Variations in the incorporation of thymidine into the DNA of some rodent species

1. 1. The ability of injected tritiated thymidine to serve as a precursor for DNA synthesis was tested in a number of rodent species. 2. 2. Radioautographs of tongue, duodenum and spleen showed good labeling for Mus musculus, Mesocricetus auratus, Glis glis, Eliomys quercinus and Scriurus carolinensis, inconstant labeling for Tamiasciurus hudsonicus and Tamias striatus, and no labeling for Marmota monax, Citellus tridecemlineatus and Citellus lateralis. 3. 3. Extraction of DNA from spleen and small intestine demonstrated a relative incorporation similar to the radioautographs. 4. 4. The urinary excretion patterns of M. musculus, M. auratus, C. tridecemlineatus and C. lateralis were similar with regards to volatile and non-volatile radioactivity; 8·5–18·9 per cent of the injected tritium was recovered as non-volatile radioactivity in the first 5 hr. 5. 5. In vitro incubatio of spleen cells with labeled thymidine demonstrated a relative incorporation in the DNA of the various species parallel to the in vivo findings. 6. 6. The urinary and in vitro findings suggest that the defect in thymidine incorporation found in several resides at the cellular level. 7. 7. The ability to incorporate thymidine showns some correlation with the phylogenetic relationship of the species tested, but no correlation with their ability to hibernate.