24 h. It is suggested that the high basal level of AT in the chick embryo might have a protective function against the persistence of the genotoxic lesion O6-methylguanine during development.