INDUCTION OF TRANSGENE EXPRESSION IN TG.AC (V-HA-RAS) TRANSGENIC MICECONCOMITANT WITH DNA HYPOMETHYLATION

Tg.AC transgenic mice have a transgene composed of a zeta-globin trans criptional control region, a v-Ha-ras coding region, and a simian viru s 40 3' polyadenylation signal sequence. Induced ectopic expression of the transgene by chemical treatment or full-skin-thickness wounding l eads to the development of skin papillomas. Reverse transcription-poly merase chain reaction assays and protein blotting indicated that the t ransgene was expressed 16-28 d after full-skin-thickness surgical woun ding. Normal unwounded skin did not express the transgene. DNA blottin g indicated that the position of the transgene remained stable during wound-induced tumorigenesis. Concomitant with the v-Ha-ras mRNA and pr otein expression was the hypomethylation of specific MspI/HpaII sites with in the transgene. These results a re consistent with the hypothes is that hypomethylation is required for the induced and sustained expr ession of the Tg.AC v-Ha-ras transgene in spontaneous and induced tumo rs in Tg.AC mice. (C) 1998 Wiley-Liss, Inc.