Primary monoclonal and secondary polyclonal growth of colon neoplastic lesions in C3H/HeN ⇆ BALB/c chimeric mice treated with 1,2-dimethylhydrazine: Immunohistochemical detection of C3H strain-specific antigen and simple sequence length polymorphism analysis of DNA

To determine the clonality and cellular origin of colon pre-neoplastic and neoplastic lesions, C3H/HeN ⇆ BALB/c chimeric mice treated with 1,2-dimethylhydrazine (DMH) were investigated immunohistochemically using a specific antibody to C3H strain-specific antigen (CSA) enabling immunohistochemica1 discrimination of C3H cells in histological sections of chimeric mouse tissues. To confirm the results of immunostaining, simple sequence length polymorphism (SSLP) analysis was performed on DNA samples extracted from histological sections of adenocarcinomas. C3H/HeN ⇆ BALB/c chimeric mice were produced by an aggregation procedure and together with BALB/c and C3H/HeN animals were given weekly s.c. injections of 20 mg/kg body weight DMH for up to 20 weeks. At weeks 20 and 35 animals were killed and autopsied. In normal colonic mucosa of the chimeras, each gland was composed entirely of either CSA-positive or -negative cells and no mixed glands were found. Cells of all focal atypias in chimeric mice were, in each case, homogeneous for one or another of the parental types. Of 91 adenomas in chimeric mice, only one comprised both types of cell. Among 119 adenocarcinomas, 12 contained cells of both parental types. In these tumors, however, the 2 phenotypes were not mixed together at random but arranged in discrete areas, with intermingling limited to the junctions. SSLP analysis demonstrated s extracted from CSA-positive and -negative tumors to exhibit the polymorphic patterns of C3H and BALB/c, respectively, while mixed CSA-positive and -negative tumors showed mixtures of both polymorphic DNA types.