Figure 4.
Total DNA from serially transplanted clonal dominant epithelial populations of five successive generations was subjected to digestion with EcoR1 followed by Southern Blot analysis. The subsequent blot was probed with a 32P‐labelled MMTV‐LTR‐specific probe. EcoR1 cuts within the genome of the MMTV, producing two host–viral junction fragments of each provirus insertion. In panel A, five specific host–viral restriction fragments (arrows) were found in the original outgrowth (lane 6), and in all of the succeeding generations. Transplant generations 2 through 5 are represented by the middle four lanes (2–5). The DNA in lane 1 is from the mammary tumour that arose in a fourthth generation outgrowth. In panel B, DNA from a fully developed R12 outgrowth (lane 7) is compared with DNA from a lobule‐limited outgrowth in the contralateral gland at parturition (lane 8). In both cases, all five MMTV‐host restriction fragments are detected.