Local Reduction of Organ Size in Transgenic Mice Expressing a Soluble Insulin-Like Growth Factor II/Mannose-6-Phosphate Receptor

Genetic evidence suggests that the insulin-like growth factor II (IGF-II)/mannose-6-phosphate receptor (IGF2R) slows growth. A soluble form of IGF2R (sIGF2R) is produced by proteolytic cleavage of the intact cellular receptor and is found at high levels in fetal and neonatal plasma. To test the hypothesis that sIGF2R modulates organ size in vivo, we generated transgenic mice expressing a mouse Igf2r complementary DNA in which the transmembrane domain sequence was deleted. The transgene was driven by the keratin-10 promoter and was expressed at the highest levels in the skin and alimentary canal. Transgenics showed disproportionately reduced size of the alimentary canal, where the wet weight was decreased by 9 -20% and the dry weight was decreased by 20 -30%, whereas the water content per unit dry weight was not significantly changed. In addition, the circulating levels of IGF-II and the latent form of transforming growth factor-1 were increased by 58 -77% and 56 -140%, respectively, whereas plasma epidermal growth factor levels showed a 24 -35% reduction. The serum and tissue activities of four lysosomal enzymes were not affected, with the exception of the colon in the line expressing the transgene at highest levels, where enzyme activities were decreased compared with control values. These results support a significant role for the sIGF2R in local modulation of organ size in vivo.