Differential staining of Dugesia tigrina sister chromatids.

Planaria were cultured in a solution of bromodeoxyuridine (BrdU) for 24 h in an attempt to produce sister chromatid differential staining (SCD) and sister chromatid exchange (SCE). SCD was produced when planaria were cultured in planarian saline solution (PSS) containing 5 x 10(-5) M BrdU. Colchicine (0.02%) was added to the BrdU/PSS culture medium 8 to 10 h before sacrifice. Animals were then vigorously dissociated into cells, centrifuged, and fixed in Carnoy's solution. Slides were prepared using the air-drying method, allowed to age for at least 1 day, stained with the fluorochrome Hoechst 33258, exposed to high intensity incandescent light, stained with Giemsa solution, and mounted. This method is the first reported SCD/SCE investigation in the Platyhelminthes and consistently yielded second division metaphases exhibiting SCD and third division metaphases exhibiting non-reciprocal SCE's composed of unifilarly BrdU-labelled DNA.