DNA STRAND-BREAK REPAIR IN REGRESSING AND DEVELOPING CHICK-EMBRYO MULLERIAN DUCTS

DNA strand-break repair was studied in an organ that regresses completely (the male Mullerian duct of the chick embryo), using the alkaline sucrose gradient method. It was found that DNA of the regressing ducts had the same sedimentation pattern as that of the developing ducts. Single-strand-break rejoining occurred in both kinds of ducts. Repair efficiency was diminished only when extensive DNA degradation was induced experimentally. High temperatures (43°C) did not modify the sedimentation profiles but repair at low temperature (0°C) resulted in the formation of an intermediate peak which was situated between the peak of the nonirradiated high-molecular weight DNA and that of the irradiated high-molecular weight DNA. The absence of DNA degradation and the presence of DNA single-strand-break repair in the regressing male Mullerian duct support the idea that aging and organ regression are different processes.