Regulation of growth: Epigenetic mechanisms?

Organism development is controlled by both genetic programs and the environment to insure a reproductive success as adults. Linear growth is an important part of the development and is mostly controlled by genetic factors. However, the variability of height in a given species does not seem to be specifically associated with SNP. This suggests that environment may play a crucial role. In agreement, an important part of height-related genes present CpG island in their proximal promoter, indicating potential involvement of epigenetic mechanisms. In mammals, the linear growth is regulated by the IGF system, with IGF-I and IGF-II during the fetal period, and IGF-I being included within the somatotropic axis during the postnatal period. Nutrition during the lactating period programs linear growth and adult size through a modulation of the somatotropic axis development and of the setting of its activity later on. The study of underlying mechanisms suggest two waves of programming, which involve both structural adaptation during the early postnatal period and permanent functional adaptation in adulthood. The former may involve a direct stimulation of axon growth of GHRH neurons by IGF-I in first weeks of life while the latter could involve permanent epigenetic modifications in adulthood.