The autoradiographic pattern of DNA synthesis in Papova virus- and N-methyl-N-nitroso urea (MNU)-induced skin tumors of the Syrian hamster (Mesocricetus auratus).

In skin tumors induced in Syrian hamsters by Papova viruses or produced chemically by dripping of methylnitroso urea (MNU) the pattern of DNA synthesis was studied in vitro and in vivo by autoradiography. The greater part of DNA synthesis in the Papova tumor of the hamster is of cellular origin. Only the cells localized adjacent to keratinizing regions of the tumors may be considered as virus-infected with progressive maultiplication of viruses. This also applies to all nuclei with cellular DNA synthesis only in the marginal chromatin. Moreover viral DNA synthesis is supposed in the cytoplasm, too. In methylnitroso urea-induced squamous cell carcinoma labeled cells were likewise found adjacent to keratinizing tumor regions and the pattern of DNA synthesis is generally not limited to the "stratum basale". With increasing malignancy the pattern of DNA synthesis is changing also in chemically induced tumors and is no longer limited to the stratum basale where it still can be demonstrated in the papilloma.