Skin papillomas and other neoplasms induced by murine sarcoma viruses in mid-gestation-infected mice

During extensive investigations on the effects of oncogenic retroviruses in developing rodents, the ability of MSV to mount a neoplastic response in CD-I Swiss mouse embryos was determined. By infecting the animals directly in utero at selected stages of post-implantation development, we detected a peculiar reaction of the embryonal tissues to certain MSVs: when mice were exposed to KiMSV at mid-gestation, the newborn developed characteristic tumors, in addition to mesenchymal cell sarcomas, not induced in fetuses and neonates. These included pulmonary alveologenic tumors and skin papillomas and were seen in mice infected on days 8 and 10 of pregnancy, roughly corresponding to 15 and 35 somites, respectively. To determine the specificity of these events, other 8- and 10-day-old embryos were infected with retroviruses of the same or different families. HaMSV and MoMSV also induced mesenchymomas and a low incidence of skin papillomas (10% and 15% compared to 40% in the KiMSV group) but not pulmonary tumors. In contrast, FBRMSV was inactive in this respect and only osteogenic sarcomas were detected in the offspring. Infecting the embryos on day 7 of pregnancy produced no tumors. Later infections (in 15-day-old fetuses and neonates) mainly induced mesenchymal sarcomas. No congenital malformations were detected in the embryos exposed to MSV during organogenesis, although some abortions and resorptions were seen.