Autoradiographic Study on DNA Synthesis in Lymphoid Tissues of the Rat Using Tritiated Thymidine and Deoxycytidine

Abstract

Labeling patterns with generally labeled tritiated deoxcytidine ([G-3H]dCyd) in lymphoid tissues were quite different from those labeled with tritiated thymidine ([methyl-3H]dThd). Thymic cortex and germinal centers of lymph node, spleen and Peyer's patch were labeled intensely with 3HdCyd but only a few lymphocytes in medulla of thymus and medullary cords of lymph node labeled with 3HdThd. The incorporation of 3HdThd into DNA was reduced significantly in the thymic cortex and germinal center of lymphoid tissues by the simultaneous administration of nonradioactive dCyd. On the other hand, the autoradiographic intensity in the labeled lymphocytes in medullary cord of lymph node did not change by administrating nonradioactive dCyd. These results support the proposition that the metabolic activities of pyrimidine utilization for DNA synthesis differ within lymphocyte populations with respect to the specific sites of origin and development within the lymphoid tissues.

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

“…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).…”

“…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). When rats were given nonradioactive CdR together with [3H]TdR, the weak labeling of cells in the thymic cortex and germinal centers decreased even further, whereas there was only slight reduction in the labeling intensity of cells in the thymic medulla and outside the germinal centers (1).…”

“…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). When rats were given nonradioactive CdR together with [3H]TdR, the weak labeling of cells in the thymic cortex and germinal centers decreased even further, whereas there was only slight reduction in the labeling intensity of cells in the thymic medulla and outside the germinal centers (1). 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).…”

“…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.…”

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

“…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).…”