NUCLEOLAR ORGANIZER REGIONS AS A MARKER OF INCIPIENT TRANSFORMATION IN A MODEL OF EXPERIMENTAL CARCINOGENESIS

Nucleolar organizer regions stained selectively with a silver colloid technique (AgNOR) were evaluated during the process of tumour promotio n in the skin of mice. Tumour promotion and control skin samples were processed for identification of AgNOR by light microscopy and submitte d to a morphometric study of the following AgNOR-related variables: nu clear area (V.NUC); AgNOR number per nucleus (N.NOR); single AgNOR are a (V.NOR); total AgNOR area per nucleus (TV.NOR) and proportion of nuc leus occupied by AgNOR (TV.NOR/V.NUC). N.NOR exhibited significant dif ferences between control and tumour tissue, but in the promotion perio d, N.NOR did not exhibit a significant rise until week 24. V.NOR and T V.NOR rose significantly as early as 2 weeks after the onset of promot ion when the cells fail to exhibit unusual microscopic features. The s ignificant increase in AgNOR material at the beginning of the promotio n period reveals the potential value of the variables assessed in the early quantitative evaluation of cellular alterations which could be l inked to the probability of tumour development. Rise in AgNOR material would indicate transcriptional activation leading to an increase in p rotein synthesis and, ultimately, to the expression of an altered phen otype.