Polyclonal origin of mouse skin papillomas.

We show that, from the earliest morphologically recognisable stages of development, mouse skin papillomas induced by a chemical initiation-promotion regime are polyclonal. We have demonstrated polyclonality directly by immunohistochemical staining of the mosaic cell populations in embryo aggregation chimaeras, a method which removes some of the uncertainties of previous conclusions based on analysis using electrophoretic polymorphisms. The findings may imply that initiation within a single cell and promotion of its clonal descendents is not a sufficient explanation for the origin of these tumours and that interaction between cells of more than one clone is involved.