The epigenetic influence of growth hormone on skeletal development.

We studied the epigenetic effect of growth hormone using mice that were transgenic for a sheep metallothionein 1a-sheep growth hormone, which was expressed beginning at 21 days postnatal age. The impact of exogenous growth hormone (GH) on various skeletal traits with special emphasis on the mandible was examined by conventional statistical analysis and finite element scaling analysis. In long bones, growth hormone enhances the proliferation rate of cartilage cells in the growth plate and should thus lead to increased lengths. Further, growth hormone is known to increase muscle mass. Our results are consistent with these developmental considerations. We found that the lengths of long bones increased in the transgenic mice compared to the control mice, while the differences in long bone width were less pronounced. In the mandible and skull, the impact of GH is most pronounced in areas of major muscle attachment, i.e., the proximal part of the mandible and the occipital and malar bones in the skull.