A long-lived thymidine pool in epithelial stem cells

Abstract

The labeling index (LI) of the individual basal cell positions of the anterior column of mouse tongue filiform papillae was assessed with time after an injection of [3H]TdR at 12.00 h (the minimum point in the circadian LI rhythm). An initial doubling of the LI in the stem cell zone due to cell division was followed, by a 2nd rise of 14-16% 16 h after injection and this occurred even in the presence of vincristine. Although the uptake of [3H]TdR and the initial LI doubling were largely prevented by a preceding injection of hydroxyurea, the 14-16% LI rise was still observed. The possible explanations are discussed, the favored one being that an average of 1 of the 6 or 7 cells (the stem cell) in each stem cell zone can store [3H]TdR in a long-lived precursor pool for at least 16 h before being utilized for DNA synthesis. This complements previously published work which suggested that on cell in each stem cell zone may selectively segregate DNA at mitosis.