Quantitative trait loci for estrogen-dependent pituitary tumor growth in the rat

Growth control is of fundamental importance to biology in general and of critical importance to cancer research in particular. Tumors develop when control of the normal growth process is lost. The rat pituitary is a model system for control of estrogen-dependent growth. Chronic estrogen treatment induces uncontrolled growth in the pituitaries of Fischer 344 (F344) rats, but not of Brown Norway (BN) rats. We have identified five quantitative trait loci (QTL) for estrogen-dependent pituitary mass (Edpm) in an F2 intercross of F344 and BN. These QTL reside on rat Chromosomes (Chrs) 2, 3, 5, and 9 and explain a total of 55% of the genetic variance in the F2. We have also detected suggestive evidence for a QTL on rat Chr 14. For Edpm2-1, Edpm2-2, Edpm3, and Edpm5, the F344 allele corresponds with increased pituitary mass, as expected. Surprisingly, for Edpm9 and the suggested QTL on Chr 14, the BN allele corresponds with increased pituitary mass. We also find evidence for interaction (epistasis) between Edpm3 and Edpm9 and between Edpm5 and the suggested QTL on Chr 14.