A Radioautographic Study of the Utilization of Deoxycytidine for the Formation of Deoxyribonucleic Acid-Thymine in Lymphocytes

Incorporation of Pyrimidine Nucleosides in Lymphoid Tissues of the Mouse Using 5-Fluorodeoxyuridine and [5-3H]Deoxycytidine

“…Furthermore, it has been shown that the ratio of radioactivity of thymine to that of cytosine in newly synthesized DNA is different among lymphoid tissues; this value in the thymus being higher than that in mesenteric lymph nodes (2,11,12). Thus, it is probable that the differences in labeling intensity between lymphocyte populations may be related to their different capacity for converting CdR to thymidine monophosphate (dTMP) and then utilizing the dTMP for DNA synthesis (1,2,12,17,18,22). Such a hypothesis has not been adequately tested ; much less have the reasons been explored which might account for the differences in the incorporation of radioactive DNA precursors by different lymphoid cell populations.…”

“…In the thymic cortex and germinal centers of mesenteric lymph nodes, however, radioautographic reactions showed more intense labeling with [G-3H] Although mitotic analyses consistently reveal high rates of cell division in the thymic cortex and germinal centers of rats and mice (1,4,5,9,10), the cells in these areas are characterized by weak labeling with tritiated thymidine ([3H]TdR), whereas lymphocytes outside these anatomical regions of the same organs are labeled intensely with the same nucleoside (1, 6-10, 12, 18, 25). Recently, tritiated deoxycytidine ([3H]CdR) or radioiodine-labeled 5-iodo-2'-deoxyuridine has been used as a substitute for [3H]TdR to study lymphocyte production (1,2,12,14,(16)(17)(18)(19)(20)(21)23). Radioautographs revealed that lymphocytes in the thymic cortex and germinal centers were much more heavily labeled with generally tritiated deoxycytidine ([G-3H]CdR) than with [3H]TdR, whereas outside the germinal centers labeling was far more intense * present address:…”

“…Recently, tritiated deoxycytidine ([3H]CdR) or radioiodine-labeled 5-iodo-2'-deoxyuridine has been used as a substitute for [3H]TdR to study lymphocyte production (1,2,12,14,(16)(17)(18)(19)(20)(21)23). Radioautographs revealed that lymphocytes in the thymic cortex and germinal centers were much more heavily labeled with generally tritiated deoxycytidine ([G-3H]CdR) than with [3H]TdR, whereas outside the germinal centers labeling was far more intense with [3H]TdR than with [G-3H]CdR (1,12,18).…”

THE USE OF DEOXYCYTIDINE LABELED WITH TRITIUM IN THE 5-POSITION FOR AUTORADIOGRAPHIC STUDY OF LYMPHOCYTES <i>IN VIVO</i>

“…This has been attributed to the ability of these cells to utilize deoxycytidine (dCyd), which circulates in a considerable amount (8), for the formation of DNA-thymine (2,3,9). Previous studies have revealed that thymus cells in the cortex and germinal-center cells of the lymph nodes are much more intensely labeled with 3HdCyd than with 3HdThd (1,5,6). In these studies, [G-3H]dCyd (generally labeled) was used so that the label might be transferred to thymine of DNA.…”

“…The majority of thymic lymphocytes (thymus cells), particularly those in the cortex, poorly label with [3H]thymidine (3HdThd) in vivo, although they rapidly divide (1,5,6,10). This has been attributed to the ability of these cells to utilize deoxycytidine (dCyd), which circulates in a considerable amount (8), for the formation of DNA-thymine (2,3,9).…”