DIFFERENT LABELLING PATTERNS IN MOUSE LYMPHOID TISSUES WITH [³H]DEOXYCYTIDINE AND [³H]THYMIDINE

Abstract

The percentages of labelled lymphocytes in smear preparations of mouse thymus were higher than those in similar preparations of mesenteric lymph nodes with either generally labelled tritiated deoxycytidine, [3H]CdR, or tritiated thymidine, [3H]TdR. Lymphocytes in the thymus cortex and in germinal centres of mesenteric lymph nodes were intensely labelled with [3H]CdR, whereas with [3H]TdR lymphocytes in the peripheral region of thymus and medullary cords of mesenteric lymph nodes were heavily labelled. The majority of lymphocytes in thymic cortex and germinal centres of mesenteric lymph nodes were labelled weakly with [3H]TdR. Thus, labelling patterns with [3H]CdR differed from those with [3H]TdR in lymphoid tissues of the mouse. Mouse lymphocytes can utilize [3H]CdR as a precursor molecule for cytosine and thymine in DNA. The ratio of radioactivity of thymine to that of cytosine was measured biochemically in DNA extracted from lymphocytes labelled with [3H]CdR. This radioactivity ratio in thymus was higher than that in mesenteric lymph nodes. These results suggest that the metabolic activities of utilizing CdR for DNA synthesis differ within lymphocyte populations in various lymphoid tissues in the mouse.

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

“…On the other hand, Fig. 4 showed that no difference in grain density was found in the testes when the animals were labeled with [G-31-1]- (12). Thus, the capacity for utilizing CdR as DNA-thymine is apparently much lower in the testis than in certain cells of the lymphoid system (12).…”

“…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). 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).…”

“…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). 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).…”