Nuclear incorporation of radioactive DNA precursors and progression of cells through S. Combined radioautographic and cytophotometric studies on normal and leukaemic bone marrow and thoracic duct lymph cells of man.

Bone marrow blast cells of nine children with untreated acute leukaemia (five lymphoid, three myeloid, one monocytic), myeloid precursor cells of a haematologically normal child and thoracic duct lymph cells of a patient with sclerodermia were pulse-labelled in vitro with tritiated thymidine and/or tritiated cytidine. Combined radioautographic and cytophotometric techniques were used for the determination of the median nuclear size and the median grain count of labelled cells in different segments of S. It was found that the median grain count reached maximum values in the second or third quarter of S in all cell populations studied, and that the variation, during S, of the median grain count appeared to be independent of the median DNA synthesis times of the cell types investigated. In six cell populations a clear-cut inverse relation existed between the number and the median grain count of labelled cells in different segments of S. In three populations this relation was less apparent and in two it was not found at all.