Abstract
Though the study of carcinogenesis with p53 gene knockout mice (p53 KO mice) is essential for investigating the relationship between the role of the p53 gene and the carcinogenic process, such experiments are difficult, because the p53 KO mouse has a short lifespan. RNA interference (RNAi), studied with interest recently, enables the knockdown of functional genes, but its application to in vivo conditions is not easy. However, some reports suggest that a method of injection with a mixture of small interfering RNA (siRNA) and collagen is effective for achieving a gene knockdown.
We injected a mixture of siRNA and collagen into the subcutis to make false p53 gene knockout skin locally, and we inspected whether we could use the skin in a radiation carcinogenesis experiment. Our method of experimental skin carcinogenesis is to put a beta-ray source on the back skin of a mouse and continue the irradiation three times a week until the mouse dies or a tumor forms. Beta-rays, which have a low penetration, have little influence on organs except the skin. On the other hand, the tumors induced by this method can be considered beta ray-induced tumors, because skin tumors are rare spontaneous tumors for mice. We hypothesized that we could approximate experiments using p53 KO mice by knocking down the skin p53 gene in the irradiated region by this method. Therefore, we tested an siRNA that knocked down the p53 gene efficiently, with a dosage of the mixture for the subcutis. Also, we examined the time after injection when the siRNA began to show an effect and how long it persisted. We set these conditions variably and obtained the optimal condition for knockdowns of the skin p53 gene.
If local gene control is achieved by this method, as well as in a radiation carcinogenesis experiment, we can apply this method not only to radiation carcinogenesis experiments, but also to UV or chemical carcinogenesis experiments.
