Identification of ornithine decarboxylase as a trait gene for growth in replicated mouse lines divergently selected for lean body mass.

Studies of lines of mice selected for body mass have shown that there is a significant genetic component affecting this trait although the nature of the genes involved remains to be elucidated. Using replicate lines of mice, our studies have shown that two different variants of the mouse ornithine decarboxylase (ODCase) gene have been selected in replicate lines of mice selected for high and low lean body mass respectively. One variant is associated with an increased peak of ODCase activity in embryos (10-13 days of gestation) in all high mass lines and with a restriction fragment length polymorphism of the expressed gene. The increased ODCase activity coincides with increased ODCase mRNA levels in the high mass selected lines. These results provide evidence implicating ornithine decarboxylase as a major factor in cell growth, and as a candidate 'trait gene'.